JPS6011913Y2 - Hydraulic circuit of hydraulic vehicle with crane - Google Patents

Description

[Detailed description of the invention] This invention includes a closed circuit in which a variable displacement hydraulic pump and a hydraulic motor are connected to each other, and a replenishment hydraulic pump that supplies oil at a constant pressure to the low-pressure side circuit of the closed circuit. The present invention relates to a hydraulic circuit for a hydraulic traveling vehicle equipped with a crane, which is driven by a closed-circuit hydraulic transmission and is equipped with a hydraulic crane that is controlled by pressure oil from a replenishment hydraulic pump.

FIG. 1 shows an example of this type of hydraulic vehicle, which is constructed as follows.

A main frame 52 is mounted on the crawler type traveling body 51, and a prime mover 53, a hydraulic crane 55, and a loading platform 56 are installed on the main frame 52. A hydraulic pump 54 for controlling the pump 56 is directly connected.

Next, the conventional hydraulic circuit for this type of hydraulically driven vehicle was replaced with a second one.
This will be explained using figures.

The T side is the traveling body circuit, and the C side is the hydraulic crane circuit.

Variable displacement hydraulic pump for traveling (hereinafter referred to as variable pump)
2A, 2B and a replenishment hydraulic pump (hereinafter referred to as replenishment pump) 3 are directly connected to the engine 1, and the variable pump 2A
and a travel hydraulic motor (hereinafter referred to as hydraulic motor) 16A are connected to each other by closed circuits 14A and 15A, and variable pump 2B and hydraulic motor 16B are connected to each other by closed circuits 14B and 15.
They are connected by B.

The suction side piping 5 of the replenishment pump 3 is led to the oil tank 4, and the discharge side piping 6 is a control valve 7 that controls the telescopic cylinder 30 of the hydraulic crane 55 and a control valve that controls the hoisting hydraulic motor 28. 8. It is connected to a control valve 9 that controls the undulation cylinder 31 and a control valve 10 that controls the swing hydraulic motor 29.

Each of the hydraulic control valves 7, 8, 9, 10, the telescopic cylinder 30, the hoisting hydraulic motor 28, the luffing cylinder 31, and the swinging hydraulic motor 29 are connected by pipes connected via rotary joints 32, respectively. .

The neutral port of each control valve 7, 8, 9.10 is connected to a relief valve 12 via a pipe 11, and the relief valve 12 is connected to a pipe 2.
1 to variable pumps 2A and 2B.

The middle of the pipe 11 is connected to circuits 14A and 14B through check valves 17 and 18, respectively, and to circuits 15B and 15A through check valves 19 and 20, respectively.

Each control valve? , 8, 9, and 10, and the oil drain pipes 22 of the variable pumps 2A, 2B are led to the oil tank 4.

When the engine 1 is driven, the replenishment pump 3
of oil is sucked in through piping 5, the pressure is increased, and the oil is sent out to piping 6.

When each of the control valves 7 to 10 is in the neutral state shown in the figure, the pressure oil passes through the neutral port of each of the control valves 7 to 10 to the piping 1.
1 and is controlled by a relief valve 12.

The pressure of the make-up pressure oil generally requires 15 kp/cyf, taking into account the operation of servo cylinders and the like that control variable elements (for example, swash plates) of the variable pumps 2A and 2B.

If the replenishment pressure is 2 to 3 kg/cIl when not driving,
There is no risk of cavitation.

Therefore, the relief valve 12 is normally set to about 15 kg/Crl.

When the swash plates 13A and 13B of the variable pumps 2A and 2B are tilted to the right, pressure oil passes through the pipes 14A and 14B to the hydraulic motor 1.
6A, 16B, each hydraulic motor 16A
, 16B are driven.

The oil thus discharged flows into the variable pumps 2A, 2B through the pipes 15A, 15B.

If the swash plates 13A and 13B are tilted to the left, the closed circuit 1 will be closed, contrary to the above.
Pressure oil flows through 4A, 14B, 15A, and 15B.

At this time, if the pressure in the low-pressure side circuit of the closed circuit becomes lower than the pressure maintained by the relief valve 12 due to oil leakage inside the closed circuit, the pressure oil controlled by the relief valve 12 is transferred to the check valve. 17, 18, 19, and 20 into the closed circuit.

This prevents negative pressure in the closed circuit and prevents accidents due to cavitation and the like.

When the set pressure of the relinif valve 12 is reached, the relief valve 12 opens, and the pressure oil passes through the pipe 21 to cool the variable pumps 2A and 2B, and returns to the oil tank 4 through the oil drain pipe 22.

Each control valve? , 8, 9. If you operate 10, replenishment pump 3
Pressure oil sent out from the hydraulic crane 55 is supplied to each actuator, that is, the telescopic cylinder 30, the hoisting hydraulic motor 28, the undulating cylinder 31, and the swinging hydraulic motor 29, thereby controlling the hydraulic crane 55.

Return oil from each actuator returns to the oil tank 4 via piping 23.

Do not run the vehicle at the same time as the crane is working (Due to the danger, running the vehicle while the crane is working is prohibited.

Therefore, during crane work, all replenishment pressure oil is returned to the oil tank 4 so that the crane cannot travel.

