JP2776702B2 - Hydraulic circuit of construction machinery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydraulic circuit for a construction machine such as a hydraulic shovel.

[0002]

[Prior art]

 (A) A conventional hydraulic circuit for construction machinery is shown in FIG.

In this conventional circuit, all the actuators of the traveling system, front linkage system and turning system of the hydraulic excavator are driven by two main pumps 11a and 11b. That is, the two main pumps 11a and 11b supply pressurized oil to left and right traveling motors 14L and 14R through a pair of traveling operation valves 12L and 12R and counter balance valves 13L and 13R, respectively. , 11b
Boom operating valves 15a, 15b, stick operating valve 16a
, 16b, pressure oil is supplied to a front linkage actuator (hydraulic cylinder) via a bucket operation valve 17 and an attachment operation valve 18, and to a swing actuator (hydraulic motor) via a swing operation valve 19.

If the circuit is to be stopped gradually at high speed in this circuit, the counter balance valves 13L and 13R close suddenly against the operator's intention, so-called jerky vibrations occur during running, and the controllability is poor. For this reason, sufficient running speed cannot be achieved.

[0005] Further, even if the driver tries to steer the vehicle slowly to the right or left, the counterbalance valve 13L or 13R corresponding to the traveling motor 14L or 14R inside the cornering generates a rapid closing and throttle function. The inertia energy is consumed as heat energy and is not effectively used, and the steering speed is suddenly reduced to increase operator fatigue.

(B) FIG. 4 shows a sub-stream of a conventional hydraulic circuit for construction machinery. This circuit comprises two main pumps 11a, 11b and boom operating valves 15a,
15b, pressure control valves 16a and 16b, bucket control valve 17 and attachment control valve 18 to front linkage actuator (hydraulic cylinder), and swing control valve 19 to swing actuator (hydraulic motor). Oil is supplied to the two main pumps 11a, 11b of the front / slewing system, and the pumps 11L, 11 of two sets of hydraulic transmission devices for traveling closed circuit (hydrostatic transmission, hereinafter referred to as HST) are provided to the two main pumps 11a, 11b.
R is additionally provided, and the two sets of motors of the HST for the traveling closed circuit are traveling motors 14L and 14R.

This HST for running closed circuit does not need the counter balance valves 13L and 13R shown in FIG. 3 so that the controllability is good and the inner motor 14L or 14R of the cornering generates running resistance during steering. And the corresponding one of the traveling HST pumps 11L or 11R performs a motor function, so that the engine E is regenerated by the motor operation of the HST pump 11L or 11R, and the other traveling HST pump 11R or 11L is driven. The pump horsepower can be increased so as to absorb the umbilical portion, so that the heat loss as described above does not occur and the steering speed does not suddenly decrease.

[0008]

As described above, the hydraulic circuit shown in FIG. 3 has problems in running performance and steering performance, and the hydraulic circuit shown in FIG. 4 is excellent in terms of performance. However, in addition to the two main pumps 11a and 11b for the front and swivel systems, two HSTs dedicated to traveling are also provided.
It requires the pumps 11L and 11R, and has a major drawback that increases the cost as a whole.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a hydraulic circuit for a construction machine which can achieve high speed traveling, secure good steering performance, and can be constructed at low cost. Is what you do.

[0010]

According to a first aspect of the present invention, there is provided a pair of traveling closed circuits comprising two sets of hydraulic transmissions formed by a main pump and a traveling motor, and each of the traveling closed circuits is drawn from the traveling closed circuits. A front / swing system open circuit for supplying pressure oil to each operation valve of the front working system and the swing system actuator, and a traveling closed circuit for selecting each traveling closed circuit and each front / swing system open circuit. Provided 4
A two-way throttle switching valve provided upstream of each of the way throttle switching valves and each of the front and turning system open circuits, a supplementary oil pump for supplying hydraulic oil to the low pressure side of each of the traveling closed circuits, and both main pump discharges The main pump discharge line is switched between the main pump discharge lines when the traveling system and the front / slewing system are interlocked, and one main pump discharge oil is supplied only to both traveling motors and the other main pump discharge oil is supplied to both front lines. A hydraulic circuit for a construction machine constituted by a traveling straight valve that supplies a turning system line and shunts the surplus oil to a traveling system line.

