Torque vectoring

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Torque vectoring is a technology employed in automobile differentials that has the ability to vary the torque to each half-shaft with an electronic system; or in rail vehicles which achieve the same using individually motored wheels. This method of power transfer has recently[ when? ] become popular in all-wheel drive vehicles. [1] Some newer front-wheel drive vehicles also have a basic torque vectoring differential. As technology in the automotive industry improves, more vehicles are equipped with torque vectoring differentials. This allows for the wheels to grip the road for better launch and handling.

Contents

History

5th-gen Prelude VTi-R with ATTS (Australia, 2011) 1997-2001 Honda Prelude VTi-R ATTS coupe (2011-11-17) 01.jpg
5th-gen Prelude VTi-R with ATTS (Australia, 2011)

In 1996, Honda and Mitsubishi released sporty vehicles with torque vectoring systems. The torque vectoring idea builds on the basic principles of a standard differential. A torque vectoring differential performs basic differential tasks while also transmitting torque independently between wheels. This torque transferring ability improves handling and traction in almost any situation. Torque vectoring differentials were originally used in racing. Mitsubishi rally cars were some of the earliest to use the technology. [2] The technology has slowly developed and is now being implemented in a small variety of production vehicles. The most common use of torque vectoring in automobiles today is in all-wheel drive vehicles.

The flagship 1996 fifth-generation Honda Prelude was equipped with an Active Torque Transfer System (ATTS) torque-vectoring differential driving the front wheels; it was known in different markets as the Type S (Japan), VTi-S (Europe), and Type SH (North America). [3] In essence, ATTS is a small automatic transmission coupled to the differential, with an electronic control unit actuating clutches to vary the torque output between each driven wheel. ATTS effectively counteracted the natural tendency of the front-engine, front-wheel-drive Prelude to understeer. [3] Honda later developed the system into their Super Handling all-wheel-drive (SH-AWD) system by 2004, which improved handling by increasing torque to the outside wheels. [4]

Lancer Evolution IV GSR with AYC (Japan, 2014) The frontview of Mitsubishi LANCER Evolution IV GSR.JPG
Lancer Evolution IV GSR with AYC (Japan, 2014)

At about the same time, the Lancer Evolution IV GSR was equipped with a similar Active Yaw Control (AYC) system in 1996. [5] AYC was fitted to the rear wheels and similarly works to counteract understeer through a series of electronically-controlled clutches that control torque output. [6]

The phrase "Torque Vectoring" was first used by Ricardo in 2006 in relation to their driveline technologies. [7]

Functional description

The idea and implementation of torque vectoring are both complex. The main goal of torque vectoring is to independently vary torque to each wheel. Differentials generally consist of only mechanical components. A torque vectoring differential requires an electronic monitoring system in addition to standard mechanical components. This electronic system tells the differential when and how to vary the torque. Due to the number of wheels that receive power, a front or rear wheel drive differential is less complex than an all-wheel drive differential. The impact of torque distribution is the generation of yaw moment arising from longitudinal forces and changes to the lateral resistance generated by each tire. Applying more longitudinal force reduces the lateral resistance that can be generated. The specific driving condition dictates what the trade-off should be to either damp or excite yaw acceleration. The function is independent of technology and could be achieved by driveline devices for a conventional powertrain, or with electrical torque sources. Then comes the practical element of integration with brake stability functions for both fun and safety.

Front/rear wheel drive

Torque vectoring differentials on front or rear wheel drive vehicles are less complex, yet share many of the same benefits as all-wheel drive differentials. The differential only varies torque between two wheels. The electronic monitoring system only monitors two wheels, making it less complex. A front-wheel drive differential must take into account several factors. It must monitor rotational and steering angle of the wheels. As these factors vary during driving, different forces are exerted on the wheels. The differential monitors these forces, and adjusts torque accordingly. Many front-wheel drive differentials can increase or decrease torque transmitted to a certain wheel. [8] This ability improves a vehicle's capability to maintain traction in poor weather conditions. When one wheel begins to slip, the differential can reduce the torque to that wheel, effectively braking the wheel. The differential also increases torque to the opposite wheel, helping balance the power output and keep the vehicle stable. A rear-wheel drive torque vectoring differential works similarly to a front-wheel drive differential.

