JP2830033B2 - Travel direction switching device for engine type forklift equipped with variable displacement hydraulic pump for variable speed - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a traveling direction switching device for an engine type forklift equipped with a variable speed variable displacement hydraulic pump.

2. Description of the Related Art Generally, a forklift that travels by a hydraulic device having a variable displacement hydraulic pump whose discharge displacement is controlled by adjusting a swash plate angle by a charge pump is described in US Pat.
The configuration shown in the figure is provided.

That is, a charge pump 42 and a variable displacement hydraulic pump 43 are connected to the engine 41, and both the pumps 42, 43 rotate following the rotation of the engine 41.
The traveling hydraulic pump 43 supplies hydraulic oil to the left and right traveling hydraulic motors M, and rotates them forward and reverse.

Hydraulic oil having a pressure proportional to the rotation speed of the engine 41 flows into the pressure reducing valve 44 from the charge pump 42 connected to the engine 41. Then, the pressure reducing valve 44 reduces the pressure of the hydraulic oil in proportion to the discharge amount of the hydraulic oil from the charge pump 42, and then flows the reduced hydraulic oil as a pilot fluid into the downstream passage pipe 46.

The swash plate of the traveling hydraulic pump 43 is a swash plate control cylinder.
The pressure difference of the pilot fluid between the front chamber and the rear chamber which is connected to the cylinder rod 49 of the cylinder 47 and is defined by the piston 48 in the cylinder 47, and the force of the spring 50 for returning the piston 48 to the center in the cylinder 47 The inclination angle of the swash plate is controlled by the balance with the above.

Accordingly, the swash plate angle of the traveling hydraulic pump 43 increases as the rotation speed of the engine 41 increases, and the discharge capacity increases. Conversely, as the rotation speed decreases, the swash plate angle decreases and the discharge capacity decreases. It is supposed to.

The increase or decrease in the discharge capacity of the traveling hydraulic pump 43 changes the rotation speed of the traveling hydraulic motor M, that is, the vehicle speed. In order to prevent a sudden change in the vehicle speed and secure good driving performance, the swash plate is used. An orifice 51 is provided in a port of the control cylinder 47. Then, the pilot fluid flowing into the cylinder 47 while the flow rate is restricted by the orifice 51 slowly moves the piston 48,
A rapid change in the swash plate inclination angle is prevented to prevent a sudden increase or decrease in the discharge pressure, and the vehicle speed is gradually increased or decreased.

[Problem to be Solved by the Invention] When the forward / reverse lever 52 is operated, for example, forward, the forward / backward valve 45 is held at the position a. And the pressure reducing valve 44
The pilot pressure passing through the passage 46 extending from the swash plate control cylinder 47 flows into the rear chamber of the swash plate control cylinder 47 via the forward / reverse valve 45, and the pilot fluid retained in the front chamber flows out to the drain tank T. You. As a result, the cylinder rod 49 moves in the extending direction, the swash plate of the hydraulic pump 43 is inclined in the forward direction, and the hydraulic motor M is rotated forward to advance the vehicle.

When the forward / reverse lever 52 is switched and the reverse operation is performed, the forward / reverse valve 45 is switched to the position b, and the front chamber of the swash plate control cylinder 47, the rear chamber rich passage pipe 46, and the drain tank T are connected. The pilot fluid flows from the pressure reducing valve 44 into the front chamber, the pilot fluid flows out from the rear chamber to the drain tank T, the cylinder rod 49 moves in the contracting direction, and the hydraulic pump 43 The swash plate is inclined in the reverse direction. Thereby, the hydraulic motor M is reversed and the vehicle moves backward.

