Hydraulic pump

Abstract

 The invention relates to a fluid working machine (1, 42), comprising at least one fluid inlet port (15, 16, 17), at least one fluid outlet port (22, 23) and a plurality of cyclically changing cavities (6, 7). The fluid working machine (1, 42) is able to supply a fluid flow rate sufficient for hydraulic applications and/or can be supplied by a fluid flow rate, sufficient to propel the fluid working machine (1, 42). At least one passive fluid connecting means (15, 16, 17, 18, 21) is provided in a fluid path, connecting the fluid inlet port (15, 16, 17) and at least one of the cyclically changing cavities (6, 7) of the fluid working machine (1, 42). At least one actuated valve (20) is provided in a fluid path, connecting said fluid inlet port (15, 16, 17) and at least one of said cyclically changing cavities (6, 7) of the fluid working machine (1, 42), wherein the actuated valve (20) can be actuated on a cycle-by-cycle basis.

Description

[0001] The invention relates to a fluid working machine, comprising at least one fluid inlet port, at least one fluid outlet port and a plurality of cyclically changing cavities, wherein said fluid working machine is able to supply a fluid flow rate sufficient for hydraulic applications and/or wherein said fluid working machine can be supplied by a fluid flow rate, sufficient to propel said fluid working machine. The invention also relates to a method of operating a fluid working machine, comprising at least one fluid inlet port, at least one fluid outlet port and a plurality of cyclically changing cavities, wherein said fluid working machine is able to supply a fluid flow rate sufficient for hydraulic applications and/or wherein said fluid working machine can be supplied by a fluid flow rate, sufficient to propel said fluid working machine.

[0002] When the pressure level of a fluid has to be increased, fluid pumps are used. Over the years, different types of pumps have been developed. For example, scroll pumps, piston and cylinder pumps, centrifugal pumps, radial blower type pumps, axial blower type pumps, rotary vane pumps or gear pumps are used. The type of pump which is chosen generally depends on the plurality of parameters. For example, the compression ratio, the fluid flow rate to be pumped, the kind of fluid to be pumped or the like can influence the decision on which type of pump to choose.

[0003] When it comes to hydraulic applications, usually hydraulic pumps of the piston and cylinder design are used. A major reason for this choice is the high compression ratio and the high fluid flux that can be achieved using this design.

[0004] In hydraulic pumps of the piston and cylinder type, a piston is moving back and forth in a cylindrical cavity. By the movement of the piston the volume of the cavity is cyclically changing. When the cavity's volume is expanding, hydraulic fluid is sucked in from the low pressure fluid reservoir. Once the piston has reached its bottom dead center, the cavity's volume starts to contract. During this contraction phase, the hydraulic fluid is expelled out of the pump's cavity towards a high pressure fluid manifold. For controlling the different fluid connections (i.e. the fluid connection between the low-pressure fluid reservoir and the pumping cavity during the intake stroke and the fluid connection between the pumping cavity and the high-pressure fluid manifold during the contraction phase of the pumping cavity) simple passive valves like check valves can be used. For driving the piston back and forth, a crankshaft or a cam which is eccentrically mounted on a rotating shaft can be used. To increase the pump's pumping ability, it is possible to increase the size of the cylinder and/or the size of the piston. However, at some point it is usually preferred to provide a plurality of pistons and cylinders. This design can make it easier to handle the high pressures, occurring with hydraulic pumps. Furthermore, the fluid output behavior of a multiple cylinder pump can be more homogeneous as compared to a single cylinder pump.

[0005] Although the piston and cylinder type design of hydraulic pumps using passive inlet and outlet valves has been proven to work well and reliably, there are still problems involved with this particular design. One problem, for example, is the adaptability of the pump's fluid output flow according to varying fluid flow demands by the hydraulic consumers. This is particularly problematic, if the demand of the hydraulic consumers is varying quickly. To solve this problem, hydraulic pumps with so-called swash plates and/or hydraulic accumulators for storing pressurized hydraulic fluid have been proposed. Hydraulic accumulators, however, are relatively heavy and need a relatively large building space. Hydraulic pumps of the swash plate design on the other hand, still have problems, in particular if the fluid flow demand of the hydraulic consumers changes very fast.

[0006] As a way to solve these problems, so called synthetically commutated hydraulic pumps have already been suggested. Synthetically commutated hydraulic pumps are a unique subset of variable displacement pumps. They are also known under the name digital displacement pump.

[0007] In hydraulic pumps of the synthetically commutated hydraulic pump design, the fluid inlet valve of the pumping cavity is replaced by an actively actuated valve. The actuation pattern of the actuated valve can be controlled by an electronic controlling unit. If the actuated valve is opened as soon as the piston has reached its top dead center (TDC) (or a short time afterwards) and remains open during the expansion phase of the pumping cavity until the piston has reached its bottom dead center (BDC), and the actuated valve will then be closed during the contraction phase of the pumping cavity, the synthetically commutated hydraulic pump will act as a standard hydraulic pump, comprising passive valves.

[0008] However, it is also possible to leave the actuated valve in its open position during a complete working cycle of the piston. In this case hydraulic fluid is pumped back and forth out of the and into the low pressure fluid reservoir.

[0009] Therefore, no effective pumping of hydraulic fluid towards the high pressure side of the synthetically commutated hydraulic pump is performed.

[0010] Another working mode can be achieved if the actuated valves will be closed at some intermediary position between the bottom dead center and the top dead center of the piston during the contraction phase of the pumping cavity. This way, only part of the cyclically changing volume of the pumping cavity will be used for pumping hydraulic oil towards the high pressure side of the synthetically commutated hydraulic pump.

[0011] The synthetically commutated hydraulic pump design is described in EP 0 361 927 B1 or US 6,651,545 B2, for example. These pumps have proven to be superior when it comes to quickly adapting to a rapidly changing fluid flow demand. Due to this ability, they have also proven to be particularly energy efficient. This is because it is no longer necessary to short-circuit pressurized hydraulic fluid to the low pressure fluid reservoir without performing useful work, simply because of the fact that momentarily an excess amount of hydraulic fluid is pumped by the hydraulic pump. The design of synthetically commutated hydraulic pumps necessitates low pressure valves, which can be quickly and precisely switched from an open into a closed state by applying an external actuation signal. In addition, the actuated valves used for synthetically commutated hydraulic pumps have to have a large cross section for hydraulic fluid to pass through them. These requirements make the design of actuated valves, which can be used for synthetically commutated hydraulic pumps, quite elaborate and hence expensive. Examples of the quite complex design of actuated valves which are usable for synthetically commutated hydraulic pumps can be found, for example, in US 2005/006759681 A1. The comparatively high complexity and the comparatively high price of the actuated valves - and therefore of the resulting synthetically commutated hydraulic machine - has hindered a wide spread application of synthetically commutated hydraulic machines so far.

