JP2002013635A - Hydraulic power transmission device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hydraulic power transmission capable of preventing the movement of a vehicle in stopping a motor. SOLUTION: In this hydraulic power transmission, having a closed circuit formed by communicating ports of a variable displacement pump 10 and a motor 20 to each other by means of passages 30 and 31, a charging passage 37 for supplying a fluid from a charging pump 35 to the passage 30 and 31 of the closed circuit at a prescribed pressure, and a neutralizing circuit 51 for flowing out the discharged fluid from the passage 30 of the closed circuit to the charging passage 37, when the discharging amount of the variable displacement pump 10 is very small, the neutralizing circuit 51 is provided with a neutralizing valve 50, which is closed when the pressure in the charging passage 37 is lowered to be less than a prescribed value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fluid pressure transmission (hydro-hydraulic power transmission) that connects a discharge port and a suction port of a variable displacement pump and a motor through a passage and transmits a driving force from the pump to the motor via a fluid pressure. More particularly, the present invention relates to a hydraulic transmission suitable for application to a drive device of a vehicle.

[0002]

2. Description of the Related Art Conventionally, a fluid pressure transmission device (hydrostar) that connects a discharge port and a suction port of a variable displacement pump and a motor to a closed circuit through a passage and transmits a driving force from the pump to the motor via a fluid pressure. Tik Transmission, commonly known as HST, is known and is used in forklifts and work vehicles. ) On pages 523-527.
FIG. 7-7 on page 527 shows an example in which a variable displacement pump and a constant displacement motor are combined.

FIG. 5 is a hydraulic circuit diagram showing a circuit of the same document. In FIG. 5, reference numeral 110 denotes a variable displacement pump whose volume changes between forward discharge, neutral, and reverse discharge when operated by a forward / reverse lever (not shown). Constant volume motors 130 and 131 connected to the drive wheels are passages forming a closed circuit. 135 is a charge pump,
105 is a prime mover for driving the variable displacement pump 110 and the charge pump 135, and 140 is a closed circuit passage 13.
A high-pressure relief valve 13 that communicates with the other passages 130 and 131 when the pressure in 0 and 131 exceeds a predetermined pressure;
8, 139 are the charge passages 1 from the charge pump 135.
37, the fluid supplied through the closed circuit passages 130, 1
A check valve 141 for supplying to the charge passage 31
7 is a low-pressure relief valve provided in a passage 142 opened into the case (not shown) to cool the inside of the case. Further, one passage 130 of the closed circuit and the charge passage 137 are connected to each other by a neutral circuit 151 having an orifice 153.

Then, the prime mover 105 is started to drive the charge pump 135 and the variable displacement pump 110, and the charge pump 135 is connected to the closed passages 130, 1 through the charge passage 137 and the check valves 138, 139.
31 is filled with fluid, and the variable displacement pump 110 discharges a flow rate set by its forward / reverse lever. That is,
In the case of neutral, there is basically no discharge flow rate, no fluid flows through the passages 130 and 131, and the constant displacement motor 1
20 does not rotate.

When the forward / reverse lever is operated forward, the variable displacement pump 110 discharges a fluid to the passage 130, for example,
The fluid drives the constant displacement motor 120 to move the vehicle forward. The fluid flowing out of the constant displacement motor 120 flows back through the passage 131 and is sucked into the variable displacement pump 110 again.

Conversely, when the forward / reverse lever is operated to reverse,
The variable displacement pump 110 discharges a fluid into the passage 131 in a direction opposite to the forward direction, and the constant displacement type motor 120 is rotated in the reverse direction by the fluid to retreat the vehicle. The fluid flowing out of the constant displacement motor 120 flows back through the passage 130 and is sucked into the variable displacement pump 110 again.

[0007] Due to the backlash and friction of the linkage from the forward / reverse lever to the variable displacement pump 110, even if the forward / reverse lever is neutral, the variable displacement pump 110 can be completely brought to a state in which the discharge amount is zero. Therefore, if the forward / reverse lever is at the neutral position, it is necessary to prevent the constant displacement motor 120 from rotating even if there is a small discharge flow rate from the variable displacement pump 110.

