Electrically-operated hydraulic actuator unit and hydraulic four-wheel-drive work vehicle

Provided an electrically-operated hydraulic actuator unit that includes an electrically-operated motor controlled by a control apparatus and actuating a volume adjusting mechanism through driving-side and driven-side arms, and a clutch mechanism in which the driven-side arm presses a contact member against a clutch case so that the driven-side arm is locked when a force from the volume adjusting mechanism is applied to the driven-side arm. The control apparatus can set duties of first to fourth drive signals to be output to the electrically-operated motor in a neutral-side start period, a neutral-side ordinary actuation period, a higher-volume-side start period and a higher-volume-side ordinary actuation period. The duties of the first and fourth drive signals are larger than that of the second drive signal, the duty of the third drive signal is larger than that of the fourth drive signal, and an integrated ON-time of the third drive signal is larger than that of the first drive signal.

FIELD OF THE INVENTION

The present invention relates to an electrically-operated hydraulic actuator unit including a variable displacement hydraulic actuator, an electric motor that generates an operating force for actuating a volume adjusting mechanism of the variable displacement hydraulic actuator and a control device that controls an actuation of the electric motor, and also relates to a hydraulic four-wheel-drive work vehicle equipped with the motor-operated hydraulic actuator unit.

BACKGROUND ART

There is a conventional variable displacement hydraulic actuator unit, including a hydraulic actuator such as a hydraulic motor or a hydraulic pump, and a volume adjusting mechanism that changes a volume of the hydraulic actuator, wherein an operating force that actuates the volume adjusting mechanism is generated by an electrically-operated motor.

This sort of variable displacement hydraulic actuator unit is configured such that the electrically-operated motor is actuated based on a difference between a current volume of the hydraulic actuator (hereinafter, referred to as a “current volume”) and a target volume thereof (hereinafter, referred to as a “target volume”), thereby matching the current volume to the target volume and maintaining the matched state.

Incidentally, the volume adjusting mechanism is always biased by a hydraulic pressure of an operating fluid toward a neutral side. Furthermore, the variable displacement hydraulic actuator unit may include a neutral biasing mechanism that biases the volume adjusting mechanism to the neutral side. In this manner, the biasing force to the neutral side is applied as an external force to the volume adjusting mechanism. Furthermore, in addition to the biasing force, an external force to the neutral side may be applied by some sort of factor to the volume adjusting mechanism or the hydraulic actuator.

When such an external force is applied to the volume adjusting mechanism, a problem occurs in which the volume of the hydraulic actuator becomes unintentionally offset from the target volume. Accordingly, in order to prevent this problem from occurring and to maintain a state in which the volume of the hydraulic actuator matches the target volume, a force that can counteract the external force (hereinafter, referred to as a “counteracting force”) is necessary.

Examples of conceivable means for obtaining the counteracting force include means for continuously supplying a required electrical power to the electrically-operated motor even after the volume of the hydraulic actuator has matched the target volume, and means for stopping the electrical power supply to the electrically-operated motor and obtaining a force of inertia (internal resistance) of the electrically-operated motor as the counteracting force.

However, if the former means is used, a large amount of electrical power is consumed, and, moreover, heat generated by the electrically-operated motor may cause operational errors, malfunctions, and the like.

On the other hand, if the latter means is used, the above-described problem still occurs when an external force exceeding the force of inertia is applied to the volume adjusting mechanism.

The present invention has been made in view of these conventional techniques, and it is an object thereof to provide an electrically-operated hydraulic actuator unit and a hydraulic four-wheel drive work vehicle in which, while allowing a volume adjusting mechanism to be actuated by an electrically-operated motor, it is possible to prevent a volume of a hydraulic actuator from being unintentionally changed by an external force applied to the volume adjusting mechanism or the hydraulic actuator.

PRIOR ART DOCUMENT

Patent Document

DISCLOSURE OF THE INVENTION

The present invention has been achieved in view of the conventional art described above, and an object thereof is to provide an electrically-operated hydraulic actuator unit and a hydraulic four-wheel-drive work vehicle, both which are capable of preventing a volume of a hydraulic actuator from being unintentionally changed by an external force applied to a volume adjusting mechanism or the hydraulic actuator while allowing the volume adjusting mechanism to be actuated by an electrically-operated motor.

In order to achieve the object, the present invention provides an electrically-operated hydraulic actuator unit including a variable displacement hydraulic actuator, an electrically-operated motor that generates an operating force for actuating a volume adjusting mechanism included in the variable displacement hydraulic actuator, and a control apparatus that controls action of the electrically-operated motor, the electrically-operated hydraulic actuator unit further including a clutch mechanism interposed between the volume adjusting mechanism and the electrically-operated motor, wherein the clutch mechanism includes a driving-side member that is rotated around a clutch reference axis by a rotational power from the electrically-operated motor, a driven-side member that is rotated around the clutch reference axis by the driving-side member and that is operatively linked to the volume adjusting mechanism, a clutch case that surrounds the driving-side member and the driven-side member, and a contact member accommodated in the clutch case so as to be rotated around the clutch reference axis along with the driven-side member by the driving-side member, the clutch mechanism being configured such that, when the driven-side member is pressed around the clutch reference axis by a force from the volume adjusting mechanism in a case where the electrically-operated motor is in a non-actuated state, the driven-side member presses the contact member against the clutch case to cause the driven-side member to be in a non-rotational locked state, whereby a power transmission from the driven-side member to the driving-side member is prevented, wherein the control apparatus includes a drive signal output portion that outputs a drive signal having a predetermined cycle to the electrically-operated motor, and a duty setting portion that sets a duty of the drive signal to be output by the drive signal output portion, wherein the duty setting portion sets a duty of a first drive signal that is to be output to the electrically-operated motor within a neutral-side start period having a predetermined time duration from a starting point in time at which an actuation of the motor toward the neutral side is started and a duty of a second drive signal that is to be output to the electrically-operated motor within a neutral-side ordinary period after the neutral-side start period when the volume adjusting mechanism has to be activated to the neutral side, while setting a duty of a third drive signal that is to be output to the electrically-operated motor within a higher-volume-side start period having a predetermined time duration from a starting point in time at which an actuation of the motor toward the higher-volume side is started and a duty of a fourth drive signal that is to be output to the electrically-operated motor within a higher-volume-side ordinary period after the higher-volume-side start period when the volume adjusting mechanism has to be activated to the higher-volume side, and wherein the duties of the first to fourth drive signal are set so that the duties of the first and fourth drive signals are larger than the duty of the second drive signal, and the duty of the third drive signal is larger than the duty of the fourth drive signal, while an integrated value of the time during which the third drive signal that is to be output within the higher-volume-side start period is on-state is larger than an integrated value of the time during which the first drive signal that is to be output within the neutral-side start period is on-state.

In the present invention, when the driven-side member is pressed around the clutch reference axis by a force from the volume adjusting mechanism in a state where the electrically-operated motor is in a non-actuated state, the driven-side member presses the contact member against the clutch case to cause the driven-side member to be in a non-rotational locked state, whereby a power transmission from the driven-side member to the driving-side member is prevented. Accordingly, the present invention can prevent the volume of the hydraulic actuator to be unintentionally changed by an external force that is applied to the volume adjusting mechanism in a direction toward the neutral side or an external force that may be applied to the variable displacement hydraulic actuator while allowing the electrically-operated motor to actuate the volume adjusting mechanism through the driving-side member and the driven-side member.

Furthermore, in the present invention, at the time when the electrically-operated motor is actuated so that the variable displacement hydraulic actuator has the target volume, actuation periods of the electrically-operated motor in the case of actuation of the volume adjusting mechanism to the neutral side and the higher volume side are each divided into a start period in which the actuation is started from the non-actuated state and an ordinary actuation period after the start period, and the actuation of the electrically-operated motor is controlled in an appropriate manner for each period. Accordingly, the present invention can properly actuate the volume adjusting mechanism.

That is to say, in consideration of the fact that the volume adjusting mechanism is biased toward the neutral side, the present invention sets the duty of the fourth drive signal that is to be output within the higher volume side ordinary actuation period larger than the duty of the second drive signal that is to be output within the neutral side ordinary actuation period, thereby preventing lack of the operating force at the time when actuating the volume adjusting mechanism to the higher volume side.

Furthermore, the driven-side member is locked if a force from the volume adjusting mechanism is applied in a case where the electrically-operated motor is in a non-actuated state, and therefore it is needed to cancel the locked state when the actuation of the volume adjusting mechanism is started, as described above.

In consideration of this point, the present invention sets the duty of the drive signal that is to be output within the start period larger than the duty of the drive signal that is to be output within the ordinary actuation period.

More specifically, in a case where the volume adjusting mechanism is needed to be actuated to the neutral side, the duty of the first drive signal that is to be output within the neutral-side start period is set larger than the duty of the second drive signal that is to be output within the neutral-side ordinary period, and, in a case where the volume adjusting mechanism is needed to be actuated to the higher volume side, the duty of the third drive signal that is to be output within the higher-volume-side start period is set larger than the duty of the fourth drive signal that is to be output within the higher-volume-side ordinary period.

Furthermore, the operating torque necessary for actuating the volume adjusting mechanism to the higher volume side is larger, by a biasing force acting on the volume adjusting mechanism to the neutral side, than the operating torque necessary for actuating the volume adjusting mechanism to the neutral side. The same is applied to the case of cancellation of the locked state.

In consideration of this aspect, in the present invention, an integrated value of the time during which the third drive signal that is to be output within the higher-volume-side start period is on-state is larger than an integrated value of the time during which the first drive signal that is to be output within the neutral-side start period is on-state. The configuration makes it possible to secure the operating torque necessary for canceling the locked state both in a case of actuation of the volume adjusting mechanism to the neutral side and the higher volume side, thereby reliably canceling the locked state.

