WO2007096719A1

WO2007096719A1 - Oil pressure system and control method therefor

Info

Publication number: WO2007096719A1
Application number: PCT/IB2007/000205
Authority: WO
Inventors: Hideto Minekawa
Original assignee: Toyota Jidosha Kabushiki Kaisha
Priority date: 2006-02-27
Filing date: 2007-01-30
Publication date: 2007-08-30
Also published as: JP2007224887A

Abstract

When an engine (2) is operating, a control device (30) opens a stop valve (34) along with stopping a pump drive motor (26), so that working oil (48) is circulated between a mechanical oil pump (22) which is driven by the engine (2) and a radiator unit (32). Furthermore, the oil pressure that is generated by the mechanical oil pump (22) is also supplied to a drive lubrication component (46). When the engine (2) is stopped, the control device (30), along with closing the stop valve (34) and limiting the amount of circulation between an electrically operated oil pump (24) and the radiator unit (32), also drives a pump drive motor (26), so that the oil pressure which is generated by the electrically operated oil pump (24) is supplied to the drive lubrication component (46).

Description

OIL PRESSURE SYSTEMAND CONTROL METHOD THEREFOR

BACKGROUND OF THE INVENTION

1. Field of the Invention

[0001] The present invention relates to an oil pressure system that is mounted upon a vehicle having an engine that is operated intermittently, and in particular relates to an oil pressure system that generates oil pressure by the rotational power of at least one of an engine and an electric motor, and to a control method therefor.

2. Background of the Invention

[0002] In the interest of resource conservation and prevention of global warming, an economy running system is becoming more widespread in which the engine of a vehicle that is stopped by a red light or the like is automatically stopped and, when an operation is performed by the driver (for example, stepping upon the accelerator pedal, terminating stepping upon the brake pedal, changing to a running stage of the shift lever, or the like), the engine is restarted. It should be understood that such an economy running system may also be termed an idling stop system or an automatic engine start and stop system. [0003] Furthermore, hybrid systems are also becoming more widespread, in which the engine may be stopped, as described above, but which are also capable of running with only the motor.

[0004] In a vehicle to which such an economy running system or a hybrid system is mounted and whose engine is operated intermittently, according to the running situation, a secondary battery such as a lead-acid battery or a lithium battery or the like is provided, in order to supply electrical power to auxiliary machinery of various types (an oil pump, an air conditioner, head lamps, and the like) when the vehicle is stopped. [0005] Generally, in a vehicle in which the engine is operated continuously, a mechanical oil pump is provided which discharges working oil using the rotatory power of the engine, and it is arranged to supply working oil (oil pressure) to a group of hydraulic components such as an automatic transmission or the like. On the other hand, according to the running situation, with an economy running vehicle or a hybrid vehicle (hereinafter simply termed an "eco-running vehicle") in which the engine may be operated intermittently, in order to maintain the appropriate working oil supply when the engine is stopped, the oil pump may be driven electrically.

[0006] For example, Japanese Patent Application Publication No. JP-A-2004-100580, describes a hybrid vehicle that is equipped with a lubrication mechanism in which an oil pump is driven by the rotational torque of the engine output shaft, and in which, while suppressing unnecessary battery consumption, the oil pump is operated at an appropriate timing. The hybrid vehicle includes an oil pump that is connected to the engine output shaft and that supplies lubricating oil to a power transmission mechanism, and a motor-generator, which can forcibly to rotate the engine output shaft. [0007] Furthermore, Japanese Patent Application Publication No. JP-A-2002-371969, describes a control device of an automatic speed change mechanismthat starts the operation of an electrically operated oil pump when needed, and with which an excessive load is not imposed upon the electrically driven oil pump. The oil pump control device includes a mechanical oil pump that, due to the drive force of the engine, generates oil pressure supplied to the automatic speed change mechanism, and an electrically operated oil pump that is driven electrically, to supply oil pressure to the automatic speed change mechanism. [0008] The structures described in Japanese Patent Application Publication No. JP-A-2004-100580 and in Japanese Patent Application Publication No. JP-A- 2002-371969 are designed to make the same level of functionality of the oil pump (discharge pressure and discharge amount and the like) available while the engine is stopped, as while it is being driven by the engine. However the amount of working oil that is supplied by the oil pump is approximately the same, whether the engine is running or is stopped, without any consideration of the device that receives the supply of generated oil pressure. As a result, there have been the problems that the driving electrical power for the oil pump while the engine is stopped is also high, and that the oil pump itself has become increased in size.

SUMMARY OF THE INVENTION

[0009] The present invention provides an oil pressure system and a control method therefor that reduces the consumption of electrical power when the engine is stopped, and can make the oil pump more compact.

[0010] A first aspect of the present invention relates to an oil pressure system in a vehicle having an engine that is operated intermittently. The oil pressure system includes: an electric motor that is driven by electrical power; an oil pressure generation unit that is adapted generates oil pressure according to the drive force of at least one of the engine and the electric motor; a distribution unit that distributes the working oil discharged from the oil pressure generation unit; a group of hydraulic components connected to the distribution unit, which, with the oil pressure generation unit, constitutes at least a single circulation path for the working oil; a limitation means that limits the circulation amount of the working oil between the oil pressure generation unit and one or more engine dependent componentswhich is a part of the group of hydraulic components whose required operational performance is reduced along with stopping of the engine; and a control unit that operates the electric motor to generate oil pressure, while the engine is stopped, along with limiting the circulation amount of the working oil circulating between the oil pressure generation unit and the one or more engine dependent components using the limitation means.

