Hydraulic piston apparatus

Abstract

 A hydraulic piston apparatus has an eccentric shaft (C), a rotor (R) having the eccentric shaft (C) eccentrically disposed therein, a plurality of pistons (P) radially disposed within the rotor (R), heads of the pistons being normally contacted with the outer periphery of the eccentric shaft (C), and working liquid current straightening means disposed in such a manner as to contact with a working liquid inlet and outlet port of each of the pistons.

Description

BACKGROUND OF THE INVENTION

[0001] This invention is related, in a broad sense, to a hydraulic piston apparatus and particularly to a hydraulic pump and a hydraulic motor as a hydraulic piston apparatus.

[0002] More specifically, it relates, in its third and seventh invention, to a variable capacity hydraulic piston apparatus of a variable capacity type which is simple in structure and has a long service life.

[0003] The "piston" used herein is of the type for feeding and receiving a hydraulic pressure within a cylinder and in which its length (whether it is long or not) with respect to its diameter is not questioned.

[0004] As for hydraulic pumps and motors, many proposals have heretofore been made. Some of the representative examples of such proposals are gear pumps, vane pumps, piston pumps, axial piston pumps and the like. As for variable capacity pumps among them, cam plate type piston pumps occupy a mainstream in pumps of the type which has a comparatively high discharge pressure as shown in Fig. 3.

[0005] The reason is that employment of pistons (plungers) 1, 1a make it easy to obtain a liquid confined pressure within cylinder chambers 2, 2a and the discharge quantity can be optionally established by changing the angle of a cam plate 3. Another reason is that management of accuracy of the outer diameters of the cylindrical pistons 1, 1a and the inner diameter of the cylinder is easy and manufacturing cost can also be reduced.

[0006] On the other hand, as is shown in Fig. 3, a linkage between the cam plate 3 and piston rods 4, 4a, and a service life of a connecting portion between an input rotational shaft 5 and the cam plate 3 have heretofore been considered to include problems. Regarding the single body of the piston, liquid current becomes an alternating current owing to reciprocating motion. A method for sealing a current plate for converting the alternating current to an unidirectional direct current also becomes a big problem.

[0007] The axial pump cannot escape from this problem as long as its has the same construction.

SUMMARY OF THE INVENTION

[0008] It is therefore an object of the present invention to provide a hydraulic piston apparatus which is simple in structure and small in size, long in service life and low in manufacturing cost.

[0009] That is, in view of the above-mentioned problems, a hydraulic piston apparatus according to the present invention is designed such that a piston is actuated using an eccentric shaft.

[0010] Concrete construction of a hydraulic piston apparatus according to the present invention will be described in detail.

[0011] The construction of a hydraulic piston apparatus of the first invention will be described first. According to this invention, first, there is an eccentric shaft. Second, there is a rotor. This rotor has the eccentric shaft eccentrically disposed therein. There are also a plurality of pistons. These pistons are radially disposed within the rotor and the heads of the pistons are normally contacted with the outer periphery of the eccentric shaft. Furthermore, there is working liquid current straightening means. This working liquid current straightening means is disposed in such a manner as to contact with a working liquid inlet and outlet port of the piston.

[0012] Next, the construction of a hydraulic piston apparatus of the second invention will be described. In this invention, first, there is an eccentric shaft. Second, there is a rotor. This rotor has the eccentric shaft concentrically disposed therein. Also, there is a stator. This stator is provided therein with the rotor and is concentrical with respect to the eccentric shaft.

[0013] Furthermore, there are a plurality of pistons. These pistons are radially disposed within the rotor, and the heads of the pistons are normally contacted with the inner periphery of the stator. And there is working liquid current straightening means. This working liquid current straightening means is disposed in such a manner as to contact with a working liquid current inlet and outlet port of the pistons.

[0014] The construction of a variable capacity hydraulic piston apparatus of the third invention will now be described, In this invention, an eccentric shaft is rotatable. Regarding all the remaining construction, please refer to the construction of the first and the second invention.