The configuration in which the integrated value of the time during which the third drive signal that is to be output within the higher-volume-side start period is on-state is larger than an integrated value of the time during which the first drive signal that is to be output within the neutral-side start period is on-state is exemplified by, for example, an embodiment in which a length of the higher-volume-side start period is longer than a length of the neutral-side start period, and the duty of the third drive signal is set to be larger than or equal to the duty of the first drive signal.

Alternatively, the configuration can be also realized by an embodiment in which a length of the higher-volume-side start period is same as a length of the neutral-side start period, and the duty of the third drive signal is set to be larger than the duty of the first drive signal.

In any one of the above-mentioned various configurations, the electrically-operated hydraulic actuator unit according to the present invention may preferably include a current volume detecting portion that detects a current volume of the variable displacement hydraulic actuator, a target volume detecting portion that detects a target volume of the variable displacement hydraulic actuator, and a difference calculating portion that calculates a difference between the current volume detected by the current volume detecting portion and the target volume detected by the target volume detecting portion.

The duty setting portion determines whether the direction in which the volume adjusting mechanism is to be actuated is the higher volume side or the neutral side, based on the difference calculated by the difference calculating portion, and then sets either a set of the duties of the first and the second drive signals or a set of the duties of the third and the fourth drive signals according to the determination result.

The configuration makes it possible to properly determine the direction in which the volume adjusting mechanism should be actuated, and also the duties of either the set of the first and second drive signals or the set of the third and fourth drive signals.

In any one of the above-mentioned various configurations of the electrically-operated hydraulic actuator unit according to the present invention, the duty setting portion may preferably include a reference duty storage portion that stores, as respective reference duties, initial values of duties that have been preset for the first to the fourth drive signals, a correction value storage portion that stores in advance correction values for correcting the reference duty according to the difference calculated by the difference calculating portion, and a first duty correcting portion that reads the correction value associated with the difference from the correction value storage portion upon the calculation of the difference by the difference calculating portion and then corrects the reference duty associated with the current period among the periods with using the read correction value.

In the preferable configuration, since the first duty correcting portion corrects the reference duty associated with the current period among the periods with using the correction value associated with the difference that is calculated by the difference calculating portion, the operating torque of the electrically-operated motor can be set in accordance with the difference. Accordingly, the preferable configuration makes it possible to suitably change a time length required to match the volume of the variable displacement hydraulic actuator to the target volume.

The correction value is preferably set to become larger as the difference calculated by the difference calculating portion becomes larger.

The configuration makes it possible to increase the operating torque of the electrically-operated motor as the difference is larger. Accordingly, the time until the current volume of the variable displacement hydraulic actuator is matched to the target volume can be shortened compared with the case in which the reference duty is not corrected in accordance with the difference.

Preferably, the duty setting portion may further include a second duty correcting portion for correcting the duty, which has been corrected by the first duty correcting portion, according to a voltage of a battery that is an electrical power source of the electrically-operated motor.

The preferable configuration can exert a following effect.

More specifically, if the voltage of the battery changes, the voltage values of the first to the fourth drive signals that are to be output to the electrically-operated motor change. As a result, the electrical power that is to be supplied to the electrically-operated motor also changes.

When the electrical power that is to be output to the electrically-operated motor changes as described above, the operating torque of the electrically-operated motor changes even if the respective duties of the first to fourth drive signals are suitably set. As a result, the operating torque becomes excessively large or small, which makes it impossible to match the volume of the variable displacement hydraulic actuator to the target volume.

On the other hand, the provision of the second duty correcting portion for correcting the duty, which has been corrected by the first duty correcting portion, according to the voltage of the battery can effectively prevent such a problem.

For example, the second duty correcting portion corrects the duty that has been corrected by the first duty correcting portion so that the duty becomes smaller in proportion to increase of the voltage of the battery.

Preferably, the duty setting portion may further include a reference duty storage portion that stores, as respective reference duties, initial values of duties that have been preset for the first to the fourth drive signals, and a reference duty correcting portion that corrects the reference duty of one of the first to fourth drive signals that is to be output associated with the current period in accordance with a voltage of a battery functioning as an electrical power source of the electrically-operated motor.

The configuration makes it possible to effectively prevent fluctuation of the operating torque of the electrically-operated motor due to change of the battery voltage.

For example, the reference duty correcting portion corrects the reference duty so that the duty becomes smaller in proportion to increase of the battery voltage.

In any one of the various configurations, the driving-side member may be configured such that side faces oriented in the circumferential direction with respect to the clutch reference axis can press, in the circumferential direction, respective side faces oriented in the circumferential direction of the driven-side member and the contact member, and, when viewed along the clutch reference axis, an outer end face of the driven-side member oriented outward in the radial direction may have a circumferential center portion in which a distance to the axis is smaller than a distance (L) from the contact member to the axis and a circumferential outer portion in which the distance to the axis is larger than the distance (L).

According to the configuration, since the outer end face of the driven-side member has the circumferential center portion in which a distance to the axis is smaller than the distance (L) from the contact member to the axis and the circumferential outer portion in which the distance to the axis is larger than the distance (L), when the driven-side member is arranged at a position around a reference (rotation center) that causing the circumferential center portion of the driven-side member to confront the contact member, the driven-side member is rotatable around the clutch reference axis so that the driven-side member and the contact member are rotated around the clutch reference axis by the driving-side member. On the other hand, when the driven-side member is pressed around the clutch reference axis by a force from the volume adjusting mechanism in a case where the electrically-operated motor is in a non-actuated state, the driven-side member presses the contact member against the clutch case so that the driven-side is in a non-rotatable locked state.

Furthermore, the present invention provides a hydraulic four-wheel-drive work vehicle including a vehicle frame, a driving power source supported by the vehicle frame, first and second wheels supported by one and the other sides in a front-and-rear direction of the vehicle frame, a hydraulic pump unit operatively driven by the driving power source, and first and second hydraulic motor units that are fluid-connected to the hydraulic pump unit and that operatively drives the first and second wheels (10,20), respectively, wherein the first hydraulic motor that operatively drives the first wheel is embodied by the electrically-operated hydraulic actuator unit according to any one of the above-mentioned various configurations.

EMBODIMENT FOR CARRYING OUT THE INVENTION

Hereinafter, an electrically-operated hydraulic actuator unit according to an embodiment of the present invention will be described with reference to the appended drawings.

FIGS. 1A to 1Cshow plan views of a hydraulic four-wheel drive work vehicle (hereinafter, referred to as a “work vehicle”)1to which the electrically-operated hydraulic actuator unit according to the present embodiment has been applied.FIG. 1Ashows a state in which the work vehicle1is traveling straight ahead, andFIG. 1Bshows a state in which the work vehicle1is turning.FIG. 2shows a diagram of a hydraulic circuit of the work vehicle1.

As shown inFIGS. 1 and 2, the electrically-operated hydraulic actuator unit according to the present embodiment is used as a hydraulic motor unit. Specifically, the electrically-operated hydraulic actuator unit according to the present embodiment functions as a hydraulic motor unit that operatively drives one of first and second wheels10and20respectively arranged on one side and the other side in the vehicle front-and-rear direction of the work vehicle1.

First, an outline of the work vehicle1will be described.

As shown inFIGS. 1 and 2, the work vehicle1includes a vehicle frame30, a pair of the first wheels10arranged on right and left sides (front wheels in this example) and a pair of the second wheels20arranged on right and left sides (rear wheels in this example) that are respectively supported on one side and the other side in the front-and-rear direction of the vehicle frame30, a driving source40that is supported on the vehicle frame30, a variable displacement hydraulic pump unit50that is operatively driven by the driving source40, an electrically-operated hydraulic actuator unit100according to the present embodiment functioning as a first hydraulic motor unit that is fluid-connected to the hydraulic pump unit50and that is for operatively driving the first wheels10, and a second hydraulic motor unit200that is fluid-connected to the hydraulic pump unit50and that is for operatively driving the second wheels20.

The electrically-operated hydraulic actuator unit100is of a variable displacement type in order to compensate for a difference between turning radiuses of the first and the second wheels10and20, which occurs when the vehicle is turning.

Specifically, as shown inFIGS. 1A and 1B, the work vehicle1is configured such that a turning radius R1of the first wheels10is smaller than a turning radius R2of the second wheels20and the difference between the turning radiuses of the first and the second wheels10and20increases as a turning angle of the vehicle increases.

In the present embodiment, as shown inFIGS. 1A and 1B, the work vehicle1is of an articulated type having, as the vehicle frame30, first and second frames31and32that are linked in a swingable manner about a substantially vertical pivotal support shaft35.

The second wheels20are supported on the second frame32, and the first wheels10are supported on the first frame31such that a length L1in the vehicle front-and-rear direction between the first wheels10and the pivotal support shaft35is longer than a length L2in the vehicle front-and-rear direction between the second wheels20and the pivotal support shaft35.

In this configuration, the turning radius R1of the first wheels10is smaller than the turning radius R2of the second wheels20, and the difference between the turning radiuses of the first and the second wheels10and20increases as the turning angle of the vehicle increases.

Note that examples of a work vehicle in which a difference occurs between the turning radiuses of a wheel on one side in the vehicle front-and-rear direction and a wheel on the other side include, in addition to the work vehicle1of an articulated type, a work vehicle in which a front wheel and a rear wheel are respectively supported on a front portion and a rear portion of a rigid vehicle frame and one of the front and rear wheels is used as a steering wheel.

The hydraulic pump unit50forms an HST in cooperation with the electrically-operated hydraulic actuator unit100and the second hydraulic motor unit200.

Specifically, as shown inFIG. 2, the hydraulic pump unit50, the electrically-operated hydraulic actuator unit100, and the second hydraulic motor unit200are fluid-connected to each other in series.

