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Differential steering is the means of steering a land vehicle by applying more drive torque to one side of the vehicle than the other.^[1] Differential steering is the primary means of steering tracked vehicles, such as tanks and bulldozers, is also used in certain wheeled vehicles commonly known as skid-steer, and even implemented in some automobiles, where it is called torque vectoring, to augment steering by changing wheel direction relative to the vehicle. Differential steering is distinct from torque steer, which is usually considered a negative side effect of drive-train design choices.

History

A British agricultural company, Hornsby in Grantham, developed a continuous track, which was patented in 1905.^[2] The Hornsby tractors featured a track-steer clutch arrangement.

Mechanisms

There are several mechanisms that have been developed to vary the torque applied to different sides of a vehicle. These include clutch-brake steering, braked-differential steering, controlled-differential steering, geared steering, Maybach double-differential steering, double-differential steering, triple-differential steering,^[1] hydraulic,^[3] and electric.^[4]

Clutch-brake

In clutch-brake differential steering, power is disconnected to one side or the other with a clutch, and the unpowered side may also have a brake applied to tighten the turn.^[1] Note that there is no differential gearset in this design. The tracks on either side of the vehicle will always turn at the same speed unless one is declutched for steering. This method is simple to implement but inefficient and only suitable for light vehicles. Also, when traveling downslope under engine braking, declutching one side to turn can result in a turn in the other direction.^[1]^[5]

Braked-differential

In brake-differential steering, power is applied to both sides through a differential and a brake is applied to one side or the other. The slowing of one side causes the other side to speed up, because of the differential, and so the vehicle maintains a constant speed. A subsequent disadvantage is that changes in rolling resistance or traction from one side to the other automatically causes the vehicle to steer unless counteracted by the driver.^[1] Differential steering of this type was used in many half-track designs to assist with making tight turns.

Controlled-differential

In controlled-differential steering, pinions within the differential are locked causing one side to rotate faster than the other. An advantage is that no power is lost to braking. A disadvantage is that only one turning radius can be performed efficiently. This method was developed by the Cleveland Tractor Company in 1921 and called the Cletrac Regenerative Steering System.^[1]

Geared

In geared differential steering, two complete gearboxes are used to provide power to either side, and one distinct turning radius can be derived from each gear ratio combination. The main disadvantage to this system is that it doubles the size and weight of the total transmission and therefore it has only been implemented experimentally.^[1]

Maybach double-differential

In the Maybach double-differential, power is transmitted through a single main transmission and then through an epicycle gear final drive on each side. A different drive speed is caused by feeding torque, from a separate "steering" transmission, into one final drive or the other using a pair of clutches. Usually the steering input turns at a fixed ratio relative to the engine, which results in a different turn radius for each main transmission ratio. This system was implemented on German Panther tanks during World War II.^[1] The drawback of this design compared to other multiple-differential designs is that applying the steering input to one track also increases the average speed of the two tracks, so the vehicle's speed is not constant.

Double-differential

In double-differential steering, as in the Maybach double-differential system, power from a second transmission is fed into an epicycle gear in the final drive of one side or the other. In this design, however, the average drive speed of the tracks is maintained by adding an idler to apply the opposite torque to the epicycle gear on other side of the turn. A pair of clutches is used to apply the steering transmission output, which only turns one direction, to the steering cross-shaft in either direction. This system was developed in 1928 by Major Wilson.^[1] Here, the steering input is used not so much to apply torque to either side but rather to control the difference in torque and speed between the two sides.

Also note that, in any of the double- or triple-differential steering methods, the efficient turn radii (e.g., with no steering clutch or brake slipping) are determined by the ratio between the steering input speed and the main drive input speed into each epicyclic final drive. This means that having multiple ratios in the steering transmission results in multiple turn radii for each main drive transmission ratio. The additional complexity in the mechanical systems and driving controls means that this capability is rarely implemented.^{[citation needed]}

Triple-differential

Triple-differential steering is similar to double-differential steering except that, rather than using a steering cross-shaft and an idler gear, it uses two steering cross-shafts connected to a steering differential. Part of the drive torque is always applied through the steering differential and the two epicyclic differentials. Brakes are used, instead of clutches, to slow down one or the other steering cross-shaft. The steering works much like braked differential steering mentioned above except that the resulting inefficiency from applying the steering brakes only affects the torque being transmitted via the steering input.^{[citation needed]}

Hydraulic

Hydraulic differential steering consists of a hydraulic drive system with one hydraulic pump and two hydraulic motors, one for each side.^[3] This system is often employed on skid-steer loaders and zero-turn mowers.