However, even when the engine 1 is not running, the variable pumps 2A and 2B, which are directly connected to the engine 1, are rotating together with the replenishment pump 3. In addition to leakage, variable pumps 2A, 2B and hydraulic motors 16A, 1
Oil leakage from 6B creates negative pressure in the raw closed circuit, causing cavitation.

To prevent cavitation, control valves 7 to 10
All you have to do is put the oil in the return pipe 23 into the replenishment pipe 11, but if you do this, the oil in the return pipe 23 can also be used during crane work during the closed circuit, which is normally only needed for traveling.
Pressure oil of approximately ku/ct must be replenished, which is extremely wasteful and results in a loss of energy.

The purpose of this invention is to provide a hydraulic circuit that can reduce energy loss when working with a crane in a neutral state without traveling, and can replenish pressure oil at the lowest pressure that does not cause cavitation. That is.

This invention is a distant relative of the above object, and includes a closed circuit that connects a variable displacement hydraulic pump and a hydraulic motor, and a supply hydraulic pump that replenishes pressure oil to the low pressure side circuit of the closed circuit. The crane is equipped with a hydraulic crane that is driven by a closed-circuit hydraulic transmission equipped with a pressure control valve that sets the pressure of the replenishment pressure oil from the replenishment hydraulic pump, and is controlled by the pressure oil from the replenishment hydraulic pump. In a hydraulic vehicle with a crane, a replenishment pressure control valve set to a pressure lower than the set pressure of the pressure control valve is installed in the return circuit to the oil tank of the control valve that controls the hydraulic crane, and the pressure control valve and replenishment pressure are The upstream side of the control valve is connected by piping, and a check valve is provided in the middle of the piping to prevent the flow of pressure oil from the pressure control valve to the replenishment pressure control valve.

Hereinafter, one embodiment of this invention will be explained with reference to FIG.

In this figure, the same reference numerals as in FIG. 2 represent the same or equivalent items.

A replenishment pressure control valve (hereinafter referred to as a control valve) 24 is installed in the return pipe 23 and is set at a pressure P2 (approximately 3 to 4 ky/al) lower than the set pressure P□ of the relief valve 12. The upstream side of the valve 24 is connected to each other by a pipe 25, and in the middle of the pipe 25 there are IJ, IJ-
A check valve 27 is provided to prevent pressure oil from flowing from the side of the valve 12 to the control valve 24 .

That is, the return pipe 23 is connected to the pipe 11 through a pipe 25 provided with a check valve 27 .

Others are the same as those in FIG. The operation during running is the same as that shown in FIG.

During crane work (not traveling), pressure oil discharged from the supply pump 3 is sent to each actuator, and the same amount of oil is returned to the piping 23.

The pressure in circuit 11 is maintained at P2 by control valve 24.

When the pressure in the closed circuits 14A, 14B, 15A, and 15B becomes lower than P2, the reverse application valves 17, 18, and 20.19 are opened to replenish the pressure oil in the recirculation 11 to the closed circuit.

If the pressure is higher than P2, the pressure oil returns to the oil tank 4 via the control valve 24 and the return pipe 26.

The check valve 27 prevents the replenishment pressure oil from flowing backward during running.

As explained above, this device installs a control valve in the return circuit of each control valve of a hydraulic crane, so that the pressure of replenishment oil to the closed circuit during crane operation can be changed to the pressure of replenishment oil to the closed circuit during crane operation. Since the pressure is set to be much lower than that of , cavitation does not occur during crane work, energy loss is extremely reduced, and efficient operation can be performed.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing an example of a hydraulic vehicle with a crane;
FIG. 2 is a system diagram showing a conventional hydraulic circuit for a hydraulic vehicle with a crane, and FIG. 3 is a system diagram showing an embodiment of the hydraulic circuit according to this invention. 1...Engine, 2A, 2B...Variable capacity hydraulic pump for traveling, 3...Hydraulic pump for replenishment, 4...Oil tank, 5. ·····Piping,
7-10...control valve, 11...piping,
12... Relief valve, 14A, 14B...
...Closed circuit, 15A, 15B...Closed circuit, 16
A, 16B......Hydraulic motor for travel, 17-20
...Check valve, 21... Piping, 23.
...Return piping, 24...Replenishment pressure control valve,
25... Piping, 26... Return piping, 2
7... Check valve, 28... Hydraulic motor for hoisting, 29... Hydraulic motor for swinging, 30...
...Compression cylinder, 31...Luffing cylinder.

Claims (1)

[Scope of utility model registration request] A closed circuit that connects a variable displacement hydraulic pump and a hydraulic motor, a replenishment hydraulic pump that replenishes pressure oil to the low-pressure side circuit of the closed circuit, and the pressure of replenishment pressure oil from the replenishment hydraulic pump. A control valve that controls a hydraulic crane in a hydraulic traveling vehicle equipped with a crane that travels by a closed-circuit hydraulic transmission equipped with a pressure control valve that operates and is equipped with a hydraulic crane that is controlled by pressure oil from a replenishing hydraulic pump. A replenishment pressure control valve set to a pressure lower than the set pressure of the pressure control valve is installed in the return circuit to the oil tank, and the upstream sides of the pressure control valve and the replenishment pressure control valve are connected by piping, and the A hydraulic circuit characterized in that a check valve is provided in the middle to prevent the flow of pressure oil from the pressure control valve to the replenishment pressure control valve.