Patent GB-1130112-A (GB)
Title: Differentials
IPC: F16H48/30
Filed: 1967-02-17
Abstract: 1,130,112. Differential gears. FORD MOTOR CO. Ltd. 17 Feb., 1967 [31 March, 1966], No. 7588/67. Heading F2D. A motor-vehicle differential friction lock 62, 64 engaged through a screw and nut drive 78, 80 by an electric motor 70 controlled by a manual push button switch (94) (Figs. 2-5, not shown) operated for vehicle starting or at low speed thereof, is released through an hydraulic speed sensitive device 114, 120 when a non- driven wheel 112, to which the sensing device is connected, exceeds a pre-selected speed (e.g. a vehicle speed of 25 m.p.h.), the sensing device controlling sets of contacts 137, 138 and 140, constituting switches (96) (97) and (108) respectively (Figs. 2 to 5), to reverse the drive motor 70 and release the lock for normal free differential action. The friction lock comprises clutch plates 62, 64, splined alternately to a half-shaft side wheel bevel gear 58 and a bevel planet carrier assembly 31, 24, sandwiched between an inner face of the carrier 24 and an axially movable bell-shaped pressure plate 66 connected by a lever 84 to the nut 78 of the motor screw drive, limit switches 98, 110 on the outer casings 12, 10 being opened by the arm 84 on clutch engagement (as shown) or release respectively to stop the motor 70. In the hydraulic sensing device, the non-driven wheel 112 drives a small hydraulic pump 114 which is connected by feed and return pipes 116, 122 to a pressure chamber 117 of a cylinder and spring- loaded piston arrangement 118, 120, the return pipe having a flow restrictor 124 therein such that the fluid pressure build up overcomes the piston spring 130 to operate the contact sets 137, 138 and 140, forming the switches (96, 97 and 108) respectively, which are arranged between a piston extension 132 and cylinder walls 134, 136 therein, when the wheel 112 reaches the speed at which clutch disengaging operation of the motor is required.  Operation.-At rest or at low vehicle speeds with the lock initially fully disengaged (Fig. 2, not shown), engagement is manually effected by pressing switch button (94) to actuate relay (92) which closes switches (100, 102 and 104) and opens switch (106) to energize motor 70 (Fig. 3, not shown), current passing through switches (97, 98 and 100) holding the relay (92) so that the manual switch button may be released. Initial movement of the clutch lever 84 closes switch 110 and on full clutch engagement, contacts and opens switch 98 cutting off current to relay (92), which opens switches (102, 104), (Fig. 4, not shown) to stop the motor 70, the switches (100 and 106) being also opened and closed respectively thereby. When the speed of the wheel 112 exceeds the pre-selected value, the speed sensing piston extension 132 moves to break the contacts 137 and 138, and make the contacts 140 whereby switches (96) and (97) are opened and switch (108) closed (Fig. 5, not shown) for reverse operation of the motor 70 for clutch disengagement, the lever 84 contacting and opening the limit switch 110 on full clutch disengagement to stop the motor 70. When the vehicle speed drops below the preselected value, the piston spring 130 overcomes the reduced fluid pressure, moving back the piston to restore the switches (96, 97 and 108) to the Fig. 2 positions ready again for manual operation of the switch button (94). The switches (96, 97 and 108) may alternatively be manually controlled to unlock the differential and, electrical or mechanical speed sensitive switches can replace the hydraulic system of Fig. 6. The position of the limit switch 98 on housing 12 can also be adjusted to vary the compressive pressure on the plates 62, 64 thereby varying the maximum torque above which clutch slippage occurs to permit differential action.