Live axle
Encyclopedia
Beam axle
A beam axle is a suspension system, also called a solid axle, in which one set of wheels is connected laterally by a single beam or shaft...
suspension system
Suspension (vehicle)
Suspension is the term given to the system of springs, shock absorbers and linkages that connects a vehicle to its wheels. Suspension systems serve a dual purpose — contributing to the car's roadholding/handling and braking for good active safety and driving pleasure, and keeping vehicle occupants...
that uses the driveshaft
Driveshaft
A drive shaft, driveshaft, driving shaft, propeller shaft, or Cardan shaft is a mechanical component for transmitting torque and rotation, usually used to connect other components of a drive train that cannot be connected directly because of distance or the need to allow for relative movement...
s that transmit power to the wheels to connect the wheels laterally so that they move together as a unit.
A live axle consists of a central differential
Differential (mechanics)
A differential is a device, usually, but not necessarily, employing gears, capable of transmitting torque and rotation through three shafts, almost always used in one of two ways: in one way, it receives one input and provides two outputs—this is found in most automobiles—and in the other way, it...
in a single housing that also contains the driveshafts that connect the differential to the driven wheels. The differential is connected to the engine via a swinging drive shaft and a universal joint
Universal joint
A universal joint, universal coupling, U joint, Cardan joint, Hardy-Spicer joint, or Hooke's joint is a joint or coupling in a rigid rod that allows the rod to 'bend' in any direction, and is commonly used in shafts that transmit rotary motion...
. The complete assembly may typically be suspended with leaf spring
Leaf spring
Originally called laminated or carriage spring, a leaf spring is a simple form of spring, commonly used for the suspension in wheeled vehicles...
s, coil spring
Coil spring
A Coil spring, also known as a helical spring, is a mechanical device, which is typically used to store energy and subsequently release it, to absorb shock, or to maintain a force between contacting surfaces...
s or air bags
Air suspension
Air suspension is a type of vehicle suspension powered by an engine driven or electric air pump or compressor. This pump pressurizes the air, using compressed air as a spring. Air suspension replaces conventional steel springs. If the engine is left off for an extended period, the car will settle...
.
In small trucks solid front axles have generally been replaced by independent front suspension.
Some live axles use trailing arm
Trailing arm
thumb|220px|Trailing arm rear suspension of [[Front-engine, front-wheel drive layout|FF]] carsA trailing-arm suspension is an automobile suspension design in which one or more arms are connected between the axle and the chassis. It is usually used on rear axles...
s, semi-trailing arms, Panhard rod
Panhard rod
A Panhard rod is a component of a car suspension system that provides lateral location of the axle...
, or Watt's linkage
Watt's linkage
Watt's linkage is a type of mechanical linkage invented by James Watt in which the central moving point of the linkage is constrained to travel on an approximation to a straight line...
to control the vertical and lateral movements of the axle. Others, particularly older vehicles, use Hotchkiss drive
Hotchkiss drive
The Hotchkiss drive is a system of power transmission. It was the dominant form of power transmission for front-engine, rear-wheel drive layout cars in the 20th century...
, in which the leaf springs provide axle location as well as suspension.
Advantages and disadvantages
As with any beam axle, the advantages of the live axle are relative simplicity, lower manufacturing costs, lighter overall vehicle weight, and the fact that the axle and suspension systems take up little interior volume. Because the axle assembly is a fairly simple and rigid arrangement, it can easily be made strong and robust, which is an advantage for vehicles with substantial power or that are intended for use in rugged environments or off-road usage. A further advantage of a live/beam axle in off-road use is that ground clearance under the axle remains constant, even if one wheel rises over a bump and the other doesn't.
Ride quality
Ride quality refers to the degree of protection offered vehicle occupants from uneven elements in the road surface, or the terrain if driving off-road. A car with very good ride quality is also a comfortable car to ride in. Cars which disturb vehicle occupants with major or minor road...
and handling
Car handling
Automobile handling and vehicle handling are descriptions of the way wheeled vehicles perform transverse to their direction of motion, particularly during cornering and swerving. It also includes their stability when moving at rest. Handling and braking are the major components of a vehicle's...
