JP2012052581A - Hydraulic travel driving device - Google Patents

Abstract

In a hydraulic travel drive device having a hydraulic closed circuit having a hydraulic pump and a hydraulic motor, an inexpensive and highly reliable device that suppresses generation of a high brake pressure when a sudden reverse operation is performed is provided. provide.
When a forward / reverse switching operation lever is switched from backward to forward, the controller determines whether the input direction of the forward / reverse switching operation lever is opposite to the traveling direction of the vehicle detected by the speed / traveling direction detector. Determine whether. If the determination result is affirmative, it is determined that a sudden reverse operation has been performed, and a command to hold the hydraulic pump tilt direction switching valve in a neutral position is issued, and a command to switch to a position corresponding to the input signal is issued. Put out with a delay.
[Selection] Figure 3

Description

  The present invention relates to a hydraulic travel drive device used for a self-propelled work vehicle, and more specifically, a variable displacement hydraulic pump provided with a bi-directional tilt mechanism and a variable displacement hydraulic motor constitute a hydraulic closed circuit. The present invention relates to a connected hydraulic travel drive device.

A variable displacement hydraulic pump having a bi-directional tilting mechanism driven by an engine and a variable displacement hydraulic motor driven by this hydraulic pump to rotate a wheel (tire) are connected by a hydraulic circuit constituting a closed circuit. 2. Description of the Related Art A hydraulic traveling drive device used for a connected self-propelled work vehicle such as a wheel loader is known.
In such a wheel loader equipped with a hydraulic travel drive device, after excavating earth and sand, gravel, etc., the so-called V-shaped excavation work is performed in which the vehicle once moves backward and then moves forward again and is loaded into the dump truck. In the V-shaped excavation work, a so-called sudden reverse operation is performed in which the forward / reverse switching operation lever is switched from the reverse position to the forward position while the vehicle is moving backward.

In a closed circuit vehicle, when the vehicle decelerates, including a sudden reverse operation, the hydraulic motor is rotated by inertial force to perform a pump operation that discharges pressure oil, and the hydraulic pump is driven to rotate by the pressure oil discharged from the hydraulic motor. The motor is operated. At this time, the brake pressure that is generated in the main circuit connecting the hydraulic pump and the hydraulic motor and generates a braking force in the hydraulic motor that performs the pump operation depends on the change rate of the absorption flow rate of the hydraulic pump that performs the motor operation. When the pump capacity suddenly decreases due to the sudden reverse operation, a high brake pressure is established on the discharge side of the hydraulic motor, and the vehicle decelerates rapidly.
High brake pressure in motor operation different from the original action of the hydraulic pump reduces the reliability of the equipment, such as damaging the variable displacement hydraulic pump, and sudden deceleration of the vehicle deteriorates operability and workability. .

  As a countermeasure for this, the pump capacity control means and the pump tilt direction switching means are constituted by a pair of electromagnetic proportional valves corresponding to the pair of control pressure chambers respectively, and the control pressure acting on the control pressure chamber during the sudden reverse operation is controlled. It is known that the change in the pump capacity is controlled gently by controlling the change with an arbitrary function (see, for example, Patent Document 1).

Patent No. 4203941

However, in the prior art, the pump displacement control means and the pump tilting direction switching means are constituted by a pair of electromagnetic proportional valves respectively corresponding to the pair of control pressure chambers. The cost increases by using two valves. Further, since the electromagnetic proportional valve is vulnerable to contamination, there is a problem that reliability is lowered.
In addition, in order to change the displacement rate of the pump mechanically in any situation without using an electromagnetic proportional valve, there is a problem that the equipment configuration becomes complicated, for example, by adding a switching valve and a throttle.

  A hydraulic travel drive device used in a self-propelled work vehicle according to the present invention includes a variable displacement hydraulic pump that is driven by an engine and includes a bidirectional tilt mechanism that discharges pressure oil in both forward and reverse directions, The variable displacement hydraulic pump is connected to the variable displacement hydraulic pump by a pair of reverse main circuits, and forms a closed hydraulic circuit together with the variable displacement hydraulic pump and the pair of main circuits, and the bidirectional displacement of the variable displacement hydraulic pump. A pump tilting cylinder connected to the rotation mechanism, and driven to tilt and drive the bidirectional tilting mechanism forward and backward; an operating means for outputting forward and reverse input signals; and a pump tilting cylinder; Based on hydraulic pump tilt direction switching means that can be switched to forward, neutral, and reverse positions, and forward and reverse input signals that are output from the operating means. If it is determined that the operation is a sudden reverse operation, the hydraulic pump tilt direction switching means is instructed to hold the neutral position, and the command to switch to the position corresponding to the input signal is issued. And a control means for delaying the operation.