For this reason, a minute fluid is recirculated from the passage 130 to the passage 131 via the orifice 153 of the neutral circuit 151. The variable displacement pump 1
As the discharge flow rate increases, the pressure in the passage 130 increases due to the restricting effect of the orifice 153, and when this pressure reaches the starting pressure of the vehicle (the pressure required to move the vehicle), the constant-volume type The motor 120 starts rotating and the vehicle starts moving.

[0009]

By the way, in the above-mentioned conventional example, since the passage 130 and the passage 131 are always communicated by the neutral circuit 151 having the orifice 153, the load side is connected to the constant displacement motor 120. Even when a rotation input is received from the motor, the discharge fluid from the constant displacement motor 120 flows into the passage 130 and passes through the neutral circuit 151 through the passage 1.
31 and the rotation of the constant displacement motor 120 could not be stopped. Thus, the case where there is a rotation input to the constant displacement motor 120 from the load side is, for example, a case where the vehicle stops on a slope, and when the parking brake is not activated, the vehicle is not braked and its own weight. She tries to slip down toward Sakashita.

In such a case, when the motor 105 is operating, the driver is present in the seat and operates the pedal brake to stop the vehicle from falling down. When the vehicle stops and forgets to apply the parking brake and leaves the vehicle, it is impossible to prevent the vehicle from sliding down.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to provide a fluid pressure transmission device that prevents movement of a vehicle when a motor is stopped.

[0012]

According to a first aspect of the present invention, there is provided a closed circuit in which ports of a variable displacement pump and a motor are connected to each other through a passage, and a fluid from a charge pump is passed through each passage of the closed circuit. A fluid pressure transmission device comprising: a charge passage for supplying a predetermined pressure; and a neutral circuit for discharging a discharge fluid from a closed circuit passage to the charge passage when a discharge amount of the variable displacement pump is minute. The circuit is provided with a neutral valve that closes when the pressure in the charge passage falls below a predetermined value.

According to a second aspect of the present invention, the neutral valve has a shut-off position and an open position where an orifice is inserted, and
It is characterized by comprising a switching valve which switches from a shut-off position by the valve spring to an open position against the valve spring by a predetermined pressure or more in the charge passage.

A third aspect of the present invention is characterized in that the charge passages are connected to respective passages of a closed circuit via check valves, and the neutral valve is built in the check valves.

According to a fourth aspect of the present invention, the orifice is disposed on a valve body of the check valve, and the neutral valve is provided in the check valve body and opens and closes the orifice.

[0016]

Therefore, in the first invention, the neutral circuit is provided with a neutral valve which closes when the pressure in the charge passage falls below a predetermined value. Therefore, when the prime mover stops and the charge pressure is not supplied to the charge passage, The neutral valve switches to the shut-off position, the closed circuit consisting of the variable displacement pump / motor and the passage is cut off from the charge passage, and even if a driving force acts on the motor from the outside, the pressure in the passage of the closed circuit increases due to the pressure rise in the passage of the closed circuit. Rotation is blocked. Therefore, even if the vehicle is stopped halfway along the slope, the vehicle does not slip down.

Further, the neutral valve determines the stop state of the vehicle based on the discharge pressure of the charge pump and operates based on the discharge pressure of the charge pump. Therefore, the neutral valve is operated by new detection means for detecting the engine stop state or by this detection means. It does not require an actuator to drive the neutral valve, and can be configured at low cost.

[0018] The second invention has the following advantages in addition to the effects of the first invention.
Since the orifice is provided in the neutral valve itself, no space is required for the orifice in the neutral circuit, and the passage configuration of the neutral circuit is simplified.

In the third invention, in addition to the effects of the first and second inventions described above, since the neutral valve is built in the check valve, there is no need to change the shape of the passage at all. In addition, the manufacturing cost can be reduced and the conventional check valve can be implemented simply by replacing the check valve with the neutral valve according to the present invention.

According to the fourth aspect of the present invention, since the orifice is provided in the check valve body extending over the charge passage and the closed circuit passage, it is necessary to separately provide a member for forming the orifice and a new passage. In addition, the number of parts can be reduced, and in this regard, the configuration can be made at a low cost.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a first embodiment of the present invention will be described with reference to the accompanying drawings.

FIG. 1 is a hydraulic circuit diagram 1 to which the present invention is applied.
Here is an example.