[0012] In US 5,538,403 A1, a variable displacement high-pressure pump for pumping fluid to an accumulation chamber is disclosed. The variable displacement high-pressure pump is used as a fuel pump for a common rail fuel injection system. The variable displacement high-pressure pump comprises two pumping units for receiving low-pressure fluid through an inlet and selectively delivering the fluid to the accumulation chamber at a high-pressure. Furthermore, a common fluid passage in fluid communication with the two pumping units is provided. Using the common fluid passage, fluid can be pumped from one of the pumping units to the respective other one of the pumping units. A valve is positioned in the common fluid passage for selectively blocking the flow of fluid between the two pumping units such that the pumping units deliver fluid to the accumulation chamber when the valve blocks the fluid flow between the two pumping units. Due to the design of the variable displacement high-pressure pump as a fuel pump, the high-pressure pump and its components (in particular the valve in the fluid passage between the two pumping units) do not have to be designed for high fluid flow rates. Contrary to this, the achievable fluid flow rates have to be much higher for hydraulic fluid working machines (hydraulic pumps and/or hydraulic motors). Therefore, the two technical fields are clearly distinct, due to the totally different fluid flow requirements. Therefore, a person skilled in the technical field of fuel pumps differs from person skilled in the technical field of hydraulic pumps. In particular, the valve in the fluid passage between the two pumping units would have to have completely different fluid flow cross-sections in the aforementioned two technical fields. However, an actuated fluid valve, which shows a high fluid flow cross-section and which can be actuated very fast and precisely at the same time (which would both be required in the technical field of hydraulic fluid working machines), seems to be prohibitively complicated and expensive at first sight.

[0013] In DE 10 2007 029 670 A1, a hydraulic working machine with a plurality of cyclically changing working cavities is suggested, comprising passive inlet and outlet valves, connecting the working cavities to a low-pressure fluid reservoir and a high-pressure fluid reservoir, respectively. For realising a partial mode, it is suggested to provide a cut-off valve between a pair of working cavities. Said cut-off valve can be opened at a certain time between the bottom dead centre and the top dead centre of the morning piston of the respective working cavity. The design the necessary cut-off valve is very complicated, because the cut-off valve has to be able to open and close very fast and precisely, has to have a large fluid flow cross-section and has to be able to remain closed under pressure differences, coming from both sides of the cut-off valve.

[0014] Therefore, it is an object of the invention to suggest a fluid working machine which shows improvements over fluid working machines according to the state of the art.

[0015] It is suggested to design a fluid working machine, comprising at least one fluid inlet port, at least one fluid outlet port and a plurality of cyclically changing cavities, wherein said fluid working machine is able to supply a fluid flow rate sufficient for hydraulic applications and/or wherein said fluid working machine can be supplied by a fluid flow rate, sufficient to propel said fluid working machine, wherein at least one passive fluid connecting means is provided in a fluid path, connecting said fluid inlet port and at least one of said cyclically changing cavities in a way that at least one actuated valve, provided in said fluid path, connecting said fluid inlet port and at least one of said cyclically changing cavities, wherein said actuated valve can be actuated on a cycle-by-cycle basis. It has to be noted that the fluid path, comprising said passive fluid connecting means and the fluid path, comprising said actuated valve can at least in part fall together and/or can at least in part be different. For example, in case of a different fluid path, the fluid path connecting said fluid inlet port and at least one of said cyclically changing cavities can be led through different parts of the fluid working machine. Also, it is possible that the fluid path can be split up, so that a first part of the fluid path connecting the fluid inlet port and at least one of the cyclically changing cavities is designed as a common fluid path, while a second part of this fluid path is split up, so that two (or even more) separate (fractional) fluid paths are formed. Regardless of the explicit design of the resulting fluid working machine an improvement over already existing fluid working machines is possible. Using the suggested design, it is possible to reduce the number of the actuated valves in fluid working machine, for example. Since the actuated valves are usually a considerable cost factor, it is hence possible to significantly reduce the manufacturing cost of the resulting fluid working machine. Nevertheless, the resulting fluid working machine can still show working characteristics, which come at least close to the working characteristics of a comparable fluid working machine according to the state of the art. Additionally or alternatively it is also possible to design the actuated valves simpler as compared to actuated valves according to the state of the art. For example, it is possible to reduce the fluid flow cross sections which have to be provided for the fluid flow. This way, it is possible to reduce the dimensions of the actuated valves, which again makes it possible to reduce the mass of the moving parts of the actuated valves. Hence, the actuator of the actuated valve can be designed smaller because it has to provide less force for actuating the valve part of said actuated valve. This again can make the design of the actuated valve significantly easier and cheaper. Again, due to the suggested design a fluid working machine can be achieved, showing at least comparable results to fluid working machines according to the state of the art, despite using a comparatively simple design for the actuated valve. In particular, because the actuated valve can be actuated on a cycle-by-cycle basis, the pumping performance of the fluid working machine (output fluid flux) can be adapted to a rapidly changing fluid flow demand very fast. Of course, the usual consequence of this design is that the actuated valve has to be designed in a relatively complex way so that it is able to open and close sufficiently fast and sufficiently precise even at high speeds of the fluid working machine (e.g. at high RPMs). In particular, the fluid working machine should be able to deliver a fluid flow rate of 1 cm³/s, 5 cm³/s, 10 cm³/s or even more, if the fluid working machine is used as a fluid pump (and/or to be propelled with such a fluid flow rate, if the fluid working machine is used as a hydraulic motor). Of course, this does not exclude that the fluid working machine can be used in times with a lower fluid flow rate. Likewise, different numbers could be used as well, in particular every natural number with the unit cm³/s.

