Patent GB-1220665-A (GB)
Title: Trailer brake control system
Inventor: GREENTREE HERBERT
IPC: B60T13/74
Filed: 1969-03-05
Abstract: 1,220,665. Trailer brakes. WARNER ELECTRIC BRAKE & CLUTCH CO. 5 March, 1969, No. 11736/69. Heading F2E. [Also in Division H1] Trailer brakes 30 are controlled by an inertia member 206, 188, 256 controlling a variable resistance 196, 198 in response to increase and decrease of deceleration such that movement of the inertia member 206, 188, 256 away from a first position stop 226, 274 to a second position causes electrical contacts to complete the electrical circuit to the trailer brakes and further movement reduces the value of the variable resistance and during engagement of the contacts the inertia member is urged to return to the second position as the rate of vehicle deceleration decreases. As shown in Figs. 2 and 5 the inertia member 206, 188 is held in its rest position against stop 226 by a permanent magnet 210. When the brakes of the tractor, such as a car (Fig. 1, not shown), are applied, an hydraulically operated brake switch S40 energizes an electromagnet 216 which repels the permanent magnet and moves the inertia member 188 so that a first contact 196f contacts a fixed contact 206 to energize the trailer brakes 30 via a resistor 198a so as to apply the trailer brakes. As the tractor is further decelerated the inertia member 188 moves further away from the stop 226 and further contacts 196e-196a contact fixed contact 206 to connect resistances 198b-198e of decreasing values into the trailer brake circuit to increase the trailer braking. The inertia member 188 is moved back to the rest position on decreasing deceleration due to the spring biasing of the contacts 196a-196f and finally is held by the pull of the permanent magnet 210. If when the tractor is braked the stop switch S40 fails at a predetermined deceleration the inertia member 188 will swing away from the stop so that the contacts 196, 206 complete the trailer brake circuit to apply the trailer brakes. The inertia member 188 and deceleration unit 34 may be mounted on the trailer or on the tractor. However, if it is required to provide automatic trailer braking if in an emergency break-away of the trailer from the tractor occurs then the inertia member 188 and unit must be on the trailer. If then break-away occurs the trailer would tilt and the inertia member 188 would swing to apply the trailer brakes. In a modification of the inertia unit 34 of Fig. 5 (Figs. 9- 13, not shown) the inertia member (188<SP>1</SP>) has a contact (364) mounted on it so that when the inertia member swings away from the stop (226<SP>1</SP>) the contact (364) rolls along a helical coil resistance on a pivoted tube 367 so as to decrease the resistance in the trailer brake circuit. In a further inertia unit 230 (Fig. 7) and (Figs. 3 and 8, not shown), the inertia member is in the form of a roller 256 which has a permanent magnet 262 to cause the roller to rest against non-magnetic separator stops 274. On deceleration the roller 256 moves up two resistor tracks 240 to decrease the resistance in the trailer braking circuit. As before, an electromagnet 258 is provided to repel the permanent magnet on closing of the brake switch S40. The inertia unit 230 may have oil filled into a fluid-tight casing 232 so as to damp the action of the roller. Emergency and test operation of trailer brakes.- A switch unit 32 mounted in the tractor (Fig. 4, not shown) has an emergency position S58C1 which energizes the trailer brakes fully or a test position where a resistor R62 is included in the trailer brake circuit. In the test position the trailer brakes are applied so that by moving the tractor the condition of the trailer brakes can be determined.