Electronic control for a stepless vehicle transmission using a control member responsive to static pressure

In a continuously variable transmission for a vehicle powered by a combustion engine, a control system for adjusting transmission ratio as a function of input parameters representing load and rate of rotation which includes first (8) and second (8') positioning elements together determining the transmission ratio, wherein, in accordance with the invention, that control system includes:

• first actuating means (49:71,73) for actuating said first positioning element (8) in response to hydrostatic pressure in a fluid;
• second actuating means (48;70,72) constituted and operated separately from said first actuating means, for actuating said second positioning element (8') in response to said hydrostatic pressure in said fluid;
• means (11,47) for providing a hydrostatic pressure in said fluid, and
• an electronic control device (55) comprising computing means (60) for producing first and second electrical output signals as a function of said input parameters,
• said first actuating means including at least one valve for controlling, in response to said first electrical output signal, the hydrostatic pressure provided by said pressure providing means (11,47) to a hydraulic medium input port (25) of said first positioning element (8),
• said second actuating means including at least one valve for controlling in response to said electrical output signal the hydrostatic pressure provided by said pressure providing means (47) to a hydraulic medium input port (15) of said second positioning means (8'),
• said at least one valve of said first actuating means and said at least one valve of said second actuating means being selectively controllable independently of each other by said electronic control device by said first and second output signals thereof.