According to a second aspect of the present invention, a counterbalance valve which operates only when the traveling and the front / slewing system are interlocked is provided in the hydraulic oil return line of the traveling closed circuit of the first aspect.

According to a third aspect of the present invention, a negative pressure is detected in each line of the traveling closed circuit according to the first aspect.
A pressure sensor for controlling the narrowing of the way throttle switching valve is provided.

[0013]

According to the first aspect of the present invention, when the traveling system is operated alone, the traveling closed circuit is opened by the 4-way aperture switching valve and the traveling motor is switched in the forward / reverse direction by the 4-way aperture switching. A normal traveling closed circuit is formed by closing the front / slewing-system open circuit with a two-way throttle switching valve and determining by a valve. When only the front / slewing system is operated, the traveling closed circuit is closed by a four-way throttle switching valve, and the front / swing system open circuit is opened by a two-way throttle switching valve. Pressure oil is supplied from the main pump of the circuit to each of the front and swivel operation valves. The shortage of oil on the low pressure side of the main pump that occurs at this time is resolved by replenishing the oil with the supplementary oil pump. When the traveling system is linked with the front / slewing system, the flow rate of the four-way and two-way throttle switching valves is adjusted by setting an appropriate stroke, so that pressure oil is supplied to both the traveling system and the front / slewing system in a well-balanced manner. . In addition, the traveling straight valve supplies the main pump discharge oil equally to the left and right traveling motors while the traveling system and the front / slewing system are interlocked, to maintain traveling straightness, and to use the other main pump discharge oil for both front and rear.・ Supply the excess oil to the slewing system line and shunt the surplus oil to the traveling system line to secure a constant traveling speed.

According to a second aspect of the present invention, when there is a possibility that runaway may occur due to insufficient running system control pressure due to front / turning system operation during downhill running, a hydraulic oil return line from the running motor is counted. The runaway of the running system is prevented by squeezing with the balance valve.

According to the third aspect of the present invention, when the traveling system runs out of control due to front / turning operation during a downhill traveling, a part of the traveling system line becomes negative pressure, and the pressure sensor detects the negative pressure. Upon detection, the 4-way throttle switching valve is throttled and controlled to prevent runaway of the traveling system.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to an embodiment shown in FIG.

As a traveling hydraulic circuit of the hydraulic shovel, 2
A pair of closed hydraulic circuits 21L and 21R for driving the running system on the left and right portions of the vehicle is constituted by a set of hydraulic transmissions (hydrostatic transmission, hereinafter referred to as HST).

The two main pumps (variable displacement pumps) 10L and 10R of each HST for the traveling closed circuit are used not only as a traveling system but also as a front / slewing system pump. However,
The HST main pumps 10L and 10R are of a one-sided tilt type rather than a neutral type having a high pressure H side port at all times and a pseudo high pressure side port which is normally at a low pressure L side but becomes high pressure only during traveling braking.

The two sets of variable displacement motors of the traveling closed circuit HST are referred to as a left traveling motor 14L and a right traveling motor 14R. Each of the traveling motors 14L, 14R is provided with cross line relief valves 22L, 22R in parallel.

From each high-pressure side line of each of the traveling closed circuits 21L and 21R, a front / turn load hold check valve 24 is connected.
The front and turning system open circuits 26L and 26R are pulled out via L and 24R. The front / slewing system open circuits 26L and 26R are operated valve groups A and B of a front working system actuator (hydraulic cylinder) and a swing system actuator (hydraulic motor).
It is an open circuit (open type to tank) that supplies pressurized oil to the tank.

Further, running load hold check valves 27L, 27R are installed in the discharge lines on the constantly high pressure H side of the HST main pumps 10L, 10R, respectively. Further, a charge & pilot pump 28 is attached to the HST main pump 10L, and a pilot pressure is supplied from the pump 28 to a required portion via a valve 29.

The traveling closed circuits 21L and 21R are provided with 4-way throttle switching valves 31L and 31R, respectively, and a 2-way throttle switching valve 32L is provided upstream of the front / slewing system open circuits 26L and 26R.
, 32R, and the throttle switching valves are used to selectively or quantitatively select the traveling closed circuits 21L, 21R and the front / slewing-system open circuits 26L, 26R.

