JPH044177B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a brake circuit for a work vehicle, and particularly to a brake circuit for a work vehicle using pressurized air as a power source.

[Background of the invention]

Brakes are one of the most important safety parts not only for work vehicles but for any traveling vehicle, and must operate reliably under any circumstances. Especially civil engineering
Work vehicles used for construction are heavy and have a large inertial energy, so poor braking can directly lead to a serious accident, so highly reliable brakes are particularly required. As a brake for such a work vehicle, a brake using pressurized air as a power source, as shown in FIG. 3, is known.

In FIG. 3, 1 is an air pressure source, an engine 2 and a compressor 3 driven by the engine 2.
, an air tank 4 that stores air compressed by the compressor 3, a check valve 5 that prevents the compressed air stored in the air tank 4 from flowing back into the compressor 3, and the air tank 4. A relief valve 6 releases the compressed air in the air tank 4 into the atmosphere when the air pressure inside the air tank exceeds a set value. 7 is a running brake valve used to decelerate and stop a running working vehicle; 8 is a working brake valve used to keep the working vehicle in a stopped state during working; are set in parallel downstream of the air supply pipe 1a. 9
is a shuttle valve, and output pipes 10 and 11 of the traveling brake valve 7 and the working brake valve 8 are connected to two inlets thereof, respectively. 12 is a pneumatic-hydraulic conversion booster, and the piston 12
An air chamber 12b and an oil chamber 12c are formed on both sides of a, and an outlet pipe 1 of the shuttle valve 9 is connected to the air chamber 12b via a rotary joint 13.
4 is connected. Reference numeral 15 denotes a brake device built into the wheel, which includes a wheel cylinder 17 connected to the oil chamber 12c of the pneumatic-hydraulic conversion booster 12 through a pressure oil pipe 16, and a brake operated by the wheel cylinder 17. Show 18
and a brake drum 19 against which the brake shoe 18 is pressed. 20 and 20a are ram cylinders on which the front wheels of the wheels equipped with the brake device 15 are suspended; 21 is an oil tank that stores hydraulic oil to be supplied to the ram cylinders 20 and 20a; and 22 and 22a are the ram cylinders. 2
23 is a ram cylinder control valve interposed between the ram cylinders 20, 20a and the oil tank 21, and 24 is an outlet pipe of the working brake valve 8. signal pressure input port 2 of the ram cylinder control valve 23
3a. 23b
23c is a throttle provided at the switching position E of the ram cylinder control valve 23, and 23c is a check valve provided at the switching position R of the ram cylinder control valve 23.

Now, as shown in FIG.
When the traveling brake valve 7 is switched from the state in which the working brake valve 8 and the working brake valve 8 are both in the switching position D to the switching position U, the air pressure in the air tank 4 is
Air supply pipe 1a, travel brake valve 7, pipe 1
0, is transmitted to the air chamber 12b of the pneumatic-hydraulic conversion booster 12 via the shuttle valve 9 and the pipe line 14.
As a result, the oil pressure in the oil chamber 12c increases, the wheel cylinder 17 is driven, and the brake shoe 1
8, the brake drum 19 is pressed and each wheel is braked. When the brake pedal 7a is released and the travel brake valve 7 is returned to the switching position D, the pressurized air in the air chamber 12b passes through the pipe 14, the shuttle valve 9, the pipe 10, and the exhaust port 7b of the travel brake valve 7. Exhausted to the outside, air chamber 12b, oil chamber 12
The pressure at c decreases, the wheel cylinder 17 is released from its operating state, and the brake system is released.

Further, when the working brake valve 8 is switched to the switching position U instead of the traveling brake valve 7, the air pressure in the air tank 4 is changed to the air supply pipe 1a, the working brake valve 8, the pipe 11, and the shuttle valve 9. , is transmitted to the air chamber 12b of the pneumatic-hydraulic conversion booster 12 via the pipe 14, and is also transmitted to the pilot pipe 2.
4, a pilot signal is transmitted to the signal pressure input port 23a of the ram cylinder control valve 23. As a result, the wheel cylinder 17 is driven and each wheel is braked, and the ram cylinder control valve 23 is switched to the switching position R to restrict the outflow of hydraulic oil from the ram cylinders 20 and 20a. 20, 20a are fixed. When the operating lever 8a is released and the working brake valve 8 is returned to the switching position D, the pressurized air in the air chamber 12b passes through the pipe 14, the shuttle valve 9, the pipe 11, and the exhaust port 8b of the working brake valve 8. is discharged to the outside,
The pressure in the air chamber 12b and the oil chamber 12c decreases and the brake device 15 is released, and the ram cylinder control valve 23 is switched to the switching position E, allowing the ram cylinders 20 and 20a to swing.

