JP2002022005A - Fluid pressure transmission gear - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fluid pressure transmission gear for preventing a vehicle from moving at a time of stopping an engine. SOLUTION: In the fluid pressure transmission gear, a port of a variable displacement pump 10 and a port of a motor 20 are communicated with each other by passages 30, 31 to constitute a closed circuit, and a charge passage 37 for supplying fluid with a predetermined pressure from a charge pump 35 to the passages 30, 31 in the closed circuit is provided. The fluid pressure transmission gear has a neutral circuit 51, which comprises: a check valve 55 for setting a flow amount of the variable displacement pump 10 so as to discharge a very little amount of the fluid to the passage 30 in a neutral state, and for allowing the fluid to flow only in one direction from the passage 30 to the passage 31 in the closed circuit; an orifice 56; and a neutral valve 50 that is closed when pressure in the passage 31 is dropped at a predetermined value or lower. The neutral circuit 51 is provided for making discharged fluid flow from the passage 30 to the passage 31 when a discharge amount of the variable displacement pump 10 is very slight.

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 device in which a discharge port and a suction port of a variable displacement pump and a motor are connected to a closed circuit through a passage, and a driving force is transmitted from the pump to the motor via a fluid pressure. The present invention relates to a hydrostatic transmission (commonly referred to as HST), and particularly to a fluid pressure transmission device suitable for application to a vehicle drive device.

[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 (or backward), the variable displacement pump 110 discharges a fluid into, for example, the passage 130, and rotates the constant displacement motor 120 with the fluid to move the vehicle forward (or backward). Let it. 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, the forward / reverse lever is moved backward (or forward).
, The variable displacement pump 110 discharges fluid into the passage 131 in the opposite direction to the above-mentioned forward movement, and rotates the constant displacement type motor 120 in the reverse direction with the fluid, so that the vehicle is moved backward (or forward).
Let it. 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 conventional example, the passage 130 and the passage 131 are always communicated with each other by the neutral circuit 151 having the orifice 153. Therefore, even when there is a rotation input to the constant displacement motor 120 from the load side, the discharge fluid from the constant displacement motor 120 flows into the passage 130 and passes through the neutral circuit 151 depending on the direction of the rotation input. Return to the passage 131,
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. And a charge passage for supplying at a predetermined pressure, wherein the discharge flow rate of the variable displacement pump is set so as to discharge a small amount to one of the passages in a neutral state, and one of the closed circuit A check valve that permits only one-way fluid flow from the passage to the other passage, an orifice, and a neutral valve that closes when the pressure in the other passage falls below a predetermined value; When the discharge amount is very small, a neutral circuit is provided for discharging the discharge fluid from one passage of the closed circuit to the other passage.

According to a second aspect of the present invention, the neutral valve has a shut-off position and an open position in which a check valve that allows only one-way fluid flow from one passage to the other passage of the closed circuit is inserted. And a switching valve that switches from the shut-off position by the valve spring to the open position against the valve spring by a predetermined pressure or more in the other passage of the closed circuit.

According to a third aspect of the present invention, the neutral valve has a shut-off position and an open position in which an orifice is inserted, and is provided with a pressure higher than a predetermined pressure in the other passage of the closed circuit from the shut-off position by the valve spring. It is characterized by comprising a switching valve that switches to an open position against the valve spring.

[0015]

Accordingly, the first aspect of the present invention provides a check valve, an orifice, and a pressure in the other passage which allow only one-way fluid flow from one passage to the other passage of the closed circuit. Because a neutral circuit having a neutral valve that closes when the pressure drops below a predetermined value is provided, when the prime mover stops and no charge pressure is supplied, the variable displacement pump
The closed circuit including the motor and the passage is disconnected from the charge passage. And a driving force acts on the motor from outside,
When the pressure in one passage of the closed circuit is increased, the neutral valve is switched to the shut-off position by the pressure decrease in the other passage, and the rotation of the motor is stopped to stop the outflow of the fluid in the one passage. When the driving force from the outside of the motor increases the pressure in the other passage of the closed circuit, the check valve of the neutral circuit stops the outflow of the fluid in the other passage, so that the rotation of the motor is prevented. Therefore, even if the vehicle is stopped halfway along the slope, the vehicle does not slip down.

