Power steering valve with chamfered lands

Claim 1

In a power steering gear comprising a fluid motor adapted to be connected to a driven member, said fluid motor having opposed fluid pressure chambers, a steering shaft, a positive displacement fluid pump, and a fluid circuit for controlling pressure distribution from said pump to said fluid motor; a valve assembly in said fluid circuit comprising a rotary valve sleeve having internal valve lands, a rotary shaft valve connected to and rotatable with said steering shaft, and external valve lands on said shaft valve; a yieldable mechanical connection between said steering shaft and said driven member, a positive driving connection between said valve sleeve and said driven member; a fluid connection between said pump and said pressure chambers comprising a first passage extending from said valve assembly to one pressure chamber and a second passage extending from said valve assembly to the other pressure chamber, a fluid supply passage extending from said pump to said valve assembly and a fluid return passage between said valve assembly and a flow inlet region of said pump; the external valve lands of said shaft valve registering with the internal valve lands of said valve sleeve whereby said registering lands define in part said first passage and said second passage, the internal valve lands on said sleeve adjacent said supply passage being chamfered throughout their length whereby a pressure buildup occurs in said pressure chambers at a controlled rate dependent on the torque applied to said steering shaft; the external lands on said shaft valve being spaced angularly about the axis of said shaft valve and being formed by axially extending crescent-shaped grooves adapted to be formed by rotary milling cutter, the internal valve lands in said sleeve being straight-through lands defined by axially extending groove adapted to be formed by a linear broaching tool, the chamfer on said internal valve lands being of uniform dimension throughout their axial extent whereby said internal lands and said chamfers are adapted to be broached simultaneously with said linear broaching tool, and end rings in said valve sleeve on either axial end of said internal lands, said end rings having an internal diameter equal to the internal diameter of said internal lands.