Patent News | "Petrol engine drives Volt 'electric' car ... sometimes"

By: Barry Park
Category: Patent News

A patent filing shows direct link between a petrol engine and wheels, casting more doubt on the Volt’s credentials.

Is the Holden Volt an electric car, as the company claims, or is it just a hybrid car with spin?

The answer appears no closer to resolution, with Holden’s US parent, General Motors, casting further doubt on the car maker’s claim that the Volt is, first and foremost, an electric car with a range-extending petrol engine.

A GM-sourced patent submitted by the car maker’s research arm, GM Global Technology Operations, to the US Patent and Trademark Office in December describes an electric vehicle drivetrain that is very similar to that used in the Volt.

However, the patent filing goes into great detail to summarise the various operating conditions of the system — which includes a pair of electric motors, a bank of batteries and a petrol engine — including one described as a ‘‘direct mechanical path between the engine and drive wheels’’.

The filing refers to an ‘‘extended-range electric vehicle’’ with ‘‘an engine having an output shaft, a planetary gear set having a node driven by the output shaft of the engine when the engine is on, and first and second electric machines’’.

‘‘The first electric machine is connected to another node, and operates as a generator when the engine is on. A one-way clutch is connected to the remaining node,’’ it reads.

‘‘The second electric machine is connected to an output side of the one-way clutch, with a shaft connecting the drive wheels to the second electric machine.

‘‘A controller provides a forward electric-only (EV) mode, a reverse EV mode, power-split mode(s), and series mode(s).

And then there is the clincher: ‘‘The series mode(s) provide a direct mechanical path between the engine and drive wheels, with the one-way clutch overrunning in the forward EV mode,’’ the filing says.

Holden energy and environment director Richard Marshall hosed down speculation at an Australian preview of the Volt last week, backing up GM’s claim that the car doesn’t have a direct link between the front wheels and the petrol engine.

GM admitted to Drive last year that the Volt would in some high speed situations directly link the engine to the wheels, claiming it was only done because in that particular situation it was found to be more efficient than first converting the energy to electricity to be used by the electric motor power the wheels.

US automotive website Edmunds Inside Line stirred up a storm late last year, claiming that under certain conditions the Volt ‘‘at times be directly driven in part by its internal combustion engine’’.

‘‘In fact, the Chevy Volt is a plug-in hybrid and it has more in common with conventional 'series-parallel' hybrids like the Toyota Prius than the marketing hype led us to believe,’’ the website said in an expose just before the Volt’s US launch.

‘‘There are circumstances in which the Volt operates with the internal combustion engine directly driving the front wheels. That's right, like a Prius.’’