JPH0539049A - Hydraulic transmission device for vehicle - Google Patents

Abstract

PURPOSE:To reduce the energy consumption of a hydraulic transmission device in which the working oil feeding sources for a hydraulic motor for a cooling fan and power steering device are integrated. CONSTITUTION:A cooling fan device 24 and a power steering device 20 are connected in series with a working oil feeding source 34 including a main pump 16 having a discharge flow rate of Qm and a subpump 17. The supply flow rate Qt of the working oil feeding source is set to the higher value between the flow rate Qfan passing through the hydraulic motor of the cooling fan device 24 and the necessary flow rate Qs of the power steering device, and when the number of revolution of the pump is lower than a prescribed value, a flow rate control valve 27 is controlled so that the flow rate Qsb supplied from the subpump becomes Qt-Qm, while if the number of revolution of the pump exceeds a prescribed value, the flow rate control valve is controlled so that the flow rate Qsb becomes 0.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydraulic drive system for a vehicle, and more particularly to a hydraulic drive system for driving an engine hydraulic drive cooling fan system and a power steering system.

[0002]

2. Description of the Related Art As one of hydraulic drive systems for vehicles such as automobiles, a pump which is rotationally driven by an engine, as described in, for example, JP-A-61-215417,
A hydraulic oil supply source including a reservoir, a hydraulic oil supply passage for supplying high-pressure hydraulic oil from the hydraulic oil supply source, and a rotational speed according to the differential pressure ΔP before and after the hydraulic oil supply passage provided in the middle of the hydraulic oil supply passage. A hydraulic motor that rotationally drives the engine cooling fan;
A bypass passage bypassing the hydraulic motor, a differential pressure control means provided in the middle of the bypass passage for controlling the differential pressure ΔP, a hydraulic oil return passage for returning hydraulic oil to a hydraulic oil supply source, a hydraulic oil supply passage, and a hydraulic oil. For a vehicle having a power steering device provided between the return passage and a hydraulic motor for a cooling fan and a power steering device driven by high-pressure hydraulic oil from one hydraulic oil supply source. Hydraulic drives have been known for some time.

According to such a hydraulic drive system, since the hydraulic motor for the cooling fan and the hydraulic oil supply source for the power steering device are integrated, when the hydraulic motor and the power steering device are respectively provided with hydraulic oil supply sources. In comparison, the number of parts such as a pump can be reduced, and fuel consumption can be improved.

[0004]

As is well known, the flow rate of hydraulic oil required to drive a power steering device is generally large in the low vehicle speed range, and the engine speed is generally low in the low vehicle speed range. Therefore, since the rotational speed of the pump rotationally driven by the engine is low and the supply flow rate thereof is also low, the pump is required to have a sufficient supply flow rate even in the low rotation range. Therefore, in the conventional hydraulic drive device described in the above-mentioned publication, the pump supplies more hydraulic oil than necessary in a high rotation range, and energy is wasted. is there.

In view of the above problems in the conventional hydraulic drive system in which the hydraulic motor for the cooling fan and the hydraulic oil supply source for the power steering system are integrated, the present invention can reduce energy consumption. An object is to provide an improved hydraulic drive system.

[0006]

According to the present invention, the above objects include main pump means for supplying high-pressure hydraulic oil at a flow rate Qm and a sub-pump for supplying high-pressure hydraulic oil at a flow rate Qsb. The engine has a hydraulic oil supply source, a hydraulic oil supply passage for supplying hydraulic oil at a flow rate Qt from the hydraulic oil supply source, an engine provided at a midway of the hydraulic oil supply passage, and at a rotational speed corresponding to the differential pressure ΔP before and after the engine. Motor for rotatably driving the cooling fan for use, a bypass passage bypassing the hydraulic motor, a differential pressure control means provided in the middle of the bypass passage for controlling the differential pressure ΔP, and a hydraulic oil for the hydraulic oil supply source. Hydraulic oil return passage, a power steering device provided between the hydraulic oil supply passage and the hydraulic oil return passage, and the hydraulic oil supply passage between the hydraulic motor and the power steering device. Pressure detecting means for detecting the pressure Ps of the main pump means, means for detecting the rotational speed Np of the main pump means, and a control device for controlling the sub-pump means and the differential pressure control means. The maximum allowable supply pressure Pp of the oil supply source and the supply flow rate Qm of the main pump means and the flow rate Qs of the hydraulic oil necessary for the power steering device, which are parameters of the rotation speed N, are stored, and ΔP is Pp-Ps. While controlling the differential pressure control means so that the hydraulic oil supply flow rate Qt of the hydraulic oil supply source is the larger of the flow rate Qfan and the flow rate Qs of the hydraulic oil passing through the hydraulic motor determined by ΔP. When the rotational speed N is below a predetermined value, the sub-pump means is controlled so that the flow rate Qsb becomes Qt-Qm, and when the rotational speed N exceeds a predetermined value. Is achieved by a vehicle hydraulic drive system configured to control the sub-pump means so that the flow rate Qsb becomes zero.