[0015] Next, the construction of a hydraulic piston apparatus of the fourth invention will be described. This invention is a hydraulic piston apparatus comprises an eccentric shaft rotor, a stator having the eccentric shaft rotor eccentrically disposed therein, a plurality of pistons radially disposed within the stator, heads of the pistons being normally contacted with the outer periphery of the eccentric shaft rotor, and working liquid current straightening means communicating with a working liquid inlet and outlet port of each of the pistons and including timing detection means such as rotary encoder for detecting the timing for rotation of the eccentric shaft rotor and a change-over valve controlled by the timing detection means.

[0016] The construction of a hydraulic piston apparatus of the fifth invention will now be described. In this invention, first, there is a rotor. Next, there are a plurality of eccentric shafts. These eccentric shafts are provided to the rotor. Furthermore, there are a plurality of pistons. Each head of the pistons is normally contacted with the outer periphery of each of the eccentric shafts and piston motion of said head is phasewise split. And there is holding means. This holding means includes a housing, a stator, etc. for holding the pistons. Furthermore, there is working liquid current straightening means. This working liquid current straightening means is communicated with a working liquid inlet and outlet port of each of the pistons and includes timing detection means such as rotary encoder for detecting the timing for rotation of the rotor and a change-over valve controlled by the timing detection means.

[0017] Next, the construction of a hydraulic piston apparatus of the sixth invention will be described. In this invention, there is a rotational shaft first. Then, there are a plurality of cylinders. The cylinders are disposed parallel with the rotational shaft. Arrangement being such that piston motion of a piston head disposed within each of the cylinders is phasewise split. And there are a plurality of piston units. These piston units are used for the plurality of cylinders, respectively. Furthermore, there is a cam. This cam is adapted to permit a part of the plurality of piston units to be engaged therewith. The cam is disposed on the rotational shaft. The piston units are caused to effect piston motion in the longitudinal direction of the rotational shaft by rotation of the rotational shaft. Finally, there is working liquid current straightening means. This working liquid current straightening means includes timing detection means such as rotary encoder for detecting the timing for rotation of the rotational shaft and a change-over valve controlled by the timing detection means.

[0018] Lastly, the construction of a variable capacity hydraulic piston apparatus of the seventh invention will be described. In this invention, the timing means includes timing variable means capable of varying the timing control time such as rotary joint or the like.

[0019] As a hydraulic piston apparatus according to the present invention was such constructed as mentioned above, the following functions were obtained. The function of a hydraulic piston apparatus of the first invention will be described first. In this invention, the rotor has the eccentric shaft disposed therein, a plurality of pistons are radially disposed within the rotor, and the heads of the pistons are normally contacted with the outer periphery of the eccentric shaft. Accordingly, the piston is actuated at a piston time difference by rotation of the rotor.

[0020] And the working liquid current straightening means is disposed in such a manner as to contact with the working liquid inlet and outlet port of the piston. Accordingly, the working liquid current is straightened here.

[0021] Next, the function of a hydraulic piston apparatus of the second invention will be described. In this invention, the rotor has the eccentric shaft concentrically disposed therein, and the stator is provided therein with the rotor, the plurality of pistons being radially disposed within the rotor, the heads of the pistons being normally contacted with the inner periphery of the stator. Accordingly, these pistons are actuated at a piston time difference by rotation of the rotor.

[0022] Furthermore, the working liquid current straightening means is disposed in such a manner as to contact with the working liquid current inlet and outlet port of the pistons. Accordingly, the working liquid current is straightened here.

[0023] The function of a variable capacity hydraulic piston apparatus of the third invention will now be described. In this invention, the eccentric shaft is rotatable. Accordingly, an intaking and discharging quantity of the working liquid is changed by changing the eccentric angle. Regarding all the remaining functions, please refer to the functions of the first and the second invention.

