At the SAE 2009 World Congress, General Motors took the opportunity to present the first front-wheel-drive version of their two-mode hybrid transaxle which has been dubbed the 2MT70.
The concept is adapted from a hybrid transmission designed by Allison for transit buses and has previously only been incorporated into rear-wheel-drive transmissions with the hope of reducing the fuel consumption of heavier and larger passenger trucks and SUVs.
The 2MT70 transaxle itself is extremely compact at a mere 15 inches in length and has the potential to bring two-mode architecture to a wider range of vehicles. It is scalable across front-wheel-drive vehicles with engines that range from a 2.0litre four-cylinder turbo-diesel to a 3.6litre direct injection, spark ignition V6 petrol engine.
As the two-mode design uses motor B to produce all reverse torque, scaling the transaxle for a larger or faster vehicle normally involves extending the length of motor B and redesigning the end casting of the transaxle so that it accommodates the increase in motor length.
It uses two 55kW active-cooled AC motor generators, each of which is connected to a planetary gearset and is capable of providing either a continuously variable speed or motive power. It uses a combination of engine speeds, motor speeds and a system of clutches to manipulate the planetary gearsets and provide two variable ranges as well as a compound split that allows the ranges to influence each other.
The project’s engineers have also developed a damper bypass clutch that couples the engine and transmission during stop/start transitions – this smoothes the operation.