[0007]

According to the above construction, the hydraulic oil supply source includes the main pump means for supplying the high pressure hydraulic oil at the flow rate Qm and the sub-pump for supplying the high pressure hydraulic oil at the flow rate Qsb. And the control device for controlling the differential pressure control means is a supply flow rate Qm of the main pump means with the maximum allowable supply pressure Pp of the hydraulic oil supply source and the rotational speed N as parameters.
And the flow rate Qs of hydraulic oil required for the power steering device
Is stored, the differential pressure control means is controlled so that ΔP becomes Pp−Ps, and the flow rate Qfan and the flow rate Qs of the hydraulic oil passing through the hydraulic motor that determines the hydraulic oil supply flow rate Qt of the hydraulic oil supply source are determined by ΔP. Whichever is larger, the flow rate Qsb is calculated when the rotational speed N is less than or equal to a predetermined value.
Is controlled to be Qt-Qm, and the flow rate Qsb is controlled to 0 when the rotational speed N exceeds a predetermined value.

Therefore, the sub-pump means is controlled so that the supply flow rate Qsb becomes the minimum flow rate Qt-Qm required to operate the hydraulic motor and the power steering device when the rotation speed N is less than a predetermined value. The energy consumed by the means is suppressed to a minimum, and the flow rate Qsb is controlled to be 0 when the rotation speed N exceeds a predetermined value, thereby avoiding wasteful consumption of energy by the sub-pump means. It

Further, according to the above-described structure, the differential pressure control means determines that the differential pressure ΔP before and after the hydraulic motor is the maximum allowable supply pressure Pp of the hydraulic oil supply source and the working pressure P of the power steering device.
The hydraulic motor is controlled so that it becomes a difference from s
It will not be operated with a pressure difference above -Ps, thus avoiding an excessive burden on the main pump means and the sub-pump means.

[0010]

Embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

FIG. 1 is a schematic configuration diagram showing one embodiment of a hydraulic drive system according to the present invention. In FIG. 1, reference numeral 10 indicates a reservoir that stores hydraulic oil. One end of the suction passage 12 and one end of the hydraulic oil return passage 14 are connected to the reservoir 10. The other end of the suction passage 12 is connected to the suction side of a main pump 16 and a sub pump 17 driven by an engine (not shown). One end of a hydraulic oil supply passage 18 for supplying high-pressure hydraulic oil is connected to the discharge side of the main pump 16, and the other ends of the hydraulic oil supply passage and the hydraulic oil return passage 14 have power of a structure known per se. It is connected to a steering (PS) device 20.
One end of a sub supply passage 19 for supplying high-pressure hydraulic oil is connected to the discharge side of the sub pump 17, and the other end of the sub supply passage is connected to the hydraulic oil supply passage 18.

A flow control (FC) valve 22 and a cooling fan device 2 are provided in the middle of the hydraulic oil supply passage 18 when viewed from the upstream side thereof.
4. A flow rate control (FC) valve 26 is sequentially provided in series. The flow control valve 22 includes a pump 16 and a hydraulic oil supply passage 18.
Is provided between the sub supply passage 19 and a portion to which the other end is connected. The flow rate control valve 22 is a flow priority valve, and supplies the hydraulic fluid of the flow rate Qm out of the hydraulic fluid of the flow rate Qmo supplied thereto to the hydraulic fluid supply passage 18 on the downstream side according to the pattern shown in FIG. The remaining amount of hydraulic fluid (Qmo-Qm) is returned to the suction passage 12 via the passage 21.

