SYSTEM FOR PREVENTING A TRAILER'S OVERRUN BRAKES FROM BEING ACTIVATED DURING REVERSING

Abstract

A overrun brake system includes a gas spring with a gas-tight cylinder and a piston with holes allowing gas to slip through so that the pressure is the same on both sides. Since the free end of the piston has a larger area than the side where the piston rod is located, the gas spring will act as a compression spring. To prevent the overrun brakes from being activated during reversing, the gas spring has a solenoid controlled valve receiving current from the reverse light circuit and closing the flow of gas through the piston when the towing unit's gear is set into reverse. When the gear is set into forward position the solenoid loses its current and a mechanical return spring opens the valve, so that the overrun brakes may act normally again.

Claims

1. An overrun brake system for a trailer, the system comprising: a coupling device adapted to connect the trailer to the towbar of a vehicle, a slide connecting the coupling device to the drawbar of the trailer and transferring retardation forces to the brakes of the trailer, a gas spring connected in parallel with the slide, the gas spring including a cylinder and piston, and a solenoid valve connecting the two sides of the piston, the solenoid valve being electrically connected to and operated by the vehicle's reverse light circuit or another electric source, the solenoid valve being open when non-energized connecting the two sides of the piston, and the solenoid valve closing preventing gas passing between the two sides of the piston when energized by the reverse light system, or the other electric source.

2. A brake system according to claim 1, wherein the solenoid valve is incorporated in the piston.

3. A brake system according to claim 1, wherein the solenoid of the solenoid valve is mounted external to the gas spring, the valve of the solenoid valve is incorporated in the piston, the valve being operated by the solenoid by a valve rod running in the piston's piston rod.

4. A brake system according to claim 1, wherein the solenoid valve is mounted external to the gas spring, with channels from each side of the piston leading to the solenoid valve through the piston's piston rod.

5. A brake system according to claim 1, wherein the slide is a tube type slide and the gas spring is mounted inside the slide.

6. A brake system according to claim 1, wherein the slide is connected to the brakes of the trailers with a mechanical mechanism, said brakes including ordinary brake shoes that give full braking power regardless of the wheels' direction of rotation.

7. A brake system according to claim 1, wherein an extra switch is inserted in the backing light circuit to avoid any uncontrolled locking of the gas spring caused by possible failures in the backing light circuit when driving forward.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The invention will now be described in detail in reference to the attached drawings, in which:

[0015] FIG. 1 shows a solenoid and valve that are included in the piston itself with current supplied through the piston rod.

[0016] FIG. 2 shows a solenoid that is mounted outside the gas spring's cylinder with a pushrod to the valve in the piston.

[0017] FIG. 3 shows a solenoid and valve built as a standalone unit, without any physical connection to the gas spring other than pipe or hose connection to both sides of the piston.

[0018] FIG. 4 shows schematically how the inventions overrun brake system with lockable gas spring may be used with hydraulic surge brakes.

[0019] The attached drawings are meant to be schematically showing the principal function of the invention's overrun brake system. Only a few examples of how the different components of the system may be combined are drawn, but the system is off course not limited to these examples. It is up to any trailer builder to find their own design.

[0020] To make this patent application as simple and transparent as possible, drawings of ordinary and well known drum and disc brakes and their transmission system like rods, Bowden cables, hydraulic network and description of how they work, are omitted.

DETAILED DESCRIPTION

[0021] FIG. 1 shows a trailer's hitch attachment connected to the ball of a vehicle's towbar. Between the coupling device 1 (release lever not shown) grabbing the ball and the trailer's drawbar there is a slide 2 allowing the coupling device 1 to be pressed towards the drawbar when the vehicle is braking. From the coupling device 1 there is a mechanical mechanism 13 transferring the forces to the brakes on each wheel. A hand brake lever 12 is connected to the mechanical transfer mechanism 13 allowing the trailer to be parked with the brakes activated. The slide 2 shown in the figure is of a tubular type and inside the slide there is mounted a gas spring 3. The gas spring 3 is fastened to the slide 2 in one end, while the other end is fastened to a fixed point on the trailer, here the end of the overrun device housing 4 which is a part of the drawbar. Thus, the gas spring is effectively connected in parallel with the slide.

