GM Voltec powertrain

The Voltec propulsion is an alternative drive concept of the car manufacturer General Motors, which came in 2010 with the Chevrolet Volt on the market since November 2011 and is also in the Opel Ampera used. The drive was developed under the direction of German engineer Frank Weber, who works after changing activities at GM and Opel since 2011 for BMW. In the presented in 2007 Chevrolet Volt concept vehicle of the Voltec propulsion was still called E-Flex drive. Two other car models have been announced for the end of 2012, in which the Voltec drive will be used. GM does not include the vehicle drive as a " hybrid ", but also led to the vehicles the abbreviation E -REV A, which stands for " extended-range electric vehicle ."

  • 3.2.1 Operating mode 3
  • 3.2.2 Operation mode 4


The motor system consists of three vehicles / engines:

  • An electric motor as the main drive, which operates in the regenerative braking as a generator,
  • An on-board generator, which is partly used also as a drive motor, and
  • A gasoline engine, which is used primarily for the drive of the generator motor.

A planetary gear with three hydraulically operated motor couplings, the three motors can be coupled in different ways. The optimum operating mode is selected automatically electronically depending on the operating condition. The motor couplings used are always either open or closed. A " slipping clutch " as it is used in cars with manual transmission, the driver for the start, there is the Voltec drive in any of drive modes, but only very briefly when changing modes.

Primarily, the driving of the vehicle is done by an electric motor with a peak output of 111 kW ( 151 hp). When the batteries of the vehicle are almost empty, the non-supercharged 1.4-liter 4- cylinder gasoline engine (84 hp) jumps with an output of 63 kW and feeds the on-board generator that now electricity provides for the main drive. The design is called a partial serial hybrid drive, since the internal combustion engine a generator with power supply that generates the power for the electric motor. There is also a partially parallel hybrid drive, because the gasoline engine at high power requirement and " empty " battery can also provide mechanical power. The battery is not charged, but only saved from further discharging.

Charging methods

Normally, the battery is recharged overnight. The charging time is at an average in the U.S. 120 - volt power port for about 10 hours, at the usual European 230 -volt connections for about 4 hours. This charging time is only with a mounted optional charging station or with an optional charging cable with Mennekes charging plug to the corresponding loading points attainable, as only then the maximum power of the board charger can be used by about 3.3 kW. Via the included charging cable with Schuko plug with 2.3 kW (10 A, charging time 6 hours) or 1.4 kW (6 A, charging time 11 hours) will be charged for reasons of comfort volts are the Chevrolet on both sides of the vehicle electrical connections available.

For those that exceed the vehicle's range on battery power, the power to the drive motor from the on-board generator is supplied; excess energy, such as the braking energy is converted into electrical power and used for charging the batteries. The battery is charged by utilizing the braking energy is called regenerative braking or regenerative braking. It also comes with other hybrid concepts, such as in Toyota's Hybrid Synergy Drive and almost all electric cars for use.

Modes of operation

The vehicle can be driven in 4 driving modes. Which mode is used is decided by the electronics on the basis of the charge state of the batteries, the required power and speed.

Electrical operation: mode one and two

When the battery is charged, ie about 26% of the theoretical maximum load, purely electric charging ( Mode 1 and 2). Mode 1 and 2 are therefore the most widely used modes, which are on the plurality of driven ( short ) routes used. Motor power is provided by a (mode 1) or two (Mode 2) electric motors, the internal combustion engine is not used in both modes.

Mode 1: Main drive motor alone

The main electric drive motor drives the sun gear of the planetary gear ( green); the ring gear (red) is connected via a coupling to the housing closed: it is. The drive power is removed via the carrier (yellow) of the planet gears (blue) with a ratio of 1:7.

Mode 2: combined use of both electric motors

At speeds above 113 km / h ( 70 mph ), the main electric drive motor can be operated only with an unfavorable efficiency, since he would have to turn over 6500 rpm. In this case, and in large power demand an engine clutch is released, and the generator is used as the second electric motor in addition to the drive. Both motors are supplied with battery power, the internal combustion engine is not used.