The above-described conventional brake device for a work vehicle is particularly suitable for a work vehicle composed of an upper rotating body and a lower traveling body. That is, air pressure source 1,
By installing the traveling brake valve 7, the working brake valve 8, and the shuttle valve 9 on the upper revolving body, and installing the pneumatic-hydraulic conversion booster 12 on the lower traveling body, the fluid passing through the rotary joint 13 can be converted into air. Therefore, when brake oil of a different type than the working machine's hydraulic oil passes through the rotary joint 13, it completely prevents the situation where the seal of the rotary joint 13 deteriorates and it infiltrates into other pipes. This is something that can be prevented.

By the way, in the brake circuit of the conventional work vehicle described above, when either one of the traveling brake valve 7 and the work brake valve 8 is switched, pneumatic pressure-hydraulic conversion is performed from the switched brake valve. In order to supply pressurized air from the air pressure source 1 to the air chamber 12b of the booster 12 and to block the air flow path leading from the switched one brake valve to the other unoperated brake valve, a shuttle is required. Valve 9 is essential.

However, shuttle valves used in brake systems for work vehicles are operated by a differential pressure between air pressures supplied to both ends, and dirt mixed in the operating air may get caught in the shuttle piston, or It is in an environment where moisture mixed in the working air tends to freeze, and it is prone to stagnation (a phenomenon in which the shuttle piston malfunctions), making it a mechanically unreliable member. In other words, when the shuttle valve causes this stay, when one of the brake valves is switched, pressurized air leaks through the shuttle valve from the exhaust port of the other brake valve that is not operated, and the air leaks into the brake circuit. There is a risk that the pressure will drop and the brakes will become inoperable.

Therefore, conventional brakes equipped with a shuttle valve as pressure air control means are unsuitable as brake systems for work vehicles that require high reliability.

[Purpose of the invention]

The present invention aims to eliminate the drawbacks of the conventional brake circuit for a work vehicle described above, and to provide a brake circuit for a work vehicle that operates reliably and has high reliability.

[Summary of the invention]

In order to achieve the above object, the present invention provides a pneumatic pressure source, a traveling brake valve and a working brake valve connected to the pneumatic pressure source, and one of the traveling brake valve and the working brake valve connected to the pneumatic pressure source. a brake device that operates when the vehicle is turned on, a ram cylinder on which a wheel equipped with the brake device is suspended, an oil tank in which hydraulic oil to be supplied to the ram cylinder is stored, and a pipe connecting the ram cylinder and the oil tank. A brake circuit for a working vehicle including a ram cylinder control valve interposed in a road and interlocked with the working brake valve,
The work brake valve is connected downstream of the travel brake valve, and when the travel brake valve is switched to the operated state while the work brake valve is not operated, the pressure from the air pressure source is An air conduit is provided for supplying the brake device through a travel brake valve and a work brake valve, and when the work brake valve is switched to an operated state while the travel brake valve is in a non-operated state, a pilot conduit for supplying pressure from the air pressure source to the signal pressure input port of the ram cylinder control valve via the working brake valve;
A bypass circuit with a check valve that only allows pressurized air to flow from the pilot pipe to the air pipe is provided between the air pipe and the pilot pipe on the downstream side of the working brake valve. and, between the output port of the travel brake valve and the output port of the work brake valve in this brake circuit, there is no backflow of pressurized air from the output port of the work brake valve to the output port of the travel brake valve. This is characterized by the provision of a bypass circuit with a check valve to prevent this.

[Embodiments of the invention]

Next, an embodiment of the present invention will be described based on FIGS. 1 and 2. In addition, in these figures, the third
Components similar to those shown in the figures are designated by the same reference numerals.

FIG. 1 is a circuit diagram showing a first embodiment of the present invention. In this figure, 30 is a running brake valve, and 31 is a working brake valve. The running brake valve 30 is provided with an input port 30a, an exhaust port 30b that communicates with outside air, and an output port 30c that communicates with the exhaust port 30b when inactive. path 1a is connected. The working brake valve 31 includes an input port 31a connected to the output port 30c of the traveling brake valve 30, an output port 31b communicating with the input port 31a when inactive, and an air supply pipe of the air pressure source 1. An input port 31c connected to the passage 1a and an output port 31d communicating with the input port 31c during operation are provided, and are connected downstream of the travel brake valve 30. 32 is an air pipe connecting the output port 30c of the traveling brake valve 30 and the input port 31a of the working brake valve 31, and 33 is an air pressure-hydraulic conversion booster between the output port 31b of the working brake valve 31. An air pipe line 34 connects the twelve air chambers 12b, and a pilot line 34 connects the output port 31d of the working brake valve 31 and the signal pressure input port 23a of the ram cylinder control valve 23. 35 is a bypass circuit connected between the air pipe line 33 and the pilot pipe line 34, and includes a check valve 36 that prevents pressurized air from flowing from the air line 33 into the pilot line 34. is interposed.