That is to say, the hydraulic pump unit50, the electrically-operated hydraulic actuator unit100, and the second hydraulic motor unit200are fluid-connected to each other such that, when the vehicle is traveling forward (i.e., when the hydraulic pump unit50is driven forward), pressurized fluid discharged from the hydraulic pump unit50is supplied to one of the electrically-operated hydraulic actuator unit100and the second hydraulic motor unit200(the electrically-operated hydraulic actuator unit100in this example), operating fluid returned from the one hydraulic motor unit is supplied to the other of the electrically-operated hydraulic actuator unit100and the second hydraulic motor unit200(the second hydraulic motor unit200in this example), and operating fluid returned from the other hydraulic motor unit is returned to the hydraulic pump unit50.

In this case, when the vehicle is traveling in reverse (i.e., when the hydraulic pump unit50is driven in reverse), pressurized fluid discharged from the hydraulic pump unit50is supplied to the other hydraulic motor unit (the second hydraulic motor unit200in this example), operating fluid returned from the other hydraulic motor unit is supplied to the one hydraulic motor unit (the electrically-operated hydraulic actuator unit100in this example), and operating fluid returned from the one hydraulic motor unit is returned to the hydraulic pump unit50.

As described above, the hydraulic pump unit50is of a variable displacement type, and functions as a main speed-change device of the work vehicle1.

Specifically, as shown inFIG. 2, the hydraulic pump unit50includes a pump shaft51that is operatively linked to the driving source40, a hydraulic pump52that is supported on the pump shaft51in a relatively non-rotatable manner about this shaft, a pump housing53that accommodates the hydraulic pump52and supports the pump shaft51in a rotatable manner about its axis, and a pump-side volume adjusting mechanism54that changes the volume of the hydraulic pump52based on an operation from the outside.

As shown inFIG. 2, the pump housing53is provided with a pair of pump-side operating fluid lines500having first end portions fluid-connected to the hydraulic pump52and second end portions exposed on the outer surface to form a pair of pump-side connecting ports500P.

As shown inFIG. 2, the pump housing53is further provided with a pump-side bypass line510that interconnects the pair of pump-side operating fluid lines500, a pump-side drain line520having a first end portion fluid-connected to the pump-side bypass line510and a second end portion exposed to an internal space of the pump housing53, and a pump-side bypass valve515.

The pump-side bypass valve515can be selectively switched between a block position at which the pump-side bypass line510is blocked and the pump-side drain line520is blocked from the pump-side bypass line510and a bypass-drain position at which the pump-side bypass line510is interconnected and the pump-side drain line520is fluid-connected to the pump-side bypass line510.

Furthermore, the pump housing53is provided with a charge line530.

Specifically, as shown inFIG. 2, the hydraulic pump unit50has, in addition to the above-described constituent components, a charge pump55that is operatively driven by the pump shaft51.

Furthermore, the charge line530has a first end portion fluid-connected to a discharge side of the charge pump55and a second end portion fluid-connected via a pair of check valves535respectively to the pair of pump-side operating fluid lines500.

Note that, inFIG. 2, reference numeral536denotes a charge relief valve that sets the pressure of oil in the charge line530, reference numeral95denotes an oil tank that functions as an oil source for the charge pump55, and reference numeral545denotes a filter that is installed in a charge suction line540through which the oil tank95and a suction side of the charge pump55are fluid-connected to each other.

Furthermore, reference numeral550denotes a drain line through which the oil tank95and the internal space of the pump housing53are fluid-connected to each other.

The pump-side volume adjusting mechanism54is actuated according to a manual operation on a speed-change operating member60included in the work vehicle1.

For example, the amount of manual operation on the speed-change operating member60can be relayed via a mechanical link mechanism61(seeFIG. 2) to the pump-side volume adjusting mechanism54.

Alternatively, a configuration is also possible in which the hydraulic pump unit50includes a pump-side actuator such as an electrically-operated motor that actuates the pump-side volume adjusting mechanism54, and the work vehicle1includes a speed-change operation-side detecting portion that detects an amount of manual operation on the speed-change operating member, a speed-change actuation-side detecting portion that detects an actuation state of the pump-side actuator, and a control apparatus90(described later), wherein the control apparatus90controls actuation of the pump-side actuator based on signals from the speed-change operation-side detecting portion and the speed-change actuation-side detecting portion such that the pump-side volume adjusting mechanism54is actuated according to the amount of operation on the speed-change operating member60.

The pump-side volume adjusting mechanism54may have, for example, a pump-side control shaft (not shown) that is rotatable about its axis, and a pump-side movable swash plate (not shown) that is operatively linked to the pump-side control shaft in a rotatable manner at an angle about its swing axis according to rotation of the pump-side control shaft about its axis.

Next, the second hydraulic motor unit200will be described.

Specifically, as shown inFIG. 2, the second hydraulic motor unit200includes a second hydraulic motor220, a second motor shaft210that supports the second hydraulic motor220in a relatively non-rotatable manner about this shaft, and a second motor housing230that accommodates the second hydraulic motor220and supports the second motor shaft210in a rotatable manner about its axis. In this example, the second hydraulic motor unit200is of a fixed displacement type in which the second hydraulic motor220has a fixed volume.

The second motor housing230is provided with a pair of second motor-side operating fluid lines240having first end portions fluid-connected to the second hydraulic motor220and second end portions exposed on the outer surface to form a pair of second motor-side connecting ports240P.

As shown inFIG. 2, the second motor housing230is further provided with a second motor-side bypass line245that interconnects the pair of second motor-side operating fluid lines240, a second motor-side drain line255having a first end portion fluid-connected to the second motor-side bypass line245and a second end portion exposed to an internal space of the second motor housing230, and a second motor-side bypass valve250.

The second motor-side bypass valve250can be selectively switched between a block position at which the second motor-side bypass line245is blocked and the second motor-side drain line255is blocked from the second motor-side bypass line245and a bypass-drain position at which the second motor-side bypass line245is interconnected and the second motor-side drain line255is fluid-connected to the second motor-side bypass line245.

Furthermore, reference numeral260denotes a drain line through which the oil tank and the internal space of the second motor housing230are fluid-connected to each other.

As shown inFIG. 2, in this example, the second hydraulic motor unit200forms a second axle driving apparatus21that drives the second wheels20.

Specifically, the second axle driving apparatus21has, in addition to the second hydraulic motor unit200, a pair of left and right second axles22that are respectively linked to the second wheels20, a second differential gear mechanism24that receives a rotational driving power input from the second motor shaft210via a second reduction gear train23and transmits the power to the pair of second axles22while allowing them to rotate at different speeds, and a second axle housing25that accommodates the second reduction gear train23and the second differential gear mechanism24and supports the pair of second axles22in a rotatable manner about their axis.

Note that the second axle housing25and the second motor housing230are formed in one piece.

Next, the electrically-operated hydraulic actuator unit100according to the present embodiment functioning as the first hydraulic motor unit will be described.

As described above, the electrically-operated hydraulic actuator unit100is of a variable displacement type, and can change the driving speed of the first wheels10according to the difference between the turning radiuses of the first and the second wheels10and20in the work vehicle1.

Specifically, as shown inFIGS. 1A and 1B, in the work vehicle1, the first and the second wheels10and20are arranged such that the turning radius of the first wheels10gradually decreases with respect to the turning radius of the second wheels20according to the turning angle of the vehicle.

Furthermore, the electrically-operated hydraulic actuator unit100that operatively drives the first wheels10is of a variable displacement type such that it can function as a speed-change device that changes the driving speed of the corresponding first wheels10according to the difference between the turning radiuses. The electrically-operated hydraulic actuator unit100according to the present embodiment is used as a first hydraulic motor unit that functions in this manner.

FIG. 3Ashows a horizontal plan view of the electrically-operated hydraulic actuator unit100.FIG. 4shows a cross-sectional view taken along the line IV-IV inFIG. 3A.

As shown inFIGS. 2 to 4, the electrically-operated hydraulic actuator unit100is configured including a first hydraulic motor120(corresponding to a variable displacement hydraulic actuator) that includes a motor-side volume adjusting mechanism135, an electrically-operated motor300such as a direct current motor that generates a; force for actuating the motor-side volume adjusting mechanism135of the first hydraulic motor120, and the control apparatus90that is in charge of controlling actuation of the electrically-operated motor300.

The electrically-operated hydraulic actuator unit100further includes a first motor shaft110that supports the first hydraulic motor120in a relatively non-rotatable manner about this shaft, and a first motor housing130that accommodates the first hydraulic motor120and supports the first motor shaft110in a rotatable manner about its axis.

The first motor housing130is provided with a pair of first motor-side operating fluid lines140having first end portions fluid-connected to the first hydraulic motor120and second end portions exposed on the outer surface to form a pair of first motor-side connecting ports140P.

As shown inFIG. 2, one of the pair of first motor-side connecting ports140P is fluid-connected via a pump/first motor line410to one of the pair of pump-side connecting ports500P, the other first motor-side connecting port140P is fluid-connected via a first motor/second motor line420to one of the pair of second motor-side connecting ports240P, and the other second motor-side connecting port240P is fluid-connected via a pump/second motor line430to the other pump-side connecting port500P.

That is to say, in this example, the hydraulic pump52, the first hydraulic motor120, and the second hydraulic motor220are fluid-connected to each other in series, and, thus, the first hydraulic motor120that operatively drives the first wheels10and the second hydraulic motor220that operatively drives the second wheels20are fluid-driven by the hydraulic pump52in a synchronized manner with each other.

