Trailer braking device

A trailer braking device having a high-pressure main hydraulic circuit of a tractor to which a trailer is attached; to a hydraulic circuit of a master brake cylinder of the tractor; and a trailer brake valve having a driver connected hydraulically to the high-pressure main hydraulic circuit and to the hydraulic circuit. The driver of the device has a piston which is subjected to a first action by an independent circuit that is activated, for example, by the stop lights and a second action produced by the operator, such as a foot acting on a brake pedal, on the hydraulic circuit of the master brake cylinder.

The present invention relates to a trailer braking device.

In tractor braking systems, when the control brake is activated lightly, the braking system of a trailer attached to the tractor, even though activated, may be unable to produce sufficient braking force, because the force necessary to activate the brakes is normally not taken into account. As a result, the trailer may not brake at all, or not sufficiently.

Conversely, in imperfectly balanced systems, the trailer may brake too much, more than the tractor, thus resulting in serious problems regarding the tractor-trailer interface devices.

As a result, the tractor brakes may be called upon to deal with enormous amounts of energy (e.g. light braking to slow down or maintain downhill speed), so, even though well designed in relation to the mass of the tractor, have a very short working life. To eliminate these drawbacks, the braking rates of the tractor and trailer are normally unbalanced to a great extent, but this has failed to provide a satisfactory solution.

Moreover, the trailer, especially light-weight trailers, may be braked too much and too sharply; in which case, operator sensitivity is to no avail.

SUMMARY OF THE INVENTION

The invention assists in synchronizing the braking forces associated with a trailer braking device to such an extent as to prevent the energy braked by one system from overloading the other, which is particularly serious in the case of long-term braking with a light load.

The invention employs an ON/OFF solenoid valve, which comes into operation when the stop signal is ON, and which provides for additional pressure (from an independent source) on the trailer brake valve driver.

In the proposed solution, the trailer brake driver comprises two separate chambers. A first is a so-called “control chamber”, which is connected directly to the tractor braking pressure, performs the same function as the currently produced chamber, and provides for regulating trailer braking pressure according to the tractor braking pressure.

The second chamber, known as “offset chamber”, only connects the independent source to the trailer brake valve when the stop signal is ON. As soon as the operator touches the brake pedal, the stop signal (i.e. stop lights) comes ON, and the ON/OFF valve is opened. When this happens, the geometry of the offset chamber is such that the pressure of the fluid inside it produces a predetermined force on the trailer brake valve driver, so as to achieve a simultaneous braking force origin, regardless of any difference in the force with which the two (tractor-trailer) braking systems are activated. This force is maintained throughout braking, in addition to the braking control force from the master cylinder of the tractor, and also provides for better distributing braking intensity between the tractor and trailer.

By evaluating the pressure in the offset chamber energy supply circuit, and appropriately designing the offset chamber, it is possible to set the trailer braking origin, with respect to the tractor braking origin, within a “brake lead area”.

Moreover, the offset chamber is purposely designed so that the offset force is added to the braking control force throughout braking control.

In a second embodiment, the hydraulic circuit is replaced by an electric current which, flowing through a coil, generates a force on permanent magnets to move a trailer brake actuating piston, which is also subjected to a force produced by the pressure in the control chamber from the master brake cylinder.

The trailer braking device is designed to assist in the elimination of the aforementioned drawbacks, and which at the same time is cheap and easy to produce.

It should be pointed out that only the parts in the attached drawings essential to a clear understanding of the present invention are numbered and described in the following description.

DETAILED DESCRIPTION OF THE INVENTION

The graph ofFIG. 1shows the performance of the component parts of a known trailer braking device. The x axis shows tractor braking pressure, and the y axis trailer braking pressure, the pattern of which, alongside variations in tractor braking pressure, is shown by curve C1. Curve C2shows the tractor braking force alongside variations in tractor braking pressure; and curve C3the trailer braking force, also as a function of tractor braking pressure.

As shown clearly inFIG. 1, a certain hysteresis exists between the trailer braking force response (curve C3) and the tractor braking force response (curve C2), i.e. a given tractor braking pressure PT must be reached before the trailer begins braking. And which is the cause of the drawbacks referred to above. The present invention works to move the start of curve C3* substantially up to the point of origin of curve C2, which, in the example shown, is the origin of the coordinates, as shown inFIG. 2.

Point PT is moved towards the predetermined “zero point” by supplying the trailer braking device immediately with a certain amount of preliminary control pressure, regardless of whether or not pressure has been generated on the master cylinder of the tractor. One method by which this can be accomplished is by commencing preliminary pressure supply as soon as the operator presses the tractor brake pedal. More specifically, preliminary pressure supply may coincide with turn-on of the stop lights.

Device100also comprises, in known manner, a master brake cylinder104of the tractor (not shown) connected hydraulically to a brake valve105of a trailer (not shown) by a third hydraulic circuit106. As explained in detail below, valve105is also connected hydraulically to first main hydraulic circuit102and second main hydraulic circuit103.

The second main circuit103comprises an ON/OFF valve107upstream from supply of the pressurized oil from second main circuit103to a driver108of valve105.