However, when the front and rear levers 52 are switched to change the traveling direction of the vehicle to change the a and b positions of the forward / backward valve 45, the front chamber and the rear chamber of the cylinder 47, the pressure reducing valve 44, and the drain tank T The pilot fluid flowing therethrough passes through the orifice 51. Therefore, the pilot fluid moves slowly, the movement of the piston 48 also lacks speed, and the swash plate of the hydraulic pump 43 also changes the inclination direction gently. Therefore, the hydraulic motor M does not rapidly switch the rotation direction in response to the switching operation of the forward / reverse lever 52, and the change in the traveling direction of the vehicle becomes poor in responsiveness.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problem, and an object of the invention is to provide a variable speed capable of changing the traveling direction in response to the operation of forward / reverse switching operation means such as a forward / reverse lever. Of the present invention is to provide a traveling direction switching device for an engine type forklift equipped with a variable displacement hydraulic pump.

Means for Solving the Problems In order to achieve the above object, the present invention provides a variable displacement hydraulic pump connected to an engine and driven by the engine, and a discharge displacement for controlling the displacement of the hydraulic pump. Adjusting means; driving means for driving the discharge capacity adjusting means at an oil pressure relative to the engine speed such that the discharge capacity of the hydraulic pump follows the engine speed; 2. Description of the Related Art In an engine type forklift equipped with a variable speed variable displacement hydraulic pump comprising a hydraulic motor driven by hydraulic oil to rotate driving wheels, a switching operation is performed to switch the forklift between forward and backward, and the switching operation is performed. Forward / backward switching operation means for changing the discharge direction of a hydraulic pump so as to switch the rotation direction of the hydraulic motor, The gist of the invention is to provide a circulation speed increasing means for increasing the hydraulic oil circulation speed from the driving means to the discharge capacity adjusting means in accordance with the switching operation of the switching operation means.

[Operation] When the forward / reverse switching operation means is switched to switch the forklift from forward to reverse or to switch from reverse to forward, the flow speed increasing means changes the pressure oil flow speed from the driving means to the discharge capacity adjusting means. To raise. As a result, the discharge capacity adjusting means quickly changes the discharge direction of the hydraulic pump in response to switching the rotation direction of the hydraulic motor.

Embodiment An embodiment in which the present invention is embodied in a hydraulic circuit of a forklift will be described below in detail with reference to FIGS.

In FIG. 1, an output shaft 2 of an engine 1 is connected to a cargo handling pump 3, a charge pump 4, and a traveling hydraulic pump 5 as a variable displacement hydraulic pump. A lift lever 7, a tilt lever 8, and an accelerator pedal 10 are sequentially connected to a throttle lever 6 of the engine 1, and the engine 1 rotates at a rotation speed according to the operation amount of the lift lever 7, the tilt lever 8, and the pumps 3 to 5 are driven.

The traveling hydraulic pump 5 is a two-way type swash plate type variable displacement hydraulic pump motor, and selects the direction in which hydraulic oil flows in the traveling pipelines 5a and 5b according to the inclination direction of the swash plate. The right-hand traveling hydraulic motors Lm and Rm are rotated forward and backward. Further, the discharge capacity of the traveling hydraulic pump 5 is adjusted so as to be large when the inclination angle of the swash plate (swash plate angle) is large, and to be small when the swash plate angle is small. The traveling motor hydraulic pressures Lm and Rm are driven at a speed according to the number of rotations.

A swash plate control cylinder 13 as a discharge capacity adjusting means is disposed adjacent to the traveling hydraulic pump 5, and a cylinder rod 14 thereof is connected to the swash plate of the traveling hydraulic pump 5. The swashplate angle is adjusted. The inside of the cylinder 13 is divided into a front chamber and a rear chamber by a piston 14a provided on a cylinder rod 14, and a pair of push springs S mounted on the piston 14a from each side wall of the cylinder 13 always keep the piston 14a in the cylinder 13a. It is held almost in the center.

The charge pump 4 discharges into the charge line 15 an amount of hydraulic oil based on the rotation speed of the engine 1. The charge line 15 is provided with a pressure reducing valve 17 which constitutes a driving means together with the charge pump 4 via an orifice 16, and reduces the pressure of the hydraulic oil discharged from the charge pump 4. Then, the decompressed hydraulic oil flows out as a pilot fluid from a pressure reducing valve 17 to a pilot fluid passage pipe 18 extending to an electromagnetically controlled forward / reverse valve 19.

