There are several ways in which a hill-start control system can be designed. Each has its advantages, each has its disadvantages. The techniques most commonly used to implement hill-start control are: incline detection, backward motion detection, clutch detection, accelerator detection, brake detection and engine torque detection.
Clutch detection: One of the most obvious applications of hill-start control is in cars with a manual transmission or stick shift. To start a car with a manual transmission, it's necessary to step on a clutch, which disengages the engine from the transmission. While the engine is disengaged, the car is no longer held in place by the engine's braking power, and if the brakes are also disengaged, which is usually the case while accelerating, the car can roll freely, especially if it's on an incline.
Incline detection: If a car is stopped on an incline while the motor is still running, there's a good chance that some kind of hill-start control will be needed. A sensor that detects an incline of more than a certain amount -- say, three degrees or more -- can send a signal to the hill-start control indicating that the vehicle has the potential to start rolling. The disadvantage of incline detection is that sometimes a car maybe on an incline without needing the hill-start control -- for instance, when a tire slips into a pothole.
Engine torque detection:This simply detects whether the engine is producing sufficient torque to accelerate the car forward. If it is, then the car is no longer in danger of rolling backward and the hill-start control is turned off.
Brake detection: This detects whether the brakes are in use and whether there is sufficient braking force to hold the car in place.
Backward motion detection:Although it isn't strictly necessary, some systems may include a means of detecting the fact that the car is rolling backward.
Systems that use incline detection work roughly like this: The incline sensor detects when the car is on a hill. A brake sensor determines whether a brake is being applied. If it's not, then the car is in danger of rolling backward, so the system automatically activates the vehicle's brakes to keep the car stationary. In a vehicle with a manual transmission, clutch detection and brake detection can be used together to sense when the vehicle is in danger of rolling backward and the brake can be activated.
But how do these various forms of detection work? And how are the brakes activated by the hill-start control system? We'll talk about that on the next page.