In FIG. 1, a portion surrounded by a two-dot chain line indicates a hydraulic transmission 1.
Numeral 0 denotes a variable displacement pump driven by the input shaft 11. The inclination of a swash plate (not shown) is indicated by the inclination of an arrow, and the discharge amount can be changed according to the inclination of the arrow. With the inclination shown in the figure, the fluid is sucked from the lower port in the figure and discharged from the upper port, and when the inclination is opposite to that shown in the figure, the fluid is sucked from the upper port in the figure and discharged from the lower port. . The inclination of the swash plate is operated by the forward / reverse lever 2. When the forward / backward lever 2 is set at the N position, the swash plate becomes zero in inclination. At this time, the swash plate has an inclination opposite to that shown in the figure.

Reference numeral 20 denotes a constant displacement motor, and an output shaft 21
, And the output shaft 21 is connected to the driving wheels 4 via a driving device of the vehicle, specifically, the final reduction gear 3 or the like. For example, when the fluid is supplied from the upper side in the drawing, the vehicle rotates in a direction to advance the vehicle, and when the fluid is supplied from the lower side in the drawing, the vehicle rotates in a direction to change the vehicle. Is proportional to the fluid supply. The port of the variable displacement pump 10 and the fixed displacement motor 2
The port 0 is connected to the ports 30 and 31 by passages 31 to form a closed circuit.

Reference numeral 35 denotes a charging pump, and the input shaft 1 connected to the prime mover 5 together with the variable displacement pump 10.
1 and supplied from the charging pump 35 through the charge passage 37 to the closed circuit passage 3
0 and 31 are supplied via check valves 38 and 39. As a result, the inside of the closed circuit is maintained at a predetermined pressure or higher even on the suction side, and cavitation due to the suction negative pressure is prevented. The charge pump 35 sucks fluid from the oil tank 6 provided outside the fluid transmission 1 through the suction pipe 7, and the charge passage 37 passes through the charge pipe 36 having the oil filter 8 outside the fluid pressure transmission 1. Then, it is configured to return to the charge passage 37 of the fluid transmission device 1.

Reference numeral 40 denotes a high-pressure relief valve for connecting the closed circuit passages 30 and 31 with each other at a predetermined pressure or higher. Reference numeral 41 denotes an opening from the charge passage 37 into the fluid pressure transmission device 1 for cooling the inside of the case (not shown). A low-pressure relief valve provided in the passage 42. Reference numeral 50 denotes a neutral valve disposed in a neutral passage 51 which connects the one passage 30 of the closed circuit to the charge passage 37, and a shut-off position 52
And a communication position 54 having an orifice passage 53. The communication position 54 is urged by the valve spring 55 to the blocking position 52, and moves to the communication position 54 against the valve spring 55 by the pressure of the charge passage 37. I have. Therefore, the neutral valve 50 is connected to the charge passage 37.
Is higher than a predetermined pressure due to the operation of the charge pump 35, that is, when the engine 5 is rotating, it is at the communication position 54 having the orifice 53, the engine 5 is stopped, and the operation of the charge pump 35 is stopped. Is located at the cut-off position 52. The fluid in the case of the fluid pressure transmission 1 is supplied to the oil tank 6 by the drain pipe 9.
Is to be returned to.

The first embodiment having the above configuration operates as follows.

When the forward / reverse lever 2 is set to the neutral N position and the prime mover 5 of the vehicle is started, the charge pump 35 is driven by the input shaft 11 connected to the prime mover 5,
The fluid discharged from the charge pump 35 is supplied to a charge pipe 36, a charge passage 37, and check valves 38 and 39.
Through the passages 30 and 31 of the closed circuit. The surplus flow rate opens the low-pressure relief valve 41, flows into the case of the fluid pressure transmission 1 through the passage 42, cools the inside of the case, and then flows to the oil tank 6 through the drain port 9, and the low-pressure relief The valve 41 maintains the charge pressure Pc in the charge passage 37 and the passages 30 and 31 forming a closed circuit. Then, the neutral valve 50 receives the charge pressure Pc and switches to the communication position 54 having the orifice 53 against the valve spring 55.

The variable displacement pump 10 basically does not discharge fluid since the forward / reverse lever 2 is at the neutral N position. Since the valve 50 is located at the communication position 54, it is returned to the other passage 31 of the closed circuit through the orifice 53, the charge passage 37, and the check valve 39, and the passages 30 and 31 are maintained at the same pressure. Will not drive.