As shown inFIGS. 2 and 4, the first motor housing130is further provided with a first motor-side bypass line145that interconnects the pair of first motor-side operating fluid lines140, a first motor-side drain line155having a first end portion fluid-connected to the first motor-side bypass line145and a second end portion exposed to an internal space of the first motor housing130, and a first motor-side bypass valve150.

The first motor-side bypass valve150can be selectively switched between a block position at which the first motor-side bypass line145is blocked and the first motor-side drain line155is blocked from the first motor-side bypass line145and a bypass-drain position at which the first motor-side bypass line145is interconnected and the first motor-side drain line155is fluid-connected to the first motor-side bypass line145.

Furthermore, reference numeral160denotes a drain line through which the oil tank95and the internal space of the first motor housing130are fluid-connected to each other.

FIG. 5shows a cross-sectional view taken along the line V-V inFIG. 3A.

As shown inFIGS. 3A and 5, the motor-side volume adjusting mechanism135has a motor-side control shaft136that is directly or indirectly supported on the first motor housing130in a rotatable manner about its axis in a state in which a first end portion of the motor-side control shaft136is projected outward from the first motor housing130, and is configured so as to change the volume of the first hydraulic motor120as the motor-side control shaft136rotates about its axis.

As shown inFIGS. 3A and 4, in the present embodiment, the first hydraulic motor120is of an axial piston type.

Accordingly, as shown inFIG. 3AtoFIG. 5, the motor-side volume adjusting mechanism135has, in addition to the motor-side control shaft136, a motor-side movable swash plate137that can slant about its swing axis and increases or decreases the volume of the first hydraulic motor120according to the slanting position about the swing axis.

The motor-side movable swash plate137is linked to the motor-side control shaft136in a slanting manner about its swing axis according to rotation of the motor-side control shaft136about its axis.

As shown inFIGS. 2 and 3A, the electrically-operated hydraulic actuator unit100according to the present embodiment forms a first axle driving apparatus11that drives the first wheels10.

Specifically, the first axle driving apparatus11has, in addition to the electrically-operated hydraulic actuator unit100, a pair of left and right first axles12that are respectively linked to the first wheels10, a first differential gear mechanism14that receives a rotational driving power input from the first motor shaft110via a first reduction gear train13and transmits the power to the pair of first axles12while allowing them to rotate at different speeds, and a first axle housing15that accommodates the first reduction gear train13and the first differential gear mechanism14and supports the pair of first axles12in a rotatable manner about their axis.

Note that the first axle housing15and the first motor housing130are formed in one piece as a single first housing.

Furthermore, in the present embodiment, as shown inFIGS. 2 and 3A, the first axle driving apparatus11includes a brake mechanism16that can selectively apply a braking force to a power transmission path in the traveling system from the first motor shaft110to the first axles12.

Preferably, the brake mechanism16is configured so as to be capable of applying a braking force to a member positioned on the upstream side in the power transmission direction of the first reduction gear train13.

With this preferable configuration, the size of the brake mechanism16can be reduced.

In the present embodiment, as shown inFIG. 3A, the brake mechanism16is configured so as to be capable of applying a braking force to the first motor shaft110.

For example, as shown inFIG. 3B, one end portion of the first motor shaft110may be projected outward from the first housing130, and the outward projected portion of the first motor shaft110may support a cooling fan17.

With this configuration, the first axle driving apparatus11including the electrically-operated hydraulic actuator unit100can be efficiently cooled down.

FIG. 6shows an end face view taken along the line VI-VI inFIG. 3A.

Furthermore,FIGS. 7 and 8respectively show cross-sectional views taken along the lines VII-VII and VIII-VIII inFIG. 3A.

The electrically-operated motor300operatively drives the motor-side control shaft136, and, as shown inFIGS. 6 and 7, includes an electrically-operated motor main body301whose drive is electrically controlled, an electrically-operated motor case305that accommodates the electrically-operated motor main body301, and an electrically-operated motor main body output shaft310that is rotated about its axis by the electrically-operated motor main body301.

The electrically-operated motor case305is detachably attached directly or indirectly to the first motor housing130.

In the present embodiment, the electrically-operated motor case305is connected via an electrically-operated motor cover315to the first motor housing130.

Specifically, as shown inFIGS. 6 and 8, the electrically-operated hydraulic actuator unit100further has the electrically-operated motor cover315to which the electrically-operated motor case305can be connected and that is connected to the first motor housing130.

In the present embodiment, as shown inFIGS. 3A and 6to8, a plate member170having an opening through which the first end portion of the motor-side control shaft136is inserted is detachably connected via a fastening member171such as a bolt to the first motor housing130.

Furthermore, the electrically-operated motor cover315is detachably connected via fastening members316such as bolts to the plate member170in a state in which the electrically-operated motor case305is connected via fastening members306such as bolts to the electrically-operated motor cover315.

The present embodiment is configured such that, upon attachment of the electrically-operated motor300to the first motor housing130, the electrically-operated motor main body output shaft310is operatively linked to the first end portion of the motor-side control shaft136.

That is to say, according to rotation of the electrically-operated motor main body output shaft310, the motor-side control shaft136rotates about its axis, and, thus, the volume of the first hydraulic motor main body120is changed.

With the thus configured electrically-operated hydraulic actuator unit100, the motor-side volume adjusting mechanism135can be actuated according to a manual operation on the steering operation member65, by electrically controlling the electrically-operated motor main body301according to the amount of manual operation on a steering operation member65, without mechanically operatively linking the steering operation member65and the motor-side volume adjusting mechanism135.

Accordingly, without any complicated mechanical link structure, the volume of the first hydraulic motor main body120can be changed according to a manual operation on the steering operation member65.

FIG. 9shows an exploded cross-sectional view in which the electrically-operated motor300has been separated from the electrically-operated motor cover315.

As shown inFIGS. 6 to 9, the electrically-operated motor300is linked to the motor-side volume adjusting mechanism135, via an operating shaft340that is connected to the motor-side volume adjusting mechanism135, and a sector gear335that is connected to the operating shaft340.

Specifically, the operating shaft340is connected to the first end portion of the motor-side control shaft136in a relatively non-rotatable manner about its axis.

The sector gear335is projected in a direction orthogonal to the motor-side control shaft136in a state where its base end portion is connected to the operating shaft340, and is provided with a gear at a free end portion thereof.

Meanwhile, as shown inFIG. 6, the electrically-operated motor300has, in addition to the above-described constituent components, a worm shaft320that is operatively connected to the electrically-operated motor main body output shaft310, a power transmission gear325that meshes with the worm shaft320, a power transmission shaft326that supports the power transmission gear325in a relatively non-rotatable manner about this shaft, and a power transmission motor output gear330that is supported on the power transmission shaft326in a relatively non-rotatable manner about this shaft, wherein, when the electrically-operated motor case305is connected to the electrically-operated motor cover315, the power transmission motor output gear330meshes with the sector gear335.

With this configuration, the electrically-operated motor main body output shaft310can be reliably operatively linked to the motor-side control shaft136when the electrically-operated motor300is attached to the electrically-operated motor cover315, and the electrically-operated motor300can be easily attached to and detached from the electrically-operated motor cover315.

Preferably, as shown inFIG. 6, the electrically-operated hydraulic actuator unit100can be provided with a first adjustment screw341that is screwed into a fixed member such as the electrically-operated motor cover315such that a tip end portion of the first adjustment screw341abuts against the sector gear335to define a swing end of the sector gear335about the operating shaft340in one direction, and a second adjustment screw342that is screwed into the fixed member such that a tip end portion of the second adjustment screw342abuts against the sector gear335to define a swing end of the sector gear335about the operating shaft340in the other direction.

With the first and the second adjustment screws341and342, the range in which the volume of the first hydraulic motor120is allowed to change can be accurately set requiring as few additional constituent components as possible.

In the present embodiment, as shown inFIG. 6, the electrically-operated motor cover315is used as the fixed member. However, it will be appreciated that the first motor housing130or the plate member170that is fixed to the first motor housing130also may be used as the fixed member.

In the present embodiment, as shown inFIGS. 6 to 9, the sector gear335is provided with a through hole336apassing through the sector gear335in the axial direction of the operating shaft340, and the electrically-operated motor cover315is provided with a fixing hole336bat a position where it faces the through hole336awhen the sector gear335is at a predetermined position about the operating shaft340.

With this configuration, when a malfunction of the electrically-operated motor300or the like occurs, as shown inFIG. 9, the electrically-operated motor300is detached from the electrically-operated motor cover315and a fixing pin336cis inserted through the through hole336aand the fixing hole336b, and, thus, the sector gear335can be fixed at the predetermined position about the operating shaft340so that the volume of the first hydraulic motor main body120can be fixed at a predetermined volume corresponding to the predetermined position.

Preferably, the fastening members306can be used as the fixing pin336c. That is to say, the fastening members306removed when the electrically-operated motor300is detached from the electrically-operated motor cover315can be used as the fixing pin336cthat is inserted through the through hole336aand the fixing hole336b.

As shown inFIGS. 3A,8, and9, the electrically-operated hydraulic actuator unit100according to this embodiment further has a sensor unit350that detects the amount of rotation of the operating shaft340about its axis.

Specifically, as shown inFIGS. 6 to 9, the sensor unit350has a sensor housing351that is attached to the electrically-operated motor cover315, a sensor shaft352that is supported on the sensor housing351in a rotatable manner about its axis so as to be positioned coaxially with the operating shaft340in a state in which the electrically-operated motor cover315is connected to the first motor housing130, a sensor arm353that has a base end portion connected to the sensor shaft352and extends in a direction orthogonal to the operating shaft340, a biasing member (not shown) that biases a detected body formed by the sensor shaft352and the sensor arm353, in one direction about the axis of the sensor shaft352, and a sensor main body (not shown) that detects the amount of rotation of the sensor shaft352about its axis.

