Differential steering

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Transmission (foreground) and engine (background) of a Centurion tank Centurion tank engine and transmission pic3.JPG
Transmission (foreground) and engine (background) of a Centurion tank

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.

Contents

History

Hornsby tractor, 1909 Hornsby.jpg
Hornsby tractor, 1909

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]

A Gehl skid-steer loader Gehl 1640 l.jpg
A Gehl skid-steer loader

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

Differential steering mechanism, either double-differential minus the clutches, or triple-differential minus the brakes Differential steering mechanism.png
Differential steering mechanism, either double-differential minus the clutches, or triple-differential minus the brakes

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 Tanklike.png
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

The German Solo 750 Solo 750.JPG
The German Solo 750
A Toro Z Master Commercial Zero-Turn mower TORO Z Master Commercial Zero-Turn Riders mower at Construct Expo Utilaje 2010.JPG
A Toro Z Master Commercial Zero-Turn mower
A self-balancing scooter or hoverboard Red self-balancing two-wheeled board with a person standing on it.png
A self-balancing scooter or hoverboard

See also

Related Research Articles

<span class="mw-page-title-main">Differential (mechanical device)</span> Type of simple planetary gear train

A differential is a gear train with three drive shafts that has the property that the rotational speed of one shaft is the average of the speeds of the others. A common use of differentials is in motor vehicles, to allow the wheels at each end of a drive axle to rotate at different speeds while cornering. Other uses include clocks and analog computers.

<span class="mw-page-title-main">Steering</span> System of components that allows vehicles to follow the desired course

Steering is a system of components, linkages, and other parts that allows a driver to control the direction of a vehicle.

<span class="mw-page-title-main">Automatic transmission</span> Type of motor vehicle transmission that automatically changes gear ratio as the vehicle moves

An automatic transmission is a multi-speed transmission used in motor vehicles that does not require any input from the driver to change forward gears under normal driving conditions.

A traction control system (TCS), also known as ASR, 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">Continuously variable transmission</span> Automotive transmission technology

A continuously variable transmission (CVT) is an automatic transmission that can change through a continuous range of gear ratios. This contrasts with other transmissions that provide a limited number of gear ratios in fixed steps. The flexibility of a CVT with suitable control may allow the engine to operate at a constant RPM while the vehicle moves at varying speeds.

<span class="mw-page-title-main">Manual transmission</span> Motor vehicle manual gearbox; stick shift

A manual transmission (MT), also known as manual gearbox, standard transmission, or stick shift, is a multi-speed motor vehicle transmission system, where gear changes require the driver to manually select the gears by operating a gear stick and clutch.

<span class="mw-page-title-main">Limited-slip differential</span> Differential gearbox that limits the rotatational speed difference of output shafts

A limited-slip differential (LSD) is a type of differential that allows its two output shafts to rotate at different speeds but limits the maximum difference between the two shafts. Limited-slip differentials are often known by the generic trademark Positraction, a brand name owned by General Motors.

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

Quattro is the trademark used by the automotive brand Audi to indicate that all-wheel drive (AWD) technologies or systems are used on specific models of its automobiles.

<span class="mw-page-title-main">Drive shaft</span> Mechanical component for transmitting torque and rotation

A drive shaft, driveshaft, driving shaft, tailshaft, propeller shaft, or Cardan shaft is a component for transmitting mechanical power and torque and rotation, usually used to connect other components of a drivetrain that cannot be connected directly because of distance or the need to allow for relative movement between them.

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.

Jeep uses a variety of four-wheel drive systems on their vehicles. These range from basic part-time systems that require the driver to move a control lever to send power to four wheels, to permanent four-wheel systems that monitor and sense traction needs at all four wheels automatically under all conditions.

A transmission control unit (TCU), also known as a transmission control module (TCM), or a gearbox control unit (GCU), is a type of automotive ECU that is used to control electronic automatic transmissions. Similar systems are used in conjunction with various semi-automatic transmissions, purely for clutch automation and actuation. A TCU in a modern automatic transmission generally uses sensors from the vehicle, as well as data provided by the engine control unit (ECU), to calculate how and when to change gears in the vehicle for optimum performance, fuel economy and shift quality.

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, to freely distribute the optimum amount of torque to all four wheels in accordance with driving conditions." The system was announced in April 2004, and first introduced in the North American market in the second generation 2005 model year Acura RL, and in Japan as the fourth generation Honda Legend.

A wheelspin occurs when the force delivered to the tire tread exceeds that of available tread-to-surface friction and one or more tires lose traction. This leads the wheels to "spin" and causes the driver to lose control over the tires that no longer have grip on the road surface. Wheelspin can also be done intentionally such as in drifting or doing a burnout.

S-AWC is the brand name of an advanced full-time four-wheel drive system developed by Mitsubishi Motors. The technology, specifically developed for the new 2007 Lancer Evolution, the 2010 Outlander, the 2014 Outlander, the Outlander PHEV and the Eclipse Cross have an advanced version of Mitsubishi Motors' AWC system. Mitsubishi Motors first exhibited S-AWC integration control technology in the Concept-X model at the 39th Tokyo Motor Show in 2005. According to Mitsubishi Motors, "the ultimate embodiment of the company's AWC philosophy is the S-AWC system, a 4WD-based integrated vehicle dynamics control system".

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<span class="mw-page-title-main">Cross-drive steering transmission</span>

A cross-drive steering transmission is a transmission, used in tracked vehicles to allow precise and energy-efficient steering.

<span class="mw-page-title-main">Drivetrain</span> Group of components that deliver power to the driving wheels

A drivetrain is the group of components that deliver mechanical power from the prime mover to the driven components. In automotive engineering, the drivetrain is the components of a motor vehicle that deliver power to the drive wheels. This excludes the engine or motor that generates the power. In marine applications, the drive shaft will drive a propeller, thruster, or waterjet rather than a drive axle, while the actual engine might be similar to an automotive engine. Other machinery, equipment and vehicles may also use a drivetrain to deliver power from the engine(s) to the driven components.

<span class="mw-page-title-main">Car controls</span> Car parts used to control the vehicle

Car controls are the components in automobiles and other powered road vehicles, such as trucks and buses, used for driving and parking.

Tank steering systems allow a tank, or other continuous track vehicle, to turn. Because the tracks cannot be angled relative to the hull, steering must be accomplished by speeding one track up, slowing the other down, or a combination of both. Half-track vehicles avoid this by combining steerable wheels and fixed-speed tracks.

References

  1. 1 2 3 4 5 6 7 8 9 Edwards, Phillip (September 1988). "Differentials, the Theory and Practice". Constructor Quarterly. Retrieved 13 November 2017.
  2. British Patent No. 16,345 (1904)
  3. 1 2 Nice, Karim (6 June 2001). "How Caterpillar Skid Steer Loaders & Multi Terrain Loaders Work". How Stuff Works. Retrieved 23 November 2017.
  4. 1 2 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.