Controls for the drive of a vehicle with differential speed steering

Claim 1

In a control for the drive of a vehicle having differential-speed steering and having a hydrostatic drive unit on each side of the vehicle for operating the drive wheels and a final control element for each of the two drive units connected with a spring-loaded servo piston capable of sliding in an operating cylinder, the improvement comprising a pressure chamber on each side of the servo piston in the operating cylinder connected with each drive unit, means providing an arbitrarily adjustable control pressure on each servo piston, first control pressure pickoff means for controlling the forward and reverse travel connected with operating cylinders of the drive units of both sides of the vehicle, two additional second control pressure pickoffs, each assigned to one turning direction connected with the operating cylinder of each drive unit of the vehicle, each servo piston being capable of being acted upon on one side by the first control pressure pickoff means for controlling the direction and speed of travel, and, on the other side, may be acted upon by a second control pressure pickoff of the pair of pickoffs assigned to turning travel for controlling the turning radius, a pilot valve located in each connection line between a second control pressure pickoff assigned to turning travel and the operating cylinder of the corresponding drive unit, an arbitrarily actuable direction and speed selection lever operatively connected to said first pressure pickoff means, means for switching each said pilot valve as a function of the position of the arbitrarily actuable direction and speed selective lever, said pilot valve connecting the control pressure from the first pressure pickoff through the second control pressure pickoff assigned to turning travel with a pressure chamber of an operating cylinder of the drive unit, an arbitrarily actuable turn selection lever operatively connected to each second control pressure pickoff, means in each said second pickoff for controlling the control pressure through said pilot valve as a function of the position of the arbitrarily actuable turn selection lever to restrict the connection from the first pressure pickoff to the operating cylinder on the drive on the inside of the curve, whereby the other pressure chamber of said operating cylinder is acted upon by the control pressure from the first control pressure pickoff means that determines at least one of the speed and the direction of travel, said second control pressure pickoff assigned to one turning direction of the control pressure pickoff pair determining the direction and radius of turning reducing the control pressure in the said one chamber of the operating cylinder on the inside of the turn while the second control pickoff on the opposite side connected to the operating cylinder on the opposite side is unchanged and acted upon by the control pressure pickoff that determines the direction and speed of travel, each said second pickoff including means for first reducing the control pressure on said one pressure chamber of said operating cylinder and then sequentially connecting said control pressure to the other pressure chamber of the operating cylinder, each pilot valve being a 4-connection/3-position valve, where a pressure reducing valve of one of the second control pressure pickoffs assigned to one turning direction is connected to each connection of the one pair of connections of a pilot valve and each of the two other connections of this pilot valve is connected to a pressure chamber of the operating cylinder of the assigned drive unit, and wherein only one control pressure line is present for the control pressure determining the speed of travel and that the direction of travel is controlled by arbitrary actuation of the pilot valves.