. The wheels cannot move independently in response to bumps. Although the overall mass of the total suspension is low, the mass of the differential and driveshafts are part of the vehicle's unsprung weight
Unsprung weight
In a ground vehicle with a suspension, the unsprung weight is the mass of the suspension, wheels or tracks , and other components directly connected to them, rather than supported by the suspension...
, so the greater unsprung mass transmits larger forces to the body of the vehicle and its occupants. Conversely, in an independent rear suspension system the differential is rigidly attached to the vehicle. The lower unsprung mass of the suspension results in a greater ability to absorb imperfections in the road. In passenger car applications, often now fitted with multi-link independent suspension
Multi-link suspension
A multi-link suspension is a type of vehicle suspension design typically used in independent suspensions, using three or more lateral arms, and one or more longitudinal arms....
, the useful ability to change toe and camber independently left to right under cornering loads is not given with a live axle.
Applications
Until the 1980s the live axle was the most common rear suspension system on rear-wheel drive cars in the United StatesUnited States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
. It remains common on truck
Truck
A truck or lorry is a motor vehicle designed to transport cargo. Trucks vary greatly in size, power, and configuration, with the smallest being mechanically similar to an automobile...
s, buses and other heavy vehicles, owing to its greater potential robustness and relatively low maintenance requirements, but most passenger cars have now adopted independent rear suspension instead.
Examples of some passenger-vehicle types that have employed a live axle with various suspension elements are:
- Leaf springLeaf springOriginally called laminated or carriage spring, a leaf spring is a simple form of spring, commonly used for the suspension in wheeled vehicles...
s — the early Land-Rover, original JeepJeepJeep is an automobile marque of Chrysler . The first Willys Jeeps were produced in 1941 with the first civilian models in 1945, making it the oldest off-road vehicle and sport utility vehicle brand. It inspired a number of other light utility vehicles, such as the Land Rover which is the second...
, 1958-90 Toyota Land Cruiser (US-models), 1979-85 Toyota Hilux (US-models), 1985-95 Suzuki Samurai (US-models) - Coil springCoil springA Coil spring, also known as a helical spring, is a mechanical device, which is typically used to store energy and subsequently release it, to absorb shock, or to maintain a force between contacting surfaces...
s — the Range RoverRange RoverThe Range Rover is a large luxury four-wheel drive sport utility vehicle produced by British car maker Land Rover. The model, launched in 1970, is now in its third generation...
1 & 2, Rover SD1Rover SD1Rover SD1 is both the code name and eventual production name given to a series of large executive cars made by British Leyland or BL through its Specialist, Rover Triumph and Austin Rover divisions from 1976 until 1986....
, Volvo 240, current (1997-) Jeep WranglerJeep WranglerThe Jeep Wrangler is a subcompact four-wheel drive sport utility vehicle and an off-road vehicle manufactured by American automaker Chrysler, under its Jeep marque – and now in its fourth generation. It is a successor to the famous World War II 'Jeep' vehicle by way of the Willys civilian...
models; ; - Panhard rodPanhard rodA Panhard rod is a component of a car suspension system that provides lateral location of the axle...
s - the Ford MustangFord MustangThe Ford Mustang is an automobile manufactured by the Ford Motor Company. It was initially based on the second generation North American Ford Falcon, a compact car. Introduced early on April 17, 1964, as a "1964½" model, the 1965 Mustang was the automaker's most successful launch since the Model A...
; Chevrolet CamaroChevrolet CamaroThe Chevrolet Camaro is an automobile manufactured by General Motors under the Chevrolet brand, classified as a pony car and some versions also as a muscle car. It went on sale on September 29, 1966, for the 1967 model year and was designed as a competing model to the Ford Mustang...