Abstract
This paper presents an innovative control strategy developed at IFP Énergies nouvelles (IFPEN), on a plug-in hybrid electric vehicle (PHEV) demonstrator car, which guarantees, under conditions, the use of the electrical boost during accelerations, without limiting the number of full-throttle accelerations with full performance.
The performance of a hybrid vehicle can generally be set in two ways :
- the performance equals those of the internal combustion engine.
- the performance equals the sum of the power provided by the internal combustion engine (ICE) and the electric path.
Using the former one forbids enhancing the vehicle performance by using the electric boost, and the internal combustion engine has to be designed to provide the maximum wheel power, which generally leads to higher fuel consumption.
Using the later one generally leads to lower fuel consumption by enhancing the engine operation (higher specific torque demand). However, those performances are not perennial: the available wheel power generally decreases after several accelerations due to battery discharge, and then finally equals the ICE maximum power.
For instance, such a behaviour has been observed on the Japan version of the Toyota Prius (1). Figure 1 shows measurements of several full-throttle accelerations in a row : once the battery SOC is low, the dynamic performances are lower.
The last acceleration showed almost no SOC deviation, which means almost no electric boost was available.
The presented strategy enables the combination of both advantages: by guaranteeing the availability of the electric power, the vehicle offers a reliable performance level, which is higher than the power offered by the internal combustion engine. At the same time, fuel consumption can be lowered by the use of an adapted, less powerful engine.
After introducing the principle of operation of such a strategy, the paper will present some simulation results, showing:
- the performance potential of such a strategy
- the CO2 additional cost of performance enhancement by using this strategy
- a comparison of this consumption/performance compromise with a traditional approach based on a higher ICE sizing
Conclusions will be discussed regarding strategy implementation in a vehicle:
- limits of validity
- best sizing of the vehicle, its architecture and its components to use this strategy · example of potential applications.
KEYWORDS: Hybrid, Dynamic Performances, Boost Consistency, Sizing Methodology