An electromagnetic flow control valve 27 and a check valve 28 are provided in the middle of the sub supply passage 19. The flow rate control valve 27 responds to the control current Is input to its solenoid, and the flow rate Qso of the hydraulic fluid of the flow rate Qso supplied to it.
The hydraulic oil of sb is supplied to the sub-supply passage 19 on the downstream side according to the pattern shown in FIG. 3, and the remaining flow rate (Qso
The hydraulic fluid (-Qsb) is returned to the suction passage 12 via the passage 31, and thereby the flow rate Qsb is controlled between the solid line and the broken line shown in FIG. The check valve 28 prevents the hydraulic oil in the hydraulic oil supply passage 18 from flowing back to the flow control valve 27.

Further, the hydraulic oil supply passage 18 is provided between the cooling fan device 24 and the portion to which the other end of the sub supply passage 19 is connected.
A relief passage 32 having a relief valve 30 in the middle is connected between the passage 31 and the passage 31, whereby the pressure of the hydraulic oil supplied from the main pump 16 and the sub pump 17 to the cooling fan device 24 reaches a predetermined maximum value. It is maintained below.

Thus, the reservoir 10 and the main pump 1
6, the sub-pump 17, the relief valve 30 and the like, the cooling fan device 24 at a flow rate Qt of high-pressure hydraulic oil below a predetermined maximum value
And a hydraulic oil supply source 34 for supplying the hydraulic oil to the above. In this case, the flow rate Qt is the sum of the flow rate Qm and the flow rate Qsb, the flow rate Qm is controlled as shown in FIG. 2, and the flow rate Qsb is controlled between the solid line and the broken line in FIG. Is controlled between the solid line and the broken line shown in FIG. 5 according to the control current Is supplied to the flow control valve 27.

The cooling fan device 24 is provided with a fan 36 and a hydraulic motor 38 provided in the middle of the hydraulic oil supply passage 18 for rotating the fan 36 at a rotational speed corresponding to the differential pressure ΔP between the front and rear.
A bypass passage 40 that connects the upstream and downstream hydraulic oil supply passages of the hydraulic motor to each other, and an electromagnetic differential pressure control valve 42 provided in the middle of the bypass passage. The differential pressure control valve 42 has a solenoid 44. If the control current supplied from the electronic control unit 70 to the solenoid is If and the flow rate of the hydraulic oil passing through the hydraulic motor 38 is Qfan, the flow rate Qbp (= Qt). -Qfan) is introduced to the downstream side of the hydraulic motor 38 via the bypass passage 40, whereby the differential pressure ΔP across the hydraulic motor 38 is controlled in proportion to the control current If.

Assuming that the rotation speed of the hydraulic motor 38 is Nfan, there is a relationship of Nfan = Kq.multidot.Qfan = Kp.multidot. (. DELTA.P) ^1/2 , where Kq and Kp are proportional constants. Therefore, the differential pressure control valve 42 controls the control current. By controlling the flow rate Qfan in accordance with If, the rotational speed Nfan is controlled to a value proportional to one half of the control current If, as shown in FIG.

The flow rate control valve 26 is a flow priority valve, and supplies the hydraulic fluid of the flow rate Qs out of the hydraulic fluid of the flow rate Qt supplied to the power steering device 20 according to the pattern shown in FIG. Qr
The hydraulic oil (= Qt-Qs) is introduced into the passage 46. The other end of the passage 46 is connected to the hydraulic oil return passage 14.

The hydraulic oil supply passage 18 between the cooling fan device 24 and the flow control valve 26 is provided with a pressure sensor 54 for detecting the pressure Ps of the hydraulic oil in the passage. An engine (not shown) is provided with a rotation speed sensor 56 that indirectly detects the rotation speed N of the pump 16 by detecting the rotation speed of the engine.

The flow control valve 27 and the differential pressure control valve 42 are controlled by the electronic control unit 70. The electronic control unit 70 includes a microcomputer 72 as shown in FIG. The microcomputer 72 may have a general structure as shown in FIG. 8, and includes a central processing unit (CPU) 74, a read only memory (ROM) 76, and a random access memory (R).
AM) 78, an input port device 80, and an output port device 82, which are connected to each other by a bidirectional common bus 84.

In the illustrated embodiment, the input port device 8
At 0, a signal indicating the pressure Ps from the pressure sensor 54, a signal indicating the rotation speed N of the pump 16 from the rotation speed sensor 56, a signal indicating whether the air conditioner is operating from the air conditioner 58, and a throttle opening from the throttle opening sensor 60. A signal indicating the opening degree and a signal indicating the engine cooling water temperature T from the water temperature sensor 62 are input.

