Rack and pinion variable ratio steering gear

Abstract

A variable ratio steering mechanism for a vehicle having an axially movable rack meshing with a helical pinion the axis thereof making an angle with the axis of the said rack, the rack having a group of teeth at its center of varying form and varying inclinations with respect to the axis of the rack, the inclination of the teeth of said group becoming less closely aligned with the pinion axis as the teeth are more remote from the center of said rack, said teeth thereby meshing with the teeth of the pinion at varying effective pitch radii in a predetermined manner.

I claim as my invention: 
     
       1. A variable ratio rack and pinion steering mechanism having an axially movable rack meshing with a helical pinion the axis of which makes an angle with the axis of the rack, the rack being characterized by having a group of teeth at its center said teeth being of varying forms and varying inclinations with respect to the axis of the rack, the inclination of the teeth of said group nearest the center being the most closely aligned with the axis of the pinion, the inclination of teeth of said group becoming less closely aligned with the pinion axis and more closely perpendicular to the axis of the rack as they move away from the center of the rack, the inclinations and forms of said group of teeth being associated with engagement of the said teeth with the pinion at varying effective pitch radii, the effective pitch radius being least at the center of the rack and increasing on either side thereof. 
     
     
       2. A variable ratio rack and pinion steering mechanism as claimed in claim 1, wherein the remainder of the teeth of the rack engage the pinion at an effective pitch radius substantially equal to the effective pitch radius at which the pinion is engaged by the outermost portions of the outer teeth of said group of teeth, said remainder of the teeth extending substantially at right angles to the axis of the rack. 
     
     
       3. A variable ratio rack and pinion steering mechanism as claimed in claim 2, wherein the sides of the remainder of the teeth of the rack are arcs of circles. 
     
     
       4. A variable ratio rack and pinion steering mechanism as claimed in claim 3, wherein the form of the teeth of the pinion is substantially involute. 
     
     
       5. A variable ratio rack and pinion steering mechanism as claimed in claim 2, wherein the form of the teeth of the pinion is substantially involute. 
     
     
       6. A variable ratio rack and pinion steering mechanism as claimed in claim 3, wherein the effective pitch radius increases symmetrically on either side of the center of the rack. 
     
     
       7. A variable ratio rack and pinion steering mechanism as claimed in claim 2, wherein the effective pitch radius increases symmetrically on either side of the center of the rack. 
     
     
       8. A variable ratio rack and pinion steering mechanism as claimed in claim 1, wherein the said group of teeth comprise a minority of the teeth of the rack, the majority of teeth being straight sided and of constant section across the width of the rack whereby they are adapted to manufacture by broaching. 
     
     
       9. A variable ratio rack and pinion steering mechanism as claimed in claim 8, wherein the form of the teeth of the pinion is substantially involute. 
     
     
       10. A variable ratio rack and pinion steering mechanism as claimed in claim 8, wherein the effective pitch radius increases symmetrically on either side of the center of the rack. 
     
     
       11. A variable ratio rack and pinion steering mechanism as claimed in claim 1, wherein the form of the teeth of the pinion is substantially involute. 
     
     
       12. A variable ratio rack and pinion steering mechanism as claimed in claim 1, wherein the effective pitch radius increases symmetrically on either side of the center of the rack. 
     
     
       13. A variable ratio rack and pinion steering mechanism having an axially movable rack meshing with a helical pinion the axis of which makes an angle to the axis of the rack, the rack being characterized by having a group of teeth at its center whose form is different at every section across the width of the rack, and having other teeth each side of said group having a constant form at every section across the width of the rack, said group of teeth providing a varying effective pitch radius, and said other teeth providing a substantially constant effective pitch radius, said constant pitch radius being always greater than the varying effective pitch radius. 
     
     
       14. In a variable ratio rack and pinion steering mechanism as claimed in claim 1, a pinion having a form determined by a generating rack having a tooth space, measured at the mid height of the tooth, more than twice the tooth thickness. .Iadd. 15. A variable ratio rack and pinion steering mechanism having an axially movable rack meshing with a helical pinion the axis of the which makes an angle with the axis of the rack, the rack being characterized by having groups of at least one tooth and of varying forms and varying inclinations with respect to the axis of the rack, the inclination of the teeth of at least one group being more closely aligned with the axis of the pinion, the inclination of teeth of said one group becoming less closely aligned with the pinion axis as they move away from the one group, the inclinations and forms of said group of teeth being associated with engagement of the said teeth with the pinion at varying effective pitch radii, the effective pitch radius being least at the position on the rack where the inclination is most closely aligned with the axis of the pinion and increasing to provide decreasing steering ratio with movement away from said one group..Iaddend..Iadd. 16. The structure of claim 15 wherein said one group is adjacent the center of the rack and the inclination of teeth of said one group becomes less closely aligned with the axis of the pinion with movement in either direction away from the center of the rack..Iaddend..Iadd. 17. The structure of claim 15 wherein said at least one group comprises two groups of teeth on opposite ends of the rack and the inclination of the teeth of both thereof becomes more closely aligned with the axis of the pinion as they approach each of the said one groups from the direction of the center portion of the rack providing increasing steering ratio with movement away from the center towards the ends of the rack.