Patent GB-605391-A (GB)
Title: Improvements relating to vehicle braking apparatus
IPC: B60T13/02
Filed: 1945-12-21
Abstract: 605,391. Electrically operated brakes. PRECISION DEVELOPMENTS CO., Ltd., and OLAH, G. Dec. 21, 1945, No. 34676. [Class 103 (i)] [Also in Group XXXVIII] Vehicle brake mechanism comprises an electric servomotor which drives an output member connected to the brakes, by means that reacts on the control member of the motor so that an indication is given to the operator of the force applied to the brakes. The motor control may be such that the motor circuit is broken and a brake applied to the motor either when the displacement of the output member corresponds to that of the control member as described in Specification 573,666, [Group XXXVIII], or when the force applied to the output member corresponds to that applied to the control member and independently of the amount of movement of the output member. The brakes may be applied directly by the control member if the current fails, the motor driving gear being automatically disconnected in this event. According to Figs. 1, 2, in which a follow-up control is provided, the control member 1 is connected to a rack bar 4 and by a pin-and-slot 3, to provide lost-motion, to an output member 5 also formed with a rack 19 and connected at 2 to the brakes. The motor 7 drives the member 5 through gearing 20, 21, 23, a toothed annulus 24 freely mounted on a disc 43 fixed to a tubular shaft 25, and gearing 26, 27, 28, the gear-wheel 26 being fixed to the shaft 25 and the wheel 28 being normally meshed with a rack 29 on the output member 5. Levers 44 pivoted on the disc 43 engage teeth on the annulus 24 and on the end 55 of a shaft 41 disposed within the shaft 25 and carrying a gear-wheel 42 engaging a rack on the underside of the bar 4. The torque of the motor is thus transmitted by the annulus 24 through the levers to the disc 43 and the output member 5 and also through the levers, in a ratio determined by the length of the arms of the levers, to the shaft 41 and the control member 1, thus enabling the operator to feel the applied force. In the event of failure of the power, the brakes may be directly applied by the member 1 through the pin-and-slot device 3 and to avoid the motor and driving gear being driven in this case, the gears 27, 28 are carried on a frame 32 which is pivoted on the shaft 25 and carries a rotary magnet 33 connected across the current supply. Normally, by means of a band 34 the armature 35 holds a cam 37 pivoted on the frame and bearing on a fixed part 38, in such a position as to keep the gear 28 engaged with the rack 29, but if the current supply fails, the frame is rocked by a spring 39 to disengage the gear. The motor control comprises gear-wheel contacts 9-12 and a brush 9A-12A for each wheel, the gears 10, 11 meshing with a degree of backlash with the gears 9, 12, but being offset circumferentially with respect to each other on the shaft 14 by a fraction of this backlash. The shafts 8, 13 of gears 9, 12 are geared to racks 18, 19 on the members 4, 5 and to prevent the contact gears from being unduly stressed when the lostmotion 3 is taken up for the direct operation of the brake, resilient couplings 30, 31 are provided in the shafts 8, 13. The circuit arrangement is shown in Fig. 2. The motor field winding 53 and a coil 48 which tends to apply a brake 15, Fig. 1, to the motor 7 are constantly energized. Movement of the members 1, 4 effects contact of teeth of the gears 9-12 as shown so that a circuit is made thus: +ve, brush 11A, gear 11, gear 9, brush 9A, motor armature 50, brush 12A, gear 12, gear 10, brush 10A, motor field 53, - ve, thus energizing the motor 7. A brake release coil 46 is similarly energized. The bar 5 is thus displaced in the same direction as the control member 1 until cessation of the movement of that member causes the teeth of gears 12, 10 to break contact. Similarly, when the member 1 is returned, teeth of gears 9, 10 and 11, 12 engage, thus reversing the current through the armature 50 and energizing the brake release coil 47. According to the modification shown in Fig. 3, the force applied to the output member 69 by the motor is proportional to that applied to the control member or pedal 56. The motor drive to the member 69 is from a pinion 65 through pinions 66 and wheel 68. Pinions 66 are carried by a lever 67 pivoted about the axis of the pinion 65 and engaging a block 58 which slides in guides 59 and carries pairs of contacts 63, 64 adapted to engage contacts 72, 73 which extend through a fixed part 74 so as to close circuits similar to those shown in Fig. 2. Depression of the pedal moves the block 58 downwards through a spring 62 which is compressed to an extent corresponding to the pedal movement. The contacts 63 are thus closed to release the brake 15 and start the motor. When the resistance to movement of the member 69 and the corresponding reaction thereof on the lever 67 reaches a value sufficient to overcome the compression of the spring 62, the block is moved upwards to break the contacts 63. The force applied to the brake may be reduced to a desired value by permitting the pedal to rise, thus closing the contacts 64, as shown, to release the brake and start the motor in the reverse direction. Specifications 556,287; 594,257 and 594,258, [both in Group XXXVIII], are referred to in the Provisional Specification.