Driver108is actually also connected hydraulically to third hydraulic circuit106originating from master brake cylinder104of the tractor as shown inFIG. 4.

As shown inFIG. 3, ON/OFF valve107is activated by turn-on of a light device109indicating initial braking of the tractor. In other words, light device109comprises, in known manner, the lights that come on at the rear of the tractor and trailer as soon as the operator touches the brake pedal.

More specifically, ON/OFF valve107is activated by light device109generating an electric signal SNG the instant the operator touches the brake pedal. The braking pressure of the trailer is locked to that of an independent circuit having a constant pressure followed immediately by additional pressure directly from the brake pedal.

A brake valve105of a trailer (not shown) is inserted by a third hydraulic circuit106; and valve105is also connected hydraulically to first main hydraulic circuit102and second main hydraulic circuit103. The second main circuit103comprises an ON/OFF valve107upstream from supply of the pressurized oil from second main circuit103to a driver108of valve105.

It should be pointed out that the present invention can also apply to pneumatic circuits substituted for at least part of the hydraulic circuits.

As shown inFIG. 4, valve105comprises a main body105ahaving a face105bagainst which rests a corresponding face108aof a main body108bof driver108. The two faces105band108ahave a common opening110connecting a chamber111, formed in main body105aof valve105, to a chamber112formed in main body108bof driver108.

Chamber112houses a piston113having a shoulder113a. Shoulder113a, together with the walls of chamber111, defines an annular offset chamber114connected hydraulically to an inlet115of second main circuit103.

Main body108bof driver108comprises a further inlet116connected to third hydraulic circuit106; and the pressure of the fluid in third hydraulic circuit106is determined by the pressure exerted by the operator on the brake pedal. Piston113acts as an “adder” to add the pressure in third hydraulic circuit106—which increases as shown by curve C1* in FIG.2—to a fixed pressure from second main circuit103, when the stop lights of the tractor and trailer come on. In known manner in brake technology, piston113acts on a plunger117.

Valve105also comprises an inlet118for pressurized oil from first main hydraulic circuit102. A conduit119originates at inlet118, and has a diaphragm120and a choke121. The pressurized oil flowing through diaphragm120and choke121activates a flow regulator122in the direction of arrow F1. Most of the oil flows through a fitting (not shown) to auxiliary distributors (not shown), while the rest is discharged to a hydraulic lifter (not shown) via a conduit123, plunger117, and an oil drain outlet124.

When the tractor brake pedal is pressed, the hydrostatic circuit oil at inlet116is pressurized, and moves piston113, a pressure regulator125, and plunger117in the direction of arrow F2, and plunger117in turn cuts off connection between oil drain outlet124and both a trailer brake fitting126and conduit123.

In this configuration, part of the oil from first main hydraulic circuit102still flows to the auxiliary distributors (not shown), while the rest is supplied to the trailer brakes via diaphragm120, a conduit127, a non-return valve128, and fitting126.

As it increases in pressure, the oil in fitting126acts on an active surface129of plunger117in opposition to the pressure exerted on piston113by the oil in the hydrostatic brake circuit of the tractor (third hydraulic circuit106).

As pressure on the tractor brake pedal increases, the oil in fitting126increases in pressure and, acting on active surface129of plunger117, moves plunger117in the direction of arrow F1in opposition to springs130of pressure regulator125.

When the oil pressure in fitting126to brake the trailer equals the pressure exerted by springs130, plunger117is stabilized and connects the oil from first main hydraulic circuit102to the lifter drain via inlet118, diaphragm120, choke122, conduit123, and oil drain124.

Diaphragm120and choke122produce a fall in pressure of the oil in pressure regulator125and move pressure regulator125in the direction of arrow F2, thus closing conduit127and, hence, non-return valve128.

Further increase in pressure on the tractor brake pedal moves piston113, pressure regulator125, and plunger117in the direction of arrow F2, thus increasing the oil pressure in the trailer braking system, and repeating the steps described above with reference to the initial braking stage.

If, for external reasons, the pressure in the trailer braking circuit increases, plunger117immediately connects inlet118and oil drain124to maintain perfectly balanced pressure between the oil in the braking system and springs130of pressure regulator125.

When the tractor brake pedal is released, the oil pressure at inlet116falls, and the system returns to the initial configuration.

TheFIG. 5embodiment differs from the one inFIG. 4by additional operation of piston113being controlled by electric as opposed to hydraulic means.

In this case, when the brake lights are operated, a constant electric current flows along an electric circuit200comprising a first coil200a, which produces a magnetic field which in turn induces current in a second coil201integral with main body108bof driver108. The electric current in second coil201in turn produces a magnetic field which interferes with permanent magnets202on piston113, so piston113moves in the direction of arrow F2.

In theFIG. 5embodiment, electromagnetic means produce the same effect on piston113as the hydraulic means in theFIG. 4embodiment.

It is a likely advantage to employ an ON/Off solenoid valve so that it only comes into operation when the stop signal is ON, and which provides for “zero-cost” additional pressure by employing existing hydraulic and/or pneumatic and/or electric circuits on the tractor.