Further, since the discharge flow rate of the variable displacement pump is set so as to discharge a small amount to one of the passages in the neutral state, only one neutral circuit is required. Can be simplified. That is, when the minute flow rate in the neutral state of the variable displacement pump is discharged from any port of the pump or the discharge direction cannot be determined, the neutral circuit shown in the present embodiment is set by reversing the operation direction. It is necessary to provide two circuits symmetrically.

Further, the neutral adjustment of the variable displacement pump, for example, the adjustment of the lever and the link system for controlling the displacement and the discharge direction of the variable displacement pump is not required to be highly accurate, and is slightly shifted in the backward direction (or slightly advanced). The adjustment can be simplified if it is adjusted toward the direction.

Since the stop state of the prime mover is determined based on the discharge pressure of the charge pump introduced through the closed circuit passage, the motor operates according to the charge pressure without requiring any special detecting means. It can be configured simply by inserting a valve,
No special detection means or actuator is required, and the configuration can be made at low cost.

Further, since the discharge pressure of the charge pump is introduced through the passage of the closed circuit, the charge passage must be extended even when the neutral valve of the neutral circuit is installed between the passages of the closed circuit. And the circuit configuration can be simplified.

[0020] The second invention provides, in addition to the effects of the first invention,
Since the neutral valve itself is provided with a check valve that allows only one-way fluid flow from one path of the closed circuit to the other path, space for the check valve is provided in the path of the neutral circuit. It is not necessary, and the path configuration of the neutral circuit is simplified.

According to the third invention, in addition to the effects of the first and second inventions, since the orifice is provided in the neutral valve itself, no space for the orifice is required in the passage of the neutral circuit, and the neutral valve is not required. The path configuration of the circuit is simplified.

[0022]

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

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

In FIG. 1, a portion surrounded by a two-dot chain line indicates a hydraulic pressure transmission device 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. In the variable displacement pump 10, the minute discharge flow rate is slightly biased and adjusted so as to be discharged from the upper port in the neutral state. The discharge direction of the variable displacement pump may be opposite to that described above, such that the discharge is performed to the passage 31 at the F position and the discharge is performed to the passage 30 at the R position. The description will be made on the assumption that the liquid is ejected.

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 figure, the vehicle rotates in a direction in which the vehicle moves forward, and when the fluid is supplied from the lower side in the figure, the vehicle rotates in a direction to retract the vehicle. Is proportional to the fluid supply. The ports of the variable displacement pump 10 and the constant displacement motor 20 are connected to each other by passages 30 and 31 to form a closed circuit. In addition, the driving direction of the constant displacement motor rotates in the reverse direction when receiving the supply of the fluid from the upper passage 30 in the drawing, and reverses the supply of the fluid from the lower passage 31. Although it may rotate in the direction in which the vehicle moves forward, hereinafter, it will be described as rotating as described above.

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. Thereby, the inside of the closed circuit is maintained at a predetermined pressure or more, and cavitation caused by the suction negative pressure is prevented. The charge pump 35 sucks fluid from the oil tank 6 provided outside the hydraulic pressure transmission device 1 through the suction pipe 7, and the charge passage 37 passes through the charge pipe 36 having the oil filter 8 outside the hydraulic pressure transmission device 1. After that, it is configured to return to the charge passage 37 of the hydraulic pressure transmission device 1.

Reference numeral 40 denotes a high-pressure relief valve for connecting the passages 30 and 31 of the closed circuit at a predetermined pressure or higher. Reference numeral 41 denotes an opening from the charge passage 37 into the fluid pressure transmission device 1 to cool the inside of the case (not shown). A low-pressure relief valve provided in the passage 42.

Numeral 50 indicates a neutral valve for connecting a neutral circuit 51 for connecting the one passage 30 and the other passage 31 of the closed circuit. The neutral valve 50 has a shut-off position 52 and a communication position 53, and is set to a shut-off position 52 by a valve spring 54. The valve is biased and switches to the communication position 53 against the valve spring 54 by the pressure in the other passage 31 of the closed circuit. Further, the neutral circuit 51 allows the flow from one passage 30 to the other passage 31 of the closed circuit and allows the flow from the other passage 31 to the one passage 3.
It has a check valve 55 and an orifice passage 56 which blocks the flow to zero.

