Constant-speed cruise control apparatus for a vehicle

Claim 1

A constant-speed cruise control apparatus for a vehicle comprising: a means for measuring an actual cruise speed for a vehicle comprising: a means for setting a target speed, a means for computing a speed deviation of said cruise speed for said target speed, a means for computing an acceleration of the vehicle on the basis of said cruise speed, a throttle valve for controlling a driving force of the vehicle, a drive means for driving said throttle valve, a means for computing a controlled variable of said drive means so as to reconcile said cruise speed with said target speed, a means for detecting the opening of said throttle valve, an automatic speed change means capable of automatically shifting up or shifting down a transmission of the vehicle, a means for storing therein cruise performance characteristics on at least two roads having different gradients from each other expressed in terms of a relationship between the cruise speed and the opening of said throttle valve, a means for estimating the gradient of a road on which the vehicle cruises on the basis of said cruise speed, the detected opening of said throttle valve and said stored cruise performance characteristics in accordance with: ##EQU3## where: tan δ 1 is a road gradient for a throttle valve opening θ 1 at said actual cruise speed, tan δ 2 is a road gradient for a throttle valve opening θ 2 at said actual cruise speed, tan δ n is the estimated gradient of the road on which the vehicle is cruising, and a control means which outputs a shift-down command to said automatic speed change means when the absolute value of said speed deviation is more than a first value, or said estimated gradient is more than a second value, and after said shift-down command is output, outputs a shift-up command to said automatic speed change means when the absolute value of said speed deviation is less than a third value and said gradient is less than a fourth value.