Furthermore, the sector gear335is provided with an engagement pin337that is projected parallel to the operating shaft340, and becomes engaged with the sensor arm353biased by the biasing member in one direction about the axis of the sensor shaft352when the electrically-operated motor cover315including the sensor unit350is connected to the first motor housing130.

With this configuration, when the electrically-operated motor cover315to which the electrically-operated motor300and the sensor unit350have been attached is connected to the first motor housing130, the sensor arm353can be engaged with the engagement pin337such that the sensor arm353rotates about the sensor shaft352according to rotation of the sector gear335about the operating shaft340.

Furthermore, when the electrically-operated motor cover315to which the electrically-operated motor300and the sensor unit350have been attached is detached from the first motor housing130, the sensor arm353is allowed to relatively move along the axial direction of the sensor shaft352with respect to the engagement pin337.

Accordingly, while the position of the sector gear335about the operating shaft340(i.e., the position of the motor-side control shaft136about its axis) is being detected by the sensor unit350, the electrically-operated motor cover315to which the electrically-operated motor300and the sensor unit350have been still attached can be easily detached from the first motor housing130.

As shown inFIG. 6, the electrically-operated hydraulic actuator unit100according to the present embodiment is further provided with a clutch mechanism360that is interposed between the electrically-operated motor300and the motor-side volume adjusting mechanism135, more specifically, between the electrically-operated motor main body output shaft310and the worm shaft320, in order to allow a rotational driving power to be transmitted from the electrically-operated motor main body output shaft310to the worm shaft320, while preventing the rotational driving power from being transmitted in the opposite direction.

FIG. 10shows a vertical cross-sectional view of the clutch mechanism360taken along the line X-X inFIG. 6.

Furthermore,FIG. 11shows a horizontal cross-sectional view of the clutch mechanism360taken along the line XI-XI inFIG. 10.

As shown inFIGS. 10 and 11, the clutch mechanism360has a driving-side arm361(corresponding to a driving-side member) that is provided at a tip end portion of the electrically-operated motor main body output shaft310so as to be projected outward in radial directions, a clutch case362that surrounds the driving-side arm361, a driven-side arm363(corresponding to a driven-side member) that is provided at an end portion of the worm shaft320on the side facing the electrically-operated motor main body output shaft310so as to be projected outward in radial directions, and contact members364that are arranged between the driven-side arm363and the clutch case362in the radial directions with respect to the axis of the electrically-operated motor main body output shaft310and the worm shaft320.

The driving-side arm361is configured such that side faces361aoriented in the circumferential direction with respect to an axis CL (corresponding to a clutch reference axis) of the electrically-operated motor main body output shaft310can press, in the circumferential direction, respective side faces363aand364aoriented in the circumferential direction of the driven-side arm363and the contact members364.

When viewed along the axis CL of the electrically-operated motor main body output shaft310and the worm shaft320, outer end faces363bof the driven-side arm363oriented outward in the radial direction each have a circumferential center portion in which the distance to the axis CL is smaller than a distance L from the contact member364to the axis CL and a circumferential outer portion in which the distance is larger than the distance L.

The outer end faces363beach having the circumferential center portion and the circumferential outer portion may be configured such that the outer end faces363bare each substantially orthogonal to a virtual line IL connecting the center point in the circumferential direction of the outer end face363band the axis CL.

The thus configured clutch mechanism360is actuated as follows.

When the electrically-operated motor main body301is rotated either in one direction about its axis (e.g., in a forward rotating direction for causing the work vehicle1to travel forward) or in the other direction (e.g., in a reverse direction for causing the work vehicle1to travel in reverse) (hereinafter, referred to as a “first direction D1”) (seeFIG. 11A), the driving-side arm361presses both the driven-side arm363and the contact members364in the first direction D1. Accordingly, the worm shaft320rotates in a direction d1, which is the same as the first direction D1(seeFIG. 11B), the movable swash plate137slants in a direction corresponding to the first direction D1.

Incidentally, the pressure of an operating fluid supplied or discharged by the first hydraulic motor120functions on the movable swash plate137as a force that slants the movable swash plate137to the neutral side (neutral direction, lower volume side). Furthermore, as necessary, the electrically-operated hydraulic actuator unit100includes a neutral spring that biases the movable swash plate137to the neutral side.

Accordingly, if the biasing force is larger than the force of inertia of the electrically-operated motor300, when the electrically-operated motor300is put in a non-actuated state (the state in which the rotation of the electrically-operated motor main body output shaft310is stopped), the movable swash plate137slants by a slight amount to the neutral side against the force of inertia of the electrically-operated motor300.

Accordingly, as shown inFIG. 11C, the worm shaft320operatively linked to the movable swash plate137rotates in a second direction d2corresponding to a direction toward the neutral side. However, the contact members364are in an unengaged state, and therefore the position of the contact members364is not changed.

As described above, when viewed along the axis CL of the worm shaft320, the outer end faces363bof the driven-side arm363each have the circumferential center portion in which the distance to the axis CL is smaller than the distance L from the contact member364to the axis CL and the circumferential outer portion in which the distance is larger than the distance L. Accordingly, when the driven-side arm363rotates in the second direction d2, the contact members364are pressed against the inner circumferential surface of the clutch case362, and, thus, the worm shaft320is put in a locked state in which it is not allowed to rotate (seeFIG. 11C).

Accordingly, after the movable swash plate137is moved by the electrically-operated motor300to a predetermined slanting position, the movable swash plate137can be reliably prevented from unintentionally slanting from the predetermined slanting position.

Hereinafter, a method for controlling the electrically-operated motor300by the control apparatus90will be described.

As described above, the electrically-operated hydraulic actuator unit100that operatively drives the first wheels10and the second hydraulic motor unit200that operatively drives the second wheels20are hydraulically driven in a synchronized manner with each other by the hydraulic pump unit50, and the turning radius R1of the first wheels10becomes smaller than the turning radius R2of the second wheels20as the turning angle of the vehicle increases.

The control apparatus90controls actuation of the electrically-operated motor300such that the speed of the first wheels10driven by the electrically-operated hydraulic actuator unit100changes according to the difference between the turning radiuses of the first and the second wheels10and20.

Specifically, the motor-side volume adjusting mechanism135of the electrically-operated hydraulic actuator unit100is configured so as to be capable of changing the volume of the first hydraulic motor120within a range including a reference volume at which the circumferential speed of the first wheels10operatively driven by the first hydraulic motor120is substantially the same as the circumferential speed of the second wheel pair20operatively driven by the second hydraulic motor220and a first volume that is larger than the reference volume.

For example, if the first wheel pair10and the second wheel pair20have the same diameter, the reference volume is the same as the fixed volume of the second hydraulic motor220.

Preferably, the first volume is a volume for reducing the circumferential speed of the first wheel pair10by a speed according to the difference between the turning radiuses of the first and the second wheel pairs10and20, which occurs when the work vehicle1is turning at the maximum turning angle.

The control apparatus90actuates the electrically-operated motor300such that the volume of the first hydraulic motor120has a volume according to the turning angle of the vehicle between the reference volume and the first volume, based on a turning angle signal from a turning angle sensor included in the work vehicle1.

More specifically, the control apparatus90actuates the electrically-operated motor300such that the volume of the first hydraulic motor120is the first volume when the vehicle1is turning at the maximum turning angle, and such that the volume of the first hydraulic motor120is a volume according to the turning angle of the vehicle between the reference volume and the first volume when the vehicle1is turning at a turning angle larger than that in straight-ahead traveling state and smaller than the maximum turning angle.

Specifically, the control apparatus90includes a computing portion (hereinafter, referred to as a “CPU”) that has control computation means for performing various computing processes, and a storage portion that has a ROM for storing control programs, control data, and the like, an EEPROM for saving set values and the like such that they are not lost even when power is removed and allowing the set values and the like to be rewritten, a RAM for temporarily storing data generated during computation by the CPU, and the like.

The storage portion stores control data related to an actuation state of the electrically-operated motor300with respect to a turning angle, and the CPU performs computing processes for controlling actuation of the electrically-operated motor300based on the turning angle information output from a sensor such as the turning angle sensor and the control data.

The control data may be, for example, in the form of a conversion formula for control, a LUT (look-up table), or the like.

The turning angle sensor may be an operation-side turning angle sensor66that detects the operation angle of the steering operation member65(seeFIG. 2) or an actuation-side turning angle sensor that detects the turning angle of the first frame31with respect to the second frame32.

Furthermore, in a work vehicle in which a front wheel pair and a rear wheel pair are respectively supported on a front portion and a rear portion of a rigid vehicle frame and one of the front wheel pair and the rear wheel pair is used as a steering wheel pair, the actuation-side turning angle sensor is configured so as to detect the steering angle of the steering wheel pair.

FIG. 12is a block diagram showing an electrical configuration of the electrically-operated hydraulic actuator unit100according to the present embodiment functioning as the first hydraulic motor unit.

As shown inFIG. 12, the electrically-operated hydraulic actuator unit100has a sensor portion680, in addition to the first hydraulic motor120, the electrically-operated motor300, and the control apparatus90. The sensor portion680is electrically connected to the control apparatus90, and has a current volume sensor350, a target volume sensor670, and a battery voltage sensor651.

The current volume sensor350is for detecting a current volume of the electrically-operated hydraulic actuator unit100(hereinafter, referred to as a “current volume”), and outputs a signal according to the current volume.

In the present embodiment, the current volume sensor350is, for example, the sensor unit350that detects the amount of rotation of the operating shaft340about its axis. Note that the current volume sensor350is not limited to the sensor unit350, and may be a sensor that detects a parameter in one-to-one correspondence with the current volume, such as the rotational position of the motor-side control shaft136about its axis or the slanting position of the motor-side movable swash plate137about its swing axis.

