Method and a system for controlling vehicle speed

Vehicle speed control system in a vehicle equipped with brake cruise control when the vehicle is travelling downhill, which system comprises:

• a sensor arranged to detect a current vehicle speed;
• a service brake;
• at least one auxiliary brake;
• and
• a control unit having a user selectable input for receiving a brake set speed, the control unit being arranged to:
• compare the current vehicle speed with a first brake set speed and control the auxiliary brakes to maintain the first brake set speed;
• detect if the service brake is manually applied to retard the vehicle speed;
• and
• when a manual application of the service brakes is detected, automatically:
• setting the brake set speed to a second brake set speed that is lower than the first brake set speed, and
• applying a brake torque using at least the auxiliary brake when the current vehicle speed exceeds the second brake set speed;
• after the setting of the brake set speed to the second brake set speed, determining that the detected current vehicle speed exceeds the second brake set speed with the auxiliary brake engaged;
• and
• in response to the detected current vehicle speed exceeding the second brake set speed, automatically applying, via the control unit, the service brake in conjunction with the auxiliary brake.