Clutches with bypass inching valve

In a hydraulic control system for a vehicle, including brake means, comprising first hydraulic passage means connecting a source of pressure fluid to fluid actuated frictional engaging means, said source being provided with pressurizing means for providing pressurized fluid in an amount proportional to the speed of the engine of said vehicle, and a bypass type inching valve system connected and parallel with said first hydraulic passage means for selectively manually reducing the hydraulic pressure supplied into said frictional engaging means in proportion to the degree of actuation of saId brake means, said bypass type inching valve system including a fluid flow constricting means disposed within said first passage means and an inching valve, said inching valve comprising:

• a. an elongated valve body forming a first bore therein with a closed end, said body having inlet, outlet and drain ports in said body which communicate with said first bore;
• b. first conduit means connecting said inlet port with said first hydraulic passage means upstream from said fluid flow constricting means;
• c. second conduit means connecting said outlet port with said first hydraulic passage means downstream from said fluid flow restricting means;
• d. sleeve spool means forming a second bore therein retained within said first bore and having a first annular groove with first radial apertures aligned with said inlet port, said sleeve spool means also having a second annular groove with second radial apertures aligned with said drain port;
• e. regulating spool means, actuatable between a first and a second position, disposed within said first bore, said regulating spool means having a flange portion which, in the first position of said inching valve, abuts one annular end surface of said sleeve spool means, said regulating spool means also having a cylindrical annular portion, depending from one side of said flange portion and forming a third bore therein open on one end, slidably disposed within said second bore, with an outer end portion of said cylindrical annular portion, in said first position, closing off the communication between said second bore and said drain port, said cylindrical annular portion also having a third annular groove with third radial apertures therein substantially aligned with said first radial apertures in said first position;
• f. first means for biasing said regulating spool means to said first position;
• g. actuating means, operatively connected with said brake means for overcoming said first biasing means and permitting said regulating spool means to move to said second position;
• and
• h. second means for biasing, interposed between said regulating spool means and said actuating means, tending to balance the forces exerted on said regulating spool means by the pressure fluid, said actuating means also progressively decreasing the force of said second biasing means as the degree of actuation of said brake means is increased, whereby when said regulating spool means is in said first position, the pressure fluid can freely flow into, through and out of said inching valve and effectively bypass said fluid flow contricting means, however, in said second position, the fluid flow through said third annular groove is blocked and thereafter said drain port is progressively opened thereby regulating the force of the pressure fluid acting on said regulating spool means, and the pressure fluid is forced to flow solely through said fluid flow constricting means.