The brake circuit of the working vehicle of the above embodiment has a first
As shown in the figure, when both the traveling brake valve 30 and the working brake valve 31 are not operated and are in the switching position D, the pressurized air from the air supply source 1 is transferred to the traveling brake valve 30 and the working brake valve. 3
1, the pneumatic-hydraulic conversion booster 1
The brake device 1 is not supplied to the air chamber 12b of the
5 does not work. Further, since no signal pressure is generated in the pilot line 34 and the ram cylinder control valve 23 cannot be switched, the ram cylinders 20, 20a
is in a swingable state.

Here, when the traveling brake valve 30 is switched to the switching position U, the air pressure in the air tank 4 is
Air supply pipe 1a, running brake valve 30, air pipe 32, working brake valve 31, air pipe 33
Air chamber 1 of pneumatic-hydraulic conversion booster 12 through
This will be communicated to 2b. Therefore, the oil pressure in the oil chamber 12c increases accordingly, the wheel cylinder 17 is driven, the brake shoe 18 is pressed against the brake drum 19, and each wheel is braked. When the brake pedal 30d is released and the travel brake valve 30 is returned to the switching position D, the pressurized air in the air chamber 12b is transferred to the air pipe line 33, the working brake valve 31, the air pipe line 32, and the travel brake valve 30. Exhaust port 3
0b to the outside, the pressure in the air chamber 12b and the oil chamber 12c decreases, and the pressure in the wheel cylinder 17
is released from its operating state and the brake device 15 is released.

Further, when the working brake valve 31 is switched to the switching position U instead of the traveling brake valve 30,
The air pressure in the air tank 4 is determined by the air supply pipe 1a,
The working brake valve 31, the pilot line 34, the check valve 36, and the bypass circuit 35 are transmitted to the air chamber 12b of the pneumatic-hydraulic conversion booster 12, and the pilot signal is transmitted through the pilot line 34 to the ram cylinder control valve. 23 is transmitted to the signal pressure input port 23a. As a result, the wheel cylinder 17 is driven and each wheel is braked, and the ram cylinder control valve 23 is switched to the switching position R, as in the case where the traveling brake valve 30 is switched, and the check valve 23c restricts the flow of hydraulic oil from the ram cylinders 20, 20a, and fixes the ram cylinders 20, 20a.

When the operating lever 31e is released and the working brake valve 31 is returned to the switching position D, the pressurized air in the air chamber 12b is transferred to the air pipe line 33 and the working brake valve 3.
1. Exhausted to the outside through the exhaust port 30b of the travel brake valve 30, air chamber 12b, oil chamber 12
c decreases and the brake device 15 is released, and the ram cylinder control valve 23 moves to the switching position E.
Returning to , the ram cylinders 20 and 20a become swingable.

FIG. 2 is a circuit diagram showing a second embodiment of the present invention.

In this embodiment, a reverse connection is made between the output port 30c of the traveling brake valve 30 and the output port 31b of the working brake valve 31 in a brake circuit configured exactly the same as that of the first embodiment. A bypass circuit 38 having a stop valve 37 is provided. This bypass circuit 38
The check valve 37 is set in a direction to prevent pressure air from flowing back from the output port 31b of the working brake valve 31 to the output port 30c of the traveling brake valve 30.

The brake circuit of the working vehicle of the second embodiment is as follows:
As shown in FIG. 2, when the traveling brake valve 30 and the working brake valve 31 are both switched from the switching position D to the switching position U, the air pressure in the air tank 4 is
The air is directly transmitted to the air chamber 12b of the air pressure/hydraulic conversion booster 12 via the air supply pipe 1a, the travel brake valve 30, and the bypass circuit 38. Therefore, in the case of the brake circuit of this embodiment, the response of the brake device 15 is faster than that of the brake circuit of the first embodiment, and the safety of the work vehicle can be further improved. Furthermore, even if the working brake valve 31 is stuck in the middle and the air circuit between the traveling brake valve 30 and the pneumatic-hydraulic conversion booster 12 is cut off, the traveling brake valve 30 can be switched. As a result, the brake device can be operated reliably, and serious accidents such as a runaway of the work vehicle can be prevented.

The operations when the running brake valve 30 is returned to the switching position D and when the working brake valve 31 is switched are completely the same as those in the first embodiment, so the explanation will be omitted.

