Hydraulic motor driving device

A motor capacity change-over actuator 10 varies a capacity of a hydraulic motor 1 in accordance with the inflow/outflow of a working fluid into/out of a drive pressure chamber 72. A motor capacity change-over valve 20 supplies the working fluid to the drive pressure chamber 72 in a supply position H and discharges the working fluid from the drive pressure chamber 72 in a discharge position L. A flow control valve 15 is interposed between the drive pressure chamber 72 and the motor capacity change-over valve 20, and therefore a shock generated upon deceleration of the hydraulic motor 1 can be alleviated without being affected by leakage of the working fluid in the motor capacity change-over valve 20.

FIELD OF THE INVENTION

This invention relates to a driving device for a hydraulic motor, which comprises a motor capacity change-over actuator.

BACKGROUND OF THE INVENTION

JP08-219004A, published by the Japan Patent Office in 1996, proposes a driving device for a swash plate hydraulic motor used to generate travel power for a hydraulic shovel.

Referring toFIG. 8, this driving device comprises a motor capacity change-over actuator93that changes a tilt angle of a swash plate of a hydraulic motor91and a motor capacity change-over valve95that changes a working fluid pressure for driving the motor capacity change-over actuator93.

In a high speed position X, the motor capacity change-over valve95supplies a pressurized working fluid in a high pressure port94B to the motor capacity change-over actuator93. The motor capacity change-over actuator93is driven to expand by the pressurized working fluid such that the tilt angle of a swash plate92of the hydraulic motor91decreases. As a result, a rotation speed of the hydraulic motor91increases.

To decelerate the hydraulic motor91, the motor capacity change-over valve95is changed over from the high speed position X to a low speed position Y. In the low speed position Y, a tank port94C communicates with the motor capacity change-over actuator93. The motor capacity change-over actuator93is operated by a reactive force from the swash plate92to contract while discharging the working fluid to a tank100. As a result, the tilt angle of the swash plate92of the hydraulic motor91increases, leading to a reduction in the rotation speed of the hydraulic motor91.

A flow control valve98constituted by a fixed orifice96and a pressure reducing valve97is provided between the motor capacity change-over valve95and the tank port94C.

The flow control valve98keeps a flow rate of the working fluid that is discharged from the motor capacity change-over actuator93to the tank100via the tank port94C during deceleration of the hydraulic motor91substantially constant. By keeping a contraction operation speed of the motor capacity change-over actuator93constant using the flow control valve98, a shock generated as the hydraulic motor91decelerates is alleviated.

SUMMARY OF THE INVENTION

In this hydraulic motor driving device, the flow control valve98is provided between the motor capacity change-over valve95and the tank port94C. When an upstream side of the flow control valve98reaches a high pressure during deceleration of the hydraulic motor91, a part of the working fluid leaks into a drain through a gap in the motor capacity change-over valve95. This working fluid leakage may cause the contraction speed of the motor capacity change-over actuator93to rise, thereby inhibiting alleviation of the shock generated as the hydraulic motor91decelerates.

It is therefore an object of this invention to provide a hydraulic motor driving device that is capable of sufficiently alleviating a shock generated when a hydraulic motor decelerates.

To achieve the object described above, this invention provides a hydraulic motor driving device that varies a capacity of a hydraulic motor using a working fluid, comprising a motor capacity change-over actuator. The motor capacity change-over actuator includes a drive pressure chamber that varies the capacity of the hydraulic motor in accordance with supply and discharge of the working fluid. The hydraulic motor driving device further comprises a motor capacity change-over valve that changes between a supply position in which the working fluid is supplied to the drive pressure chamber and a discharge position in which the working fluid is discharged from the drive pressure chamber, and a flow control valve that is disposed between the drive pressure chamber and the motor capacity change-over valve to adjust a flow rate of the working fluid discharged from the drive pressure chamber.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring toFIG. 1of the drawings, a swash plate type variable capacity hydraulic motor1installed in a hydraulic shovel as a travel power source is operated by an oil pressure supplied selectively to ports P1and P2formed in a hydraulic motor driving device. An aqueous solution may be used instead of working oil.

The hydraulic motor driving device includes a main passage11linking a motor port M1of the hydraulic motor1to the port P1, and a main passage12linking a motor port M2of the hydraulic motor1to the port P2.

