Pulley thrust pressure control apparatus for belt-type continuously variable transmission

摘要

A pulley thrust pressure control apparatus for a belt-type continuously variable transmission comprises a pulley thrust pressure valve unit 40 for setting a low pulley thrust control pressure and a high pulley thrust control pressure greater than the low pulley thrust control pressure; a shift valve 53 for supplying the low and high pulley thrust control pressures selectively into drive and driven cylinders 14 and 19 of drive and driven pulleys in correspondence with the position of a spool thereof; a drive pressure feedback passage 39c for causing the pressure inside the drive cylinder 14 to act on the spool as a positional control force; and a driven pressure feedback passage 39d for causing the pressure inside the driven cylinder 19 to act as a positional control force on the spool in the direction opposite of that cause by the pressure from the drive pressure feedback passage. When control of the pulley thrust pressures is carried out by this apparatus, a minimum pressure required for the drive and driven cylinders is insured without increasing the load on the pump which supplies hydraulic oil into the drive and driven cylinders. In addition, control of the speed ratio of the transmission is performed steadily with little change in the pressure.