Lotus Evora 414E Hybrid conceptFebruary 25, 2010
Green-Car-Guide.com regards the Lotus Evora 414E Hybrid concept as one of the most significant electric car concepts that we’ve seen, especially coming at the same time as the government has confirmed grants up to £5,000 towards ultra-low emission cars.
This is because with this concept, Lotus has made a real effort to address many of the things that drivers don’t like about electric cars – from the range limitation issue to the lack of excitement without a conventional gearbox.
The Evora high performance technology demonstrator has a battery and electric motor together with a petrol engine that acts as a generator.
If you’re worried that this will be a slow electric car, think again; it’s called the 414E Hybrid because it produces 414 PS of power, and it gets from 0-60 mph in less than 4 seconds. It also comes with a sports mode with a 7-speed paddle shift – an interesting and innovative concept for an electric car.
The 414E Hybrid concept has two electric motors driving each of the rear wheels independently via a single speed geartrain, with electrical power stored in a lithium polymer battery pack.
Additional range is provided by the Lotus Range Extender engine, a 1.2 litre, three-cylinder unit – which is actually the same engine as appears in the recently announced Proton hybrid city car concept.
The generator converts mechanical energy to electrical energy to replenish the battery pack charge and provides additional vehicle range in a small lightweight package. The generator is also used as a motor to start the range extender engine.
For everyday commuting journeys, up to 35 miles can be travelled using battery power. The battery can be charged overnight using a conventional domestic mains supply through a socket concealed by the rear number plate. This permits the vehicle to operate with zero tailpipe emissions.
For longer journeys that exceed the battery capacity, the highly efficient range extender engine is used as a generator to supply the motor with electrical power and top up the battery, and this means that over 300 miles can be travelled before the petrol engine needs to be refuelled, or the battery needs to be recharged from the mains.
This is a similar principle to that in the forthcoming Vauxhall Ampera, however a key difference with the Lotus is that the Lotus Range Extender engine is designed specifically for series hybrid vehicles.
The engine, which provides 48 PS of power via the integrated electrical generator, has reduced engine mass (85 kg), assembly costs, package size and improved emissions and engine durability. It can be operated on alcohol-based fuels and/or petrol.
All the operation and management of the range extender engine, the power management of the batteries and motor control are controlled by Lotus’ electronic control units and software systems. Full energy management of all the operating systems is the key to maximising performance and operation while minimising energy consumption and CO2 emissions.
Lotus says that their solution is far more energy efficient, weight efficient and cost effective than fitting the vehicle with a larger and more expensive battery, which for the majority of short journeys is a redundant weight, and which increases energy requirements.
With regard to the total lifetime CO2 emissions of the vehicle, including the energy required to manufacture and run it, the range extender solution has a lower overall CO2 footprint than a fully electric car of comparable performance and operating range running with a larger battery.
The lithium polymer battery pack is mounted in the centre of the vehicle for stability and safety and the single speed geartrain is integrated into a common transmission housing, so enabling torque vectoring for stability control of the vehicle.
Lotus is keen to stress that the Evora 414E Hybrid provides less of a psychological step-change for people familiar with high performance cars compared to other electric and hybrid sports cars. The car has a simulated paddle shift gear change offering ultra quick gear changes reminiscent of a dual clutch transmission, while actually single speed. This enhances the driver interaction with the vehicle and provides a driving experience similar to current internal combustion engine high performance sports cars.
The Evora 414E Hybrid uses a column mounted paddle shift to simulate the gear change and a synthesised engine sound changes frequency with virtual gear selection. The drive torque is even 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. The most significant aspect that this offers the driver is 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. The simulated gearchange capability can be selected for greater driving involvement or switched off for more relaxed driving.
Integrated with the 7 speed, paddle shift transmission is the Lotus Engineering and Harman International developed HALOsonic suite of noise solutions. The first of which is Electronic Sound Synthesis. This generates engine sounds inside the vehicle through the audio system where it provides an exciting sports sound in line with the brand and nature of the vehicle together with a high level of driver feedback.
In addition, it also generates sound on the outside of the vehicle through speakers mounted at the front and rear to provide a warning to increase pedestrian safety, which is especially important for electric and hybrid vehicles which can be difficult to hear at slower speeds.
There are four driver selectable engine sounds currently on the vehicle, two of which have been designed to have characteristics of a multi-cylinder conventional V6 and V12 engine.
The Evora Hybrid also has Lotus-developed torque vectoring dynamics. Torque vectoring, which is the capacity to generate different torques at each of the driving wheels, is particularly suited to electric vehicles and significantly reduces the conflict between stability and response.
A key benefit of separate motors to drive each rear wheel individually is that this facilitates a much higher level of vehicle dynamics control. Driving the wheels with different levels of torque can not only generate all the capabilities of a conventional ESP system using energy regeneration as opposed to brake application, but it can also actively drive each wheel forward at different rates, producing a turning moment at the rear of the vehicle in addition to the steering input.
This can be used to enhance low speed manoeuvrability and ease of parking but can also be used to produce a much greater level of straight line high speed stability. Incorporating lateral sensors the system also provides stability control capabilities and levels of steering response normally only associated with heavy and expensive rear steer systems. This can provide automatic correction of both understeer and oversteer characteristics.
As well as showcasing new developments in plug-in, range-extended electric propulsion and new electronic technologies to enhance driver involvement, the concept also shows the adaptability of the Lotus Versatile Vehicle Architecture (VVA) that underpins the Evora 414E Hybrid and a dramatic new roof system and interior concept from Lotus Design. The complete chassis has remained unchanged from the Evora which maintains the structural integrity and strength performance of the original car.
All we need Lotus to do now is put the car into production.
The Lotus Evora 414E Hybrid concept will be unveiled at the Geneva Motor Show – see our full report from Geneva next week.
Keywords: Lotus Evora 414E Hybrid concept, Lotus Range Extender engine, Geneva Motor Show, Lotus Engineering, Harman International, HALOsonic.