The hydraulic motor1is rotated in a positive rotation direction by working oil supplied from the port P1to the motor port M1through the main passage11, whereby the hydraulic shovel is caused to advance via a traveling device. Further, the hydraulic motor1is rotated in a negative rotation direction by working oil supplied from the port P2to the motor port M2through the main passage12, whereby the hydraulic shovel is caused to reverse via the traveling device.

A counterbalance valve2is interposed on the main passages11and12. The counterbalance valve2operates in accordance with a pressure balance between pilot pressures led respectively from the ports P1and P2through pilot passages5and6.

When the hydraulic motor1rotates in the positive direction, pressurized working oil is supplied to the port P1. The pressurized working oil is led to the pilot passage5, and therefore the counterbalance valve2is maintained in a positive rotation position A. When the hydraulic motor1rotates in the negative direction, pressurized working oil is supplied to the port P2. The pressurized working oil is led to the pilot passage6, and therefore the counterbalance valve2is maintained in a negative rotation position B.

When the hydraulic motor1is inoperative, the ports P1and P2are both held at a low pressure. Since the pilot pressures led from the ports P1and P2through the pilot passages5and6are both low, the counterbalance valve2is changed over to a stop position C, and as a result, the main passages11and12are closed.

Fixed orifices16are interposed respectively in the pilot passages5and6. When the counterbalance valve2changes over from the position A or B to the stop position C, the fixed orifice16applies resistance to a flow of working oil that is discharged to a drain through the pilot passage5or the pilot passage6. The resistance applied to the discharged working oil by the fixed orifice16reduces a change-over speed of the counterbalance valve2such that the hydraulic motor1is stopped gently from a positive rotation condition or a negative rotation condition.

The variable capacity hydraulic motor1includes a swash plate32, and a pair of motor capacity change-over actuators10for varying a tilt angle of the swash plate32, or in other words a pump capacity. By varying the tilt angle of the swash plate32, the respective motor capacity change-over actuators10vary a displacement volume of a piston of the hydraulic motor1in two stages. As a result, a rotation speed of the hydraulic motor1is varied between a low speed and a high speed.

Working oil is supplied to the respective motor capacity change-over actuators10via a motor capacity change-over valve20.

A branch passage21branching from the main passage11, a branch passage22branching from the main passage12, a drain passage23communicating with a tank port T1, and a pair of actuator passages24communicating with the pair of motor capacity change-over actuators10are connected to the motor capacity change-over valve20.

The motor capacity change-over valve20changes between two positions, namely a high speed position H and a low speed position L, in accordance with a pilot pressure in a pilot port PS. The pilot pressure in the pilot port PS biases the motor capacity change-over valve20toward the high speed position H. Meanwhile, the motor capacity change-over valve20is biased toward the low speed position L by a spring41.

When the pilot pressure in the pilot port PS is low, the motor capacity change-over valve20is held in the low speed position L by a biasing force of the spring41. In the low speed position L, the motor capacity change-over valve20connects the pair of actuator passages24to the drain passage23. When the pair of actuator passages24are connected to the drain passage23, the motor capacity change-over actuators10supporting the swash plate32are held in a contraction position by a reactive force received from the swash plate32. As a result, the swash plate32maintains a large tilt angle such that the hydraulic motor1rotates at a low speed.

When the pilot pressure in the pilot port PS is high, the motor capacity change-over valve20is held in the high speed position H against the biasing force of the spring41. In the high speed side position H, the motor capacity change-over valve20connects the pair of actuator passages24to the branch passages21and22. Pressurized working oil supplied through the actuator passage24from the branch passage21or the branch passage22drives one of the motor capacity change-over actuators10to expand. As a result, the tilt angle of the swash plate32decreases such that the hydraulic motor1rotates at a high speed.

The motor capacity change-over valve20changes between the low speed position L and the high speed position H in accordance with variation in the pilot pressure in the pilot port PS. The high speed position H corresponds to a supply position for supplying working oil to the motor capacity change-over actuator10, while the low speed position L corresponds to a discharge position for discharging the working oil from the motor capacity change-over actuator10.

Incidentally, if the pair of motor capacity change-over actuators10contract at high speed during an operation to decelerate the hydraulic motor1, the rotation speed of the hydraulic motor1decreases rapidly, and as a result, a deceleration shock is generated.

In the hydraulic motor driving device, a flow control valve15is provided in each actuator passage24to prevent this deceleration shock. The flow control valve15ensures that the rotation speed of the hydraulic motor1decreases gently by suppressing a flow rate of the working oil discharged from the corresponding motor capacity change-over actuator10to or below a fixed rate.

