ECH-26
< SYSTEM DESCRIPTION >
[HRA2DDT]
SYSTEM
Air Conditioning Power
The amount of power absorbed by the air conditioning is useful for the engine control to compute the torque
requirement for air conditioning. Therefore, ECM can adapt dynamically the engine speed regulation depend-
ing on the load variations.
The power absorbed by the air conditioning depends on the refrigerant pressure and the compressor speed.
The air conditioning system power correction for idle speed regulation avoids engine speed undershoots and
overshoots at the compressor compressed volume variation.
Alternator
ECM controls idle speed depending on charge status of alternator.
MINIMUM AVAILABLE TORQUE
The minimum available torque is used for the minimum driver set-point calculation and the intersystem infor-
mation.
The minimum torque is designed with a hyperbolic shape depending on the difference between the engine
speed and the idle speed set-point:
• When the engine speed is under the idle speed set-point, the minimum torque is equal to the hyperbolic
torque which increases to avoid an engine stalling.
• When the engine speed is over an engine speed threshold, the minimum torque reaches the torque for the
minimum manifold pressure with a ramp.
The torque for the minimum manifold pressure is designed to avoid any oil consumption (oil vapor back up in
the intake manifold).
It is estimated in function of the engine capacity displacement, the manifold air volume, the manifold air pres-
sure, the manifold air temperature, the cylinder fill-up efficiency, the ignition efficiency and the number of cylin-
ders. It is corrected in function of the coolant temperature to avoid ‘poor combustion’.
When the engine starts, a specific torque set-point is calculated to ensure the engine start. This torque is
dependent of the engine speed and the coolant temperature.
At first, a calculation of the starting torque value is performed. In case of a difficult start (too long), this torque
may be increased thanks to ramp.
The start torque offset is progressively set to zero to ensure a transition with the current torque set-point.
MAXIMUM AVAILABLE TORQUE
The maximum available torque results of a minimum selection including all powertrain constraints:
• Transmission torque limitation
• Maximum engine torque
• Torque reduction for the heating protection
• Low gasoline level in the tank
Transmission torque limitation
This limitation is the maximum torque to protect the transmission from a mechanical overload:
• For a manual transmission, the limitation value of the torque is function of the engine speed and the trans-
mission ratio.
• For an automatic transmission, the limitation value is directly supplied by the automatic transmission.
Maximum engine torque
The maximum torque depends on the engine speed and fail-safe mode of the throttle valve. This limit is com-
puted and corrected with:
• Number of available cylinders
• Intake air temperature
• Atmospheric pressure
• Engine speed
• Over-torque limit
• Torque losses (friction, pumping, etc.) to calculate the maximum effective engine torque
Torque for the heating protection
This torque limit is dedicated to the protection of the engine from an overheating. It depends on the engine
speed, the engine coolant temperature, the intake air temperature and the vehicle speed.
Protection torque
This torque is computed in function of the low gasoline level in the tank and the engine speed.
Fail-safe
The ECM limits a engine torque in case of malfunction of engine component or ECM.