The target volume sensor670is for detecting a target volume of the electrically-operated hydraulic actuator unit100(hereinafter, referred to as a “target volume”), and outputs a signal according to the target volume.

In the present embodiment, the target volume sensor670is a turning angle sensor such as the turning operation-side sensor66, but there is no limitation to this.

The battery voltage sensor651is for detecting a voltage of a battery650(an electrical power source of the electrically-operated motor300) mounted in the work vehicle1(hereinafter, referred to as a “battery voltage”), and outputs a signal according to the battery voltage.

The control apparatus90includes the CPU and the storage portion, and controls the sensor portion680and the electrically-operated motor300(the motor-side volume adjusting mechanism135) in association with each other as follows.

In the present embodiment, when the motor-side volume adjusting mechanism135is actuated by the electrically-operated motor300, the electrically-operated motor300is actuated such that the volume matches the target volume indicated by the signal output from the target volume sensor670.

Assuming that a period from when actuation of the motor-side volume adjusting mechanism135is started until when the volume of the electrically-operated hydraulic actuator unit100reaches the target volume is referred to as an actuation period, an actuation period in the case of actuation of the motor-side volume adjusting mechanism135to the neutral side and an actuation period in the case of actuation to the higher volume side are each divided into a predetermined start period in which the time when the actuation is started is taken as a starting point and an ordinary actuation period, and the actuation of the electrically-operated motor300is controlled in an appropriate manner for each period.

That is to say, in the electrically-operated hydraulic actuator unit100according to the present embodiment, a biasing force to the neutral side is acting on the motor-side volume adjusting mechanism135, and, thus, a necessary operating torque that is to be output to the motor-side volume adjusting mechanism135differs between the actuation to the neutral side and the actuation to the higher volume side.

Furthermore, when starting the actuation of the motor-side volume adjusting mechanism135, the locked state of the clutch mechanism360has to be canceled. Accordingly, for example, even in the case of actuation to the neutral side, the necessary operating torque differs between a short period (start period) from the start of the actuation until a predetermined time has passed and an ordinary actuation period after the start period. The same is applied to the case of actuation to the higher volume side.

In consideration of this aspect, in the present embodiment, as shown inFIG. 13, a continuous actuation period of the motor-side volume adjusting mechanism135to the neutral side is divided into a neutral-side start period P1having a predetermined length (time) in which the time when the actuation to the neutral side is started is taken as a starting point and a neutral-side ordinary actuation period P2after the neutral-side start period P1. Furthermore, a continuous actuation period to the higher volume side is divided into a higher-volume-side start period P3having a predetermined length (time) in which the time when the actuation to the higher volume side is started is taken as a starting point and a higher-volume-side ordinary actuation period P4after the higher-volume-side start period P3. The duty of drive signal (drive pulse) is set such that respective operating torque are generated by the electrically-operated motor300for the periods P1to P4.

Note that, in the description below, drive signals (drive pulses) that are to be output to the electrically-operated motor300in the neutral-side start period P1, the neutral-side ordinary drive period P2, the higher-volume-side start period P3, and the higher-volume-side ordinary drive period P4are respectively referred to as first to fourth drive signals.

In order to realize such control, the control apparatus90causes the CPU to execute a program unique to the present embodiment stored in the storage portion, thereby functioning as a current volume detection processing portion901, a target volume detection processing portion902, a battery voltage detection processing portion903, a difference calculating portion904, a duty setting portion905, and a drive signal output portion906.

The current volume detection processing portion901performs a process that detects the current volume of the electrically-operated hydraulic actuator unit100based on the signal output from the current volume sensor350. The current volume sensor350and the current volume detection processing portion901form a current volume detecting portion.

The target volume detection processing portion902performs a process that detects the target volume of the electrically-operated hydraulic actuator unit100(hereinafter, referred to as a “target volume”) based on the signal output from the target volume sensor670. The target volume sensor670and the target volume detection processing portion902form a target volume detecting portion.

The battery voltage detection processing portion903performs a process that detects the battery voltage based on the signal output from the battery voltage sensor651. The battery voltage sensor651and the battery voltage detection processing portion903form a battery voltage detecting portion.

The difference calculating portion904calculates a difference D between the current volume and the target volume. In the present embodiment, the difference calculating portion904calculates (Target volume−Current volume) as the difference D. For example, if the target volume corresponds to a position obtained by rotating the operating shaft340about its axis by 30 degrees from a predetermined reference position that causes the motor-side volume adjusting mechanism135to be in the neutral state, and the current volume corresponds to a position obtained by rotating the operating shaft340by 10 degrees from the reference position, the difference calculating portion904obtains 20 (=30−10) degrees as the difference D.

The duty setting portion905sets the duties of the first to the fourth drive signals that are to be output to the electrically-operated motor300.

The duty setting portion905first determines whether the direction in which the motor-side volume adjusting mechanism135is to be actuated is the higher volume side or the neutral side, based on the difference D calculated by the difference calculating portion904, and sets either a set of the duties of the first and the second drive signals or a set of the duties of the third and the fourth drive signals according to the determination result.

Specifically, assuming that the difference D is obtained as (Target volume−Current volume) as described above, the duty setting portion905determines that the direction in which the motor-side volume adjusting mechanism135is to be actuated is the higher volume side if the difference D is a positive value, and determines that the direction in which the motor-side volume adjusting mechanism135is to be actuated is the neutral side if the difference D is a negative value.

Furthermore, if it is determined that the direction in which the motor-side volume adjusting mechanism135is to be actuated is the neutral side, the duty setting portion905sets a duty (first duty) Dt1of the first drive signal that is to be output to the electrically-operated motor300in the neutral-side start period P1and a duty (second duty) Dt2of the second drive signal that is to be output to the electrically-operated motor300in the neutral-side ordinary drive period P2after the neutral-side start period P1.

On the other hand, if it is determined that the direction in which the motor-side volume adjusting mechanism135is to be driven is the higher volume side, the duty setting portion905sets a duty (third duty) Dt3of the third drive signal that is to be output to the electrically-operated motor300in the higher-volume-side start period P3and a duty (fourth duty) Dt4of the fourth drive signal that is to be output to the electrically-operated motor300in the higher-volume-side ordinary drive period P4after the higher-volume-side start period P3.

The duty setting portion905has a timer (not shown), and actuates the timer when the actuation is started, thereby determining the current period based on a current measurement value of the timer (measurement time).

That is to say, based on the current measurement value of the timer, the duty setting portion905determines whether the current point in time is in the neutral-side start period P1or in the neutral-side ordinary drive period P2at the time of actuation of the motor-side volume adjusting mechanism135to the neutral side, or determines whether the current point in time is in the higher-volume-side start period P3or in the higher-volume-side ordinary drive period P4at the time of actuation to the higher volume side.

The lengths (times) of the neutral-side start period P1and the higher-volume-side start period P3are determined in advance. Furthermore, in the present embodiment, as shown inFIG. 13, the higher-volume-side start period P3is set as a period having a time T2, which is longer than a time T1of the neutral-side start period P1.

The duty setting portion905determines the current period (described above) and sets the duty (described below), for example, in predetermined cycles. Hereinafter, a method for setting the first to the fourth duties Dt1to Dt4will be described.

As shown inFIG. 12, the duty setting portion905has the functions of a reference duty storage portion9051, a correction value storage portion9052, a first duty correcting portion9053, a limit processing portion9054, and a second duty correcting portion9055, and sets the first to the fourth duties Dt1to Dt4using the portions9051to9055.

The reference duty storage portion9051stores in advance initial values of duties that have been preset for the first to the fourth drive signals as reference duties.

For example, as shown inFIG. 14, “Dtb1” is preset as a reference duty of the first drive signal that is to be output in the neutral-side start period P1, “Dtb2” is preset as a reference duty of the second drive signal that is to be output in the neutral-side ordinary drive period P2, “Dtb3” is preset as a reference duty of the third drive signal that is to be output in the higher-volume-side start period P3, and “Dtb4” is preset as a reference duty of the fourth drive signal that is to be output in the higher-volume-side ordinary drive period P4. Furthermore, the reference duty storage portion9051stores in advance a corresponding relationship between the periods P1to P4and the reference duties Dtb1to Dtb4in the form of a table.

As described above, when the actuation is started, the locked state of the clutch mechanism360has to be canceled both in the case of actuation of the motor-side volume adjusting mechanism135to the higher volume side and in the case of actuation to the neutral side. In order to cancel the locked state, an operating torque required becomes larger than the operating torque required for the ordinary actuation period.

In consideration of this aspect, in the present embodiment, as shown in the relational expression (1), the reference duty Dtb1of the first drive signal that is to be output in the neutral-side start period P1is set to be larger than the reference duty Dtb2of the second drive signal that is to be output in the neutral-side ordinary drive period P2, and, as shown in the relational expression (2), the reference duty Dtb3of the third drive signal that is to be output in the higher-volume-side start period P3is set to be larger than the reference duty Dtb4of the fourth drive signal that is to be output in the higher-volume-side ordinary drive period P4.

Furthermore, as described above, the motor-side volume adjusting mechanism135is biased to the neutral side. Accordingly, an operating torque required is larger in the case of actuation of the motor-side volume adjusting mechanism135to the higher volume side than in the case of actuation to the neutral side.

In consideration of this aspect, as shown in the relational expression (3), the reference duty Dtb4of the fourth drive signal that is to be output in the higher-volume-side ordinary drive period P4is set to be larger than the reference duty Dtb2of the second drive signal that is to be output in the neutral-side ordinary drive period P2.

