초록 ▼

For work vehicles, for example, cold weather can be a problem. Disengaging the vehicle clutch (26) aids starting by reducing engine loads during starting. Where the clutch (26) is hydraulically actuated, it can be disengaged by keeping fluid pressures below required engagement pressure when supplyin

For work vehicles, for example, cold weather can be a problem. Disengaging the vehicle clutch (26) aids starting by reducing engine loads during starting. Where the clutch (26) is hydraulically actuated, it can be disengaged by keeping fluid pressures below required engagement pressure when supplying other elements common to the clutch hydraulic circuit. Apparatus is provided which during starting directs fluid to, for example, pump drive bearings (20) at less than clutch engagement pressure. An input signal to the apparatus from the vehicle operator after engine start-up then builds pressure to activate the clutch (26) while continuing to supply the pump drive bearings (20) for lubrication. Upon a preselected fluid flow to the apparatus, such as at engine shutdown, the apparatus automatically returns to the condition at which available pressure levels are less than required for clutch engagement. Thus, cold starting problems are substantially eliminated by automatically providing a clutch disengaged situation in the vehicle during engine start-up.

대표청구항 ▼

A hydraulic circuit (10), comprising: fluid supply means (12) for delivering pressurized fluid flow; first and second means (16,18) for operating at first and second preselected fluid pressure levels of fluid flow thereto, respectively, said first preselected pressure level being less than said seco

A hydraulic circuit (10), comprising: fluid supply means (12) for delivering pressurized fluid flow; first and second means (16,18) for operating at first and second preselected fluid pressure levels of fluid flow thereto, respectively, said first preselected pressure level being less than said second preselected pressure level; first and second fluid pathways (24,28) establishing fluid flow from said fluid supply means (12) to said first and second means (16,18), respectively; a main valve element (30) having a bore (44), a spool (40) and inlet and outlet grooves (36,38), said spool (40) being movable in said bore (44) from a first (62) toward a second (63) position in response to fluid pressure in said second fluid pathway (28) being at said second preselected pressure level and from said second (63) toward said first (62) position in response to fluid pressure in said second fluid pathway (28) being at a reduced pressure level relative to said second preselected pressure level, said inlet groove (36) being positioned in fluid communication with said fluid supply means (12) and, at said first and second positions (62,63), in controlled fluid communication with said outlet groove (38) through said first and second fluid pathways (24,28), respectively, said outlet groove (38) being positioned in fluid communication with said first means (16); and pilot means (32) for automatically initiating a fluid pressure level at less than said second preselected pressure level in said second fluid pathway (28) and opening said first fluid pathway (24) to fluid flow in response to fluid flow being blocked from said fluid supply means (12) into said second fluid pathway (28) and for simultaneously blocking fluid flow through said first fluid pathway (24) and initiating fluid flow through said second fluid pathway (28) in response to a preselected input signal, said pilot means (32) including a pilot valve element (34) movable between a first position at which said inlet groove (36) is positioned in fluid communication with said outlet groove (38) through said pilot valve element (34) and a second position at which said inlet groove (36) is blocked from fluid communication with said outlet groove (38) through said pilot valve element (34).