Important!! This part of site is an attempt to organize and add to the web resources for the Rover SD1 to form a cohesive and easily usable guide for those of us without easy access to expert repair and/or advice. It is not offered in any way as a definitive source and we take no responsibility for any errors that may exist. Webmaster. Rene Winters.

Hella GR 65 Cruise Control The next electrical system which we will examine is the Hella GR 65 cruise control system fitted as standard or as an option on some Rovers. Operating Principles We will begin by looking at the driver operation of the system. It is controlled by this stalk switch which can be moved both horizontally and vertically. Let us start with the switch in the horizontal OFF position at which the system is inactive. Pulling the switch forwards to the ON position activates the system ready for operation. If you briefly raise the switch to the SET position as you are driving along, the speed at which you are driving will be memorised; provided the speed exceeds the minimum required, you can now take your foot off the accelerator pedal and the car will maintain the selected speed. You can still accelerate the car by pressing the accelerator pedal. But as soon as you release the pedal the cars speed will return to that at which the cruise control was set. If you now hold the switch up in the SET position, the car will continue accelerating until the switch is released, when the cruise control will hold the car at the new higher speed. Braking, declutching, moving the switch briefly downwards to the OFF position, disengages the cruise control. This will also occur if the road speed differs from the set speed by 25%. The originally set speed will still be memorised and can be re-engaged by moving the switch horizontally to the RES (resume) position.

Now let us see how it works. Here we see the system fitted to a Rover with a 3500 engine. 1. is a vacuum pump control unit which provides the vacuum which operates the system. 2A. and 2B. are switches and vent valves, one for the brake pedal and one for the clutch pedal where a manual gearbox is fitted, 3. is a line fuse, 4. is the control switch. 5. is an electronic control unit, 6. an overspeed relay. 7. is a speed transducer which is fitted to the gearbox and the final item, 8. is a vacuum operated actuator.

Theoretically, the system looks like this. We have annotated the picture so that the numbers correspond with those we used when showing the location of the components. If you analyse the circuit you will see that it comprises 4 basic parts. Most important of all is the Electronic Control Unit which is basically the brain of the system.

Secondly, there is a system by which the electronic control unit can monitor the driver's requirements from the control switch, brake and clutch pedals.

The third system enables the electronic control unit to monitor the road speed via the gearbox speed sensor and engine speed from an ignition input.

Finally there is a vacuum system by which the electronic control unit controls the engine speed.

Now let us see how it works. When the control switch is moved from OFF to ON it completes a circuit providing power to the other control functions.

Moving the switch to SET, RES or OFF merely sends further signals to the electronic control unit. The electronic control unit analyses these signals compares them with existing vehicle speed information and operates the actuator through the vacuum system.

This system comprises a pump which provides vacuum to the actuator to control its position.

The vacuum system incorporates two vent valves which are incorporated in the brake and clutch switches. These valves open, venting the vacuum system when either pedal is depressed, providing an instant response from the cruise control.