Patent GB-861788-A (GB)
Title: Improved control system for a rotary vehicle drive member
IPC: B62D11/08
Filed: 1957-04-10
Abstract: 861,788. Clutch-brake control. GENERAL MOTORS CORPORATION. April 10, 1957 [April 30, 1956], No. 11718/57. Class 80 (2). [Also in Groups XXXI and XXXIV] A fluid-pressure control for a friction clutch 16 and brake 18, particularly for use in conjunction with another identical clutch-brake unit 20, 24 and control for driving, steering and braking a tracked or wheeled vehicle, comprises a control valve unit 25, manually operable to decrease progressively clutch-engaging pressure for clutch disengagement and subsequently to increase progressively brake pressure, and the manual force necessary to operate the valve has different rates of increase at the various stages (as described below) whereby the operator can feel the said stages. Clutch-brake arrangement.-Each clutch 16, 20 is arranged between a central driving-shaft 14, driven by the output shaft of a variable-speed gear, and the driven wheel shafts 17, 21, the brakes 18, 24 being arranged between the wheel. shafts and the vehicle frame. In the right-hand unit. Fig. 2, annular pistons 68, 129, energized through lines 67, 63, respectively, engage the clutch and brake. The brake 18 can also be applied manually by turning a lever 133 attached to the brake piston 129, to cause the latter to ride axially up balls 135 carried in cam tracks in the piston and fixed frame, such balls causing self-energization which is present also during fluid-pressure operation. A restricted pressure line 139 feeds cooling oil to the brake through passages 146, whilst the clutch may be cooled similarly or by oil leaking past its piston. The clutch is also cooled and lubricated during the engagement period by oil supplied, as described below, through a line 93, Fig. 1. Control.-In the steering control shown in Fig. 1, each clutch-brake unit 16, 18 and 20, 24 is controlled by a valve 25, 26, respectively, the valves being operable in unison or independently through a single lever and suitable linkage. Each control valve has an associated timing valve 80, 81, for regulating the rate of clutch engagement. Each control valve, e.g. 25, comprises an operating element 25, acting through a regulator spring 33 on the cup-shaped end 29 of a valve element 30 having differential lands a, b, and normally pressed upwards against a stop-shoulder 61 by a spring 57. In the normal, unoperated, upper position shown, line pressure from a source 66 passes through ports 52, 53 and line 67 to the clutch 16 of its unit whilst the corresponding brake 18 is exhausted through a line 63 and ports 45, 46. Depressing the operating element 25 moves the valve element 30 downwards, first disengaging the clutch progressively and later engaging the brake progressively, each stage being indicated to the operator by an opposing feel. Initially the control element 25 compresses the regulator spring 33 alone until compression is sufficient to overcome the lower spring 57 whereupon the valve-element 30 is moved downwards against a reduced spring rate due now to the series compression of both springs 33, 57. During this first stage, clutch pressure 67, equal to full line pressure 52, assists downward valve movement by acting on the large lower land b. When the upper valve land a cuts off line pressure at 52, a second stage follows in which the land b gradually exhausts the clutch line 67 at 55, the consequent reduction of clutch pressure reducing the downward fluid pressure acting on the valve land b, necessitating the operator applying additional compression to the spring 33, which, with the lower spring 57, acts as a pressure regulator so that the operator feels a progressively increasing opposition in proportion as clutch pressure diminishes. When the clutch is fully disengaged, downward fluid pressure on the land b vanishes, and further valve movement, in a third stage, is at the lower rate of both springs 33, 57 in series, without fluid-pressure assistance, until, in a fourth stage, the cup end 29 cuts off an exhaust 46 from, and the valveelement 30 supplies line pressure 52 to, the brake-apply line 63, the consequent increase in brake pressure acting upwards on the cup element 29 and spring 33 to provide an increased feel resistance to operation. The clearance between the stem of the valve-element 30 and adjacent lands is such as to provide a flowretarding restriction. When the operating element 25 finally contacts the cup end 29 of the valve 30, further valve movement is positive, and braking pressure rises to full line value with instantaneous increase in feel resistance followed bv further increase in resistance due to compression of the lower spring 57 alone. Gradual clutch engagement on release of the valve-operating element 25 is provided by the timing valve 80, which comprises a piston 82 subject to upward pressure from the clutchapply line 67, and to downward pressure of a spring 88 and also by the same clutch-apply pressure 67 reaching the upper face of the piston through a restrictor 95, which delays downward pressure, permitting the piston initially to rise and exhaust the clutch-apply line 67 at 91, such exhaust being gradually cut off by build-up of clutch pressure above the piston. The exhaust 91 passes through a line 93 to cool and lubricate the clutch during the enging period only. During disengagement downward fluid pressure is rapidly exhausted from the piston through a check-valve 94 by-passing the restrictor 95, and clutch-release is rapid. Specification 861,789 is referred to.