Electric

A three-wheeled differentially steered robot

Electric differential steering consists of two or more electric motors—one for each side of the vehicle, or up to as many as one per wheel—that are driven at different speeds (or directions), depending on steering needs.^[4] It is often implemented in wheeled robots.

Hand

Most traditional wheelchairs are maneuvered by differential steering when propelled by the occupant.

Turning radius

Depending on implementation, friction between drive mechanism and ground, and available power, a vehicle with differential steering may have a zero turning radius or a curb-to-curb turning circle equal to the length of the vehicle by driving each side at the same speed but in opposite directions. This is also called a neutral turn.^[6] Vehicles on which only one drive wheel on each side is rigidly aligned and all others are free to caster, such as wheelchairs and wheeled robots, require the least power to turn. Vehicles with long continuous tracks on each side which must slide on the ground in order to turn at all require more power.

Examples

Tanks, armored personnel carriers, armoured vehicle-launched bridge, self-propelled anti-aircraft weapon, and similar military vehicles
Bulldozers, excavators, tractors, snowcats, trenchers, and other heavy equipment
Skid-steer loaders and their derivatives
Amphibious ATVs
Zero-turn mowers
Differential wheeled robots
Wheel chairs
Self-balancing scooters

References

^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ Edwards, Phillip (September 1988). "Differentials, the Theory and Practice". Constructor Quarterly. Retrieved 13 November 2017.
^ British Patent No. 16,345 (1904)
^ ^a ^b Nice, Karim (6 June 2001). "How Caterpillar Skid Steer Loaders & Multi Terrain Loaders Work". How Stuff Works. Retrieved 23 November 2017.
^ ^a ^b Moloughney, Tom (28 September 2021). "2022 Rivian R1T First Drive Review: Electric Off-Road Dominance". InsideEVs. Retrieved 5 October 2021.
^ McGuigan, Stuart J.; Moss, Peter J. (November 1998). "A Review of Transmission Systems for Tracked Military Vehicles". Journal of Battlefield Technology. 1 (3). Retrieved 23 November 2017.
^ Green, Michael; Brown, James D. (2008). Tiger Tanks at War. MBI Publishing Company. p. 46. ISBN 9781610600316.

[PE-1] ^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ Edwards, Phillip (September 1988). "Differentials, the Theory and Practice". Constructor Quarterly. Retrieved 13 November 2017.

[2] British Patent No. 16,345 (1904)

[HSW-3] Nice, Karim (6 June 2001). "How Caterpillar Skid Steer Loaders & Multi Terrain Loaders Work". How Stuff Works. Retrieved 23 November 2017.

[insideevs20210928-4] Moloughney, Tom (28 September 2021). "2022 Rivian R1T First Drive Review: Electric Off-Road Dominance". InsideEVs. Retrieved 5 October 2021.

[5] McGuigan, Stuart J.; Moss, Peter J. (November 1998). "A Review of Transmission Systems for Tracked Military Vehicles". Journal of Battlefield Technology. 1 (3). Retrieved 23 November 2017.

[6] Green, Michael; Brown, James D. (2008). Tiger Tanks at War. MBI Publishing Company. p. 46. ISBN 9781610600316.

