Front Drive Halfshafts - Front Drive Halfshafts - System Operation and Component Description

Description and Operation

System Operation

The powertrain and the transmission of torque through the powertrain on vehicles with front-wheel drive are as follows:

• engine,
• Transaxle input shaft
• Transmission output shafts
• Differential
• Drive shafts
• wheel hub assembly,
• Wheel

Halfshafts transmit rotary motion through constant velocity joints in a uniform manner, i.e. the angular velocities on the drive side and the output side do not vary from one another. This avoids irregularities in the powertrain and additional stresses from neighboring components.
The outer CV joints use balls, have no length compensation and engage in the wheel hubs.
The intermediate shaft (right side) is correctly positioned and secured in the differential by the intermediate shaft center bearing.
The left CV joint is locked in the differential by a snap-ring.
To allow the vehicle suspension to operate, the inner CV joints have tripod joints which allow changes in the torque transmission angle and length compensation when an axial shift occurs between the transmission and the wheel. The wheel-side constant velocity joints are attached to the wheel hubs.

Component Description

CV joint with length compensation

The length compensation of the halfshaft needed due to the suspension is achieved on the axle drive side by constant velocity joints with length compensation. In the case of front-wheel drive vehicles these CV joints are mounted on the transmission side and in the case of rear-wheel drive vehicles on the wheel side.
A CV joint with length compensation is also called a tripod joint, because the outer cup has three large, elongated recesses arranged at equal intervals around the periphery, in which three needle-bearing-mounted rollers are able to move axially. The cross-section clearly shows how the left shaft terminates inside the joint, where it supports three short shaft stubs (called a spider), on which the needle-bearing-mounted rollers are arranged.

 

1___Needle-bearing-mounted rollers

2___Halfshaft stub

3___Spider

4___Boot

 

The CV joint with length compensation transmits the torque uniformly from the axle drive (sprung mass) to the driving wheel (unsprung mass). Therefore during a rotation, in contrast to universal joints for example, there is no lead or lag of the driven elements relative to the driving elements. Due to the uniform transmission of torque, even on deflection, constant velocity joints with length compensation are also called homokinetic joints.
The maximum deflection angle is approx. 20° and the length compensation needed, mainly due to the vehicle suspension, is up to approx. 30 mm. In view of the high stresses, the sliding surfaces are hardened. Constant velocity slip joints are permanently lubricated with grease. Their protective boots should be checked regularly for damage, to prevent grease from escaping and dirt from getting in, thus causing rapid wear.

Constant velocity joint without length compensation

In the case of large deflection angles on the driving wheels of front-wheel drive vehicles, this half shaft joint transmits torque with minimal effect on the steering.
Ball cup

 

1___Ball cup of a constant velocity joint without length compensation

2___Milled and hardened ball races

Ball races are milled inside a ball cup connected to the wheel.

1___Ball

2___Ball star

3___Half shaft stub

4___Snap ring

5___Carrier

6___Ball cup

 

Races are also milled in the outside of the ball star connected to the half shaft. The balls are held by a suitable cage and allow the joint to transmit force in a uniform (homokinetic) manner up to a deflection angle of approx. 47°. This allows full wheel deflection with front-wheel drive, despite the half shaft.
Cross-section through front drive half shaft

 

1___Outer CV joint without length compensation (ball cups shown complete)

2___Boot tightening strap – outer boot (large)

3___Outer CV joint boot

4___Front axle driveshaft

5___Boot tightening strap – outer boot (small)

 

The illustration shows a cross-section of a front drive half shaft through the wheel suspension with a CV joint without length compensation. The CV joint engages in the wheel hubs.
Ball joints are therefore also called constant velocity fixed joints and are permanently lubricated with grease. Their protective boots should be checked regularly for damage, to prevent grease from escaping and dirt from getting in. When replacing boots make sure they contain exactly the right quantity of grease; it is also necessary to inject a certain quantity into the joint.

Gaiter

 

1___Recess for large boot tightening strap

2___Recess for small boot tightening strap

 

The boot tightening straps ensure dustproof and waterproof seating on the half shaft.
The rubber boot protects the CV joint from moisture and dirt and the joint grease from drying out.
The rubber compound of the boot ages and becomes brittle and must be checked for cracks during vehicle maintenance.