Hydraulic power unit

Abstract

 In order to obtain a hydraulic power unit of small dimensions and simple construction, particularly adapted for double-acting hydraulic actuators, the pump (A) of the power unit is constituted by a reversible pump, activated, for example, by a reversible electric motor, while the two mouths (B, B') of the pump, each of which can operate alternately as a suction mouth and as a delivery mouth, are each connected or connectible, possibly by means of a hydraulic distributor (R), at one side to conduits (C, C' or C", C"') for connection to the user and at the other side to the tank (H) for the hydraulic liquid either by means of associated unidirectional valves (F, F') opening in the direction of the flow from the tank (H) to the respective mouth (B, B'), or - parallelly with said unidirectional valves (F, F') - by means of associated automatic pressure relief valves (L, L').

Description

[0001] This invention relates to a hydraulic power unit particularly adapted for hydraulic circuits for activating double-acting hydraulic actuators or reversible-movement users, and comprising a pump, a tank for the hydraulic liquid and valves for connecting the pump to the tank.

[0002] The invention aims to provide a hydraulic power unit of the specified type permitting to selectively activate in either direction reversible-movement users, for example double-acting hydraulic actuators, and to readily reverse the direction of operation even without a sliding valve, said power unit being of easy and economical construction while ensuring high reliability and long duration, as well as extremely reduced dimensions, whereby it can be advantageously used in all circumstances where space problems are to be solved.

[0003] This problem is solved by the invention by means of a hydraulic power unit of the type described above and characterized in that the pump is of reversible type and may be selectively activated in either direction, for example by means of a reversible electric motor, while two mouths of the pump, each of which can operate alternately as a suction mouth and as a delivery mouth, are each connected or connectible at one side to the user and at the other side to the hydraulic liquid tank, either by means of an associated unidirectional valve which opens only in the direction of the flow from the tank to the respective mouth, or - in parallel with said unidirectional valve - by means of an associated automatic pressure relief valve.

[0004] Preferably, the unidirectional and/or pressure relief valves are so constructed as to permit a limited seepage of hydraulic liquid towards the tank in the closure direction of the unidirectional valves and in the closure position of the pressure relief valves.

[0005] Therefore, in order to activate a double-acting user in either direction, it is sufficient to activate in either direction the reversible pump of the power unit according to the invention, for example by accordingly revesing by means of an electrical switch the direction of rotation of the respective actuating electric motor. Hydraulic liquid is sent to the user from one of the mouths of the pump, operating as a delivery mouth, while the other one, operating as a suction mouth sucks and receives the hydraulic liquid returned from the user.

[0006] In as much as, generally, in the double-acting users, the flowrate of the delivery hydraulic liquid is substantially the same as the flowrate of the returned hydraulic liquid, in either operative directions, in the power unit according to the invention the hydraulic liquid tank substantially has the only purpose of compensating for any possible small differences of flowrate between the hydraulic liquid delivered to the user and that returned from the user. As a consequence, the hydraulic liquid tank of the power unit according to the invention may be very small, i.e. of minimum dimensions, and it may be easily integrated with the power unit.

[0007] Preferably, according to a further characteristic of the invention, which permits to further simplify the construction of the hydraulic power unit, the two mouths of the reversible pump communicate with two annular circuits which are parallelly connected either to the hydraulic liquid tank by a common connecting conduit, and to the user by means of two connecting conduits operating alternately, one as a delivery conduit and the other as a return conduit, and vice versa, the two unidirectional valves being interposed in one of these annular circuits and the pressure relief valves in the other annular circuit, at opposite sides of the common connecting conduit to the hydraulic liquid tank.

[0008] When the user being activated by the hydraulic circuit operated by the power unit according to the invention and formed for example by a double-acting actuating cylinder, automatically maintains its position, where it has been moved, and is not to be maintained in this position by said hydraulic actuating circuit, then, the two mouths of the reversible pump of the power unit according to the invention may be connected directly to said user, each through a corresponding connection conduit, for example, to the hydraulic actuating cylinder on two opposite sides of its piston. In this circumstance, to activate the actuating cylinder in either direction, the reversible pump of the power unit is just to be activated in either direction by specifically selecting the corresponding direction of rotation of the respective actuating electric motor. The activation of the actuating cylinder in either direction is immediate, in that said cylinder is connected to the pump of the power unit by means of a hydraulic circuit always completely full of oil which is pressurized immediately.