All-wheel drive

Most torque vectoring differentials are on all-wheel drive vehicles. A basic torque vectoring differential varies torque between the front and rear wheels. This means that, under normal driving conditions, the front wheels receive a set percentage of the engine torque, and the rear wheels receive the rest. If needed, the differential can transfer more torque between the front and rear wheels to improve vehicle performance.

For example, a vehicle might have a standard torque distribution of 90% to the front wheels and 10% to the rear. When necessary, the differential changes the distribution to 50/50. This new distribution spreads the torque more evenly between all four wheels. Having more even torque distribution increases the vehicle's traction. [9]

There are more advanced torque vectoring differentials as well. These differentials build on basic torque transfer between front and rear wheels. They add the capability to transfer torque between individual wheels. This provides an even more effective method of improving handling characteristics. The differential monitors each wheel independently, and distributes available torque to match current conditions.

Electric vehicles

In electric vehicles all-wheel drive is typically implemented with two independent electric motors, one for each axle. In this case the torque vectoring between the front and rear axles is just a matter of electronically controlling the power distribution between the two motors, which can be done on a millisecond scale. [10] In the case of EVs with three or four motors, even more precise torque vectoring can be applied electronically, with millisecond-specific per wheel torque control in the quad-motor case, [11] and two wheels of per wheel control plus one of per axle control in the tri-motor case.

Torque vectoring can be even more effective if it is actuated through two electric motor drives located on the same axle, as this configuration can be used for shaping the vehicle understeer characteristic and improving the transient response of the vehicle, [12] [13] The Tesla Cybertruck (scheduled for 2022) tri-motor model has one axle with two motors, while the Rivian R1T (in production in 2021) has two motors on each axle, front and rear. [11]

A special transmission unit was used in the experimental 2014 car MUTE of the Technical University of Munich, where the bigger motor is providing the driving power and the smaller for the torque vectoring functionality. The detailed control system of the torque vectoring is described in the doctoral thesis of Dr.-Ing. Michael Graf. [14]

In case of electric vehicles with four electric motor drives, the same total wheel torque and yaw moment can be generated through a near infinite number of wheel torque distributions. Energy efficiency can be used as a criterion for allocating torque across the wheels. [15] [16] This approach is used in the Rivian R1T light-duty truck introduced in 2021. [11]

Rail vehicles

Research is taking place into using torque vectoring to actively steer railway wheelsets on the track. Claimed benefits include a drastic reduction of wear on both track and wheel and the opportunity to simplify or even eliminate the mechanically complex, heavy and bulky bogie.

Stored Energy Technology Limited has built and successfully demonstrated their torque vectoring Actiwheel system which employs a wheel hub motor of their own design. [17]

German Aerospace Centre unveiled a full scale mockup of torque vectoring running gear intended for their Next Generation Train at Innotrans 2022. [18]

See also

Related Research Articles

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A traction control system (TCS), is typically a secondary function of the electronic stability control (ESC) on production motor vehicles, designed to prevent loss of traction of the driven road wheels. TCS is activated when throttle input and engine power and torque transfer are mismatched to the road surface conditions.

<span class="mw-page-title-main">Four-wheel drive</span> Type of drivetrain with four driven wheels

Four-wheel drive, also called 4×4 or 4WD, refers to a two-axled vehicle drivetrain capable of providing torque to all of its wheels simultaneously. It may be full-time or on-demand, and is typically linked via a transfer case providing an additional output drive shaft and, in many instances, additional gear ranges.

<span class="mw-page-title-main">Understeer and oversteer</span> Vehicle dynamics terms

Understeer and oversteer are vehicle dynamics terms used to describe the sensitivity of a vehicle to steering. Oversteer is what occurs when a car turns (steers) by more than the amount commanded by the driver. Conversely, understeer is what occurs when a car steers less than the amount commanded by the driver.

