Centurion tank engine and transmission pic3

Differential steering is the means of

steering Steering is a system of components, linkages, and other parts that allows a driver to control the direction of the vehicle. Introduction The most conventional steering arrangement allows a driver to turn the front wheels of a vehicle using ...

a land

vehicle A vehicle (from la, vehiculum) is a machine that transports people or cargo. Vehicles include wagons, bicycles, motor vehicles (motorcycles, cars, trucks, buses, mobility scooters for disabled people), railed vehicles (trains, trams), wa ...

by applying more drive torque to one side of the vehicle than the other. Differential steering is the primary means of steering

tracked vehicle Continuous track is a system of vehicle propulsion used in tracked vehicles, running on a continuous band of treads or track plates driven by two or more wheels. The large surface area of the tracks distributes the weight of the vehicle b ...

s, such as

tank A tank is an armoured fighting vehicle intended as a primary offensive weapon in front-line ground combat. Tank designs are a balance of heavy firepower, strong armour, and good battlefield mobility provided by tracks and a powerful engin ...

s and

bulldozer A bulldozer or dozer (also called a crawler) is a large, motorized machine equipped with a metal blade to the front for pushing material: soil, sand, snow, rubble, or rock during construction work. It travels most commonly on continuous track ...

s, is also used in certain wheeled vehicles commonly known as

skid-steer A skid loader, skid-steer loader, SSLs or skidsteer is a small, rigid-frame, engine-powered machine with lift arms that can attach to a wide variety of buckets and other labor-saving tools or attachments. Skid-steer loaders are typically four-whee ...

, and even implemented in some automobiles, where it is called

torque vectoring 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 ...

, to augment steering by changing wheel direction relative to the vehicle. Differential steering is distinct from

torque steer In physics and mechanics, torque is the rotational equivalent of linear force. It is also referred to as the moment of force (also abbreviated to moment). It represents the capability of a force to produce change in the rotational motion of the ...

, which is usually considered a negative side effect of drive-train design choices.

History

A British agricultural company, Hornsby in

Grantham Grantham () is a market and industrial town in the South Kesteven district of Lincolnshire, England, situated on the banks of the River Witham and bounded to the west by the A1 road. It lies some 23 miles (37 km) south of the Lincoln and ...

, developed a continuous track, which was patented in 1905. 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, ''hydraulic'', and electric.

Clutch-brake

In clutch-brake differential steering, power is disconnected to one side or the other with a

clutch A clutch is a mechanical device that engages and disengages power transmission, especially from a drive shaft to a driven shaft. In the simplest application, clutches connect and disconnect two rotating shafts (drive shafts or line shafts). ...

, and the unpowered side may also have a

brake A brake is a mechanical device that inhibits motion by absorbing energy from a moving system. It is used for slowing or stopping a moving vehicle, wheel, axle, or to prevent its motion, most often accomplished by means of friction. Background ...

applied to tighten the turn. 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.

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. 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 A pinion is a round gear—usually the smaller of two meshed gears—used in several applications, including drivetrain and rack and pinion systems. Applications Drivetrain Drivetrains usually feature a gear known as the pinion, which may ...

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 The turning diameter of a vehicle is the minimum diameter (or "width") of available space required for that vehicle to make a circular turn (i.e. U-turn). The term thus refers to a theoretical minimal circle in which for example an aeroplane, a ...

can be performed efficiently. This method was developed by the Cleveland Tractor Company in 1921 and called the ''Cletrac Regenerative Steering System''.

Geared

In geared differential steering, two complete

gearbox Propulsion transmission is the mode of transmitting and controlling propulsion power of a machine. The term ''transmission'' properly refers to the whole drivetrain, including clutch, gearbox, prop shaft (for rear-wheel drive vehicles), differe ...

es are used to provide power to either side, and one distinct turning radius can be derived from each

gear ratio A gear train is a mechanical system formed by mounting gears on a frame so the teeth of the gears engage. Gear teeth are designed to ensure the pitch circles of engaging gears roll on each other without slipping, providing a smooth transmission ...

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.

Maybach double-differential

In the Maybach double-differential, power is transmitted through a single main transmission and then through an

epicycle gear An epicyclic gear train (also known as a planetary gearset) consists of two gears mounted so that the center of one gear revolves around the center of the other. A carrier connects the centers of the two gears and rotates the planet and sun gea ...

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 The Panther tank, officially ''Panzerkampfwagen V Panther'' (abbreviated PzKpfw V) with ordnance inventory designation: ''Sd.Kfz.'' 171, is a German medium tank of World War II. It was used on the Eastern and Western Fronts from mid-1943 to ...

s during World War II. 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 The Idler refers to someone idle: * An idle game * A slacker, a person who habitually avoids work * Idler-wheel, a system used to transmit the rotation of the main shaft of a motor to another rotating device * Idler circuit, a circuit in a paramet ...

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. 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.

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.