[0011] According to this first aspect of the present invention, when the engine is stopped, a limitation is imposed upon the amount of the working oil that is circulated to the engine dependent components of hydraulic components in which the required operational performance may be reduced when the engine is stopped. By doing this, it is possible to suppress the amount of working oil that is discharged from the oil pressure generation unit and is circulated between the oil pressure generation unit and the group of hydraulic components. Accordingly, even when generating the same level of oil pressure using the drive force of the electric motor, as is generated by the drive force of the engine, it is possible to reduce the drive load upon the electric motor, because the discharge amount of the oil pressure generation unit is suppressed. Furthermore, it is also possible to reduce the discharge amount that is required from the oil pressure generation unit. [0012] The one or more engine dependent components may include, for example, a radiator unit that cools the working oil by heat dissipation.

[0013] The control unit may include an oil temperature sensor that determines the temperature of the working oil, and a working oil cooling means that mitigates the limitation of the circulation amount by the limitation means and may also start the engine to generates oil pressure when the circulation amount is limited by the limitation means and the temperature of the working oil is greater than or equal to a first threshold value. [0014] The control unit may include an oil temperature sensor that determines the temperature of the working oil, and a working oil temperature elevation means that limits the circulation amount by the limitation means, when the oil pressure is being generated by the engine and the oil temperature is less than or equal to a second threshold value. [0015] It would also be acceptable for the control unit to stop the electric motor during operation of the engine. [0016] The vehicle may be adapted to be further capable of running due to the drive force generated by a motor-generator that outputs less power than the engine; and the group of hydraulic components may include, in addition to the one or more engine dependent components, a power transmission mechanism that receives the drive force generated by the engine and the motor-generator and transmits the drive force to the vehicle wheels.

[0017] The oil pressure generation unit may include a first oil pump that is driven by the engine, and a second oil pump that is driven by the electric motor and that discharges less working oil as compared with the first oil pump.

[0018] According to the first aspect of the present invention, it is possible to implement an oil pressure system that reduces the consumption of electrical power while the vehicle is stopped, and in which a more compact oil pump may be used. [0019] A second aspect of the present invention relates to a control method for an oil pressure system mounted to a vehicle of which an engine is operated intermittently and including: an electric motor which is driven by electrical power; an oil pressure generation unit which is adapted to be capable of generating oil pressure according to the drive force of at least one of the engine and the electric motor; a distribution unit which distributes the working oil which is discharged from the oil pressure generation unit; and a group of hydraulic components connected to the distribution unit, which, with the oil pressure generation unit, constitutes at least a single circulation path for the working oil, and which includes at least one engine dependent component, the required operational performance of which is reduced along with stopping of the engine. The control method includes: a step of detecting the operational state of the engine; and a step of operating the electric motor to generate oil pressure when the engine is stopped and the circulation amount of the working oil circulating between the oil pressure generation unit and the engine dependent component is limited.

[0020] According to the second aspect of the present invention, it is possible to implement an oil pressure system that reduces the consumption of electrical power while the vehicle is stopped, and in which a more compact oil pump may be used.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The foregoing and further objects, features and advantages of the invention will become apparent from the following description of preferred embodiments with reference to the accompanying drawings, wherein like numerals are used to represent like elements and wherein:

Fig. 1 is a schematic structural diagram of a eco-running vehicle which is equipped with an oil pressure system according to an embodiment of the present invention;

Fig. 2 is a more detailed schematic structural diagram of this oil pressure system;

Figs. 3A and 3B are schematic figures showing paths for working oil in this oil pressure system;

Fig. 4 is a schematic figure showing a path for working oil in this oil pressure system during warming up operation;

Fig. 5 is a flow chart showing the control structure of a program which is executed by a control device; and

Fig. 6 is a schematic structural diagram of a hybrid vehicle which is equipped with an oil pressure system according to a variant embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0022] Embodiments of the present invention will now be explained in detail with reference to the drawings. It should be understood that, to portions in the figures which are the same or which correspond to one another, the same reference symbols are affixed, and repetitive explanation is omitted.

[0023] Fig. 1 is a schematic structural diagram of an eco-running vehicle 100 which is equipped with an oil pressure system according to an embodiment of the present invention. It should be understood that although, by way of example, the oil pressure system of the present invention is here explained in the case of application to a FF (Front engine Front drive) vehicle, in fact the oil pressure system according to the present invention may also be applied to a vehicle of a different type than the FF type.

[0024] This eco-running vehicle 100 comprises an engine 2, an automatic speed change mechanism 4, drive wheels 6, an alternator (ALT) 14, a belt 12, a battery (BAT) 16, and an oil pressure system 20. And, with this eco-running vehicle 100, the engine 2 is operated intermittently according to the running situation. In concrete terms, an ECU (Electrical Control Unit) not shown in the figures stops the engine 2 automatically (idling stop), and restarts the engine 2, according to the amount by which an accelerator pedal is stepped upon due to actuation by the driver, according to the amount by which a brake pedal is stepped upon, and according to the selected position of a shift lever or the like. [0025] The engine 2 is an internal combustion engine which is driven by the combustion of a fuel such as, for example, gasoline, diesel oil, LPG, or the like, and the drive force which is generated is supplied via an output shaft to the automatic speed change mechanism 4, the oil pressure system 20, and the alternator 14.

