JPH03219167A - Oil pressure closing circuit for construction machine - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to a hydraulic closed circuit used in construction machines such as wheel loaders.

B. Prior Art FIG. 5 shows a conventional travel hydraulic closed circuit for a wheel loader.

In FIG. 5, a hydraulic motor 3 is connected in a closed circuit to a variable displacement hydraulic pump 2 driven by a prime mover 1 through a pair of main pipes 11 and 12. As shown in FIG. Now, switch the forward/backward switching lever (not shown) to the forward position, and then press the travel pedal 4.
When the pedal is operated, a signal corresponding to the amount of pedal operation is input to the controller 5, and the controller 5 operates the pump regulator 6 in accordance with this input signal to control the amount and direction of tilting of the hydraulic pump 2. As a result, the hydraulic pump 2 discharges an amount of pressure oil corresponding to the amount of tilting of the pipe 11, for example, and the hydraulic motor 3 is driven by this discharged oil.
As a result, the wheels connected to the hydraulic motor 3 are driven and the vehicle moves forward. The traveling speed depends on the amount of tilting of the hydraulic pump 2, that is, the amount of operation of the traveling pedal 4. In addition, return oil from the hydraulic motor 3 returns to the hydraulic pump 2 through a pipe line 12.

Here, 7a and 7b are cross relief valves that open when the circuit pressure of the main conduit 12.11 exceeds a predetermined relief pressure. That is, when the travel pedal 4 is released while the vehicle is moving forward at high speed, the controller 5 controls the hydraulic pump 2.
Since the amount of tilting is decreased toward zero, brake pressure is built up in the pipe line 12, and when the pressure exceeds the above-mentioned relief pressure value, the relief valve 7a opens. As a result, the pipe lines 11 and 12 are communicated with each other, so that the pressure in the pipe line 12 is reduced, and damage to the pipe lines 11 and 12 due to high pressure is prevented. Thereafter, when the pressure in the pipe line 11 drops below the relief pressure, the relief valve 7a closes.

C0 Problems to be Solved by the Invention By the way, when the travel pedal 4 is released while driving, the hydraulic motor 3 remains closed even after the relief valve 7a is once opened and closed.
rotates due to inertia and discharges pressure oil into the pipe line 12, and this discharged oil applies torque Tp (kg f-) to the hydraulic pump 2.
m) is given. Here, the capacity of the hydraulic pump 2 (depending on the amount of tilting) is qp (cc/rev), and the pipe lines 11, 1
If the differential pressure between the two is P (kgf/ci), it becomes qp-P 2O0π, and this torque TP causes the hydraulic pump 2 to rotate and rotate the prime mover 1 at an increased speed. At this time, since the amount of tilting of the hydraulic pump 2, that is, the pump capacity qp is decreasing toward zero, the torque Tρ is also decreasing.

When this becomes less than the loss torque TL of the prime mover 1 due to piston frictional resistance or the like, the accelerated rotation of the prime mover 1 is canceled.

However, for example, when the vehicle weight is large and the inertial load is large, the pipe line differential pressure P increases, so the torque T
P is large, and the rotation of the hydraulic motor 2 due to this torque TP may cause the prime mover 1 to rotate beyond the allowable rotational speed (hereinafter referred to as overrun) and be damaged.

A technical problem of the present invention is to reduce the torque TP by reducing the pipe line differential pressure P.

Means for Solving the Problems 00 To be explained with reference to FIG. 1 showing an embodiment, the present invention comprises a variable displacement expansion hydraulic pump 2 driven by a prime mover 1;
The present invention is applied to a hydraulic closed circuit of a construction machine that is connected to a hydraulic pump 2 in a closed circuit through a pair of main pipes 11 and 12 and includes a hydraulic motor 3 driven by oil discharged from the hydraulic pump 2.

and a communication position A that communicates the pair of main pipes 11 and 12.
and a switching valve 21 that can be switched to a shutoff position B to shut off.
It is equipped with switching control means 22 and 23 that detects that the rotation speed of the prime mover 1 has exceeded a predetermined value based on the allowable rotation speed and switches the switching valve 21 to the communication position A, thereby achieving the above technical problem. do.