According to this invention, it is determined whether or not the operation is a sudden reverse operation by the control means, and if it is determined that the operation is a sudden reverse operation, the hydraulic pump tilt direction switching means is held at the neutral position for a predetermined time, and thereafter Switch to the position corresponding to the input signal. Therefore, generation of a high brake pressure is suppressed.
Further, since the work is facilitated without increasing the number of parts, the cost can be reduced and the reliability of the work can be ensured.

1 is a circuit diagram of a hydraulic travel drive device according to the present invention. The figure for demonstrating the timing of operation | movement of each part in the hydraulic travel drive device shown in FIG. The processing flow figure as Embodiment 1 of the hydraulic travel drive device of this invention. The figure for demonstrating the timing of operation | movement of each part in hydraulic travel drive apparatus concerning Embodiment 2 of this invention. FIG. 5 is a process flow diagram for performing operation timing of each unit in the hydraulic travel drive device illustrated in FIG. 4. The figure for demonstrating the timing of operation | movement of each part in hydraulic travel drive apparatus concerning Embodiment 3 of this invention.

--Embodiment 1--
Hereinafter, a hydraulic travel drive apparatus according to the present invention will be described with reference to the drawings.
FIG. 1 is a circuit diagram of a hydraulic travel drive apparatus according to the present invention.
As shown in FIG. 1, a hydraulic travel drive device 1 mounted on a self-propelled work vehicle such as a wheel loader or a skid steer loader has a variable displacement hydraulic pump having a bi-directional tilt mechanism driven by an engine E. 11. The variable displacement hydraulic pump 11 has a bi-directional tilt mechanism that discharges pressure oil to both a pair of main circuits including a forward main circuit 51a and a reverse main circuit 51b.

  A variable displacement hydraulic motor 12 driven by the variable displacement hydraulic pump 11 is disposed in a pair of main circuits including the forward main circuit 51a and the reverse main circuit 51b. The variable displacement hydraulic pump 11, the variable displacement hydraulic motor 12, the forward main circuit 51a, and the reverse main circuit 51b constitute a hydraulic closed circuit.

  A servo piston 21 of a pump tilt cylinder 20 is connected to the bidirectional tilt mechanism of the variable displacement pump 11. A reverse-side control chamber 22a and a forward-side control chamber 22b are disposed on both sides of the servo piston 21, and each control chamber 22a, 22b has a spring (biasing force) for biasing the servo piston 21 toward the center. Members) 23a and 23b are provided. A pair of springs 23a and 23b are balanced while the servo piston 21 is held at the neutral position while a command to hold the hydraulic pump tilt direction switching valve 30 to be described later is held at the neutral position. The tank pressure (same pressure) acts on the control chamber. When the servo piston 21 moves from the center position to the right in FIG. 1 (reverse drive control chamber 22a side), the variable displacement pump 11 discharges the pressure oil to the forward main circuit 51a, and the servo piston 21 is moved from the center position. 1, the variable displacement pump 11 discharges the pressure oil to the reverse main circuit 51b. The capacity of the pressure oil discharged to each main circuit 51a, 51b increases in proportion to the amount of movement from the center of the servo piston 21.

  Pressure oil is introduced into the control chambers 22 a and 22 b of the pump tilt cylinder 20 via a hydraulic pump tilt direction switching valve 30. The hydraulic pump tilt direction switching valve 30 is a solenoid valve, and is switched to a reverse position a, a neutral position n, and a forward position b by a signal from the controller 71. Although not shown, the control pressure generator 25 includes a charge pump, a pressure reducing valve, and the like, and supplies hydraulic oil having a predetermined pressure corresponding to the engine speed to the hydraulic pump tilt direction switching valve 30.

  A motor capacity controller 72 is connected to the variable capacity motor 12. The motor capacity control unit 72 changes the motor capacity of the variable capacity motor 12 according to a command from the controller 71. The rotation of the variable displacement motor 12 rotates the wheel W of the wheel loader, and the wheel loader moves forward or backward. 73 is a speed / traveling direction detector that detects the traveling speed V of the wheel loader and the traveling direction of forward (F) and backward (R), and sends the detected speed and traveling direction to the controller 71.

  The forward, neutral, and reverse movements of the wheel loader are switched by operating the forward / reverse switching operation lever 75. The forward / reverse switching operation lever 75 sends forward (F), neutral (N), and reverse (R) input signals to the controller 71 during the lever switching operation.

  2A and 2B are diagrams for explaining the operation and timing of each part of the wheel loader shown in FIG. 1. FIG. 2A is a circuit pressure of main circuits 51a and 51b, and FIG. (C) is the switching position of the hydraulic pump tilt direction switching valve 30, (D) is the actual pump tilt angle, (E) is the vehicle speed, and (F) is the capacity of the variable displacement hydraulic motor 12. , Respectively, shows changes over time. In each figure, the case of the present embodiment is shown by a solid line, and as a comparison, the conventional case, that is, the case where the neutral position of the hydraulic pump tilting direction switching valve 30 is not held during a sudden reverse operation is shown by a dotted line. Yes.

