While exploiting of a car, drivers constantly face the necessity in torque biasing between drive wheels. While car is on the move, its wheels fall on different bumps. One of the wheels moves on the road, when another one lifts off. Therefore, one wheel receives heavier load, than another. The same effect occurs, when one of the drive wheels is on slippery surface (ice, mud, snow etc.). During turn, the radius of movement of near-side wheels is smaller than of off-side wheels.
• Types of limited-slip differentials.
• Comparison of limited-slip differentials.
• Installation of limited-slip differentials.
Types of limited-slip differentials.
All the examples mentioned above have a negative impact on vehicle composure and steerability. There are also severe loads on steering wheel, transmission components, increased fuel consumption and tire wear out.
To remove these negative attributes, differential was implemented into car transmission, which transfers all loads from engine to wheels. Planetary differentials of classic construction with symmetric torque distribution were installed in early build cars.
This type of differential removed all the disadvantages only in part. In the beginning of 1930s the use of limited-slip differentials was investigated. They were installed in sport cars first, then – in production off-roadsters and road cars. Mostly wide-spread LSDs are following:
- self-locking frictional multidisc differential. It consists of body frame, planet pinion, spider pin, outbound differential axles, axle shaft gears, disc packs. The discs are connected with differential body frame and spider pins one at a time. The discs are sprung with spring;
- self-locking hydraulic differential. Its construction is similar to the one mentioned above, but there are press valve and fluid pump instead of springs;
- gearless differential. It consists of separator, outward and inner gears, rotators, 2 differential axles, crown wheel and body frame;
- thermo-coupler consists of body frame, primary shaft, main shaft, disc packs (of primary and main shaft), hub, pressure disk, 2 circular pressure pistons, circular actuating piston, trim coil spring.
- self-locking differential (QUAIFE). Consists of body frame, right and left planet wheels, side gears (left and right), 2 output shafts;
- 1-st type Torsen. It has body frame, right and left planet wheels, right and left side gears, 2 output shafts;
- 2-nd type Torsen, which consists of body frame, planet wheel connected to right side gear, planet wheel connected to left side gear, left and right output shafts.
Comparison of limited-slip differentials.
Let’s observe the operation of some (most wide-spread) LSDs.
Self-locking frictional multidisc differential.
Its work is based on synchronous rotation of differential axles and body frame, while on straight path and different rotation, while maneuver. In this case friction comes into operation and delivers additive torsion torque to decelerate gear. This type is usually used for sports vehicle because of increased friction disk wear out;
Self-locking hydraulic LSD.
Friction disks draw under piston, which is under pressure from liquid of 1 or 2 gear-type pump. Its negative attributes are approximately the same as of sprung friction;
It is based on gearless couplings instead of planet gear. Due to small difference of differential axles rotational speed, gearless couplings mutually rotate and block the axles, while slipping. Pros: simple construction, comprehensible assembling, low cost. Cons: abrupt work, low efficiency, increased fuel consumption. That’s why it is mostly installed on military machines;
Its operation is based on filling of friction wheelspace with dilatant fluid. With increasing of differential axles rotation difference grows the friction temperature. Due to this, fluid viscosity increases and, as a result, disc coupling. Pros: simple construction and easy to use. Cons: low efficiency, bulky construction, inertance in use. Because of massiveness of their construction, they are used for interaxle differentials;
In this type of differential axles and planet pinions are closed in body frame (in special holes), arranged in 2 rows parallel to body frame pivot centre. Planet pins from different rows clamber each other with screw teeth;
- 1-st type Torsen. Every differential axle has its own planet pins connected two by two with planet pins of another differential axle.
- 2-nd type Torsen. Skew gears and spiral planet pins are used. The planet pin’s axles are parallel to differential axles.
The operational principle of three last types is based on wedging out hypoid or screw couplings.
Installation of limited-slip differentials.
Differentials are installed in every type of car. One differential is installed for cars with one driving axle. It is installed on driving axle between wheels.
Two differentials are used for cars with add-on second driving axle: one for each axle, also between wheels. In cars with permanent 4WD 3 differentials are installed: one between axles, two between wheels.
The cross-axle differential distributes load between the wheels depending on their operating condition. And interaxle differential distributes load between axles.
All types of differentials can be installed between axles of all-wheel drive vehicles and between wheels of all-wheel drive and two-wheel drive vehicles. Thermo-coupler is installed mostly between axles, due to its massiveness.
To install a differential, it is necessary to study constructional peculiarities of transmission thoroughly and determine the type suitable for installation (despite omnitude of differential production, there are differences, because of which the installation is impossible without specific modifications).
The installation of limited-slip differentials must be performed by highly qualified specialists.