[0024] Next, the function of a hydraulic piston apparatus of the fourth invention will be described. In this invention, the stator having the eccentric shaft rotor eccentrically disposed therein is provided with the plurality of pistons radially disposed within the stator, and heads of the pistons are normally contacted with the outer periphery of the eccentric shaft rotor. Accordingly, the pistons are actuated at a piston time difference by rotation of the eccentric shaft rotor.

[0025] And the working liquid current straightening means communicating with the working liquid inlet and outlet port of each of the pistons and including timing detection means such as rotary encoder for detecting the timing for rotation of the eccentric shaft rotor and a change-over valve controlled by the timing detection means straightens the working liquid current as working liquid current straightening means having no sliding portion.

[0026] The function of a hydraulic piston apparatus of the fifth invention will now be described. In this invention the plurality of eccentric shafts are provided to the rotor, the plurality of pistons being disposed such that each head of the pistons is normally contacted with the outer periphery of each of the eccentric shafts and piston motion of the head is phasewise split, the pistons being held by the holding means. Accordingly, the pistons are actuated at a piston time difference by rotation of the rotor.

[0027] And the working liquid current straightening means is communicated with a working liquid inlet and outlet port of each of the pistons and includes timing detection means such as rotary encoder for detecting the timing for rotation of the rotor and a change-over valve controlled by the timing detection means. Accordingly, the working liquid current is straightened by switching the change-over valve in such a manner as to match the timing with rotation of the rotor.

[0028] Next, the function of a hydraulic piston apparatus of the sixth invention will be described. In this invention, the plurality of cylinders are disposed parallel with the rotational shaft. Arrangement being such that piston motion of a piston head disposed within each of the cylinders is phasewise split. And the plurality of piston units are used for the plurality of cylinders, respectively. Accordingly, there can be obtained phasewise split piston motion. Concretely, the rotational shaft is provided with the cam and this cam is adapted to permit a part of the plurality of piston units to be engaged therewith. The cam is disposed on the rotational shaft. This cam causes the piston units to effect piston motion in the longitudinal direction of the rotational shaft in accordance with rotation of the rotational shaft. Accordingly, a piston motion is effected by this rotation. Finally, the working liquid current straightening means including the timing detection means such as rotary encoder for detecting the timing for rotation of the rotational shaft and the change-over valve controlled by the timing detection means straightens the working liquid current from the pistons.

[0029] Lastly, the function of a variable capacity hydraulic piston apparatus of the seventh invention will be described. In this invention, the timing means includes timing variable means capable of varying the timing control time. Accordingly, the intaking and discharging quantity of the working liquid can be varied by this. Regarding all the remaining functions, please refer to the functions of the fourth and the fifth invention respectively.

BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Fig. 1 is a front sectional view of one embodiment of a hydraulic piston apparatus according to the present invention.

[0031] Fig. 2 is a side view of a modified embodiment of Fig. 1.

[0032] Fig. 3 is a side view of one embodiment of the prior art.

[0033] Fig. 4 is a chart showing a relation between intaking and discharging quantities of working liquid of the embodiment of Fig. 1 into and from each piston and time.

[0034] Fig. 5 is an illustration, when taken at each port, of Fig. 4.

[0035] Fig. 6 is a front sectional view of one embodiment of another embodiment.

[0036] Fig. 7 is an explanatory view of one embodiment of the conventional piston.

[0037] Fig. 8 is a front sectional view of one embodiment of a variable capacity type hydraulic piston apparatus.

[0038] Fig. 9 is a comparison chart of angle of rotation of a cam of the embodiment of Fig. 8 and an average discharging rate of working liquid.

[0039] Fig. 10 is a front sectional view of one embodiment of still another invention.

[0040] Fig. 11 is one example in which pistons are linearly arranged, Fig. 11a is a front view of a cam portion thereof, and Fig. 9(b), and Fig.11(b) is a whole side sectional view.

[0041] Fig. 12 is an illustration of the pistons P radially arranged, Fig. 12(a) is a front view of a portion of cams C1 through C3, and Fig. 12(b) is a side sectional view of its entirety.

[0042] Fig. 13 is a chart showing the change-over timing of three port valves for intaking and discharging working liquid in a cylinder chamber of the embodiment of Fig. 10.

