Toyota has revealed the full powertrain details of the Yaris Hybrid-R concept that it teased a few weeks ago. The intriguing concept uses a 420-hp 4WD driveline that's derived from racing. In an interesting twist, Toyota uses a combination of super capacitor and motor-generator, in place of the battery pack that typically powers the motors in contemporary hybrids.
Toyota says that the super capacitor has a higher power density than an NiMH hybrid battery, along with faster charge/discharge speeds. This makes it suitable for the fast bursts of boosting power needed, both in the TS030 Hybrid race car and in the Yaris Hybrid-R, which Toyota envisions as a track-focused hot hatch. The super capacitor is charged via regenerative braking provided by the dual rear electric motors.
Each 60-hp motor is mounted at a rear wheel. These aren't electric mode, fuel economy-boosting supplements, but performance-enhancing boosters designed to quicken acceleration. In this capacity, they assist the 300-hp 1.6-liter four-cylinder turbo "Global Race Engine". That engine is mounted up front and works through a 6-speed sequential gearbox.
By mounting electric motors at each rear wheel, Toyota has developed a system that can split the torque, increasing cornering and handling capabilities. The automaker explains this more concisely than we can hope to, so we'll leave it to it:
"Depending on the radius of the curve, the system can send more torque to the outside rear wheel allowing higher cornering speeds into the corner (middle-speed curves), apply more braking force to the inside wheel (fast curves), or even brake and accelerate each wheel independently (slow curves) to adjust the yaw effect for a better line, to limit steering angle, and understeer."
As Toyota mentioned in its original teaser, the Yaris Hybrid-R has two driving modes, one for road and one for track. In road mode, the super capacitor powers the electric motors for boosts up to 10 seconds in duration. The combined power of the electric motors is slashed to 40 hp. In track mode, the motors shoot their full 120 horses out for up to five seconds, providing short, potent bursts.
The Hybrid-R has a third 60-hp motor, a non-drive unit. Located between the engine and the transmission, this motor is purely a generator, sending power to the super capacitor during deceleration and acting as a traction control device. In the latter role, the motor-generator sends power directly to the rear motors in cases where engine power and torque threaten to overwhelm the front tires and destabilize the car. The excess torque is converted into electric energy and routed to the rear wheels.
A 420-hp Yaris hybrid hot hatch with racing technology seems like the quintessential "never going to build it" concept car, but equally strange things have been known to happen. At the very least, you can look forward to moving beyond sketch and onwards to real, live photos when it debuts at the 2013 Frankfurt Motor Show.