An inching lever 20 is provided on the spool 17a of the pressure reducing valve 17.
Are connected, and the inching lever 20 is an electric motor for adjustment.
The motor shaft 17b is connected via a rod 20a. Then, the rotation of the electric motor 17b tilts the inching lever 20, and the flow rate of the pilot fluid flowing into the passage pipe 18 is controlled.

Based on the operation position of the forward / reverse lever 9 as the forward / backward switching operation means, the passing conduit 18 passes through the forward / backward valve 19 at the a position or the b position, and then a pair of front and rear pilot conduits 18a,
The swash plate control cylinder 13 communicates with the front chamber or the rear chamber of the swash plate control cylinder 13 through one of the pilot pipes 18a and 18b which is selected according to switching of the forward / backward position of the forward / backward valve 19. It has become. Of these pilot lines 18a and 18b, those not connected to the passage line 18 are connected to the drain tank T via the forward / reverse valve 19. When the forward / reverse valve 19 is at the position c, the pilot lines 18a and 18b
8 and from the drain tank T.

Orifices 21 are provided in the pilot lines 18a, 18b immediately before the input ports of the cylinder 13, respectively. Pilot fluid whose flow rate is regulated by the orifices 21 is sent into the cylinder 13. In the rear pilot line 18b, there is provided a bypass line 22 connected to the rear chamber of the cylinder 13 so as to bypass the orifice 21, and a normally closed electromagnetic member constituting a flow speed increasing means provided in the pipe is provided. By opening and closing the on-off valve 23, the bypass pipe 22 and the rear chamber of the cylinder 13 are communicated or shut off.

Further, when the forward / reverse valve 19 is operated to the position a as shown, the on-off valve 23 is opened and the pilot fluid passing through the bypass pipe 22 flows into the rear chamber of the cylinder 13. Since the pilot fluid flows out from the front chamber to the drain tank T, the pressure in the rear chamber is increased from that in the front chamber, and the cylinder rod
14 inclines the swash plate in the forward direction. As a result, the hydraulic pump 5 discharges the hydraulic oil from one of the discharge ports to rotate the hydraulic motors Lm and Rm in the normal direction, thereby moving the vehicle forward.

When the forward / reverse valve 19 is operated to the position "b", the pilot fluid flows into the front chamber from the bypass pipe 22 via the open / close valve 23 which is also opened, and the tank T
, The pressure of the front chamber is increased from that of the rear chamber, and the cylinder rod 14 tilts the swash plate in the reverse direction.
As a result, the hydraulic pump 5 discharges the hydraulic oil from the other discharge port to reverse the hydraulic motors Lm and Rm, thereby moving the vehicle backward.

Further, when the forward / reverse valve 19 is at the position a, for example,
As the engine speed increases, the pilot pressure from the pressure reducing valve 17 increases, and the cylinder pressure 14 moves to the left by the pilot pressure, and the swash plate angle of the hydraulic pump 5 increases. Conversely, when the engine speed decreases, the hydraulic pump 5
Of the swash plate becomes smaller. In these cases, when the on-off valve 23 is closed and the pilot fluid flows into the plate chamber of the cylinder 13 while the flow rate is controlled by the orifice 21, the rod 14 of the cylinder 13 moves slowly. Therefore, the swash plate angle of the hydraulic pump 5 does not suddenly change, and a sudden increase or decrease in the traveling speed due to a sudden change in the rotational speed of the hydraulic motors Lm, Rm is avoided, and no impact is applied to the vehicle.

Further, the charge line 15 is branched into an exchange line 24 downstream of the orifice 16, and a discharge line 25 extending from the pressure reducing valve 17 is connected to the exchange line 24.
Hydraulic oil flowing from the charge pump 4 through the replacement pipeline 24 is filtered by the filter 26, and when an excessive load occurs in the pipeline, the pressure is reduced by the pressure reducing valve 27, and the traveling pipelines 5a, 5b
The traveling pipeline 5 that has been heated and circulated between the traveling hydraulic pump 5 and the traveling hydraulic motors Lm, Rm by being mixed with the hydraulic oil in the inside.
Reduce the oil temperature in a and 5b.

