Toyota Hybrid-R drivetrain details

At the 2013 Frankfurt Auto Show on September 10, Toyota will present a new concept car based on its Yaris hatchback that leverages the automaker’s hybrid technology developed for its TS030 Hybrid Le Mans prototype.

We’ve already had our first look at the concept, dubbed the Toyota Yaris Hybrid-R, and learned that it will feature a complex hybrid system combining a gasoline engine with an electric drive system. Now we have an in-depth look at the technology.

The Yaris Hybrid-R develops a total 313kW from a gasoline-electric hybrid powertrain, consisting of a turbocharged 1.6-litre four-cylinder engine working in parallel with two electric motors to form a through-the-road all-wheel-drive system. The setup also makes use of a supercapacitor to harvest and store energy, just like the TS030 Hybrid prototype.

The engine, which rates at 224kW on its own, is a turbocharged four-cylinder unit with direct injection and was developed by Germany’s TMG in accordance with various international sporting regulations. While the engine drives the front wheels, each rear wheel is powered by a 45kW electric motor--the same as that used in the Prius C hybrid. The two electric motors work as electric generators when the car is braking, and supplement the gas engine’s performance under high load.

As mentioned, energy recovered under braking is stored in a supercapacitor. Compared to the standard nickel metal-hydride battery used in the Prius C, the supercapacitor has a higher power density and a fast power charge/discharge speed. This makes it perfectly suited to the demands of track driving in delivering brief, immediate bursts of power.

The level of power depends on the duration of energy delivery required. So, when Yaris Hybrid-R is running in “road” mode, the supercapacitor releases energy for a maximum 10 seconds per charge, and the total power of the two electric motors is reduced to 30kW. In “track” mode, the motors reach a combined maximum of 90kW for up to five seconds per charge, reflecting the more frequent braking and acceleration in circuit driving.

But the Yaris Hybrid-R has one more electric motor. This third unit, also rated at 45kW, is located between the engine and six-speed sequential transmission. This operates as a generator, both during deceleration to feed power to the supercapacitor, and during acceleration to power the rear electric motors. The latter only happens when engine power and torque exceed the front wheels’ grip limit.

Thus, the generator works like an advanced traction control system, redirecting torque as electric energy to the rear wheels, to boost acceleration and improve handling rather than simply to limit engine power. A similar system is utilised in Ferrari’s LaFerrari supercar. The rear electric motors also improve handling; each motor can be used independently as a generator or a motor to achieve the same effect as a torque vectoring differential. Such electrical systems will become commonplace in performance cars. Not only do they reduce fuel consumption but they also improve performance and handling.

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