Abstract:
A hydraulic circuit control device that selectively supplies oil to a first oil passage and a second oil passage by an oil pump, the control device includes: an oil passage switching unit adapted to connect the oil pump to either the first oil passage or the second oil passage; a control mode switching unit adapted to switch the control mode of the electric motor to either a torque control mode or a speed control mode; an oil passage selecting unit adapted to select whether to connect the oil pump to the first oil passage or the second oil passage; and a control unit adapted to perform control so that the control mode switching unit switches the control mode to the torque control mode when the first oil passage has been selected, and perform control so that the control mode switching unit switches the control mode to the speed control mode when the second oil passage has been selected.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a hydraulic circuit control device that selectively supplies oil to two oil passages with an oil pump.  
         [0003]     Priority is claimed on Japanese Patent Application No. 2005-102507, filed Mar. 31, 2005, and Japanese Patent Application No. 2005-336782, filed Nov. 22, 2005, the contents of which are incorporated herein by reference.  
         [0004]     2. Description of Related Art  
         [0005]     A vehicle drive system has been developed in which either the front or rear wheels are powered by a main drive source such as an internal combustion engine, while an auxiliary drive source is provided by an electric motor for the other wheels.  
         [0006]     Under normal driving conditions in a vehicle equipped with such a drive system, the main drive source drives the front or rear wheels, while the auxiliary drive source is activated to transmit drive power to the other wheels when, for example, setting off in adverse road conditions. In such a vehicle, a hydraulic engaging/disengaging device such as a hydraulic clutch is provided in the power transmission mechanism to deliver power from the driving electric motor serving as the auxiliary drive source, with such a clutch being suitably controllable in accordance with the vehicle running state. For example, at times when driving or regeneration of the electric motor is not required, by using the clutch to cut off power transmission with the electric motor, drive power loss arising from co-rotation of the electric motor can be reduced.  
         [0007]     A control unit for a hydraulic actuator resembling the engaging/disengaging device described above has been proposed that provides an accumulator in the oil passage leading to the actuator to reduce the power loss of the oil pump (see, for example, Japanese Unexamined Patent Application, Publication No. 2003-54279).  
         [0008]     In this control unit for an actuator, the accumulator is installed in the oil passage on the actuator side, and a check valve that only allows inflow of oil to the actuator side is interposed between the oil pump and the actuator, with the oil pump operating only when the pressure in the accumulator falls.  
         [0009]     In the aforementioned control unit, the oil supplied from the oil pump is supplied only to the oil passage on the actuator side, which requires a high pressure. However, there is a clear need for shared use of the same oil pump for oil passages that require a low pressure and a high flow rate for lubrication and the like.  
         [0010]     One solution that has been studied is to provide in the oil pump supply passage an oil passage switching valve that switches connection between the oil passage that requires a high pressure and the oil passage that requires a low pressure and a high flow rate, and operate the oil passage switching valve in accordance with requirements on the system side. In this case, it would be necessary to control the pump driving electric motor that drives the oil pump simultaneously with switching the oil passages in order to adjust the oil being supplied to a suitable oil pressure and flow rate.  
         [0011]     However, in the case of always using speed control to control the pump driving electric motor, sudden fluctuations in the hydraulic load when used for the oil passage that requires a high pressure may cause step out of the electric motor.  
         [0012]     Controlling the pump driving motor by torque control has also been investigated, but in this case, overspeed of the electric motor occurs when used for the oil passage that requires a low pressure and a high flow rate, leading to high power consumption, which is not desirable from the standpoint of energy conservation.  
       SUMMARY OF THE INVENTION  
       [0013]     The present invention has as its object providing a control unit for a hydraulic circuit that can effectively use a common oil pump for an oil passage that requires a high pressure and an oil passage that requires a low pressure and high flow rate without causing problems such as step out and increased power consumption of the pump driving electric motor.  
         [0014]     In order to attain the aforementioned object, the present invention provides a hydraulic circuit control device that selectively supplies oil to a first oil passage that requires a high pressure and a second oil passage that requires a low pressure and high flow rate by an oil pump driven by an electric motor, the control device including: an oil passage switching unit adapted to connect the oil pump to either the first oil passage or the second oil passage; a control mode switching unit adapted to switch the control mode of the electric motor to either a torque control mode or a speed control mode; an oil passage selecting unit adapted to select whether to connect the oil pump to the first oil passage or the second oil passage; and a control unit adapted to perform control so that the control mode switching unit switches the control mode of the electric motor to the torque control mode when the oil passage selecting unit has selected the first oil passage, and to perform control so that the control mode switching unit switches the control mode of the electric motor to the speed control mode when the oil passage selecting unit has selected the second oil passage.  
         [0015]     In the present invention, when the oil passage selecting unit selects whether to supply oil to the first oil passage or the second oil passage, in accordance with that selection result, the oil passage switching unit and the control mode switching unit are separately controlled by the control unit. By means of the control performed by the control unit, when the oil pump is to be connected to the first oil passage that requires a high pressure, the pump driving electric motor is controlled in the torque control mode, and when the oil pump is to be connected to the second oil passage that requires a low pressure and high flow rate, the pump driving electric motor is controlled in the speed control mode.  
         [0016]     The oil passage selecting unit may be adapted to perform oil passage selection based on at least one of a pressure of the first oil passage and a flow rate of the second oil passage.  
         [0017]     In this case, when, for example, selecting the oil passage based on the pressure of the first oil passage, the pressure of the first oil passage is monitored so that when the pressure deviates from the set pressure condition, the first oil passage is chosen as the oil passage to connect to the oil pump. Thereby, oil supply is always provided in accordance with the requirements of the first oil passage side. Similarly, when selecting the oil passage based on the flow rate of the second oil passage, the flow rate of the second oil passage is monitored so that when the flow rate deviates from the set flow rate condition, the second oil passage is chosen as the oil passage to connect to the oil pump. Thereby, oil supply is always provided in accordance with the requirements of the second oil passage side.  