Referring toFIG. 2, the constitution of the hydraulic motor1will be described.

The hydraulic motor1includes an interior space defined by a motor casing30and a port block40. A cylinder block31and the swash plate32are accommodated in the interior space.

The cylinder block31is fixed to an outer periphery of a rotary shaft36supported by the motor casing30and the port block40. A plurality of cylinders34disposed parallel to the rotary shaft36are formed in the cylinder block31at equal angular intervals in a circumferential direction. A piston33is accommodated in each cylinder34. The piston33is held in contact with the swash plate32via a shoe.

Pressurized working oil is supplied to each cylinder34from the main passage11or12inFIG. 1. The pressurized working oil supplied to the cylinder34drives the piston33to expand and contract in an axial direction relative to the cylinder34. By operating the plurality of pistons33held in contact with the swash plate32to expand and contract successively in accordance with predetermined rotary angle positions, the cylinder block31is driven to rotate. The rotary shaft36rotates integrally with the cylinder block31, and a resulting rotary torque is output as power for causing the hydraulic shovel to travel.

The cylinder block31completes a single revolution when all of the pistons33complete a single reciprocation within the cylinders34.

The swash plate32is supported on the motor casing30to be capable of tilting via a pair of ball bearings. The swash plate32is driven by the pair of motor capacity change-over actuators10such that the tilt angle thereof is varied. The swash plate32is changed over between two positions, namely a maximum tilt angle corresponding to the low speed position and a minimum tilt angle corresponding to the high speed position. The figure shows the swash plate32at the maximum tilt angle.

The motor capacity change-over actuator10includes a drive piston70having a closed-end cylindrical shape. The drive piston70is accommodated to be free to slide within a cylinder71formed in the motor casing30.

A drive pressure chamber72is defined between the cylinder71and the drive piston70. The actuator passage24is connected to the drive pressure chamber72.

A compressed spring73for biasing the swash plate32in a tilt angle reduction direction via the drive piston70is disposed in the drive pressure chamber72. The drive piston70is pressed against a back surface of the swash plate32at all times by a biasing force of the spring73.

The pressurized working oil led from the branch passages21and22inFIG. 1is introduced into the drive pressure chamber72through the actuator passages24. The drive piston70is caused to project from the cylinder71by a working oil pressure in the drive pressure chamber72, thereby pressing the back surface of the swash plate32toward the high speed position together with the biasing force of the spring73. Meanwhile, a pressing force exerted on the swash plate32by the respective pistons33biases the swash plate32toward the low speed position. Thus, the swash plate32displaces between the high speed position and the low speed position in accordance with the working oil pressure in the drive pressure chamber72. When the tilt angle of the swash plate32is changed over between the high speed position and the low speed position, a stroke distance of the pistons33reciprocating within the cylinders34varies, and as a result, a rotation speed of the cylinder block31varies.

Referring toFIG. 4, the counterbalance valve2, the motor capacity change-over valve20, and the pair of flow control valves15are accommodated in the integrated port block40.

The counterbalance valve2is interposed between the ports P1and P2formed in the port block40and the main passages11and12. In the port block40, the branch passage21branches from the main passage11and the branch passage22branches from the main passage12. The motor capacity change-over valve20is provided between the branch passages21and22and the pair of actuator passages24formed in the port block40. The flow control valve15is provided at a midway point on each actuator passage24.

The counterbalance valve2includes a spool50that is accommodated to be free to slide in a valve hole48formed in the port block40. Pilot pressure chambers43and44are formed in the port block40to face respective ends of the spool50.

When the hydraulic motor1is operated to rotate positively or negatively, a pressure in the high pressure side port P1or P2is led to the pilot pressure chamber43or the pilot pressure chamber44through the pilot passage5or the pilot passage6. The spool50displaces from the stop position C to an operating position A or an operating position B in accordance with the pilot pressure led to the pilot pressure chamber43or the pilot pressure chamber44. As a result, the port P1and the port P2communicate with the main passage11and the main passage12, respectively. The fixed orifices16are interposed respectively in the pilot passage5and the pilot passage6.

A spring3that biases the spool50toward the stop position C is accommodated in the pilot pressure chamber43. A spring4that biases the spool50toward the stop position C is accommodated in the pilot pressure chamber44. The spool50is maintained in the stop position C shown in the figure by respective biasing forces of the springs3and4when the pilot pressure is not exerted thereon. In the stop position C, working oil outflow from the main passages11and12is blocked.

