Patent GB-1482721-A (GB)
Title: Variable weight transfer device for road-rail tractor couplers
IPC: B61C15/00
Filed: 1975-01-27
Abstract: 1482721 Railway mules; rail/road vehicles WHITING CORP 27 Jan 1975 [28 Jan 1974] 3465/75 Headings B7H and B7D A tractor adapted for use on rails or roads includes a coupler 25, 26 for coupling to a rail car and means 29, 30 for transferring weight from the rail car to the rail-wheels 27a, 28a to increase traction, the weight transfer force being varied automatically by an hydraulic control circuit in response to the pulling or pushing traction needs of the tractor when moving. The front and rear weight transfer cylinders 29, 30 are connected between the pivoted coupler plates 25, 26 and the frame 22 of the tractor, and hydraulic supply thereto is controlled by driver operable valves 41, 42 and a valve assembly 40 which is responsive to the tractor speed, engine torque, transmission state or draft force and hence to the traction need. Valves 41, 42 have three positions respectively for raising, lowering or shutting off the cylinders 29, 30 and may be solenoid or manually actuated. Valve assembly 40 includes, an arrangement whereby the pressure supplied to the valves 41, 42 may be varied to meet the traction needs either step-wise, Fig. 2, or continuously (Fig. 3, not shown). The stepwise control assembly includes a valve 65 controlled by spring 65a and pressure parts 65b, 65c, relief valves 67, 66 set to open at respectively higher and lower valves, and a three position control valve 68 which is solenoid operated by a signal generator responsive to the traction needs. Valve 65 is arranged so that reduction of pressure at port 65b decreases the pressure in line 48a to valves 41, 42. Control valve 68 is in the blocked position 68b when no signal is applied to either of its solenoids through lines 86, 85, hence only relief valve 67 is connected to drain through line 70. In this case the pressure at port 65b is at its highest and the maximum pressure is supplied to line 48a. When a signal is applied to valve 68 to cause it to go to position 68a, drain line from relief valve 66 is connected to exhaust and the pressure at port 65b drops to that of the setting of valve 66 thus reducing the pressure in line 48a. If the signal causes valve 68 to occupy position 68c port 65b is connected by line 72 to drain and the minimum pressure exists in line 48a. In another embodiment (Fig. 3) the valves 66-68 are replaced by a continuously variable relief valve (158). A valve 73 in line 48a prevents any sudden pressure increases due to bumpy tracks. The signal generator may be speed sensitive (Fig. 5, not shown), responsive to a mechanical or hydraulic transmission (Figs. 4 and 6, not shown), responsive to engine torque or may be responsive to the draft force. In the latter case the coupling head stem 132 is surrounded by sliding plates 134, 135 separated by a resilient pad 136, each plate carrying a switch contact member 143, 145. As the draft force alters the plates more relatively to control actuation of the switch 144 or a potentiometer (165) (Fig. 10, not shown). Road wheels 35, 36 on the tractor may be raised and lowered by cylinders 37, 38 controlled by a driver actuable valve 43. Front and rear shock absorbers 33, 34 are connected to valves 41, 42 and the weight transfer cylinders 29, 30 to prevent the springs 31, 32 bottoming under full load.