When the forward / reverse switching lever 75 is switched to reverse (R) from the state of FIG. 1, a signal w <b> 2 is sent from the controller 71 to the solenoid of the hydraulic pump tilt direction switching valve 30. As a result, the solenoid is excited, and the hydraulic pump tilt direction switching valve moves to the left in FIG. 1 and switches to the reverse position a. When an accelerator pedal (not shown) is depressed, pressure oil is introduced from the control pressure generator 25 into the backward control chamber 22a of the pump tilt cylinder 20. When the control pressure of the reverse side control chamber 22a acting on the servo piston 21 exceeds the total urging force of the spring 23a and the spring 23b, the servo piston 21 is discharged while discharging the pressure oil in the forward side control chamber 22b. 1 moves to the left.
Then, the pressure oil is discharged from the variable displacement pump 11 to the reverse main circuit 51b. Due to the pressure oil discharged to the reverse main circuit 51b, the variable displacement motor 12 rotates in the reverse direction, the wheel W is driven, and the wheel loader travels in the reverse direction.

  When the forward / reverse switching lever 75 is switched to forward (F), a switching signal w 1 is sent from the controller 71 to the solenoid of the hydraulic pump tilt direction switching valve 30. As a result, the hydraulic pump tilt direction switching valve 30 moves to the right in FIG. 1 and switches to the forward position b. When an accelerator pedal (not shown) is depressed, pressure oil is introduced from the control pressure generator 25 into the forward-side control chamber 22b of the pump tilt cylinder 20. The servo piston 21 moves rightward in FIG. 1 by the control pressure in the forward side control chamber 22b. As a result, pressure oil is discharged from the variable displacement pump 11 to the forward main circuit 51a, the variable displacement motor 12 rotates in the forward direction, the wheel W is driven, and the wheel loader travels in the forward direction.

In the above description, whether the vehicle is moving forward or backward, the pump capacity increases in proportion to the increase in the control pressure by the pressure oil introduced into the control chamber 22a or 22b, and the servo piston 21 reaches the stroke end. The pump capacity is maximum and the traveling speed is maximum V ₀ .
The traveling speed and the traveling direction are detected by a speed / traveling direction detector 73 and sent to the controller 71.

FIG. 3 is a process flow diagram showing the operation of the hydraulic travel drive device of the present embodiment. This processing flow is executed by the tilt control program of the controller 71. Hereinafter, Embodiment 1 of the hydraulic travel drive device of the present invention will be described with reference to FIGS.
In step S1, it is determined whether or not the forward / reverse switching operation lever 75 is switched. When there is no switching operation, the presence or absence of the switching operation is monitored every predetermined time.
In the present embodiment, as shown in FIG. 2 (E), a state in which the wheel loader is backward at maximum speed V _0. In this state, a signal w2 is sent from the controller 71 to the hydraulic pump tilt direction switching valve 30, and the hydraulic pump tilt direction switching valve 30 is in the reverse drive position a. In this state, as shown in FIG. 2 (B), at time t ₀ , the forward / reverse switching operation lever 75 is suddenly operated backward (R) to forward (F) without stopping at neutral (N). When this is done, the controller 71 determines that the switching operation is present, based on the input signal from the forward / reverse switching lever 75.

  If the presence or absence of the switching operation is affirmed in step S1, the forward (F) and reverse (R) input signals input from the forward / reverse switching operation lever 75 to the controller 71 and the speed / traveling direction detector in step S2. It is determined whether the signal indicating the traveling direction of the wheel loader input from 73 to the controller 71 is opposite. Here, the reverse means that if one is forward, the other is backward, and if one is backward, the other is forward. In step S2, if the determination is affirmative, the process proceeds to step S3, and if the determination is negative, the process proceeds to step S5.

When the wheel loader is moving backward at the maximum speed V ₀ , immediately after the forward / reverse switching lever 75 is switched to forward (F), the wheel loader is moving in the backward direction due to the inertial force. Affirmed in If the determination in step S2 is affirmative, in step S3, the controller 71 instructs the hydraulic pump tilt direction switching valve 30 to hold the hydraulic pump tilt direction switching valve 30 at the neutral position n. As a result, the signal w1 sent from the controller 71 to the hydraulic pump tilt direction switching valve 30 is turned off, and the hydraulic pump tilt direction switching valve 30 is set to the neutral position n as shown in FIG. Switch to.

After performing the process of step S3, it is determined in step S4 whether or not the speed V of the wheel loader is V ₁ or less. If affirmative in step S4, the process proceeds to step S5, and if negative, the process returns to step S3. Here, in step S2, it is determined that the traveling direction indicated by the forward (F) and backward (R) input signals of the forward / reverse switching operation lever 75 is opposite to the traveling direction of the wheel loader. Processing is performed when the reverse operation is performed. That is, as shown in FIG. 2B, the hydraulic pressure is maintained until t ₁ when the speed V of the wheel loader is equal to or lower than V _{1 in} spite of the state where the forward / reverse switching lever 75 is switched forward. The type pump tilting direction switching valve 30 is held at the neutral position n (see FIG. 2C).