The E9 action switching control means 22, 23 switches the switching valve 21 to the communication position A when detecting that the rotation speed of the prime mover 1 has exceeded a predetermined value based on its allowable rotation speed. As a result, the pair of main pipes 11.12 are communicated with each other, the differential pressure P between the two pipes 11.12 is reduced, and the torque TP that the hydraulic pump 2 receives from the oil discharged from the hydraulic motor 3 is reduced. The rotation of the prime mover 1 is suppressed and overrun of the prime mover 1 is prevented.

In the above-mentioned sections and section E, which describe the present invention in detail, figures of embodiments are used to make the present invention easier to understand, but the present invention is not limited to the embodiments.

F. Embodiment FIG. 1 is a circuit diagram showing an embodiment of the present invention, and parts similar to those in FIG. 5 are denoted by the same reference numerals, and the explanation will focus on the differences.

In FIG. 1, a two-position electromagnetic switching valve (hereinafter referred to as electromagnetic valve) 21 is provided in a conduit 13 connecting the main conduits 11 and 12 mentioned above. This solenoid valve 21 is switchable between a position A (communicating position) which communicates the amphibian pipe line 11.12 and a position B (blocking position) which blocks the main pipe line 11.12. When a high level signal is input to section 21a, it switches from position B to position A. 23 is
This is a rotation speed sensor that detects the rotation speed N of the prime mover 1, and the detected rotation speed N is input to the function generator 22. The rotation speed N of the function generator 22 is a predetermined value N.

When the voltage exceeds this level, a high level signal is output. Here, this predetermined value N. is set to a value slightly lower than the allowable limit rotational speed of the prime mover 1.

Next, the operation of the embodiment will be explained.

Now, the travel pedal 4 is being operated and the vehicle is moving forward at high speed, and at this time, the solenoid valve 21 shuts off the circuits 11 and 12.
in position. When the travel pedal 4 is released in this state, the amount of tilting of the hydraulic pump 2 gradually decreases and the pressure in the pipe line 12 increases, so the relief valve 7a opens as described above and connects the main pipe lines 11 and 12. When the pressure in the pipe line 12 becomes lower than the relief pressure, the relief valve 7a closes. After that, the oil discharged from the hydraulic motor 3 to the pipe line 12 causes the hydraulic pump 2 to
is rotated, and the prime mover 1 is conversely rotated at an increased speed by the hydraulic pump 2.

Here, the rotation speed sensor 23 detects the rotation speed N of the prime mover 1 and inputs it to the constant time generator 22, and the detected rotation speed N is the predetermined value N mentioned above. If it is above, function generator 2
2 outputs a high level signal to the solenoid section 21a of the electromagnetic valve 21. As a result, the solenoid valve 21 is switched from the B position to the A position, and the pipes 11 and 12 are communicated with each other.
The differential pressure P between the pipes 11 and 12 becomes zero.6 As a result, the torque Tp becomes zero, and the accelerated rotation by the hydraulic pump 2 of the prime mover 1 is canceled.

When the rotational speed of the prime mover 1 reaches a predetermined value N0, the function generator 22 outputs a low level signal, so the solenoid valve 21
switches again to position B and the main lines 11, 12 are cut off. Therefore, a differential pressure is generated in the main pipes 11 and 12, and the torque TP rises again, so that the rotational speed N of the prime mover 1 rises.When this reaches a predetermined value N0 or more, the solenoid valve 21 is switched to the A position, and the torque TP increases again. , 12 are communicated. While repeating these operations, the vehicle decelerates, and when the amount of tilting of the hydraulic pump 2 becomes zero, the rotation of the prime mover 1 by the hydraulic pump 2 is completely released.

According to the above, when the rotational speed of the prime mover 1 exceeds a predetermined value, the pipes 11 and 12 communicate with each other, and the differential pressure P between them.

That is, since the torque TP becomes zero, increased rotation of the prime mover 1 by the hydraulic pump 2 is prevented, and overrun is prevented.

In the configuration of the above embodiment, the solenoid valve 21 operates as a switching valve.
The function generator 22 and the rotation speed sensor 23 constitute switching control means.

Further, FIG. 2 shows another embodiment, in which a throttle 32 is provided in the discharge pipe line 15 of a hydraulic pump 31 driven by the prime mover 1, and the pipe pressure on both sides of the throttle 32 is inputted to a differential pressure gauge 33. . The differential pressure gauge 33 calculates the differential pressure between the two pipes based on the input pressure, and inputs the calculation result to the function generator 34 . This differential pressure depends on the rotational speed of the prime mover 1, and when this differential pressure exceeds a predetermined value, that is, when the rotational speed of the prime mover 1 exceeds a predetermined value, the function generator 34 controls the electromagnetic valve 21.
A high level signal is output to the solenoid section 21a of the solenoid section 21a to switch it to the human position. In this case, the hydraulic pump 31
．． Aperture 32. The differential pressure gauge 33 and the function generator 34 constitute a switching control means, which also provides the same effect as described above.