When the forward / reverse lever 2 is operated to the forward F position, the swash plate of the variable displacement pump 10 is tilted, and the variable displacement pump 10 sucks fluid from the lower port in the figure and fluid from the upper port in the figure. Discharge. Although a part of the discharged fluid returns to the passage 31 through the orifice 53 of the neutral circuit 51 as described above, the pressure in the passage 30 increases due to the passage resistance of the orifice 53 and is supplied to the constant displacement motor 20. You. When the pressure of the discharged fluid reaches the starting pressure of the vehicle (the pressure required to move the vehicle), the constant displacement motor 20 starts rotating and the vehicle starts moving. When the forward / reverse lever 2 is moved to the reverse R position, the operation is the same as in the forward movement.

When the forward / reverse lever 2 is switched to the neutral position N to stop the vehicle, the motor 5 is stopped, and the charge pump 35 and the variable displacement pump 10 are stopped, the fluid in the passages 30 and 31 of the closed circuit flows. Therefore, the constant displacement motor 20 also stops. The pressure in the charge passage 37 decreases, and accordingly, the neutral valve 5 of the neutral circuit 51
0 is switched to the cutoff position 52 by the action of the valve spring 55, and the closed circuit including the variable displacement pump 10, the passages 30 and 31, and the constant displacement motor 20 is disconnected from the charge passage 37.

Therefore, when the vehicle stops on an uphill slope without operating the parking brake, the rotational force from the drive wheels 4 in the backward direction is reduced by the final reduction gear 3 and the output shaft 21.
1 and acts on the constant displacement motor 20, and a rotational force opposite to that at the time of forward movement acts on the constant displacement motor 20 to increase the pressure in the passage 30 in order to discharge fluid to the upper port in FIG. 1. Let it. Since the fluid in the passage 30 is prevented from flowing out by the check valve 38 and the neutral valve 50 at the shutoff position 52, the rotation of the constant displacement motor 20 is restricted by the increase in the pressure in the passage 30, and the vehicle moves downhill. There is no downfall. It should be noted that a minute leak from the neutral valve 50 or each sliding portion of the pump / motor cannot be prevented, and a permissible slight movement corresponding thereto occurs over time.

When the vehicle is parked on a downhill slope without operating the parking brake, the rotational force in the forward direction from the drive wheels 4 is transmitted through the final reduction gear 3 and the output shaft 21 to the constant displacement motor. 20 and the constant displacement motor 20
1 exerts the same rotational force as that at the time of forward movement, attempts to discharge fluid to the lower port in FIG. 1, and increases the pressure in the passage 31. Since the fluid in the passage 31 is prevented from flowing out by the check valve 39, the rotation of the constant displacement motor 20 is restricted by the increase in the pressure in the passage 31, and the vehicle does not fall downhill. Even in this case, it is impossible to prevent minute leakage from each sliding portion of the pump / motor, and a permissible slight movement corresponding thereto occurs with the passage of time.

In this embodiment, since the stop state of the vehicle is determined by the discharge pressure of the charge pump, a valve that operates according to the charge pressure is inserted without requiring any special detecting means. It does not require any special detection means or actuator, and can be configured at low cost.

2 to 4 show a second embodiment of the present invention. FIG. 2 is a sectional view, FIG. 3 is a structural view showing a sectional view taken along the line III-III of FIG. 2, and FIG. 2 is a partially enlarged view showing a characteristic portion of FIG. 1, and the same portions as those in FIG.

2 and 3, the variable displacement pump 10, the constant displacement motor 20, and the charge pump 35 are
The charge pump 35 is accommodated in a space formed by the case 60, the passages 31 and 32 of the closed circuit, and the port block 61 for accommodating the respective valves, and the charge pump 35 is arranged on the back surface of the port block 61 to form an integral block as a whole. It is configured as follows.
That is, the variable displacement pump 10 and the constant displacement motor 20
Is built in a space formed by the case 60 and the port block 61 while being supported by the input shaft 11 and the output shaft 21. Further, a charge pump 35 is disposed at a tip end portion of the input shaft 11 that penetrates the port block 61.

