JPH0322057Y2 - - Google Patents

Description

[Detailed Description of the Invention] (Industrial Field of Application) This invention relates to an air brake device used in a tractor that can drive a trailer.

(Prior Art) Generally, in a large vehicle, the magnitude and distribution of the load differs greatly between when the vehicle is empty and when it is loaded. As one of the air brake devices suitable for these vehicles,
For example, Utility Model Publication No. 52-24709 or Japanese Unexamined Patent Publication No. 51
- As shown in each publication of No. 131027, there is a brake valve that discharges compressed air at a pressure proportional to the driver's operation from a compressed air source to the piping system, and a brake valve that applies the discharge pressure from the brake valve to the axle. There are known load-responsive control valves that perform pressure reduction control in proportion to the magnitude of the load being applied, and actuators that operate wheel brakes when supplied with pressure.

(Problem to be Solved by the Invention) The load responsive control valve has a diaphragm on one side of the piston, and has a load sensing valve that changes the effective area of pressure acting on the piston as the piston moves up and down. It has been found that when the air brake device is applied to an air brake device for a tractor, the following problems occur. The problem is that when a tractor is towing a trailer or not towing a trailer, even if the brake pressure is controlled to be proportionally reduced, the pressure is too high and the rear wheels are likely to lock. These problems are particularly noticeable in semi-trailers, which receive the load on the trailer side on the axle of the rear wheels of the tractor. This is due to the fact that the load applied to the rear wheels of the tractor changes more greatly between when the trailer is towed and when it is not towed, compared to other vehicles such as trucks.

As a method of solving the above-mentioned problems, it is possible to consider increasing the pressure reduction ratio of the load response control valve. However, countermeasures to this problem include the problem that the valve itself becomes larger because the diameter of the diaphragm is increased, or that different load response control valves must be prepared depending on the vehicle type.

Of course, it is also conceivable to apply a highly accurate rear wheel lock prevention technique applied to trucks, etc., as disclosed in, for example, Japanese Patent Application Laid-Open No. 105863/1983. However, this technology requires a control circuit to perform complex information processing such as calculating the corner brake fluid pressure based on the live load or comparing the corner brake fluid pressure and the brake fluid pressure, making the control complex. Therefore, it is difficult to obtain stable performance.

(Means for solving the problem) Therefore, in this invention, taking into account that the above-mentioned problem is unique to tractors that pull trailers, the load response control valve itself remains as it is, and in addition, the following By adding such means, we are trying to solve the problem with a simple method.

That is, the applying means is provided in parallel with a switching valve that is switched depending on whether or not the trailer is towed, and is closed when the trailer is not towed and opens when the trailer is towed, and when a predetermined pressure is reached. This is a valve device that blocks pressure supply to the actuator side.

(Function) When towing a trailer, the braking force distribution between the rear and front wheels can be maintained appropriately by the action of the load response control valve itself. On the other hand, when the trailer is not towed, in addition to the action of the load response control valve, the action of the valve device prevents the braking force of the rear wheels from exceeding a predetermined pressure even if the discharge pressure from the brake valve increases. There is no.

(Embodiment) FIG. 1 is a brake piping diagram showing an embodiment of this invention.

The compressed air generated by the compressor is accumulated in the main reservoir 10, and is further stored in the check valve 1.
The air is accumulated in the rear and front air reservoirs 14R and 14F through 2R and 12F. Each air reservoir 14R, 14F has a brake valve 16
The brake valve 16 discharges air pressure according to the amount of depression of the pedal 16a.
This air pressure actuates the relay valve 18, which is able to supply the same pressure from the air reservoir 14R to the brake chamber 20 as the incoming pressure. The brake chamber 20 is an actuator that is supplied with pressure to actuate the wheel brakes.
Although the front brake chamber is omitted in FIG. 1, the front brake chamber is the same as the rear brake chamber.

In such an air brake circuit, the load sensing valve 2, which is the load response control valve mentioned above,
2 is arranged and connected between the brake valve 16 and the relay valve 18. The load sensing valve 22 is well known in the art and has a function of reducing the pressure of the discharge force from the brake valve 16 in proportion to the magnitude of the load acting on the rear axle of the tractor. As an operational characteristic of the load sensing valve 22, a braking force distribution diagram between the front and rear wheels when the trailer is not being towed is shown by a broken line a in FIG. It will be understood that the diagram indicated by the broken line a deviates considerably from the ideal braking force distribution diagram shown by the thin solid line b in the figure.