FIG. 3 shows yet another embodiment, in which the hydraulic pilot type two-position switching valve 41 is switched to open/close the main pipes 11, 12 using the differential pressure explained in FIG. 2 above. In other words, the pressure before and after the throttle 32 in the pipe line 15 is guided to the pilot boat of the switching valve 41, and when the pipe pressure upstream of the throttle 32 is higher than the downstream pipe pressure by a predetermined value or more, switching is performed. Valve 41 switches from position b to position a, opening main line 11.12. In this case,
Hydraulic pump 31 and throttle 32 constitute a switching means.

FIG. 4 shows yet another embodiment, in which the differential pressure in the main pipes 11 and 12 is controlled in accordance with the rotational speed of the prime mover 1. That is, a three-position electromagnetic proportional valve 51 is provided in the pipe 13 connecting the main pipes 11 and 12, and the function generator 52 is operated when the prime mover rotation speed detected by the rotation speed sensor 23 is N.
. When the output becomes higher than that, an output proportional to the output is inputted to the solenoid section 51a of the electromagnetic proportional valve 51, and the electromagnetic proportional valve 51 switches accordingly. According to this, as the rotation speed of the prime mover 1 increases, the opening degree of the electromagnetic proportional valve 51 increases, and the differential pressure in the main pipes 11 and 12 decreases accordingly, so that the hydraulic pump 2 is connected to the hydraulic motor 3. The torque received by the discharged oil is reduced, and overrun of the prime mover 1 is prevented.

Further, according to this embodiment, there are also the following effects.

That is, the solenoid valve 21 of the embodiment shown in FIG.
There are only 2 positions, and when it is in the 8th position, the pipe 12
A brake is applied to the hydraulic motor 3 due to the pressure, but when the solenoid valve 21 is in the A position, the brake is not applied because the pressure in the pipe line 12 is reduced. Therefore, as described above, when the A and B positions of the solenoid valve 21 are repeatedly switched, the deceleration of the vehicle becomes jerky. On the other hand, the switching valve shown in FIG. 4 is an electromagnetic proportional valve, and since its opening degree changes gradually, the pressure in the conduit 12 changes gradually, and the vehicle decelerates smoothly without jerking. This improves the feeling of deceleration.

Although the above description has been made regarding the running hydraulic closed circuit of a wheel loader, the present invention can also be applied to hydraulic closed circuits of other construction machines.

G3 Effects of the Invention According to the present invention, the pair of main pipes connecting the hydraulic pump and the hydraulic motor are brought into communication when it is detected that the rotational speed of the prime mover has exceeded a predetermined value based on its permissible rotational speed. , the differential pressure between the two-way pipes is reduced, the torque that the hydraulic pump receives from the oil discharged from the hydraulic motor is reduced, and rotation of the prime mover by the hydraulic pump is suppressed, thereby preventing overrun of the prime mover.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing one embodiment of a hydraulic closed circuit according to the present invention, and FIGS. 2 to 4 are circuit diagrams showing other embodiments. FIG. 5 is a diagram showing a conventional hydraulic closed circuit. 1: Prime mover 2: Variable displacement hydraulic pump 3: Hydraulic motor 11, 12: Main pipe 21: Solenoid valve
22, 34, 52: Function generator 23: Rotation speed sensor
31: Hydraulic pump 32; Throttle 51: Electromagnetic proportional valve 41: Switching valve

Claims (1)

[Scope of Claims] A variable displacement hydraulic pump driven by a prime mover, connected in a closed circuit to the hydraulic pump by a pair of main pipes,
A hydraulic closed circuit for a construction machine including a hydraulic motor driven by oil discharged from the hydraulic pump, a switching valve that can be switched between a communicating position and a blocking position, in which the pair of main pipes are communicated with each other; and the prime mover. 1. A hydraulic closed circuit for construction machinery, comprising switching control means for switching the switching valve to a communication position upon detecting that the rotational speed of the switching valve has exceeded a predetermined value based on an allowable rotational speed.