The four-way throttle switching valves 31L, 31R provided in the traveling closed circuits 21L, 21R are not merely throttle valves, but also control the hydraulic pressure supplied to the traveling motors 14L, 14R to control the forward / backward movement of the vehicle. It is a 4-way directional switching valve that switches.
The two-way throttle switching valves 32L and 32R are supplied with the oil discharged from the main pumps 10L and 10R for the traveling closed circuit (also used) via the front and turning load hold check valves 24L and 24R.

The four-way throttle switching valves 31L, 31R and the two-way throttle switching valves 32L, 32R are capable of adjusting the flow rate by setting an appropriate stroke when not only the fully open position and the fully closed position but also the interlocking of the traveling system and the front / slewing system. By doing so, an appropriate amount of pressure oil can be supplied to both the traveling system and the front / turning system.

That is, the four-way throttle switching valve 31L,
31R is a flow control position represented by a throttled passage
Traveling motors 14L, 14 corresponding to T main pumps 10L, 10R
It is also a flow control valve for restricting and controlling the amount of oil supplied to the R and the amount of oil returned from the motors 14L and 14R.
The way throttle switching valves 32L and 32R are also flow control valves for controlling the amount of oil supplied to the front / swirl system operation valve groups A and B at a flow control position represented by a passage with a throttle.

When the two HST main pumps 10L, 10R are used for the front / swirl system, the circuits 26L, 26R are open type (open circuit in which the return oil returns to the tank).
The suction oil of the ST main pumps 10L and 10R tends to be insufficient. In order to prevent this, single tilt main pump 10L, 10R
The normal low pressure L side suction line is connected to a centrifugal pump 36 as a supplementary oil pump for replenishing the hydraulic oil sucked from the hydraulic oil tank 35 via two suction make-up check valves 34L and 34R. After the pressure of the suction oil (suction oil from the tank 35) is increased by the centrifugal pump 36, it is supplied as pump suction oil to the traveling closed circuits 21L and 21R via the suction make-up check valves 34L and 34R.

In the hydraulic circuit shown in FIG. 1, a straight travel valve 37 is provided between the two main pump discharge lines. The traveling straight valve 37 supplies the discharge oil of the main pump 10R to the 4-way throttle switching valve 31R in the illustrated neutral position, and connects the discharge line of the left main pump 10L to the right throttle switching valve 31R in the upward switching position. And the discharge line of the right main pump 10R to the left front / swirl system operation valve group A.
This is a four-way two-position switching valve that supplies a part of the discharge oil of R through a built-in orifice 37a and a check valve 37b, which are also diverted to a traveling system line.

When the operation levers of the traveling system and the front / turn system are operated to the full stroke,
One of the four-way throttle switching valves 31L and 31R is in a full shift position (full open), the straight traveling valve 37 is a full shift position (upward switching position), and the two-way throttle switching valve 32L is a completely closed position and two-way throttle switching. Valve 32R is to be switched to the fully open position.

Therefore, the traveling system and the front
When the full stroke operation of the swivel system is interlocked, the straight travel valve 37 switches both the main pump discharge lines to switch the one main pump 10
The discharge oil of L is supplied only to both the traveling motors 14L and 14R, and the discharge oil of the other main pump 10R is supplied to both the front and turning system lines and the surplus oil is divided and supplied to the traveling system line.

Further, on the return lines from the traveling motors of the four-way throttle switching valves 31L, 31R in the traveling closed circuits 21L, 21R, the traveling load hold check valves 27L, 27R are provided.
Balance valve 41L that switches the pressure generated between the valve and the 4-way throttle switching valve 31L, 31R as pilot pressure
, 41R are provided respectively. The counter balance valves 41L and 41R are configured to be maintained in a fully open state by a solenoid irrespective of the pilot pressure except when the traveling system and the front / slewing system are interlocked.

Next, the operation of the embodiment shown in FIG. 1 will be described.

