GB617222A - Improvements in or relating to variable speed power transmission apparatus for vehicles - Google Patents

Abstract

617,222. Change-speed control. BROCKHOUSE ENGINEERING (SOUTHPORT), Ltd., and GATISS, A. L. Aug. 20, 1946, No. 24745. [Class 80 (ii)] [Also in Group XXXVII] A motor-vehicle two-speed gear, e.g. of the Wilson epicyclic type, driven through a hydrokinetic transmitter such as a torque-converter (e.g. as described in Specification 436,740, [Group XXIX]), is controlled automatically by a vehicle-speed responsive switch 27, which alone enforces an upshift above a predetermined speed, whilst downshift is effected only below a slightly lower speed and then only when the power demand on the driving unit exceeds a predetermined value, as determined by overtravel of the accelerator-pedal (kick-down shift) ; by excessive torque-reaction on the reaction-member of the converter; or by excessive pressure in the converter, acting to close a switch 35. Solenoids 17, 18, 19 operate, through hydraulic valves, a clutch and brakes, introducing respectively high, low and reverse in the gear (not shown), subject to a manual switch 12, having four positions 13, 14, 15, 16, providing respectively automatic drive; non- automatic low-speed; neutral and reverse. In the automatic position shown, the live batterylead is connected to a relay coil 22, which completes a circuit to earth through the normally open kick-down switch 35 and, in series therewith, the centrifugal switch 27. Above a predetermined speed, the contacts 28, 29 of the centrifugal switch are open and the relay de-energized, to complete a circuit, through its armature 26 and upper contact 25, to the high-speed solenoid 17, so that high-speed remains engaged irrespective of the condition of the kick-down switch 35. Reduction in vehicle-speed below the predetermined value closes the centrifugal switch 27, but this alone does not produce downshift which only occurs when the kick-down switch 35 is closed to complete the energizing circuit of the relaycoil 22, which breaks the high-speed contact 25 and makes a contact 24 feeding the lowspeed solenoid 18, and also closing a contact 23 to energize a hold-on relay coil 21, the earth circuit of which is completed through the centrifugal switch 27 alone, which ensures that low-speed persists irrespective as to whether the kick-down switch 35 is re-opened, as by accelerator-release, until the vehicle-speed increases sufficiently to open the centrifugal switch 27, de-energizing the hold-on relay coil 21 and effecting upshift irrespective of the kick-down switch 35. The centrifugal switch 27, Fig. 2, comprises a rotating plate 37 of insulating material, carrying contacts 29, 28, the former, 29, fixed to the plate and earthed to a supporting shaft; the latter, 28, mounted on an arm 41 carrying a centrifugal mass 48 and supported by a blade-spring hinge 42 on a post 43, connected to a live slip-ring 31, Fig. 1. Linked to the hinged arm 41 at 47 is a sliding plunger 46, carrying an adjustable contactclosing spring 50, both plunger and spring being arranged diametrally so as to be free of centrifugal side-load. To provide a differential speed setting to avoid hunting, the contactclosing spring 50 is assisted by a solenoid 51, connected at one end 54 to a second live slipring 55, Fig. 1, and earthing at its other end 52 through the switch-contacts 28, 29 so as to be energized only when the contacts are closed. Thus, the centrifugal mass 48 opens the contacts 28, 29 in opposition to both the spring 50 and the solenoid 51, whilst the spring 50 alone effects closure, which thus occurs at a lower speed than the opening speed. The solenoid 51 acts on the lower end of the plunger 46 through a polepiece 59 which is screw-adjustable to vary the air-gap 60 and thus the differential speed setting. The switch operates in an oilbath.