[0016] According to a preferred embodiment at least one of said actuated valves of said fluid working machine is arranged in a common fluid path of at least two of said cyclically changing cavities. Using this embodiment it is possible to significantly reduce the overall cost for the fluid working machine, since generally the overall number of actuated valves can be reduced. In particular it is possible that a single actuated valve is used for two or even more cyclically changing cavities. Despite of this reduction in the number of actuated valves it is possible that one, several and/or all of the connected cyclically changing cavities is (are) able to perform idle strokes, part strokes and/or full strokes. It is also to be noted that at least part of the cyclically changing cavities can not only be in the same phase of their working cycles, but can also be out of phase from each other, i.e. in different phases of their respective working cycle.

[0017] It is possible to design the fluid working machine in a way that at least one of said actuated valves and at least one of said passive fluid connecting means are arranged in series and/or in parallel. As a rule of thumb, when using an arrangement of at least one actuated valve and at least one passive valve in series, usually the overall number of actuated valves within the resulting fluid working machine can be reduced. When using at least one actuated valve and at least one passive fluid connecting means in parallel, usually the design of the actuated valve can be simplified (for example by reducing the fluid flow cross section, thus simplifying the design for the actuator part of the actuated valve and/or reducing the force which has to be produced by the actuator part of the actuated valve). This is because in parallel arrangement of at least one actuated valve and at least one passive fluid connecting means the possible fluid flow rates through the respective valves can add up to a higher overall fluid flux. This can be the case during certain time intervals and/or when considering the mean average over several working cycles of the cyclically changing cavities. In an arrangement in series, however, one of the valves, for example the passive fluid connecting means, can be used to provide a closure of the fluid path even if the other valve (for example the actuated valve) is still in an open position for performing a different task, for example for supplying fluid to another cyclically changing cavity.

[0018] It is further preferred that at least one of said actuated valves and a plurality of said passive fluid connecting means, in particular of passive fluid connecting means which are connecting to different cyclically changing cavities, are connected to at least one common fluid chamber of said fluid working machine. This common fluid chamber can be used for distributing a common fluid path (for example the first section of a fluid path) to a plurality of different fluid paths (e.g. "parallel" fluid paths). The common fluid chamber can be designed as a simple bifurcation or can comprise a certain volume. Using a simple bifurcation, the overall design volume of the fluid working machine can be reduced. However, if the common fluid chamber has a certain volume it is possible to "smear out" pressure pulses, thus reducing noise and/or the wear of the components, for example. Preferably the common fluid paths are comprising the actuated valve(s), while the "parallel" fluid paths comprise the passive fluid connecting means. This way the number of the more expensive actuated valves can be reduced as compared to the overall number of the relatively cheap passive fluid connecting means. This way the overall cost of the resulting fluid working machine can be reduced. This is usually even the case, if the reduction in the number of actuated valves necessitates an increase in the number of passive fluid connecting means.

[0019] Preferably the fluid working machine is designed in a way that at least one high-pressure valve is provided in a fluid path between at least one of said fluid outlet ports and at least one of said cyclically changing cavities, or in particular between at least one of said fluid outlet ports and at least one of said common fluid chambers. In particular, such a fluid path can be established towards the high pressure fluid manifold of the fluid working machine (depending on the position of the at least one high-pressure valve). Preferably at least one of said high-pressure valves is designed as a passive fluid connecting means, for example a biased-closed check valve. This way costs can be saved and the design of the fluid working machine can be simplified. In particular it is possible that the common fluid chamber is used as some kind of a "general fluid distributing chamber" which is not only used during the intake stroke, but also during the output stroke of the one or several cyclically changing cavities.

[0020] Furthermore, it is possible that the fluid working machine is designed in a way that at least one of said passive fluid connecting means is arranged in a fluid path which is going at least in part through a preferably common driving unit of said plurality of cyclically changing cavities and/or which is at least in part going through a part of at least one of said cyclically changing cavities which is neighboring said preferably common driving unit, or is designed as a passive valve unit, in particular as a poppet valve and/or as a spool valve. Using the suggested design, it is not only possible to use the head-part of the piston-and-cylinder arrangement (i.e. the part, being on the opposite side of the crankshaft), but also the bottom-part (i.e. the part, being in the vicinity of the crankshaft). This way, the overall fluid flow area can be further increased. In particular, a fluid flow area can be provided which can even exceed the fluid flow area provided by fluid working machines according to the state of the art. This is done by using areas of the cyclically changing cavities (e.g. in a piston-and-cylinder arrangement) which are so far generally not used. This is even possible without (significantly) increasing dead volumes. The common driving unit can be in particular a common crankshaft, which is present in the radial piston pump or even a so-called "wedding cake"-type pump, for example. In such a common crankshaft an opening like an elongated ditch can be provided. If the dimensions of the ditch and of an opening leading towards the pumping cavity are appropriately adapted, it is even possible that this combination can work as a passive fluid connecting means (the latter can be sure with a different design, as well). Such a passive fluid connecting means can show the behavior of a passive and/or of an actuated valve (at least to a certain extent). By the expression "cyclically changing cavities" not only the cavity itself, but also neighboring parts of this cavity are encompassed. In particular, the piston-like part is encompassed by this expression. For example, a fluid path leading through a part of at least one of the cyclically changing cavities can be designed as a bore in a piston-like structure of the fluid working machine. Usually, a fluid path of the presently suggested type will be arranged in parallel to a fluid path, comprising the "real" actuated valve(s).

[0021] According to a preferred embodiment, each cyclically changing cavity may be equipped with at least one (additional) low pressure passive fluid connecting means to admit fluid directly into but not out of the cyclically changing cavity. A low pressure passive fluid connecting means may be a check valve biased to the closed position and oriented so that fluid cannot escape the cyclically changing cavity through it. A low pressure passive fluid connecting means may be an enlongated ditch formed in the crankshaft as described above, the ditch being arranged to let fluid into but not out of the cyclically changing cavity by virtue of its being fluidly connected with the cyclically changing cavity when the cyclically changing cavity is expanding and fluidly disconnected from the cyclically changing cavity when the cyclically changing cavity is contracting. Preferably fluid admitted through a low pressure passive fluid connecting means comes directly or indirectly from a reservoir of low pressure fluid brought to the fluid working machine or held within the fluid working machine. Of course, a plurality of (additional) low pressure passive fluid connecting means can be provided as well. The (additional) low pressure passive fluid connecting means can be (at least in part) of the same design or can be (at least in part) of a different design.

