Division 5.1 Methods for establishing retarder drag losses
United Kingdom
The retarder drag torque loss is a function of the retarder rotor speed. Since the retarder can be integrated in different parts of the vehicle driveline, the retarder rotor speed depends on the drive part (= speed reference) and step-up ratio between drive part and retarder rotor as shown in Table 2.
Table 2
Retarder rotor speeds
| Configuration | Speed reference | Retarder rotor speed calculation |
|---|---|---|
A. Engine Retarder | Engine Speed | nretarder = nengine * istep-up |
B. Transmission Input Retarder | Transmission Input Shaft Speed | nretarder = ntransm.input * istep-up = ntransm.output * itransm * istep-up |
C. Transmission Output Retarder or Propshaft Retarder | Transmission Output Shaft Speed | nretarder = ntransm.output * istep-up |
where:
step-up ratio = retarder rotor speed/drive part speed
transmission ratio = transmission input speed/transmission output speed
Retarder configurations that are integrated in the engine and cannot be separated from the engine shall be tested in combination with the engine. This section does not cover these non-separable engine integrated retarders.
Retarders that can be disconnected from the driveline or the engine by any kind of clutch are considered to have zero rotor speed in disconnected condition and therefore have no power losses.
The retarder drag losses shall be measured with one of the following two methods:
- (1)
Measurement on the retarder as a stand-alone unit
- (2)
Measurement in combination with the transmission