[0043] Fig. 14 is a front sectional view showing a tracer valve and a change-over cam according to another embodiment of Fig. 10 and nearby.

[0044] Fig. 15 is a side view showing a tracer valve and a change-over cam according to still another embodiment of Fig. 10 and nearby.

[0045] Fig. 16 is a front sectional view of one embodiment of a swing motor of Fig. 15.

[0046] Fig. 17 is a block diagram of one embodiment showing a countermeasure for time delay required for change-over.

[0047] Fig. 18 is a side sectional view of another embodiment of Fig. 1.

[0048] Fig. 19 is a side sectional view of still another embodiment of Fig. 1.

[0049] Fig. 20 is a side view of one embodiment showing the construction of a hydraulic piston apparatus according to still another invention and in which a part of its pistons is omitted.

[0050] Fig. 21 is a front view of the embodiment of Fig. 20.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0051] Several embodiments of a hydraulic piston apparatus according to the present invention will be described in detail hereunder with reference to the accompanying drawings.

[0052] One embodiment of the first invention will be described first in which a rotor is provided with three piston and cylinder assemblies embedded therein at equal 120° distances.

[0053] Fig. 1 is a front sectional view of the above, and Fig. 2 is a side view thereof. In order to facilitate an easy understanding, in Fig. 2, a first cylinder S is in a position at 0° in the sectional view and a third cylinder S2 is in a position at 180° and therefore four cylinders are provided or embedded.

[0054] The stator ST and a cam C acting as an eccentric shaft are fixed. When the rotor R is rotated clockwise, the piston P1 is moved toward the center of the rotor R along the cam C in an initial stage of its rotation in Fig. 1. Therefore, it intakes working liquid from a port A (in the drawing, a spring for urging the piston P against the rotor R is omitted. The same is true hereinafter). Similarly, the piston P3 intakes the working liquid from the port A. On the other hand, the piston 2 is moved outward to discharge the working liquid to a port B.

[0055] Fig. 4 shows a chart showing a relation between the working liquid intaken or discharged and strokes of the pistons P1 through P3 when the rotor R is rotated clockwise and presuming the position of the piston P1 of Fig. 1 is 0° . The waveforms shown in Fig. 4 are obtained when the configuration of the cam C is determined such the action of the pistons P resemble to a sine waveform every time the rotor R makes one full rotation.

[0056] Each piston P, as shown in Fig. 4, repeats intaking and discharging operation in a state displaced phasewise by 120° . However, if looked per each port, grooves A1 and B1 act as current straighteners. Therefore, if the intaking and discharging states of the working liquid of the respective pistons P are composed, the port A keeps intaking the working liquid and the other port B keeps discharging the working liquid as shown in Fig. 5.

[0057] The grooves A1 and B1 do the same work as the cam plate type pump. If the rotating direction of the rotor R is reversed, the port A discharges the working liquid and the port B intakes it this time. If the stroke of the piston P is represented by D and the diameter by d, the discharge capacity and intake capacity per on full rotation of the rotational shaft becomes 3Dπ d₂/4 in case of three pistons P.

[0058] In this case, sealing of the grooves A1 and B1 for performing a current straightening function becomes very difficult because of the presence of a space between the rotor R and the stator ST. Therefore, in order to reduce the dimension of this space, the following method was contemplated.

[0059] In Fig. 6 showing one embodiment of the second invention, a current straightening shaft is disposed at an inner side of the rotor R and has current straightening grooves A2 and B2 formed in its outer surface. Each of the current straightening grooves A2 and B2 is provided with a port. If the center of the stator ST is displaced from the centers of the rotor R and current straightening shaft RF, it works quite in the same way as that of Fig. 1. Although the sealing between the rotor R and the current straightening shaft RF becomes much easier because the dimension of the space formed therebetween is smaller than that mentioned above, the sliding portion is not eliminated.

