JPH0349283Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a traveling hydraulic circuit for a hydraulically driven vehicle, and is particularly suitable for a traveling hydraulic circuit of a working vehicle such as a wheeled hydraulic excavator.

[Background of the idea]

Unlike the so-called mechanical drive system, where the axle is mechanically connected to the output shaft of the engine and the gears or shafts, open-circuit hydraulically driven work vehicles do not require the use of the engine accelerator pedal to slow down or stop the vehicle. However, the engine brake cannot be applied because the hydraulic oil simply circulates within the circuit. For this reason, compared to a general vehicle that uses both the foot brake and engine brake to brake, it relies only on the foot brake, and especially when driving downhill, the excessive use of the foot brake causes abnormal heat generation such as brake sew. There is a problem that early abnormal wear becomes noticeable. On the other hand, the hydraulic brake may be applied by reducing the diameter of the passageway at the neutral position of the counterbalance valve, directional control valve, etc. in the travel hydraulic circuit. However, in this case, the hydraulic brake is activated every time you take your foot off the pedal of the pilot valve (not shown) that operates the directional control valve, which not only worsens the feeling during braking, but also reduces the flow of hydraulic fluid due to constant throttling. There is a problem in that the heat generation increases, which promotes the generation of bubbles as the oil temperature rises, causing noise and vibration in various devices, and reducing the orifice diameter is naturally restricted.

A traveling hydraulic circuit of a conventional hydraulically driven vehicle will be explained using FIG. 4 using a wheel type hydraulic excavator as an example. In the figure, 1 is an engine, 2 is a hydraulic pump driven by the engine 1, 3 is a direction control valve that controls the flow of pressure oil discharged from the hydraulic pump 2 and determines the forward and reverse directions of the vehicle, and 4 is a direction control valve. A hydraulic motor driven by pressure oil via the control valve 3, 5 a counterbalance valve interposed between the hydraulic motor 4 and the directional control valve 3 and switched by the pressure oil sent from the directional control valve 3, 6, and 8 is a relief valve that operates in response to overload of the hydraulic motor 4, 7 and 9 are check valves attached to the relief valves 6 and 8, and 10 is a tank. The illustrated directional control valve 3 and counterbalance valve 5 are both in the neutral position, and all the pressure oil discharged from the hydraulic pump 2 is returned to the tank 10 and does not travel.
When the directional control valve 3 is switched to the forward position in this state, the pressure oil passes through the pipe 11 and the pilot pipe 13 and operates the counterbalance valve 5.
The hydraulic oil discharged from the hydraulic pump 2 is supplied to the hydraulic motor 4 via the pipe 15, and the hydraulic oil that drives the hydraulic motor 4 is connected to the pipe 16, the counterbalance valve 5, the pipe 12, and the direction. It is returned to the tank 10 via the control valve 3, and the vehicle moves forward. In the case of backward movement, the direction control valve 3 is switched to the reverse position so that the pressure oil flows in the opposite direction to that during the forward movement. Next, when decelerating or stopping the vehicle from the forward or reverse state, the direction control valve 3 and counterbalance valve 5 are returned to the neutral position by releasing the pedal of the accelerator valve (not shown). Then, the hydraulic oil discharged from the hydraulic motor 4 flows through the pipe line 16,
It is returned to the hydraulic motor 4 through the counterbalance valve 5, the pipe line 12, the directional control valve 3, the pipe line 11, the counterbalance valve 5, and the pipe line 15 in this order, and circulates within the circuit. For this reason, as mentioned above, the problem arises that the engine brake cannot be used and the vehicle relies solely on the foot brake.

[Purpose of invention]

The present invention solves the problems of the prior art described above, and is a traveling hydraulic circuit for a hydraulically driven vehicle that can apply a hydraulic brake equivalent to an engine brake without deteriorating the good feeling during braking. The purpose is to provide

[Summary of the idea]

The present invention provides a switching valve between the hydraulic motor and the directional control valve, which is equipped with a restriction that limits the flow rate of oil discharged from the hydraulic motor when the vehicle is running, in an open-circuit hydraulic circuit for a hydraulically driven vehicle. This is a running hydraulic circuit for a hydraulically driven vehicle that is installed in the circuit so that a hydraulic brake equivalent to an engine brake can be applied without deteriorating the feeling during braking.

