JPS4882527A - - Google Patents

Abstract

1376113 Hydrostatic transmissions CLARK EQUIPMENT CO 23 Jan 1973 [24 Jan 1972] 3372/73 Headings F2D and F2W In a hydrostatic transmission having a variable displacement swashplate pump 14 driven by an internal combustion engine (Fig. 2, not shown) which supplies fluid to front wheel 10 motors 42 and 44 only for two-wheel drive, and to rear wheel 12 motors 76 and 78 also, for fourwheel drive, means are provided so that a smooth transition between two- and four-wheel drive and vice-versa may be effected at any speed. In the condition illustrated four-wheel drive is engaged with the output (in forward drive) of the pump 14 passing via a line 46 to a flow divider 48 from which half the pump output passes to motors 42, 44 via a line 50 and a divider-combiner unit 52 and half to motors 76, 78 via line 66, valve 64, and lines 70 and 72. To engage two-wheel drive a control 118 is operated to close valve 64 and put line 66 into communication through line 84, section 90 of a valve 88 also operated by control 118, and a line 92 with the inlet 62 to the pump and then the valve 88 is gradually moved further to cause the line 84 to be put in communication with the output of the pump 14 through section 94 of valve 88 and line 96. When this has been done the vehicle moves at twice the speed in two-wheel drive that it has in four-wheel drive. A system of valves 180, 186, 188 can return fluid to a reservoir 100 to protect the pump from overload. An auxiliary pump 150 supplies make up fluid through one-way valves 156, 158, 164, 166, 170 and 172 and also supplies pressure fluid to a servo-control 23 to aid operation of the pump 14 swash-plate. On steering of the wheel 12 by linkwork 128, 126 and 122 a cable connection 132 adjusts the divider-combiner 52 to apportion fluid to the front (non-dirigible) wheels accordingly. In an alternative embodiment (Fig. 6, not shown) the valves 48 and 88 are replaced by a combinerdivider valve (200) (similar to valve 52) which, in conjunction with a farther valve which can divert the fluid from the rear-wheel motors 76, 78 to the input to the pump 14, can effect the smooth changeover to two-speed drive by being adjusted so that it supplies all fluid to the front motors, and not just one half. Hydrostatic braking is effected by returning the swash plate of the pump 14 to its neutral position or by reversing it. The valves 88 and 64 (as well as a valve 98 which returns fluid in the circuit to wheels 76, 76 to the reservoir 100) are operated from control lever 118 via push-pull cables (Fig. 4, not shown). The vehicle may operate in reverse by reversing the flow from the pump, when the divider-combiner valves act in the return lines.