[0026] The automatic speed change mechanism 4 is mechanically connected to the output shaft of the engine 2 and to the drive wheels 6, and, along with transmitting the drive force which is inputted from the engine 2 to the drive wheels 6, also changes the ratio of the output rotational speed to the drive wheels 6 with respect to the input rotational speed from the engine 2 (i.e. the speed change ratio) according to commands from some external unit not shown in the figure. ^■ As one example, this automatic speed change mechanism 4 may be structured as a belt type stepless speed change mechanism (a CVT: Continuously Variable Transmission) which can vary its speed change ratio in a stepless (continuous) manner. And this automatic speed change mechanism 4 includes a drive force engaging element 8 and a speed change mechanism 10.

[0027] The drive force engaging element 8 is a device for controlling the drive force which is being transmitted from the engine 2 to the drive wheels 6, and it is made to transmit torque via working oil between a member upon its input side and a member upon its output side. As one possible example, this drive force engaging element 8 may be a torque converter.

[0028] The speed change mechanism 10 comprises a drive side pulley and a driven side pulley, both of which have V-groove shaped pulley grooves, and also comprises a belt which is stretched over these pulleys, and is built so that, by increasing the groove width of the pulley groove on one of these pulleys while reducing the groove width of the pulley groove on the other pulley, the wrapped radiuses (the effective diameters) of the belt upon these pulleys are changed continuously, so that the speed change ratio is changed in a stepless manner.

[0029] The alternator 14 receives the drive force of the engine 2 via a belt 12 which is stretched between it and the output shaft of the engine 2, and is an electricity generation means for generating electrical power. As one example thereof, the alternator 14 may be a permanent magnet type DC generator, which is rotated by the driving force of the engine 2, and which generates voltage according to its rotational speed. And the alternator 14 supplies this DC power which it generates to the battery 16.

[0030] The battery 16, on the one hand, is adapted to be capable of being charged up by the DC electrical power which is supplied from the alternator 14, and, on the other hand, is adapted to be able to supply electrical energy which it has accumulated to the oil pressure system 20. As examples thereof, this battery 16 may be a lead-acid battery or a lithium ion battery or the like.

[0031] The oil pressure system 20 generates oil pressure by using at least one of the drive force of the engine 2 and the electrical power from the battery 16 as a power source, and supplies this working oil to the automatic speed change mechanism 4 and the like. For example, this oil pressure system 20 maintains supply of a predetermined oil pressure by using either the drive force of the engine 2 or the electrical power from the battery 16, during the period while the ignition key is kept ON due to actuation by the driver. And this oil pressure system 20 comprises a mechanical oil pump (MP) 22, an electrically operated oil pump (EP) 24, a pump drive motor 26, a driver 28, and a control device 30. [0032] The mechanical oil pump 22 is mechanically coupled to the output shaft of the engine 2, and generates oil pressure due to the rotational drive force of the engine 2. On the other hand, the electrically operated oil pump 24 is mechanically coupled to the pump drive motor 26, and generates oil pressure due to the rotational drive force of the pump drive motor 26. And the electrically operated oil pump 24 is chosen so that its discharge capability (its discharge amount or its discharge pressure) is lower, as compared with the discharge capability of the mechanical oil pump 22.

[0033] As an example, in the mechanical oil pump 22 and the electrically operated oil pump 24, an impeller and vanes or the like may be rotated by the engine 2 and by the pump drive motor 26 respectively, to generate oil pressure.

[0034] The pump drive motor 26 is rotationally driven by electrical power, supplied from the driver 28. As one example, the pump drive motor 26 may be a sensorless DC brushless motor. [0035] According to a control command from the control device 30, the driver 28 converts the DC electrical power which it receives from the battery 16 to a predetermined voltage, which it supplies to the pump drive motor 26.

[0036] The control device 30 performs control so that oil pressure is supplied from at least one of the mechanical oil pump 22 and the electrically operated oil pump 24, according to the operational state of the engine 2. In concrete terms, on the one hand, only while the engine 2 is stopped, the control device 30 rotationally drives the pump drive motor 26 by supplying a drive command to the driver 28, and thus generates an oil pressure from the electrically operated oil pump 24; while on the other hand, while the engine 2 is operating, it stops the pump drive motor 26. In the following, the structure and the operation of this oil pressure system 20 will be described in detail.

[0037] Fig. 2 is a schematic structural diagram showing the oil pressure system 20 in more detail. This oil pressure system 20 further includes an oil pan 40, a strainer 42, a non return valve 38, a distribution unit 44, a group of hydraulic components 50, and a temperature detection unit 36.

[0038] The oil pan 40 is a vessel which accumulates the working oil 48, and on the one hand it supplies the working oil 48 to the mechanical oil pump 22 and the electrically operated oil pump 24, while on the other hand it receives the working oil 48 which circulates around the group of hydraulic components 50 and then returns.

[0039] The strainer 42 is disposed within the oil pan 40 to dip into the working oil 48, and it filters out foreign matter which included in the working oil 48, such as dust or sludge or the like, and supplies the working oil 48 to the mechanical oil pump 22 and the electrically operated oil pump 24 after filtration thereof.

