Double-declutching

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In motor vehicles with a manual gearbox, double-declutching refers to a process when engaging a lower gear and "double clutch" means a process when engaging a higher gear.

General

Downshifting with double-declutching and upshifting with double clutches is considered to be essential when engaging non- synchronized gears in transmissions . The reason for this is that such transmissions, in contrast to synchronized transmissions, are not able to automatically adapt the higher speed of the lower gear to the lower speed of the gear above. The driver has to adjust the speed of the transmission to the faster-turning lower gear by means of an intermediate gas surge. Conversely, he has to adapt the speed of the transmission to the slower-turning higher gear by double clutching.

method

The process of downshifting takes place in five steps:

  1. Depress the clutch pedal
  2. Move the shift lever to the neutral position
  3. Release the clutch pedal again
  4. Briefly accelerate
  5. Depress the clutch pedal again and engage the lower gear

When the shift lever is in neutral and the clutch is closed, part of the transmission is coupled to the engine speed while the other part is coupled to the speed of the wheels via the differential. The double-declutching accelerates the speed of the engine-side transmission branch and brings it to the same speed (synchronous speed) as possible as the wheel-side transmission branch, so that shifting can also be carried out without synchronizer rings or with defective synchronization.

The process of upshifting is similar:

  1. Depress the clutch pedal
  2. Move the shift lever to the neutral position
  3. Release the clutch pedal again to bring the speed of the transmission shaft to the appropriate and now lower speed of the now higher gear
  4. Depress the clutch pedal again and engage the higher gear

Sometimes the double clutch can be omitted because the viscosity of the gear oil also brakes the auxiliary shaft somewhat.

Double-declutching in modern transmissions

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The gears in the transmissions of today's cars are completely synchronized by synchronizer rings ( synchromesh transmission ), which means that the double-declutching has lost a lot of its importance. While double-declutching was still essential in cars without a synchromesh gearbox, it is almost no longer used in normal road traffic and is no longer part of driver training. As a rule, it is only used for sporty driving, on the one hand to prevent the car from becoming restless due to load change reactions, on the other hand to optimize the shifting process (keeping the speed when downshifting on a hill or enabling better acceleration after the shifting process), as well as to protect the clutch (which then only slips briefly) and the synchronization mechanism. Even in normal road traffic, the double-declutching spares the synchronization mechanism and the clutch considerably.

With sequential transmissions, double-declutching is usually given automatically in sport mode. This overcomes the deceleration torque of the motor, so that the carriage accelerates again more quickly and the cardan shaft is protected (no load changes). With automatic transmissions, on the other hand, double- declutching is unnecessary because of the torque converter .

Double domes

The double clutch is not necessary if you take the throttle back discreetly. When the load changes in the transmission, the gear can be pulled out without using the clutch. Then continue as described above. By accelerating, the drive plate is brought to the correct speed, disengaged, the lower gear engaged and re-engaged.

Special characteristics

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