Engine torque: Notes

Fig 1: Identifying Engine Torque Components

Courtesy of SAAB-SCANIA OF AMERICA, INC.

Fig 2: Communication Diagram - ECM To P-BUS

Courtesy of SAAB-SCANIA OF AMERICA, INC.

The engine control module (ECM) converts the air mass/combustion into information on engine torque. This information is transmitted on the P-bus.

The ESP control module uses the engine torque information to calculate the current drive wheel torque and detect faults in the system.

Engine speed and vehicle speed are used to calculate the current ratio for cars with manual transmission. The control module in cars with automatic transmission transmits information about the selected ratio on the P-bus.

When engine torque and the current ratio are known, the control module can calculate the drive wheel torque. This is used to calculate the magnitude of any braking and limiting of engine torque.