Browse Publications Technical Papers 2012-28-0031
2012-01-09

Self-Adjusting Clutch for the 2 nd Generation 2012-28-0031

For years the trend in engine development has been toward higher torques while keeping piston displacement nearly constant. Because the space available has remained practically constant, this development has led to a clear rise in the performance density of the clutch system. Torque capacity has thus increased by about 50 % while clutch size has remained steady (Figure 1).
The loads on the power train and thus also on the clutch system have increased markedly. This trend necessarily leads to higher release loads during clutch operation.
One of the first responses to this development was the LuK SAC (self-adjusting clutch) with loadcontrolled wear adjustment. In the passenger car segment, SUV applications, off -road models and smaller vans in particular set high requirements for wear resistance. The use of the SAC has proven itself in these vehicles because of the high torques and the high running performance achieved in past several years. Despite rising torques, the SAC is also widely used in the area of passenger cars because of the moderate release loads.
The first development goals of the SAC were:
  • To increase the wear range (longer service life)
  • To reduce the operating load (comfort)
  • Downsizing
  • To reduce the bearing stroke (reducing space and cost)
Increased torque capacity with continued moderate release loads, or, alternatively, the ability to reduce the difference between the maximum and minimum release load (drop-off) - these are the characteristics of the SAC2. This has been implemented by means of the degressive leaf spring to connect the pressure plate with the cover and the sensor fingers on the main diaphragm spring. The sensor load of the degressive leaf springs is thus introduced via the pressure plate. At high axial excitation of the crankshaft - a common phenomenon in newer engines - the system can, however, be dynamically excited in connection with the mass of the pressure plate.

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