Vehicle Suspension Systems: Types, Function, and Diagnosis

Mechanical Suspension Types Explained

Understanding the various types of mechanical suspension is crucial for vehicle performance and comfort:

• Rigid Axle: A single metal beam attached to the vehicle body via the suspension and shock absorber system, extending across the entire width of the vehicle. Wheels are mounted on the same axis, meaning the oscillatory movement of one wheel directly affects the other.
• De Dion Axle (Bridge Axle): This is a hybrid system combining elements of rigid axles and independent suspension. It is attached to each rear wheel and designed to accommodate the differential, which is mounted to the frame and considered part of the sprung mass. This design generally improves both comfort and performance.
• Independent Suspension: In this system, each wheel has its own axis, allowing for individual movement. This significantly minimizes the transmission of sprung mass oscillations from the body to the chassis, enhancing ride quality.

Common Independent Suspension Designs:

• Deformable Parallelogram (Double Wishbone)
• McPherson Strut
• Trailing Arms
• Multilink

Industrial Vehicle Suspension Systems

Suspension systems in industrial vehicles are similar to those in automobiles, but with a key difference: comfort is often a secondary consideration. The primary goal is to efficiently support the heavy loads for which the vehicle is designed. While modern systems often incorporate air springs, traditional mechanisms include parabolic springs, trapezoidal springs, and coil springs.

Historically, these vehicles were assembled using rigid axles and various types of leaf springs or longitudinal springs.

• The leaf spring system facilitates clamping, serving as a robust union between the axle and chassis support. While highly effective for heavy loads, they are often noisy and require significant cleaning and greasing.
• The less common coil spring system requires a separate control arm or link bar for the axle. Oscillation damping in these systems is achieved with telescopic shock absorbers.

Motorcycle and Quad Suspension Systems

Two and Three-Wheel Motorcycles:

Motorcycles typically feature a front fork system and a rear swingarm with an articulated telescopic shock absorber and spring. This system allows the wheel to be mounted between the fork legs and provides steering direction via the upper fork bearing. Front forks can be either conventional or inverted.

Four-Wheel ATVs (Quads):

For 4-wheel ATVs (Quads), the front suspension often uses overlapping trapezoidal (A-arm) systems to achieve independent wheel movement. The rear may feature an H-shaped swingarm attached to the chassis on one side and the wheel on the other, allowing for its specific axis of rotation.

Suspension System Diagnosis and Testing

Proper suspension system diagnosis is essential to ensure active safety and driving comfort. It's important to note that the suspension directly affects other critical mechanisms such as steering, brakes, and axles, which is why a comprehensive check is vital. The influence of temperature on shock absorbers is significant, as their buffering capacity depends on the oil's temperature. Before any suspension test, always monitor tire pressure.

Suspension Inspection Without a Test Bench:

A thorough visual and manual inspection can reveal many issues. This includes checking:

• Cushions and bushings
• Silent blocks and compression caps
• Protective boots
• Mounting components for noise
• Oil leaks at the shock absorber stem or body
• Tires for uneven wear
• Ball joints, control arms, and wheel hubs

Perform a bounce test and a visual dynamic test to assess basic functionality.

Suspension Testing with a Test Bench:

For more precise diagnostics, specialized test benches are used:

Roller Test Bench:

This bench calculates the static weight of each axle and the dynamic weight during the test. These two values are then compared to assess individual wheel performance and left-to-right symmetry. It also compares the performance values between the left and right wheels.

Plate Test Bench:

This bench is designed to distinguish suspension rebounds caused by braking forces during the test. An asymmetry exceeding 20% between the two wheels of an axle is considered excessive, indicating that the suspension requires review and potential repair.