The generator is thus now used as the motor and drives the ring gear (red), which is now rotating in the same direction as the sun gear, but much slower. Thus the speed of the sun gear and thus also the main drive motor can be reduced with respect to stationary ring gear.

Range Extender mode

The accumulator is discharged to 26 % of its theoretical capacity, the internal combustion engine is started. It drives the generator to supply driving current; at the same time the battery charge level is kept constant. In the range-extender mode drive power is either done only by the main electric drive motor, while in parallel the internal combustion engine at a constant speed provides the necessary traction current, or main drive motor and internal combustion engine providing the driving power together. Again, the electronics automatically decides in which mode driven.

Mode 3

The vehicle continues to be driven exclusively by the main electric drive motor. There is no connection between the ring gear and generator. The internal combustion engine via the generator generates electric power that is used on the power electronics for the drive of the main drive motor. For optimum efficiency of the internal combustion engine irrespective of the running speed of the vehicle at a constant speed in Mode 3.

Mode 4

If in this range extender mode high power requested ( fast speed or mountainous terrain ), the coupled to the generator combustion engine can be mechanically coupled to the ring gear. Since several additional energy conversions (internal combustion engine - generator - electric motor ) account, so that the efficiency of the entire system is held up and down about 113 km / h (70 mph) limits the maximum speed of the main electric drive motor. Now also supplies the engine directly acting on the wheels drive power. Whether the generator can also be used as an additional electric drive motor now, is unclear. All three engines, two electric and combustion engine, now drive together to the vehicle.

For other assumptions, the small electric motor or generator (in the factory literature of the manufacturer drive motor "A" referred to ) is used in this mode as a generator to supply the driving current for the large electric motor / generator ( driving motor "B"), then the necessary counter torque on the sun gear of the planetary transmission and thus provides also drives the vehicle. At the same time decreases as the speed of the drive motor "B". A similar operation, the Hybrid Synergy Drive of the Toyota Prius.


The lithium- ion battery has a capacity of 16 kWh and a mass of 198 kg. The traction battery is (parallel 3 each, 96 in number ) from 288 cells, the traction voltage is thus about 350 V. The vehicle electronics are programmed to maintain the state of charge of the battery is between 30% and 80 % in order to extend its life, so that effectively only 8.8 kWh used.

However, may be taken according to the onboard computer display of series vehicles up to 10.5 kWh. Meanwhile be driving reports that the battery level may drop to 26% (4.16 kWh), and up to 10.5 kWh can be consumed (upper limit thus 14.66 kWh). This would mean that the batteries would be operated in the range 26-92 % of rated capacity, so a margin of 66 % of rated capacity.

Despite nearly identical capacity, the mass of the Voltec propulsion batteries is almost 70 % less than that of the built up to 1999 General Motors EV1. The battery pack is heated at low outdoor temperatures by means of an integrated electrical heating element and water as the transfer medium and cooled at high ambient or operating temperatures through the electrically powered by high voltage air conditioning to ensure optimum operating conditions. General Motors is on the battery pack for a period of eight years or 160,000 kilometers.

Electric Consumption

The electrical consumption, the U.S. Agency for Environmental Protection EPA has determined, is 22.4 kWh per 100 km. This corresponds to a gasoline equivalent of 2.53 l/100 km (93 miles per gallon) with a fully charged battery on the first 56.3 km (35 miles).

Gasoline consumption

Since a car with Voltec drive only consumes fuel when its batteries are discharged, a fuel consumption figure must always be viewed against the background of whether the car is pure electric, mixed or - for fully discharged battery pack - via the detour of electricity exclusively using the internal combustion engine is moved. In the latter case, the fuel consumption is 6.36 l/100 km (37 mpg ) and 3.92 l/100 km (60 mpg ) gasoline equivalent in combined operation according to EPA.