|The Twizy Renault Sport F1 concept. Click to enlarge.
Renault engineers have built an “F1” concept version of the Twizy EV featuring a Kinetic Energy Recovery System (KERS) based on the solution used by Renault-powered Formula 1 race cars.
Twizy Renault Sport F1 is consequently equipped with two electric motors—i.e. the original motor (17 hp/13 kW) onto which the F1-style KERS with its own motor has been grafted. When the KERS is activated, Twizy Renault Sport F1’s power output climbs instantly by a factor of six, from 17 to 97 horsepower (72 kW). This boost is available for approximately 14 seconds, just as it is in the case of a Formula 1 car. Thanks to this additional power, the concept car is capable of accelerating from standstill to 100 km/h in the same time as Mégane R.S.
The KERS system, the result of close collaboration between engineers at Renault Sport Technologies and their colleagues at Renault Sport F1, comprises three main elements:
- An electric motor-generator unit (MGU) directly linked to the driveshaft;
- Specific lithium-ion batteries; and
- A KERS Control Unit (KCU).
Because the Twizy Renault Sport F1 isn’t nearly as fast as a single-seater race car, the kinetic energy produced under deceleration is insufficient to charge the KERS’ battery. To get round this problem, the engineers at Renault Sport Technologies and Renault Sport F1 developed a system that enables the battery to be charged by siphoning power from the main motor.
|The Twizy Renault Sport F1 powertrain. Click to enlarge.
|Layout of the powertrain components. Click to enlarge.
This solution gives the driver total independence over how the KERS is used. The driver can choose between two modes for the KERS used for Twizy Renault Sport F1, using the controls located on the steering wheel.
Recovery mode: with this mode activated, the electric motor functions like a conventional generator, drawing power like a dynamo to convert the mechanical energy produced by Twizy main motor into electrical energy. Up to 4kW can be siphoned off in this way to charge the battery while on the move.
Boost mode: the energy recovered using the Recovery Mode can be re-employed whenever the driver wishes by pressing on the button located on the steering wheel. This reverses the process. Instead of serving as a generator, the KERS’ motor-generator unit (MGU-K) now functions as a motor to bring a power boost to the principal motor to which it is directly linked via the driveshaft.
The MGU-K fits inside a 10 cm-diameter cylinder and can rev to as high as 36,000 rpm. The maximum power output of the MGU-K is 60 kW (approximately 80 hp). The charging process and the way the stored energy is delivered are controlled by a control unit which is itself linked to Twizy Renault Sport F1’s ECU (Electronic Control Unit).
When the system is triggered, the maximum revs of Twizy’s motor rise to 10,000 rpm for a top speed of 110 km/h (68 mph).
The KERS is equipped with its own battery capable of very short charge/discharge cycles. The package weighs barely 30 kg (66 lbs), battery included.
Given that the peak revs of the KERS and Twizy’s principal motor are 36,000 rpm and 10,000 rpm respectively, the connection between the two was one of the chief challenges of the project. Synchronisation is ensured by a 1:3.6 reducer gear which uses the same drive gear as that of the F1 V8 engine.
The KERS uses a pressurized lubrication system to enable the bearings to withstand peak revs of 36,000 rpm. Meanwhile, in order to prevent the KERS battery from overheating despite the constraints to which it is exposed, Twizy Renault Sport F1 is equipped with water cooling. Both these systems are existing Renault Sport Technologies solutions.