         [0018]     The present invention provides a hydraulic circuit control device mounted in a drive device of a vehicle including wheels; a first electric motor that has a coil and a cooling portion and drives the wheels; a power transmission device that has a lubricating portion and transmits the drive power of the first electric motor to the wheels; and a hydraulic clutch mounted in the power transmission device that performs engagement and disengagement of drive power between the first electric motor and the wheels, the control device including: a first oil passage that requires a high pressure and is connected to the hydraulic clutch; a second oil passage that requires a low pressure and high flow rate and is connected to at least one of the cooling portion and the lubricating portion; an oil pump that is driven by a second electric motor and that selectively supplies oil to the first oil passage and the second oil passage; an oil passage switching unit adapted to switch the connection of the oil pump to either the first oil passage or the second oil passage; a control mode switching unit adapted to switch the control mode of the second electric motor to either a torque control mode or a speed control mode; an oil passage selecting unit adapted to select whether to connect the oil pump to either the first oil passage or the second oil passage; and a control unit adapted to perform control so that the control mode switching unit switches the control mode of the second electric motor to the torque control mode when the oil passage selecting unit has selected the first oil passage, and to perform control so that the control mode switching unit switches the control mode of the second electric motor to the speed control mode when the oil passage selecting unit has selected the second oil passage.  
         [0019]     When the hydraulic clutch is performing an engagement or disengagement operation, large fluctuations in the hydraulic load occur. However, when supplying oil to the clutch side, since the second electric motor is controlled in the torque control mode, the second electric motor is hardly affected by the hydraulic load. When supplying oil to the cooling portion of the first electric motor or the lubricating portion of the power transmission system, since the second electric motor is controlled in the speed control mode, overspeed of the second electric motor is prevented.  
         [0020]     The hydraulic circuit control device of the present invention may further include a drain passage connected to the second oil passage, and a relief valve adapted to discharge oil in the second oil passage to the drain passage when a pressure of the second oil passage is equal to or greater than a first predetermined value.  
         [0021]     In this case, when the viscosity of the oil increases at low temperatures, causing the pressure in the second oil passage to be equal to or greater than the first predetermined value, the relief valve discharges the oil in the second oil passage to the drain passage. Because of this, when the second electric motor is operating in speed control mode, an excessive load caused by the change in viscosity of the oil no longer acts on the second electric motor. Therefore, the energy efficiency of the second electric motor can be raised and step loss can be prevented in the second electric motor that is speed controlled.  
         [0022]     In the hydraulic circuit control device of the present invention, the second oil passage may have an upstream portion and a downstream portion that has a cooling oil passage that connects to the cooling portion and a lubricating oil passage that connects to the lubricating portion, with an orifice provided in the lubricating oil passage, and a pressure regulating valve provided in the cooling oil passage and adapted to make oil flow into the cooling portion when the pressure of the upstream portion is equal to or greater than a second predetermined value.  
         [0023]     In this case, when oil discharged from the oil pump is supplied to the second oil passage side, a pressure differential occurs upstream and downstream the orifice in the lubricating oil passage, so that the pressure gradually rises at the side of the branch portion before the orifice. When the pressure at the branch portion side rises to be equal to or greater than the second predetermined value, the pressure regulating valve opens. Oil then is supplied from the branch portion side to the cooling portion of the first electric motor, and the pressure of the oil supplied to the lubricating portion is limited to lower than the second predetermined value.  
         [0024]     The hydraulic circuit control device of the present invention may further include a spray unit provided in the cooling portion, being adapted to discharge oil introduced through the cooling oil passage onto the coil.  
         [0025]     In this case, when oil is supplied to the cooling oil passage, the oil is directly sprayed onto the coil of the first electric motor via a spray mechanism. Accordingly, oil uniformly and forcefully falls on the entire coil of the first electric motor, with the sprayed oil penetrating to the interior so that the entire coil can be efficiently cooled by the oil.  
         [0026]     The relief valve and the pressure regulating valve may be integrally formed.  
         [0027]     In this case, when the pressure at the branch portion side rises to the second predetermined value as oil discharged from the oil pump is supplied to the second oil passage side, the valve body opens the cooling oil passage to supply oil to the cooling portion of the first electric motor, with the supply pressure on the lubricating oil passage side then decreasing. When the pressure at the branch portion side rises to be equal to or greater than the first predetermined value, the valve body opens the drain passage to discharge oil in the second oil passage, and so thereby the pressure in the second oil passage is held lower than the first predetermined value. Accordingly, limiting the pressure of the lubricating oil passage under ordinary use conditions and relief of the oil when the oil viscosity rises can be performed by a single valve body. This can lower manufacturing costs and reduce the weight and size of the apparatus.  
         [0028]     According to this invention, when supplying oil to the first oil passage that requires a high pressure, the second electric motor is controlled in the torque control mode, and when oil is supplied to the second oil passage that requires a low pressure and high flow rate, the second electric motor is controlled in a speed control mode. Therefore, a common oil pump can be effectively used without causing problems such as step out of the second electric motor and increased power consumption of the second electric motor.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0029]      FIG. 1  is a schematic outline view of the control system for the oil pump hydraulic circuit and the pump driving electric motor including the embodiment of the present invention.  
         [0030]      FIG. 2  is a schematic outline view of the vehicle in which the embodiment is implemented.  
         [0031]      FIG. 3  is a longitudinal sectional view of the driving system employing the pump driving electric motor in  FIG. 2 .  
         [0032]      FIG. 4  is an enlarged sectional view of a portion of  FIG. 3 .  
         [0033]      FIG. 5  is a schematic outline view of the control system for the pump driving electric motor of the same embodiment.  
         [0034]      FIG. 6  is a flowchart showing the flow of control of the controller for the same embodiment.  
         [0035]      FIG. 7  is a flowchart showing the flow of control of the controller for the same embodiment.  
         [0036]      FIG. 8  is a timing chart for the same embodiment.  
         [0037]      FIG. 9  is a timing chart for a different pattern of the same embodiment.  
         [0038]      FIG. 10  is a sectional view showing the cooling portion structure of the electric motor of the same embodiment.  
         [0039]      FIG. 11  is a sectional view of the pressure regulating valve of the embodiment during pressure regulating operation.  