[0022] According to a preferred embodiment the fluid working machine is designed in a way that at least one of said cyclically changing cavities is designed as a cylinder-and-piston device. This design proved to be well suited for achieving the usual design parameters of fluid working machines, in particular of fluid working machines which are used for hydraulic systems. This is of course also true for fluid working machines of the synthetically commutated hydraulic machine type.

[0023] Preferably the fluid working machine is designed in a way that at least two of said cyclically changing cavities are displaced out of phase by at least 100 °, 105°, 110°, 115°, 120°, 125°, 130°, 135°, 140°, 145°, 150°, 155°, 160°, 165° or 170° and/or not more than 120 °, 125 °, 130°, 135 °, 140 °, 145 °, 150 °, 155 °, 160°, 165°, 170° or 175°. Using such a design, the fluid working machine can be easily arranged on a wall of a device, the fluid working machine is used for, for example. This can be achieved, for example, by arranging two cylinders at a respective angle, in case the fluid working machine is of the piston-and-cylinder type. Apart from the geometrical advantages, the suggested design can also prove to be advantageous with respect to the fluid flow patterns and/or with respect to the occurring pressures of the pumped fluid during the working cycle of the fluid working machine. In particular said displacement at an angle of less than 180° (or the respective number) can provide for a phase shift of less than 180° of the contraction phases of the working cycle of the fluid working machine. Thus, the period where the at least two cyclically changing cavities are expanding simultaneously can provide a preferably finite or even an elongated period where no fluid flows from the cyclically changing cavities into a common fluid chamber. The period where both cyclically changing cavities are expanding simultaneously can also be used for lowering the pressure within a common fluid chamber, used for distributing fluid to or receiving fluid from the cyclically changing cavities, or to allow such a depressurisation to be carried out. This can also be true, if additional depressurization means are provided. Such a depressurization, however, can prove to be necessary and/or advantageous for opening an actuated valve. This is because otherwise the actuated valve generally would have to be opened against a differential pressure between its two sides. Hence, if the differential pressure is smaller or even nonexistent, the opening movement of the actuated valve is easier. Hence, it is possible that the actuated valve can be designed with the less powerful actuator. Depending on the design of the fluid working machine it is even possible that this depressurization is a necessary requirement for being able to open the actuated valve at all.

[0024] According to another possible embodiment of the suggested fluid working machine, at least one of said cyclically changing cavities and/or at least one of said common fluid chambers and/or at least one of said passive fluid connecting means and/or at least one of said actuated valves comprises at least one fluid depressurization means, which is preferably designed as a controllable depressurization means. Usually, a fluid depressurisation means is able to release fluid from a common fluid chamber so as to reduce the pressure of fluid in it. Preferably a fluid depressurising means releases fluid directly or indirectly to a reservoir of low pressure fluid brought to the fluid working machine or held within the fluid working machine. As previously discussed, such a depressurization can be a necessary requirement for being able to open an actuated valve. By using such a depressurization it is usually at least possible to design the actuated valve in a simpler and/or less powerful way. The depressurization does not necessarily have to decrease the differential pressure to zero or "almost" zero. Instead, even an only "moderate" or "substantial" decrease in differential pressure can prove to be advantageous. The fluid depressurising means is preferably operable to release fluid during at least part of periods where at least two (or even all) cyclically changing cavities are expanding simultaneously (in particular those cyclically changing cavities, connecting to the same common fluid chamber), and even more preferably releases fluid only when no or essentially no fluid flows from the cyclically changing cavities into a common fluid chamber. Preferably the fluid depressurising means is designed and arranged in a way that it is capable of depressurising the common fluid chamber at or shortly after the point of minimum volume of the at least one cyclically changing cavity which is latest in phase of all the at least one cyclically changing cavities. Preferably the fluid depressurising means becomes incapable of depressurising the common fluid chamber at or shortly before the point of maximum volume of the at least one cyclically changing cavity which is earliest in phase of all the at least one cyclically changing cavities.

[0025] It is possible to design the fluid working machine in a way that at least one of said fluid depressurization means is designed as an orifice or as a fluid connection prolonging means, wherein said fluid connection prolonging means is designed and arranged in a way to initiate and/or to prolong an open state of at least one of said passive fluid connecting means and/or at least one of said actuated valve means. Using such a design, a relatively easy and cheap way of designing a depressurization means can be achieved. In particular, it is possible to provide for a depressurization means without causing unnecessary and/or undue additional sealing surfaces. This way, it is possible to sustain a very high efficiency of the resulting fluid working machine.

[0026] According to a preferred design of the fluid working machine, at least one of said actuated valves is designed as an electrically actuated valve, which is preferably comprising a latching device, in particular a magnetic latching device and/or a latching device for latching said actuated valve in an end position. An electrical actuation of the actuated valve is generally particularly useful, since it is usually relatively easy to design a controlling unit which outputs electrical signals. For example, standard microcontrollers can be used for calculating the timing of the actuation signals. The output signal from the microcontroller can be easily amplified to actuate the actuated valve, using standard amplifiers. Therefore a fluid working machine which is precisely controllable and still relatively cost-efficient can be provided. By using a latching device, the overall consumption of electrical energy can be reduced. It has to be noted that in that synthetically commutated fluid working machine the actuated valves usually remain in an end position for quite elongated time intervals. Therefore, using a latching device, it is possible to significantly reduce the electrical current, or it is even possible to completely switch off the electrical current, while still securely holding the actuated valve in an end position. Therefore the mean average of electrical energy consumed can be lowered significantly. The end position can be in particular an open position and/or a closed position. Actuating the valve preferably moves the valve away from at least one of its end positions today, putting it in the opposite state of open or closed to when it was in an end position. Preferably the actuated valve is a direct acting actuated valve, which allows it to actuate with maximum speed and/or minimum delay. A direct acting valve can be particularly designed and arranged in a way that it primarily uses electrical energy to open and/or close the valve. Preferably the actuated valve is a biased actuated valve, which naturally moves towards an end position.

[0027] The controlling unit preferably actively controls the actuated valves in phased relationship to cycles of cyclically changing cavity volume. By "in phased relationship to cycles of cyclically changing cavity volume" we usually mean that the timing of active control of one or more actuated valves is determined with reference to the phase of the volume cycles of the cyclically changing cavities. Accordingly, the fluid working machine typically comprises cyclically changing cavity phase determining means, such as a position sensor. For example, where the cycles of cyclically changing cavity volume are mechanically linked to the rotation of a shaft, the fluid working machine preferably comprises a shaft position sensor, and optionally a shaft speed sensor, and the controller is operable to receive a shaft position signal from the shaft position sensor, and optionally a shaft speed signal from a said shaft speed sensor. In embodiments which comprise a plurality of cyclically changing cavities, with a phase difference between the volume cycles of different cyclically changing cavities, the controller will typically be operable to determine the phase of individual cyclically changing cavities.

