Fast engine torque control, increasing load
The fast method of control is used when the engine load changes rapidly, e.g. idle when turning the steering wheel rapidly so that the power steering pump puts a load on the engine. The increased torque requirement from the engine must then be compensated by a rapid increase in engine torque or the idling speed will drop. This fast compensation is done using previous ignition timing, giving higher torque.
Scheme 601
After the fast compensation, ECM will gradually increase the throttle area in order to get more air mass into the engine while the ignition is retarded slightly. This allows ECM to maintain a torque reserve so that it can again perform fast compensation for changed engine loads.
Scheme 602
Slow torque control, load change
Slow engine torque control is used when driving under constant load, i.e. when the load does not vary or varies slowly. In this case, ECM operates mainly with throttle area to regulate the engine torque.
Scheme 603
For higher torque requirements, turbo control will also be used to increase the air mass in the engine so that it produces the requested engine torque.
Scheme 604
Scheme 605
Torque control
The principle of idling control is that the engine works with a "torque reserve". Since ignition timing is retarded compared to that which would generate the best torque, engine torque can quickly increased by setting engine timing earlier. Slow changes are handled by throttle control.
Scheme 606
With an idling speed exceeding the nominal, there will be an excess of engine torque and the idling function will then request a lower value until the nominal idling speed has been attained. When the idling speed is below the nominal value, there will be a torque deficiency and the idling speed will have to be increased to attain nominal idling speed.
ECM reads the value for the torque (Nm) necessary to keep engine speed at the requested value from its memory. This value is also an indication of the engine's internal friction and is used for correction during torque calculation.
Scheme 607
Function principle, torque limitation during TCS/ESP control
ECM works with the throttle area and ignition timing control to reduce engine torque during TCS/ESP control. In the event of large limitations, turbo control will also be actuated to reduce engine torque.
Ignition timing control generates quicker torque changes, while regulating the throttle area is slower. Turbo control is the slowest.
Scheme 608
Calculation, engine torque
Engine torque is primarily calculated using air mass per combustion and engine speed. But, ignition timing and current lambda value also affect the torque calculation. Retarded ignition timing generates lower engine torque. This is the case in knock control. As regards the lambda value, there is an optimal lambda value for each operating point. If the engine runs richer or leaner than the optimal value, engine torque reduces.
Note that a lambda value lower than the optimal value (richer mixture) produces lower torque.
The calculation also takes into account the torque used by the engine itself, i.e. the internal friction. Values for air mass, engine speed, coolant temperature and idling torque are used for this calculation.
Scheme 609
Torque limitation, automatic gearbox
Engine torque must occasionally be limited for the sake of comfort in gear changing and in certain cases also for reasons of durability.
Engine torque limitation, bus from TCM
TCM determines the maximum engine torque to be allowed. During gear changing, engine torque is often reduced somewhat for comfort. Torque can also be reduced for reasons of durability.
Engine torque limitation, stalling
Engine torque for a stalling gearbox is limited to 200 Nm to protect the gearbox.
Scheme 610
Scheme 611
Torque limitation, manual gearbox
ECM calculates the current gear via vehicle speed and engine speed. The following gears are subject to torque limitation
- 1st gear
- Reverse gear
Torque limitation in the event of a diagnostic trouble code
Certain diagnostic trouble codes cause torque to be limited in order to prevent damage.
Scheme 612
Specifications
800 g jar
See also:
• INTERIOR LIGHTING AND READING LAMPS, 4D/5D