[0040] The mechanical oil pump 22 pumps up the working oil 48 via the strainer 42, imparts a predetermined discharge pressure (oil pressure) to it, and supplies it to the distribution unit 44. In the same manner, the electrically operated oil pump 24 also pumps up the working oil 48 via the strainer 42, imparts a predetermined discharge pressure (oil pressure) to it, and supplies it to the distribution unit 44. It should be understood that since, as described hereinafter, when the engine 2 is stopped, the amount of circulation of the working oil 48 which is pumped up by the electrically operated oil pump 24 is limited, accordingly it is possible to reduce the discharge amount per unit time of the electrically operated oil pump 24, as compared with the mechanical oil pump 22. Due to this, as compared with the mechanical oil pump 22, it is possible to make the electrically operated oil pump 24 more compact.

[0041] The non return valve 38 is disposed between the discharge side of the electrically operated oil pump 24 and the distribution unit 44, and prevents reverse flow of the working oil 48 from the distribution unit 44 to the electrically operated oil pump 24. In other words since, directly after the engine 2 has stopped, the oil pressure at the distribution unit 44 is elevated to the discharge pressure of the mechanical oil pump 22, accordingly the non return valve 38 prevents reverse flow of the working oil 48 from the distribution unit 44, so that the starting of the electrically operated oil pump 24 is facilitated.

[0042] The distribution unit 44 distributes the working oil 48 which is discharged by the mechanical oil pump 22 or by the electrically operated oil pump 24 to the group of hydraulic components 50.

[0043] The group of hydraulic components 50 is connected to the distribution unit 44, and constitutes at least a single circulation path with the mechanical oil pump 22 and the electrically operated oil pump 24, via the oil pan 40. And this group of hydraulic components 50 comprises a drive lubrication component 46, a radiator unit 32, and a stop valve 34. [0044] The drive lubrication component 46 comprises an oil pressure driven component which takes, as its drive source, the working oil 48 which is discharged from the mechanical oil pump 22 or the electrically operated oil pump 24, and a mechanical member which is lubricated by this working oil 48. As an example, this drive lubrication component 46 may include the group of structural components consisting of the drive force engaging element 8 and the speed change mechanism 10 (Fig. 1) which are included in the automatic speed change mechanism 4. As example of oil pressure driven components, there may be cited an oil pressure adjustment valve of a torque converter, which is an example of the drive force engaging element 8, a drive valve of a pulley of the speed change mechanism 10, and a brake drive mechanism or the like. Furthermore, as an example of a mechanical member which is lubricated, there may be cited the gears which are comprised in the speed change mechanism 10, and the differential gears and bearings which link it to the drive shaft of the engine 2, and the like.

[0045] The radiator unit 32 is disposed at the front section of this eco-running vehicle 100, and it cools the working oil 48 which flows in from the distribution unit 44 by heat dissipation. In other words, the radiator unit 32 performs heat exchange between the atmosphere and the working oil 48 that is flowing in the circulation path, which is defined between the radiator unit 32 and one of the mechanical oil pump 22 and the electrically operated oil pump 24.

[0046] The stop valve 34 is disposed between the distribution unit 44 and the radiator unit 32, and limits the flow amount of the working oil 48 which flows in from the distribution unit 44, according to a control command from the control device 30. In other words, the stop valve 34 may be considered as a limitation means which limits the circulation amount of the working oil 48 between the mechanical oil pump 22 and the electrically operated oil pump 24, and the radiator unit 32, according to a control command. [0047] The temperature detection unit 36 is disposed to dip into the working oil 48 within the oil pan 40, and it detects the oil temperature of this working oil 48, and transmits its detection result to the control device 30.

[0048] The control device 30 decides upon the operational state of the engine 2 based upon the rotational speed NE. And, if the engine 2 is stopped, the control device 30 limits, with the stop valve 34, the amount of circulation of the working oil 48 between the electrically operated oil pump 24 and the radiator unit 32, which is one example of an engine dependent component whose required operational performance drops along with stopping of the engine 2. At the same time, the control device 30 starts the pump drive motor 26 and generates oil pressure from the electrically operated oil pump 24. [0049] As described above, the drive lubrication component 46 includes an oil pressure adjustment valve of a torque converter or the like. If the engine 2 is stopped, since the drive force which is inputted into the torque converter is zero, no heat loss takes place in the torque converter. Furthermore, the drive lubrication component 46 includes the gears which make up the speed change mechanism 10, and the differential gears and bearings and the like which link it to the drive shaft of the engine 2. When the engine 2 is stopped, since this type of mechanical member is also maintained in the stationary state, accordingly, also, no heat is generated along with its lubrication. Due to this, the required operational performance from the radiator unit 32, in other words its requested cooling performance, drops along with the engine 2 being stopped. Accordingly, if the engine 2 is stopped, it is not necessary for the working oil 48 to be circulated to the radiator unit 32 to an excessive amount, and, by limiting the amount of this type of circulation, it is possible to reduce the electrical power consumption of the pump drive motor 26, and to make the electrically operated oil pump 24 more compact. [0050] Figs. 3A and 3B are schematic figures showing paths for the working oil 48 in this oil pressure system 20. Fig. 3A shows the path for the working oil 48 when the engine 2 is operating. And Fig. 3B shows the path for the working oil 48 when the engine 2 is stopped.