[0060] As is shown in Fig. 7, the situation is quite the same to a structure formed of a combination of the pistons P1 through P3 with cranks 6a through 6c radially disposed. That is, in a mechanism for straightening an alternating current according to reciprocal motion of the piston P, it is necessary to rotate the current straightening plate strictly in synchronism with the crankshaft. Although there is a type for effecting the rotation in accordance with the opening and closing operation of the valve as an internal combustion engine like a gasoline engine, the present inventor does not know any example where this is used in a working liquid pressure pump, a motor, etc. It seems to him that the problem of internal leakage due to enormous working liquid pressure is again the neck.

[0061] In the above mentioned type of a working liquid current straightening structure, the problem of working liquid leakage is always accompanied. Furthermore, in order to make it variable capacity, the conventional pump and motor are all formed in a structure in which stroke of the piston P is variable.

[0062] In the first mentioned structure, variable capacity can be obtained by controlling the displacing amount of the cam C. However, as the cam C receives the pressure of the piston P straight, a simple structure and an improved strength are demanded in order to increase reliability. Therefore, in order to control the displacing amount of the cam C, a large-scaled mechanism is resulted and the initial object is impossible to achieve. Moreover, this is no use at all for solving the problem of working liquid leakage of the current straightening mechanism.

[0063] There will be described a method for making the capacity variable while maintaining a constant stroke next.

[0064] In the structure of Fig. 1, the cam C is displaced in the direction of 0° . If the cam C is slightly rotated to set the direction of displacement in the direction of 270° and the rotor R is rotated clockwise as in one embodiment of the third invention shown in Fig. 8, the piston P1 intakes the working liquid within 0° to 90° and discharges the working liquid within 90° to 180° . Moreover, the intaking and discharging rates are equal. And it discharges the working liquid within 180° to 270° and discharges it within 270° to 0° . Thus, both are equal. Therefore, the balance of the intaken working liquid and the discharged working liquid becomes zero. The same is true to the port B. The rotor R is merely rotated idle and the discharging rate becomes zero. Of course, the ripple portion exists but in case of three cylinders, the ripple portion is also intaken and discharged between the cylinders. Therefore, the ripple portion which appears on the outside piping is extremely reduced. Furthermore, if the number of the cylinders is increased, the ripple portion is more decreased. Therefore, thoughtless employment of multicylinder is not advantageous in view of strength. From a practical view point, approximately three to 9 cylinders are proper.

[0065] The discharging quantity Q of the pump, as shown in Fig. 9, becomes maximum when the facing direction of the cam C is 0° . The discharging quantity Q is decreased when the cam C is rotated whether clockwise or counterclockwise. When in a position of 90° or 270° , it becomes Q = 0. When it is further rotated, the facing direction of Q is reversed this time and it becomes -Q_max when in a position of 180° . From this, it will be understood that the discharging direction can be reversed without changing the rotating direction of the rotor R. That is, this means that a two-way type variable capacity pump is accomplished only by unidirectional rotation. Moreover, in this case, the cam C can be rotated with a very simple mechanism and the neighbor of the cam C is nothing to do with the working liquid leakage and thus convenient.

[0066] Next, it is necessary to solve the problem of sealing at the current straightening portion.

[0067] At the time when the current is straightened, if there is a sliding portion, it means that leakage of the working liquid is generated from at portion. Therefore, it is ideal to omit the sliding portion, if possible. Of course, parts such as rotary joints, etc. are commercially available, but they also have a sliding portion and thus require mechanical sealing.

[0068] In view of the above, the inventor of the present invention has developed one as shown in Fig 10 which is one embodiment of the fourth invention. The piston P1 is changed over and connected to a port A or a port B with a three-port two-position electromagnetic valve V1. Other pistons P2 and P3 are also connected to the port A or B with three-port two-position electromagnetic change-over valves V2 and V3 respectively.

[0069] When the cam C integral with the input shaft is rotated, the pistons P1 through P3 are reciprocally moved in association with the rotation of the cam C to cause the working liquid to be intaken to and from the respective cylinder chambers. In this cam C, if a bearing Br is provided as shown in Fig. 10, the connecting portion between the piston P and the cam C is not slidingly moved. Accordingly, there is no worry about friction and wear.