[0009] However, when the user being activated by the hydraulic circuit operated by the power unit according to the invention, and formed for example by a double-acting actuating cylinder does not maintain automatically the position where it has been moved, but it spontaneously tends to assume another position, and is then to be locked in every position thereof by said hydraulic actuating circuit, the power unit according to the invention comprises also a hydraulic distributor which is interposed between the two mouths of the reversible pump and the two connecting conduits communicating with opposite ends of the user, for example with a double-acting actuating cylinder at opposite sides of its piston, said distributor being urged by return springs towards an intermediate closure and locking position, wherein it will shut off the communication between the two mouths of the pump and the two communication conduits to the user, keeping the latter in its position, while it is alternately moved in either direction by a pilot pressure derived from the mouth of the pump acting as a delivery mouth, and is thus moved into either of two opening and actuating positions, wherein it connects the two mouths of the pump to the two connecting conduits for the user. Again, notwithstanding the arrangement of a hydraulic distributor and the locking of the user in its position by means of the respective hydraulic actuating cylinder, in order to reverse the action of the user the direction of operation of the pump of the power unit according to the invention is only to be reversed, for example by reversing the direction of rotation of the respective actuating electric motor.

[0010] A preferred embodiment of the power unit according to the invention is characterized in that the pump is received and enclosed in the recess formed between two halves of the body of the power unit and used as a tank for the hydraulic liquid, one of said halves of the body of the power unit being secured to the flange of a reversible electric motor coupled to the pump, while the other half of the body of the pump contains the two unidirectional valves, the two pressure relief valves, the possible hydraulic distributor, the ducts connecting the various portions of the power unit and the connectors for the ducts for connection to the user. This embodiment is of great constructional simplicity, and of extremely small dimensions.

[0011] In a particularly advantageous modified embodiment, from the standpoint of simplicity and of constructional compactness, of the power unit according to the invention, the reversible pump is constituted by a grear pump, while the two halves of the body of the power unit constitute the two opposed covers of the body of the pump at both sides of the pair of gears and extend radially beyond the outline of the body of the pump and are peripherally sealingly connected to each other by means of a ring member so as to form the hydraulic liquid tank around the pump.

[0012] These and other characteristics of the invention will be apparent from the following description of an embodiment thereof shown as a non-limitating example in the accompanying drawings, wherein:

Fig. 1 shows the hydraulic diagram of a power unit according to the invention;

Fig. 2 is a longitudinal sectional view of the power unit, parallel to the axis of the pump and respective actuating electric motor;

Figs. 3, 4 and 5 are cross-sectional views of the power unit on the lines III-III, IV-IV and V-V of Fig. 2;

Fig. 6 is a fragmentary longitudinal sectional view on the line VI-VI of Fig. 5.

[0013] The illustrated power unit is designed to operate a hydraulic circuit for activating, for example, a double-acting hydraulic actuating cylinder (not shown). The power unit comprises an oil tank H and a reversible oil pump A, that is a pump capable of delivering oil when actuated in either direction. In the illustrated embodiment, said reversible pump A is constituted by a gear pump. The two mouths B and B' of this reversible pump A, therefore, can each operate, alternately, as a delivery mouth and as a suction mouth. The pump A is activated by a reversible electric motor 1, either D.C.-operated or A.C.-operated, of which the direction of rotation may be selected, for example, by means of an electric switch (not shown).

[0014] The two mouths B and B' of the reversible pump A are connected to an oil tank H, each through the associated branch D and D' of an annular circuit communicating with the tank H through a common communication conduit G. Interposed in each branch D, D' of said circuit, at opposite sides of their common conduit G for communication with the oil tank H, is a unidirectional valve F and P' which opens in the direction of flow from the oil tank toward the respective mouth B or B' of the pump A, while it closes in the opposite direction. The two unidirectional valves F, F' also prevent the oil delivered through a mouth B or B' of the pump A from reaching the other mouth B' or B.