The pressure in the other passage 31 of the closed circuit is increased to the charge pressure Pc because the fluid is supplied from the charge passage 37 via the check valve 39 during the operation of the prime mover 5. Therefore, the neutral valve 50 is at the communication position 53 when the prime mover 5 is operating, and when the pressure in the other passage 31 of the closed circuit is lower than the charge pressure Pc due to the stop of the prime mover 5 or the like. It is located at the blocking position 52. The fluid in the case of the fluid pressure transmission 1 is returned to the oil tank 6 by the drain pipe 9.

Next, the operation will be described.

When the prime mover 5 of the vehicle is started with the forward / reverse lever 2 in the neutral N position, 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 case, and then cools the oil tank 6 through the drain port 9.
To the charge passage 3 by the low pressure relief valve 41.
7 and the passages 30 and 31 forming a closed circuit are maintained at the charge pressure Pc. Then, the neutral valve 50 receives the pressure in the other passage 31 of the closed circuit adjusted to the charge pressure Pc, and is switched to the communication position 53 against the valve spring 54.

Since the forward / reverse lever 2 is at the neutral position N, the variable displacement pump 10 basically does not discharge fluid, but is adjusted to discharge a small amount from the upper port. Since the neutral valve 50 of the neutral circuit 51 is located at the communication position 53, the neutral valve 50 is returned to the other passage 31 of the closed circuit via the check valve 55 and the orifice 56, and the passages 30 and 31 are maintained at the same pressure. Motor 2
It does not drive 0.

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 from the upper port in the figure. Discharge fluid. Although a part of the discharged fluid is returned to the passage 31 through the check valve 55 and the orifice 56 as described above because the neutral valve 50 of the neutral circuit 51 is at the communication position 53, the discharged fluid is partially returned by the passage resistance of the orifice 56. The pressure inside 30 rises and is supplied to constant displacement motor 20. 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 starts rotating and the vehicle starts moving forward. When the forward / reverse lever 2 is moved to the reverse R position, the lever 2 operates in the same manner as at the time of forward movement and moves in the backward direction.

When the forward / reverse lever 2 is switched to the neutral N position in order to stop the vehicle, the motor 5 is stopped, and the variable displacement pump 10 is stopped.
Does not flow, the constant displacement motor 20 also stops. Further, since the charge pump 35 is also stopped, the pressure in the charge passage 37 decreases. In this state, the fluid in the closed circuit passage 31 is confined by the variable displacement pump 10, the constant displacement motor 20, the check valve 39, and the check valve 55 of the neutral circuit 51.
0 is also a variable displacement pump 10 and a constant displacement motor 2
0, the outflow of the fluid is prevented by the check valve 39, and the outflow from the check valve 55 through the orifice 56 of the neutral circuit 51 is confined in an allowed state.
Both 0 and 31 are maintained at the charge pressure Pc.

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.
Acts on the constant displacement motor 20 through the shaft, and a reverse rotational force acts on the constant displacement motor 20 in the forward direction, thereby sucking fluid from the lower port in FIG. 1 and attempting to discharge the fluid to the upper port. The pressure in the passage 31 is reduced and the passage 30
Increase pressure inside. The pressure drop in this passage 31 is
This means a decrease in the pressure for holding the neutral valve 50 at the communication position 53, and the neutral valve 50 is switched to the shut-off position 52 by the valve spring 54. As a result, the fluid in the passage 30 is prevented from flowing out by 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 descends downhill. Does not occur. 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 stopped on a downhill slope without operating the parking brake, the rotational force in the forward direction from the driving wheels 4 is transmitted to the constant displacement motor via the final reduction gear 3 and the output shaft 21. 20 and the constant displacement motor 20
Exerts the same rotational force as during forward movement, and increases the pressure in the passage 31 in an attempt to discharge fluid to the lower port in FIG. As a result, the neutral valve 50 is opened, but the fluid in the passage 31 is prevented from flowing out by the check valve 55 of the neutral circuit 51. Therefore, 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 as described above.

The above operation has been described assuming that the driving direction of the constant displacement motor 20 is to advance the vehicle with the fluid from the passage 30 and to retract the vehicle with the fluid from the passage 31. May rotate in the opposite direction, that is, the vehicle may move backward due to the minute discharge flow rate of the variable displacement pump 10, and in this case, the discharge fluid in the forward direction of the vehicle is not recirculated. Efficient. In this case, the variable displacement pump 10 discharges to the passage 30 at the R position and discharges to the passage 31 at the F position.

