JPS63176734A - Four-wheel-drive device - Google Patents

Abstract

PURPOSE:To improve assembling freedom by allowing one of engine output shafts to freely drive one of driving wheels through a transmission, coupling a hydraulic pump to the other engine output shaft, and coupling the other engine output shaft to a hydraulic motor for driving the same, through a check valve or the like. CONSTITUTION:One output shaft 1a of an engine 1 drives one driving wheels 1g, 1h through a transmission 1b, a drive shaft 1c, a differential gear 1e and a drive shaft 1f. The other output shaft 2a of the engine 1 drives a hydraulic pump 2 and coupled to a hydraulic motor 3 through hydraulic conduits 6, 7. The hydraulic motor 3 drives the other driving wheels 3d, 3e through a drive shaft 3a, a differential gear 3b and a drive shaft 3c. A check valve, a release valve, etc. are arranged between the hydraulic pump 2 and the hydraulic motor 3. Since a propeller shaft is not required when a four wheel drive transmission is assembled in the body, assembling freedom can be improved.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a four-wheel drive device.

[Prior Art] Conventionally, four-wheel drive systems for automobiles are capable of driving all four wheels, so they not only effectively exert their driving or braking force when driving on slippery roads, but also It is also useful for steering stability when turning, and has attracted particular attention in recent years.

The configuration of these four-wheel drive devices is that output power from the engine mechanically drives the front wheels or rear wheels on the one hand via a transmission, and on the other hand rotates the rear wheels or front wheels. It is configured to be driven.

[Problems to be Solved by the Invention] However, as mentioned above, in these four-wheel drive devices, both the front wheels and the rear wheels are mechanically driven via the drive shaft. The configuration of the mechanical drive path has become extremely complex.

Moreover, the complicated configuration of the drive path itself imposes various constraints on the design of the chassis, etc., resulting in a lack of flexibility in the design. A tunnel structure is required for this purpose, and the floor structure inside the vehicle cannot be made into a uniform flat structure.

An object of the present invention is to provide a four-wheel drive device that eliminates the above-mentioned drawbacks and has increased design flexibility.

[Means for solving problems] The present invention has the following configuration.

An output shaft of an engine in an automobile drives drive wheels via a transmission, and a hydraulic pump is interlocked with any drive system from the output shaft of the engine to the drive wheels, and the hydraulic pump includes: A hydraulic motor is interlocked via a hydraulic pipe, and the hydraulic motor is interlocked with the B17 wheel. Between the discharge pipe side of the hydraulic pump and the discharge pipe side of the hydraulic motor, there is a: When the amount of pressure oil discharged in the hydraulic motor is larger than the amount of pressure oil discharged, the discharge pipe side of the hydraulic motor and the discharge pipe side of the hydraulic pump are communicated, and b = conversely, When the hot water discharged from the hydraulic pump is larger than the amount of pressure oil discharged from the hydraulic motor, the communication is closed.

[Function] The power from the engine drives the drive wheels from its output shaft through the transmission, and at the same time the hydraulic pump is also driven by the engine, and as a result, the pressure oil discharged from the hydraulic pump flows through the hydraulic pipe. The engine drives the hydraulic motor, which in turn drives the wheels, and eventually the engine also drives the driving wheels and the wheels that are linked to the hydraulic motor.

In the above drive, a: If the tire of the wheel that is linked to the hydraulic motor is worn out or has a lower air pressure than the drive wheel, and the diameter of that wheel is smaller than the diameter of the drive wheel, b: Or, the hydraulic motor If the side of the wheel that is interlocked with the hydraulic motor is interlocked with the steering wheel and the steering wheel is operated beyond a predetermined steering angle, the wheel that is interlocked with the hydraulic motor rotates faster than the drive wheel.

This means that the hydraulic motor that is linked to that wheel will rotate faster than the normally rotating hydraulic pump (when the drive wheel and wheels are not slipping on the road surface). As a result, the pressure oil discharge 1f discharged by the hydraulic motor is lower than the discharge flow stitch in which the hydraulic pump discharges pressure oil.
t u increases.