[0028] By "actively controls" (and related terms such as "active control") we particularly include the possibilities that the controller is operable to selectively cause an actuated valve to do one, more or all of open, close, remain open and/or remain closed. The controller may only be able to affect the state of an actuated valve during a portion of a working cycle. For example, the controller may be unable to open an actuated valve against a pressure difference during times when pressure within the working chamber is substantial. Typically, the controller actively controls the actuated valve by transmitting a control signal either directly to an actuated valve or to an actuated valve driver, such as a semiconductor switch. By transmitting a control signal, we particularly Include transmitting a signal which denotes the intended state of an actuated valve (e.g. open or closed) or a pulse which denotes that the state of an actuated valve should be changed (e.g. that the valve should be opened or closed), or a pulse which denotes that the state of an actuated valve should be maintained. The controller may transmit a signal on a continuous basis and stop or change the signal to cause a change in the state of an actuated valve, for example, the actuated valve may comprise a normally closed solenoid opened valve which is held open by provision of an electric current and actively closed by switching off the current.

[0029] According to a preferred embodiment, the fluid working machine is designed as a synthetically commutated hydraulic machine. Such fluid working machines are particularly energy efficient, and are thus preferred. Such synthetically commutated hydraulic machines generally require elaborate and hence expensive actuated valves. Therefore, the advantages of the suggested design can have a particularly large impact if applied to synthetically commutated hydraulic machines.

[0030] According to a preferred embodiment the fluid working machine is designed in a way that a pumping stroke of at least one of said cyclically changing cavities pumps a fluid volume of at least 1 ml, 2 ml, 3 ml, 4 ml, 5 ml, 6 ml, 7 ml, 8 ml, 9 ml and/or 10 ml. The respective number can be in particular the pumped fluid volume of a full pumping stroke. Using the suggested volumes, a fluid working machine can be achieved which is usable for driving hydraulics, for example. This is because in hydraulic applications, a sufficiently fast movement of the respective hydraulic components is essential. With the suggested volumes, such a sufficiently fast movement of the hydraulic components can usually be sustained.

[0031] Furthermore, a method of operating a fluid working machine, comprising at least one fluid inlet port, at least one fluid outlet port and a plurality of cyclically changing cavities is suggested, wherein said fluid working machine is able to supply a fluid flow rate sufficient for hydraulic applications and/or wherein said fluid working machine can be supplied by a fluid flow rate, sufficient to propel said fluid working machine, wherein the fluid input of at least one of said plurality of cyclically changing cavities is sucked in from said fluid inlet port through at least one passive fluid connecting means, and wherein the method is modified in a way that at least one actuated valve, selectively connecting at least one of said fluid inlet ports and at least one of said cyclically changing cavities is provided, wherein said actuated valve can be actuated on a cycle-by-cycle basis. When operating a fluid working machine according to the presently suggested method, the already discussed features and advantages will be achieved analogously.

[0032] In particular is possible to operate the fluid working machine according to the previously described method, wherein a fluid working machine according to the previously described design is used.

[0033] Of course, it is also possible to further modify the method in the sense of the previous description (and in the sense of the embodiments, described in the following).

[0034] The present invention and its advantages will become more apparent, when looking at the following description of embodiments of the invention, which will be described with reference to the accompanying figures, which are showing:

Fig. 1:

a first embodiment of a synthetically commutated hydraulic pump in a schematic drawing;

Fig. 2:

a graph showing the behavior of different units in an operation cycle of a synthetically commutated hydraulic pump;

Fig. 3:

a second embodiment of a synthetically commutated hydraulic pump in a schematic drawing.

[0035] In Fig. 1 a schematic sketch of a synthetically commutated hydraulic pump 1 according to a first embodiment is shown. The synthetically commutated hydraulic pump 1 comprises two cylinders 2, 3, in which an associated piston 4, 5 moves up and down. By the movement of the pistons 4, 5 within the cylinders 2, 3, two different pumping cavities 6, 7 of cyclically changing volume are provided.

[0036] The up and down movement of the pistons 4, 5 within the respective cylinder 2, 3 is initiated by a contact of a bottom part 8, 9 of the pistons 4, 5 with the radial surface 10 of the rotating crankshaft 11. The crankshaft 11 is mounted off-axis on a rotating axis 12, so that the respective eccentric cams 46, 47 of the crankshaft 11 rotate eccentrically around the rotating axis 12 and work like a cam for the respective piston 4, 5. Although in Fig. 1 the crankshaft 11 is drawn as two separate units, lying beside each other, it is preferred that the synthetically commutated hydraulic pump 1 comprises only one rotating crankshaft 11 and the two cylinders 2, 3 and pistons 4, 5 are arranged on two eccentrics 46, 47 themselves arranged along an axial direction of the crankshaft 11 behind each other.Likewise, the hydraulic pump 1 could be also designed in a way that he one rotating eccentric camshaft 46 is provided with the two pistons 4,5 arranged angularly spaced apart around it (which is the case in the wedding cake type pump, for example). The view chosen for the synthetically commutated hydraulic pump 1 in Fig. 1 should therefore be understood as a schematic drawing, showing mainly the working principle of the synthetically commutated hydraulic pump 1.

[add reference 46 and 47 as crankshaft eccentrics and point crankshaft 11 to both eccentrics]

[0037] The movement of the pistons 4, 5 - and therefore the changing volumes of the pumping cavities 6, 7 - is out of phase from each other. In the presently shown embodiment, the volume of the pumping cavity 6 lags the volume of the pumping cavity 7 by less than 180°, presently by 170°. However, different angles are also possible. The phase difference between the volumes of the two pumping cavities 6, 7 is presently realized by an appropriate phase difference between the two eccentric camshafts 46, 47.

