Cruise control system for a vehicle

Claim 1

A cruise control system for a vehicle having an internal combustion engine, an engine output control member, and an accelerator pedal connected to said engine output control member for operating said engine output control member in accordance with a requirement by an operator, said system comprising: actuator means connected to said engine output control member for controlling engine output without operation of said accelerator pedal by an operator; first detecting means for detecting an actual vehicle speed; target value setting means for setting a target vehicle speed to be maintained by said cruise control system; second detecting means for detecting commencement of a cruise control mode of operation; electric signal forming means for forming electric signals for operating the actuator means and thereby controlling engine output and vehicle speed; timer means for detecting first and second predetermined time lapses after detection of commencement of the cruise control mode of operation by said second detecting means; first control means for controlling said electric signal forming means, prior to detection of said first predetermined time lapse by said timer means, so as to form a fixed level electric signal for quickly moving the actuator means to prevent a temporary decrease of the vehicle speed; second control means for calculating feedback factors based upon deviations between the actual vehicle speed detected by said first detecting means and the target vehicle speed set by said target value setting means, and for controlling said electric signal forming means, after detection of said first predetermined time lapse by said timer means, so as to form electric signals which are modified by said feedback factors; and feedback gain control means for controlling gain of said feedback factors so that a value of said gain deceases after detection of said second predetermined time lapse by said timer means, whereby a quick and stable feedback control is realized.