Comparison of Transmissions
Every conventional vehicle drivetrain today, is equipped with a torque converter since either the propulsion characteristic is not suitable or the required control area cannot be realized without conversion or if at all, only in association with large losses. The selection criteria for torque converters, Similar to engines, can be classified into the three areas:
Operating Behavior,
Economy, and
Influence on the Environment.
The following transmissions will be compared:
-Manual Transmission in Countershaft Design (MT)
-Automatic Transmission with Hydrodynamic Converter (AT)
-Double-Clutch Transmission (DCT)
-U Transmission (UT)
-High performance Hydrostatic Transmission (HT)
a) Operating Behavior
In order to have a high excess torque in each operating area, the transmission should convert the delivery map of the reciprocating engine in such a way that the maximum torque curve approaches the ideal power curve. CVTs fulfill this requirement. In CVTs an improved approach to the ideal power curve can be achieved by raising the number of gears.
The shifting time of manual transmissions with 0.5-1.0 s corresponds to that of automatic transmissions. CVTs continuously adjust to the particular driving condition. The shifting time here, depends on the magnitude of the desired change in ratios. Since extreme adjustments are required only rarely (kick down), CVTs have advantages when it comes to shifting time.
Manual transmissions that can only be shifted by a torque interruption, produce high acceleration and deceleration forces when shifting gears. These forces generally depend on how the clutch is operated by the driver. In automatic transmissions the dependence on the driver does not exist. In the ideal transmission, shifting from one gear to another would take place continuously variable and hence without jerks. When operating CVTs in practice, an essential problem consists in the driver expecting an increasing number of revolutions with a rising vehicle speed when accelerating the vehicle. The CVT with a subjectively complete separation of engine and vehicle behavior is contradictory to the usual impression and is hence not really considered as pleasant.
The shifting and information expense of the driver is high only in manual transmissions. The remaining systems are run automatically. With regards to the convenience of operation however, the degree of automation and the possibilities for intervention result only in minor differences.