Gliding (vehicle)

A look on a dashboard at driving speed of 50 km/h. Upper picture shows gliding, where the combustion engine is turned off. Picture below shows coasting where the engine in idling. A disengaged clutch or transmission in neutral.

Gliding is an energy-efficient driving operating mode of a motor vehicle, turning off the internal combustion engine when driving to save fuel. Coasting is disengaging the engine from the wheels in idle mode by disengaging the clutch or setting the transmission or gearbox to neutral position,[1] using the accelerated kinetic energy to keep the vehicle going, but lose speed to the existing drag. In hybrid electric vehicles this functionality is part of the concept and performed automatically by the engine controller. Vehicles with a conventional internal combustion engine, coasting can be performed manually, gliding when having a gear box.[2] It is illegal in some states. An extra button to stop the engine was shown in 1979 on International Motor Show Germany,[3] but newer standard in any vehicle. A so-called eClutch (electronic controlled clutch) uses an actuator to disengage the clutch when the driver leaved the accelerator.[4]

A start-stop system turns the engine off when the vehicle is stopped. Gliding is tuning off the engine while the vehicle is still moving.Safety relevant components like power steering or vacuum servo required to be operated electric, but most vehicles drive it by the combustion engine, only. The fuel saving is depending on the road and traffic conditions, least on the altitude profile of the road. It is assumed to save up 7 % fuel in the NEFZ driving cycle, in real road traffic conditions up to 10 % are estimated.

Coasting

Idle coasting is riding the vehicle at a higher speed than the idle speed of the engine and disengaging the engine from the wheels by setting the transmission or gearbox to neutral position or disengage the clutch, remaining the engine in idle mode.[5][6][7]

Gliding a conventional vehicle

Pushing the clutch pedal disengages the engine from the powertrain like wheels, drive shafts and gearbox. Releasing the accelerator makes the engine slowing down to idle. Turning of the ignition takes further affects. Pulling the key causes locking the steering wheel. Some vehicles drop head- or stoplights when ignition is turned off. After the engine is stopped, applying the brake longer time or give a few pushes to the brake releases the reserve of the vacuum servo, causing a lost of the brake support. A belt driven power steering fails immediately. Real hybrid vehicles have electric driven support of power steering and brake. Bigger engines and engines with higher compression ratio can cause damage to components of the powertrain at a rough start over clutch from gliding vehicles kinetic power or trailing drag. Using a higher gear decreases the torque force on the powertrain. By turning off the ignition the engine control unit (ECU) needs to detect the engine shafts position. Some ECUs need several rotations of the camshaft to detect ignition an injection timing points. Starting the engine in coldstart takes temporary more fuel until operation temperature of the engine is detected by the ECU.

Gliding vehicles equipped with torque converter based automatic transmissions might cause a damage. Also restarting the engine by clutch from the vehicles kinetic energy or drag is not possible. It is required to use the starter.

See also

References and Remarks

  1. ↑ Konrad Reif, Karl E. Noreikat, Kai Borgeest: Kraftfahrzeug-Hybridantriebe.
  2. ↑ bosch-presse.de Erweitertes Start/Stopp-System von Bosch spart noch mehr Kraftstoff, retrieved 14 September 2013
  3. ↑ IAA 1979 - Porsche 928 S, uploaded 11 January 2016
  4. ↑ pressrelations.de Die eClutch spart Sprit und erhöht den Komfort, retrieved 19 September 2013
  5. ↑ bmwgroup.com Publication to the Press on 6 May 2013, retrieved 15 September 2013
  6. ↑ porsche.com (PDF; 10,7 MB) 911, retrieved 15 September 2013
  7. ↑ BMW offers gliding on manual transmissions, Porsche on dual-clutch transmission.
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