<span class="mw-page-title-main">Quattro (four-wheel-drive system)</span> Sub-brand by Audi

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<span class="mw-page-title-main">Electronic brakeforce distribution</span>

Electronic brakeforce distribution or electronic brakeforce limitation (EBL) is an automobile brake technology that automatically varies the amount of force applied to each of a vehicle's wheels, based on road conditions, speed, loading, etc, thus providing intelligent control of both brake balance and overall brake force. Always coupled with anti-lock braking systems (ABS), EBD can apply more or less braking pressure to each wheel in order to maximize stopping power whilst maintaining vehicular control. Typically, the front end carries more weight and EBD distributes less braking pressure to the rear brakes so the rear brakes do not lock up and cause a skid. In some systems, EBD distributes more braking pressure at the rear brakes during initial brake application before the effects of weight transfer become apparent.

<span class="mw-page-title-main">Drive wheel</span> Any wheel of a motor vehicle that transmits force

A drive wheel is a wheel of a motor vehicle that transmits force, transforming torque into tractive force from the tires to the road, causing the vehicle to move. The powertrain delivers enough torque to the wheel to overcome stationary forces, resulting in the vehicle moving forwards or backwards.

<span class="mw-page-title-main">BMW xDrive</span> Four-wheel drive system developed by BMW

BMW xDrive is the marketing name for the all-wheel drive system found on various BMW models since 2003. The system uses an electronically actuated clutch-pack differential to vary the torque between the front and rear axles. Models with the DPC torque vectoring system also have a planetary gearset to overdrive an axle or rear wheel as required.

ATTESA is a four-wheel drive system used in some automobiles produced by the Japanese automaker Nissan, including some models under its luxury marque Infiniti.

Super Handling-All Wheel Drive (SH-AWD) is a full-time, fully automatic, all-wheel drive traction and handling system, which combines front-rear torque distribution control with independently regulated torque distribution to the left and right rear wheels. This way the system freely distributes the optimum amount of torque to all four wheels according to the driving conditions." The system was announced in April 2004, and was introduced in the North American market in the second generation 2005 model year Acura RL, and in Japan as the fourth generation Honda Legend.

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All Wheel Control (AWC) is the brand name of a four-wheel drive (4WD) system developed by Mitsubishi Motors. The system was first incorporated in the 2001 Lancer Evolution VII. Subsequent developments have led to S-AWC (Super All Wheel Control), developed specifically for the new 2007 Lancer Evolution. The system is referred by the company as its unique 4-wheel drive technology umbrella, cultivated through its motor sports activities and long history in rallying spanning almost half a century.

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<span class="mw-page-title-main">Individual wheel drive</span> Drivetrain where wheels to receive torque from motors independent of each other

Individual-wheel drive (IWD) is a wheeled vehicle with a drivetrain that allows all wheels to receive torque from several motors independent of each other. The term was coined to identify those electric vehicles whereby each wheel is driven by its own individual electric motor, as opposed to conventional differentials.

The Symmetrical All-Wheel Drive is a full-time four-wheel drive system developed by the Japanese automobile manufacturer Subaru. The SAWD system consists of a longitudinally mounted boxer engine coupled to a symmetrical drivetrain with equal length half-axles. The combination of the symmetrical layout with a flat engine and a transmission balanced over the front axle provides optimum weight distribution with low center of gravity, improving the steering characteristics of the vehicle. Ever since 1986, most of the Subaru models sold in the international market are equipped with the SAWD system by default, with the rear wheel drive BRZ and kei cars as the exceptions.

Crosswind stabilization (CWS) is a relatively new advanced driver-assistance system in cars and trucks that was first featured in a 2009 Mercedes-Benz S-Class. CWS assists drivers in controlling a vehicle during strong wind conditions such as driving over a bridge or when overtaking a semi-truck. CWS uses yaw rate, lateral acceleration, steering angle, and velocity sensors to determine how much assistance to give the driver in a certain scenario whether it be at different speeds or while turning. Using different components throughout the vehicle like brakes, differentials, and suspension, CWS can implement the readings from force sensors to properly assist the driver in a given situation.