         [0040]      FIG. 12  is a sectional view of the pressure regulating valve of the embodiment during relief operation.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0041]     The embodiment of the present invention is described below with reference to the accompanying drawings. This embodiment applies the hydraulic circuit control device according to the present invention to a hydraulic system provided in a drive device  1  for auxiliary drive use in a vehicle  3  shown in  FIG. 2 .  
         [0042]     The entire constitution of the vehicle shown in  FIG. 2  and the drive device  1  shown in  FIGS. 3 and 4  shall initially be described. The vehicle  3  shown in  FIG. 2  is a hybrid vehicle having a drive unit  6  in which an internal combustion engine  4  and an electric motor  5  are connected in series. The drive power of the drive unit  6  is transmitted to front wheels Wf via a transmission  7 , and the drive power of a drive device  1  for auxiliary driving provided separate to the drive unit  6  is transmitted to rear wheels Wr. The drive device  1  is driven by an electric motor  2  (wheel driving electric motor). The electric motor  5  of the drive unit  6  and the electric motor  2  of the rear wheel Wr-side drive device  1  are connected to a power drive unit (PDU)  8  via a battery  9 . Power supply from the battery  9  and energy regeneration from the electric motors  5  and  2  to the battery  9  is performed via the PDU  8 .  
         [0043]      FIG. 3  shows the entire longitudinal sectional view of the drive device  1 , with  10 A and  10 B in the drawing denoting the left and right axles of the rear wheels of the vehicle. A housing  11  of the drive device  1  is provided so as to cover the periphery from approximately the intermediate position between both axles  10 A and  10 B to the axle  10 B side, being supported and fixed to the bottom of the vehicle  3  as well as to the axle  10 B (see  FIG. 2 ). Also, the entire housing  11  is formed to be approximately cylindrical, with the wheel driving electric motor  2 , a planetary gear reducer  12  that reduces the rotational speed of the electric motor  2 , and a differential  13  that distributes the power of the reducer  12  to the left and right axles  10 A and  10 B arranged to be coaxially housed therein.  
         [0044]     In the present embodiment, the planetary gear reducer  12  and the differential  13  constitute the power transmission device in the drive device  1 .  
         [0045]     A stator  14  of the electric motor  2  is fixedly disposed to the wheel-side end inner periphery of the housing  11  (right side in  FIG. 3 ). An annular rotor  15  is disposed to be rotatably arranged on the inner periphery side of the stator  14 . A cylinder shaft  16  that encloses the outer periphery of the axle  10 B is coupled to the inner periphery portion of the rotor  15 . This cylinder shaft  16  is supported by an edge wall  17  and an intermediate wall  18  so as to be coaxial with the axle  10 B via a shaft bushing  19 . Also, a resolver  20  is provided between the outer periphery of one side of the cylinder shaft  16  and the edge wall  17  of the housing  11  to feed back rotation information of the rotor  15  to a controller (not illustrated) for control of the electric motor  2 .  
         [0046]     The planetary gear reducer  12  is provided with a sun gear  21 , a plurality of planetary gears  22  that mesh with the sun gear  21 , a planetary carrier  23  that supports the planetary gears  22 , and a ring gear  24  that is meshed with the outer periphery of the planetary gears  22 . The drive power of the electric motor  2  is input from the sun gear  21 , and the reduced drive power is output through the planetary carrier  23 .  
         [0047]     The sun gear  21  is integrally formed with the outer periphery of a sleeve  25  disposed coaxially with the outer periphery side of the axle  10 B. One end side of the sleeve  25  is coupled in an integrally rotatable manner to the cylinder shaft  16  of the electric motor  2  side. Each the planetary gear  22  has a large-diameter first gear  26  that is directly meshed with the sun gear  21  and a second gear  27  with a diameter smaller than that of the first gear  26 . Each first gear  26  and each second gear  27  are integrally formed coaxially and in a state of being offset in the axial direction. The ring gear  24  is rotatably disposed in a side position of the first gear  26  in the axial direction, with its inner periphery side meshed with the small-diameter second gear  27 . The ring gear  24  is held in an integrally rotatable manner by a rotating drum  29  of a hydraulic clutch  28  that is described below, and rotatably supported in the housing  11  via this rotating drum  29 .  
         [0048]     The differential  13  is provided with a differential case  31  in which a rotatable pinion  30  is installed in a protruding manner in the interior, and a pair of side gears  32   a  and  32   b  that mesh with the pinion  30  in the differential case  31 . These side gears  32   a  and  32   b  are separately coupled to the left and right axles  10 A and  10 B. On the outer surface of the differential case  31 , the planetary carrier  23  of the planetary gear reducer  12  is integrally provided in an extending manner. The differential case  31  is supported by an edge wall  34  at the chassis center side of the housing  11  and the intermediate wall  18  via a bushing  33 .  
         [0049]     A cylindrical space is secured between the ring gear  24  and the edge wall  34  in the housing  11 , and the hydraulic clutch  28  is disposed in that space. In the hydraulic clutch  28 , a plurality of fixed plates  35  that are spline fitted to the inner periphery surface of the housing  11  and a plurality of rotating plates  36  that are spline fitted to the outer periphery surface of one end of the rotating drum  29  are alternately arranged in the axial direction. Pressure contact and release of the fixed plates  35  and the rotating plates  36  are operated by an annular piston  37 . The piston  37  is housed to freely advance and retract in the annular cylinder chamber  38  formed at the edge wall  34  of the housing  11 . Feeding high-pressure oil into the cylinder chamber causes the piston  37  to advance, and discharging oil from the cylinder chamber  38  causes the piston  37  to retract. The hydraulic clutch  28  is connected to a hydraulic circuit  39  shown in  FIG. 1 , with this hydraulic circuit to be described in detail later.  
         [0050]     In this hydraulic clutch  28 , the fixed plates  35  lock rotation in the housing  11 , and the rotating plates  36  integrally support the ring gear  24 . As a result, when both the fixed plates  35  and the rotating plates  36  are pressure contacted by the piston  37 , braking force is applied to the ring gear  24  by the friction engagement between the plates  35  and  36 . When the pressure contact by the piston  37  is released, free rotation of the ring gear  24  is again permitted.  