In all of the above embodiments, a pneumatic-hydraulic conversion booster 12 is set between the pneumatic pressure source 1 and the wheel cylinder 17, and a pneumatic-hydraulic brake is used in which the wheel cylinder 17 is hydraulically operated. Although this is an embodiment, the gist of the present invention is not limited thereto, and a pneumatic brake that directly supplies pressurized air from a pneumatic source to the wheel cylinder 17 may also be used. In this case, naturally, the pneumatic-hydraulic conversion booster 12 becomes unnecessary.

〔Effect of the invention〕

As mentioned above, since the brake circuit of the work vehicle of the present invention omits the shuttle valve, there is no possibility of occurrence of stall, and there is no brake malfunction caused by this, and the brake circuit is highly reliable. can be provided. Therefore,
Decelerating and stopping the vehicle by operating the driving brake valve, and selecting parking of the vehicle by operating the work brake valve are performed reliably, and abnormal wear of the brake shoe due to improper switching of the brake valve is prevented. This can improve vehicle safety and workability. Furthermore, since the shuttle valve is omitted and only one or two bypass circuits each having one check valve are newly added, implementation can be achieved at low cost.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing a first embodiment of a brake circuit for a work vehicle according to the present invention, FIG. 2 is a circuit diagram showing a second embodiment of a brake circuit for a work vehicle according to the present invention, and FIG. The figure is a circuit diagram showing a brake circuit of a conventional work vehicle. 1: Air pressure source, 7: Brake valve for traveling, 8: Brake valve for work, 9: Shuttle valve, 12: Air pressure hydraulic conversion booster, 15: Brake device, 17:
Wheel cylinder, 18: Brake shoe, 1
9: Brake drum, 20, 20a: Ram cylinder, 21: Oil tank, 23: Ram cylinder control valve, 24: Pilot pipe, 30: Brake valve for traveling, 31: Brake valve for work, 32, 33:
Air pipe line, 34: Pilot pipe line, 35, 38:
Bypass circuit, 36, 37: check valve.

Claims (1)

[Claims] 1. A pneumatic pressure source, a traveling brake valve and a working brake valve connected to the pneumatic pressure source, and a system that operates when either the traveling brake valve or the working brake valve is switched. A brake device, a ram cylinder on which a wheel equipped with the brake device is suspended, an oil tank in which hydraulic oil to be supplied to the ram cylinder is stored, and a pipe line connecting the ram cylinder and the oil tank. and a ram cylinder control valve that is linked to the working brake valve, the working brake valve is connected downstream of the traveling brake valve, and the working brake valve is not operated. An air pipe line is provided for supplying pressure from the air pressure source to the brake device via the traveling brake valve and the working brake valve when the traveling brake valve is switched to an operating state in the state, When the working brake valve is switched to the operating state while the traveling brake valve is not operated, pressure from the air pressure source is transferred to the signal pressure input port of the ram cylinder control valve via the working brake valve. A pilot pipe is provided between the air pipe and the pilot pipe on the downstream side of the working brake valve, and only the flow of pressurized air from the pilot pipe to the air pipe is allowed. A brake circuit for a work vehicle, characterized in that a bypass circuit with a check valve is provided. 2. A pneumatic pressure source, a traveling brake valve and a working brake valve connected to this pneumatic pressure source, a brake device that operates when either one of the traveling brake valve or the working brake valve is switched, and the brake a ram cylinder on which a wheel equipped with the device is suspended; an oil tank in which hydraulic oil to be supplied to the ram cylinder is stored; and a working brake valve interposed in a pipe connecting the ram cylinder and the oil tank. In a brake circuit for a working vehicle equipped with a ram cylinder control valve that is interlocked with a ram cylinder control valve, the working brake valve is connected downstream of the traveling brake valve, and when the working brake valve is not operated, the traveling brake valve is An air pipe line is provided for supplying pressure from the air pressure source to the brake device via the travel brake valve and the work brake valve when the brake valve is switched to the operating state, and the travel brake valve is activated. a pilot conduit that supplies pressure from the air pressure source to the signal pressure input port of the ram cylinder control valve via the working brake valve when the working brake valve is switched to the operating state from a non-operating state; A check valve is provided between the air pipe and the pilot pipe on the downstream side of the working brake valve, and a check valve that only allows pressurized air to flow from the pilot pipe to the air pipe. A bypass circuit is provided between the output port of the travel brake valve and the output port of the work brake valve, and a bypass circuit is provided between the output port of the travel brake valve and the output port of the work brake valve, and a bypass circuit is provided for supplying pressurized air from the output port of the work brake valve to the output port of the travel brake valve. A brake circuit for a work vehicle characterized by having a bypass circuit equipped with a check valve to prevent backflow.