Computationally Efficient Model for On-Board Simulation of Heavy Duty Diesel Engines
Simulating the translatory motion of a vehicle during a gear shift gives a good
basis to evaluate performance and comfort of a gear shift. This evaluation can
be used for gear shifting strategy in an automatic transmission. A model of a
diesel engine and it’s electronic control system is developed to capture the engines
behaviour in a vehicle simulation environment. The modelled quantities are brake
torque, fuel consumption and exhaust gas temperature and are based on engine
speed and pedal position. In order to describe these outputs the inlet air flow
and boost pressure are also modelled and used as inner variables. The model is
intended to be implemented on board a vehicle in a control unit which has limited
computational performance. To keep the model as computationally efficient as
possible the model basically consists of look-up tables and polynomials. First order
systems are used to describe the dynamics of air flow and exhaust temperature.
The outputs enables gear shift optimization over three variables, torque for vehicle
acceleration, fuel consumption for efficiency and exhaust temperature to maintain
high efficiency in the exhaust after treatment system.
The engine model captures the low frequent dynamics of the modelled quantities
in the closed loop of the engine and it’s electronic control system. The model
only consists of three states, one for the pressure build up in the intake manifold
and two states for modelling the exhaust temperature. The model is compared
to measured data from a engine test cell and the mean absolute relative error
are lower than 6.8%, 7.8% and 5.8% for brake torque, fuel consumption and exhaust
gas temperature respectively. These results are considered good given the
simplicity of the model.
Per Darnfors and Alfred Johansson
2012
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Last updated: 2021-11-10
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