[0038] In Fig. 1, the second piston 5 (in Fig. 1 on the right side) is still moving out of its cylinder 3. Therefore the volume of the second pumping cavity 7 is still increasing. This can be seen by the position of the eccentric cam 46, which is some 20° before the bottom dead center of the second piston 5. The rotating direction of the crankshaft 11 and eccentric cam 46 is indicated by an arrow A. In the example shown, the fluid flow into the pumping cavity 7 is going through the bottom part 9 of piston 5. Consequently, the piston 5 has a hollow interior 14, so that fluid can pass through the piston 5. The hollow interior 14 needs not necessarily to be designed as shown in Fig. 1. Instead, it is also possible that only a bore with a relatively small diameter (as compared to the outer diameter of piston 5) is provided within the piston 5. Furthermore, a plurality of bores could also be provided.

[0039] Furthermore, a (second) groove 16 is provided within the radial surface 10 of the crankshaft 11. The dimensions of the second groove 16 (in particular its circumferential dimension) is chosen in a way that the groove 16 lies in the vicinity of the opening 14 in the bottom part 9 of the corresponding piston 5, whenever the piston 5 is moving downwards, i.e. the volume of the pumping cavity 7 is expanding. Therefore, fluid can flow through the bottom part of the second piston 5, whenever the volume of the second cavity 7 is increasing (fluid flow indicated by arrow B). When the second piston 5 is moving upwards (and hence the volume of the pumping cavity 7 is decreasing), however, the second groove 16 lies away from the hollow interior 14 at the bottom part 9 of piston 5. Therefore, the fluid passage is blocked and no fluid can pass through the bottom part 9 of the piston 5. Of course, an appropriately arranged first groove 15 is provided on the radial surface 10 of the crankshaft 11 for corresponding interaction with the bottom part 8 of the first piston 4 as well.

[0040] The downward movement of the pistons 4, 5 out of the respective cylinders 2, 3 can be assisted by a spring 45, which is arranged between said parts in a way that the piston 4, 5 and the cylinder 2, 3 are pushed away from each other.

[0041] On the left side of Fig. 1, the first piston 4 is moving upwards into the corresponding cylinder 2. Therefore, the volume within the first pumping cavity 6 is decreasing. As can be seen from Fig. 1, the first groove 15 does not lie in the vicinity of the hollow interior 13 of the bottom part 8 of the first piston 4. Therefore, the fluid passage through the bottom part 8 of piston 4 is blocked. Therefore, the (pressurized) fluid is pushed out of the pumping cavity 6 through the (passive) check valve 17 into a common fluid distribution chamber 19. The distribution chamber 19 is used by both cylinders 2, 3. The passive check valve 17 is open due to the pressure differences between the pumping cavity 6 and the (common) distribution chamber 19.

[0042] Furthermore, an electrically actuated valve 20 and a high-pressure valve 21 are arranged connecting to the distribution chamber 19. In the position of the actuated valve 20, as shown in Fig. 1, the actuated valve 20 is in its closed position. Therefore, the fluid that is expelled out of one of the two cylinders 2, 3 is leaving the distribution chamber 19 through the high pressure check valve 21 towards the high pressure fluid manifold 22. From the high-pressure fluid manifold 22, the pressurized hydraulic fluid can be sent to hydraulic consumers, for example. The fluid flow out of the pumping cavity 6 towards the high pressure fluid manifold 22 is indicated by an arrow C in Fig. 1. If the actuated valve 20 remains in its closed position during the complete working cycle of both cylinders 3, 4, the synthetically commutated hydraulic pump 1 essentially behaves like a standard hydraulic pump, well known in the state of the art. This is the so called full stroke pumping mode of the synthetically commutated hydraulic pump 1.

[0043] If the actuated valve 20 will remain open during a complete working cycle of the synthetically commutated hydraulic pump 1, the fluid leaving the pumping cavity 6, 7 will simply be returned towards the low pressure manifold 23, for example the crankshaft case of the crankshaft 11, from which the pumping cavities 6, 7 intake hydraulic oil through the grooves 15, 16. This is the so-called idle mode of the synthetically commutated hydraulic pump 1.

[0044] However, with a synthetically commutated hydraulic pump 1 an "intermediary" state between the idle mode and the full stroke mode can be realized as well. This is the so-called part stroke pumping mode. To realize such a part stroke pumping mode, the actuated valve 20 will be placed into its opened position when (or before) the respective piston 4, 5 (in the present embodiment second piston 5) reaches its bottom dead center (BDC). Therefore, in the beginning of the contraction phase of the respective pumping cavity 6, 7, the hydraulic fluid leaving the pumping cavity 6, 7 will simply be returned to the low pressure fluid manifold 23. However, after a certain traveling distance of the piston 4, 5, the actuated valve 20 will be closed. Starting from this point, the hydraulic fluid, leaving the pumping cavity 6, 7 will be pressurized and leaves the distribution chamber 19 towards the high pressure fluid manifold 22 through the high-pressure check valve 21 (as indicated by arrow C).

[0045] Although in the previous description the first (left) piston 4 was solely described in its contraction phase, while the second (right) piston 5 was only described in its expansion phase, it is to be understood that both pistons 4, 5 will cyclically be in an expansion and contraction phase, depending on the angular position of the crankshaft 11.

[0046] The actuation pattern of the different valves is shown in more detail in the actuation graph 24 of Fig. 2. In the actuation graph 24, the following is shown (from top to bottom): the position 25 of the actuated valve 20; the position 26 of the second (right) piston 5; the position 27 of the second (right) check valve 18; the position 28 of the first (left) piston 4; the position 29 of the first (left) check valve 17; the position 30 of the high pressure valve 21; the pressure p 31 in the distribution chamber 19; the fluid flow rate 32 through the high-pressure valve 19. In connection with the position line 25, 27, 29, 30 indicating the position of the different valves 17, 18, 20, 21, the "higher" state of the respective line 25, 27, 29, 30 indicates an open position of the respective valve 17, 18, 20, 21, while the "lower" stage of the respective line 25, 27, 29, 30 indicates a closed state of the respective valve 17, 18, 20, 21.

[0047] At the time of the bottom dead center 33 (BDC) of the second (right) piston 5, fluid begins leaving the second pumping cavity 7 towards the fluid distribution chamber 19 through the second check valve 18. Since the actuated valve 20 is in its opened position (see line 25), the fluid is simply returned to the low pressure fluid manifold 23 so that the pressure in the distribution chamber 19 (graph 31) remains constant at its lower level. Therefore, no fluid is pumped in the direction of the high-pressure fluid manifold 22 (line 32 at zero level).