The above embodiment has the following features.

Normally, it is not possible to determine the discharge direction as to whether a small flow rate of the variable displacement pump in the neutral state is discharged from any port of the pump, and two neutral circuits shown in this embodiment are prepared. It is necessary to provide them symmetrically in opposite directions. However, in this embodiment, only one neutral circuit is required by discharging a minute flow rate in the neutral state of the variable displacement pump from one of the pumps, and the neutral circuit can be simplified.

Further, the neutral adjustment of the variable displacement pump is not required to have high precision, but may be adjusted slightly toward the backward direction (or slightly toward the forward direction), and the adjustment is simplified.

Further, since the stop state of the vehicle is determined based on the discharge pressure of the charge pump introduced through the closed circuit passage, the vehicle operates according to the charge pressure without requiring any special detecting means. It can be constructed simply by inserting a valve, and does not require any special detection means or actuator, and can be constructed at low cost.

Further, since the discharge pressure of the charge pump is introduced through a closed circuit passage, the charge passage must be extended even when a neutral valve of a neutral circuit is installed between the closed circuit passages. And the circuit configuration can be simplified.

FIGS. 2 to 4 show a second embodiment of the present invention. FIG. 2 is a sectional view, FIG. 3 is a sectional view taken along the line III-III of FIG. 2, and FIG. FIG. 2 is a partially enlarged view showing a characteristic portion, and the same portions as those in FIG. Although the present invention includes the case where there is a minute discharge when the vehicle moves backward as described above, the present embodiment describes the case where the variable displacement pump has a minute flow rate when the vehicle moves forward.

In the hydraulic pressure transmission 1 of the embodiment shown in FIGS. 2 and 3, the variable displacement pump 10, the constant displacement motor 20, and the charge pump 35 are connected to the case 60 and the passages 31 and 32 of the closed circuit and each of them. The valve is accommodated in a space formed by the port block 61 for accommodating the valve, and the charge pump 35 is disposed on the back surface of the port block 61 so as to form an integral block as a whole. That is, the variable displacement pump 10 and the constant displacement motor 20 are provided with the input shaft 11 in a space formed by the case 60 and the port block 61.
And is supported by 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 at the input shaft 11 and arranged at equal intervals around the input shaft 11 and extending in the axial direction. The pistons 13 which are fitted, and which are urged in the extension direction by a spring built in the cylinder, that is, in the left direction in the drawing, come into contact with the protruding ends of the pistons 13 through thrust bearings, and And a valve plate 15 disposed between the cylinder block 12 and the port block 61. In the variable displacement pump 10, when 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 the figure, the piston 13 Performs a retracting motion with respect to the fluid, thereby sucking fluid from the port 17 (or port 16) shown in FIG.
The fluid is discharged from 7). This variable displacement pump 10
In the neutral state, the initial angle of the swash plate 14 is set so that the discharge flow rate is not completely reduced to zero and a minute fluid is discharged from the port 16.

The constant displacement motor 20 is supported on the output shaft 21 and is disposed at equal intervals around the output shaft 21 and has a plurality of cylinders extending in the axial direction. A piston 23 that is fitted and urged in a direction of extension by a spring built in the cylinder, that is, a leftward direction in FIG.
A thrust bearing 24, which is inclined and abuts a protruding end of each piston 23, and a valve plate 2 which is disposed between the cylinder block 22 and the port block 61.
5 is comprised. In this constant displacement motor 20, the thrust bearing 24 is inclined, and the motor shown in FIG.
When fluid is supplied from the port 26 among the ports 26 and 27, the thrust bearing 2 is extended when the piston 23 is extended.
By the guidance of 4, for example, rotation is given to the cylinder block 22 in the clockwise direction (forward direction) in FIG. 3, and the output shaft 21 is rotated in the counterclockwise direction. Further, when the fluid is supplied from the port 27, when the piston 23 is extended, 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 rotates counterclockwise in FIG. To 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. Are closed by plugs. Also, the port block 61
Has a pressure receiving surface that receives the pressure of the passage 30 and a pressure receiving surface that receives the pressure of the passage 31 at a portion connecting the passages 30 and 31, and when one of the pressures becomes a predetermined value or more, one of the pressures Is released to the other side. Check valves 38 and 39 which are disposed between the charge passage 37 and the passages 30 and 31 and supply the fluid in the charge passage 37 to the passages 30 and 31 when the pressure in the charge passage 37 is higher than the pressure in the passages 30 and 31. And