Subsequently, an electrical configuration in this embodiment will be described.

The accelerator operation amount sensor 28 is constituted by a potentiometer, detects the depression angle of the accelerator pedal 10, and outputs a detection signal to the controller 29. The engine speed sensor 30 includes a pickup coil, and the engine 1
And outputs a detection signal to the controller 29.

The brake operation amount sensor 31 includes a potentiometer, detects the depression angle of the brake pedal 11, and outputs a detection signal to the controller 29. Forward / backward position sensor 33
Consists of a limit switch, forward and backward lever 9
The reverse and neutral positions are detected, this detection signal is output to the controller 29, and the forward / reverse valve 19 is switched to the positions a, b, and c. The inching lever angle sensor 34 includes a potentiometer, detects the angle of the inching lever 20, and outputs a detection signal to the controller 29.

The controller 29 calculates the depression amount of the accelerator pedal 10 according to the signal from the accelerator operation amount sensor 28, and calculates the target operation angle of the inching lever 20 based on the calculated depression amount. The controller 29 calculates the depression amount of the brake pedal 11 based on the signal from the brake operation amount sensor 31, and calculates the target operation angle of the inching lever 20 based on the calculated depression amount. The controller 29 determines the current rotational speed of the engine 1 based on a signal from the engine rotational speed sensor 30. Further, the controller 29 calculates the angle of the inching lever 20 according to a signal from the inching lever angle sensor 34.

The controller 29 determines the operating position of the forward / reverse lever 9 according to a signal from the forward / backward position sensor 33. Also,
When the controller 29 detects a switching operation of the forward / reverse lever 9 according to a signal from the forward / backward position sensor 33, the controller 29 outputs a duty signal of a duty command value D according to a predetermined program to the electromagnetic on-off valve 23, and outputs the duty command. The on-off valve 23 is opened so that the opening degree V according to the value D is obtained.
Then, the pilot fluid is caused to flow through the bypass pipe 22 avoiding the orifice 21, and the pilot fluid flows into and out of the rear chamber of the cylinder 13 quickly.

More specifically, as shown in FIG. 2, after the switching operation of the forward / reverse lever 9, the turning speed of the hydraulic pump 5 in the inclination direction of the swash plate is changed in consideration of the stable switching of the traveling direction of the vehicle. Times t1, t2, and 3 for gradually increasing, fully opening, and gradually decreasing the opening degree V of the on-off valve 23 so that
t3 (t1 <t2 <t3) is previously obtained logically or experimentally.

The controller 29 has different duty command values D depending on the area to which the elapsed time t after the operation of the forward / reverse lever 9 belongs.
To adjust the opening degree V of the on-off valve 23. That is, the controller 29 receives a signal from the forward / reverse position sensor 33 every 1 mm, determines the state of the forward / reverse lever 9,
When the switching operation is performed, the duty signal is output to the on-off valve 23, and in the gradually increasing region from the end of the switching operation until the time t = t1, the duty command value D = t / t1 and the opening degree V of the on-off valve 23 is set. Is controlled to rise from zero to 100%.

Then, in the fully open holding region from the elapsed time t1 to t2, the duty command value D is set to 1 and the opening degree V of the on-off valve 23 is controlled to be maintained at 100%. Further, in the gradually decreasing region from the elapsed time t2 to t3, the duty command value D = ｛− (t−t2)
Control is performed based on the equation of (t3−t2)｝ + 1 to lower the opening degree V of the on-off valve 23 from 100% to zero.

The controller 29 is provided with a storage area for storing the traveling direction of the vehicle. Based on a signal from the forward / reverse position sensor 33, a flag indicating the current traveling direction (DN flag) and a traveling direction one millisecond earlier are stored. A flag (DF flag) is provided. When the DN flag and the DF flag are respectively zero, they indicate the backward movement of the vehicle, and when they are 1, they indicate the forward movement of the vehicle.

Now, the operation of the traveling direction switching device configured as described above will be described below with reference to FIG.