When the traveling system is operated alone, the four-way throttle switching valves 31L, 31R are switched to one of the full shift fully open positions to open the traveling closed circuits 21L, 21R, and the two-way throttle switching valves 32L, 31L are opened. By switching 32R to the fully closed position and closing the front / slewing-system open circuits 26L and 26R, a normal HST system for a traveling closed circuit is formed. Therefore, the advantage described in (B) in the section of [Conventional Art] is obtained. In this case, the travel straight-ahead valve 37 is set to the neutral position shown in the drawing when the travel is operated alone.

When only the front / slewing system is operated, the four-way throttle switching valves 31L and 31R are switched to the neutral fully closed positions to close the traveling closed circuits 21L and 21R and to switch the two-way throttle. By switching the valves 32L and 32R to the fully open position to open the front / swirl system open circuits 26L and 26R, while the HST main pumps 10L and 10R supply pressure oil to the H-side port, the main pump discharge oil is discharged. Can be supplied to the two-way throttle switching valves 32L, 32R from the front / swing load / hold check valves 24L, 24R, and the pressure oil can be supplied to the operation valve groups A, B of the front / swing system.

The lack of oil in the suction line (L side) of the traveling closed circuits 21L, 21R at this time is caused by the hydraulic oil tank 35
The oil is forcibly fed by the centrifugal pump 36 to the normal low pressure L side of the HST main pumps 10L, 10R via the suction make-up check valves 34L, 34R.

When the traveling system and the front / slewing system are interlocked, the four-way throttle switching valves 31L and 31R and the two-way throttle switching valves 32L and 32R are set to appropriate strokes so as to match the load pressure of each actuator. By adjusting the throttle opening to an appropriate value, pressure oil is supplied to both the traveling system and the front / slewing system.

When the operating levers of the traveling system and the front / slewing system are operated up to the full stroke, the main pump 10L is fully opened through the fully opened 4-way throttle switching valve 31L and the fully opened traveling straight valve 37L. Since the pressure oil is supplied only to the way throttle switching valve 31R, the imbalance between left and right traveling is eliminated, and the straightness of the vehicle is ensured. Also, the main pump 10
R supplies pressure oil to the front / slewing system operation valve group B via the fully opened 2-way throttle switching valve 32R, and to the front / slewing system operation valve group A via the fully opened traveling straight valve 37. further,
A part of the pressure oil supplied to the operation valve group A is supplied to a diverting orifice 37a and a check valve 37b built in the straight traveling valve 37.
Through the main pump 10L to the traveling pressurized oil supply line through the main pump 10L.
% Running speed can be secured.

Further, during the interlocking of the traveling system and the front / turning system, the counter balance valves 41L and 41R are not fully opened due to the solenoid demagnetization, and the counter balance function (throttle function) is exhibited only by the pilot pressure. If there is a risk of runaway due to a decrease in the control pressure of the traveling system when the front and turning systems are interlocked when descending (during traveling downhill), return oil from the traveling motors 14L and 14R should be supplied to the return line. The runaway of the traveling system is prevented by squeezing by the counter balance valves 41L and 41R.

Next, FIG. 2 shows another embodiment of the present invention.
The hydraulic circuit of FIG. 2 does not include the counter balance valves 41L and 41R of the circuit of FIG. Furthermore, FIG.
In this circuit, pressure sensors 51L, 52L, 51R, and 52R are provided on a pressure oil supply line from the 4-way throttle switching valves 31L and 31R to the traveling motors 14L and 14R, respectively.

The pressure sensors 51L, 52L, 51R, 52R
Determines whether the side going forward or backward during a running system and a front / turn system is downhill or uphill, and if downhill, the pressure sensor 51L or 52L, 51R or 52R is under negative pressure (that is, runaway). , The corresponding 4-way throttle switching valve 31L or 31R is throttled toward the neutral side, the return passage is slightly obstructed, and an algorithm for preventing runaway of the traveling motors 14L and 14R is applied to each of the 4-way throttle switching valves 31L and 31R. Install in the driver.

The circuit shown in FIG. 2 operates similarly to the circuit shown in FIG. 1 when only the traveling system is used and when only the front / turning system is used. When the turning system is interlocked, the throttle function of the throttle switching valves 31L, 31R operates based on the detection signals from the pressure sensors 51L, 52L, 51R, 52R in the circuit of FIG. 2 to prevent the vehicle from running away. Can be.