[0051] As shown in Fig. 3A, when the engine 2 is operating, along with stopping the pump drive motor 26, the control device 30 opens the stop valve 34, so that the working oil 48 is circulated between the radiator unit 32 and the mechanical oil pump 22 due to its being driven by the engine 2. Furthermore, the oil pressure, which is generated by the mechanical oil pump 22 is also supplied to the drive lubrication component 46. [0052] On the other hand, as shown in Fig. 3B, when the engine 2 is stopped, the control device 30 closes the stop valve 34, so that, along with the amount of circulation of the working oil 48 between the electrically operated oil pump 24 and the radiator unit 32 being limited, the pump drive motor 26 is operated and the oil pressure which is generated by the electrically operated oil pump 24 is supplied to the drive lubrication component 46. [0053] Cooling the working oil

Since, as described above, when the engine 2 is stopped, cooling of the working oil 48 by the radiator unit 32 is not performed, accordingly it may also be supposed that the oil temperature of the working oil 48 may be excessively elevated. Thus, if the oil temperature of the working oil 48 is elevated, the control device 30 performs a cooling operation for the working oil.

[0054] In concrete terms, the control device 30 decides upon the oil temperature of the working oil 48 which has been detected by the temperature detection unit 36. And if, during limitation of the circulation amount between the electrically operated oil pump 24 and the radiator unit 32 by the stop valve 34, it is decided that the temperature of the working oil 48 is greater than or equal to a first threshold value, then the control device 30 opens the stop valve 34, and, along with mitigating the limitation of the amount of circulation, generates oil pressure with the mechanical oil pump 22 by starting the engine 2. For example, this first threshold value may be set to an upper limit permitted temperature for the working oil 48, and, if the oil temperature of the working oil 48 becomes greater than or equal to this upper limit permitted temperature, then the control device 30 circulates the working oil 48 to the radiator unit 32 with the mechanical oil pump 22, and thereby initiates cooling of the working oil 48.

[0055] In other words if, while the engine 2 is stopped, during oil pressure supply by the electrically operated oil pump 24, the oil temperature of the working oil 48 becomes greater than or equal to the first decision value, then the control device 30 starts the engine 2, and circulates the working oil 48 between the mechanical oil pump 22 and the radiator unit 32, thus cooling the working oil 48 with the radiator unit 32. After the engine e2 has been started in this manner, the control device 2 stops the pump drive motor 26, and thus stops the generation of oil pressure from the electrically operated oil pump 24. [0056] It should be understood that since, as described above, almost no heat loss takes place when the engine 2 is stopped, accordingly in practice the frequency with which the engine 2 is started only with the objective of cooling the working oil 48 is quite low. [0057] Raising the temperature of the working oil

During the late night or the early morning in the winter, or in a very cold district, sometimes the oil temperature of the working oil 48 decreases and its viscosity becomes excessively high. When the viscosity of the working oil 48 becomes high in this manner, its beneficial effect for lubrication is reduced, which is undesirable. In these circumstances, the control device 30 is able to elevate the temperature of the working oil 48 so that it attains the optimum temperature range for use.

[0058] In concrete terms, the control device 30 decides upon the temperature of the working oil which has been detected by the temperature detection unit 36. And, during generation of oil pressure by the engine 2, in other words during generation of oil pressure by the mechanical oil pump 22, if it is decided that the oil temperature of the working oil 48 is less than or equal to a second threshold value, then the control device 30 closes the stop valve 34, and limits the amount of circulation between the mechanical operated oil pump 22 and the radiator unit 32. Since, by doing this, the amount of dissipation of heat in the working oil by the radiator unit 32 is decreased, accordingly the oil temperature of the working oil 48 is elevated. For example, this second threshold value may be set to the lower limit permitted temperature of the working oil 48, and, if the oil temperature of the working oil 48 becomes less than this permitted lower limit temperature, then the control device 30 elevates the oil temperature of the working oil 48, thus executing so called warming up operation.

[0059] Fig. 4 is a schematic figure showing the path of the working oil 48 in the oil pressure system 20 during warming up operation.

[0060] During warming up operation, along with the control device 30 closing the stop valve 34 and limiting the amount of circulation between the mechanical oil pump 22 and the radiator unit 32, also the oil pressure which is generated by the mechanical oil pump 22 driven by the engine 2 is supplied to the drive lubrication component 46. [0061] In the following, the control structure of the program which is executed by the control device 30 will be explained. Fig. 5 is a flow chart of the control structure of the program which is executed by the control device 30. The control device 30 executes the flow chart shown in Fig. 5 repeatedly at a predetermined cycle (for example, every 100 msec).

[0062] In Fig. 5, the control device 30 acquires the rotational speed NE of the engine 2 (in a step SlOO). And, based upon this rotational speed NE of the engine 2, the control device 30 decides whether or not the engine 2 is operating (in a step S 102). [0063] If it has decided that the engine 2 is operating (i.e. in the case of NO in the step S 102), then the control device issues a control command for setting the stop valve 34 to "closed" (in a step S 104). And the control device 30 issues a drive command to the driver 28, and operates the pump drive motor 26 (in a step S 106).