Now, the forward / reverse lever 9 is held at the forward position, and the vehicle is moving forward. Then, the controller 29 sets an initial value in step (hereinafter, step is simply referred to as S) S1 based on the signal from the forward / reverse position sensor 33. That is, DN flag = 1, DF flag = 1, count value = 0, t3 = 10
00 (milliseconds).

Subsequently, when the forward / reverse lever 9 is switched to the reverse position to move the vehicle backward, the controller 29 determines whether or not the vehicle is moving forward in S2 based on a signal from the forward / backward sensor 33, and further determines in S3 whether the vehicle is moving forward. Is determined to be in reverse, and since the vehicle is in reverse, the DN flag is set to zero instead of 1 in S4. Subsequently, when the controller 29 compares the DF flag and the DN flag in S5 and determines that the two are different, the controller 29 sets the count value to t3, that is, 1000 in S6, and then in S7.
The contents of the DF flag are rewritten to the contents of the DN flag, that is, the DF flag is changed from 1 to zero in this case.

Next, the controller 29 determines in step S8 that t3 (ie, 1000)
Is subtracted from the current count value (1000 in this case) to calculate the elapsed time t (zero). Then, since the elapsed time t has not reached t1 in S9, a signal of the duty command value D = t / t1 is output to the on-off valve 23 in S10 to start to open it. Then, based on the opening degree V of the on-off valve 23, the cylinder
The pilot fluid flows out of the rear chamber 13 into the drain tank T, and the hydraulic pump 5 starts to incline the swash plate in the backward direction.

Thereafter, the operation of the controller 29 returns to S2, and performs the above-described processing up to S4. And in S5, one millisecond before
Since the DF flag = 0 and the current DN flag = 0 are the same, the controller 29 obtains the current count value by subtracting 1 from the count value = 1000 in S11, and this count value exceeds zero in S12. After confirming that, move to S7, S8 ~ S1
Return to S2 via 0.

When this operation is repeated, t = t3−count value calculated in S8 increases by 1 millisecond, and the duty command value D gradually increases in S10.

Therefore, the opening degree V of the on-off valve 23 gradually increases until it reaches 100%, and the flow rate and flow velocity of the pilot fluid flowing into the front chamber of the cylinder 13 increase. Therefore, the swash plate of the hydraulic pump 5 moves from the forward side to the reverse side while increasing the operation speed.

When the elapsed time t becomes equal to or longer than t1 in S9, the controller 29 confirms in S13 that the elapsed time t <t2, sets the duty command value D = 1 in S14, and returns to S2. By repeating this operation, the opening / closing valve 23 opens.
V100%, that is, fully opened, the inclination direction of the swash plate is changed at the maximum operation speed.

Further, the value of the elapsed time t in S8 increases and t ≧ t2
Then, after confirming that t <t3 in S15, the duty command value D = (1 / (t3−t2)) · (t−t2) + in S16.
Set to 1 and return to S2. Based on this duty command value D, the on-off valve 23 is gradually closed until the opening degree V becomes zero,
The swash plate lowers the operation speed and tilts further to the reverse side.

Further, when the count value becomes equal to or less than zero in S12, the controller 29 determines that t3, that is, 1000 milliseconds has elapsed, and holds the closed state without outputting a current to the on-off valve 23 in S15. At this time, the inclination direction of the swash plate is completely shifted to the forward side, and thereafter, the on-off valve 23 is kept in the closed state, and the pilot fluid is supplied to the cylinder 13 through the orifice 21 according to the operation of the accelerator pedal 10 or the brake pedal 11. It is appropriately increased or decreased in the front room and the rear room.

Then, when the forward / reverse lever 9 is switched to the forward direction, it is determined in S2 that the vehicle is moving forward based on the signal from the forward / reverse sensor 33, and then the DN flag is set to 1 in S18, and the S flag is set.
Go to step 5 and compare the DF flag and DN flag one millisecond earlier. Then, since the DF flag is zero, the process of the controller 29 proceeds to S6, and the same operation as that at the time of the reverse movement of the vehicle is performed.