[0041]

According to the first aspect of the invention, the traveling closed circuit and the front / turning system open circuit are selected by the 4-way throttle switching valve and the 2-way throttle switching valve, and the front / turning is performed from the traveling closed circuit. Since the hydraulic oil shortage to the system open circuit is replenished by the refueling pump, the main pump for the traveling closed circuit can also be used for the front and turning system open circuit, and the hydraulic circuit for construction machinery can be constructed at low cost. When the traveling system is operated alone, the traveling speed can be increased by a normal traveling closed circuit formed by each switching valve, and good steering performance can be secured. The travel system and the front / slewing system can be linked by setting an appropriate throttle opening corresponding to the load pressure of each actuator by the flow rate adjusting function of each throttle switching valve. further,
The straight travel valve can supply pressurized oil to the left and right travel motors in a well-balanced manner, thereby ensuring travel straightness. Especially,
The traveling linear valve switches both main pump discharge lines when the traveling system and the front / slewing system are interlocked, supplies one main pump discharge oil only to both traveling motors, and supplies the other main pump discharge oil to both front pumps.・ Because the oil is supplied to the turning system line and the surplus oil is diverted and supplied to the traveling system line, the traveling speed does not extremely decrease even during the interlocking, and the traveling speed is reduced to 50% or more of the traveling alone (maximum). Can always be secured.

According to the second aspect of the present invention, the hydraulic oil return line of the traveling closed circuit is provided with the counterbalance valve which operates only when the traveling and the front / slewing system are interlocked, so that the traveling oil can be reduced during traveling downhill. The runaway phenomenon of the traveling system can be prevented by the counter balance valve even when the front / slewing system is operated.

According to the third aspect of the present invention, since each line of the traveling closed circuit is provided with a pressure sensor for detecting the negative pressure of each line and controlling the four-way throttle switching valve to be narrowed down, the traveling downhill is provided. Even if the front / slewing system is operated, the runaway phenomenon of the traveling system can be prevented by the 4-way throttle switching valve controlled by the pressure sensor.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing one embodiment of a hydraulic circuit of a construction machine according to the present invention.

FIG. 2 is a circuit diagram showing another embodiment of the above hydraulic circuit.

FIG. 3 is a circuit diagram showing an example of a conventional hydraulic circuit for construction machinery.

FIG. 4 is a circuit diagram showing another example of a conventional hydraulic circuit for construction machinery.

[Explanation of symbols]

 10L, 10R Main pump 14L, 14R Travel motor 21L, 21R Travel closed circuit 26L, 26R Front / swivel system open circuit 31L, 31R 4 way throttle switching valve 32L, 32R 2 way throttle switching valve 36 Centrifugal pump as bunkering pump 37 Traveling straight valves 41L, 41R Counter balance valves 51L, 52L, 51R, 52R Pressure sensors A, B Front / slewing system operation valve group

Claims (3)

(57) [Claims] 1. A pair of traveling closed circuits comprising two sets of hydraulic transmissions formed by a main pump and a traveling motor; and a pressure drawn from each traveling closed circuit to each operation valve of a front working system and a turning system actuator. A front / swing system open circuit for supplying oil; a 4-way throttle switching valve and a front / swing provided in each running closed circuit to select the respective traveling closed circuits and the respective front / swiring system open circuits. A two-way throttle switching valve provided upstream of the system open circuit, a supplementary oil pump for replenishing hydraulic oil to the low pressure side of each of the traveling closed circuits, and a travel system provided between both main pump discharge lines. When the front and swivel systems are interlocked, both main pump discharge lines are switched so that one main pump discharge oil is supplied only to both traveling motors and the other main pump discharge oil is supplied to both front and rear pumps.
A hydraulic circuit for a construction machine, comprising: a traveling straight valve that supplies a revolving oil to a revolving system line and shunts the surplus oil to a traveling system line. 2. The hydraulic circuit for a construction machine according to claim 1, wherein a counterbalance valve that operates only when the traveling and the front / slewing system are linked is provided in the hydraulic oil return line of the traveling closed circuit. . 3. A construction machine according to claim 1, further comprising a pressure sensor for detecting a negative pressure in each of the lines of the traveling closed circuit and controlling the throttle of the four-way throttle switching valve. Hydraulic circuit.