[0015] The two mouth B, B' of the pump A are also connected each to the associated branch M and M' of a second annular circuit, parallel to the first annular circuit D, D' and communicating with the oil tank H through the same communication conduit G, to which it is connected at N. Interposed in each branch M, M' of said second circuit is an automatic pressure relief valve L, L' designated also "maximum pressure valve". The oil tank H communicates with a filling or connection conduit P the pouth of which is closed by a plug Q. Finally, each mouth B and B' of the pump A is connected to the hydraulic actuating cylinder by a respective conduit C, C^* derived from the respective branch D, D' of the first annular circuit.

[0016] The unidirectional valves F, F' are designed so that, though opening in the direction of flow from the tank H to the associated mouth B, B' of the pump A, they permit a limited seepage of oil also in the opposite direction, that is from the respective mouth B, B' to the tank H. Similarly, the pressure relief valves L and L', though opening at a pre-established maximum pressure, may be designed so as to permit - also in their closed position - a limited seepage of oil from the respective mouth B, B' to the tank H.

[0017] The above portion of the power unit can be used, as such, in hydraulic circuits for activating double-acting actuating cylinders that are not to be locked in position by the aid of said hydraulic circuit. By activating the pump A in the direction wherein the mouth B operates as a delivery mouth, the pressurized oil is delivered through the conduit C to the hydraulic actuating cylinder onto one side of its piston, which, therefore, is moved in the corresponding direction, while the oil discharged from the actuating cylinder at the other side of its piston is returned through the conduit C' to the other mouth B' of the pump, operating as a suction mouth. If the amount of oil returned from the actuating cylinder is smaller than that required to ensure the delivery of the pump A, the mouth B' draws the difference from the oil tank H through the associated unidirectional valve F'. On the contrary, when the amount of oil returned from the actuating cylinder through the conduit C^* is greater than that being sucked by the mouth B', a higher pressure is created on the side of the latter and the exceeding oil is returned to the tank H either by seeping through valves F' or L' or by partially opening the pressure relief valve L'. To move the piston of the actuating cylinder in the opposite direction, the direction of rotation of the actuating motor 1 for the pump A is reversed, which pump is then activated in the opposite direction, whereby its mouth B' becomes a delivery mouth. The flow of oil is then reversed, while any possible difference of rate between the flow of oil sent to the actuating cylinder and the flow of oil returned from the actuating cylinder is compensated for as described above.

[0018] It is apparent that in the power unit according to the invention, the oil tank H, substantially, has the only function to compensate for any difference of rade between the oil flow sent to the user and the oil flow returned from the user, whereby it may be of very small size and integrated with a structure of minimum dimensions, as described hereinafter. When, for example, due to particular requirements of the user, an oil tank of greater capacity than the equipped reduced tank H is required, the plug Q may be removed and the mouth of the connection conduit P may be connected to a supplementary oil tank.

[0019] When the double-acting actuating cylinder, activated by the hydraulic circuit operated by the power unit, does not stop automatically in the position where it has been moved, but it is to be kept in this position with the assistance of said actuating hydraulic circuit, then said portion of the power unit is completed with a distributor sliding valve R interposed between the two conduits C and C' communicating directly with the mouths B and B' of the pump A, and two conduits C" and C''' connected to the actuating hydraulic cylinder on opposite sides of its piston. The distributor sliding valve R is diagrammatically shown in Fig. 1 and, in a practical embodiment, in Fig. 6, and is slidable longitudinally in the two directions indicated by the arrows U and U1 in Fig. 1. The ends of the distributor sliding valve R are acted upon by two opposed return springs T and T' tending to move the distributor sliding valve R to an intermediate rest and closure position and to keep it thereat, as shown in Fig. 1 and wherein any communication between the conduits C, C' and the two corresponding conduits C" and C'" is shut off. The oil in the hydraulic actuating circuit of the actuating cylinder, therefore, cannot flow in any direction, whereby the double-acting actuating cylinder connected to said hydraulic circuit and specifically to the two conduits C" and C"' is locked and is kept automatically in its position.

