Rocket Fuel

Tech Talk v39 – The Engine: Part 2

The Brains in the Elio Engine:  How the Elio Engine Management System Blends Fuel-Efficiency, Torque and Power

Last week we talked about Elio’s reasons for designing their own engine. This week we will discuss the engine management system, the “brains” of the powertrain. As we work toward reaching our target of 84 MPG, the engine management system plays a crucial role. It ensures that various engine components are working together to achieve maximum efficiency.

There are many components in the control system of the Elio Powertrain. The first is the engine control unit (ECU) which also can be incorporated into a powertrain control module (PCM). The ECU is a computer with software that controls the various subsystems on the engine. These subsystems include fuel injection, ignition, variable valve timing (VVT), throttle, exhaust gas recirculation (EGR), positive crankcase ventilation (PCV) and evaporative emissions canister (EVAP). To accomplish this task the ECU must receive many signals (information) from various sensors such as accelerator pedal position, throttle position, intake manifold air temperature, intake manifold pressure, crank position sensor, cam position sensor, oil temperature and the coolant temperature sensors.

ECU Picture

The fuel injection system precisely controls the air fuel mixture at an optimized balance of engine fuel efficiency and emissions control efficiency. This control is accomplished by changing the duration of the fuel injector pulsewidth and the pressure in the fuel rail.

The ignition system is comprised of coils and sparkplugs. The coils are charged (filled with electrical energy) by the ECU with low voltage (<15V) and current (<7amps for 1 – 2 milliseconds). When a spark event is needed, the coil discharges instantaneously at a very high voltage on the order of 30 kV or more. This electrical energy jumps the gap in the sparkplug and this spark ignites the air-fuel mixture.

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The crankshaft position sensor measures the crankshaft position as the engine rotates. The CAM sensor measures the camshaft position. The crank and cam positions are used to make sure the spark and fuel injectors are firing and injecting at the correct time.  Once the ECU has sensor data, it then makes a calculation and outputs the correct spark timing and fuel injector pulsewidth. The calculations that take place are all about operating the engine at the best operating point.

The optimal spark time and injector time will be set during the calibration of the engine while running on a dynamometer. The calibration team will measure the burn rate, the combustion efficiency and maximum brake torque. The oil and coolant temperature sensors are used to modify the spark and injector timing based on engine operating temperatures and environmental temperatures.

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One of the potential technology features of the Elio engine is the two-step valve lift system (VVA) which uses switching tappets. The two-mode tappets allow switching between two different valve lift profiles which allows the engine to change its airflow capacity.  One mode increases airflow capacity for more torque/power in city driving. The other mode decreases airflow to reduce pumping work during light load operation such as highway driving.

The switching tappet consists of two nested housings, the inner and outer housing. The inner housing is actuated by the center cam lobe while the outer housing is actuated by lobes on either side of the center lobe. The outer housing presses against a lost motion spring when the hydraulic actuation circuit is at low pressure. In this mode the center lobe determines the valve lift. Both housing parts can be linked by means of a coupling mechanism, a high pressure hydraulic chamber. In the locked condition, the high lift is transmitted via the outer housing to the valve. As in the standard tappet, valve lash adjustment can be by hydraulic or mechanical means.

The Elio engine uses a cooled Exhaust Gas Recirculation (EGR) system. The EGR system will be used to improve fuel consumption of the engine by reducing pumping losses and lowering peak cylinder temperatures which reduces NOx emissions. When the EGR is cooled it further reduces combustion temperatures and reduces engine knocking. This enables the engine to have a high mechanical compression ratio which helps improve fuel economy and performance. The EGR system is controlled by the ECU and will allow a specific amount of EGR into the intake manifold to be distributed into the combustion chamber.

All of these elements together will result in an engine that meets our fuel efficiency requirements, but also provides performance that our customers demand. It’s not an easy balancing act, but the world-class team at IAV is making it happen.

Part three of the engine Tech Talk series will look at the machining of the Elio prototype engine.

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