Elio Motors, the start-up developing a $6,800, 84-mpg- (2.8l/100 km) three-wheeled vehicle with a target date of 2016, unveiled its engine prototype: a 0.9-liter, 3-cylinder unit developed by IAV. To provide its customers with high fuel efficiency and still provide the performance consistent with today’s passenger vehicles, the Elio Motors engine must operate efficiently at two different loads—lower loads representative of highway cruising, and more demanding loads associated with the fast starts of city driving.
The original engine concept for the three-wheeler was to take the Geo Metro engine and create a template for the Elio engine; the Metro engine was compact, perceived to be efficient, had the correct power requirements, and is relatively inexpensive to produce. As the team began to dive into some of the details and changes to meet the desired Elio targets, it found that the Geo Metro engine would not meet the fuel efficiency targets to enable the vehicle fuel economy goal of 84 mpg highway.
|Current prototype of the Elio. Click to enlarge.|
Too, the Elio is considerably lighter than anything else on the market today; the Geo Metro engine was optimized for running at the higher load used in a heavier and larger vehicle.
After running computer simulations, it was apparent that a new engine design was needed to work with the Elio vehicle to achieve this goal and still maintain a top speed of more than 100 MPH with goal of 0-to-60 MPH in less than 10 seconds.
We are literally trying to reinvent the auto industry, so why go the conventional route and rework someone else’s engine? There really was nothing available that combined the speed and power that we want and our customers deserve. IAV came through with an outstanding execution of today’s best technology that will be a cornerstone to delivering a world-class vehicle.—Paul Elio, President and CEO of Elio Motors
The engine development program focused on determining the technical features needed to achieve the targets. The team looked at the Geo Metro design to see if modernizing the 30-year-old strategy would make it more efficient. The outcome was to maintain the three cylinder architecture, but update the cylinder block, cylinder heads, CAM cover, front cover, oil pan, crankshaft, camshaft, valvetrain, pistons, connecting rods, bearings and water pump to Elio specifically designed components.
This allowed the engine development team the flexibility to keep the design simple, efficient and easy to manufacture while enabling all of the major fuel economy related attributes—combustion system, friction and pumping energy—to be enhanced. Many parts were identified as cost and risk reductions to be sourced as currently produced off-the-shelf components.
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 (sourced from Continental) and will allow a specific amount of EGR into the intake manifold to be distributed into the combustion chamber.
The ECU controls the various subsystems including, in addition to the EGR unit, fuel injection, ignition, variable valve timing (VVT), throttle, positive crankcase ventilation (PCV) and evaporative emissions canister (EVAP). To accomplish this task, the ECU receives signals 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.
The final parts were recently machined and assembled and the prototype was started and run through several tests on a dynamometer.
Crash testing simulation. Recently, Elio Motors and Altair simulated a belted occupant and driver airbag in a frontal crash. Previous crash simulations for the Elio were done with only the vehicle structure. The addition of the simulated occupant, airbag and belts helped the engineering team understand the predicted occupant kinematics for a given crash pulse, make design changes and reevaluate to support achieving safety performance requirements.
A crash pulse is a time-history signature of a vehicle collision event and its characteristics such as shape, peak acceleration and duration influence occupant safety.
This model is referred to as the Full Vehicle Model with Restraints and Crash Dummy. The crash dummy is the Hybrid III 50th percentile anthropomorphic test device (ATD) that is the most commonly used worldwide (and required by Federal regulation in the US) for frontal impact testing and simulation. The Hybrid III standard crash dummy approximates an average North American male, about 5'9" tall and weighing approximately 172 lbs (78 kg).
One of the keys to good occupant safety performance is how the crash energy is being managed. This is done using a crush zone. An effective crush zone is an area of the frame that is designed to crush/collapse/stack or deform in a controlled manner so that the structure will absorb as much of the impact energy as possible. The Elio’s front rails are designed with effective crush zones to manage the impact energy and allow the occupant restraint system to perform well. The front rails can be tuned through design, crush initiators and reinforcements to give the ideal crash pulse for enhanced occupant safety.
In addition to energy management, it is critical that the structure be strong to prevent intrusion into the occupant compartment. The Elio is designed using a spaceframe architecture, which utilizes a set of tubular steel struts, custom fitted and arranged in straight or curved geometric patterns for shape and/or strength. Optimally positioned, the struts will promote the greatest rigidity in structure for three-dimensional load-bearing points. The sturdy spaceframe construction along with the use of advanced high strength steels (i.e. Martensite, Boron and High Strength Low Alloy steels), provides enhanced structural strength to minimize intrusion into the occupant compartment during an impact.
Elio and its manufacturing partner Comau will build the vehicle at a manufacturing facility in Shreveport where General Motors previously built the Hummer H3 and Chevy Colorado.
More than 40,000 people have put down money to reserve a spot to purchase one of the Elio vehicles.