The variable displacement pump 10 has a plurality of cylinder blocks 12 supported on the input shaft 11 and arranged at equal intervals around the input shaft 11 and extending in the axial direction. A piston 13 which is fitted and urged in a direction of extension by a spring built in the cylinder, that is, in the left direction in the figure;
The swash plate 14 which comes into contact with the protruding end of each piston 13 via a thrust bearing, is guided by a bush arranged between the piston 60 and the inner surface of the case 60, and can swing around the center O, the cylinder block 12 and the port block 61. And a valve plate 15 disposed between the two. In the variable displacement pump 10, the swash plate 14 is in the N position in the drawing, that is, in the neutral state, and when the swash plate 14 is tilted in the F direction (or the R direction) in FIG. 2 and the port 17 (or port 1) shown in the right diagram of FIG.
The fluid is sucked in from 6), and the fluid is discharged from the other port 16 (or port 17).

The constant displacement motor 20 is supported by the output shaft 21 and is disposed at equal intervals around the output shaft 21 and has a cylinder block 22 having a plurality of cylinders extending in the axial direction. The pistons 23 which are fitted and urged in the extension direction by a spring built in the cylinder, that is, urged in the left direction in the figure, and the thrust bearings 24 which are in contact with the protruding ends of the pistons 23 and which are arranged obliquely. And a valve plate 25 arranged between the cylinder block 22 and the port block 61.
It is composed of In this constant displacement motor 20, the thrust bearing 24 is inclined, and when a fluid is supplied from the port 26 of the two ports 26 and 27 shown in FIG.
3, the counterclockwise rotation (forward direction) in FIG. 3 is applied to the cylinder block 22, and the output shaft 21 rotates counterclockwise. Further, when the fluid is supplied from the port 27, the thrust bearing 24 guides the cylinder block 22 to rotate clockwise in FIG. 3 when the piston 23 extends, and the output shaft 21 moves clockwise (retreat direction) in FIG. Rotate.

The port 16 and the port 26 are communicated by a passage 30 provided in a port block 61, and the port 17 and the port 27 are communicated by a passage 31 provided in the port block 61. The port block 61 has a passage 30 at a portion connecting the passages 30 and 31.
And a high-pressure relief valve 40 for releasing one pressure to the other when one of the pressures is equal to or higher than a predetermined value. A check valve 39 disposed between the charge passage 37 and the passage 31 to supply the fluid in the charge passage 37 to the passage 31 when the pressure in the charge passage 37 is higher than the pressure in the passage 31; And a check valve 38 that supplies the fluid in the charge passage 37 to the passage 30 when the pressure in the charge passage 37 is higher than the pressure in the passage 30.

The check valve 38 is configured in combination with a neutral valve 70 as shown in FIG. That is, the port block 61 is provided with a stepped hole 71 having a large diameter portion communicating with the passage 30 and a small diameter portion communicating with the charge passage 37. The stepped portion of the stepped hole 71 is tapered and has a valve seat. 72. Inside the stepped hole 71, a cylindrical guide 73, a pilot spool 74 slidably guided by the guide 73, and a check valve body 75 slidably fitted at the tip of the pilot spool 74 are incorporated. ing. That is, the check valve body 75 is
The valve portion 77 is seated on the valve seat 72 by being pressed by the check spring 76 seated on the step 3, the stepped hole 75a slidably fitted to the tip of the pilot spool 74, and the stepped portion of the stepped hole 75a. An orifice passage 78 for communicating a portion separated by a predetermined distance L1 with a rear outer periphery of the valve portion 77 is provided.
4 becomes the stopper. The pilot spool 74 is biased toward the check valve body 75 by a spring 79 at the rear end,
When the charge pressure Pc of the charge passage 37 is equal to or less than a predetermined value, the check valve body 75 is pressed through the stepped portion of the stepped hole 75a. A plug 80 is screwed into the open end of the stepped hole 71 of the port block 61 to support the spring 79 of the pilot spool 74 and prevent the guide 73 from coming off. A pin 81 for restricting the retreat stroke of the pilot spool 74 is driven into the plug 80. And the check valve element 75
The check valve body 75 can be moved by a distance L2 between the guide spool 73 and the pilot spool 74.
The stroke can be performed by an interval L3 between the two. The above dimensions have a relationship of (L1 + L2) <L3. Here, the check valve 38 is constituted by the valve seat 72 of the stepped hole 71, the check valve body 75, and the valve spring 76, and the check valve body 75
, The orifice 78, the pilot spool 74 and the valve spring 79 constitute a neutral valve 70.

