Patent GB-895170-A (GB)
Title: Control systems for industrial trucks
IPC: B66F9/20
Filed: 1960-05-09
Abstract: 895,170. Spring-applied brakes. CLARK EQUIPMENT CO. May 9, 1960 [June 8, 1959], No. 19807/61. Divided out of 895,168. Class 103 (1). In a control system for an industrial fork-lift truck wherein the brake means associated with a traction-wheel is normally applied and operator's hand control means is connected to camming means which controls valve means for controlling the application of fluid pressure to pressure-responsive means for releasing the brake to modulate the brake release pressure as a function of the position of the hand control means, the latter is actuatable in opposite directions from a neutral position to actuate the camming means to effect application of the brake release pressure when the hand control means is moved in either direction from a neutral position. In the embodiment illustrated, a single control handle 50 effects control of the traction of the truck and also controls the release of the brakes. External-shoe drum brakes associated with brake drums 188 and 190 of drive motors 42, 43 are normally applied by springs 172, 174, as shown in Fig. 3. To apply the brakes, control handle 50 is rotatable in a forward or reverse direction to rotate cam 104 and actuate brake valve control arm 134 to operate valve assembly 156 and apply the brakes by supplying fluid under pressure to brake cylinders 168 and 170-the degree of rotation of the control handle governing the degree of brake release. The brakes are hydraulically released from the same source of fluid pressure which operates a power steering cylinder 362, i.e. a steering motor and pump 210, 212 which supply pressure fluid through conduit 368 from a reservoir 366 so that the braking system is continuously supplied with fluid at steering cylinder pressure whenever the control handle 50 is actuated. When the brakes are fully applied in the neutral position of the handle 50 a minimum fluid pressure is directed to the cylinders 168, 170 (not shown in Fig. 9) and under this condition the valve plunger 154 is in the position illustrated in Fig. 9 which permits the spring 158 to remain in a relatively relaxed condition and the modulating valve 160 is seated with a small force against the end of fluid passage 374. This permits pressure fluid entering at port 372 to flow through passages 376 and 378 in a spool valve 380 and thence through an unrestricted passage 382 an annular passage 384, ports 386 and passage 374 (formed in a valve body sleeve insert 388), into a conduit 390 by way of modulating valve 160, and thence to a sump 392 by way of a second modulator valve 394 which opens conduit 390 to the sump through conduits 396 and 398. When it is desired to release the brakes, valve plunger 154 will be actuated inwardly of chamber 402 upon rotation in either direction of the cam 104 thus compressing spring 158 against the valve 160 to regulate a pressure of, say, 65 pounds per square inch within the brake system. The fluid flowing into conduits 374 and 382 from port 372 is thus applied to the brake cylinders at the pressure regulated by valve 160 to release the brakes. Excess pressure fluid from the steering system flows to sump 392 through valve 160, conduit 390 and valve 394. An auxiliary control knob 340 provides alternative means for controlling the vehicle. A restriction 412 in the passageway 410 limits the flow from the steering system under conditions of high pressure so that the quantity of pressure and fluid which is bypassed through the brake system is carefully regulated. Provision is made for controlling the degree of braking according to the weight of the truck which varies according to the capacity load on the fork. This takes the form of a secondary modulating valve 394 which operates in conjunction with a lift cylinder 20 to control piston 428 which, in turn, controls valves 394 to control the sensitivity of the braking effort according to the load on the fork. A parking brake is provided so that when the operator leaves the truck the brake is automatically applied. This takes the form of a pedal 52 which is provided with a light tensionspring 456 so that the pedal 52 is raised whenever the operator leaves the truck and the brakes are automatically applied by rotating the bell-crank 464 and operating a link 468 which is connected at 470 to a lower cam 124 to rotate the latter in a clockwise direction and return it to its neutral brake applied position. When the operator first gets on the truck and depresses pedal 52 the linkage does not effect the position of cam 124 inasmuch as the lost motion arrangement is provided in the linkage which does not cause movement of the link 468 when the pedal is moved downwardly. Specifications 818,457, 876,286, 895,171 and 895,172 also are referred to.