[0048] The situation changes as soon as the actuated valve 20 is closed at the closing time 34. Because the return fluid flow in the direction of the low pressure fluid manifold 23 is blocked, the pressure within the distribution chamber 19 will rise to the pressure level of the high-pressure fluid manifold 22 (see line 31). As soon as the pressure level in the distribution chamber 19 has reached the pressure level of the high-pressure fluid manifold 22 (more precisely: slightly exceeded said pressure level), the high pressure check valve 21 will open (change of position 30 of the high-pressure valve 21 at the time 35). Therefore, fluid is ejected towards the high pressure fluid manifold 22 (see line 32) and the pressure level within the distribution chamber 21 will essentially remain constant (line 31).

[0049] At the time 36 the first (left) piston 4 has reached its bottom dead center and starts to contract. Hence, the volume of the second pumping cavity 7 is contracting (see line 28 for the first piston 4 and line 26 for the second piston 5). Therefore, the pressure within the first pumping cavity 6 will rise and the first check valve 17 will open as soon as the pressure level within the first pumping cavity 6 has reached the pressure level of the distribution chamber 19. At this point in time, both pumping cavities 6, 7 will contribute to the fluid output flow of the synthetically commutated hydraulic pump 1 towards the high pressure fluid manifold 22. Therefore, line 32 shows an increase. At the top dead center 37 of the second piston 5, the second pumping cavity 7 will stop contracting, therefore the second check valve 18 will close (line 27), so that the overall fluid flow (line 32) will be provided solely by first pumping cavity 6. At the top dead center 38 of the first piston 4 (see line 28), the first pumping cavity 6 stops contracting. Now both pumping cavities 6, 7 are expanding (see lines 26, 28). However, if both check valve 17, 18 would be solely of a passive check valve type, both check valves 17, 18 would be closed during the expansion phase of the respective pumping cavity 6, 7, leaving the distribution chamber 19 at an elevated pressure. However, the actuated valve 20, used in the embodiment of Fig. 1, is not able to open against a substantial pressure difference between the distribution chamber 19 and the low pressure fluid reservoir 23. Therefore, the pressure in the distribution chamber 19 must be allowed to drop, so that the actuated valve 20 can be opened.

[0050] In the embodiment of the synthetically commutated hydraulic pump 1, shown in Fig. 1, an opening pin 39 is provided for this purpose. The opening pin 39 will hold the first check valve 17 in its open position for a short time after the top dead center 38 (TDC) of the first piston 4. Therefore, the expansion of the first pumping cavity 6 will lead to a pressure drop within the pumping cavity 19 (see line 31). As soon as the pressure in the distribution chamber 19 has dropped to its zero level at time 40 (more precisely: to the pressure level in the low pressure fluid manifold 23), the actuated valve 20 can be opened (see line 25) and the first check valve 17 is allowed to close (see line 29). If the closing time of the first check valve 17 is delayed a little bit past the point when the pressure in the distribution chamber has reached its low pressure level (and the fluid connection through the first groove 15 and the bottom part 8 of first piston 4 is not yet established), the developing underpressure in the first pumping chamber 6 can even be used for opening the actuated valve 20.

[0051] Of course, the depressurization could also be achieved by different means, other than the presently used opening pin 39. For example, an actuated valve 20, being able to open against an elevated pressure could be used. Furthermore, an actuated valve 20 could be used, which has an internal depressurization means. For this, the valve described in British application GB 2430246 A could be used, for example. Another possibility would be to simply provide for an orifice, establishing a fluid channel with a limited cross section between the distribution chamber 19 and the low pressure fluid manifold 23.

[0052] It has to be mentioned that the offset between the working cycles of second pumping cavity 7 and first pumping cavity 6 has to be smaller than 180°. Otherwise, there would be simply no time and/or no possibility for a depressurization of the distribution chamber 19. Therefore, it would be problematic - if possible at all - to open the actuated valve 20 for realizing an idle mode and/or a part stroke mode of the synthetically commutated hydraulic pump 1. In the presently shown example, the suggested phase difference of presently 170° provides for a sufficiently large time interval between the top dead center 38 of first piston 4 and bottom dead center 41 of second piston 5 (the point where the second pumping cavity 7 starts to shrink again), so that a depressurization can be performed.

[0053] In Fig. 3, a schematic drawing of a second embodiment of a synthetically commutated hydraulic pump 42 is shown. This synthetically commutated hydraulic pump 42 can show essentially the same basic design features as the synthetically commutated hydraulic pump 1, shown in Fig. 1. The presently suggested synthetically commutated hydraulic pump 42 is arranged at a sidewall 43 of a device 44. The two cylinders 3, 4 of the synthetically commutated hydraulic pump 42 are arranged at an angle, which can be for example 160°, 170° or the like. The two pistons 4, 5, moving back and forth in the respective cylinders 2, 3, share the same crankshaft 11. The crankshaft 11 can be simply formed as a cylindrical block and does not have to have a special shaping of its surface 10. Of course, grooves 15, 16 (not shown) have to be provided to allow for "breathing" of the respective pumping cavity 6, 7 through the bottom part 8, 9 of the respective pistons 4, 5. To allow for a selective fluid connection between the first pumping cavity 6 and the first groove 15 on one hand and the second pumping cavity 7 and the second groove 16 on the other hand, a slight offset of the two cylinders 2, 3 in an axial direction of the crankshaft 11 can be provided. However, it is also possible to reduce the size (in particular in the axial direction of the crankshaft 11) of the opening of the hollow interior 13, 14 of the respective piston 4, 5 in their bottom-area 8, 9, to provide for such a separation in an axial direction of the crankshaft 11. It is also possible for both pistons 4, 5 to communicate with a single groove 15 in a single eccentric cam 47 forming part of crankshaft 11.