Therefore, here, a two-position electromagnetic switching valve 24 and a restriction valve 26 are provided in parallel between the brake valve 16 and the load sensing valve 22. A check valve 28 connected in parallel with these two valves is for ensuring rapid release of the brake. Further, reference numeral 30 is a brake switch that performs electrical switching using air pressure.

The two-position electromagnetic switching valve 24 is open when the trailer is being towed and is closed when the trailer is not being towed. On the other hand, the restriction valve 26 can prevent the pressure supplied from the inlet port 26a and discharged through the outlet port 26b from exceeding a predetermined value. The predetermined value is the effective pressure receiving area determined by the seal ring 26e around the piston 26d inside the main body 26c,
and a spring 26f that applies a biasing force to the right in the figure to the piston 26d.

FIG. 2 shows a control circuit for switching the electromagnetic switching valve 24. As shown in FIG. The voltage of the battery 32 is applied through the brake switch 30 to the brake lamp 34 on the tractor side, the relay coil 36a, the motorcycle detection switch 38 consisting of the coil 38a and the reed switch 38b, and further through the coupling 40 to the brake lamp 42 on the trailer side. be done. The relay having the coil 36a has a b contact 36b which is turned on in a demagnetized state, and the solenoid 24a of the electromagnetic switching valve 24 is connected in series to the b contact 36b. Therefore, when the brake valve 16 is operated and the brake switch 30 is turned on during trailer towing, the coil 38a of the motorcycle detection switch 38 is energized, thereby turning on the reed switch 38b. Therefore, the relay coil 36a is excited and the relay contact 36b
is turned off, and the solenoid 24a of the electromagnetic switching valve 24 is demagnetized. That is, the electromagnetic switching valve 24 is in the open state shown in FIG. 1, and the discharge pressure from the brake valve 16 is freely supplied to the load sensing valve 22 side. On the other hand, when the trailer is not towed, the coupling by the coupling 40 is removed, so the coil 38 of the motorcycle detection switch 38 is disconnected.
a is in a demagnetized state, so the reed switch 38b is turned off and the relay coil 36a is also in a demagnetized state. As a result, the relay contact 36b is always on, and when the brake switch 30 is turned on, the solenoid 24a is energized, so the electromagnetic switching valve 24 is switched to the closed state opposite to that shown in FIG. As a result, on the rear side, the discharge pressure from the brake valve 16 can be supplied to the load sensing valve 18 only through the restriction valve 26. From the above, according to the air brake device for a tractor according to the illustrated embodiment, as shown by the thick solid line c in FIG. 3, the load sensing valve 22
It is possible to obtain a braking force distribution diagram having an operating point P due to the limit valve 26 and an operating point Q due to the restriction valve 26.

(Effects of the invention) This invention is equipped with a valve device that can block the supply of compressed air at a predetermined pressure or higher when the trailer is not being towed. This can effectively prevent the rear wheels from locking up.

[Brief explanation of drawings]

Fig. 1 is a piping diagram showing an embodiment of the air brake device for a tractor of this invention, Fig. 2 is a diagram showing an example of a control circuit for an electromagnetic switching valve, and Fig. 3 is a diagram showing a braking force distribution diagram. be. 16... Brake valve, 20... Brake chamber (actuator), 22... Load sensing valve (load response control valve), 24... Solenoid switching valve,
26...Restriction valve, 38...Motorcycle detection switch.

Claims (1)

[Scope of utility model registration request] a brake valve that discharges compressed air at a pressure proportional to the driver's operation from a compressed air source to the piping system;
An air brake device for a tractor, comprising a load response control valve that controls the discharge pressure from the brake valve to be reduced in proportion to the magnitude of the load acting on the axle, and an actuator that is supplied with pressure and operates a wheel brake. between the brake valve and the actuator, in addition to the load response control valve, a switching valve that is switched depending on whether or not the trailer is towed, and is closed when not towed and opened when towed; An air brake device for a tractor, which is provided with a valve device that is provided in parallel with the switching valve and blocks pressure supply to the actuator side when a predetermined pressure is reached.