In a portion of the port block 61 adjacent to the high-pressure relief valve 40, a vertical hole 63 opened from the outside of the port block by opening a horizontal hole 62 for introducing a fluid in the passage 31 to the high-pressure relief valve 40, A passage is formed by a lateral hole 64 whose opening end is closed by a plug, which is opened to the side surface of the passage 30 and the passage 30, and a neutral circuit 51 is formed by providing a neutral valve 50 described later in the vertical hole 63. I have. The neutral circuit 51 will be described with reference to FIG.
In FIG. 4, the side hole 6 for the high-pressure relief valve 40 is shown.
2 is different from FIG. 2 only in that a lateral hole 65 whose opening end is closed by a plug and which is open to the passage 31 is used. In FIG. 4, the vertical hole 63 is slidably fitted into the vertical hole 63 and urged in a pressing direction by a valve spring 67 disposed between the vertical hole 63 and a plug 66 closing the open end of the vertical hole 63. And a valve spool 68 which is urged in the push-up direction by the pressure of the passage 31 acting on the end face from the side. When the pressure in the passage 31 is low and pushed by the valve spring 67 and is in the lower position, the spool 68 is blocked from the lateral hole 64 (blocking position), and is in the upper position against the valve spring 67 due to the pressure in the passage 31. Side hole 6
And a passage 69 (communication position) communicating with the passage 4.
9 communicates with a lateral hole 65 (the lateral hole 62 in FIG. 3). In this passage 69, an orifice 70 and a check valve 7 are provided.
1 is provided in series, and the check valve 71 permits the movement of the fluid from the passage 30 side to the passage 31 side and prevents the backflow thereto. The check ball of the check valve 71 is prevented from falling off by a pin.

The hydraulic transmission 1 according to the second embodiment having the above-described configuration includes the prime mover 5 on the input shaft 11 and the output shaft 2
1, the final reduction gear 3 and the drive wheels 4 are connected as in the first embodiment, and the charge pump 35 is connected to the suction pipe 7.
Then, the fluid is sucked from the oil tank 6 via the oil tank 6 and the fluid is supplied to the charge passage 37 via the charge pipe 36, the oil cooler 8a, and the oil filter 8, thereby operating as follows.

The variable displacement pump 10 is driven 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 is supplied to the hydraulic pressure transmission device 1 through the passage 42 to open the low-pressure relief valve 41, flow into the case 60 of the hydraulic pressure transmission device 1, cool the case 60, and then drain the oil through the drain port 9. It flows to 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. Then, the valve spool 68 of the neutral valve 50 receives the pressure of the passage 31 (the same pressure as the charge pressure Pc) on the end face, retreats against the valve spring 67, and is moved to the upper communication position.

Variable displacement pump 10 in neutral position
Fluid discharged from the passage 30 through the lateral hole 6
4 to the valve spool 68 and the orifice 7 of the valve spool 68 of the neutral valve 50 in the communicating position.
0, the passage 69 passes through the check valve 71, reaches the side hole 65, is returned to the passage 31, and maintains the passages 30 and 31 at the same pressure.
The constant displacement motor 20 is not driven.

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. The discharged fluid is partially discharged from the passage 30 through the orifice 7 in the valve spool 68 of the neutral valve 50.
0 and the passage 31 through the check valve 71 as described above.
The pressure in the passage 30 rises due to the passage resistance of the orifice 70 and is supplied to the port 26 of the constant displacement motor 20. This pressure is the starting pressure of the vehicle (the pressure required to move the vehicle). Is reached, the constant displacement motor 20 starts rotating and the vehicle starts moving forward. When the swash plate 14 of the variable displacement pump 10 is tilted to the reverse R position by the forward / reverse lever, the same operation as that at the time of forward movement is performed, and the vehicle moves backward.

While the vehicle is being driven, one of the passages 30 and 31 constituting 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. . Then, the pressure is adjusted to the charge pressure Pc in order to open the check valve 38 (or the check valve 39) and adjust the pressure so that the pressure in the low-pressure side passage does not become lower than the charge pressure Pc.