1 synthetically commutated hy-

draulic pump

2 first cylinder

3 second cylinder

4 first piston

5 second piston

6 first pumping cavity

7 second pumping cavity

8 first bottom part

9 second bottom part

10 radial surface

11 crankshaft

12 rotating axis

13 first hollow interior

14 second hollow interior

15 first groove

16 second groove

17 first check valve

18 second check valve

19 distribution chamber

20 actuated valve

21 high-pressure check valve

22 high-pressure fluid manifold

23 low-pressure fluid manifold

24 actuation graph

25 position of actuated valve 20

26 position of second piston 5

27 position of second check valve

18

28 position of first piston 4

29 position of first check valve 17

30 position of high pressure check valve 21

31 pressure in distribution chamber 19

32 fluid flow rates through high-pressure valve 21

33 bottom dead center of second piston 5

34 closing time of actuated valve 20

35 opening time of high pressure check valve 21

36 bottom dead center of first piston 4

37 top dead center of second piston 5

38 top dead center of first piston 4

39 opening pin

40 zero pressure in distribution chamber 19

41 bottom dead center of second piston 5

42 synthetically commutated hydraulic pump

43 sidewall

44 device

45 spring

46 eccentric cam

47 eccentric cam

Claims

1. Fluid working machine (1, 42), comprising at least one fluid inlet port (15, 16, 17), at least one fluid outlet port (22, 23) and a plurality of cyclically changing cavities (6, 7), wherein said fluid working machine (1, 42) is able to supply a fluid flow rate sufficient for hydraulic applications and/or can be supplied by a fluid flow rate, sufficient to propel said fluid working machine (1, 42),
wherein at least one passive fluid connecting means (15, 16, 17, 18, 21) is provided in a fluid path, connecting said fluid inlet port (15, 16, 17) and at least one of said cyclically changing cavities (6, 7),
characterized by at least one actuated valve (20), provided in a fluid path, connecting said fluid inlet port (15, 16, 17) and at least one of said cyclically changing cavities (6, 7), wherein said actuated valve (20) can be actuated on a cycle-by-cycle basis.

2. Fluid working machine (1, 42) according to claim 1, characterised in that at least one of said actuated valves (20) is arranged in a common fluid path of at least two of said cyclically changing cavities (6, 7).

3. Fluid working machine (1, 42) according to claim 1 or 2, characterized in that at least one of said actuated valves (20) and at least one of said passive fluid connecting (15, 16, 17, 18, 21) means are arranged in series and/or in parallel.

4. Fluid working machine (1, 42) according to any of the preceding claims, characterised in that at least one of said actuated valves (20) and a plurality of said passive fluid connecting means (15, 16, 17, 18, 21), in particular of passive fluid connecting means (15, 16, 17, 18, 21) which are connecting to different cyclically changing cavities (6, 7), are connecting to at least one common fluid chamber (19).

5. Fluid working machine (1, 42) according to any of the preceding claims, in particular according to claim 4, characterized by at least one high-pressure valve (21), provided in a fluid path between at least one of said fluid outlet ports (22, 23) and at least one of said cyclically changing cavities (6, 7), in particular between at least one of said fluid outlet ports (22, 23) and at least one of said common fluid chambers (19).

6. Fluid working machine (1, 42) according to any of the preceding claims, characterised in that at least one of said passive fluid connecting means (15, 16, 17, 18, 21) is arranged in a fluid path which is going at least in part through a preferably common driving unit (11) of said plurality of said cyclically changing cavities (6, 7) and/or which is at least in part going through a part (8, 9) of at least one of said cyclically changing cavities (6, 7) which is neighbouring said preferably common driving unit (11), or is designed as a passive valve unit (15, 16, 17, 18, 21), in particular as a poppet valve (17, 18, 21) and/or as a spool valve.

7. Fluid working machine (1, 42) according to any of the preceding claims, characterised in that at least one of said cyclically changing cavities (6, 7) is designed as a cylinder-and-piston device.

8. Fluid working machine (1, 42) according to any of the preceding claims, characterised in that at least two of said cyclically changing cavities (6, 7) are displaced out of phase by at least 100°, 105°, 110°, 115°, 120°, 125°, 130°, 135°, 140°, 145°, 150°, 155°, 160°, 165° or 170° and/or not more than 120°, 125°, 130°, 135°, 140°, 145°, 150°, 155 °, 160 °, 165 °, 170 ° or 175 °.

9. Fluid working machine (1, 42) according to any of the preceding claims, characterised in that at least one of said cyclically changing cavities (6, 7) and/or at least one of said common fluid chambers (19) and/or at least one of said passive fluid connecting means (15, 16, 17, 18, 21) and/or at least one of said actuated valves (20) comprises at least one fluid depressurization means (39), which is preferably designed as a controllable depressurization means (39).

10. Fluid working machine (1, 42) according to any of the preceding claims, in particular according to claim 9, characterised in that at least one of said fluid depressurization means (39) is designed as an orifice or as a fluid connection prolonging means (39), wherein said fluid connection prolonging means is designed and arranged in a way to initiate and/or to prolong an open state of at least one of said passive fluid connecting means (15, 16, 17, 18, 21) and/or at least one of said actuated valve means (20).

11. Fluid working machine (1, 42) according to any of the preceding claims, characterized in that at least one of said actuated valves (20) is designed as an electrically actuated valve (20), preferably comprising a latching device, in particular a magnetic latching device and/or a latching device for latching said actuated valve (20) in an end position.

12. Fluid working machine (1, 42) according to any of the preceding claims, characterised in that said fluid working machine (1, 42) is designed as a synthetically commutated hydraulic machine.

13. Fluid working machine (1, 42) according to any of the preceding claims, characterised in that a pumping stroke of at least one of said cyclically changing cavities (6, 7) pumps a fluid volume of at least 1 ml, 2 ml, 3 ml, 4 ml, 5 ml, 6 ml, 7 ml, 8 ml, 9 ml and/or 10 ml.

14. Method of operating a fluid working machine (1, 49), comprising at least one fluid inlet port (15, 16), at least one fluid outlet port (22, 23) and a plurality of cyclically changing cavities (6, 7),
wherein said fluid working machine (1, 42) is able to supply a fluid flow rate sufficient for hydraulic applications and/or wherein said fluid working machine (1, 42) can be supplied by a fluid flow rate, sufficient to propel said fluid working machine (1, 42),
wherein the fluid input of at least one of said plurality of cyclically changing cavities (6, 7) is sucked in from said fluid inlet port (15, 16, 17) through at least one passive fluid connecting means (15, 16, 17, 18, 21),
characterized by at least one actuated valve (20), selectively connecting at least one of said fluid inlet ports (15, 16, 17) and at least one of said cyclically changing cavities (6, 7), wherein said actuated valve (20) can be actuated on a cycle-by-cycle basis.

15. Method according to claim 14, characterised in that said fluid working machine (1, 42) is designed according to any of claims 1 to 13.

Drawing