[1]

[2]

[3]

[4]

[5]

[6]

@@ Line 1: / Line 1: @@
+{{Short description|The steering method used by tanks and similar tracked vehicles}}
-{{about|differential torque for steering|unintentional torque disequilibrium|torque steer|intentional torque targeting|torque vectoring}}
+{{About|differential torque for steering|unintentional torque disequilibrium|torque steer|intentional torque targeting|torque vectoring}}
 {{single source|date=November 2017}}
+{{Use dmy dates |date=May 2022}}
 [[File:Centurion tank engine and transmission pic3.JPG|right|thumb|Transmission (foreground) and engine (background) of a [[Centurion tank]]]]
-'''Differential steering''' is the means of [[steering]] a land [[vehicle]] by applying more or less drive torque to one side of the vehicle than the other.<ref name = "PE">{{cite web
+'''Differential steering''' is the means of [[steering]] a land [[vehicle]] by applying more drive torque to one side of the vehicle than the other.<ref name = "PE">{{cite web
 | url = http://www.scmec.us/diffs3.html
 | title = Differentials, the Theory and Practice
-| author = Phillip Edwards
+| first = Phillip
+| last = Edwards
 | date = September 1988
 | publisher = Constructor Quarterly
@@ Line 19: / Line 23: @@
 | url = https://science.howstuffworks.com/transport/engines-equipment/skid-steer2.htm
 | title = How Caterpillar Skid Steer Loaders & Multi Terrain Loaders Work
-| author = Karim Nice
+| first = Karim
+| last = Nice
+| date = 6 June 2001
 | publisher = How Stuff Works
+| accessdate = 2017-11-23}}</ref> and electric.<ref name=insideevs20210928/><!-- senses slip on each wheel with millisecond granularity, "distributes the proper amount of power to each wheel, precisely as needed.  Able to steer in "Tank Turn" mode, with software operating each of the four wheels of the [[Rivian R1T]] independently.<ref name=insideevs20210928/> -->
-| accessdate = 2017-11-23}}</ref> and electric.
 ===Clutch-brake===
-In clutch-brake differential steering, power is disconnected to one side or the other with a [[clutch]], and the unpowered side may also have a [[brake]] applied to tighten the turn.<ref name = "PE"/> This method is simple to implement but inefficient and only suitable for light vehicles.<ref name = "PE"/><ref>{{cite web
+In clutch-brake differential steering, power is disconnected to one side or the other with a [[clutch]], and the unpowered side may also have a [[brake]] applied to tighten the turn.<ref name = "PE"/> Note that there is no differential gearset in this design.  The tracks on either side of the vehicle will always turn at the same speed unless one is declutched for steering.  This method is simple to implement but inefficient and only suitable for light vehicles. Also, when traveling downslope under engine braking, declutching one side to turn can result in a turn in the other direction.<ref name = "PE"/><ref>{{cite journal
 | url = http://www.argospress.com/articles/1998/a-review-of-transmission-systems-for-tracked-military-vehicles
+|url-access=subscription
 | title = A Review of Transmission Systems for Tracked Military Vehicles
-| author = Stuart J. McGuigan; Peter J. Moss
+| first1 = Stuart J.
+| last1 = McGuigan
+| first2 = Peter J.
+| last2 = Moss
 | date = November 1998
-| publisher = ''Journal of Battlefield Technology''
+|journal=Journal of Battlefield Technology
+|volume=1
+|issue=3
 | accessdate = 2017-11-23}}</ref>
 [[Image:Gehl 1640 l.jpg|thumb|right|A [[Gehl Company|Gehl]] skid-steer loader]]
 ===Braked-differential===
 In brake-differential steering, power is applied to both sides through a [[Differential (mechanical device)|differential]] and a brake is applied to one side or the other. The slowing of one side causes the other side to speed up, because of the differential, and so the vehicle maintains a constant speed. A subsequent disadvantage is that changes in rolling resistance or traction from one side to the other automatically causes the vehicle to steer unless counteracted by the driver.<ref name = "PE"/> Differential steering of this type was used in many half-track designs to assist with making tight turns.
 ===Controlled-differential===
-In controlled-differential steering, [[pinions]] within the differential are locked causing one side to rotate faster than the other. An advantage is that no power is lost to braking. A disadvantage is that only one [[turning radius]] is possible. This method was developed by the [[Cleveland Tractor Company]] in 1921 and called the ''Cletrac Regenerative Steering System''.<ref name = "PE"/>