When the speed V of the wheel loader becomes V ₁ or less, the hydraulic pump tilt direction switching valve 30 matches the forward (F) direction switched by the forward / reverse switching operation lever 75 in step S5. Switch to forward position b. In this case, a signal w1 is sent from the controller 71 to the hydraulic pump tilt direction switching valve 30, the solenoid is excited, and the hydraulic pump tilt direction switching valve 30 moves rightward in FIG. The position is switched to the forward position b (see FIG. 2C). After step S5, the tilt angle of the variable displacement hydraulic pump 11 varies according to the output pressure of the control pressure generator.
If the result in step S2 is negative, there is no need to perform a sudden reverse operation process, and the process proceeds to step S5, where the hydraulic pump tilting direction switching valve 30 is immediately moved forward (switched by the forward / reverse switching operation lever 75). F) Switch to the forward position b that matches the direction.

The pressure of the main circuit after time t ₀ when the sudden reverse operation is performed will be described with reference to FIG.
Since the hydraulic pump tilt direction switching valve 30 is switched to the neutral position n at time t ₀ , the pressure oil from the control pressure generator 25 is blocked by the hydraulic pump tilt direction switching valve 30. In this state, the servo piston 21 receives a thrust corresponding to the urging force of the spring 23b on the forward side control chamber 22b and the spring 23a on the reverse side control chamber 22a, and drains the pressure oil in the forward side control chamber 22a. However, it moves at a gentle speed in the right direction in FIG. Immediately after the forward / reverse switching lever 75 is switched to forward (F), the variable displacement hydraulic motor 12 continues to rotate backward due to inertial force, and the forward main circuit 51a sets the motor rotational speed. Pump operation is performed to discharge the corresponding pressure oil. Since the variable displacement hydraulic pump 11, the variable displacement hydraulic motor 12, the forward main circuit 51a, and the reverse main circuit 51b constitute a hydraulic closed circuit, the variable displacement hydraulic motor 12 operates as a hydraulic pump. The variable displacement hydraulic pump 11 operates as a hydraulic motor driven by the variable displacement hydraulic motor 12 in order to continue the supply of pressure oil to the forward main circuit 51a. However, since the servo piston 21 moves slowly toward the neutral position and the rate of decrease in the pump capacity of the variable displacement hydraulic pump 11 is slow, the forward main circuit that is generated depending on the rate of change in the absorption flow rate of the pump. braking pressure established in 51a, as shown by the solid line shown in FIG. 2 (a) lower, wheel loader during the time t ₀ to t _1, it performs slowly decelerate.

As shown in FIG. 2 (E), at time t ₁ when the speed V of the wheel loader becomes V ₁ or less, the hydraulic pump tilt direction switching valve 30 is switched to the forward position b (FIG. 2 (C)). Reference), pressure oil is introduced from the control pressure generator 25 into the forward control chamber 22b. Then, the servo piston 21 is moved rightward in FIG. 1 by the total pressure of the control pressure of the pressure oil introduced into the forward control chamber 22b and the urging force of the springs 23a and 23b, and a sudden reverse operation is started. To do.
The variable displacement hydraulic motor 12 that continues to rotate due to an inertial force during a sudden reverse operation operates as a hydraulic pump.

Since the variable displacement hydraulic pump 11 operates as a hydraulic motor and rotates the engine E, the forward main circuit 51a corresponds to the absorption flow rate change of the hydraulic pump operating as the hydraulic motor, that is, the tilting speed of the hydraulic pump. A large brake pressure is generated. This point is different from the case of the hydraulic open circuit, and in a motor operation different from the original action of the hydraulic pump, a large load is easily applied to the variable displacement hydraulic pump 11, and it is possible to deal with damage and reliability. Needed. However, in the case of the wheel loader in the present embodiment, the hydraulic pump tilt direction switching valve 30 is held at the neutral position n until the speed V ₁ is reached, so that the vehicle speed during the sudden reverse operation is sufficiently reduced. Since the discharge flow rate of the hydraulic motor that generates the brake pressure is small, the brake pressure can be reduced.

In FIGS. 2A, 2C, 2D, and 2E, as a comparison, the case of a conventional hydraulic travel drive device is indicated by a dotted line. In the conventional hydraulic travel drive device, when the forward / reverse switching lever 75 is switched to forward (F), as shown in FIG. 2 (C), the hydraulic pump tilt direction switching valve 30 is simultaneously moved to the forward position b. Switch to. In other words, the hydraulic traveling drive apparatus suddenly reverse operation is started in a state close to the maximum speed V _0. Accordingly, at this time, the brake pressure P ₀ (see FIG. 2A) generated in the forward main circuit 51a is a large value of about 50 MPa, for example. On the other hand, in this embodiment, since the wheel loader starts a sudden reverse operation after time t ₁ when the speed becomes V ₁ or less, the maximum brake pressure P ₁ generated in the forward main circuit 51 a is P _0. It is possible to suppress the pressure to a considerably lower level, for example, about 45 MPa or less.