Check valves53and54forming a part of the counterbalance valve2are accommodated in the spool50. When the spool50is positioned in the stop position C, the check valve53permits a flow of working oil from the port P1to the motor port M1but blocks a reverse flow. Likewise when the spool50is positioned in the stop position C, the check valve54permits a flow of working oil from the port P2to the motor port M2but blocks a reverse flow.

The motor capacity change-over valve20includes a motor capacity change-over spool60accommodated to be capable of sliding in a valve hole49formed in the port block40.

A motor capacity change-over pilot pressure chamber67is defined in the valve hole49to face one end of the motor capacity change-over spool60. Another end of the motor capacity change-over spool60is elastically supported by the spring41. The spring41biases the motor capacity change-over spool60toward the low speed side position L.

When the pilot pressure led into the motor capacity change-over pilot pressure chamber67from the pilot port PS increases, the motor capacity change-over spool60displaces rightward in the figure against the spring41, whereby the motor capacity change-over valve20is changed over from the low speed side position L to the high speed side position H. In the high speed side position H, the branch passage21and one of the actuator passages24communicate via an annular groove formed in an outer periphery of the motor capacity change-over spool60.

Further, the branch passage22and the other actuator passage24communicate via another, similar annular groove. As a result, pressurized working oil is supplied to one of the pair of motor capacity change-over actuators10. The motor capacity change-over actuator10to which the pressurized working oil is supplied expands, thereby reducing the tilt angle of the swash plate32, and as a result, the rotation speed of the hydraulic motor1increases.

When the pilot pressure led into the motor capacity change-over pilot pressure chamber67from the pilot port PS decreases, the motor capacity change-over spool60is displaced leftward in the figure by a biasing force of the spring41, whereby the motor capacity change-over valve20is changed over from the high speed side position H to the low speed side position L. As a result, communication between the branch passages21and22and the actuator passages24is blocked, and the pair of actuator passages24communicate respectively with the drain passage23.

In the low speed side position L, the working oil in the respective motor capacity change-over actuators10flows out into the drain passage23through the actuator passages24. The respective motor capacity change-over actuators10thereby contract, causing the tilt angle of the swash plate32to increase, and as a result, the rotation speed of the hydraulic motor1decreases.

Referring toFIGS. 3A-3C, the flow control valve15interposed in the actuator passage24includes a flow control spool63interposed to be capable of sliding in a valve hole42formed in the port block40. For ease of description, a part of the actuator passage24between the flow control valve15and the motor capacity change-over actuator10will be referred to hereafter as a passage24A, and a part between the flow control valve15and the motor capacity change-over valve20will be referred to as a passage24B.

The flow control spool63is formed in a cylindrical shape constituted by a cylindrical wall63A and a bottom portion63B formed on one end of the cylindrical wall63A. A metering orifice61, a through hole62, and an annular groove64are formed in the flow control spool63. The metering orifice61penetrates a center of the bottom portion63B of the flow control spool63such that the passage24A communicates with an inside of the flow control spool63by a small flow sectional area at all times. The flow control spool63is biased rightward in the figure, or in other words toward the passage24A, by a spring65.

The annular groove64is formed in an outer periphery of the cylindrical wall63A of the flow control spool63. The through hole62penetrates the cylindrical wall63A to connect the inside of the flow control spool63to the annular groove64.

The passage24B extending to the motor capacity change-over valve20is formed in the port block40to face the cylindrical wall63A of the flow control spool63.

A pressure in the passage24A acts on the bottom portion63B of the flow control spool63on the periphery of the metering orifice61. A pressure on the inside of the flow control spool63and an elastic supporting force of the spring65act on the flow control spool63in an opposite direction to the aforementioned pressure. The flow control spool63slides within the valve hole42in accordance with a differential pressure between the passage24B and the passage24A, or in other words a pressure loss of the metering orifice61.

Referring toFIG. 3A, when the pressure in the passage24A is low, the flow control spool63is in a rightmost position of the figure. When the flow control spool63is in this position, working oil can flow between the passage24A and the passage24B via the metering orifice61, the through hole62, and the annular groove64, as shown by an arrow in the figure, for example. This position of the flow control spool63will be referred to as a fully open position of the flow control valve15. When the flow control valve15is in the fully open position, flow resistance thereof is generated by the metering orifice61.

