A New Approach for Designing and Testing Engine Coolant Pump Electrically Actuated 2020-01-1161
Fuel consumption reduction and CO2 emissions saving are the present drivers of the technological innovation in Internal Combustion Engines for the transportation sector. Among the numerous technologies which ensure such benefits, the role of the cooling pump has been recognized, mainly referred to the possibility to improve engine performances during warm up. During engine homologation, an additional benefit on the fuel consumption can be also reached reducing the energy demand of the pump. In fact, during the cycle, propulsion power requested by the vehicle is low and the importance of the energy absorbed by the pump became significant, since the pump operates far from its maximum efficiency. Indeed, the pump is usually designed at high load working point (Best Efficiency Point, BEP), where the cooling request is maximum: starting from these design conditions, when the pump operates at lower engine coolant requests (as it happens very frequently and more specifically during the homologation cycle of the engine), its efficiency can be very low. This aspect invites pump designer to take care about the choosing of the design point, privileging engine operating points which are more frequent during real operation.
In this paper, a dynamic test bench for engine coolant pumps has been developed and engineered. It has been linked to a software procedure which evaluates, according to a vehicle’s mission profile, the propulsion power of the vehicle, the engine speed and, definitively, the pump speed. The knowledge of the cooling circuit and, specifically, the pressure-flow rate relationship of the circuit, allows the calculation of flow rate and pressure delivered in each point of the mission. From the pump efficiency, the instantaneous mechanical power requested by the pump can be calculated, i.e. that subtracted from the engine. The integral of this instantaneous power allows the calculation of the energy requested by the engine over the sequence of operation.
The dynamic pump test bench allows to reproduce the real working condition of the pump for a specific sequence of engine operating conditions, and in particular, when this sequence is represented by a homologation WLTP, the one on which emissions and CO2 are measured and referred to an unit of distance (passenger or light duty vehicles). When a Real Driving is specified (as it happens to evaluate the emissions in real driving, RDE), the test bench is able to reproduce the real sequence of operation of the pump as, consequently, the measurement of all relevant quantities.
An electrical water pump was designed following the new design concept over a WLTC cycle. Thanks to the comparison between electric and the hydraulic cumulated energy, efficiency of the pump was identified during dynamic working conditions. These experimental results claimed the necessity of a novel design of the pump having resulted an average propulsion power of the pump over the WLTP 10 % lower than the value which would be associated to a pump designed at its BEP when the engine power is maximum.