Patent GB-895168-A (GB)
Title: Control systems for industrial trucks
IPC: B66F9/20
Filed: 1960-05-09
Abstract: 895,168. Control of D.C. motors; controllers. CLARK EQUIPMENT CO. May 9, 1960 [June 8, 1959], No. 16244/60. Class 38 (3). An industrial lift-truck for handling material in warehouse access aisles of relatively narrow width comprises a control handle 50 in addition to a steering-wheel and a switch for extending and retracting an upright, a parking brake being controlled by means of pedal 52. Upward movement of handle 50 effects inward motion of plunger 94 for controlling lifting action through an hydraulic motor, a first pump motor being energized for low-speed operation and then a second motor for high-speed lifting. Downward movement of the control handle controls lowering movement of the forks. A safety interlock button 80 must first be depressed before the control handle is actuated downwardly to provide lowering movement of the forks. Rotation of the control handle 50 about its own axis actuates a master controller for traction motors 42, 43, a second control handle 93 being adapted to actuate a plunger 95 for valve 96 whereby the mast is extended or retracted. The valve 96 is coupled to a cam for closing a switch in circuit with a pump motor. Rotation of handle 50 for forward drive of the truck effects counterclockwise rotation of cam 104, the shape of track 120 being such that cam 124 rotates in a counter-clockwise direction irrespective of the direction of rotation of the upper cam. A follower arm 134 is associated with a valve 156 for causing a regulating valve to modify the pressure in brake cylinders 168, 170, against the force of springs 172, 174, of brake shoes 176, 178. When rotation of the control handle has actuated the upper cam to a position in which valve plunger 154 is fully depressed, the rotational force due to roller 146 ceases, further motion of the handle allowing follower 142 to engage detents representing the operational speeds of the vehicle. During motion of the speed control cam from a neutral position to a full-speed position, five switches are actuated successively, a double-throw direction switch DS being actuated by cam 205 for forward or reverse operation. A steer pump motor is started, and the traction motors are connected in series to a battery-section with two resistors in circuit. Thereafter, the resistors are removed from circuit and then the traction motors are connected across the full battery, the resistors being re-introduced for a short period. Further acceleration is obtained by connecting the motors in parallel. A mechanical timing device for delaying movement of the controller between notches comprises a balance-wheel associated with a pawl. A fly-ball governor 310, responsive to motor speed, permits dog 326 to hold yoke 330 and prevent rotation of rod 108 when the speed is above a predetermined value. This blocks movement of the controller between forward and reverse under these conditions, and holds in in a neutral position. The timing device above-mentioned provides a delay interval when the controller is being rapidly returned to the neutral brake-applied position and prevents the driver from throwing the truck into reverse when he intends to apply the brakes. An auxiliary control-knob 340 is provided for operating the truck in reverse, this knob being linked with cam 104. A switch is located at the operator's station for extending and retracting the mast. The speed of the truck is automatically restricted when this switch is actuated. Specifications 818,457, 876,286, 895,170, 895,171 and 895,172 are referred to.