In the hydraulic pressure transmission 1 of the second embodiment having the above-described configuration, the prime mover 5 is provided on the input shaft 11, and the final reduction gear 3 and the drive wheels 4 are provided on the output shaft 21 of the first embodiment. By sucking fluid from the oil tank 6 into the charge pump 35 via the suction pipe 7 and supplying fluid to the charge passage 37 via the charge pipe 36, the oil cooler 8a, and the oil filter 8, the following operation is performed. Activate

The variable displacement pump 10 is operated by a forward / reverse lever or the like.
Is set to the neutral N position, the prime mover 5 of the vehicle is started, and the charge pump 35 is driven by the input shaft 11,
The discharge fluid of the charge pump 35 is a charge pipe 36,
Oil cooler 8a, oil filter 8, charge passage 3
7 and check valve 38, 39, closed circuit passage 3
The excess flow rate is supplied to the hydraulic pressure transmission device 0, 31 and the low pressure relief valve 41 is opened through the passage 42, flows into the case 60 of the hydraulic pressure transmission device 1 to cool the case 60, and then flows through the drain port 9. It flows to the oil tank 6. The low pressure relief valve 41 maintains the charge pressure Pc in the charge passage 37 and the passages 30 and 31 forming a closed circuit. And the pilot spool 7 of the neutral valve 70
Numeral 4 receives the charge pressure Pc at the tip end surface and retreats against the valve spring 79 to open the orifice 78.

Variable displacement pump 10 in neutral position
, The fluid is closed via the orifice 78, the charge passage 37, and the check valve 39 because the pilot spool 74 moves to the retracted position and the orifice 78 is opened. It is returned to the other passage 31 of the circuit and does not drive the constant displacement motor 20.

The variable displacement pump 1 is driven by a forward / reverse lever.
When the zero swash plate 14 is inclined in the F direction, the variable displacement pump 10 sucks the fluid in the closed circuit from the port 17 and discharges the fluid from the port 16. A part of the discharged fluid is returned from the passage 30 to the passage 31 through the orifice 78 as described above. When the pressure reaches the starting pressure of the vehicle (the pressure required to move the vehicle), the constant displacement motor 20 starts rotating and the vehicle starts moving. When the swash plate 14 of the variable displacement pump 10 is tilted to the reverse R position by the forward / reverse lever, the operation is performed in the same manner as at the time of forward movement, and the vehicle moves backward.

While the vehicle is being driven, one of the passages 30 and 31 forming a closed circuit has a high pressure on the fluid sending side, but the other passage has a low pressure on the fluid returning side. When the pressure in the low-pressure side passage becomes equal to or lower than the charge pressure Pc, the check valve 38 (or the check valve 39) is opened and the pressure is adjusted, so that the pressure is adjusted to the charge pressure Pc.

The check valve 38 has a check valve body 75
The pilot spool 74 is retracted to a dimension L3 which is greater than or equal to the sum of the orifice position L1 and the check valve element moving dimension L2 even if the orifice 78 is retracted and the position of the orifice 78 is retracted. It is opened regardless of whether the valve 38 is opened or closed.

To stop the vehicle, the variable displacement pump 10 is set to the neutral N state by the forward / reverse lever, and the motor 5 is stopped to stop the charge pump 35 and the variable displacement pump 10. Stop. Thereafter, the pressure in the charge passage 37 decreases, and accordingly, the pilot spool 74 moves the valve spring 7.
The orifice 78 is closed by switching to the projecting position by the operation of No. 9. Therefore, the variable displacement pump 10, the passages 30, 3
1. The closed circuit composed of the constant displacement motor 20 is cut off from the charge passage 37.

Therefore, when the vehicle stops on an uphill slope without operating the parking brake, the rotational force in the reverse direction from the driving wheels 4 is transmitted through the final reduction gear 3 and the output shaft 21 to the constant displacement motor. By applying a rotating force to the port 20 opposite to that at the time of forward movement, an attempt is made to discharge fluid to the port 26 and the pressure in the passage 30 is increased. The fluid in the passage 30 is prevented from flowing out by closing the check valve 38 and the orifice 78 with the pilot spool 74, and the rotation of the constant displacement motor 20 is restricted by the increase in the pressure in the passage 30, and the vehicle moves downhill. Prevents sliding down.