[0020] Derived from the conduit C communicating with the mouth B of the pump A is a pilot conduit S opening into a pressure chamber formed at an end portion of the distributor sliding valve R, acted upon by the return spring T. Similarly, derived from the conduit C' communicating with the other mouth B' of the pump A is a pilot conduit S' opening into a pressure chamber formed at the other end portion of the distributor sliding valve R, acted upon by the return spring T'. By rotating the reversible pump A in the direction whereby its mouth B operates as a delivery mouth, the pressure created in the conduit C acts entirely or partially through the pilot conduit S on the respective end of the distributor slinding valve R, whereby said sliding valve is displaced against the action of the opposing return spring T' in the direction of the arrow U (downwardly in Fig. 1 and toward the right in Fig. 6). The distributor sliding valve R is thus moved to a first opening position wherein it connects the two conduits C and C' to the conduits C" and C"', whereby the delivery pressure created through the mouth B is allowed to act in the end portion of the hydraulic actuating cylinder connected to the conduit C", while the other end portion of the actuating cylinder is connected through the conduit C"' to the suction mouth B' of the pump. The piston of the actuating cylinder is moved accordingly. The pump A is then stopped, so as to eliminate the pressure acting through the pilot conduit S on the distributor sliding valve R and the latter is returned by the spring T' to its intermediate rest and closure position, wherein it locks the piston of the actuating cylinder in the position it has reached. However, by activating the pump A in the opposite direction, the delivery of the oil occurs through the mouth B' of said pump and the delivery pressure created in the conduit C' acts entirely or partially through the pilot conduit S' in the pressure chamber at the other end portion of the distributor sliding valve R acted upon by the return spring T'. The pressure chamber at the opposite end of the distributor sliding valve R, however, communicates through the pilot conduit S and conduit C with the mouth B of the pump, which operates now as a suction mouth. The distributor sliding valve R is then moved against the action of the spring T in the direction of the arrow U1 (upwardly in Fig. 1 and toward the left in Fig. 6) to a second opening position, where it again communicates the conduits C and C' to the conduits C" and C"'. Now, however, the pressurized oil delivered by the mouth B' acts in the other end portion of the hydraulic actuating cylinder, connected to the conduit ct", while the opposite end of said actuating cylinder is connected through the conduit C" to the suction mouth B of the pump A. The piston of the actuating cylinder is then moved in a direction opposite to the former and is locked in its new position when the pump A is stopped and the distributor sliding valve R is moved back to its intermediate closure position by the action of the return spring T.

[0021] In case of break in the electric current and, therefore, of impossibility to activate the pump A, in order to permit the hydraulic actuating cylinder to be unlocked and manually moved in either direction, for example to move it from an end position to an intermediate or rest position, the distributor sliding valve R may be selectively and also manually moved to either of its two opening positions, wherein it connects the mouths B and B' of the pump A through the respective conduits C, C^* to the two conduits C", C"'. For this purpose, in the exemplary embodiment shown in Fig. 6, at an end of the distributor sliding valve R, co-axially with the latter, is axially slidably arranged a control stem Z provided with a side notch 19 cooperating with a corresponding small spring-urged retainer ball 20. Said stem Z sealingly exits from the recess in the distributor sliding valve R and its outer end is provided with a transverse end cutout Z', wherein a screw-driver or the like can be engaged. Normally, the control stem Z is retracted outwards in a rest position, shown in Fig. 6 and wherein it does not interfere with the distributor sliding valve R when the latter is moved to its opening end position near said control stem Z (to the right in Fig. 6). By manually pushing the control stem Z inwards (to the left in Fig. 6) it pushes the distributor sliding valve R and moves it to its end opposite opening position wherein the two conduits C" and C"' are communicated to the conduits C and C' and, therefore, to the annular circuit M-M of the power unit. In this position, the control stem may be locked, by rotating it by means of a screwdriver engaged in the end cutout Z' so as to engage the spring-urged retainer ball 20 into the side notch Z'. Therefore, the distributor sliding valve R is also locked in the said end opening position. Now, by opening one and/or the other of the pressure relief valves L, L', the flow of oil can freely enter the tank H and outflow therefrom, whereby the hydraulic actuating cylinder can be moved manually as desired. To lock said actuating cylinder in the new position, where it has been moved, it is sufficient to unlock the control stem Z by rotating it so as to disengage its notch 19 from the spring-urged retainer ball 20. The return spring T then brings the distributor sliding valve R back to its intermediate rest and closure position.