         [0051]     On the exterior of the wheel-side edge wall  17  of the housing  11 , an oil pump  40  for supplying oil to the hydraulic clutch  28 , the cooling portion of the electric motor  2 , and the lubricating portion (of the power transmission device) in the housing  11 ; a pump driving electric motor  41  for driving the oil pump  40 ; and an accumulator  42  that accumulates oil in a pressure-accumulated state at the stage prior to supplying it to the hydraulic clutch  28  are provided as shown in  FIGS. 3 and 4 . These are housed in a cover  43  as block-shaped and fixed along with the cover  43  to the edge wall  17 .  
         [0052]     The pump driving electric motor  41  is a brushless motor that has an annular rotor  44  as shown close-up in  FIG. 4 . An annular stator  45  that is a size larger than the rotor  44  is fixed to the outer surface of the edge wall  17  via a bracket  46 . A sleeve  47  that is fixed to the inner periphery of the rotor  44  is supported by the edge wall  17  and the bracket  46  via a bushing  48 . The rotor  44  and the stator  45  in this state are coaxially disposed on the outer periphery side of the axle  10 B.  
         [0053]     The oil pump  40  is an external gear pump, with a pair of gears  49  for pump operation disposed in parallel alignment on the outer periphery of the pump driving electric motor  41 . Rotation of the electric motor  41  is transmitted to one of the gears  49  of the oil pump  40  by a gear transmission mechanism  50 .  
         [0054]     In the accumulator  42 , an annular chamber  51  that has depth in the axial direction is integrally formed along the edge of the inner periphery of the cover  43 . An annular piston  52  is housed to freely advance and retract in the annular chamber  51 , with the piston  52  biased by a spring  53  for accumulating pressure.  
         [0055]     When driving the axles  10 A and  10 B on the rear wheel Wr side with the drive device  1  of the above constitution, by supplying the oil pressure of the oil pump  40  to the hydraulic clutch  28 , the clutch  28  is turned ON, and by effecting friction engagement of the fixed plates  35  and the rotating plates  36 , the ring gear  24  becomes fixed with respect to the housing  11 . When the ring gear  24  is thus fixed, the reducing ratio of the planetary gear reducer  12  is fixed, with drive power transmitted without loss between the sun gear  21  and the planetary carrier  23 . Accordingly, the drive power of the electric motor  2  at this time is lowered to the set reducing ratio by the planetary gear reducer  12 , and transmitted to the left and right axles  10 A and  10 B of the vehicle by means of the differential  13 .  
         [0056]     When the rotation speed of the rear wheels Wr exceeds the rotation speed of the electric motor  2  such as when driving by the drive device  1  on a downslope and the like, by discharging the oil in the hydraulic clutch  28 , the clutch  28  is turned OFF, whereby braking of the ring gear  24  is released. When the ring gear  24  is thus free to rotate, the ring gear  24  rotates idly in the housing  11  in tandem with the rotation of the axles  10 A and  10 B, and as a result, the rotor  15  of the electric motor  2  is no longer forcibly rotated by the rotation force of the axles  10 A and  10 B.  
         [0057]     Accordingly, the drive device  1  can prevent excess rotation of the electric motor  2  and generation of axle friction.  
         [0058]     The hydraulic circuit  39  shown in  FIG. 1  shall now be described. The hydraulic circuit control device according to the present invention is implemented to the control system of this hydraulic circuit  39 .  
         [0059]     In the hydraulic circuit  39 , oil discharged from the oil pump  40  is selectively switched to a clutch oil passage  58  and a low-pressure oil passage  57  through a pilot-operating valve  55 , which is a solenoid valve, and a selector valve  56 . The low-pressure oil passage  57  is continuous with a suitable position in the housing  11  for supplying oil to the cooling portion of the electric motor  2  and lubricating portions of the power transmission device such as the planetary gear reducer  12  and the differential  13 . A check valve  61  is set between the clutch oil passage  58  and the selector valve  56  to prevent reverse flow of oil from the clutch oil passage  58  to the selector valve  56 . A clutch operating valve  59  that consists of a solenoid valve is set in the clutch oil passage  58 , and a branched oil passage  60  that leads to the accumulator  42  is provided further upstream from than the clutch operating valve  59 . A pressure sensor  62  that monitors the pressure in the accumulator  42  is provided in the branched oil passage  60 , with detection signals from the pressure sensor  62  being fed to a controller  110  (ECU). The clutch oil passage  58  is an oil passage that requires a high pressure in order to engage and disengage the hydraulic clutch  28 , and so constitutes a first oil passage in the present invention. In addition, the low-pressure oil passage  57  is an oil passage that requires a low-pressure and high flow rate for cooling and lubrication purposes, and so constitutes a second oil passage in the present invention.  
         [0060]     The pilot-operating valve  55  and the selector valve  56  in the hydraulic circuit  39  constitute an oil passage switching unit in the present invention.  
         [0061]     The selector valve  56  is provided with a spool  112  that allows or blocks communication of a pump oil passage  111 , which connects the oil pump  40  and the check valve  61 , with respect to the low-pressure oil passage  57 , and a spring  113  that biases the spool  112  to the left in  FIG. 1 . The pressure of the pump oil passage  111  always acts on the end face of the spool  112  on the left side in  FIG. 1  via a back-pressure passage  114 , while the operating pressure produced by the pilot-operating valve  55  acts on the right-side end face of the spool  112  via a pilot passage  115 .  
         [0062]     The pilot-operating valve  55  is a solenoid three-way valve that is controlled by the controller  110 . When power is supplied to the solenoid (i.e., when it is ON), the pump oil passage  111  is connected to the pilot passage  115 , which causes pressure of the pump oil passage  111  to act on the right-side end face of the spool  112  in  FIG. 1 . At this time, since the same pressure acts on the end faces of both sides of the spool  112 , the spool  112  moves to the left side in the drawing due to the force of the spring  113 . Thereby, the low-pressure oil passage  57  is cut off, so that the pump oil passage  111  is only connected to the clutch oil passage  58 . Also, when power is cut to the solenoid of the pilot-operating valve  55  (i.e., when it is OFF), simultaneously with cutting the connection between the pump oil passage  111  and the pilot passage  115 , the pilot passage  115  becomes connected to a drain port  116 , whereby the pressure acting on the right-side end face of the spool  112  is opened. At this time, the spool  112  moves to the right side due to the pressure of the pump oil passage  111  acting on the left-side end face of the spool  112 , making the pump oil passage  111  continuous with the low-pressure oil passage  57 .  
