Hydraulic control device, particularly for power steering

Claim 1

A hydraulic control device for a power steering system comprising: (a) a manually rotatable steering shaft; (b) a double-action hydraulic jack comprising a cylinder, a piston slidably disposed in said cylinder so as to divide said cylinder into a first chamber and a second chamber, and a rod extending from said piston through said chambers, one end of said rod being operatively connected to said steering shaft to convert rotary motion of said steering shaft into linear motion of said rod; (c) a torque sensor operatively connected to said steering shaft to sense torque applied manually thereto; (d) a constant-flow pump; (e) a first path of fluid communication leading from said constant-flow pump to said first chamber; and (f) a second path of fluid communication leading from said constant-flow pump to said second chamber, said hydraulic control device comprising: (g) an electrohydraulic distributor valve comprising: (i) a body having a bore therein and (ii) a slide valve slidably disposed in said bore, said slide valve having a first land at a first end of said slide valve, a second land in the middle of said slide valve, and a third land at a second end of said slide valve opposite to the first end thereof, said first and second lands being separated by a first annular groove and said second and third lands being separated by a second annular groove, said slide valve being shorter than said bore, whereby said bore is divided into a first control chamber fluid pressure in which acts on said first end of said slide valve, a second control chamber fluid pressure in which acts on said second end of said slide valve, a first annular valve chamber between said first and second lands, and a second annular valve chamber between said second and third lands; (h) a third path of fluid communication leading from said first path of fluid communication to said first annular valve chamber, said third path of fluid communication communicating with said first annular valve chamber at a point which ensures unobstructed communication over the entire range of movement of said slide valve; (i) a fourth path of fluid communication leading from said second path of fluid communication to said second annular valve chamber, said fourth path of fluid communication communicating with said second annular valve chamber at a point which ensures unobstructed communication over the entire range of movement of said slide valve; (j) a fifth path of fluid communication leading from said first annular valve chamber to tank, said fifth path of fluid communication communicating with said first annular valve chamber at a point such that communication is unobstructed when said slide valve is in its null position and when said slide valve moves from its null position in a first direction but is progressively throttled when said slide valve moves from its null position in a second direction opposite to said first direction; (k) a sixth path of fluid communication leading from said second annular valve chamber to tank, said sixth path of fluid communication communicating with said second annular valve chamber at a point such that communication is unobstructed when said slide valve is in its null position and when said slide valve moves from its null position in said second direction but is progressively throttled when said slide valve moves from its null position in said first direction; (l) a seventh path of fluid communication communicating control pressure which is a function of the pressure in said first path of fluid communication to said first control chamber; (m) an eighth path of fluid communication communicating control pressure which is a function of the pressure in said second path of fluid communication to said second control chamber; (n) a ninth path of fluid communication containing a first variable orifice communicating said seventh path of fluid communication to tank; (o) a tenth path of fluid communication containing a second variable orifice communicating said eighth path of fluid communication to tank; (p) a performance sensor; and (q) an electronic processing control, said electronic processing control having inputs from said torque sensor and said performance sensor and outputs to said first and second variable orifices, whereby: (r) when said first and second variable orifices are closed, said slide valve is maintained in its null position by balanced control pressures in said first and second control chambers, said third and fifth paths of fluid communication are unobstructedly communicated to tank through said first annular valve chamber, and said fourth and sixth paths of fluid communication are unobstructedly communicated to tank through said second annular valve chamber; (s) when said first variable orifice is opened while said second variable orifice remains closed, the control pressure in said first control chamber is reduced, causing the control pressure in said second control chamber to move said valve slide in said second direction, throttling said fifth path of fluid communication and thereby boosting pressure in said first chamber; and (t) when said second variable orifice is opened while said first variable orifice remains closed, the control pressure in said second control chamber is reduced, causing the control pressure in said first control chamber to move said valve slide in said first direction, throttling said sixth path of fluid communication and thereby boosting the pressure in said second chamber.