+In controlled-differential steering, [[pinions]] within the differential are locked causing one side to rotate faster than the other. An advantage is that no power is lost to braking. A disadvantage is that only one [[turning radius]] can be performed efficiently. This method was developed by the [[Cleveland Tractor Company]] in 1921 and called the ''Cletrac Regenerative Steering System''.<ref name = "PE"/>
 ===Geared===
-In geared differential steering, two complete [[gearbox]]es are used to provide power to each side, and one distinct turning radius can be derived from each [[gear ratio]]. The main disadvantage to this system is that it doubles the size and weight of the total transmission and therefore it has only been implemented experimentally.<ref name = "PE"/>
+In geared differential steering, two complete [[gearbox]]es are used to provide power to either side, and one distinct turning radius can be derived from each [[gear ratio]] combination. The main disadvantage to this system is that it doubles the size and weight of the total transmission and therefore it has only been implemented experimentally.<ref name = "PE"/>
 ===Maybach double-differential===
-[[File:Differential steering mechanism.png|right|thumb|Differential steering mechanism, either double-differential minus the clutches, or triple-differential minus the brakes]]
-In the Maybach double-differential, power is transmitted to each side through a single, main transmission and then through an [[epicycle gear]] on each side. A different drive speed is caused on one side or the other by feeding torque from a separate transmission into one epicycle gear or the other. Each gear ratio of this second transmission generates a distinct turning radius. A pair of clutches is used to select which track the steering input is applied to.  This system was implemented on German [[Panther tank]]s during World War II.<ref name = "PE"/>
+In the Maybach double-differential, power is transmitted through a single main transmission and then through an [[epicycle gear]] final drive on each side. A different drive speed is caused by feeding torque, from a separate "steering" transmission, into one final drive or the other using a pair of clutches. Usually the steering input turns at a fixed ratio relative to the engine, which results in a different turn radius for each main transmission ratio.  This system was implemented on German [[Panther tank]]s during World War II.<ref name = "PE"/>  The drawback of this design compared to other multiple-differential designs is that applying the steering input to one track also increases the average speed of the two tracks, so the vehicle's speed is not constant.
 ===Double-differential===
+[[File:Differential steering mechanism.png|right|thumb|Differential steering mechanism, either double-differential minus the clutches, or triple-differential minus the brakes]]
-In double-differential steering, power from a second transmission is fed an epicycle gear in the final drive of one side or the other, as in the Maybach double-differential system, but constant drive speed is achieved by adding an [[Idler-wheel|idler]] to apply the opposite torque to the epicycle gear on the other side. A pair of clutches is used to apply the steering input, which only turns one direction, to the steering cross-shaft in either direction. This system was developed in 1928 by Major Wilson.<ref name = "PE"/>
+In double-differential steering, as in the Maybach double-differential system, power from a second transmission is fed into an epicycle gear in the final drive of one side or the other.  In this design, however, the average drive speed of the tracks is maintained by adding an [[Idler-wheel|idler]] to apply the opposite torque to the epicycle gear on other side of the turn. A pair of clutches is used to apply the steering transmission output, which only turns one direction, to the steering cross-shaft in either direction. This system was developed in 1928 by Major Wilson.<ref name = "PE"/>  Here, the steering input is used not so much to apply torque to either side but rather to control the difference in torque and speed between the two sides.
+Also note that, in any of the double- or triple-differential steering methods, the efficient turn radii (e.g., with no steering clutch or brake slipping) are determined by the ratio between the steering input speed and the main drive input speed into each epicyclic final drive.  This means that having multiple ratios in the steering transmission results in multiple turn radii for each main drive transmission ratio.  The additional complexity in the mechanical systems and driving controls means that this capability is rarely implemented.{{cn|date=October 2021}}
 ===Triple-differential===