[0064] Furthermore, the control device 30 acquires the oil temperature of the working oil 48 from the temperature detection unit 36 (in a step S108), and determines whether or not this oil temperature is greater than or equal to a first threshold value (in a step SIlO). [0065] If the oil temperature of the working oil 48 is greater than or equal to the first threshold value (i.e. in the case of YES in the step SIlO), then the control device 30 starts the engine 2 (in a step S 112). It should be understood that this starting of the engine 2 is implemented by the control device 30 outputting a starting request for the engine 2 to an engine ECU or the like, not shown in the figures. And the control device 30 issues a control command for setting the stop valve 34 to "open" (in a step S114), and thus performs cooling of the working oil 48. Moreover, the control device 30 issues a stop command to the driver 28, and thereby stops the pump drive motor 26 (in a step S116). [0066] After stopping the pump drive motor 26 (after the step S 116), or if the oil temperature of the working oil 48 is not greater than or equal to the first threshold value (i.e. in the case of NO in the step SIlO), then the control device returns to the initial processing.

[0067] If it is decided that the engine is operating (i.e. in the case of YES in the step S102), then the control device 30 issues a drive command to the driver 28, and stops the pump drive motor 26 (in a step S118). And the control device 30 issues a control command for setting the stop valve 34 to "open" (in a step S 120).

[0068] Furthermore, the control device 30 acquires the oil temperature of the working oil 48 from the temperature detection unit 36 (in a step S 122), and determines whether or not this oil temperature is less than or equal to a second threshold value (in a step S 124). [0069] If the temperature of the working oil 48 is less than or equal to the second threshold value (i.e. in the case of YES in the step S 124), then the control device 30 issues a control command for setting the stop valve 34 to "closed" (in a step S 126), and thus performs elevation of the temperature of the working oil 48.

[0070] After having issued the control command for setting the stop valve 34 to "closed" (i.e. after the step S126), or if the oil temperature of the working oil 48 is not less than or equal to the second threshold value (i.e. in the case of NO in the step S124), then the control device returns to the initial processing.

[0071] In this embodiment of the present invention: the pump drive motor 26 may be considered as being an "electric motor"; the mechanical oil pump 22 and the electrically operated oil pump 24 may be considered as being "oil pressure generation units"; the mechanical oil pump 22 may be considered as being a "first oil pump"; the electrically operated oil pump 24 may be considered as being a "second oil pump"; the stop valve 34 may be considered as being a " limitation means "; and the control device 30 may be considered as being a "control unit". And the control device 30 may be considered as including an "oil temperature sensor", a "working oil cooling means", and a "working oil temperature elevation means". [0072] A variant embodiment

In the embodiment described above, an example of the oil pressure system of the present invention was applied to an eco-running vehicle, but it would also be possible to apply the oil pressure system of the present invention to a hybrid vehicle. [0073] Fig. 6 is a schematic structural diagram of a hybrid vehicle 200 which is equipped with an oil pressure system according to a variant embodiment of the present invention. [0074] In this hybrid vehicle 200, instead of the automatic speed change mechanism 4 of the eco-running vehicle shown in Fig. 1, there is provided a power transmission mechanism 4#; and it may be considered that a motor-generator (MG) 3, a power control unit (PCU) 5, and a battery 7 are provided instead of the belt 12, the alternator 14, and the battery 16. And this hybrid vehicle 200 is adapted to be capable of running due to the drive force generated by at least one of the engine 2 and the motor-generator 3. [0075] It may be considered that the drive separation mechanism 9 provided in the power transmission mechanism 4# is a replacement for the drive force engaging element 8 in the automatic speed change mechanism 4 shown in Fig. 1. And the power transmission mechanism #4 mechanically connects together the output shaft of the engine 2, the rotation shaft of the motor-generator 3, and the drive wheels 6, and is capable of transmitting the drive force of at least one of the engine 2 and the motor-generator 3 to the drive wheels 6. [0076] The drive separation mechanism 9, as one example thereof, may consist of a single pinion type planetary gear device which includes three rotation elements: a sun gear, a carrier, and a ring gear. And the sun gear, the carrier, and the ring gear may be respectively linked to the engine 2, to the motor-generator 3, and to the speed change mechanism 10.

[0077] Since the structure of the speed change mechanism 10 is the same as that shown in Fig. 1, the detailed explanation thereof will not be repeated. [0078] The motor-generator 3 is a synchronous electric motor which receives three phase electrical power from the power control unit 5 and creates drive force, and, in particular, it consists of a permanent magnet type synchronous electric motor which is made from a rotor in which permanent magnets are embedded.

[0079] The power control unit 5 receives DC electrical power from the battery 7, and according to a rotational speed command and a torque command and the like which it receives from an ECU not shown in the figure, it generates AC electrical power which it supplies to the motor-generator 3. Furthermore, this power control unit 5 converts AC electrical energy which is supplied from the motor-generator 3 into DC electrical power, which it supplies to the battery 7.

[0080] The battery 7 is adapted, on the one hand, to be capable of accumulating the DC electrical power which is supplied from the power control unit 5, and, on the other hand, to be capable of supplying the electrical energy which it has accumulated to the power control unit 5 and the oil pressure system 20. As an example, this battery 7 may be a nickel hydrogen battery or a lithium ion battery or the like. It should be understood that, in order to correspond to the counterelectromotive voltage which is generated along with the rotation of the motor-generator 3, the battery 7 may generate a high voltage as compared to the battery 16 shown in Fig. 1 (for example, around 300 V). [0081] Since the other structures are the same as in the eco-running vehicle 100 shown in Fig. 1, the detailed explanation thereof will not be repeated here. [0082] With the hybrid vehicle 200 shown in Fig. 6, the proportions of the drive force which are apportioned to the engine 2 and to the motor-generator 3 are selected optimally according to the driving conditions. In concrete terms, during light load conditions such as when starting off from rest, during low speed running, and when descending a gentle slope and the like, in order to avoid the low efficiency combustion region of the engine 2, the engine 2 is stopped, and the hybrid vehicle 200 is propelled only by the drive force from the motor-generator 3 (in the following, this will also be termed "EV running"). During normal running, the engine 2 is started, and the hybrid vehicle 200 is propelled by the drive force of the engine 2. And, during acceleration, the hybrid vehicle 200 is propelled by the drive force from the motor-generator 3, in addition to the drive force of the motor 2. During deceleration and during braking, the kinetic energy of the vehicle is converted into electrical energy by the motor-generator 3, and, along with recovering this energy to the battery 7, the engine is stopped, so that unnecessary consumption of fuel is suppressed. In this manner, with the hybrid vehicle 200, the engine 2 can be intermittently stopped even during running.

