Voltec drive

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Motors of a Chevrolet Volt at a public exhibition in a metro station in Washington DC, the internal combustion engine on the left, the electric motor on the right

The Voltec drive is an alternative drive concept from the car manufacturer General Motors , which came onto the market in 2010 with the Chevrolet Volt and has also been used in the Opel Ampera since November 2011 . The drive was developed under the direction of the German engineer Frank Weber, who has worked for BMW since 2011 after changing activities at GM and Opel . In the Chevrolet Volt concept vehicle presented in 2007, the Voltec drive was still called the E-Flex drive. GM announced two more car models for the end of 2012, in which the Voltec drive should be used; however, they were not made.

A second version of the Voltec powertrain was introduced with the 2016 model year of the Chevrolet Volt.

GM does not designate the vehicle drive as "hybrid drive", but introduced the abbreviation E-REV for the vehicles, which stands for "extended-range electric vehicle". "Voltec" is variously regarded as a suitcase word from the terms Volt , " Vortec " and Technology .

principle

The engine system consists of three working machines / prime movers :

  • an electric motor as the main drive, which also works as a generator during recuperation ,
  • an on-board generator , which is sometimes also used as a drive motor, and
  • a gasoline engine, which is mainly used to drive the generator engine.

A planetary gear with three hydraulically -operated motor couplings the three motors can be coupled in different ways. The optimum operating mode is selected electronically, fully automatically, depending on the operating status. The motor couplings used are always either open or closed. A "slipping clutch", as used by the driver in cars with manual gearboxes, does not exist in any of the driving modes with the Voltec drive, but only very briefly when changing modes.

The vehicle is primarily powered by an electric motor with a peak output of 111  kW (151  hp ). When the vehicle's batteries are largely discharged, the uncharged 1.4-liter four-cylinder petrol engine with an output of 63 kW (84 hp) starts up and feeds the on-board generator, which now supplies electricity for the main drive . The design is referred to as a partially serial hybrid drive , as the internal combustion engine supplies a generator with energy that generates the electricity for the electric motor. It is also a partially parallel hybrid drive , since the gasoline engine can also provide mechanical drive power when the power requirement is high and the battery is “empty”. However, the battery is not charged, but only protected from further discharge.

Charging method

Usually the battery (16 kWh) is charged overnight or at work. The charging time is about 10 hours on a 120-volt power connection common in the USA, and about 4 hours on the 230-volt connections common in Europe. However, this charging time can only be achieved with a permanently installed optional charging station or with an optional charging cable with Mennekes charging plug at the corresponding charging points, as this is the only way to use the maximum power of the on-board charger of around 3.3 kW. Via the included charging cable to the low voltage grid - outlets may be in Europe only with 2.3 kW (10 A, charging time 6 hours) or 1.4 kW (6 A, charging time 11 hours) are loaded.

For trips that exceed the range of the vehicle in battery mode, the power for the drive motor is supplied by the on-board generator. Excess energy, such as B. when driving downhill or when “braking” ( regenerative brake ), is converted into electrical current (recovered, recuperated ) and used to charge the batteries. The recovery of energy is also used in other hybrid concepts (e.g. Toyota's Hybrid Synergy Drive ) and almost all electric cars .

Operating modes

For illustration purposes, a simplified representation of a planetary gear with two planetary gears, three or more are common;
green: sun gear,
blue: planetary gears,
red: ring gear,
pale yellow: axles / carriers of the blue planetary gears

The vehicle can be driven in 4 driving modes. The electronics decide which mode to use based on the charge level of the batteries, the required performance and the speed.

Electric operation: mode one and two

When the battery is charged, i.e. over 26% of the theoretical maximum charge, it is operated purely electrically (modes 1 and 2). Modes 1 and 2 are therefore the most common modes that are used on the majority of the (short) journeys. Drive power is provided by one (mode 1) or both (mode 2) electric motors; the combustion engine is not used in either mode.

Mode 1: main drive motor alone

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

With high performance requirements such as B. at a speed of more than approx. 70  miles per hour (113 km / h) the electronics switch to mode two.

Mode 2: combined operation of both electric motors

At speeds over 113 km / h (70 mph), the electric main drive motor can only be operated with unfavorable efficiency, since it would then have to rotate over 6500 rpm. In this case and when the power demand is high, a motor clutch is released and the generator is used as a second electric motor in addition to the drive. Both motors are fed with battery power, the combustion engine is not used.

The generator is now used as a motor and drives the ring gear (red), which now rotates in the same direction as the sun gear, but much more slowly. This allows the speed of the sun gear and thus also of the main drive motor to be reduced opposite the ring gear.

Range extender operation

When the accumulator is discharged to 20% of its theoretical capacity, the internal combustion engine is started. It drives the generator to provide traction current; at the same time, the battery charge level is kept constant. In range extender operation, drive power is either only provided by the electrical main drive motor, while the internal combustion engine supplies the necessary traction current at a constant speed, or the main drive motor and internal combustion engine provide the drive power together. Here, too, the electronics automatically decide which mode to use.

Operating mode 3

The vehicle continues to be driven exclusively by the main electric drive motor. There is no connection between ring gear and generator. The internal combustion engine generates electrical energy via the generator, which is used via the power electronics to drive the main drive motor. For optimal efficiency of the internal combustion engine, it runs in mode 3 at a constant speed regardless of the speed of the vehicle.