However, in this case, there is a difference between the discharge pipe side of the hydraulic pump and the discharge pipe side of the hydraulic motor. When the amount increases, the discharge pipe side of the hydraulic motor is communicated with the discharge pipe side of the hydraulic pump.

b: Conversely, when the amount of pressure oil discharged from the hydraulic pump is greater than the amount of pressure oil discharged from the hydraulic motor, the communication is closed. When the pressure oil flow portion on the side increases, the increase causes the pressure oil to communicate from the discharge pipe side of the hydraulic motor to the discharge pipe side of the hydraulic pump, and the hydraulic motor rotates freely.

Therefore, as the hydraulic motor rotates faster in this way, the hydraulic motor causes the pressure pump to rotate faster,
This prevents the rotational circumferential speeds of the front and rear wheels of an automobile from becoming inconsistent.

In addition, even when the hydraulic motor is rotating rapidly as described above, the drive wheels that the hydraulic pump is linked to will slip on the road surface due to engine drive, and this will cause the hydraulic motor to When the rotational speed of the hydraulic pump becomes higher than the rotational speed, the following effects occur.

When the rotation speed of the hydraulic pump side rotates faster than the speed of the hydraulic motor side, the amount of pressure oil discharged to the discharge pipe side of the hydraulic pump increases, and as a result, the amount of pressure oil discharged to the discharge pipe side of the hydraulic pump increases. The hydraulic pressure becomes high, - the communication between the discharge pipe side of the hydraulic motor and the discharge pipe side of the hydraulic pump is closed, and the pressure oil discharged from the hydraulic pump directly drives the hydraulic motor, It is in a four-wheel drive state, including not only the drive wheels but also one wheel linked to the hydraulic motor.

[Example code] Hereinafter, the present invention will be explained based on examples.

FIG. 1 shows a system diagram of a four-wheel drive system as an embodiment of the present invention, in which the output shaft 1a of the engine 1 is connected to the gear shift e! 1b, drive shaft 1c, final gear reducer 1e (hereinafter referred to as differential 1e), and drive shaft i
The configuration is such that drive wheels 1g and 1h are driven via f.

Here, the transmission 1b may be any transmission such as a gear transmission, a turbo torque converter, or a continuously variable transmission.In short, the output shaft 1a is connected to the drive shaft 1c via the transmission 1b. Any configuration is sufficient as long as it transmits power to.

The drive shaft 2a of the hydraulic pump 2 is linked to the drive shaft 1c. Hydraulic pipes 6 and 7 are interposed between the hydraulic pump 2 and the hydraulic motor 3, and the hydraulic motor 3 is connected to the drive shaft i3a, the final It is configured to drive drive wheels 3d and 3e via a gear reduction gear 3b (hereinafter referred to as a differential 3b) and a drive shaft 3C.

Between the branch line 4c in the hydraulic line 6 and the branch line 4d in the hydraulic line 7, check valves 4a, 4b, 4g, and 41, a relief valve 4f, and a hydraulic source 4 are used to supply known pressure oil. A supercharging and relief arrangement is provided.

Branch pipe 5c of hydraulic pipe 6 and branch pipe 5 of hydraulic pipe 7
A switching button t5 is interposed between the pipe 4e and the pipe 4e.

In the configuration of the embodiment of the present invention, its operation will be explained below.

In a two-wheel drive in which only the driving wheels 1g and ih are driven by the engine 1 and the wheels 3d8 and 3e are not driven, the displacement volume of the hydraulic pump 2 and the hydraulic motor 3 is set to zero.

On the other hand, as explained below, the engine 1 is connected to the wheel 3.
When using four-wheel drive that also drives d and 3e, set the displacement of hydraulic pump 2 and hydraulic motor 3 to their maximum values. automatic 1
1ξ is being driven in the forward direction, the current to the solenoid 5a is cut off, and the switching position of the switching valve 5 is set to 5A by an internal spring.

Power from engine 1 is transferred to its output shaft 1a, transmission lb
, the drive wheels 1g and 1h are driven through the drive shaft 1c, the differential 1e, and the drive shaft 1f, and at the same time the hydraulic pump 2 is driven by the drive+blc, and as a result, the pressure oil discharged from the hydraulic pump 2 flows through the hydraulic pipe 6. The hydraulic motor 3 drives the wheels 3d and 3e via the drive shaft 3a, the differential 3b and the drive shaft 3c, and the pressure oil that has completed its work in the hydraulic motor 3 is transferred to the hydraulic pipe. It returns to the inlet of the hydraulic pump 2 via line 7.