Referring toFIG. 3C, when the pressure in the passage24A is high, the flow control spool63moves to a leftmost position in the figure against the spring65. When the flow control spool63is in this position, communication between the annular groove64and the passage24B is blocked. As a result, the flow of working oil through the actuator passage24is blocked. This position will be referred to as a blocked position.

Referring toFIG. 3B, when the flow control spool63is positioned between the fully open position and the blocked position, the working oil can flow between the passage24A and the passage24B at a limited flow rate.

When the flow control valve15is in this position, flow resistance is generated in accordance with a flow sectional area of the working oil between the annular groove64and the passage24B. The flow sectional area between the annular groove64and the passage24B decreases as the pressure in the passage24A increases. Further, as the pressure in the passage24B increases, a working oil pressure on the inside of the flow control spool63rises, leading to an increase in the flow sectional area between the annular groove64and the passage24B.

When the motor capacity change-over valve20is in the H position, the pressure in the passage24B is high and the flow control valve15is in the fully open position. In this case, pressurized working oil is supplied from the branch passage21or22to the motor capacity change-over actuator10via the annular groove64, the through hole62, the metering orifice61, and the passage24A. As a result, the motor capacity change-over actuator10expands, causing the tilt angle of the swash plate32to decrease.

When the motor capacity change-over valve20is in the L position, the pressure in the passage24B is lower than when the motor capacity change-over valve20is in the H position, and therefore the flow control valve15is held in a position for displacing the flow control spool63in a closing direction from the fully open position, as shown inFIG. 3B.

In this state, the motor capacity change-over actuator10is caused to contract by the reactive force exerted on the motor capacity change-over actuator10by the swash plate32. As a result, the working oil in the motor capacity change-over actuator10flows out into the drain passage23through the actuator passage24and the motor capacity change-over valve20.

In the flow control valve15interposed in the actuator passage24, working oil flows from the passage24A to the passage24B via the metering orifice61, the through hole62, and the annular groove64, and as a result, flow resistance corresponding to the flow sectional area between the annular groove64and the passage24B is generated. The flow sectional area narrows as the pressure in the passage24A increases, and therefore the flow rate of the working oil that flows out of the motor capacity change-over actuator10into the drain passage23through the actuator passage24is suppressed to or below a fixed rate.

By having the flow control valve15hold the flow rate of the working oil that flows out of the motor capacity change-over actuator10into the drain passage23through the actuator passage24at or below a fixed rate in this manner, a speed at which the tilt angle of the swash plate32is increased by the motor capacity change-over actuator10is suppressed to or below a fixed speed. As a result, shock generation can be prevented during deceleration of the hydraulic motor1.

The flow control valve15is disposed between the motor capacity change-over actuator10and the motor capacity change-over valve20, and therefore the motor capacity change-over valve20is positioned downstream of the flow control valve15relative to the flow of working oil flowing out from the motor capacity change-over actuator10. A part of the working oil flowing out of the motor capacity change-over actuator10may leak into a drain through a gap between the motor capacity change-over spool60of the motor capacity change-over valve20and the valve hole49. However, this working oil leakage in the motor capacity change-over valve20does not affect a contraction speed of the motor capacity change-over actuator10, and therefore the shock generated by the flow control valve15during deceleration of the hydraulic motor1can be alleviated sufficiently.

When the motor capacity change-over valve20changes over from the low speed side position L to the high speed side position H such that the pressurized working oil led from the branch passage21,22flows into the motor capacity change-over actuator10, the flow control valve15shifts to the fully open position such that the flow sectional area for the working oil between the through hole62and the annular groove64reaches a maximum. Accordingly, the pressurized working oil supplied to the port P1(P2) flows rapidly into the motor capacity change-over actuator10via the branch passage21(22) and the actuator passage24, thereby securing acceleration responsiveness in the hydraulic motor1.

The flow control valve15is structured such that the flow sectional area of the working oil narrows as the pressure in the passage24A increases, and therefore a maximum value of the flow sectional area can be set to be larger than the fixed orifice. As a result, the effects of working oil contamination can be suppressed, and a favorable characteristic can be maintained in the long term.

Referring toFIGS. 5-7, a second embodiment of this invention will be described.

Referring toFIGS. 5 and 6, in a hydraulic motor driving device according to this embodiment, the flow control valve15is built into the motor capacity change-over actuator10.

