Patent GB-1262684-A (GB)
Title: A steering system for a vehicle having endless tracks
IPC: B62D11/08
Filed: 1969-03-28
Abstract: 1,262,684. Endless track vehicles. KLOCKNER-HUMBOLDT-DEUTZ AG. 28 March, 1969 [13 April, 1968], No. 16428/69. Heading B7H.  A steering system for a vehicle having endless tracks, which system comprisos a steering coupling and a steering brake for each endless track and separate spool valves 4 and 5 for actuating hydraulic cylinders of the steering coupling (via a cylinder 19) and the steering brake (via a cylinder 23) respectively of each endless track, the steering coupling and the steering brake being engageable and disengageable by a pressure medium and a spring force respectively and a pressure limiting valve. 56 connected to a pressure duct 2 which feeds pressure fluid to both valves of the control device, each valve spool comprises a throttle groove 37, 39 with the throttling action being varied by displacement of the valve spools, there being compression springs 26, 27 in chambers 28, 29 engaging end faces of the valve spools so as to oppose the throttling action. Each of the chambers 28, 29 is permanently connected through a throttle element to the associated coupling and brake cylinders with the end face of each valve spool remote from the compression spring being also connected to the associated coupling and brake cylinders whereby, when the valve spools reach their end positions towards the compression springs, the coupling and brake cylinders are connected via their respective valve spools to a non-pressurized reservoir 17. Each compression spring chamber 28, 29 of each valve spool is sealed from the reservoir 17 by means of a sealing member 45, 49 biased by a spring 43. In operation when the pump 1 is started and the spools 4, 5 are in a neutral position, as shown, then the driving coupling will be actuated and the steering brake released. The pressure limiting valve 56 is supplied with pressure fluid which when the cylinders 19, 19<SP>1</SP>, 23, 23<SP>1</SP> have been actuated increases in pressure and causes a spool 60 to move upward against a spring 59 such that fluid passes to the valve along duct 55, into chamber 68 and thence to the non- pressurized reservoir 17 via duct 69 and a filter 70. Activation of the steering coupling and brake can be controlled by rods 41 and 42 which are connected to the sealing members 45, 49 and thus can regulate the pressure in chambers 28, 29 which in turn determines the position of the spools 4, 5. If the pressure in, say, chamber 28 is completely vented spool 4 will move to the left and connect the steering coupling to the non- pressurized reservoir 17 via bores 35, 30, 10 and 46 and duets 51 and 16. After operation of the steering coupling 19 and brake 23, a large quantity of fluid may be temporarily needed for subsequent re-engagement which causes a drop in pressure in the hydraulic system. This causes a drop in pressure in chamber 67 of the pressure limiting valve wherein spring 59 moves spool 60 downward, thus connecting the pump 1 to ducts 72 and 73. The pressure in duct 73 has no effect on spool 4<SP>1</SP> due to the pressure in the chamber 28<SP>1</SP> and the spring 26<SP>1</SP>. However, the pressure in chamber 28 is low so that the pressure in duct 72 causes spool 4 to move to the left thus limiting or cutting off the flow of fluid to the cylinder 19. When the cylinder 23 is filled and the pressure in the system rises, the spool of the pressure-limiting valve 56 moves to cut off fluid from ducts 72 and 73 thus allowing the spool 4 to be moved to the right to permit fluid to flow to cylinder 19. The brakes can be operated independently of the steering couplings by valves 53, 53<SP>1</SP> which can vent chambers 29, 29<SP>1</SP> direct to reservoir 17. If the filter 70 becomes blocked a valve 85 is actuated and allows pump pressure to be transmitted via duct 73 to spool 4<SP>1</SP>. When vent rod 41<SP>1</SP> is operated the pressure will move the spool to its left end position and not let it return when rod 41<SP>1</SP> is returned to its starting position. This makes the vehicle unsteerable and clearly indicates the defect. Pressure fluid is also supplied to a gear-box 81. If the pressure in the duct 80 drops due perhaps to a defective gasket in the bore, a valve 75 is operated causing pump pressure to be connected via duct 72. to spool 4. Thus after operation of rod 41 the vehicle will be rendered unsteerable in the same manner as with the blocked filter. The filter could be positioned directly downstream of the pump 1. Also the casings 6, 6<SP>1</SP> may be divided along line a to give remote control of the valve spools 4, 4<SP>1</SP> and 5, 5<SP>1</SP>. In this instance, the divided channels 47, 47<SP>1</SP> and 50, 50<SP>1</SP> may be connected by hose or tube ducts of small crosssection.