In the hydraulic action, the pressure oil discharged from the hydraulic pump 2;
11 is in a relationship such that the amount is sufficient to drive the hydraulic motor 3 even when the drive wheels 1g and 1h are not slipping on the road surface, so the hydraulic conduit 6
The oil pressure at is closing the check valve 4a.

In addition, in the above action, when the oil pressure in the hydraulic line 6 becomes abnormally high, the oil pressure pushes open the check valve 4g via the branch line 4c, and opens the line 4h and the relief valve 4f. When the oil pressure in the oil pressure line 7 drops below the boost pressure of, for example, 3 atmospheres, the pressure oil from the oil pressure source 4 is relieved from the oil pressure source 4 through the pipe line 4e. Pipe line 4e, check valve 4b and branch pipe line 4d
On the other hand, during reverse operation, which will be described later, the pressure on the hydraulic pipe line 7 side becomes high, and the hydraulic pipe line 6 is supercharged.
When the pressure on the hydraulic line 7 becomes low or abnormal pressure occurs in the hydraulic line 7, the pressure oil in the hydraulic line 7 flows through the branch line 4d and the check valve 4.
1 and the relief valve 4f, and the supercharging to the hydraulic line 6 side is such that the pressure oil from the hydraulic source 4 is relieved through the line 4e and the relief valve 4f.
, the hydraulic line 6 via the check valve 4a and the branch line 4c.
This "rewriting" action is a known action.

In the above drive, a: The outer diameters of the tires of the wheels 3d and 3e that are linked to the hydraulic motor 3 are worn out compared to those of the drive wheels 1g and 1h, or as a result of their air pressure being lower, the wheels 3d and 3e
is smaller than the diameter of the driving wheels 1g and lh, b = or when the wheels 3d and 3e are interlocked with the steering and the steering is operated to a predetermined steering angle or more.

Wheels 3d and 3e rotate further than drive wheels 1g and 1h.

This means that the hydraulic motor 3 that is linked to the wheels 3d and 3e rotates faster than the rotational speed of the normally rotating hydraulic pump 2 (when the drive wheels 1g and 1h are not slipping on the road surface). As a result, the amount of pressure oil discharged by the hydraulic motor 3 is greater than the amount of pressure oil discharged by the hydraulic pump 2, and the effect in this case is as follows.

With respect to the flow of pressure oil discharged from the hydraulic pump 2 to the hydraulic pipe line 6 side, the amount fi of the pressure oil discharged by the hydraulic motor 3 to the hydraulic pipe line 7 side, that is, the hydraulic motor 3 As the amount of pressurized oil sucked from the pump increases, the pressure on the hydraulic pipe line 6 side tends to become evacuated.

In addition, in this case, the switching valve 5 is at the switching position 1'ζi5
Since the setting is A, the hydraulic line 7, the branch lines 4d and 5b, and the line 4e are in communication. Therefore, the hydraulic line 6 is evacuated, and the pressure oil flow rate on the side of the hydraulic line 7 is When the pressure increases, the pressure oil in the hydraulic pipe 7 pushes open the check valve 4a from the branch pipe 5b, the switching valve 5, and the pipe 4e, and returns the pressure oil from the branch pipe 4C to the hydraulic pipe 6. That is, in this state, the hydraulic pipes 7 and 6 are in the same low pressure state, and the hydraulic pump 2 and the hydraulic motor 3 are under no load.

Also, as mentioned above, the hydraulic motor 3 rotates quickly and the wheels 3
d and 3e are not driven by the engine 1, the drive wheels 1g and 1h slip on the road surface due to the drive of the engine 1, and as a result, the rotational speed of the hydraulic pump 2 is lower than the rotational speed of the hydraulic motor 3. When becomes high, the following effects occur.

When the rotation speed of the hydraulic pump 2 rotates faster than the rotation speed of the hydraulic motor 3, the side of the discharge pipe in the hydraulic pump 2 (
The amount of pressure oil to the hydraulic line 6) increases, and as a result, the oil pressure on the side of the hydraulic line 6 increases, and the pressure in the hydraulic line 6 is passed through the branch line 4C to the check valve. 4a is closed, and as a result, the side of the hydraulic line 7 becomes the low pressure side with respect to the hydraulic line 6, and the pressure oil discharged from the hydraulic pop 2 directly drives the hydraulic motor 3, and the engine 1 is not only the driving wheels 1g and 1h, but also the front F wheels 3d, l and 3.
It will be in a four-wheel drive state including e.