[0070] Springs are built in the cylinder chambers of the respective pistons P1 through P3 so that the pistons P are normally urged against the cam C. However, if a preliminary pressure is applied to the whole working liquid pressure circuit, the pistons P are normally urged against the cam C due to the preliminary pressure. In this case, therefore, springs are not required.

[0071] Furthermore, as is shown in Fig. 11 showing one embodiment of the fifth and the seventh invention, a rotary encoder E is mounted on the shaft in order to detect an angle of rotation of the input shaft. Fig. 11 shows one example wherein the pistons P are linearly arranged, Fig. 11(a) is a front view of the cam C portion thereof, and Fig. 11(b) is a side sectional view of its entirety. Fig. 12 shows another example wherein the pistons P are radially arranged, Fig. 12(a) is a front view of the cams C 1 through 3 portions, and fig. 12(b) is a side sectional view of its entirety. In order to simplify the drawing, the number of the pistons is an even number.

[0072] There can be contemplated a combination type of Fig. 11 with Fig. 12. That is, instead of providing radial type pistons arranged in a multiplex manner or providing radial type pistons on the same plane (though it becomes large), the pistons are arranged in the longitudinal direction of the rotor R. Owing to the foregoing arrangement, the number of pistons can be unlimitedly increased as a multiplex radial type.

[0073] As is shown in Fig. 10, if the three-port two- position electromagnetic change-over valve V1 is connected to the port A from the time when the cam C is fixed in the direction of 0° and the piston P1 is pushed upto the top dead point until the cam C is rotated clockwise to the direction of 180° , i.e., during a section of from 0° to 180° , the working liquid is intaken through the port A. During the next section of from 180° to 360° , the valve V1 is switched to the port B and the working liquid is discharged through the port B. This state is depicted in Fig. 13 showing the incoming and outgoing state of the working liquid to and from the cylinder chamber and the switching timing of the three-port valve.

[0074] Similarly, the piston P2 is switched in the state where the phase is delayed by 120° and the piston P3 is switched in further delayed state by 120° . This is quite the same function as that of the current straightening grooves A1 and B1 shown in Fig. 1 and it becomes; discharging quantity Q = max. Likewise, if the switching timing of all three-port valves V1 through V3 is delayed by 45° , Q becomes a half of the max. If it is further delayed by 45° , it becomes Q = 0. Therefore, by delaying the switching timing of the three-port valve in accordance with the angle information of the rotary encoder, the same effect can be obtained as that which can be obtained by rotating the angle of the eccentric cam C of Fig. 2.

[0075] In the above embodiment, the rotary encoder E was used in order to detect the angle of rotation of the input shaft (eccentric cam C). It is to be noted that the types of the encoder are not questioned and they may be optical type, magnetic type and mechanical type as long as they can detect the angle with high accuracy.

[0076] In the foregoing, a method for electrically switching the ports was described. One example for performing the same procedure by a mechanical method will be described next.

[0077] As is shown in Fig. 14, the three-port tracer valves 10a, 10b and 10c are equally radially arranged on a ring 10 and the rotational shaft 12 connected to the rotor R is provided with a change-over cam 11 (having a configuration able to be switched every 180° ) for controlling the valves 10a, 10b and 10c. And by rotating the angle of the ring 10 rightward and leftward, the switching timing o the straightening current can be adjusted in the same manner as mentioned in the preceding paragraph. By this, it becomes a variable capacity type.

[0078] This ring 10 can also be made into a two-way discharging variable capacity type pump by means of rotation by ± 90° about a position of 90° or 270° while maintaining the unidirectional rotation of the rotational shaft 12. When the tracer valves 10a, 10b and 10c are not desirous to be rotated, the same effect can be obtained by shifting the phase of the change-over cam 11 with respect to the eccentric cam C for driving the pistons C. A concrete example of this, as shown in Fig. 15, is designed such that a swinging motor 13 is interposed between the cam C and the change-over cam 11, and a working liquid pressure P_s is applied to the center of the rotational shaft 12 from an external portion via the rotary joint 14. As the singing motor 13 has a shaft 13a which is rotated to an angle where the internal spring 13b and working liquid pressure P_s are balanced, the phase of the change-over cam 11 can easily be controlled only by the working liquid pressure.