According to the first embodiment, the controller 71 determines whether or not the operation is a sudden reverse operation. If it is determined that the operation is a sudden reverse operation, the hydraulic pump tilt direction switching valve 30 is held at the neutral position n. Issue a command. This state is maintained until the speed of the wheel loader becomes a predetermined speed V ₂₁ or less. In a state where the hydraulic pump tilt direction switching valve 30 is held at the neutral position n, the pressure oil from the control pressure generating unit 25 is shut off by the hydraulic pump tilt direction switching valve 30, and the servo piston 30 It is moved toward the neutral position only by the urging force of 23b. For this reason, the movement of the servo piston 30 is more gradual than when the servo piston 30 is moved toward the forward position by the biasing force of the spring 23b together with the forward control pressure introduced into the control chamber 22b of the pump tilt cylinder 20. Become.
Therefore, the tilting operation of the bi-directional tilting mechanism of the variable displacement hydraulic pump 11 driven by the servo piston 30 becomes gentle, and the generation of high brake pressure is suppressed. Thus, when it is detected that the sudden reverse operation has been performed, the hydraulic pump tilt direction switching valve 30 is held at the neutral position n for a predetermined time, and then switched to the forward position b. There is an effect that costs can be reduced and work reliability can be ensured.

In the above-described embodiment, the case of performing a sudden reverse operation from reverse to forward has been described. However, as shown in the process flow diagram of FIG. 3 described as a processing method including both cases of forward and reverse, the present invention. This hydraulic travel drive device can perform the same processing even when performing a sudden reverse operation from forward to reverse.
Further, the present invention is not limited to the case of operating immediately from reverse (R) to forward (F), but after switching from reverse (R) to neutral (N), forward from neutral (N) before sufficient deceleration (vehicle speed ≧ V ₁ ). The present invention can also be applied when switching to (F).
In the first embodiment, the motor capacity shown in FIG. 2F is the motor capacity of the variable displacement hydraulic motor 12 and is kept constant in this embodiment.
However, the wheel loader of the present invention can further reduce the brake pressure by changing the capacity of the hydraulic motor in response to the sudden reverse operation. Hereinafter, such an embodiment will be described.

--Embodiment 2--
4 and 5 show Embodiment 2 of the hydraulic travel drive apparatus of the present invention, FIG. 4 is a diagram for explaining the timing of the operation of each part in the hydraulic travel drive apparatus, and FIG. It is a processing flow figure which performs the timing of operation | movement of each part in the hydraulic travel drive device shown in figure.
5 is different from FIG. 3 only in that the process shown in step S11 is added between step S3 and step S4 in FIG. The rest is the same. Therefore, contents related to step S11 will be described.

During reverse wheel loader, when sudden reverse operation to switch to the forward at once (F) the forward-reverse switching operation lever 75 from the reverse (R) at time t _0, the controller 71 detects this abrupt reverse operation. The controller 71 instructs the hydraulic pump tilt direction switching valve 30 to switch to the neutral position n, whereby the hydraulic pump tilt direction switching valve 30 is held at the neutral position n. This is the process from step S1 to step S3. In step S11, the controller 71 issues a command to increase the motor capacity of the variable displacement hydraulic motor 12 to the motor capacity control unit 72 while the hydraulic pump tilt direction switching valve 30 is held at the neutral position n. .

The increase in motor capacity is controlled using a ramp function as shown in FIG. As a result, the motor capacity increases linearly with time. When the motor capacity increases while the pump tilt of the hydraulic travel drive device 1 is decelerating at the neutral position, the brake pressure acting on the hydraulic closed circuit increases in accordance with the changing speed of the motor capacity.
As described above, in the hydraulic closed circuit, immediately after the sudden reverse operation, the variable displacement hydraulic motor 12 operates as a hydraulic pump, and the variable displacement hydraulic pump 11 operates as a hydraulic motor. For this reason, the kinetic energy of the traveling wheel loader is decelerated by being consumed by the variable displacement hydraulic motor 12 acting as a pump. When the capacity of the variable displacement hydraulic motor 12 performing the pumping action increases, the discharge flow rate of the pressure oil discharged from the variable displacement motor 12 to the main circuit increases, and thus the pressure of the main circuit increases. Since the pressure (brake pressure) for driving the variable displacement hydraulic pump 11 increases, the kinetic energy of the wheel loader is consumed quickly. In this way, the deceleration time of the wheel loader is shortened and the braking force is increased. Here, the magnitude of the braking force of the wheel loader is proportional to the product of the brake pressure and the motor capacity.