As described above, in this embodiment, after the forward / reverse lever 9 is switched, the on-off valve 23 is opened for a predetermined time to switch the inclination direction of the swash plate. Thereby, the cylinder 13
The pilot fluid quickly flows into or out of the rear chamber,
At the same time, the pressure in the room is rapidly increased or decreased, the cylinder rod 14 moves quickly, and the switching speed of the swash plate of the traveling hydraulic pump 5 in the inclination direction also increases following this moving speed. Therefore, the discharge direction of the traveling hydraulic pump 5 is changed, and the traveling direction of the vehicle is quickly switched.

In addition, within a predetermined time t after the operation of the forward / reverse lever 9, at the start and at the end, the opening degree V of the on-off valve 23 is gradually increased to gradually increase the switching speed in the traveling direction of the vehicle. , The switching speed of the traveling direction is gradually reduced. As a result, the traveling direction is not suddenly changed, and the occurrence of an impact due to the switching of the traveling direction is avoided, so that stable traveling of the vehicle is guaranteed.

The present invention is not limited to the above-described embodiment, and can be implemented in the following states.

As shown in FIG. 4, bypass pipes 22a and 22b are provided in both pilot pipes 18a and 18b, and open / close valves are provided in respective pipes 22a and 22b.
23a and 23b are arranged and opened and closed by a signal from the controller 29. With this configuration, for example, the cylinder 13
When the pilot fluid flows into the front chamber through the on-off valve 23a through the on-off valve 23a, it flows out from the other to the drain tank T via the on-off valve 23b, and the traveling direction change of the vehicle in response to the switching operation of the forward / reverse lever 9 is more rapid. Performed with responsiveness.

As shown in FIG. 5, a flow chamber 36 without a throttle is formed in one of the on-off valves 23 and an orifice chamber 35 is provided in the other, and the configuration is simplified by omitting the orifice in the pipeline.

[Effects] As described in detail above, according to the present invention, it is possible to quickly change the direction of the forklift in the forward or backward direction in response to the operation of the forward or backward switching operation means. Here, forklifts are often used in narrow warehouses, and at that time, a so-called switchback operation for switching between forward and backward movement is frequently performed. Ideal for switchback travel.
In addition, since the direction change of the forward / backward movement is quickly performed by operating the forward / backward switching operation means, there is an advantage that the brake is not heavily used at the time of the switchback operation and the brake life is extended.

[Brief description of the drawings]

FIG. 1 is a hydraulic and electrical circuit diagram showing an embodiment of the traveling direction changing device of the present invention, FIG. 2 is a diagram showing a transition of a duty command value, FIG. 3 is a flowchart showing an operation of a controller, FIGS. 4 and 5 are hydraulic circuit diagrams showing another example of the present invention, and FIG. 6 is a hydraulic circuit diagram showing a conventional example. Engine: 1, traveling hydraulic pump as variable displacement hydraulic pump ... 5, charge pump as drive means ...
4. Forward / reverse lever as forward / reverse switching operation means ... 9
Swash plate control cylinder as discharge capacity adjusting means ... 13,
A pressure reducing valve as a driving means ... 17, an electromagnetic on-off valve as a flow speed increasing means ... 23, a hydraulic motor ... Lm, Rm.

Claims (1)

(57) [Claims] 1. A variable displacement hydraulic pump connected to an engine and driven by the engine, a displacement control means for controlling a displacement of the hydraulic pump, and a displacement of the hydraulic pump following an engine speed. A driving unit that drives the discharge capacity adjusting unit with an oil pressure corresponding to the rotation speed of the engine, and a hydraulic motor that is driven by hydraulic oil discharged from the hydraulic pump and rotates a driving wheel for traveling. An engine type forklift equipped with a variable displacement hydraulic pump for variable speed, comprising: a switching operation for switching forward and backward movement of the forklift, and the switching operation changes a discharge direction of the hydraulic pump to switch a rotation direction of the hydraulic motor. Forward / reverse switching operation means to be changed; Traveling direction switching device in the engine-type forklift having a variable-speed variable displacement hydraulic pump formed by providing a velocity increasing means for increasing the pressure oil flow rate to the unit.