Pressure medium control system for auxiliary power steering systems

#This invention relates to a rotary control valve assembly for controlling operation of a servomotor in an auxiliary power steering system for an automotive vehicle, and more particularly to an improvement to the control valve assembly disclosed in my prior copending application Ser. No. 825,477, filed Aug. 17, 1977, abandoned in favor of continuation application, Ser. No. 37,031, filed May 8, 1979, now U.S. Pat. No. 4,232,586.

#According to my prior copending application, a pressure medium control system is disclosed having a rotary plug valve which is journaled at its opposite axial ends by anti-friction bearings mounted in an associated control bushing. In this manner, precise response and perfect functioning is assured since hydraulic jamming of the rotary plug valve and an uncontrolled increase in friction caused thereby, is reliably avoided. The objective of the present invention is to further improve the operational behavior of said pressure medium control system.

#Generally, control valve edges on the valve lands formed between the longitudinal passage grooves on a rotary plug valve, are arranged symmetrically on the periphery of the valve element and may be provided with phase control bevels. Such an arrangement is disclosed, for example, in German Pat. No. 1,181,077, column 4, lines 54-55 and in U.S. Pat. No. 4,063,490 to Duffy. The objective associated with such arrangements is to obtain a symmetrical distribution of equal fluid flow forces in order to avoid any resultant transverse force and development of friction therefrom on the rotary plug valve surfaces. Such control bevels are advantageous for regulating pressure that is switched on and off.

#The invention will be explained in more detail hereinafter on the basis of the drawings wherein:

#FIG. 1 is a partial longitudinal section view of a steering gear with a rotary plug valve embodying the control bevels in accordance with the present invention,

#FIG. 2 is an enlarged transverse section view of the rotary plug valve taken substantially through a plane indicated by section line II--II in FIG. 1, and

#Referring now to the drawings, FIGS. 1 and 2 show a rotary plug valve in accordance with the invention consisting of a rotary plug element 12 and a control bushing 26. On the cylindrical surface of the rotary plug element 12, axially extending, longitudinal passage grooves 16 and 17 are milled in. The longitudinal passage grooves are connected by inlet conduit channels 18 and an annular groove 19 in the control bushing to an inlet fitting connection 20. Longitudinal passage grooves 17 are connected by exhaust channels 21 in the control bushing to a discharge chamber 22 in communication with a fluid return line (not shown). A cylindrical bore 23 of the control bushing 26 is also provided with longitudinal passage grooves 24 and 25 which are connected in alternating order by means of separate pressure outlet ports 27 and 28 with two opposing pressure chambers of a servomotor 29 such as chamber 29a shown in FIG. 1 on one side of the servomotor piston 29b.

#According to the invention, the control edges formed at the intersections of the cylindrical surface of the rotary plug 12 and only one of the three longitudinal grooves 16 communicating with the inlet channels 18, have control bevels 30 as shown in FIG. 2. The control bevels could also be formed at the edges of one of the longitudinal grooves 17 leading to the exhaust channel 21 for fluid return. The channels 18 or 21, grooves 16 or 17 and grooves 24 and 25 form three parallel flow paths between the outlet ports 27 and 28 and either inlet 20 or discharge chamber 22. However, the two control bevels 30 are confined to only one of the parallel flow paths because they both open into a common inlet channel 18 communicating with a single one of the grooves 16 in the embodiment shown in FIG. 2.

#In the embodiment shown in FIG. 3, the adjacent control edges of one pair of adjacent longitudinal passage grooves 31 and 32 have been provided with control bevels 33 for communication with the servomotor pressure chambers. In this embodiment the inlet channel 18 and exhaust channel 21 in communication with the inlet and return lines respectively, lead to a bridge 34 and 35 spacing the grooves 31 and 32 of the rotary valve plug 12. As in the case of the embodiment of FIG. 2, the three parallel flow paths are established between the inlet or return and the outlets through channels 18 or 21 and the passage grooves in the rotary plug valve and control bushing, including the passage grooves 31 and 32. The two control bevels 33 are also confined to one of the parallel flow paths by opening into a common inlet channel 18, communicating however, with only two adjacent grooves, 31 and 32, in the rotary valve plug for the embodiment shown in FIG. 3.