Trailer Brake System

This invention relates generally to brake systems for towing vehicle and trailer combinations.

The manufacture, sale and use of towed recreational vehicles of the camping or mobile home variety has accelerated at a rapid rate. These trailers must of course be provided with effective brakes adapted for operation in conjunction with the towing vehicle brakes. Many presently offered towing vehicle-trailer braking systems provide high degrees of reliability and control.

The general object of the present invention is to provide a braking system for a trailer which further improves braking control of a towed and towing vehicle combination.

A more specific object is to provide such a towing vehicle-trailer braking system which offers improved brake balance, braking control reliability, and stopping ability under all normally encountered braking conditions with all normally available combinations of towing and towed vehicles. A related object is to offer a consequent increase in confidence level to the towing vehicle driver.

Another object is to provide such a system which requires but relatively few major components, which can be relatively quickly and easily installed, and which can be offered at relatively low cost.

Yet another object is to provide such a braking system which can be utilized with trailer brakes of the hydraulic caliper disc type. An associated object is to provide such a system which minimizes or eliminates entirely the phenomena of brake fade during heavy brake usage such as can be encountered when slowing and stopping from high speed. Also minimized are related brake grab or premature lock-up.

Still another object is to provide a towing vehicle-trailer brake system which can be used by a wide variety of towing vehicles and a wide variety of trailers without noticeable differences in overall braking characteristics or differences in the braking performance as different combinations of towing vehicles and trailers are considered.

A further object of the invention is to provide a brake system of the type described which can be used with a vacuum over hydraulic or vacuum suspended trailer brake booster unit. An associated object is to provide such a system which can be easily adapted for use with either an air over hydraulic or hydraulic over hydraulic booster unit as well.

Still another object is to provide such a trailer brake system which will accommodate direct adaptation of an anti-skid control to the system.

Other objects and advantages of the invention will become apparent upon reading the following detailed description and upon reference to the drawings. Throughout the drawings, like reference numerals refer to like parts.

FIG. 1 is a schematic diagram showing a novel brake system embodying the present invention;

FIG. 2 is a schematic diagram similar to FIG. 1 showing a modified version of the novel brake system; and

FIG. 3 is a schematic diagram of a trailer brake power unit, an associated trailer brake master cylinder, and related apparatus.

While the invention will be described in connection with preferred embodiments, it will be understood that it is not intended to limit the invention to these embodiments. On the contrary, it is intended to cover all alternatives, modifications and equivalents included within the spirit and scope of the invention and as defined by the appended claims.

Turning first to FIG. 1 there is shown, in schematic form, an embodiment of the present novel braking system in use with a towing vehicle 10 and towed trailer 11. In general, the towing vehicle 10 carries an engine 14 for propelling the towing vehicle 10 and the trailer 11. A towing vehicle brake system 15 selectively energizes associated brakes (not shown). Mounted within and upon the trailer 11 is a trailer fluid brake system 16, and a control 17 mounted in and upon the trailer 11 which energizes and controls the trailer fluid brake system 16.

More specifically, when a driver of the towing vehicle 10 desires to retard its progress, he depresses a brake pedal 20 in well known manner. If the brakes on the towing vehicle 10 are of the hydraulic variety, and are of the "power brake" type, a power booster 21 is energized and actuates a hydraulic brake master cylinder 22. Appropriate hydraulic pressure is directed to towing vehicle rear wheel brakes through a hydraulic line 23, and to front wheel brakes through another line 24. Brake warning lights and other devices can be actuated through an appropriate switch 25.

An electromechanical transducer control 30 mounted on the towing vehicle 10 is energized by increased hydraulic pressure through an interconnector line 31. To provide a smooth infinitely controllable braking action to the trailer 11 in accordance with the invention, this controller 30 modulates the towing vehicle hydraulic brake system brake pressure, and provides a correspondingly modulated electrical signal which varies systematically in accordance with fluid pressure experienced in the towing vehicle brake system interconnector line 31. A manual override switch 32 can be included if desired to operate the trailer braking system 16 directly from the towing vehicle 10. Appropriate electrical lines 33 and 34 connect the controller 30 to the towing vehicle electrical system battery or engine-driven generator, and to the system electrical ground, respectively. The electrical signal is transmitted by the controller 30 along appropriate wiring 36 through a quick-disconnect plug 37 and trailer wiring 38 to the trailer brake controller 17 mounted upon the trailer 11. To maintain a common electrical ground, a wire 39 electrically interconnects appropriate grounding members of the trailer 11 and towing vehicle 10 through a ground wire interconnect plug 40.