-Triple-differential steering is similar to double-differential steering except that, rather than using a steering cross-shaft and an idler gear, it uses two steering cross-shafts connected to a steering differential.  Part of the drive torque is always applied through the steering differential and the two epicyclic differentials.  Brakes are used, instead of clutches, to slow down one or the other steering cross-shaft.  The steering works much like braked differential steering mentioned above except that the resulting inefficiency from applying the steering brakes only affects the torque being transmitted via the steering input.
+Triple-differential steering is similar to double-differential steering except that, rather than using a steering cross-shaft and an idler gear, it uses two steering cross-shafts connected to a steering differential.  Part of the drive torque is always applied through the steering differential and the two epicyclic differentials.  Brakes are used, instead of clutches, to slow down one or the other steering cross-shaft.  The steering works much like braked differential steering mentioned above except that the resulting inefficiency from applying the steering brakes only affects the torque being transmitted via the steering input.{{cn|date=October 2021}}
 ===Hydraulic===
@@ Line 58: / Line 74: @@
 ===Electric===
 [[Image:Tanklike.png|right|thumb|A three-wheeled differentially steered robot]]
-Electric differential steering consists of two electric motors, one for each side, that are driven at different speeds, depending on steering needs. It is often implemented in [[Differential wheeled robot|wheeled robot]]s.
+Electric differential steering consists of two or more electric motors—one for each side of the vehicle, or up to as many as one per wheel—that are driven at different speeds (or directions), depending on steering needs.<ref name=insideevs20210928>{{cite news |last=Moloughney|first=Tom |title=2022 Rivian R1T First Drive Review: Electric Off-Road Dominance |work=InsideEVs |date=28 September 2021 |url=https://insideevs.com/reviews/536129/2022-rivian-r1t-first-drive-review/ |access-date=5 October 2021 }}</ref>  It is often implemented in [[Differential wheeled robot|wheeled robot]]s.
 === Hand ===
@@ Line 66: / Line 83: @@
 Depending on implementation, friction between drive mechanism and ground, and available power, a vehicle with differential steering may have a zero turning radius or a ''curb-to-curb turning circle'' equal to the length of the vehicle by driving each side at the same speed but in opposite directions. This is also called a ''neutral turn''.<ref>{{cite book
 | title = Tiger Tanks at War
-| author = Michael Green, James D. Brown
+| first1 = Michael
+| last1 = Green
+| first2 = James D.
+| last2 = Brown
 | date = 2008
 | publisher = MBI Publishing Company.
 | page = 46
+| isbn = 9781610600316
-| url = https://books.google.com/books?id=KLIH9ZKEsXAC&lpg=PA46&ots=DEX1qvTj2Z&dq=tank%20turn%20radius&pg=PA46#v=onepage&q=tank%20turn%20radius&f=false}}</ref> Vehicles on which only one drive wheel on each side is rigidly aligned and all others are free to caster, such as wheelchairs and wheeled robots, require the least power to turn. Vehicles with long continuous tracks on each side which must slide on the ground in order to turn at all require more power.
+| url = https://books.google.com/books?id=KLIH9ZKEsXAC&q=tank+turn+radius&pg=PA46}}</ref> Vehicles on which only one drive wheel on each side is rigidly aligned and all others are free to caster, such as wheelchairs and wheeled robots, require the least power to turn. Vehicles with long continuous tracks on each side which must slide on the ground in order to turn at all require more power.
 == Examples ==
 [[Image:Solo 750.JPG|thumb|The German [[:de:Solo 750|Solo 750 <sup>(WP:DE)</sup>]]]]
 [[File:TORO Z Master Commercial Zero-Turn Riders mower at Construct Expo Utilaje 2010.JPG|thumb|right|A Toro Z Master Commercial Zero-Turn mower]]
+[[Image:Red self-balancing two-wheeled board with a person standing on it.png|thumb|A [[self-balancing scooter]] or hoverboard]]
 * [[Tank]]s, [[armored personnel carrier]]s, [[armoured vehicle-launched bridge]], [[self-propelled anti-aircraft weapon]], and similar military vehicles
 * [[Bulldozer]]s, [[excavator]]s, [[tractor]]s, [[snowcat]]s, [[trencher (machine)|trencher]]s, and other heavy equipment
@@ Line 82: / Line 105: @@
 * [[Differential wheeled robot]]s
 * [[Wheel chair]]s
+* [[Self-balancing scooter]]s
 == See also ==
@@ Line 87: / Line 111: @@
 == References ==
-{{reflist}}
+{{Reflist}}
 [[Category:Automotive steering technologies]]