Double Wishbone (Parallelogram) Suspension System
Comprehensive Guide to Double Wishbone (Parallelogram) Suspension System
The Double Wishbone Suspension, also known as the Parallelogram Suspension, is a popular suspension design used in many high-performance and luxury vehicles. It is known for its superior handling characteristics, ride comfort, and stability compared to simpler suspension systems like the MacPherson strut. This guide will walk you through the design, components, advantages, and how it works in detail.
What is a Double Wishbone Suspension System?
A Double Wishbone Suspension is a type of independent suspension that uses two wishbone-shaped arms (control arms) to locate the wheel. These control arms are typically placed in a parallel configuration, with one arm positioned above the other, allowing the wheel to move vertically while maintaining its orientation relative to the road.
The system allows for precise control over wheel camber, caster, and toe angles, providing excellent handling and cornering performance.
Components of a Double Wishbone Suspension
Upper Control Arm (Upper Wishbone):
- A smaller A-shaped arm that connects the top of the wheel hub to the vehicle’s frame or chassis.
- Allows the wheel to move up and down while keeping it stable laterally.
Lower Control Arm (Lower Wishbone):
- A larger A-shaped arm that connects the bottom of the wheel hub to the chassis.
- Works with the upper control arm to manage the wheel's vertical movement.
Steering Knuckle:
- The component to which the wheel hub and control arms are connected. It pivots during steering and houses the wheel bearing.
Ball Joints:
- Flexible joints located at the ends of the control arms, allowing for movement in multiple directions while keeping the components securely connected.
Shock Absorber and Coil Spring:
- The shock absorber and coil spring are typically mounted between the lower control arm and the vehicle’s body.
- The spring absorbs shocks from road irregularities, while the damper controls the rebound of the suspension.
Anti-Roll Bar (Sway Bar):
- A bar that connects both sides of the suspension system, reducing body roll during cornering by distributing weight more evenly.
How the Double Wishbone Suspension Works
Vertical Wheel Movement
The upper and lower control arms move up and down as the wheel encounters road bumps. Since both arms are connected to the vehicle’s chassis at fixed points and the wheel hub, the wheel is able to move vertically without changing its angle significantly, preserving tire contact with the road.
Camber Control
Camber refers to the tilt of the wheel relative to the road surface. In a double wishbone suspension, as the wheel moves up and down, the design allows for the camber to change progressively to improve traction during cornering. This dynamic camber change improves the tire’s contact patch, offering better grip and handling.
Independent Movement
The independent suspension allows each wheel to move independently, meaning one wheel can move up or down due to road irregularities without affecting the opposite wheel. This improves ride comfort and vehicle stability on uneven surfaces.
Key Advantages of Double Wishbone Suspension
Improved Handling:
- The double wishbone suspension offers precise control over the wheel’s camber angle, providing better handling in high-speed cornering. Camber changes dynamically as the suspension moves, maximizing tire grip.
Better Stability:
- Since each wheel moves independently, the system offers superior stability during turns and over rough terrain.
Customizability:
- Engineers can fine-tune the suspension geometry (caster, camber, and toe) to optimize the vehicle’s handling characteristics.
Reduced Body Roll:
- With the combination of an anti-roll bar and the suspension geometry, body roll during cornering is minimized.
Enhanced Comfort:
- The design absorbs road irregularities better than simpler suspension systems, leading to a smoother ride.
Disadvantages of Double Wishbone Suspension
Complexity:
- The double wishbone suspension is more complex and has more components than simpler designs like the MacPherson strut, making it harder to manufacture, repair, and maintain.
Space Requirements:
- The double wishbone system occupies more space in the engine bay or wheel wells, making it less ideal for compact cars.
Higher Cost:
- Due to the complexity of its design and materials required, double wishbone suspensions are more expensive to produce and repair.
Real-World Applications
The double wishbone suspension is commonly found in performance cars, luxury vehicles, and sports cars, where precise handling and ride quality are critical. Some examples of vehicles that use this suspension system include:
- Honda Accord (previous generations)
- Lexus IS and GS series
- Mazda MX-5 Miata
- Ferrari 458 Italia
- BMW 3-Series (in some configurations)
Comparison with Other Suspension Types
Double Wishbone vs. MacPherson Strut
- Handling: Double wishbone offers better handling due to greater control over camber angles, while MacPherson strut is simpler and cheaper but offers less performance in aggressive cornering.
- Space: MacPherson strut takes up less space, making it popular in front-wheel-drive vehicles, whereas double wishbone requires more room.
- Cost: MacPherson strut is more cost-effective and easier to manufacture, while double wishbone is more expensive but provides higher performance.
Double Wishbone vs. Multi-Link Suspension
- Complexity: Multi-link suspensions are even more complex than double wishbones, with more control arms and linkages, providing even finer control over wheel movement.
- Performance: Multi-link suspensions can offer even better ride quality and handling, but they are more expensive and harder to maintain.
How to Maintain a Double Wishbone Suspension System
To keep the double wishbone suspension working properly, regular maintenance is crucial:
Inspect Ball Joints: Worn ball joints can lead to wheel misalignment and unstable handling.
Check Control Arm Bushings: Over time, rubber bushings on the control arms can wear out, leading to sloppy handling and excessive wheel movement.
Shock Absorber Maintenance: Regularly check and replace shock absorbers to maintain ride comfort and control over the suspension.
Alignment Check: Ensure the vehicle’s alignment is checked and adjusted periodically to maintain the desired suspension geometry for optimal performance.
Conclusion
The Double Wishbone Suspension System is an advanced design that offers superior control, handling, and ride comfort, making it ideal for performance-oriented and luxury vehicles. Although more complex and costly than simpler systems, its ability to manage wheel angles and provide independent movement gives it a significant advantage on the road.
Understanding the benefits and maintenance needs of this system can help car enthusiasts and engineers appreciate its value and ensure it remains in top working condition for optimal vehicle performance.
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