[0079] A counter measure for a time delay required for switching will now be described.

[0080] In a recent time, it becomes possible to vary the speed of rotation of an electric motor at a low cost by inverter driving. If the capacity of a pump can be varied and the speed of rotation can be varied, control accuracy can be improved in the vicinity of microcapacity A_min.

[0081] In this case, control disadvantages are taken place. That is, it takes a certain time from the time when the angle of rotation of the rotational shaft 12 is detected till the time when controlling of the current straightening valve is over. The reason is as follows. If the speed of rotation of the rotational shaft 12 is varied, the time requires for the rotational shaft 12 to make one full rotation is varied. However, if the delay time τ of the straightening current is constant, the switching phase is greatly displaced in proportion to the speed of rotation.

[0082] This situation will be understood from the following expression.

[0083] That is,


wherein x is phase correcting value, v is a speed of rotation RPM, π is 180° , and τ is delayed time sec.

[0084] If V = 1500 RPM and the current straightening time is τ = 0.01sec, the following relation can be obtained.


And the phase is displaced by so great as 90° . Only by displaying the phase by 90° , the capacity is varied from Q = max to Q = 0. Therefore, if an error so great as 90° is taken place, it becomes impossible to use. Therefore, as is shown in Fig. 17, a correct angle position of the shaft is detected by a signalφ from the rotary encoder, phase shifting is sequentially performed by the number of cylinders at the rate of 360° /n wherein n represents the number of cylinders and signals of φ ₁, φ ₂ ... ... φ ₃ are produced in a phase processing circuit.

[0085] Then, they are converted to speed signals by a speed converting circuit and a phase correcting calculation is performed in according with the above relation to figure out a corrected phase angle x and then, n pieces of signals φ are advanced in parallel in phase by a phase advancing circuit. By such phase advanced signals φ ₁', φ ₂' ... ... φ ₃',n pieces of current straightening change-over valves are controlled. If correction is performed in this way, the pump is normally operated.

[0086] Although three-cylinders are employed in the above examples only excepting the last one, three to nine cylinders of radial arrangement on one stage can be considered for a practical use. In that case, if the number of cylinders is represented by n, the cylinders are equally dividedly arranged at a ratio of 360° /n and the phase may be performed at that ratio. Although the function as a pump was described, in case of a working liquid pressure pump, most of all can be used as a liquid pressure motor immediately. Even in this system, there is no inconvenience in function as a liquid pressure motor. Therefore, all of the above description can be applied as a liquid pressure two-way variable capacity pump and a two-way variable capacity motor.

[0087] The current straightening grooves A1 and B1 shown in Fig. 1 may be brought to the side of the stator ST as shown in Fig. 18. This is true to Fig. 18.

[0088] Although it was described in Fig. 17 that the signal φ from the rotation detecting means is converted to a speed signal, it may be designed such that a rotation speed detector besides the angle detector is mounted on the shaft and the advance phase circuit is controlled based on the signal.

[0089] Lastly, one embodiment of the construction of a hydraulic piston apparatus of the sixth invention will be described with reference to a side view of Fig. 20 and a front view of Fig. 20. In Fig. 20, two pistons are omitted for simplicity of the drawing.

[0090] First, there are a rotational shaft SP, and a piston PS disposed in parallel relation with the rotational shaft SP. this piston PS is designed as follows. That is, there are a plurality of cylinders SY. The plurality of cylinders SY are disposed such that piston motion of piston heads PH in the cylinders SY is phasewise equally divided. Concretely, three pistons PS are arranged at a distance of 120° in this embodiment as shown in Fig. 21. And the piston units PU are caused to perform a piston motion in the state where the piston units PU are displaced in phase by 120° . The plurality of piston units PU are inserted in the plurality of cylinders SY respectively.