Operating mode 4

If high power is required in this range extender operating state (high speed or mountainous terrain), the internal combustion engine coupled to the generator can also be coupled mechanically to the ring gear. Since several additional energy conversions (combustion engine - generator - electric motor) are not required, the efficiency of the overall system is kept high and the maximum speed of the main electric drive motor is limited from approx. 113 km / h (70 mph). Now the internal combustion engine also delivers drive power that acts directly on the wheels. It is not clear whether the generator can now also be used as an additional electric drive motor. All three motors, two electric and the combustion engine, now drive the vehicle together.

According to other assumptions, the small electric motor or generator ( called drive motor "A" in the manufacturer's literature ) is used as a generator in this mode to supply the drive current for the large electric motor / generator ( drive motor "B" ), which then supplies the necessary counter torque on the sun gear of the planetary gear and thus also drives the vehicle. At the same time the speed of the drive motor "B" decreases. The Hybrid Synergy Drive in the Toyota Prius works in a similar way .

accumulator

The lithium-ion battery has a capacity of 16 kWh and a mass of 198 kg. The drive battery consists of 288 cells (3 each in parallel, 96 in series), the supply voltage is thus around 350 V. The vehicle electronics are programmed to keep the charge level of the battery between 30% and 80% in order to extend its service life so that effectively only 8.8 kWh can be used.

However, according to the display on the on-board computer, the series vehicles can draw up to 10.5 kWh. Driving reports are now available that the battery charge level can drop to 18% (4.16 kWh) and up to 10.5 kWh can be used. This would mean that the batteries would be operated in the range of 20 to 85% of the nominal capacity, i.e. a range of 65% of the nominal capacity.

Despite the almost identical capacity, the mass of the Voltec drive battery is almost 70% less than that of the General Motors EV1, which was built until 1999 . At low outside temperatures, the battery pack is heated by means of an integrated electrical heating element and water as the transmission medium, and at high ambient or operating temperatures it is cooled by the high-voltage electrically operated air conditioning system to ensure optimal operating conditions. General Motors gives a warranty of eight years or 160,000 km on the battery unit.

Electric consumption

The electrical consumption determined by the US Environmental Protection Agency (EPA) is 22.4 kWh / 100 km. This corresponds to a gasoline equivalent of 2.5 l / 100 km (93 miles per gallon ) with a fully charged battery for the first 56.3 km (35 miles).

Fuel consumption

Since a car with a Voltec drive only consumes gasoline when its batteries are discharged, the consumption information must always be considered against the background of whether the car is purely electric, mixed or - in the case of completely discharged batteries - via the detour of power generation exclusively with help of the internal combustion engine is moved. In the latter case, the gasoline consumption is 6.4 l / 100 km (37 mpg) and 3.9 l / 100 km (60 mpg) gasoline equivalent in combined operation according to the EPA .

Individual evidence

  1. ↑ a b c d The Voltec System - Energy Storage and Electric Propulsion . Retrieved May 4, 2014.
  2. ↑ BMW hires Frank Weber, former lead engineer for the Chevy Volt ( English ) BMWblog.com. Retrieved October 20, 2011.
  3. ↑ GM plans to add to Chevrolet Volt and Opel Ampera ( German ) www.autogazette.de. Retrieved October 20, 2011.
  4. ^ Lyle J. Dennis, MD: GM Calls the Volt to E-REV . In: GM-Volt.com . Retrieved November 23, 2007.
  5. ↑ Chevrolet Volt Specifications (PDF; 51 kB)
  6. ↑ a b www.autogazette.de: the Volt in calming mode  ( page no longer available , search in web archives )  Info: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice.@1@ 2Template: Dead Link / www.autogazette.de  
    • E-motor speed limitation by coupling the combustion engine in range extender mode
  7. ↑ a b c d e f g Clarification: Gas Engine Can Help Drive the Chevrolet Volt Starting at 30 MPH ( English ) gm-volt.com. Retrieved October 19, 2011.
    • The combustion engine never starts when the battery is charged .
    • The battery is not charged by the combustion engine, but only kept at 30%.
    • Automatic mode selection based on battery charge status, required power, speed.
  8. ↑ Loading time information
  9. ^ Opel: Opel Ampera, Technische Daten ( Memento from November 9, 2013 in the Internet Archive ), accessed May 11, 2012
  10. ↑ heise Autos, October 31, 2010: Chevrolet Volt: First driving impressions from the hopefuls , accessed May 11, 2012
  11. ^ Opel blog: Energy from the coffee pack , accessed May 9, 2012
  12. ↑ Ulrich Eberle, Rittmar of Helmolt: Sustainable transportation based on electric vehicle concepts: A Brief overview (U. Eberle / R. von Helmolt) . Royal Society of Chemistry . May 14, 2010. Retrieved June 8, 2010.
  13. ^ Lyle J. Dennis, MD: Latest Chevy Volt Battery Pack and Generator Details and Clarifications . In: GM-Volt.com . Retrieved August 29, 2007.
  14. ↑ Greenfuelsforecast.com ( Memento from July 11, 2011 in the Internet Archive )
  15. ↑ Chevroletvoltage.com
  16. ↑ EPA announces consumption values ​​of the Chevrolet Volt (as of November 25, 2010) ( Memento of January 2, 2011 in the Internet Archive )
  17. ↑ Volt receives EPA ratings and label: 93 mpg-e all-electric, 37 mpg gas-only, 60 mpg-e combined