         [0063]     Accordingly, connection of the clutch oil passage  58  and the low-pressure oil passage  57  to the oil pump  40  is controlled by ON/OFF operation of the pilot-operating valve  55 .  
         [0064]     The clutch operating valve  59  is a solenoid three-way valve that is controlled by the controller  110  similarly to the pilot-operating valve  55 . When power is supplied to the solenoid, the branched oil passage  60  that leads to the accumulator  42  is connected to the hydraulic clutch  28  and the hydraulic clutch  28  is engaged. When power is cut to the solenoid, the connection of the hydraulic clutch  28  with the branched oil passage  60  side is cut off, and the hydraulic clutch  28  becomes connected to a drain port  117 , whereby engagement of the hydraulic clutch  28  is released.  
         [0065]     Also, the pump driving electric motor  41  that drives the oil pump  40  receives power from the battery  9  (see  FIG. 2 ) via the PDU  8  (see  FIG. 2 ), and is drive-controlled by the controller  110  via a motor driver circuit  118 .  
         [0066]     The controller  110  commences driving of the pump driving electric motor  41  upon receiving a command from a main controller of the vehicle that is not illustrated. It controls the pilot-operating valve  55  and the pump driving electric motor  41  so that the pressure Poil in the accumulator  42  is maintained within a definite pressure range (AL≦Poil≦AH) in which engagement and disengagement of the hydraulic clutch  28  is possible. Three operation modes for the pump driving electric motor  41 , namely, Hi mode, Low mode, and Ini mode, are provided in a motor driver circuit  118 , with the mode changed in accordance with a mode switching command received from the controller  110 .  
         [0067]     Each operation mode shall now be described in detail. The Hi mode is the mode used for when operating the oil pump  40  with a high pressure and low flow rate under normal driving conditions. The pump driving electric motor  41  is controlled by setting a torque value as the target value based on a current command issued from the controller  110  (torque control mode).  
         [0068]     The Low mode is the mode used for when operating the oil pump  40  with a low pressure and high flow rate under normal driving conditions. The pump driving electric motor  41  is controlled by setting a speed value as the target value based on a rotation speed command issued from the controller  110  (speed control mode).  
         [0069]     The Ini mode is the mode used for when operating the oil pump  40  with a greater current than during the Hi mode directly after starting the pump driving electric motor  41 . The pump driving electric motor  41  is torque controlled based on a current command issued from the controller  110 .  
         [0070]     Accordingly, the controller  110  and the motor driver circuit  118  perform control of the pump driving electric motor  41  via torque control in the Hi mode or the Ini mode, and via speed control in the Low mode.  
         [0071]     The controller  110  is provided with an oil passage selecting unit  120  that selects whether to supply oil discharged from the oil pump  40  to the clutch oil passage  58  or the low-pressure oil passage  57 ; and a control unit  121  that controls the ON/OFF of the pilot-operating valve  55  and the control mode switching for the pump driving electric motor  41  in accordance with the selection result of the oil passage selecting unit  120 . In this embodiment, the oil passage selecting unit  120  receives a pressure signal from the pressure sensor  62  in the branched oil passage  60  and, based on that signal, selects an oil passage that supplies oil.  
         [0072]     Specifically, the controller  110  constantly monitors the pressure Poil in the accumulator  42  via the signal from the pressure sensor  62 . The oil passage selecting unit  120  selects the clutch oil passage  58  when the pressure Poil is under the lower limit pressure AL and selects the low-pressure oil passage  57  when the pressure Poil exceeds the upper limit pressure AH. When the oil passage selecting unit  120  has selected the clutch oil passage  58 , the pilot-operating valve  55  is turned ON, the pump oil passage  111  is connected to only the clutch oil passage  58 , and the control mode of the pump driving electric motor  41  is switched to the Hi mode, which is the torque-control mode. When the oil passage selecting unit  120  has selected the low-pressure oil passage  57 , the pilot-operating valve  55  is turned OFF, the pump oil passage  111  is connected to the low-pressure oil passage  57  and the control mode of the pump driving electric motor  41  is switched to the Low mode, which is the speed-control mode.  
         [0073]     A speed sensor  122  and an oil temperature sensor  123  are connected to the input side of the controller  110 . In the state of the control mode being set to the Low mode, and the hydraulic clutch  28  having stopped power transmission (that is, when in two-wheel drive mode), the controller  110  determines whether to stop operation of the pump driving electric motor  41  based on output signals from these sensors  122  and  123 . Under these conditions, when the vehicle speed is lower than a set vehicle speed V 1  and the oil temperature is less than a set temperature T 1 , the controller  110  stops operation of the pump driving electric motor  41 .  
         [0074]     Control performed by the controller  110  shall be described below with reference to the flowcharts in  FIGS. 6 and 7 .  
         [0075]     In step S 101 , a detection signal is received from the pressure sensor  62 , and the pressure Poil of the accumulator  42  is detected. Next, in step S 102 , it is confirmed that the startup completion signal (the signal that enables the transition to the ordinary control mode) is input from the motor driver circuit  118 . When the input of the startup completion signal is confirmed, the processing proceeds to step S 103 , and when it has not been input, the processing proceeds to step S 108 , where the operation mode of the pump driving electric motor  41  is set to the Ini mode.  
         [0076]     In step S 103 , it is determined whether the pressure Poil of the accumulator  42  has exceeded the upper limit pressure AH. When it has exceeded the upper limit pressure AH, the processing proceeds to step S 104 , where the operation mode of the pump driving electric motor  41  is set to the Low mode. When the pressure Poil of the accumulator  42  has not exceeded the upper limit pressure AH, the processing proceeds to step S 105 , where it is determined whether the pressure Poil of the accumulator  42  is below the lower limit pressure AL. When the pressure Poil is below the lower limit pressure AL, the processing proceeds to step S 106 , where the operation mode of the pump driving electric motor  41  is set to the Hi mode. When the pressure Poil of the accumulator  42  is not below the lower limit pressure AL, the processing proceeds to step S 107 , and the operation mode is set to the same mode as the current mode.  