The braking system illustrated in FIG. 1 is of the vacuum system variety, and a vacuum conduit or hose line 41 provides a vacuum drawn through an intake manifold of the engine 14 in well known manner. A check valve 42 prevents vacuum loss in the system when the engine 14 is not operating. Vacuum drawn from the trailer controller 17 is rotated through the hose disconnect device 43 and trailer conduit 44.

As explained above, the trailer-mounted electromechanical brake control 17 systematically and infinitely varies, over a given range, fluid pressure and consequent braking action in the trailer brake system 16, in accordance with the sensed variation of the electrical signal transmitted by the controller 30. This braking action is provided by a trailer brake power booster unit 50.

As illustrated in FIG. 3, the power booster unit 50 includes a power can 51 in which are defined two power chambers 52, and 53, divided by a flexible diaphragm 54. When an electrical signal is applied through electrical wiring 36 and 38 as described above, a valve 56 positioned to permit air to be exhausted from one of these chambers 52 through a stub line 57 into a vacuum supply chamber 60. This supply tank 60 accommodates repeated braking action or surges in trailer brake vacuum demand. Air entering the vacuum supply tank 60 is drawn off by the vacuum conduit 44. Simultaneously, air is drawn from the second power can chamber 53 through a connector line 63 and safety check valve 64 to the vacuum conduit 44. The check valve 64 serves to prevent vacuum loss in the second chamber 53 in the event of inadvertent vacuum conduit parting or other system failure.

Appropriate alteration of the electrical signal in the electrical wiring 38 repositions the valve 56 to close off the vacuum stub line 57 and open an air inlet port or line 66 so as to admit air into the first power can chamber 52. When this occurs, the diaphragm 54 moves (to the right as shown in FIG. 3) and correspondingly moves an interconnector 68. This interconnector 68 forms part of or is attached to a piston rod 70 extending from a trailer hydraulic master brake cylinder 71. Movement of the piston rod 70 causes corresponding motion of the piston 72 and consequent increase or decrease in hydraulic pressure within the trailer system brake line 16. Changes in this brake system hydraulic pressure serves to operate the trailer brakes 74, which here are of the hydraulic disc type.

A manually operated brake release valve 75 is provided to admit ambient-pressure air into the second power can chamber 53 so as to move the diaphragm in a direction causing brake release when desired. This valve thus permits the trailer brakes to be released for repositioning or other trailer movement of a limited nature even though the trailer may be disconnected from the towing unit.

A modified embodiment of the invention is shown in FIG. 2, and is especially adapted for use in towing vehicles 10 which are provided with a diesel engine 80, or some other type which does not provide a vacuum source. In addition, the embodiment illustrated in FIG. 2 can be used for any other installation where it is believed undesirable to utilize a vacuum created by the power plant 80. Here, depressing the towing vehicle brake pedal 20 actuates the transducer 30 as described above. However, an electrically driven vacuum supply pump 85 is mounted upon the trailer 11, and exhausts the vacuum supply tank 60 through a normally closed check valve 86. This pump 85 is driven by an appropriate motor 87; the motor 87 is, in turn, energized when necessary by a low pressure vacuum switch 88 which senses vacuum in the tank 60 through a tap line 89. Power is supplied to both the switch 88 and the motor 87 through an appropriate electrical line 92 and breakaway plug 93 from a battery/generator or alternator combination 94 mounted upon the towing vehicle 10. An appropriate breakaway cable 100 secured at one end 101 to the towing vehicle 10 can be used to energize an electric breakaway switch 102 so as to operate the solenoid valve 56 in the event of inadvertent physical disconnection of the towing vehicle 10 from the trailer 11. When the breakaway switch 102 operates the solenoid valve 56, air is admitted into the power can 50 to apply the trailer brakes 74, as described above.