[0022] In the Figs. 2 to 6 is shown an exemplary embodiment of the power unit according to the invention. In this circumstance, the pump A is constituted by a reversible gear pump. The two gears 7 and 7' are arranged, in a known manner, between two opposed dual wear-bushings 6 and 6', wherein the shafts 8 and 8' of said gears 7 and 7' are supported. The dual bushings 6, 6' and the two gears 7, 7' interposed therebetween are accommodated in a corresponding recess of the pump body 5 which is sealingly tightened between the two covers 3 and 4 by means of tierods 10 passed through the pump body 5 and through the two covers 3 and 4. The two covers 3 and 4 of the pump are formed by circular plates of such a diameter as to extend beyond the outline of the pump body 5. The two covers are sealingly peripherally connected by an intermediate tubular member 12 and seals 13, 13' and thus form, together with said tubular member 12, around the pump body 5, a closed chamber constituting the oil tank H.

[0023] The circular plates constituting the covers 3 and 4 will mate by means of planar surfaces against the corresponding end faces of the pump body 5 and against the outer ends of the dual wear-bushings 6, 6' and are provided with gaskets 17 which are indicated by hatching in Fig. 4. These gaskets extend all around the bushings 6, 6' at the pump body 5 and around the shafts 8, 8' of the two gears 7, 7' at the wear-bushings 6, 6', while defining at the intermediate portion between the two shafts 8, 8' and on the side of the cover 4, two opposite chambers 18, 18' operating alternately, one as a delivery chamber and the other as a suction chamber, and vice versa, according to the direction of operation of the pump A. These two chambers 18, 18' communicate with opposite sides of the meshing region of the two gears 7, 7' through corresponding openings 16 B and 16 B' formed between the pump body 5 and the dual wear-bushing 6 on the side facing towards the cover 4. Said openings 16 B and 16 B' constitute the two mouths of the pump, operating alternately one as a delivery mouth and the other as a suction mouth, and vice versa, according to the direction of operation of the pump A.

[0024] The two chambers 18, 18' also communicate each with a hole formed in the cover 4. These holes constitute the conduits D and D' and extend by means of co-axial lengths C, C' to the distributor sliding valve R which is accommodated in a corresponding substantially diametral bore formed in said cover 4. Two parallel holes extend from the distributor sliding valve R and open at the outer end surface of the cover 4 and constitute the conduits or connectors C", C'" for coupling the power unit to the respective hydraulic circuit user, for example a hydraulic actuating cylinder.

[0025] In a transverse plane of the cover 4, that is in a plane perpendicular to the holes D, D', two parallel holes M, M' are formed the diameter of which is reduced by steps as they extend inwards, and which intersect the two holes D and D^r. The larger diameter outer portion of these holes M, M' accommodates the two pressure relief valves L, L', while the reduced diameter inner portion thereof, at the opposite side with respect to the intersection with the holes D, D', accommodates the unidirectional valves F, F^* as particularly clearly shown in Figs. 2 and 5. The inner ends of the holes M, M' communicate at N with each other and with an adjacent angular hole G opening at the inner end surface of the cover 4 in the oil tank H, thus communicating said holes M, M' with said tank H. The first stretch of the hole G extends to open at the periphery of the cover 4, where it is closed by means of a plug. This extension of the first stretch of the angular hole G constitutes the conduit P for connection to a supplementary oil tank. The intermediate tubular member 12 is provided at the periphery thereof with a filling hole which is closed by means of a threaded plug 14 having a filling and compensating small valve 15 in the form of a non-return valve which opens from the outside towards the interior.

[0026] The constructional embodiment of the power unit according to the Figs. 2 to 6 ensures a compact and small-sized unit containing the pump A, the oil tank H and every required auxiliary elements and is easily secured to the flange 101 of the reversible actuating electric motor 1 by means of the cover 3 and axial connecting tierods 11 passed through the two covers 3, 4 and through the oil tank H exteriorly of the pump body 5. The shaft 8 of a gear 7 exits to the outside through the cover 3 and a sealing member 9, and is coupled to the co-axial shaft 2 of the motor 1.