         [0077]     When the processing proceeds to any of steps S 104 , S 106 , S 107 , and S 108 , it always next proceeds to step S 109 . In the subsequent steps, various different controls are executed in accordance with the operation mode set in the previous state and other vehicle conditions.  
         [0078]     In step S 109 , it is determined whether the set operation mode is the Hi mode. In the case of being the Hi mode, the processing proceeds to step S 110 , and in the case of not being the Hi mode, the processing proceeds to step S 112 . In step S 110 , without regard to whether connection of the hydraulic clutch  28  is performed, since the operation mode is in the Hi mode, which requires the supply of high pressure oil to the accumulator  42 , the control of the pump driving electric motor  41  is set to torque control. In step S 111 , the current command of the pump driving electric motor  41  is set to the current Ih in accordance with the electric motor load pressure, and by turning on the pilot-operating valve  55  the oil emitted from the oil pump  40  is supplied to the clutch oil passage  58  (accumulator  42 ).  
         [0079]     When proceeding from steps S 109  to S 112 , it is determined whether the set operation mode is the Low mode. In the case of the Low mode, the processing proceeds to step S 113 , and if not the Low mode the processing proceeds to step S 119 . In the event of proceeding to step S 119 , since the operation mode is the Ini mode, after the control of the pump driving electric motor  41  is set to torque control, in step S 120  the current command of the pump driving electric motor  41  is set to startup current I 1  and the pilot-operating valve  55  is turned OFF.  
         [0080]     In step S 113 , it is determined whether the clutch operating valve  59  is ON. If it is ON, the processing proceeds to step S 114 , and if it is OFF, the processing proceeds to step S 116 . When the processing proceeds to step S 114 , since the hydraulic clutch  28  is engaged in the Low mode in the state of the pressure of the accumulator  42  being in the set pressure range, the control of the pump driving electric motor  41  is set to speed control. In step S 115 , the rotation number command for the pump driving electric motor  41  is set to Np 1  and the pilot-operating valve  55  is turned OFF.  
         [0081]     When the processing proceeds to step S 116  in the state of the clutch operating valve  59  being OFF, it is determined whether the current vehicle speed Vcar is less than a set vehicle speed V 1 . When equal to or greater than the set vehicle speed V 1 , the processing proceeds to step S 114 , similarly to when the hydraulic clutch  28  is engaged, and the control of the pump driving electric motor  41  is set to speed control. Also, when the vehicle speed Vcar is less than the set vehicle speed V 1 , the processing proceeds to step S 117 , where it is determined whether the current oil temperature Toil is less than a set oil temperature T 1 . When the oil temperature Toil at this time is equal to or greater than the set oil temperature T 1 , the processing proceeds to S 114 , similarly to when the hydraulic clutch  28  is engaged, and the control of the pump driving electric motor  41  is set to speed control.  
         [0082]     When the oil temperature Toil is less than the set oil temperature T 1 , the processing proceeds to S 118 , where the pump driving electric motor  41  is turned OFF and the pilot-operating valve  55  is turned OFF. That is, when the processing proceeds to step S 118 , when in Low mode and the clutch operating valve  59  is OFF, since both the vehicle speed Vcar and the oil temperature Toil are sufficiently low, it is determined that there is no need to supply oil to the clutch oil passage  58  or the low-pressure oil passage  57 , and operation of the oil pump  40  is stopped.  
         [0083]     The flow of control is as described above, but the operation during actual driving is as presented in the timing chart of  FIG. 8 . This timing chart is explained below.  
         [0084]     In  FIG. 8 , symbol (a) denotes the state of the pump driving electric motor  41  in a stopped condition. When the pressure of the actuator  42  is lower than the lower limit pressure AL at time (b) of startup, the controller  110  instructs a current according to the electric motor (EOP) load pressure PH, and the pump driving electric motor  41  is started by torque control. Then, the pilot-operating valve  55  is turned ON and high-load operation is performed in time period (c) until the pressure of the accumulator  42  reaches the upper limit pressure AH.  
         [0085]     At time (d), when the pressure of the accumulator  42  reaches the upper limit pressure AH, by turning off the pilot-operating valve  55 , the oil passage connected to the oil pump  40  is switched to the low-pressure oil passage  57  of the low-load side. At this time, the controller  110  instructs the electric motor (EOP) rotation number (Np 1 ), and the pump driving electric motor  41  is operated by rotation speed control. In addition, at time (d), the clutch operating valve  59  is ON and the vehicle switches to four-wheel-drive mode. In time period (e), low-load operation is performed with the pilot-operating valve  55  turned off until the pressure in the accumulator  42  reaches the lower limit pressure AL.  
         [0086]     At time (f), when the pressure of the accumulator  42  reaches the lower limit pressure AL, the pilot-operating valve  55  is turned on and the oil passage connected to the oil pump  40  is switched to the clutch oil passage  58  on the high-load side. The controller instructs a current according to the electric motor (EOP) load pressure PH and runs the pump driving electric motor  41  in torque control. From this time on in time period (g), high load operation is performed with the pilot-operation valve  55  turned on until the pressure of the accumulator  42  reaches the upper limit pressure AH.  
         [0087]     When the pressure of the accumulator  42  again reaches the upper limit pressure AH at time (h), by turning off the pilot-operation valve  55 , the oil passage connected to the oil pump  40  is switched to the low-pressure oil passage  57  similarly to at time (d), and the controller  110  instructs the electric motor (EOP) rotation number (Np 1 ) and runs the pump driving electric motor  41  in rotation speed control.  
         [0088]     At time (i), the clutch operating valve  59  switches off, and the vehicle changes to two-wheel-drive mode.  