The input port device 80 appropriately processes the signal input thereto, and in accordance with the instruction of the CPU 74 based on the program stored in the ROM 76, the CPU and the RAM.
The processed signal is output to 78. R
OM76 is the control program shown in FIG. 9, FIG. 2 and FIG.
0 to the map corresponding to the graph shown in FIG. 17, and the flow rate Q of the hydraulic oil passing through the power steering device 20.
remember s The CPU 74 is adapted to perform various calculations and signal processing as described later based on the control program shown in FIG. The output port device 82 is the CPU 7
According to the instruction No. 4, a control signal is output to the solenoid 44 of the differential pressure control valve 42 via the drive circuit 86, and a control signal is output to the solenoid of the flow rate control valve 27 via the drive circuit 88.

Next, the operation of the illustrated embodiment will be described with reference to the flow chart shown in FIG.

First, in the first step 10, a signal indicating the pressure Ps from the pressure sensor 54, a signal indicating the rotation speed N of the pump 16 from the rotation speed sensor 56, and whether or not the air conditioner 58 is operating the air conditioner. The signal indicating the throttle opening, the signal indicating the throttle opening from the throttle opening sensor 60, and the signal indicating the engine cooling water temperature T from the water temperature sensor 62 are read, and then the process proceeds to step 20.

In step 20, it is judged whether or not the air conditioner 58 is operating, and when it is judged that the air conditioner is operating, the process proceeds to step 60, in which the air conditioner is not operated. If it is determined that there is not, the process proceeds to step 30.

In step 30, it is judged whether or not the engine is in the idle state based on the signal from the throttle opening sensor 60. If it is judged that the engine is in the idle state, the step is carried out. When it is determined that the vehicle is not in the idle state, the process proceeds to step 50.

In step 40, the control amount K1 is calculated from the map corresponding to the graph shown in FIG. 10. Similarly, in step 50, the control amount K1 is calculated from the map corresponding to the graph shown in FIG. K1 is calculated.

In step 60, it is judged whether or not the engine is in the idle state, and when it is judged that the engine is in the idle state, step 80
If it is determined that the vehicle is not in the idle state, the process proceeds to step 70.

At step 70, the control amount K1 is calculated from the map corresponding to the graph shown in FIG. 12, and similarly at step 80, the control amount K1 is calculated from the map corresponding to the graph shown in FIG. K1 is calculated.

Thus, steps 40, 50, 70, 80
In this case, the control amount K1 is calculated based on whether the air conditioner is operating, whether the engine is in the idle state, and the cooling water temperature of the engine.

In step 90, the control amount K2 based on the rotational speed N of the pump 16 is calculated based on the map corresponding to the graph shown in FIG. 14, and in step 100, the control amount K2 is calculated.
The control amount K3 based on the pressure Ps is calculated based on the map corresponding to the graph shown in FIG. 5, and then in step 110, the difference K4 (= K2-K3) between these control amounts is calculated.

The pattern of the graph of FIG.
It is a pattern that is set so as not to give an excessive load to.

In the next step 120, the control amount K4
Is determined to be negative, and if it is determined that K4 <0, then K4 is 0 in step 130.
Is set to step 140, the process proceeds to step 140, and when it is determined that K4 <0 is not satisfied, step 140 is directly executed.
Go to.

In step 140, the controlled variable K1 is K
It is determined whether or not 4 or less, and when it is determined that K1 ≤ K4 is not satisfied, the routine proceeds to step 160,
If it is determined that K1≤K4, the routine proceeds to step 150.

In step 150, the cooling fan device 2
The control current If supplied to the solenoid 44 of the differential pressure control valve 42 of No. 4 is set to K1. In step 160, the control current If is set to the control amount K4, and the next step 17
At 0, the control current If is output to the solenoid 44,
After that, the process proceeds to step 180.

In step 180, the flow rate Qfan of the hydraulic oil corresponding to the control current If is calculated based on the map corresponding to the graph shown in FIG. 16, and then step 19 is executed.
Go to 0.

In step 190, step 180
It is determined whether or not the calculated flow rate Qfan is less than or equal to the flow rate Qs of the hydraulic oil passing through the power steering device 20, and when it is determined that Qfan ≤Qs is not satisfied, the routine proceeds to step 210. , Qfan ≦ Qs, the routine proceeds to step 200.

In step 200, the hydraulic oil supply flow rate Q
t is set to Qs, and in step 210 the flow rate Qt
Is set to Qfan.