[0083] By the way, with a normal hybrid vehicle, in order to enhance the overall combustion efficiency (i.e. the fuel consumption), a motor-generator 3 is provided for performing the task of propulsion during conditions of light load. Due to this, in a parallel type or a parallel/series type hybrid vehicle, a motor-generator 3 is chosen which is of comparatively low output as compared with that of the engine 2. Furthermore, when the engine 2 is stopped, the motor-generator 3 generates drive force by utilizing the electrical energy which has been accumulated in the battery 7 (EV running), but the time period over which it is possible to sustain operation upon the electrical energy which is accumulated in the battery 7 is comparatively short.

[0084] Accordingly even if it is possible, when the engine 2 is stopped, for example, to propel the hybrid vehicle 200 only with the drive force of the motor-generator 3 (EV running), since the drive force which is transmitted to the drive wheels 6 via the power transmission mechanism 4# is comparatively small, accordingly the heat loss per unit time which is generated is also small. Furthermore, since the time period over which it is possible to sustain operation upon the motor-generator 3 when the engine 2 is stopped is comparatively short, accordingly the heat loss amount which is generated in the power transmission mechanism 4# during operation on the motor-generator 3 is also small. [0085] Accordingly, in the same manner as shown in Fig. 2, with the oil pressure system 20 according to this embodiment, when the engine 2 is stopped, both when the vehicle is stationary and during EV running, along with closing the stop valve 34 and limiting the amount of circulation between the electrically operated oil pump 24 and the radiator unit 32, the pump drive motor 26 is operated and the oil pressure which is generated by the electrically operated oil pump 24 is supplied to the drive lubrication component 46.

[0086] Since the oil pressure system 20 according to this embodiment can also be applied to the hybrid vehicle 200, accordingly it is possible to reduce its consumption of electrical power, and to make its oil pump more compact.

[0087] Since the control structure of the program for this variant embodiment of the present invention is the same as that shown in Fig. 5, the detailed explanation thereof will be omitted.

[0088] It should be understood that although, in the variant embodiment of this invention, an example of an oil pressure system 20 which includes a mechanical oil pump 22 and an electrically operated oil pump 24 is shown, it would also be acceptable to employ a structure in which, while the engine is stopped, the mechanical oil pump 22 is driven by the drive force generated by the motor-generator 3. According to this type of structure, by limiting the amount of circulation between the mechanical oil pump 22 and the radiator unit 32 while the engine is stopped, it is possible to reduce the consumption of electrical power, and moreover it is possible to reduce the overall volume which is occupied by the oil pump, since the electrically operated oil pump 24 becomes unnecessary.

[0089] It should be understood that although, in the above described embodiment and variant embodiment of the present invention, examples were shown of structures in which a limitation was imposed upon the amount of circulation of the working oil to the radiator unit 32, as one example of an "engine dependent component", it would also be possible to apply the present invention to various engine dependent components, other than the radiator unit 32. For example, it would also be acceptable to arrange to employ a structure in which a limitation is imposed upon the amount of circulation of the working oil to a component for which lubrication is not required while the engine 2 is stopped, such as a gear or a crank shaft which is included in the engine 2.

[0090] Furthermore although, in the above described embodiment and variant embodiment of the present invention, a structure was explained in which the stop valve 34 was employed which set the flow conduit to the radiator unit 32 to either open or closed, it would also be acceptable to arrange to utilize a structure in which a limitation was imposed upon this flow amount in a plurality of stages, or steplessly. In other words, instead of the stop valve 34, it would also be possible to build the oil pressure system according to the present invention by using a flow adjustment valve or the like. [0091] Moreover, according to the above described embodiment and variant embodiment of the present invention, while the engine is stopped, a limitation is imposed upon the amount of circulation of the working oil to the radiator unit, whose required cooling performance has decreased along with the engine being stopped. By doing this, it is possible to suppress the discharge amount which is requested from the electrically operated oil pump which generates oil pressure while the engine is stopped. Due to this, even in the case of generating oil pressure using the drive force of the electric motor to the same level as the oil pressure generated by the drive force of the engine, it is possible to reduce the drive load upon the. pump drive motor, since the discharge amount of the oil pump is suppressed. Accordingly, it is possible to implement reduction of the electrical power consumption required for oil pressure generation while the engine is stopped, and moreover it is possible, at the same time, to make the electrically operated oil pump more compact.