Reverse operation of the automobile: In this case, in conjunction with setting the shift lever in the transmission 1b to the reverse position, current is passed through the solenoid 5a, thereby setting the switching valve 5 to the switching position 5B.

Further, by setting the shift lever to the reverse position as shown in and engaging the clutch installed in the transmission 1b, the rotational direction of the drive shaft 2a changes from 1 to 1i.
It rotates in the opposite direction to the case of j-adic and the hydraulic pump 2
The side of the discharge pipe line is the side of the hydraulic pipe line 7.

This means that in the case of the forward operation, the vj switching valve 5
is set to the switching position 5A, the discharge line side (hydraulic line 6) of the hydraulic pump 2 and the hydraulic motor 3
A pipe is connected to the discharge pipe side (hydraulic pipe line 7) of the hydraulic motor 3 to allow the flow of pressure oil from the discharge pipe side of the hydraulic pump 2 to the discharge pipe side of the hydraulic pump 2, and to prevent the reverse flow. In contrast to the 6j configuration in which a directional valve (check valve 4a) is interposed, in the case of reverse operation, the switching valve 5 is set to the switching position 5B, and the rotation direction of the drive shaft 2a is reversed. This allows pressure oil to flow from the discharge pipe side (hydraulic pipe line 6) of the γ hydraulic motor 3 to the discharge pipe side (hydraulic pipe line 7) of the hydraulic pump 2, and vice versa, in the same way as forward movement. One-way valve (check valve 4b) that blocks the flow
) was intervened. ) composition.

Therefore, in the case of this backward operation, the same effect as in the case of forward operation is obtained.

In the above embodiment, a: the drive wheels 1g and lh and the wheels 3d and 3e are not slipping on the road surface, b=the vehicle is traveling straight, C: and each drive wheel Under the above normal conditions in which the rotational speeds of wheels 1g and 1h and wheels 3d and 3e are the same, hl of the pressure oil discharged by hydraulic pump 2 to its discharge pipe side is equal to the discharge of hydraulic motor 3. The flow rate is set to satisfy a condition that is larger than the flow rate.

In this way, in the above configuration, the discharge flow rate from the hydraulic pump 2 is set to be large in its normal state, so a: The increased discharge amount is equivalent to the hydraulic pressure. This causes the motor 3 to rotate faster.
The circumferential speed of the wheels 3d and 3e is increased compared to the speed of the vehicle relative to the road surface in normal conditions, which means that the wheels 3d and 3e are driven while sliding on the road surface, causing wear on the tires. As shown in b: or L a:, adjust the wheels 3d and 3e to such an extent that the wheels 3d and U3e do not slip on the road surface.
When the frictional resistance between the hydraulic pump 2 and the road surface is large, pressure oil is relieved from the discharge pipe side of the hydraulic pump 2 via the relief valve 4f, and there is still a drawback that energy loss occurs accordingly.

Such a drawback is that in the above normal state, the flow jIt discharged by the hydraulic pump 2 to its discharge pipe side is slightly reduced (for example, the flow jIt is reduced by 5 or 11 degrees). It is solved by

In this way, if the flow rate that the hydraulic pump 2 discharges to the discharge 'lτ path side is made slightly smaller, its action will be relatively faster than the extraction motor 3 side or the hydraulic pump 2. This normal tl corresponds to υj-turned noyi・&.
Even in the case of
The discharge pipe side and 1! Throughout this process, the hydraulic pump 2 and extraction motor 3 are placed under no load.

In addition, when the drive wheels 1g and 1h slip on the road surface as shown in "-", the rotational speed of the hydraulic pump 2 becomes "-" and the By driving the hydraulic motor 3 in this manner, the wheels 3d and 3e become driving wheels relative to the road surface, and assist the slipping of the driving wheels 1g and 1h.

Engine braking action: When engine braking is applied, that is, when the accelerator pedal is returned to zero or a predetermined range near zero, the switching valve 5 is activated in response to the returned signal of the accelerator pedal for forward travel. Switching position:! Set to 15B.