That is to say, in the configuration in which the fourth drive signal in the higher-volume-side ordinary drive period P4is the same magnitude as the second drive signal in the neutral-side ordinary drive period P2(i.e., is a drive signal having the same duty as the second duty), the torque output from the electrically-operated motor300may be insufficient as the operating torque necessary for actuating the motor-side volume adjusting mechanism135in the higher-volume-side ordinary drive period P4. According to the present embodiment, this problem can be effectively prevented from occurring.

Furthermore, as described above, the operating torque necessary for canceling the locked state in the case of actuation of the motor-side volume adjusting mechanism135to the higher volume side is larger, by a biasing force acting on the motor-side volume adjusting mechanism135to the neutral side, than the operating torque necessary for canceling the locked state in the case of actuation of the motor-side volume adjusting mechanism135to the neutral side. In consideration of this aspect, as shown in the relational expression (4), in the present embodiment, the reference duty Dtb3of the third drive signal that is to be output in the higher-volume-side start period P3is set to be larger than the reference duty Dtb1of the first drive signal that is to be output in the neutral-side start period P1.

That is to say, in the configuration in which the third drive signal in the higher-volume-side start period P3is the same magnitude as the first drive signal in the neutral-side start period P1(i.e., is a drive signal having the same duty as the first duty), the torque output from the electrically-operated motor300may be insufficient as the operating torque necessary for actuating the motor-side volume adjusting mechanism135in the higher-volume-side start period P3. According to the present embodiment, this problem can be effectively prevented from occurring.

The correction value storage portion9052stores in advance a correction value α for correcting the reference duty according to the difference D calculated by the difference calculating portion904.

For example, as shown inFIG. 15, in the present embodiment, the range of values 0 to DN that the difference D can take is divided into a plurality of ranges, a correction value “α1” is preset for the range “0 to D1” of the difference D, a correction value “α2” is preset for the range “D1to D2”, a correction value “α3” is preset for the range “D2to D3”, and a correction value “αN” is preset for the range “DN−1 to DN”. Furthermore, the correction value storage portion9052stores in advance a corresponding relationship between the ranges 0 to D1, . . . , and DN−1 to DN of the difference D and the correction values α1, . . . , and αN in the form of a table.

When the difference calculating portion904calculates the difference D, the first duty correcting portion9053reads the correction value α associated with the difference D from the correction value storage portion9052, and uses the read correction value to correct the reference duty associated with the current period among the periods P1to P4.

For example, if the difference D calculated by the difference calculating portion904is “D21” (D2<D21<D3), the first duty correcting portion9053reads a correction value “α3” associated with the difference “D21” from the correction value storage portion9052. Furthermore, if the current period is, for example, the higher-volume-side start period P3, the first duty correcting portion9053performs a correction that adds the correction value “α3” to the reference duty “Dtb3” associated with the higher-volume-side start period P3.

It is assumed that the correction value α increases as the difference D increases.

That is to say, assuming that the difference D is obtained as (Target volume−Current volume) as described above, the value (the correction value α) that is to be added to the duty is set to be larger as the current volume is smaller with respect to the target volume (as the difference D is larger), and the absolute value of the value (the correction value α) that is to be subtracted from the duty is set to be larger as the current volume is larger with respect to the target volume (as the difference D is smaller).

FIG. 16shows an exemplary change over time of the reference duty stored in the reference duty storage portion9051(arrow X) and an exemplary change over time of the duty corrected by the first duty correcting portion9053(arrow Y) in the case of driving to the higher volume side (in the case where the current volume is smaller than the target volume).

InFIG. 16, the hatched portions indicate values (correction values) that are to be added to the reference duty.

If such a correction value α is used to correct the reference duty, the electrically-operated motor300can be actuated with an operating torque that is larger as the current volume is farther from the target volume. Accordingly, the rate of an increase in the rotational speed of the electrically-operated motor300can be increased as the current volume is farther from the target volume, and, thus, the time until the volume of the electrically-operated hydraulic actuator unit100reaches the target volume can be shortened compared with the case in which the reference duty is corrected using the correction value that is constant regardless of the magnitude of the difference D.

The first duty correcting portion9053generates information indicating the thus corrected duty as duty information, and outputs this duty information to the limit processing portion9054for the subsequent step.

If the duty information acquired from the first duty correcting portion9053indicates a duty exceeding 100(%), the limit processing portion9054converts that duty into (replaces the duty with) 100(%) and outputs duty information indicating the converted duty to the second duty correcting portion9055for the subsequent step. That is to say, the limit processing portion9054limits, to 100(%), the duty indicated by the duty information that is to be output to the second duty correcting portion9055for the subsequent step.

Note that, if the duty information acquired from the first duty correcting portion9053does not indicate a duty exceeding 100(%), the limit processing portion9054outputs the acquired duty information without any processing to the second duty correcting portion9055for the subsequent step.

The second duty correcting portion9055corrects the duty indicated by the duty information output from the limit processing portion9054, according to the battery voltage detected by the battery voltage detection processing portion903.

When the battery voltage changes, the voltage values (signal levels) of the first to the fourth drive signals that are to be output to the electrically-operated motor300are different from those when the battery voltage does not change. In this manner, when the voltage values of the first to the fourth drive signals change, even if the duty is constant, the electrical power of each drive signal, that is, the value of electrical power that is to be supplied to the electrically-operated motor300changes, and, thus, the operating torque and the like from the electrically-operated motor300become offset from nominal values. That is to say, the control performance of the electrically-operated motor300changes. In particular, when the battery voltage becomes larger than the nominal value, the operating torque becomes larger than the nominal value, the volume of the hydraulic pump52increases to be larger than the target volume, which is particularly problematic.

Thus, in the present embodiment, the second duty correcting portion9055corrects the duty indicated by the duty information output from the limit processing portion9054, using a table (not shown). This table prescribes a relationship between a battery voltage Vs detected by the battery voltage detection processing portion903, and a correction factor β used by the second duty correcting portion9055to correct the duty indicated by the duty information output from the limit processing portion9054.FIG. 17is a graph showing the relationship between the battery voltage Vs and the correction factor β prescribed in the table. Note that, inFIG. 17, the horizontal axis indicates the battery voltage Vs, and the vertical axis indicates the correction factor β.

As shown inFIG. 17, if the battery voltage Vs is in the range of 0 to Vs1, where the value is relatively small, the correction factor β is set at “1”.

Meanwhile, if the battery voltage Vs is in the range of Vs1to Vs2, the correction factor β is set at values plotted as a line segment indicated by the arrow Z. The correction factor β at that time is set so as to become smaller in proportion to an increase in the battery voltage Vs as shown inFIG. 17, in order to avoid the above-described problem in which, when the battery voltage becomes larger than the nominal value, the operating torque becomes larger than the nominal value, and the volume of the hydraulic pump52increases to be larger than the target volume.

The second duty correcting portion9055extracts from the table the correction factor β associated with the battery voltage Vs detected by the battery voltage detection processing portion903, and multiplies the duty indicated by the duty information output from the limit processing portion9054by the correction factor β.

For example, assuming that the current battery voltage Vs is detected to be 15 (V) and the correction factor β associated with this battery voltage is 0.6, if the duty indicated by the duty information output from the limit processing portion9054is 60(%), the second duty correcting portion9055corrects the duty “60(%)” into “36 (=60×0.6)”.

With this processing, the control performance of the electrically-operated motor300can be prevented from being changed.

If the duty corrected according to the battery voltage Vs is for the first drive signal, the second duty correcting portion9055takes the corrected duty as the first duty Dt1, and outputs duty information indicating this duty to the drive signal output portion906for the subsequent step.

In a similar manner, if the duty corrected according to the battery voltage Vs is for the second drive signal, the second duty correcting portion9055takes the corrected duty as the second duty Dt2and outputs duty information indicating this duty to the drive signal output portion906for the subsequent step. If the corrected duty is for the third drive signal, the second duty correcting portion9055takes the corrected duty as the third duty Dt3and outputs duty information indicating this duty to the drive signal output portion906for the subsequent step. If the corrected duty is for the fourth drive signal, the second duty correcting portion9055takes the corrected duty as the fourth duty Dt4and outputs duty information indicating this duty to the drive signal output portion906for the subsequent step.

The drive signal output portion906generates drive signals having a predetermined cycle based on the duty information output from the second duty correcting portion9055, and outputs them to the electrically-operated motor300.

That is to say, the drive signal output portion906generates the first drive signal having the duty Dt1and outputs it to the electrically-operated motor300if the duty information acquired from the duty setting portion905indicates the duty Dt1for the first drive signal, generates the second drive signal having the duty Dt2and outputs it to the electrically-operated motor300if the duty information indicates the duty Dt2for the second drive signal, generates the third drive signal having the duty Dt3and outputs it to the electrically-operated motor300if the duty information indicates the duty Dt3for the third drive signal, and generates the fourth drive signal having the duty Dt4and outputs it to the electrically-operated motor300if the duty information indicates the duty Dt4for the fourth drive signal.

FIG. 18is a flowchart showing the process by the control apparatus90.

As shown inFIG. 18, if the steering operation member65is operated (YES in Step #1), the current volume detection processing portion901performs a process that detects the current volume of the electrically-operated hydraulic actuator unit100based on the signal output from the current volume sensor350, the target volume detection processing portion902performs a process that detects the target volume of the electrically-operated hydraulic actuator unit100based on the signal output from the target volume sensor670, and a process that detects the battery voltage based on the signal output from the battery voltage sensor651(Step #2).

Next, the difference calculating portion904calculates the difference D between the current volume and target volume in Step #2(Step #3), and the first duty correcting portion9053determines whether or not the difference D is zero (the current volume has reached the target volume) (Step #4).

If it is determined that the difference D is not zero (NO in Step #4), the first duty correcting portion9053reads the correction value α associated with the difference D from the correction value storage portion9052(Step #5), and reads the reference duty associated with the current period among the periods P1to P4from the reference duty storage portion9051(Step #6). Furthermore, the first duty correcting portion9053corrects the reference duty read in Step #6using the correction value read in Step #5(Step #7).