  In other words, as shown in the first embodiment, the hydraulic pump tilt direction switching valve 30 is provided as compared with the case where the hydraulic pump tilt direction switching valve 30 is held only at the neutral position n and the motor capacity is not increased. When the motor capacity of the variable displacement hydraulic motor 12 is increased while being held at the neutral position n, the braking force of the wheel loader increases and the wheel loader decelerates earlier. At this time, the change rate of the motor capacity is controlled using a ramp function so that the brake pressure increases within a range that does not affect the reliability of the hydraulic equipment including the variable displacement hydraulic pump 11.

As shown in FIG. 4 (F), the motor capacity of the variable displacement hydraulic motor 12, hydraulic pump tilting direction switching valve 30 is over time from the capacitive q ₀ at time t ₀ has been switched to the neutral position n Ascend linearly. Then, at time t ₁ ′, the capacity q ₁ becomes larger than the capacity q ₀ and thereafter becomes constant. Since the rate of deceleration of the wheel loader is larger than that in the first embodiment, the time interval at which the wheel loader changes from the maximum speed V ₀ to the speed V ₁ is shorter than that in the first embodiment. In other words, the time _{t 1} 'is than the time _{t 1} shown in embodiment 1, a short time interval from time _{t 0.}

Then, after the speed becomes equal to or lower than the predetermined speed V ₁ at time t ₁ ′, the motor capacity is maintained at q ₁ and does not increase, so that the brake pressure does not increase due to the increase in motor capacity.
Further, since the rapid reverse operation is started after time t ₁ ′, the capacity change speed of the pump increases, and a brake pressure corresponding to the braking force sufficient to generate the vehicle deceleration corresponding thereto is generated. Here, since the braking force of the variable displacement hydraulic motor performing the pump operation is proportional to the product of the brake pressure and the motor capacity, the motor capacity increases from q ₀ to q ₁ at the start of the sudden reverse operation. Thus, the brake pressure can be reduced to about q ₀ / q ₁ .
For this reason, the maximum pressure P ₁ ′ of the forward main circuit 51a is lower than the pressure P ₁ of the forward main circuit 51a in the first embodiment, for example, about 40 MPa or less.
4 (A) and 4 (C), the dotted line indicates the conventional case where the hydraulic pump tilt direction switching valve 30 is switched to the forward position a simultaneously with the switching of the forward / reverse switching operation lever 75.
As described above, also in the second embodiment, the same effect as in the first embodiment can be obtained. Moreover, in the second embodiment, an effect that the traveling start time in the reverse direction by the hydraulic traveling drive device 1 can be shortened can be obtained.

  In addition, in the increase of the motor capacity in step 11 in the second embodiment, it is desirable to set the upper limit value to a value lower than that in the case of normal traveling that is not a sudden reverse operation. During a sudden reverse operation, a traveling operation in the reverse direction is started in a state where the wheel loader is not completely stopped, and thus a larger hydraulic brake is applied than this in the normal traveling. Therefore, the upper limit value of the motor capacity is set lower than that in the case of normal traveling. As a result, it is possible to prevent an abnormality in running performance such as sudden deceleration due to braking due to an excessive motor capacity.

  The gradient of the change rate of the motor capacity is adjusted by the ramp function so as to correspond to the operating condition of the wheel loader. For example, when the speed when a sudden reverse operation is performed is large, the slope of the ramp function is increased to increase the hydraulic brake. On the other hand, when the speed when the sudden reverse operation is performed is small, the slope of the ramp function is reduced to weaken the hydraulic brake. As described above, by changing the slope of the ramp function according to the speed at the start of the sudden reverse operation, a good hydraulic brake can be obtained during the sudden reverse travel, and the operability can be improved.

--Embodiment 3--
6 (A) and 6 (F) are diagrams for explaining Embodiment 3 of the hydraulic drive device of the present invention, FIG. 6 (A) is the circuit pressure of the main circuit, and FIG. 6 (F) is the variable capacitance. The change over time is shown for the capacity of each type of hydraulic motor.
In the second embodiment, as illustrated in FIG. 4 (A), the pressure of the forward-side main circuit 51a is once, maximum 'time _{t a} and the time _{t 1} between the' after time _{t 0} and _{t 1} The pressure is P ₁ ′, and a V-shaped curve is formed in the meantime. This is a phenomenon that occurs because of increased from the time t ₀ the motor capacity at a predetermined rate of change will be explained below.

  As the motor capacity increases, the motor discharge flow rate increases at a predetermined change speed, and the brake pressure PBq (pressure of the forward main circuit 51a) accompanying the motor capacity change also increases at the predetermined change speed (dPBq / dt). As a result, the vehicle speed V decreases at a predetermined change speed depending on the brake pressure. When the motor rotation speed decreases with a decrease in the vehicle speed V, the motor discharge flow rate decreases at a predetermined change speed, so that the brake pressure PBv accompanying the vehicle speed reduction decreases at a predetermined change speed (dPBv / dt). Therefore, the pressure change curve of the forward-side main circuit 51a in FIG. 4A and the vehicle speed change curve in FIG. 4E are associated with a predetermined change speed (dPBq / dt) of brake pressure and a reduction in vehicle speed accompanying the change in motor capacity. It becomes a curve depending on a predetermined change speed (dPBv / dt) of the brake pressure.