In this engine/brake state, engine 1
applies the brakes to drive wheels 1g and lh, so
The rotational speed of the hydraulic pump 2 that is linked to the drive wheels 1g and lh also tends to decrease, and as a result, the flow rate of the pressure oil discharged from the hydraulic pump 2 to the hydraulic pipe 6 also tends to decrease.

On the other hand, the wheels 3d and 3e drive the hydraulic motor 3 via the drive shaft 3c, the differential 3b, and the drive shaft 3a by running on the road surface, and the pressure oil discharged by the drive is transferred to the hydraulic pipe 7. The hydraulic pump 2 is driven via.

In this case, the hydraulic motor 3 is the hydraulic pump 2.
, the hydraulic line 7 is in a high pressure state, and the high pressure closes the check valve 4b via the branch line 4d, and as a result, the branch line 5C and the switching valve 5
The hydraulic pipe line 6 is prevented from communicating with the hydraulic pipe line 7 via the hydraulic pipe line 7.

-1- In the case of engine braking at the time of reverse driving, the shift lever of the transmission 1b is set to the reverse position, and the accelerator pedal is returned to a predetermined range at or near zero. When set to
By detecting this state, the switching valve 5 is set to the switching position 5A.

However, in this case of backward operation, the hydraulic pump 2
Since the pressure oil discharged from the hydraulic pump 2 is opposite to that in the forward operation, the relationship between the side where the pressure oil is discharged from the hydraulic pump 2 and the switching position of the switching valve 5 is different between the backward operation and the forward operation. The structure has relatively the same relationship, and the effect during reverse operation is also the same as the effect during forward a rotation.

In the above embodiment, when the flow rate of pressure oil discharged from the hydraulic motor 3 becomes larger than the flow rate of pressure oil discharged from the hydraulic pump 2 due to the presence of the switching block F4a or 4b, , the check valve 4a or 4b is automatically opened to communicate the hydraulic pressure 76/path 7 with the hydraulic pipe line 6, and here, the flow rate of pressure oil discharged from the hydraulic pump 2 is equal to the displacement volume Dp of the hydraulic pump 2. and the rotation speed np of the drive shaft 2a (DpXnp), and the pressure oil discharge flow rate from the hydraulic motor 3 is the product (DmXnm) of the displacement volume Dm of the hydraulic motor 3 and the rotation speed nm of the drive shaft 3a.
).

Therefore, the configuration consisting of the switching Jr5 and the change valve 4a or 4b may be configured as follows.

When detecting CD p X n p) and (D m
The bypass valve is opened to connect the hydraulic line 6 and the hydraulic line 7, and conversely, when (DpXnp)>(DmXnm), the bypass valve is closed and the hydraulic motor is operated by the pressure oil from the hydraulic pump 2. 3 should be in a state where it is driven.

Furthermore, in the above description, the side of the drive wheels 1g and 1h is the side to be steered, and this occurs when the automobile is running at low speed. So-called tight cornering braking (if the steered wheel side tries to rotate more sharply than the non-steered wheel side due to a large steering angle, if the steered wheel side and the non-steered wheel side are driven directly) When a phenomenon in which the steering wheel side acts as a brake occurs, the displacement volume of the hydraulic pump 2 is reduced to prevent the hydraulic motor 3 from being driven excessively, or a bypass valve is provided as described above. In that case, just open the bypass valve.

Furthermore, in the above case, (DpXnp) and (DmX
nm) detection and bypass valve operation.

Alternatively, the displacement of the hydraulic pump 2 and the hydraulic motor 3 may be controlled by a calculator (not shown).

In addition, when hydraulic transmission is not performed between the hydraulic pump 2 and the hydraulic motor 3, a latch such as a dog clutch is installed between the drive shafts 2a and/or 3a in order to eliminate unnecessary loss in the power transmission system. Alternatively, the hydraulic pump 2 and/or the extraction motor 3 may be separated.

Further, in the above embodiment, the hydraulic pump 2 is connected to the drive shaft I
Although the configuration is such that the hydraulic pump 2 is connected to the input side of the transmission 1b, that is, the output shaft 1a, the hydraulic pump 2 may be moved around the input side of the transmission 1b, that is, the output shaft 1a. However, in this case, the transmission i
Each time the gear ratio b is switched, it is necessary to control the displacement volume Dp of the hydraulic pump 2 to a required value so that the discharge flow % (DpXnp) from the hydraulic pump 2 becomes a predetermined value.