When the vehicle is stopped on a downhill without operating the parking brake, the rotational force in the forward direction from the driving wheels 4 is transmitted through the final reduction gear 3 and the output shaft 21 to the constant displacement motor. When a rotational force is applied to the port 20 in the same direction as that at the time of forward movement, the fluid
Increase pressure inside. The fluid in the passage 31 is prevented from flowing out by the check valve 39, the rotation of the constant displacement motor 20 is restricted by the increase in the pressure in the passage 31, and the vehicle is prevented from falling downhill.

In the present embodiment, since the neutral valve 70 is incorporated in the check valve 38, there is no need to change the shape of the port block 61 at all, and the manufacturing cost can be reduced. It can be implemented simply by replacing the conventional check valve with the check valve with the neutral valve according to the present embodiment.

Also, the valve itself is a check valve element 75 which has already straddled the charge passage 37 and the closed circuit passage 30.
Since the orifice 78 is provided at the bottom, it is not necessary to separately provide a member for forming an orifice or a new passage, the number of parts can be reduced, and the configuration can be made inexpensively.

In the above embodiment, the pump and the motor are described using the swash plate pump and the swash plate motor.
Although not shown, an oblique-axis pump / oblique-axis motor, a vane pump / vane motor, or another type of popping motor may be used.
The type of the pump and the motor need not always be the same, such as using a vane motor for the motor.

Although a pump using a variable displacement pump in which the discharge direction of fluid is changed has been described, a variable displacement pump in which only the discharge volume changes without changing the discharge direction is shown, although not shown. Well, in this case,
It is applicable by using a switching valve that switches the passage between the pump and the motor in accordance with the retreat, and it is desirable that the volume of the pump be linked to, for example, the accelerator opening.

Further, although the motor has been described as a constant displacement motor, the present invention is not limited to this, and a variable displacement motor can be similarly operated.

[Brief description of the drawings]

FIG. 1 is a hydraulic circuit diagram of a hydraulic transmission showing a first embodiment of the present invention.

FIG. 2 is a sectional view showing a second embodiment of the present invention.

FIG. 3 is a cross-sectional view taken along the line III-III of FIG. 2;

FIG. 4 is a partially enlarged view of the check valve of FIG. 3;

FIG. 5 is a hydraulic circuit diagram of a conventional hydraulic transmission.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 fluid pressure transmission device 2 forward and backward lever 3 final reduction gear 4 drive wheel 5 prime mover 6 oil tank 10 variable displacement pump 11 input shaft 16, 17 port 20 constant displacement motor 21 output shaft 26, 27 port 30, 31 passage 35 Charge pump 37 Charge passage 38, 39 Check valve 40 High pressure relief valve 41 Low pressure relief valve 50, 74 Neutral valve 51 Neutral circuit 53, 78 Orifice

Claims (4)

[Claims] 1. A closed circuit in which ports of a variable displacement pump and a motor communicate with each other through a passage, a charge passage for supplying a fluid from a charge pump at a predetermined pressure to each passage of the closed circuit, and a variable passage. A neutral circuit for discharging the discharge fluid from the closed circuit passage to the charge passage when the discharge amount of the positive displacement pump is very small, wherein the pressure in the charge passage is a predetermined value in the neutral circuit. A fluid pressure transmission device comprising a neutral valve that closes when the pressure drops below. 2. The neutral valve has a shut-off position and an open position in which an orifice is inserted, and opens from a shut-off position by a valve spring against a pressure of a predetermined amount in a charge passage against the valve spring. The fluid pressure transmission device according to claim 1, further comprising a switching valve that switches to a position. 3. The charge passage according to claim 1, wherein the charge passage is connected to each passage of a closed circuit via a check valve, and the neutral valve is built in the check valve. The fluid pressure transmission according to any of the preceding claims. 4. The check valve according to claim 3, wherein the orifice is disposed in a valve body of the check valve, and a neutral valve is provided in the check valve body to open and close the orifice.
The hydraulic transmission according to claim 1.