Hydraulic

Hydraulic differential steering consists of a

hydraulic drive system Hydraulic machines use liquid fluid power to perform work. Heavy construction vehicles are a common example. In this type of machine, hydraulic fluid is pumped to various hydraulic motors and hydraulic cylinders throughout the machine and ...

with one

hydraulic pump Hydraulic pumps are used in hydraulic drive systems and can be hydrostatic or hydrodynamic. A hydraulic pump is a mechanical source of power that converts mechanical power into hydraulic energy ( hydrostatic energy i.e. flow, pressure). It generat ...

and two

hydraulic motor A hydraulic motor is a mechanical actuator that converts hydraulic pressure and flow into torque and angular displacement (rotation). The hydraulic motor is the rotary counterpart of the hydraulic cylinder as a linear actuator. Most broadly, ...

s, one for each side. This system is often employed on

skid-steer loader A skid loader, skid-steer loader, SSLs or skidsteer is a small, rigid-frame, engine-powered machine with lift arms that can attach to a wide variety of buckets and other labor-saving tools or attachments. Skid-steer loaders are typically four-whee ...

s and

zero-turn mower A zero-turn riding lawn mower (colloquially, a ''z-turn'') is a standard riding lawn mower with a turning radius that is effectively zero when the two drive wheels rotate in opposite direction, like a tank turning in place. Different brands and ...

Electric

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. It is often implemented in

wheeled robot A wheel is a circular component that is intended to rotate on an axle bearing. The wheel is one of the key components of the wheel and axle which is one of the six simple machines. Wheels, in conjunction with axles, allow heavy objects to be ...

Hand

Most traditional

wheelchair A wheelchair is a chair with wheels, used when walking is difficult or impossible due to illness, injury, problems related to old age, or disability. These can include spinal cord injuries ( paraplegia, hemiplegia, and quadriplegia), cerebr ...

s 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''. 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

TORO Z Master Commercial Zero-Turn Riders mower at Construct Expo Utilaje 2010

Tank A tank is an armoured fighting vehicle intended as a primary offensive weapon in front-line ground combat. Tank designs are a balance of heavy firepower, strong armour, and good battlefield mobility provided by tracks and a powerful engin ...

armored personnel carrier An armoured personnel carrier (APC) is a broad type of armoured military vehicle designed to transport personnel and equipment in combat zones. Since World War I, APCs have become a very common piece of military equipment around the world. Acc ...

armoured vehicle-launched bridge An armoured vehicle-launched bridge (AVLB) is a combat support vehicle, sometimes regarded as a subtype of military engineering vehicle, designed to assist militaries in rapidly deploying tanks and other armoured fighting vehicles across gap-t ...

self-propelled anti-aircraft weapon An anti-aircraft vehicle, also known as a self-propelled anti-aircraft gun (SPAAG) or self-propelled air defense system (SPAD), is a mobile vehicle with a dedicated anti-aircraft capability. Specific weapon systems used include machine guns, ...

, and similar military vehicles *

Bulldozer A bulldozer or dozer (also called a crawler) is a large, motorized machine equipped with a metal blade to the front for pushing material: soil, sand, snow, rubble, or rock during construction work. It travels most commonly on continuous track ...

excavator Excavators are heavy construction equipment consisting of a boom, dipper (or stick), bucket and cab on a rotating platform known as the "house". The house sits atop an undercarriage with tracks or wheels. They are a natural progression fro ...

tractor A tractor is an engineering vehicle specifically designed to deliver a high tractive effort (or torque) at slow speeds, for the purposes of hauling a trailer or machinery such as that used in agriculture, mining or construction. Most common ...

snowcat A snowcat (short for snow and caterpillar) is an enclosed-cab, truck-sized, fully tracked vehicle designed to move on snow. Major manufacturers are Pisten Bully (Germany), Prinoth (Italy) and Tucker (United States). Snow groomers A snow ...

s, trenchers, and other heavy equipment *

Skid-steer loader A skid loader, skid-steer loader, SSLs or skidsteer is a small, rigid-frame, engine-powered machine with lift arms that can attach to a wide variety of buckets and other labor-saving tools or attachments. Skid-steer loaders are typically four-whee ...

s and their derivatives *

Amphibious ATV An amphibious all-terrain vehicle, amphibious ATV, (or AATV) is a small, all-wheel drive, all-terrain amphibious vehicle, used for recreation, farm-, hunting, utility or industry tasks, by enthusiasts and professionals worldwide. They are legall ...

s *

Zero-turn mower A zero-turn riding lawn mower (colloquially, a ''z-turn'') is a standard riding lawn mower with a turning radius that is effectively zero when the two drive wheels rotate in opposite direction, like a tank turning in place. Different brands and ...

s * Differential wheeled robots *

Wheel chair A wheelchair is a chair with wheels, used when walking is difficult or impossible due to illness, injury, problems related to old age, or disability. These can include spinal cord injuries (paraplegia, hemiplegia, and quadriplegia), cerebral pa ...

s *

Self-balancing scooter A self-balancing scooter (also hoverboard, self-balancing board, segway or electric scooter board) is a self-balancing personal transporter consisting of two motorized wheels connected to a pair of articulated pads on which the rider places their ...

References

{{Reflist Automotive steering technologies