| 摘要 |
1509510 Power-assisted steering mechanism GENERAL MOTORS CORP 4 Nov 1976 [14 Nov 1975 (2)] 45900/76 Heading B7H A power-assisted steering gear comprises an input shaft 12, a worm screw 70 extending through a piston nut 74, and a control valve assembly including a valve spool 42 coupled to the input shaft 12 by a pin 44, and a valve body 38 coupled to a head portion 68 of the worm screw 70 by a pin and slot connection 93 and a retainer ring 98 which prevents axial separation of the worm screw and the valve body. A housing 10 for the gear has a stepped bore with small, intermediate and large diameter portions 62, 40, 76 accommodating the input shaft 12, valve body 38 and piston nut 74 respectively. An adjustable plug 122 closing the large diameter bore portion 76 supports a thrust bearing 120 for the worm screw 70, and a second thrust bearing 54 is disposed between the housing 10 and the valve body 38. To reduce the overall length of the gear, the plug 122 has a recess 134 into which the piston nut 74 extends at one end of its stroke, and the piston nut 74 has a skirt 108 which at the other end of its stroke extends over a portion of the valve body 38 projecting from the intermediate diameter bore portion 40 into the large diameter bore portion 76. A torsion bar 22 is connected between the input shaft 12 and a cap 32 coupled to the valve body 38 by a pin 39. The head portion 68 of the worm screw 70 has fingers which project through openings in the cap 32 into recesses in a head portion 18 of the input shaft 12 to limit relative rotation of the shaft and worm screw. Rack teeth 102 on the piston nut 74 mesh with a gear sector 106 connected to a pitman shaft. The worm shaft 70 and the piston nut 74 engage through multi-start threads having a modified acme form in which the crest of the nut thread contacts the roof of the worm thread so that the friction radius is minimized to improve efficiency and the fluid leakage path through the threads is reduced. The nut threads also have increased thickness to closely fit into the worm threads to further reduce the leakage. |