[0091] Furthermore, the rotational shaft SP is provided with a cam CS. This cam CS is formed of a groove having a shape formed of a continuous letters of S. Engaged in this cam CS are cam groove guides as a part of the plurality of piston units PU. In addition, this cam CS is adapted to cause the respective piston units PU to effect a piston motion in accordance with the rotation of the rotational shaft SP.

[0092] Lastly, there is a working liquid current straightening means. Although this working liquid current straightening means is not illustrated, this is something like that of Fig. 4 and that of Fig. 5, and comprises timing detecting means such as rotary encoder, etc., for detecting the timing of the rotation of the rotational shaft, and a change-over valve controlled by the timing detecting means.

[0093] As a hydraulic piston apparatus according to the present invention is such constructed as mentioned above, such effects as described in the above description on each invention were produced. Particularly, it became a hydraulic piston apparatus which is very simple in construction and which has a long service life. Furthermore, in the third and seventh invention, a variable capacity type hydraulic piston apparatus became easy.

Claims

1. A hydraulic piston apparatus comprising:
   an eccentric shaft;
   a rotor having said eccentric shaft eccentrically disposed therein;
   a plurality of pistons radially disposed within said rotor, heads of said pistons being normally contacted with the outer periphery of said eccentric shaft; and
   working liquid current straightening means disposed in such a manner as to contact with a working liquid inlet and outlet port of each of said pistons.

2. A hydraulic piston apparatus
   an eccentric shaft;
   a rotor having said eccentric shaft concentrically disposed therein;
   a stator having said rotor contained therein and placed eccentric with respect to said eccentric shaft;
   a plurality of pistons radially disposed within said rotor, heads of said pistons being normally contacted with the inner periphery of said stator; and
   working liquid current straightening means disposed in such a manner as to contact with a working liquid inlet and outlet port of each of said pistons.

3. A variable capacity hydraulic piston apparatus as claimed in claim 1 or claim 2, wherein said eccentric shaft is rotatable.

4. A hydraulic piston apparatus comprising:
   an eccentric shaft rotor;
   a stator having said eccentric shaft rotor eccentrically disposed therein;
   a plurality of pistons radially disposed within said stator, heads of said pistons being normally contacted with the outer periphery of said eccentric shaft rotor; and
   working liquid current straightening means communicating with a working liquid inlet and outlet port of each of said pistons and including timing detection means such as rotary encoder for detecting the timing for rotation of said eccentric shaft rotor and a change-over valve controlled by said timing detection means.

5. A hydraulic piston apparatus comprising:
   a rotor;
   a plurality of eccentric shafts provided to said rotor;
   a plurality of pistons each head of which is normally contacted with the outer periphery of each of said eccentric shafts, piston motion of said head being phasewise split;
   holding means such as housing, stator, etc. for holding said pistons; and
   working liquid current straightening means communicating with a working liquid inlet and outlet port of each of said pistons and including timing detection means such as rotary encoder for detecting the timing for rotation of said rotor and a change-over valve controlled by said timing detection means.

6. A hydraulic piston apparatus comprising:
   a rotational shaft;
   a plurality of cylinders disposed parallel with said rotational shaft, piston motion of a piston head disposed within each of said cylinders being phasewise split;
   a plurality of piston units for said plurality of cylinders;
   a cam disposed on said rotational shaft and for permitting a part of said plurality of piston units to be engaged therewith, said cam being adapted to cause said piston units to effect piston motion in the longitudinal direction of said rotational shaft; and
   working liquid current straightening means including timing detection means such as rotary encoder for detecting the timing for rotation of said rotational shaft and a change-over valve controlled by said timing detection means.

7. A variable capacity hydraulic piston apparatus as claimed in claim 4, claim 5 or claim 6, wherein said timing means includes timing variable means capable of varying the timing control time such as rotary joint or the like.

Drawing