In the embodiment 2, _'at the time t _a before the pump 11 is discharged pressure oil to the forward side main circuit 51a, the pressure of the forward-side main circuit 51a is the maximum value P _1' time t ₁ reaches, thereafter, It shows a downward trend.

Embodiment 3, as shown in FIG. 6 (A), as a substantially flat shape pressure of the main circuit during the time t _a and t _{1 ',} those with improved deceleration rate of the hydraulic drive system . That is, by increasing the motor capacity change rate from the time t _a, increases the predetermined rate of change of the brake pressure associated therewith (dPBq / dt). As a result, the vehicle speed reduction change speed is reduced, and the brake pressure change speed (dPBv / dt) accompanying the vehicle speed change is reduced. Embodiment 3, as shown in FIG. 6 (A), and a substantially constant brake pressure generated in the forward side main circuit 51a from time t _a to time t _{1 '.} Therefore, it is possible to improve the reduction in the vehicle speed reduction rate during the time t _a to the time t ₁ ′ compared to the second embodiment.

The pressure of the forward-side main circuit 51a as shown in FIG. 6 (A), hydraulic pump tilting direction switching valve 30 is between the time t _{1 'from} the time t _a which is switched to the neutral position n, approximately to a certain maximum pressure P _{1 ',} the motor capacity, as shown in FIG. 6 (F), a hydraulic pump tilting direction switching valve 30 is from time to time t ₀ has been switched to the neutral position n t _a And the change rate of the motor capacity between time t _a and time t ₁ ′ is changed. That is, the slope of the ramp function used for controlling the motor displacement, than during the time t ₀ to time t _a, so that the direction of during the time t _a to time t _{1 'increases.}

As described above, the increase in capacity of the variable displacement hydraulic pump 12, so increasing the braking pressure, by increasing the changing speed of the motor capacity during the time t _a to time t _{1 ',} FIG. 6 (A as shown in), it is possible to _'pressure of the forward main circuit 51a of until a substantially constant pressure P _1' from the time t _a time t ₁ and.
In the third embodiment, the same effects as in the first and second embodiments can be obtained. In addition, the third embodiment has an effect that the maximum pressure generated in the main circuit can be suppressed while ensuring the deceleration performance of the wheel loader.

In the second and third embodiments, the case where the function used for controlling the change in motor capacity is a ramp function has been described. However, the function used for controlling the change in the motor capacity is not limited to the ramp function, and may be a curved function such as an exponential function, for example. Also, when changing the rate of change of the motor capacity at time ta as in the embodiment 3, the change point is not only once t _a, a plurality of times may be changed. In this case, the function for controlling the change rate of the motor capacity used at each change point can be arbitrarily applied according to the vehicle body and the driving state of the wheel loader, such as a ramp function or a curve.

In each of the above embodiments, the timing at which the hydraulic pump tilting direction switching valve 30 is switched from the neutral position n to the input direction input from the forward / reverse switching lever 75 is equal to or less than the predetermined speed V _1. When it was detected. However, the timing for switching the hydraulic pump tilt direction switching valve 30 from the neutral position n to the input direction of the forward / reverse switching operation lever 75 may be determined by another method. For example, in accordance with the speed of the wheel loader, a time for the wheel loader to be reduced to a predetermined speed is set in advance, and after this time has elapsed, the hydraulic pump tilt direction switching valve 30 is switched from the neutral position to the forward / reverse direction. The input direction of the operation lever 75 may be switched.

  Further, in each of the above-described embodiments, the determination of the sudden reverse operation is made based on the input direction of the forward / reverse switching operation lever 75 and the traveling direction detected by the speed / traveling direction detector 73. However, the sudden reverse operation may be determined by other methods. For example, it may be determined that a sudden reverse operation has been performed when an operation of backward → neutral → forward or forward → neutral → reverse is performed within a predetermined time. Alternatively, a switch dedicated to the sudden reverse operation may be provided, and it may be determined that the sudden reverse operation has been performed when the forward / reverse switching operation lever 75 is operated simultaneously with turning on the switch.

  In addition, the hydraulic travel drive device of the present invention can be variously modified and configured within the scope of the invention, in summary, a hydraulic travel drive device used for a self-propelled work vehicle, Connected to a variable displacement hydraulic pump driven by an engine and equipped with a variable displacement hydraulic pump with a bi-directional tilt mechanism that discharges pressure oil in both forward and reverse directions, and a pair of forward and reverse main circuits The variable displacement hydraulic pump and the variable displacement hydraulic pump that constitutes a hydraulic closed circuit together with the pair of main circuits and the bidirectional displacement mechanism of the variable displacement hydraulic pump are connected to the bidirectional displacement mechanism. Connected to the pump tilt cylinder, operation means for outputting forward and reverse input signals, and pump tilt cylinder, switching to forward, neutral and reverse positions Based on the hydraulic pump tilt direction switching means and the forward and reverse input signals output from the operating means, it is determined whether or not it is a sudden reverse operation. Any control means may be provided as long as it is provided with a control means for instructing the hydraulic pump tilting direction switching means to hold at the neutral position and delaying the switching instruction to the position corresponding to the input signal.