[0022] The gas spring is built according to known principles as a closed cylinder with constant gas overpressure. A piston rod 8 is passing through a stuffing box/gland 6 in one end of the cylinder. A piston 5 is mounted on the piston rod 8 inside the cylinder, the piston 5 having openings allowing the gas to flow freely through holding the gas pressure constant on both sides of the piston.

[0023] Due to the piston rod 8 occupying a part of the piston's surface on one side, the opposite side of the piston will have a larger area affected by the constant gas pressure. The force affecting the open side of the piston will therefore constantly be larger than on the side where the piston rod is mounted, and thus the unit will work as a compression spring.

[0024] The invention's gas spring is made using the same principle but has in addition a solenoid controlled valve 17 coupled to the trailer's reversing light circuit or alternately from another electrical source. The other electrical source may be a dedicated switch for supplying power to the solenoid valve in trailers and vehicles without a normal reverse light circuit, such as an ATV. When the car is set into reverse, the solenoid is supplied with current from the trailer's reversing light circuit and the valve becomes closed. When gas cannot flow freely from one side to the other of the piston, the gas spring is locked.

[0025] If the slide of the ball hitch attachment is fully extended so that the trailer's brakes are not on when the car is set into reverse, the locked gas spring will prevent the slide from moving and thus the braking is fully inactivated during reversing.

[0026] When the car's gear is removed from the reverse position, the current to the reversing light is cut and the solenoid's mechanical return spring will open the valve again restoring normal braking function.

[0027] As a safety measure, an extra switch may be inserted in the backing light circuit to avoid any uncontrolled locking of the gas spring caused by possible failures in the backing light circuit when driving forward

[0028] In the embodiment of the invention shown in Fig. A the solenoid valve 17 is incorporated in the piston 5 with the conductors 7 supplying current to the solenoid routed out through the piston rod 8.

[0029] FIG. 2 shows an embodiment where the solenoid itself is located external to the gas spring while the valve part is incorporated in the piston. A valve rod 9 is transferring the movement of the solenoid's pallet to the valve. The valve is opening/closing a number of channels 11 connecting the two sides of the piston.

[0030] FIG. 3 shows an embodiment of the invention wherein the whole solenoid valve 17 is mounted externally to the gas spring. Channels 11 from each side of the piston are routed through the piston rod 8 out to the solenoid valve.

[0031] FIG. 4 shows an embodiment of the invention with hydraulic transfer of the retardation forces to the brakes. The slide 2 is transferring the forces to a master cylinder 16 which is connected to the brakes (i.e. to slave cylinders in each wheel) via hydraulic lines 10.

[0032] Since the invention's gas spring with solenoid controlled valve always is mounted in parallel with the slide in mechanical overrun brakes and in parallel with the master pump in hydraulic surge brakes, the braking system will be 100% intact during driving whatever possible leaks occurring in the gas spring, solenoid controlled valve or their connections. The gas spring will only work as a shock absorber and returning spring during driving and as a pushrod during reversing. This relates to both mechanical and hydraulic overrun brakes.

[0033] In the case of hydraulic surge brakes, the lockable gas spring, which is mounted in parallel with the master cylinder, takes all compressing forces and leaves the master cylinder completely undepressurized. A leak in the lockable gas spring, however, will not affect the braking effect at all.

[0034] By using the inventive system with lockable gas spring, it is no need for Rcknnatic or similar brake systems and drum brakes with ordinary brake shoes may be used, providing full braking effect both forward and backward when using the hand brake.

[0035] An advantage of the invention is that trailers equipped with original gas springs as dampers may have these readily exchanged with the invention's lockable gas springs and get the same advantages regarding no activation of brakes when reversing.

[0036] The system with solenoid and valve closing and opening the flow of gas through or around the piston may be designed in several ways, but in the attached drawing only some alternatives are schematically shown as examples.