[0092] Furthermore, according to the above described embodiment and variant embodiment of the present invention, during generation of oil pressure by the electrically operated oil pump, if the oil temperature of the working oil becomes high, the cooling of the working oil is performed by starting of the engine. Accordingly, it is possible to keep the temperature of the working oil at an optimum temperature. [0093] Yet further, according to the above described embodiment and variant embodiment of the present invention, if the oil temperature of the working oil becomes excessively low during generation of oil pressure by the engine, the temperature of the working oil is elevated by restricting the flowing of the working oil into the radiator unit. Accordingly, it is possible to keep the temperature of the working oil at an optimum temperature.

[0094] In the embodiments disclosed herein, all of the features are shown by way of example, and should not be considered as being limitative of the present invention in any way. The scope of the present invention is not defined by the above description and explanation, but only by the scope of the appended Patent Claims; and, moreover, it is intended to include all changes having the same meaning and within the range of the scope of the Patent Claims.

Claims

1. An oil pressure system mounted to a vehicle of which an engine is operated intermittently, characterized by comprising: an electric motor which is driven by electrical power; an oil pressure generation unit which is adapted to be capable of generating oil pressure according to the drive force of at least one of the engine and the electric motor; a distribution unit which distributes a working oil which is discharged from the oil pressure generation unit; a group of hydraulic components connected to the distribution unit, which, with the oil pressure generation unit, constitutes at least a single circulation path for the working oil; a limitation means which limits the circulation amount of the working oil between the oil pressure generation unit and one or more engine dependent components which is a part of the group of hydraulic components whose required operational performance is reduced along with stopping of the engine; and a control unit which, while the engine is stopped, along with limiting the circulation amount of the working oil which circulates between the oil pressure generation unit and the one or more engine dependent components using the limitation means, also operates the electric motor to generate oil pressure.

2. An oil pressure system according to claim 1, wherein the one or more engine dependent components include at least one of a radiator unit for cooling the working oil by heat dissipation, and a component which does not require lubrication when the engine is stopped.

3. An oil pressure system according to claim 2, wherein the control unit includes: an oil temperature sensor which determines the temperature of the working oil; and a working oil cooling means which, during limitation of the circulation amount by the limitation means, when it has been decided that the oil temperature is greater than or equal to a first threshold value, along with mitigating the limitation of the circulation amount by the limitation means, also generates oil pressure by starting the engine.

4. An oil pressure system according to claim 2, wherein the control unit includes: an oil temperature sensor which determines the temperature of the working oil; and a working oil temperature elevation means which, during generation of oil pressure by the engine, when it has been decided that the oil temperature is less than or equal to a second threshold value, limits the circulation amount by the limitation means.

5. An oil pressure system according to any one of claims 1 to 4, wherein the control unit stops the electric motor during operation of the engine.

6. An oil pressure system according to any one of claims 1 to 5, wherein: the vehicle is adapted to be further capable of running due to the drive force which is generated by a motor-generator whose output is low as compared to the engine; and the group of hydraulic components includes, in addition to the one or more engine dependent components, a power transmission mechanism which receives the drive force generated by the engine and the motor-generator and transmits it to the vehicle wheels.

7. An oil pressure system according to any one of claims 1 to 6, wherein the oil pressure generation unit comprises: a first oil pump which is driven by the engine; and a second oil pump which is driven by the electric motor, and whose discharge capability is low, as compared with the first oil pump.

8. An oil pressure system mounted to a vehicle of which an engine is operated intermittently, comprising: an electric motor which is driven by electrical power; an oil pressure generation unit which is adapted to be capable of generating oil pressure according to the drive force of at least one of the engine and the electric motor; a distribution unit which distributes a working oil which is discharged from the oil pressure generation unit; a group of hydraulic components connected to the distribution unit, which, with the oil pressure generation unit, constitutes at least a single circulation path for the working oil; a limitation device which limits the circulation amount of the working oil between the oil pressure generation unit and one or more engine dependent components which is a part of the group of hydraulic components whose required operational performance is reduced along with stopping of the engine; and a control unit which, while the engine is stopped, along with limiting the circulation amount of the working oil which circulates between the oil pressure generation unit and the one or more engine dependent components using the limitation device, also operates the electric motor to generate oil pressure.

9. A control method for an oil pressure system mounted to a vehicle of which an engine is operated intermittently and comprising: an electric motor which is driven by electrical power; an oil pressure generation unit which is adapted to be capable of generating oil pressure according to the drive force of at least one of the engine and the electric motor; a distribution unit which distributes the working oil which is discharged from the oil pressure generation unit; and a group of hydraulic components connected to the distribution unit, which, with the oil pressure generation unit, constitutes at least a single circulation path for the working oil, and which includes at least one engine dependent component, the required operational performance of which is reduced along with stopping of the engine; the control method comprising: a step of detecting the operational state of the engine; and a step of, if the engine is stopped, along with limiting the circulation amount of the working oil which circulates between the oil pressure generation unit and the engine dependent component, also operating the electric motor to generate oil pressure.

10. A control method for an oil pressure system according to claim 9, further comprising: a step of deciding upon the temperature of the working oil; and a step of, during limitation of the circulation amount of the working oil, if it is decided that the oil temperature is greater than or equal to a first threshold value, along with mitigating the limitation of the circulation amount, also generating oil pressure by starting the engine.

11. A control method for an oil pressure system according to claim 9, further comprising: a step of deciding upon the temperature of the working oil; and a step of, during generation of oil pressure by the engine, if it is decided that the oil temperature is less than or equal to a second threshold value, limiting the circulation amount.