         [0089]     At this time, since the pressure of the accumulator  42  is in a definite range between the lower limit pressure AL and the upper limit pressure AH, the oil temperature Toil is lower than T 1 , and the vehicle speed Vcar is equal to or greater than V 1 , the pump driving electric motor  41  maintains its operation condition without stopping. That is, since lubrication of the power transmission device is required with a high vehicle speed Vcar, the running of the pump driving electric motor  41  is continued. At time (j), when the vehicle speed Vcar falls below V 1 , even if the supply of oil is stopped to the low-pressure oil passage  57 , it is determined that there is no lubrication or cooling problem, and the pump driving electric motor  41  is stopped.  
         [0090]      FIG. 9  shows a timing chart under another driving condition.  
         [0091]     The driving condition in the first half of this timing chart resembles that of  FIG. 8 , but the driving condition of the latter half, particularly from time (i) to time (j), partially differs.  
         [0092]     Namely, at time (i), the clutch operating valve  59  is turned off and the vehicle switches to two-wheel-drive mode. The pressure of the accumulator  42  is in a set pressure range between the lower limit pressure AL and the upper limit pressure AH, and the vehicle speed Vcar is slower than V 1 , but since the oil temperature Toil is equal to or greater than T 1 , the pump driving electric motor  41  maintains its operating condition without stopping. That is, in this case, since it is necessary to continue cooling of the wheel driving electric motor  2  because the oil temperature Toil is high, running of the pump driving electric motor  41  is continued. When the oil temperature Toil subsequently falls below T 1  at time (i), even if the supply of oil is stopped to the low-pressure oil passage  57 , it is determined that there is no lubrication or cooling problem, and the pump driving electric motor  41  is stopped.  
         [0093]     Next, the low-pressure oil passage  57  of the oil pressure circuit  39  shown in  FIG. 1  shall be explained in detail below.  
         [0094]     In the low-pressure oil passage  57 , the upstream side oil passage  57   a  connected to the selector valve  56  branches into a lubricating oil passage  70  and a cooling oil passage  71 . The lubricating oil passage  70  supplies oil to the lubricating portions of the drive power transmission devices (the planetary gear reducer  12  and the differential  13 ) as lubricating oil, while the cooling oil passage  71  supplies oil to the cooling portions (the regions requiring cooling) of the wheel driving electric motor  2  as cooling oil. In the lubricating oil passage  70  there is provided an orifice  72 , and in the cooling oil passage  71  there is a pressure regulating valve  73  that regulates and relieves the pressure within the low-pressure oil passage  57  in cooperation with the orifice  72 .  
         [0095]     The lubricating oil passage  70  opens at a suitable position to be able to supply oil to the planetary gear reducer  12  and the differential  13 . The cooling oil passage  71  is connected to a stator cover  74  that encloses a stator coil  14   a  (coil) of the electric motor  2  as shown in  FIG. 10 . This stator cover  74  is integrally provided with the housing  11  shown in  FIG. 3 , with an approximately semicircular oil filling chamber  75  formed in the upper half of the interior. The oil filling chamber  75  is connected to the cooling oil passage  71  via an introduction port  76 , and a plurality of small-diameter spray holes  77  are formed on the inner periphery of the oil filling chamber  75  whereby oil can be directly discharged onto the outer surface of the stator coil  14   a . The oil filling chamber  75  and the spray holes  77  formed in this stator cover  74  constitute a spray mechanism  78  that directly discharges oil onto the stator coil  14   a . Since the diameter of the spray holes  77  is small in the spray mechanism  78 , oil is not discharged from the spray holes  77  onto the stator coil  14   a  until the pressure in the oil filling chamber  75  reaches a specified pressure. At the point when the pressure in the oil filling chamber  75  has risen to or surpassed the specified pressure, oil is discharged onto the stator coil  14   a  in small droplets.  
         [0096]     In the pressure regulating valve  73 , a spool  79  that is a valve as shown in  FIG. 11  is slidably accommodated in a valve chamber  80 . The pressure in the lubricating oil passage  70  is adjusted by displacement of the spool  79  in accordance with pressure on a branched portion  81  of the lubricating oil passage  70  and the cooling oil passage  71 , and when the pressure of the branched portion  81  has risen to or above a set pressure, the oil inside is drained.  
         [0097]     Specifically, in approximately the center position in the axial direction of the valve chamber  80 , an inlet port  82  connected to the branched portion  81  of the cooling oil passage  71  and an outlet port  83  connected to the cooling portion side of the electric motor  2  are offset in the axial direction. An operating pressure port  84  is provided on the end portion of the valve chamber  80  on the outlet port  83  side, and an air port  85  is provided on the other end portion of the valve chamber  80  on the inlet port  82  side, with a drain portion  86  provided between the outlet port  83  and the air port  85 . The operating pressure port  84  is connected to the branched portion  81  via a pressure induction passage  87 . An orifice  88  for restricting sensitive pressure fluctuations is provided in the pressure induction passage  87 . A spring  89  is interposed between the other end portion of the valve chamber  80  and the spool  79 , with the spool  79  being constantly biased to the one end side of the valve chamber  80  by the spring  89 . A first land portion  90 A, a second land portion  90 B, and a third land portion  90 C are formed spaced apart in the axial direction on the outer periphery of the spool  79  and sandwiching annular grooves  91 A and  91 B. In an initial state in which the pressure of the branched portion  81  is sufficiently low, as shown in  FIG. 11  the first and second land portions  90 A and  90 B of the spool  79  block communication between the outlet port  83  and the other ports  84  and  82 , and the second and third land portions  90 B and  90 C block communication between the inlet port  82  and the other ports  83  and  84 .  
         [0098]     When pressure on the branched portion  81  side is introduced to the inlet port  82  and the operating pressure port  84  from the initial state shown in  FIG. 11 , the thrusts acting on the opposing surfaces of the second land portion  90 B and the third land portion  90 C, which have the same surface area, cancel each other out. The spool  79  then moves due to the balance of the rightward thrust in  FIG. 11  acting on the operating pressure port  84  and the reactive force of the spring  89 . In the pressure regulating valve  73 , when the pressure on the branched portion  81  side becomes a set pressure (second predetermined pressure), the inlet port  82  and the outlet port  83  mutually communicate due to the displacement of the second land portion  90 B, and oil is supplied from the branched portion  81  to the oil filling chamber  75  of the stator cover  74  through the cooling oil passage  71 . At this time, the amount of oil supplied to the lubricating oil passage  70  decreases, and the pressure of the lubricating oil passage  70  is restricted to be lower than the second predetermined pressure.  