In step 220, the flow rate Qm of the hydraulic oil supplied from the main pump 16 through the flow rate control valve 22 is calculated based on the map corresponding to the graph shown in FIG. 2, and in step 230. The flow rate Qsb of the hydraulic oil to be supplied from the sub pump 17 via the flow control valve 27 Qsb = (Q
t-Qm) is calculated.

In step 240, it is judged whether or not the number of revolutions N of the pumps 16 and 17 exceeds the reference value N ₄ , and if it is judged that N> N ₄ is not satisfied, the step is carried out. When it is determined that N> N ₄ is performed, the process proceeds to step 260.

In step 250, the control current Is supplied to the flow control valve 27 is set to 0, and step 26
At 0, the control current Is is calculated based on the map corresponding to the graph shown in FIG. 17, and at the next step 270, the control current Is is output to the flow control valve 27, and then to step 10. Return.

Thus, according to this embodiment, step 9
At 0, the control amount K2 corresponding to the maximum pressure Pp of the hydraulic oil that can be supplied by the hydraulic oil supply source 34 is calculated without receiving an excessive load on the pump, and it is consumed by the power steering device 20 in step 100. The control amount K3 corresponding to the pressure Ps is calculated, and the difference between these two control amounts K2 and K3 is calculated in step 110 to control the differential pressure ΔP for operating the cooling fan device 24. The quantity K4 is calculated.

Further, in steps 20 to 80, based on the information on whether the air conditioner is operating, whether the engine is in the idle state, and the cooling water temperature T of the engine,
A control amount K1 corresponding to the differential pressure ΔP for optimally cooling the engine is calculated according to the operating state of the engine.

Then, in steps 140 to 170, K
When 1≤K4, the control current If corresponding to K5 is output to the differential pressure control valve 42, so that the engine is optimally cooled according to its operating state, and when K1> K4, K
By outputting the control current If corresponding to 4 to the differential pressure control valve, reliable operation of the power steering device is ensured and the engine is cooled as effectively as possible without imposing an excessive load on the pump and the like.

Further, in step 180, the hydraulic motor passage flow rate Qfan corresponding to the differential pressure ΔP is calculated, and step 1
90 to 270, the supply flow rate Qt of the hydraulic oil supply source 34 is calculated to be the larger one of the hydraulic motor passing flow rate Qfan and the flow rate Qs passing through the power steering device 20, and the rotation of the pumps 16 and 17 is calculated. When the number N does not exceed the reference value N ₄ , the flow rate Qsb of the hydraulic oil to be supplied from the sub pump 17 via the flow rate control valve 27 is Qt.
-Qm, the flow rate control valve 27 is controlled according to the flow rate Qsb, so that both the cooling fan device 24 and the power steering device are reliably operated, and the energy consumed by the sub-pump 17 is minimized. The flow rate Qsb is controlled to be 0 when the rotation speed N exceeds the reference value N ₄ , thereby avoiding wasteful consumption of energy by the sub-pump.

Although the present invention has been described above in detail with reference to specific embodiments, the present invention is not limited to such embodiments, and various other embodiments are also possible within the scope of the present invention. It will be apparent to those skilled in the art that it is possible.

[0047]

As is apparent from the above description, according to the present invention, the supply flow rate Qsb of the sub-pump means is the minimum necessary to operate the hydraulic motor and the power steering device when the rotation speed N is less than or equal to a predetermined value. Limit flow rate Qt-
Since it is controlled to become Qm, both the cooling fan and the power steering device can be operated reliably, and the energy consumed by the sub-pump means can be suppressed to a minimum, and the rotation speed N is a predetermined value. When it exceeds, the flow rate Qsb is controlled to be 0, so that it is possible to prevent wasteful consumption of energy by the sub-pump means.

Further, according to the present invention, the differential pressure control means is controlled so that the differential pressure ΔP before and after the hydraulic motor becomes a difference between the maximum allowable supply pressure Pp of the hydraulic oil supply source and the working pressure Ps of the power steering device. Therefore, the hydraulic motor is not operated at a pressure difference of Pp-Ps or more, and therefore it is possible to prevent the main pump means and the sub-pump means from being overloaded.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing one embodiment of a hydraulic drive system according to the present invention.

FIG. 2 is a graph showing the relationship between the rotation speed N of the main pump and the supply flow rate Qm of the main pump.