[Example of idea]

An embodiment of the present invention will be explained with reference to FIGS. 1 to 3. In the figure, the same reference numerals as in FIG. 4 indicate the same things. FIG. 1 shows the first embodiment, where 17 is an ON/OFF switching valve (in the case shown, an electromagnetic switching valve) installed in the pipe line 16, and the OFF position is between the hydraulic motor 4 and the directional control valve. 3, and in the ON position, the hydraulic motor 4 and the directional control valve 3 are communicated through the throttle. The rest of the structure is the same as that shown in FIG. 4 above. The throttle provided at the ON position limits the flow rate of oil discharged from the hydraulic motor 4 while the vehicle is running.
The OFF switch is operated independently from other valves while driving. When the switching valve 17 is in the OFF position,
The operations of moving the vehicle forward and backward and decelerating or stopping the vehicle are the same as those described in FIG. When the switching valve 17 is switched to the ON position in this state, the flow rate on the discharge side of the hydraulic motor 4 is restricted by the throttle provided in the switching valve 17, and the pressure increases to apply the hydraulic brake. The way the hydraulic brakes are applied depends on the degree of throttle, but the throttle is determined for conditions that require hydraulic brakes equivalent to engine brakes, especially when going downhill. Switching valve 17
When set to the ON position and a hydraulic brake equivalent to an engine brake is applied, abnormal heat generation and early wear of the brake shoe etc. are prevented, and good feeling during braking is maintained. In addition, the hydraulic brake is not activated every time the pedal of an accelerator valve (not shown) is released, but is activated as necessary, such as when descending a slope, so that the above-mentioned noise and vibration caused by the increase in the temperature of the hydraulic oil may occur. Nor.

FIG. 2 shows a switching valve 18 installed in the pipe line 16.
In this embodiment, an output port in the ON position provided with a restriction is replaced with a counterbalance valve 5 and communicated with a tank 10, and a make-up circuit is provided that communicates a pipe line 15 with the tank 10 via a check valve.
The other configurations are the same as in FIG. 1. By providing this make-up circuit, in addition to the effects achieved by the embodiment shown in FIG. 1, there is an effect of preventing the hydraulic oil in the travel hydraulic circuit from becoming too high and improving the heat balance.

In FIG. 3, the switching valve 19 installed in the pipe line 16 is set to 3 positions, and the switching valve 17 shown in FIG.
In addition to the OFF configuration, a STOP/ON/OFF configuration is implemented with a STOP position, which is a cutoff position that throttles the entire amount of oil discharged from the hydraulic motor 4 and cuts off communication with the counterbalance valve 5, tank 10, etc. In this example, the other configurations are the same as in FIG. 1. this
By providing the STOP position, in addition to the effects of the embodiment shown in FIG.
It has the effect of being able to be switched to the STOP position and used as a brake in an emergency.

[Effect of idea]

As explained above, the present invention provides a switching valve equipped with a restriction that limits the flow rate of oil discharged from the hydraulic motor when the vehicle is running in the open-circuit hydraulic circuit of a hydraulically driven vehicle. Because it is interposed in the circuit between the brake and the engine, it has a remarkable practical effect by being able to apply a hydraulic brake equivalent to an engine brake when braking a hydraulically driven vehicle without deteriorating the feeling during braking. .

[Brief explanation of the drawing]

1 to 3 are diagrams showing embodiments of the present invention. FIG. 1 is an explanatory diagram of the first embodiment, and FIG. 2 is an explanatory diagram of the first embodiment, and FIG. FIG. 3 is an explanatory diagram of a third embodiment in which the switching valve is in three positions and a STOP position is provided. FIG. 4 is an explanatory diagram of an example of a travel hydraulic circuit for a conventional hydraulically driven vehicle. DESCRIPTION OF SYMBOLS 1... Engine, 2... Hydraulic pump, 3... Directional control valve, 4... Hydraulic motor, 5... Counter balance valve, 10... Tank, 17, 18, 19...
...Switching valve.

Claims (1)

[Scope of Claim for Utility Model Registration] 1. A hydraulic pump driven by an engine, a direction control valve that controls the flow of pressure oil discharged from the hydraulic pump and determines the forward and backward direction of the vehicle, and In a running hydraulic circuit of an open-circuit hydraulically driven vehicle equipped with a hydraulic motor driven by pressure oil, a switching valve equipped with a restriction that limits the flow rate of oil discharged from the hydraulic motor when the vehicle is running is connected to the hydraulic motor. A traveling hydraulic circuit for a hydraulically driven vehicle, characterized in that the circuit is interposed between the directional control valve and the directional control valve. 2. A hydraulically driven vehicle according to claim 1, wherein the switching valve is provided with an OFF position that communicates with the hydraulic motor and the directional control valve, and an ON position that communicates with the hydraulic motor through a throttle. travel hydraulic circuit. 3. A request for registration of a utility model characterized in that a switching valve is provided with an OFF position that communicates with a hydraulic motor and a directional control valve, and an ON position that communicates through a throttle, and that the ON position is connected to a tank. A travel hydraulic circuit for a hydraulically driven vehicle according to item 1. 4. Registration of a utility model characterized in that the switching valve is provided with an OFF position where the hydraulic motor and the directional control valve communicate with each other, an ON position where the hydraulic motor and the directional control valve communicate with each other through a throttle, and a cutoff position where the entire flow is throttled and communication is cut off. A traveling hydraulic circuit for a hydraulically driven vehicle according to claim 1.