         [0099]     As the temperature decreases the oil viscosity rises, the oil resistance of the cooling oil passage  71  increases. When this occurs, oil is hindered from flowing from the inlet port  82  of the pressure regulating valve  73  to the outlet port  83 , and as a result, the pressure in the low-pressure oil passage  57  including the branched portion  81  gradually rises. When the pressure on the branched portion  81  side thus gradually rises, the thrust acting on the spool  79  via the operating pressure port  84  rises. When the pressure on the branched portion  81  side reaches a first predetermined pressure that is higher than the second predetermined pressure, the drain port  86  opens due to the displacement of the third land portion  90 C, and oil is discharged from the inlet port  82  to the drain port  86 , as shown in  FIG. 12 . Thereby, the pressure throughout the entire low-pressure oil passage  57  is inhibited from becoming higher than the first predetermined pressure.  
         [0100]     In the discharge piping of the oil pump  40 , a high-pressure relief valve  95  is provided as shown in  FIG. 1 , and the pressure of the oil supplied to the clutch oil passage  58  thereby is restricted to a prescribed pressure or less. The second predetermined pressure is a lower pressure than the prescribed pressure of this high-pressure relief valve  95 .  
         [0101]     As described above, when supplying oil to the clutch oil passage  58  that requires a high pressure, the control device of this hydraulic circuit (the control device that controls the hydraulic circuit  39 ) controls the pump driving electric motor  41  by torque control. When supplying oil to the low-pressure oil passage  57  that requires a low pressure and high flow rate, the control device of this hydraulic circuit controls the pump driving electric motor  41  by speed control. Therefore, step out of the pump driving electric motor  41  due to large fluctuations in the hydraulic load accompanying operation of the hydraulic clutch  28  can be reliably prevented. Moreover, when sending oil at a low pressure and high flow rate through the low-pressure oil passage  57 , excessive power consumption due to overspeed of the pump driving electric motor  41  can be reduced.  
         [0102]     The control device of the hydraulic circuit constantly monitors the pressure of the accumulator  42  side of the clutch oil passage  58  with the pressure sensor  62 . When the detected pressure in the accumulator  42  deviates from a set pressure range, the oil passage selecting unit  120  selects the clutch oil passage  58 . Therefore, it is always possible to achieve oil passage selection in accordance with the request of the clutch oil passage  58  and the optimum electric motor control mode based on that selection.  
         [0103]     Moreover, in the control device of the hydraulic circuit, since the pressure regulating valve  73  with a relief function is interposed in the low-pressure oil passage  57  that sends oil for lubrication and cooling, even if the viscosity of oil rises at low temperatures, the spool  79  of the pressure regulating valve  73  can restrict the pressure of the low-pressure oil passage  57  to be less than the first predetermined pressure by opening the drain port  86 . Accordingly, in this device, when the pump driving electric motor  41  is running in speed control mode, overloads caused by fluctuations in the oil viscosity have no impact on the pump driving electric motor  41 . Therefore, the energy efficiency of the pump driving electric motor  41  can be raised, and step out of the speed-controlled pump driving electric motor  41  due to overloading can be prevented.  
         [0104]     Since restricting the rotation speed of the pump to a specified rotation speed is particularly difficult in the case of operating the oil pump  40  by the sensor-less type pump driving electric motor  41  as in the present embodiment, the implementation of the pressure regulating valve  73  of the present invention is effective.  
         [0105]     In the control device of this hydraulic circuit, with respect to the low-pressure oil passage  57  that branches into the lubricating oil passage  70  and the cooling oil passage  71 , since the orifice  72  is interposed in the lubricating oil passage  70  and the pressure regulating valve  73  is provided in the cooling oil passage  71 , the pressure of the oil supplied to the lubricating portion during normal operation can be kept lower than the second predetermined pressure by the pressure regulating valve  73 .  
         [0106]     Since pressure adjustment of the lubricating oil passage  70  during normal usage and oil relief of the low-pressure oil passage  57  during abnormally high pressure can be performed by the single spool  79  of the pressure regulating valve  73  in the present embodiment, compared to the case of separately providing two types of valves, the manufacturing cost can be reduced and the weight and size of the device can be reduced.  
         [0107]     The present invention is not limited to the aforementioned embodiment, and design modifications are possible without departing from the spirit or scope of the present invention. For example, the above embodiment applied the control device according to the present invention to the hydraulic circuit  39  that switches the oil passage for clutch control and the oil passage for cooling/lubrication in the drive device  1  for auxiliary drive use. However, the application of this invention is not limited to the drive device  1 , and is applicable to other devices provided they have a hydraulic circuit for switching of an oil passage that requires a high pressure and an oil passage that requires a low pressure and high flow rate.  
         [0108]     In the embodiment described above, the oil passage selecting unit  120  in the controller  110  selects the oil passage based on the pressure of the clutch oil passage  58 , which is the first oil passage (that is, the pressure of the accumulator  42 ). However, depending on the application use of the hydraulic circuit, selection of the oil passage may be performed based on the flow rate of the second oil passage that requires a low pressure and high flow rate.  
         [0109]     In the embodiment described above, the oil temperature Toil is measured, and the temperature of the wheel driving electric motor  2  is indirectly determined from the oil temperature Toil. However, a temperature sensor may be installed in the wheel driving electric motor  2  to directly measure the temperature of the wheel driving electric motor  2 , or the temperature of the wheel driving electric motor  2  may be estimated from the electric current passing through the wheel driving electric motor  2 .  
         [0110]     While preferred embodiments of the invention have been described and illustrated above, it should be understood that these are exemplary of the invention and are not to be considered as limiting. Additions, omissions, substitutions, and other modifications can be made without departing from the spirit or scope of the present invention. Accordingly, the invention is not to be considered as being limited by the foregoing description, and is only limited by the scope of the appended claims.