Claims

1. A hydraulic power unit, particularly adapted for hydraulic actuating circuits of double-acting hydraulic actuators or reversible-movement users and comprising a pump (A), a tank (H) for the hydraulic liquid and valves (F, F', L, L') for connecting the pump (A) to the tank (H), characterized in that the pump (A) is of the reversible type and may be selectively activated in either direction, for example by means of a reversible electric motor (1), while the two mouths (B, B') of the pump (A) each of which can operate alternately as a suction mouth and as a delivery mouth, are each connected or connectible at one side to the user (conduits C, C', or C", C'") and at the other side to the tank (H) of the hydraulic liquid either by means of an associated unidirectional valve (F, F') opening only in the direction of the flow from the tank (H) to the respective mouth (B, B'), or - parallelly with said unidirectional valve (F, F') by means of an associated automatic pressure relief valve (L, L').

2. A power unit according to claim 1, characterized in that the unidirectional valves (F, F') and/or pressure relief valves (L, L') permit a limited seepage of hydraulic liquid towards the tank (H) in the closure direction of the unidirectional valves (F, F') and in the closure position of the pressure relief valves (L, L').

3. A power unit according to claims 1 and 2, characterized in that the two mouths (B, B') of the pump (A) communicate with two annular circuits (D, D', and M, M') which are parallelly connected either to the tank (H) of the hydraulic liquid by means of a common connection conduit (G), and to the user by means of two connection conduits (C, C') operating alternately one as a delivery conduit and the other as a return conduit, and vice versa, the unidirectional valves (F, F') being interposed in one (D, D') of these annular circuits and the pressure relief valves (L, L') in the other annular circuit (M, M'), on the opposite sides of the common conduit (G) for connection to the tank (H) of the hydraulic liquid.

4. A power unit according to one of the preceding claims, characterized in that it comprises a hydraulic distributor (R) interposed between the two mouths (B, B') of the pump (A) and two conduits (C", C"') connected to the user, operating alternately one as a delivery conduit and the other as a return conduit, and vice versa, said distributor (R) being urged by return springs (T, T') towards an intermediate closure and locking position, wherein it will shut off the communication between the two mouths (B, B') of the pump (A) and the two conduits (C", C"') for connection to the user, while it is alternately moved in either direction by means of a pilot pressure (pilot conduits S, S') derived from the mouth of the pump operating as a delivery mouth, and is thus moved to either of two opening and actuating positions, wherein it connects the two mouths (B, B') of the pump (A) to the two conduits (C", C"') for connection to the user.

5. A power unit according to claim 4, characterized by means (Z, Z', 19, 20) to move the distributor (R) manually to one of its opening and actuating positions and to keep it in said position.

6. A power unit according to one of the preceding claims, characterized in that the pump (A) is accommodated and enclosed in the chamber formed between two halves of the body of the power unit and operating as a tank (H) for the hydraulic liquid, one (3) of these halves of the body of the power unit being secured to the flange (101) of a reversible electric motor (1) coupled to the pump, while the other half (4) of the body of the power unit contains the two unidirectional valves (F, F'), the two pressure relief valves (L, L'), the possible hydraulic distributor (R), the connectors for the conduits (C", C'") for communication to the user and the conduits (D, D', M, M', G, C, C', S, S') for communication between the various portions of the power unit.

7. A power unit according to claim 6, characterized in that the pump (A) is constituted by a reversible gear pump, while the two halves (3, 4) of the body of the power unit constitute the two opposite covers of the pump body (5) at both sides of the pair of grears (7, 7') and extend radially beyond the outline of the pump body (5), and they are peripherally sealingly connected by means of an annular member (12) so as to form around the pump (A) the tank (H) for the hydraulic liquid.

8. A power unit according to the preceding claims, characterized in that the tank (H) for the hydraulic liquid communicates with a conduit (P) the mouth of which, normally sealingly closed by means of a plug Q, can be connected with a supplementary tank of hydraulic liquid.

Drawing