Referring toFIG. 7, the flow control spool63of the flow control valve15is accommodated to be free to slide in a valve hole82formed in the drive piston70of the motor capacity change-over actuator10. Similarly to the first embodiment, the flow control spool63is formed in a cylindrical shape constituted by the cylindrical wall63A and the bottom portion63B. Similarly to the first embodiment, the metering orifice61, the through hole62, and the annular groove64are formed in the flow control spool63. The flow control spool63is elastically supported so as to be oriented toward the drive pressure chamber72by a spring65that is supported by the drive piston70. A stopper77that restricts displacement of the flow control spool63in the direction of the drive pressure chamber72is fixed to the valve hole82.

A port75is formed in the driving piston70in a position that overlaps the annular groove64. The actuator passage24, which communicates with the port75at all times regardless of a sliding position of the driving piston70, is formed in the motor casing30.

The flow control spool63slides within the valve hole82in accordance with a differential pressure between the drive pressure chamber72and the port75, or in other words the pressure loss of the metering orifice61. A flow sectional area between the annular groove64and the port75varies in accordance with a sliding position of the flow control spool63within the valve hole82. More specifically, when the flow control pool63is in a position shown in the figure, i.e. in contact with the stopper77, the flow sectional area between the annular groove64and the port75reaches a maximum. The flow sectional area between the annular groove64and the port75then decreases as the flow control spool63slides through the driving piston70in an axial direction from this position so as to compress the spring65.

When the driving piston70of the motor capacity change-over actuator10receives the reactive force of the swash plate32so as to displace in a direction for increasing the tilt angle, or in other words a direction for reducing the rotation speed of the hydraulic motor1, the drive pressure chamber72contracts such that the working oil flows out of the drive pressure chamber72into the drain passage23via the actuator passage24and the motor capacity change-over valve20in the low speed position L.

At this time in the flow control valve15, as shown by an arrow in the figure, the working oil that flows to the inside of the flow control spool63from the drive pressure chamber72via the metering orifice61flows out into the actuator passage24via the through hole62, the annular groove64, and the port75.

As the pressure of the working oil in the drive pressure chamber72rises, the flow control spool63displaces in the direction for compressing the spring65. As a result, the flow sectional area between the annular groove64and the port75decreases. The flow sectional area narrows as the pressure in the drive pressure chamber72increases, and therefore the flow rate of the working oil that flows out of the motor capacity change-over actuator10into the drain passage23through the actuator passage24is suppressed to or below a fixed rate, whereby the speed with which the tilt angle of the swash plate32increases is suppressed to or below a fixed speed.

In this embodiment also, similarly to the first embodiment, the shock that is generated during deceleration of the hydraulic motor1can be alleviated sufficiently without being affected by leakage of the working oil in the motor capacity change-over valve20.

Furthermore, in this embodiment, the flow control valve15is built into the motor capacity change-over actuator10, and therefore the flow control valve15and the motor capacity change-over actuator10can be formed as a single unit, enabling a reduction in the number of components constituting the hydraulic motor driving device.

The contents of Tokugan 2009-240330, with a filing date of Oct. 19, 2009 in Japan, are hereby incorporated by reference.

Although the invention has been described above with reference to certain embodiments, the invention is not limited to the embodiments described above. Modifications and variations of the embodiments described above will occur to those skilled in the art, within the scope of the claims.

For example, in the above embodiments, a hydraulic motor driving device that uses working oil was described, but this invention may also be applied to a driving device for a hydraulic motor that uses various types of working fluids other than working oil.

The hydraulic motor driving device according to the above embodiments is used on the swash plate type hydraulic motor1, but this invention may also be applied to a driving device for any type of hydraulic motor that can be subjected to capacity variation using an actuator.

The hydraulic motor driving device according to the above embodiments is used on the bidirectional rotation type hydraulic motor1including the pair of motor capacity change-over actuators10that are activated in accordance with the rotation direction of the hydraulic motor1. However, this invention may also be applied to a driving device for a unidirectional rotation type hydraulic motor, and in this case, the hydraulic motor driving device should include a single motor capacity change-over actuator10and a single flow control valve15.

INDUSTRIAL FIELD OF APPLICATION

As described above, this invention brings about favorable effects in terms of alleviating a shock occurring during deceleration of a hydraulic motor used to generate travel power in a construction machine such as a hydraulic shovel.