Reasons for Clutch & Launch switches

Question:

What are the reasons for Clutch & Launch switches?

Answer:

Clutch Switch is for sensing pressure on the Clutch pedal. This effectively allows the ECU to sense that the driver has rested his foot on the clutch and potentially disengaging the clutch mechanism. This allows the ECU to do two things, prevents the gearbox doing down shifts and damaging the engine, e.g. if the car was in top gear the driver rests his foot on the clutch, the engine is disengaged from the clutch and the rpm drops. The driver could effectively then downshift from top to 1st gear, let the clutch up and obviously destroy the engine.

The second use for this switch is that when the driver is in the car, the system senses that the clutch is being pressed and therefore allows the paddles to select a gear safely.

If at least one wheel speed sensor is fitted, a minimum speed can be programmed into the ECU so that the engine can go down the gearbox. This is normally programmed to the maximum rpm below the rev limiter in first gear e.g. if 1st gear was 60mph at 10,000rpm*, then unless the wheel speeds were below 60mph when the clutch was pressed, then no gear changes will happen until below that speed.

*Please note that this is designed to help save damage to your engine, but it cannot protect against rate of change damage e.g. if your engine is at tickover for example and the wheel speeds are at 60mph, when the clutch is released at tickover, the engine acceleration is likely to be too great and the valve train will lose control, this can cause valve to piston contact and damage.

If a clutch switch is not fitted, then the driver would need to press the neutral button to tell the ECU that he is ready to select a gear, he then pulls an up or down paddle whilst holding the neutral button. The ECU will then select a gear.

The Launch switch is used to control Launch and provided the Launch circuit is fitted and set up, this can be used in a similar way, but you must remember that Launch is designed to operate when the clutch is on the floor and therefore if the driver simply rests his foot on the clutch pedal then he can actually have the clutch disengaged but not have triggered the switch and therefore downshifts could still occur and damage the engine.

So my suggestion is normally Clutch switch is most important for safety and should always be considered the first option and the Launch switch is for Launch and only used as a back up.