Further, in the above embodiment, it is assumed that the tire outer diameters of the drive wheels 1g and lh and the wheels 3d and 3e are equal on average, including variations.

However, in the above embodiment, in the above-mentioned normal state, the configuration in which the relationship (DpXnp) < (DmXnm) is set is such that the magnitudes of DP and Dm are made equal and the driving wheels 1g and lh For the outer diameter of wheel 3
A configuration may be adopted in which the outer diameters of d and 3e are made small.

If the outer diameters of the wheels 3d and 3e are made small in this way, the relationship n p < nm will be established, and (D p
This is because X n p) < (DmX nm).

[Effects of the Invention] As is clear from the above description, the effects of the present invention are as follows.

l) When the engine 1 is installed on the drive wheels 1g and 1h, the drive path for the other wheels 3d and 3e can be configured via the hydraulic pipes 6 and 7, which can be bent freely. , unlike conventional four-wheel drive systems, it does not require a propeller shaft.

Therefore, there is no need for a tunnel for the propeller shaft in the chassis, and the interior of the vehicle can be made larger.

2) When the amount of pressure oil discharged from the 7u1 pressure motor 3 is greater than the amount of pressure oil discharged from the hydraulic pump 2, the discharge pipe side of the hydraulic motor 3 and the discharge pipe side of the hydraulic pump 2 are communicated. Due to this configuration, when the driving wheels are not slipping, the wheels 3d and 3e on the non-driving wheel side due to the difference in wheel size etc.
Even when the drive wheels 1g and 1h rotate quickly, the drive wheels 1g and 1h
As a result of the side rotating with respect to the road surface, there is no possibility of accelerating tire wear on the drive wheels.

3) Furthermore, the relationship between the displacement volume of the hydraulic pump 2 and the displacement volume of the hydraulic motor 3 is
The discharge flow rate of the pressure oil discharged from the hydraulic motor 3 is the discharge flow rate of the pressure oil discharged by the hydraulic motor 3 when the vehicle is traveling straight and the driving wheels 1g and lh and the wheels 3d and 3e are not slipping on the road surface. When the relationship is <+fi, which is less than the flow rate, the drive wheels 1g and 1h are in a state where they do not slip on the road surface, that is, the drive wheels 1
When the vehicle can travel only with G and lh, the hydraulic drive between the hydraulic pump 2 and the hydraulic motor 3 is left unloaded to reduce unnecessary power loss and prevent the drive wheels 1g and 1h from slipping on the road surface. Wheels 3d and 3e only if
assists in driving. This results in a more efficient four-wheel drive system.

[Brief explanation of the drawing]

FIG. 1 shows a system diagram of a four-wheel drive device as an embodiment of the present invention. The main symbols used in the examples are as follows. 1: Engine, 1b=Transmission, 1g and 1h
: Drive wheel, 2: Web pressure pump, 3: Hydraulic morph, 3d and 36; Ilj wheel, 4a and 4b: Check valve, 5: Switching valve.

Claims (1)

[Claims] 1. The output shaft of the engine in the automobile drives the drive wheels via a transmission, and a hydraulic pump is linked to any drive system from the output shaft of the engine to the drive wheels. A hydraulic motor is interlocked with the hydraulic pump via a hydraulic conduit, the hydraulic motor is interlocked with wheels, and between the discharge conduit side of the hydraulic pump and the discharge conduit side of the hydraulic motor, a: When the amount of pressure oil discharged from the hydraulic motor is larger than the amount of pressure oil discharged from the hydraulic pump, the discharge pipe side of the hydraulic motor is communicated with the discharge pipe side of the hydraulic pump. , b: Conversely, when the amount of pressure oil discharged from the hydraulic pump is greater than the amount of pressure oil discharged from the hydraulic motor, the communication is closed. car. 2. The relationship between the displacement volume of the hydraulic pump and the displacement volume of the hydraulic motor is based on the assumption that the discharge flow rate of the pressure oil discharged from the hydraulic pump is based on the assumption that the vehicle is traveling straight and the drive wheels and wheels are not slipping on the road surface. The four-wheel drive device according to claim 1, wherein the value is smaller than the discharge flow rate of the pressure oil discharged by the hydraulic motor in this state.