<span class="mw-page-title-main">Rivian R1T</span> Battery electric mid-size pickup truck

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References

  1. ↑ Ireson, Nelson (Dec 28, 2010). "The 2012 Ford Focus Gets Torque Vectoring, We're not Thrilled". MotorAuthority.com. Retrieved 2 November 2012.
  2. ↑ "Torque Vectoring and Active Differential". Torque-vectoring.belisso.com. 2009-11-22. Retrieved 2012-03-12.
  3. 1 2 Nazarov, Dimitar (2016). "What Is ATTS". CarThrottle. Retrieved 1 August 2022.
  4. ↑ Kunii, Rikiya; Iwazaki, Akihiro; Atsumi, Yoshihiro; Mori, Atsushi (October 2004). "Development of SH-AWD (Super Handling-All Wheel Drive) System". Technical Review. Honda R&D. 16 (2).
  5. ↑ Sawase, Kaoru; Sano, Yoshiaki (April 1999). "Application of active yaw control to vehicle dynamics by utilizing driving/breaking force". JSAE Review. 20 (2): 289–295. doi:10.1016/S0389-4304(98)00070-8.
  6. ↑ "Active Yaw Control". The Clemson University Vehicular Electronics Laboratory. Retrieved 7 March 2023.
  7. ↑ Wheals, J.; Deane, M.; Drury, S.; Griffith, G.; Harman, P.; Parkinson, R.; Shepherd, S.; Turner, A. (2006). Design and Simulation of a Torque Vectoring™ Rear Axle. World Congress & Exhibition. Society of Automotive Engineers. doi:10.4271/2006-01-0818. ISSN   0148-7191.
  8. ↑ "Torque Vectoring" (PDF). VehicleDynamicsInternational.com.
  9. ↑ "Torque Vectoring: The Hyper-Smart, Fuel-Efficient Future of All-Wheel Drive". Popular Mechanics . 2009-10-01. Retrieved 2012-03-12.
  10. ↑ Davies, Alex (2014-10-10). "The Model D Is Tesla's Most Powerful Car Ever, Plus Autopilot". Wired.com . Retrieved 2014-10-11. Musk said the added efficiency is thanks to the electronic system that will shift power between the front and rear motors from one millisecond to the next, so each is always operating at its most efficient point.
  11. 1 2 3 Moloughney, Tom (28 September 2021). "2022 Rivian R1T First Drive Review: Electric Off-Road Dominance". InsideEVs. Retrieved 5 October 2021.
  12. ↑ De Novellis, L.; Sorniotti, A.; Gruber, P.; Orus, J.; Rodríguez, J.M.; Theunissen, J.; De Smet, J. (2015). "Direct Yaw Moment Control Actuated through Electric Drivetrains and Friction Brakes: Theoretical Design and Experimental Assessment". Mechatronics. 26: 1–15. doi: 10.1016/j.mechatronics.2014.12.003 .
  13. ↑ Goggia, Tommaso; Sorniotti, Aldo; De Novellis, Leonardo; Ferrara, Antonella; Gruber, Patrick; Theunissen, Johan; Steenbeke, Dirk; Knauder, Bernhard; Zehetner, Josef (May 2015). "Integral Sliding Mode for the Torque-Vectoring Control of Fully Electric Vehicles: Theoretical Design and Experimental Assessment". IEEE Transactions on Vehicular Technology. 64 (5): 1701–1715. doi: 10.1109/TVT.2014.2339401 . S2CID   32516116.
  14. ↑ Graf M., 'Methode zur Erstellung und Absicherung einer modellbasierten Sollvorgabe für Fahrdynamikregelsysteme', Technical University of Munich, 2014.
  15. ↑ De Novellis, Leonardo; Sorniotti, Aldo; Gruber, Patrick (May 2014). "Wheel Torque Distribution Criteria for Electric Vehicles With Torque-Vectoring Differentials". IEEE Transactions on Vehicular Technology. 63 (4): 1593–1602. doi: 10.1109/TVT.2013.2289371 . S2CID   2982503.
  16. ↑ Chen, Yan; Wang, Junmin (September 2012). "Fast and Global Optimal Energy-Efficient Control Allocation With Applications to Over-Actuated Electric Ground Vehicles". IEEE Transactions on Control Systems Technology. 20 (5): 1202–1211. doi:10.1109/TCST.2011.2161989. S2CID   8730039.
  17. ↑ Actiwheel, a revolutionary traction technology SET Limited
  18. ↑ A high-tech running gear for the train of the future DLR Portal
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