DESCRIPTION OF SYMBOLS 1 Hydraulic travel drive device 11 Variable displacement hydraulic pump 12 Variable displacement hydraulic motor 20 Tilt cylinder for pump 21 Servo piston 22a, 22b Control chamber 23a, 23b Spring 71 Controller 72 Motor capacity control unit 73 Speed / travel direction detector 75 Forward / reverse switching lever

Claims (9)

A variable displacement hydraulic pump that is driven by an engine and includes a bidirectional tilt mechanism that discharges pressure oil in both forward and reverse directions;
A variable displacement hydraulic motor that is connected to the variable displacement hydraulic pump by a pair of forward and reverse main circuits, and that forms a hydraulic closed circuit together with the variable displacement hydraulic pump and the pair of main circuits;
A pump tilt cylinder connected to the bi-directional tilt mechanism of the variable displacement hydraulic pump and driving the bi-directional tilt mechanism to move forward and backward; and
Operating means for outputting forward and reverse input signals;
Hydraulic pump tilt direction switching means connected to the pump tilt cylinder and switched to forward, neutral and reverse positions;
Based on forward and reverse input signals output from the operation means, it is determined whether or not it is a sudden reverse operation. If it is determined that the operation is a sudden reverse operation, the hydraulic pump tilt direction switching means is determined. A hydraulic travel drive device for use in a self-propelled work vehicle, comprising: control means for performing a command to hold at a neutral position and performing a delay command for switching to a position corresponding to an input signal.   2. The hydraulic travel drive apparatus according to claim 1, wherein the pump tilt cylinder is disposed on both sides of the servo piston and the servo piston, and applies a control pressure to the servo piston by supplying pressurized oil. 3. Chambers and urging means for constantly urging the servo pistons provided in each of the control chambers, and while the command to hold the hydraulic pump tilt direction switching valve in a neutral position is being performed, A hydraulic travel drive device for use in a self-propelled work vehicle, wherein the same pressure is applied to a pair of control chambers so that the piston is held neutral.   3. The hydraulic travel drive apparatus according to claim 1, further comprising: a traveling direction detection unit that detects a traveling direction of forward or reverse traveling; and a speed detection unit that detects a speed of a self-propelled work vehicle; The forward or reverse travel direction detected by the travel direction detection means is opposite to the forward or reverse input signal output from the operation means, and the speed detected by the speed detection means is a reference. A hydraulic travel drive device for use in a self-propelled work vehicle, characterized in that it is determined to be a sudden reverse operation when the speed is higher than the speed.   The hydraulic travel drive apparatus according to any one of claims 1 to 3, wherein the control means performs a command to hold the hydraulic pump in the neutral position with respect to the hydraulic pump tilting direction switching means, and then the speed detection means. When the detected speed is equal to or lower than a predetermined speed, the hydraulic pump tilt direction switching means is instructed to switch from the neutral position to a position corresponding to the input signal output from the operating means. A hydraulic travel drive device for use in a self-propelled work vehicle.   5. The hydraulic travel drive apparatus according to claim 1, wherein the control means determines that the operation is a sudden reverse operation, and the hydraulic pump tilt direction switching means is held in a neutral position. A hydraulic travel drive apparatus for use in a self-propelled work vehicle, comprising hydraulic motor capacity control means for increasing the capacity of the variable displacement hydraulic motor in a state where   6. The hydraulic travel drive apparatus according to claim 5, wherein the increase in the capacity of the variable displacement hydraulic motor by the hydraulic motor capacity control means is performed by control using a motor capacity change speed as a parameter. A hydraulic travel drive used for a work vehicle.   7. The self-propelled operation according to claim 5, wherein an increase in the capacity of the variable displacement hydraulic motor by the hydraulic motor capacity control means is performed by a control using a ramp function. A hydraulic travel drive for use in a vehicle.   7. The hydraulic travel drive apparatus according to claim 5, wherein the increase of the capacity of the variable displacement hydraulic motor by the hydraulic motor capacity control means is performed by control using a function that changes the capacity increase speed in a curve. A hydraulic traveling drive device used for a self-propelled working vehicle characterized by the above. 9. The hydraulic travel drive apparatus according to claim 5, wherein an increase in the capacity of the variable displacement hydraulic motor by the hydraulic motor capacity control unit when the control unit determines that the operation is a sudden reverse operation. A self-propelled working vehicle comprising means for lowering an upper limit value of the variable capacity hydraulic motor when the control means is not determined to be a sudden reverse operation. The hydraulic travel drive used.

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