When the variable displacement pump 10 is set in the neutral N state by the forward / reverse lever to stop the vehicle, and the motor 5 is stopped to stop the variable displacement pump 10, the constant displacement motor 20 is also stopped. Since the charge pump 35 also stops, the pressure in the charge passage 37 also decreases. In this state, the fluid in the passage 31 of the closed circuit is
0, confined by a constant displacement motor 20, a check valve 39 and a check valve 71 of a neutral valve 50,
Further, the closed circuit passage 30 is also provided with the variable displacement pump 1.
0, the outflow of the fluid is prevented by the constant displacement motor 20 and the check valve 38, and the outflow from the check valve 71 through the orifice 70 of the neutral valve 50 is confined in an allowed state. Both are maintained at the charge pressure Pc.

Therefore, when the vehicle stops on an uphill slope without operating the parking brake, the rotational force in the backward direction from the drive wheels 4 is transmitted to the fixed displacement motor via the final reduction gear 3 and the output shaft 21. A reverse rotational force acts on the port 20 to discharge the fluid to the port 26, thereby reducing the pressure in the passage 31 and increasing the pressure in the passage 30. The pressure drop in the passage 31 weakens the maintenance of the communication position, and the neutral pressure of the neutral valve 5
The zero valve spool 68 is switched from the communicating position to the shut-off position. As a result, the fluid in the passage 30 is prevented from flowing out by the neutral valve 50 at the shutoff position, and the rotation of the constant displacement motor 20 is restricted by the increase in the pressure in the passage 30, and the vehicle descends downhill. Absent.

When the parking brake is not operated and the vehicle is stopped on a downhill, 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. 20 by applying a rotational force in the same direction as the forward movement to discharge the fluid to the port 27.
Increase the pressure in 1. Since the fluid in the passage 31 is prevented from flowing out by the check valve 71 at the communicating position with the valve spool 68 of the neutral valve 50, the passage 31
The rotation of the constant displacement motor 20 is regulated by the pressure rise inside the
The vehicle is prevented from falling downhill.

In this embodiment, since the neutral valve itself is provided with a check valve that allows only one-way fluid flow from one passage of the closed circuit to the other passage, the neutral circuit is No space is required for the check valve in the passage, and the passage configuration of the neutral circuit is simplified.

Further, since the orifice is inserted into the neutral valve itself, no space is required for the orifice in the passage of the neutral circuit, and this also simplifies the passage configuration of the neutral circuit.

In the above embodiment, the pump and the motor have been 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 the fluid changes is described as the pump, although not shown, a variable displacement pump in which only the discharge volume changes without changing the discharge direction may be used. 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 one embodiment of the present invention.

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

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

4 is an enlarged sectional view of the neutral circuit in 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, 67, 68 Neutral valve 51, 62, 63, 64, 65 Neutral circuit 55, 71 Check valve 56, 70 Orifice

Claims (3)

[Claims] 1. A closed circuit in which ports of a variable displacement pump and a motor communicate with each other through a passage, and a charge passage for supplying a fluid from a charge pump at a predetermined pressure to each passage of the closed circuit. In the hydraulic pressure transmission device, the discharge flow rate of the variable displacement pump is set so as to be discharged in a small amount to one of the passages in a neutral state, and the one-way flow from one passage to the other passage of the closed circuit is set. It has a check valve that allows only fluid flow, an orifice, and a neutral valve that closes when the pressure in the other passage falls below a predetermined value, and discharges when the discharge amount of the variable displacement pump is minute. A fluid pressure transmission device comprising a neutral circuit that allows fluid to flow from one passage of a closed circuit to another passage. 2. The neutral valve has a shut-off position and an open position in which a check valve that allows only one-way fluid flow from one passage of the closed circuit to the other passage is inserted. 2. The switching valve according to claim 1, wherein the switching valve is configured to switch from the shut-off position by the valve spring to the open position against the valve spring by a predetermined pressure or more in the other passage of the closed circuit. Fluid pressure transmission. 3. The neutral valve has a shut-off position and an open position in which an orifice is inserted, and the neutral valve applies a pressure equal to or higher than a predetermined value in the other passage of the closed circuit from the shut-off position by the valve spring to the valve spring. 3. The hydraulic power transmission according to claim 1, wherein the hydraulic pressure transmission is configured by a switching valve that switches to an open position.