The limit processing portion9054determines whether or not the duty corrected in Step #7by the first duty correcting portion9053is a value exceeding 100(%) (Step #8), and, if it is determined that the duty is a value exceeding 100(%) (YES in Step #8), performs a limit process that converts that duty into (replaces the duty with)100(%) and outputs duty information indicating the converted duty to the second duty correcting portion9055for the subsequent step (Step #9). On the other hand, if it is determined in Step #8that the duty is not a value exceeding 100(%) (NO in Step #8), the limit processing portion9054skips the processing in Step #9, and outputs without any processing the duty information acquired from the first duty correcting portion9053to the second duty correcting portion9055for the subsequent step.

After the processing in Step #8or #9, the second duty correcting portion9055corrects the duty indicated by the duty information output from the limit processing portion9054according to the battery voltage detected in Step #2(Step #10).

Furthermore, the drive signal output portion906outputs a drive signal having a predetermined cycle to the electrically-operated motor300based on the duty information output from the second duty correcting portion9055(Step #11), and the procedure returns to the processing in Step #2.

Subsequently, if the first duty correcting portion9053determines in Step #4that the difference D is zero (YES in Step #4), the setting of the duty by the setting portion905is stopped, and the output of the drive signal by the drive signal output portion906is also stopped (Step #12).

As described above, in the present embodiment, the clutch mechanism360is included. Accordingly, even if an external force to the neutral side exceeding the force of inertia of the electrically-operated motor300is applied to the motor-side volume adjusting mechanism135at the time when the electrically-operated motor300has been put in a non-actuated state, the volume of the electrically-operated hydraulic actuator unit100can be prevented from being unintentionally changed.

As a result, while allowing the motor-side volume adjusting mechanism135to be actuated by the electrically-operated motor300, it is possible to prevent the volume of the electrically-operated hydraulic actuator unit100from being unintentionally changed by an external force applied to the motor-side volume adjusting mechanism135or the like.

Furthermore, the duty of the fourth drive signal that is to be output in the higher-volume-side ordinary drive period P4is set to be larger than the duty of the second drive signal that is to be output in the neutral-side ordinary drive period P2, and, thus, when starting actuation to the higher volume side of the motor-side volume adjusting mechanism135that is biased to the neutral side, the operating torque can be prevented from being insufficient, and the motor-side volume adjusting mechanism135can be reliably actuated.

Furthermore, for the case of actuation of the motor-side volume adjusting mechanism135to the neutral side, the neutral-side start period P1is provided separately from an ordinary drive period (the neutral-side ordinary drive period P2) that generates an operating torque necessary for causing the driving-side arm361to rotate both the driven-side arm363and the contact members364, and the duty of the first drive signal that is to be output in the neutral-side start period P1is set to be larger by the required amount than the duty of the second drive signal that is to be output in the neutral-side ordinary drive period P2, and, thus, when starting actuation of the motor-side volume adjusting mechanism135to the neutral side, the locked state of the clutch mechanism360can be reliably canceled.

Furthermore, for the case of driving to the higher volume side, the higher-volume-side start period P3is provided separately from an ordinary drive period (the higher-volume-side ordinary drive period P4) that generates an operating torque necessary for causing the driving-side arm361to rotate both the driven-side arm363and the contact members364, and the duty of the third drive signal that is to be output in the higher-volume-side start period P3is set to be larger than the duty of the fourth drive signal that is to be output in the higher-volume-side ordinary drive period P4, and, thus, when starting actuation to the higher volume side of the motor-side volume adjusting mechanism135that is biased to the neutral side, the locked state of the clutch mechanism360can be reliably canceled.

Furthermore, the configuration is such that the reference duty is corrected using a correction value that is larger as the current volume of the electrically-operated hydraulic actuator unit100is farther from the target volume, and, thus, the operating torque of the electrically-operated motor300can be increased as the current volume is farther from the target volume. Accordingly, the rate of an increase in the rotational speed of the electrically-operated motor300can be increased, and, thus, the time until the electrically-operated hydraulic actuator unit100reaches the target volume can be shortened.

Furthermore, the second duty correcting portion9055corrects the duty indicated by the duty information output from the limit processing portion9054according to the current battery voltage, and, thus, even when the battery voltage changes, the control performance of the electrically-operated motor300can be prevented from being changed.

In the present embodiment, an example was described in which the electrically-operated hydraulic actuator unit according to the present invention is applied to one of the first and the second hydraulic motor units for driving the first and the second wheel pairs, in a work vehicle including the hydraulic pump unit and the first and the second hydraulic motor units, wherein a difference occurs between the turning radiuses of the first and the second wheel pairs. However, the electrically-operated hydraulic actuator unit according to the present invention may be embodied in other forms.

For example, the electrically-operated hydraulic actuator unit according to the present invention may be used as a hydraulic motor unit for widening the transmission range in a work vehicle.

Specifically, in a work vehicle including a vehicle frame, a driving source, first and second wheel pairs that are arranged on one side and the other side in a vehicle front-and-rear direction of the vehicle, a variable displacement hydraulic pump unit that is operatively driven by the driving source, and a hydraulic motor unit that forms an HST in cooperation with the hydraulic pump unit and drives one of the first and the second wheel pairs, the electrically-operated hydraulic actuator unit according to the present invention can be used as the hydraulic motor unit.

In this case, the electrically-operated hydraulic actuator unit functions as a sub speed-change device. That is to say, the work vehicle further includes a main speed-change device operating member for performing an operation that inputs an instruction for a main speed-change operation by the hydraulic pump unit, a sub speed-change operating member for performing an operation that inputs an instruction for a sub speed-change operation by the electrically-operated hydraulic actuator unit, a sub speed-change operation-side detecting portion that detects an amount of manual operation on the sub speed-change operating member (the target volume of the electrically-operated hydraulic actuator unit), a sub speed-change actuation-side detecting portion that detects an actuation state (a current volume) of the electrically-operated hydraulic actuator unit, and a control apparatus, wherein the electrically-operated hydraulic actuator unit acts with the sub speed-change operation being controlled by the control apparatus based on signals from the sub speed-change operation-side detecting portion and the sub speed-change actuation-side detecting portion such that a volume adjusting mechanism of the electrically-operated hydraulic actuator unit is actuated according to the amount of manual operation on the sub speed-change operating member.

Alternatively, the electrically-operated hydraulic actuator unit according to the present invention may be used as a hydraulic pump unit.

Specifically, in a work vehicle including a vehicle frame, a driving source, first and second wheel pairs that are arranged on one side and the other side in a vehicle front-and-rear direction of the vehicle, a hydraulic pump unit that is operatively driven by the driving source, and a hydraulic motor unit that forms an HST in cooperation with the hydraulic pump unit and drives one of the first and the second wheel pairs, the electrically-operated hydraulic actuator unit according to the present invention can be used as the hydraulic pump unit.

In this case, the electrically-operated hydraulic actuator unit functions as a main speed-change device. That is to say, the work vehicle further includes a main speed-change operating member for performing an operation that inputs an instruction for a main speed-change operation by the hydraulic pump unit, a main speed-change operation-side detecting portion that detects an amount of manual operation on the main speed-change operating member (the target volume of the electrically-operated hydraulic actuator unit), a main speed-change actuation-side detecting portion that detects an actuation state (a current volume) of the electrically-operated hydraulic actuator unit, and a control apparatus, wherein the electrically-operated hydraulic actuator unit acts with the main speed-change operation being controlled by the control apparatus based on signals from the main speed-change operation-side detecting portion and the main speed-change actuation-side detecting portion such that a volume adjusting mechanism of the electrically-operated hydraulic actuator unit is actuated according to the amount of manual operation on the main speed-change operating member.

In the present embodiment, regarding setting conditions of the duties of the first to the fourth drive signals, the duty Dt3of the third drive signal that is to be output in the higher-volume-side start period P3is set to be larger than the duty Dt1of the first drive signal that is to be output in the neutral-side start period P1on the assumption that the length of the higher-volume-side start period P3is set to be longer than the length of the neutral-side start period P1, but there is no limitation to this. For example, the duty Dt3may be the same as the duty Dt1, in the case where the length of the higher-volume-side start period P3is set to be much longer than the length of the neutral-side start period P1.

On the other hand, on the assumption that the length of the higher-volume-side start period P3is set to be the same as the length of the neutral-side start period P1, the third duty Dt3has to be set to be larger than the first duty Dt1.

In summary, a gist of the present invention lies in an aspect that the operating torque of the electrically-operated motor300in the higher-volume-side start period P3is set to be larger than the operating torque of the electrically-operated motor300in the neutral-side start period P1, focusing on the facts that the motor-side volume adjusting mechanism135is biased to the neutral side and that the locked state of the clutch mechanism360has to be canceled, and the present invention can be embodied in various forms as long as an integrated value of the time during which the third drive signal that is to be output in the higher-volume-side start period P3is on-state is larger than an integrated value of the time during which the first drive signal that is to be output in the neutral-side start period P1is on-state.

Furthermore, in the present embodiment, the first duty correcting portion9053is provided that corrects the reference duty associated with the current period among the periods P1to P4using the correction value associated with the difference calculated by the difference calculating portion904, but the first duty correcting portion9053is not an essential constituent component, and the present invention includes an embodiment in which correction by the first duty correcting portion9053is not performed.

In this case, the electrically-operated hydraulic actuator unit may be provided with, instead of the second duty correcting portion9055, a reference duty correcting portion that corrects a duty read from the reference duty storage portion9051according to a current battery voltage and outputs duty information indicating the corrected duty to the drive signal output portion906.

DESCRIPTION OF THE REFERENCE NUMERALS