Patent GB-745201-A (GB)
Title: Variable speed transmission construction
IPC: F16H47/08
Filed: 1950-08-01
Abstract: 745,201. Hydraulic brakes. ROCHE, C. R. Aug. 1, 1950 [Aug. 9, 1949], No. 19228/50. Class 103 (1). [Also in Group XXIV] The main pressure-line 70 of a liquid-pressure servo-system, for actuating reduced- and reverse-drive reaction band-brakes 21, 27, 17 and disc-clutches 14, 20, in a planetary changespeed gear (see Group XXIV) on a motor vehicle, is supplied by input- and outputdriven pumps 50, 54 through separate non- return valves 68, 76 and the output of the inputdriven pump 50 is exhausted at 92 when outputpump pressure rises sufficiently to depress a spring-loaded piston-valve 88 by acting thereon through an upper piston 94 which itself forms a separate pressure-regulating valve for relieving excess pressure of the output-driven pump, also at 92. At low output speeds, the output of the output-driven pump 54 is exhausted through a port 140 of a valve 116 which also provides pressure-augmentation for the high-torque low and reverse ratios. Alternatively the brakes may have pressure-intensifiers combined with their pistons. The servo-system has also cushioning means comprising a common or separate air-pressure storage cavities, e.g. 200, arranged above the liquid level and communicating with the brakes &c. Control (see Group XXIV) is by a manual selector valve 64, giving neutral, forward, low and reverse, acting conjointly with an accelerator-pedal-loaded outputdriven centrifugal governor 110. In the normal starting position F, the manual selector valve 64 supplies pressure liquid through a line 100 to the low-speed brake 27 which takes effect through a one-way clutch 28. A line 115 is also pressurized to act on the underface of the piston of a pressure-augmenting valve 116 which is thereby raised to supply line-pressure through a path 70, 115, 135, 134 to the underface of a pressure-regulating valve 72 of the input-pump 50, supplementing spring-loading to result in a pump pressure about double (160 lb/sq. in.) its normal value. At the same time the pressureaugmenting valve 116 exhausts the output pump 54 at 140. Clutch-introduced speeds are engaged by the governor 110 actuating a selector valve 108 which also reduces servo pressure to normal. In its two-way low-speed position the manual selector valve 64 feeds the piston 164 of the brake 21 through the line 100 of the one-way acting brake 27 (which remains on) and branches 165, 170. Pressure augmentation remains effective as before, and also when the selector valve 64 is moved to supply the piston 182 of the reverse brake band 17. Cushion means, above referred to, is shown applied to the one-way low-speed and reverse brake pistons 104, 182, but may be applied to all. This comprises in each case an air receiver 200, with a ball check-valve 206, above liquid level to permit replenishment with air when operating pressure is released. Each brake-system is also fed through a restrictor 205, and in the feed line 100 of the one-way low-speed brake 27 there is also an additional restrictor 204 in parallel with a check-valve 202, which closes to reverse flow so that the brake cylinder must exhaust through the additional restrictor, thus providing gradual release of the low-speed brake 27 when the manual selector valve 64 is moved from neutral or low speed to reverse, so that the reverse brake drum 16 is held stationary through the gear train by the effect of the low-speed brake 27 long enough for the reverse brake-band 17 to engage its drum 16 without shock. In Fig. 3 (not shown) there is a single cushioning air receiver, with check-valve and restrictor communicating with the common supply main 70 to be effective for all brakes and clutches. Both the pump change-over valve 88 and the input-pump regulating valve 72 have dashpot damping. The manual selector valve 64 is modified to eliminate pressure-augmentation on the two-way low-speed brake 21. Alternatively the pressure-augmenting valve 116 may be eliminated, and pressure augmentation made effective only in reverse, by direct connection between the manual selector valve 64 and the input-pump regulating valve 72. To reduce the necessary brake pressure, the reverse brake band is applied by tandem separate coaxial pistons, each having separate interconnected cylinders. In Fig. 4, the reverse or other brake-band is applied by twin pistons 280c, 176c fast on a common stem, pressure from the inlet duct 180c reaching the main piston 280c directly and the auxiliary piston 176c through a pressure-responsive valve 308 which, in the idle position, exhausts the auxiliary piston 176c at 320. The space between the pistons is permanently exhausted at 302c. Initially the auxiliary piston 176c receives no liquid from the pump, since only relatively light pressure is required to move the main piston 280c to the brake-applying position, during which time it takes along the auxiliary piston 176c, which draws in liquid from the pump exhaust line 320, so that by the time the brakeapplying pressure builds up on the main piston and opens the valve 308, the cylinder of the auxiliary piston is already filled with liquid and provides rapid response. To provide air cushioning without a separate air receiver, the main piston 280c has a check-valve 206c above the sump liquid-level 305, to allow the piston to draw in cushioning air when actuating pressure is released. The brake-actuating servo shown in Fig. 5 provides pressure intensification. Pressure from the supply line 180d reaches the left face of the main piston 280d through an intermediate chamber 220d, which provides cushioning due to air-entry through a ball check-valve 224d, as before, and a restrictor 360. Light initial pressure moves the main piston 280d to brake-applying position, after which pressure builds up, opening a valve 308d to supply pressure to the left face of an auxiliary piston 176d, which moves to the right, taking along an integral smaller piston 338, which covers holes 335 (below sump oil level) in its cylinder 333, through which liquid has been previously supplied to the main piston 280d. Liquid thereby trapped in the small cylinder 333 receives an intensified pressure from the larger auxiliary piston 176d and transmits it to the main piston 280d. With this pressureintensification, which may be used with each brake-band, the pressure-augmentation arrangements of Fig. 2 may be eliminated. Specification 745,210 is referred to.