1. Field of the Invention
The present invention relates to a control apparatus for a continuously variable V-belt transmission and more particularly to the control apparatus capable of selecting either a coast down operation or a deceleration with engine brake applied by detecting an intention of a vehicle operator.
2. Discussion of Prior Art
A V-belt type continuously variable transmission used for an automobile power transmission apparatus includes a primary shaft connected with a crankshaft of an engine, a primary pulley provided on the primary shaft and whose width of a groove of the pulley is variable, a secondary shaft as an output shaft, a secondary pulley provided on the secondary shaft and a drive belt looped over these two pulleys. Engine speed is continuously changed by changing a ratio of winding diameters of the drive belt on the respective pulleys and is transmitted to the secondary shaft.
Japanese Patent Application Laid-open No. Toku-Kai-Hei 9-166216 discloses a control apparatus for controlling a ratio of winding diameters of a drive belt to pulleys, namely a speed ratio. The control apparatus inputs signals indicative of accelerator pedal opening angles, primary pulley speeds, secondary pulley speeds, vehicle speeds, engine speeds and the like and performs a control of speed ratio based on these input signals.
In the control apparatus, when an operator takes his or her foot from an accelerator pedal during operating a vehicle, the speed ratio is controlled so as to be shifted up in order to improve fuel economy and to enhance driveability. Accordingly, when the accelerator pedal is released, the speed ratio is stuck to an over-drive position and the vehicle travels by inertia with an engine brake applied.
On the other hand, when the vehicle driver releases the accelerator pedal, he or she sometimes intends to decelerate the vehicle while engine brake is exerted. For example, when the vehicle travels on winding roads, since moderate engine brakes are obtained by easing his or her foot off the accelerator pedal, the frequency of depressing a brake pedal for deceleration decreases and as a result the a burden of the operator can be substantially reduced. However, when the operator takes his or her foot from the accelerator pedal, the prior control apparatus fixes the speed ratio to an overdrive position and the vehicle runs by inertia irrespective of an intention of the operator. As a result, the operator must depress the brake pedal for deceleration after taking the foot from the accelerator pedal.