FIG. 3 is a graph showing a relationship between a control current Is supplied to a flow rate control valve of a sub pump and a supply flow rate Qs of a sub pump.

FIG. 4 is a graph showing the relationship between the rotation speed N of the sub pump and the supply flow rate Qsb of the sub pump.

FIG. 5 is a rotational speed N of a pump and a supply flow rate Q of a hydraulic oil supply source.
It is a graph which shows the relationship with m.

FIG. 6 is a graph showing the relationship between the control current If supplied to the differential pressure control valve of the cooling fan device and the rotational speed Nf of the hydraulic pump and the fan.

FIG. 7 is a graph showing a relationship between a supply flow rate Qt of a hydraulic oil supply source and a flow rate Qs to a power steering device.

8 is a block diagram showing an electronic control device for controlling the differential pressure control valve of the cooling fan device shown in FIG. 1. FIG.

9 is a flowchart showing the control achieved by the electronic control device shown in FIG.

FIG. 10 is a graph showing a relationship between a cooling water temperature T of the engine and a control amount K1 when the air conditioner is not operated and the engine is not in an idle state.

FIG. 11 is a graph showing the relationship between the engine coolant temperature T and the controlled variable K1 when the air conditioner is not operating and the engine is in the idle state.

FIG. 12 is a graph showing the relationship between the engine coolant temperature T and the controlled variable K1 when the air conditioner is operating and the engine is not in the idle state.

FIG. 13 is a graph showing the relationship between the engine cooling water temperature T and the controlled variable K1 when the air conditioner is operating and the engine is in the idle state.

FIG. 14 is a graph showing the relationship between the rotational speed N of the pump and the control amount K2.

FIG. 15 is a graph showing the relationship between the pressure Ps in the hydraulic oil supply passage between the cooling fan device and the power steering device and the control amount K3.

FIG. 16 is a graph showing the relationship between the control current If supplied to the differential pressure control valve of the cooling fan device and the flow rate Qfan supplied to the hydraulic pump.

FIG. 17 is a graph showing the relationship between the flow rate Qs to the power steering device and the control current Is supplied to the flow rate control valve of the sub pump.

[Explanation of symbols]

 10 ... Reservoir 14 ... Hydraulic oil return passage 16 ... Main pump 17 ... Main pump 18 ... Operating oil supply passage 20 ... Power steering device 24 ... Cooling fan device 27 ... Flow control valve 34 ... Hydraulic oil supply source 42 ... Differential pressure control valve 54 ... Pressure sensor 70 ... Electronic control device

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Claims (1)

[Claims] 1. A hydraulic oil supply source including a main pump means for supplying high-pressure hydraulic oil at a flow rate Qm and a sub-pump for supplying high-pressure hydraulic oil at a flow rate Qsb, and a flow rate Qt from the hydraulic oil supply source. A hydraulic oil supply passage for supplying hydraulic oil, a hydraulic motor provided in the middle of the hydraulic oil supply passage for rotating and driving an engine cooling fan at a rotational speed according to a differential pressure ΔP before and after, and bypassing the hydraulic motor. Bypass passage, a differential pressure control means provided in the middle of the bypass passage for controlling the differential pressure ΔP, a hydraulic oil return passage for returning hydraulic oil to the hydraulic oil supply source, the hydraulic oil supply passage and the operation. A power steering device provided between the oil return passage, pressure detecting means for detecting a pressure Ps in the hydraulic oil supply passage between the hydraulic motor and the power steering device, and the main port. Means for detecting the rotation speed N of the pump means and a control device for controlling the sub-pump means and the differential pressure control means. The control device has a maximum allowable supply pressure Pp and a rotation speed N of the hydraulic oil supply source. The flow rate Qm supplied to the main pump means and the flow rate Qs of hydraulic oil required for the power steering device are stored as parameters, and the differential pressure control means is controlled so that ΔP becomes Pp-Ps. The hydraulic oil supply flow rate Qt of the hydraulic oil supply source is calculated to be the larger of the flow rate Qfan and the flow rate Qs of the hydraulic oil passing through the hydraulic motor determined by ΔP, and the rotational speed N is equal to or less than a predetermined value. The sub-pump means is controlled so that the flow rate Qsb becomes Qt-Qm, and the sub-pump means is controlled so that the flow rate Qsb becomes 0 when the rotation speed N exceeds a predetermined value. Gosuru As configured vehicular hydraulic drive system.