Apparatus for controlling line pressure used in V-belt type continuously variable transmission for automobile

Claim 1

A control device, for a continuously variable belt transmission device comprising a driving pulley assembly including an axially fixed pulley member and an axially movable pulley member, a driven pulley assembly including an axially fixed pulley member and an axially movably pulley member, an endless belt assembly which is fitted in a power transmitting manner around said driving pulley assembly and said driven pulley in V-shaped grooves defined between said axially fixed and said axially movable pulley members thereof to provide power transmission therebetween at a transmission speed change ratio, and first and second pressure chambers for said driving and driven pulley assemblies respectively, each of which according to a supply of hydraulic fluid pressure to it alters the axial distance between its respective axially fixed pulley member and its respective axially movable pulley member so as to alter the effective pulley radius of its respective one of said driving and driven pulley assemblies, said control device supplying a line pressure to said second pressure chamber for said driven pulley assembly, and comprising: a throttle valve having means for generating a throttle pressure Pth as an increasing function of all throttle positions θ in an intake path of an engine; a transmission ratio detecting valve comprising: (a) a transmission ratio pressure port, (b) restriction means communicating said transmission ratio pressure port with a source of said line pressure, (c) a drain in fluid communication with said transmission ratio pressure port, (d) a spool movable for selectively closing said drain, whereby a transmission ratio pressure P γ is established at said transmission ratio pressure port, (e) mechanicla means for moving said spool for opening said drain in response to an increase in said transmission ratio γ and for closing said drain in response to a decrease in said transmission ratio, (f) means for moving said spool in a direction for opening said drain in response to an increase in the pressure at said transmission ratio pressure port, and for closing said drain in response to a decrease in the pressure at said transmission ratio pressure port, whereby said transmission ratio pressure increases to equal said line pressure below a predetermined transmission ratio γ1, and whereby said predetermined transmission ratio varies as a decreasing function of said transmission ratio pressure; and a line pressure generating valve having means for accepting said throttle pressure and said transmission ratio pressure as control pressures and for establiding said line pressure as an increasing function of said throttle pressure and a decreasing function of said transmission ratio pressure.