|Lotus 414E hybrid. Click to enlarge.|
Lotus has begun testing of its Evora 414E plug-in series hybrid technology demonstrator. (Earlier post.) The Evora 414E is powered by two EVO Electric motor packs driving the rear wheels through an Xtrac transmission with a 17 kWh battery pack that can be charged by the Lotus range extender engine or directly from the grid.
In normal driving, Evora 414E will run purely on electricity stored in the battery pack for up to 30 miles (48 km). With the Lotus range extender and the electric traction motors powering the vehicle through an Xtrac 1092 transmission, the Evora 414E is targeted to produce 55g of CO2/km emissions on the NEDC.
|Cutaway showing location of major powertrain elements. Click to enlarge.|
The supercharged Lotus 1.3-liter, 3-cylinder range extender engine was design-protected to run on either gasoline or renewable bio alcohol fuels (methanol and ethanol). It drives an EVO electric generator which produces electrical energy to either charge the battery pack or power the EVO traction motors directly.
The supercharged version of the range extender uses a belt-driven centrifugal supercharger to produce 50 kW peak electrical power at 3,500 rpm, with a naturally aspirated version producing a maximum 35 kW. The engine is optimized to generate power at engine speeds between 1,500 and 3,500 rpm allowing a lightweight simple 2 valve per cylinder engine architecture and eliminating the need for a complex 4 valve per cylinder design.
(Lotus plans to offer the range extender in both 3- and 2-cylinder versions, with output of 50 kW, 35 kW and 20 kW.)
|Range extender engine and generator. Click to enlarge.|
The generator supplied by Fagor Automation is driven directly off the crankshaft to reduce weight, package size and cost. The engine, generator and power electronics are controlled using a Lotus controller to improve communication and efficient running of the systems.
Should the driver require more performance, under hard acceleration, for example, the electricity will come from both the battery storage and the small range extender engine.
Total system torque is 1,000 N·m (738 lb-ft); power is 408 hp (304 kW). The 414E accelerates from 0-60 mph in around 4 seconds, with a top speed of 130 mph (209 km/h). (As a comparison, the 2010 Tesla Roadster featured torque of 400 N·m for the Sport model; the four synchronous motors in the coming Mercedes-Benz SLS AMG E-CELL (earlier post) are currently targeted to deliver 880 N·m of torque.)
The car has a simulated paddle shift gear change offering ultra quick gear changes reminiscent of a dual clutch transmission. This enhances the driver interaction with the vehicle and provides a driving experience similar to current internal combustion engine high performance sports cars, Lotus says. The Evora 414E Hybrid uses a column mounted paddle shift to simulate the gear change and a synthesized engine sound changes frequency with virtual gear selection.
The drive torque is also modulated to simulate a physical feeling of a gearshift jolt. The virtual gearshift simulation, like a conventional gearbox, is used to change the driving characteristics and response of the vehicle.
This offers the driver the ability to control the vehicle deceleration by simulating engine braking through a virtual downshift in gears. Unlike true engine braking, the Lotus system does not dissipate the energy of the moving vehicle through internal engine friction but uses the electric motors to regenerate the energy back into the battery. While many electric and hybrid vehicles provide engine braking, this is generally at a fixed rate or pre-selected rate. In some driving situations this can either be too aggressive, slowing the vehicle unnecessarily, or too light, requiring additional braking application.
The Lotus system effectively allows the driver to select the appropriate level of regeneration by simulating stepping down by one, two or even three gears. The simulation of engine braking through both the gear noise change and the retardation of the vehicle is fully intuitive to a driver familiar with a conventional gearbox, according to Lotus. The simulated gear change capability can be selected for greater driving involvement or switched off for more relaxed driving.
Simon Corbett, Principal Vehicle Dynamics Test and Development Engineer at Lotus Engineering, has been doing the majority of the development testing over the last few weeks and comments:
The Evora S has 400 Nm of torque which in such a lightweight car is already a healthy figure. But the Evora 414E has two and a half times that amount! The acceleration sensation is almost indescribable, the surge of torque is like an ocean wave!
Group Lotus plc, is based in Norfolk, UK, and has three operating divisions: Lotus Cars, Lotus Engineering and Lotus Racing.
Lotus Cars builds world class, high performance sports cars including the award-winning Evora, the iconic Elise and the stunning Exige. Lotus New Era, the future product line-up, was unveiled in Paris on 30th September 2010 featuring the new Esprit, Elan, Elite, Elise and Eterne.
Lotus Engineering provides comprehensive and versatile consultancy services to many of the world’s OEMs and Tier 1 suppliers and is an internationally recognized automotive engineering consultancy.
Lotus Racing (formerly Lotus Motorsport) operates the motorsports activities of Lotus and includes the strategy to return the Lotus name to a great number of series including endurance racing with GT2, GT4 and LMP2, single seater racing with GP2, GP3 and IndyCar. Lotus also competes in Formula 1 with the Lotus F1 Team, racing in the iconic Black and Gold livery.