What are Shocks and Struts?
Shocks and struts are essential components of a vehicle’s suspension system, responsible for absorbing shocks and vibrations from the road and providing a smooth and comfortable ride. They work in tandem with the springs to dampen the oscillations caused by uneven surfaces and maintain proper vehicle control.
Importance of Shocks and Struts in Vehicles
Shocks and struts serve several vital functions:
- Damping and Shock Absorption: Their primary role is to absorb and dissipate the energy from road irregularities, bumps, and impacts, preventing this energy from being directly transmitted to the vehicle’s body and passengers. This damping action ensures a smoother and more comfortable ride.
- Vehicle Stability and Control: By controlling the motion of the wheels and minimizing excessive bouncing or oscillations, shocks and struts contribute to better vehicle stability, handling, and control, especially during braking, acceleration, and cornering maneuvers.
- Load Support: In the case of struts, they also serve as structural components, supporting a significant portion of the vehicle’s weight through the suspension springs. This load-bearing function is crucial for maintaining proper ride height and vehicle dynamics.
Differences Between Shocks and Struts
Structural Differences
Shocks and struts are both part of a vehicle’s suspension system, but they have distinct structural designs:
- Shocks are individual components that control the up-and-down motion of the suspension . They consist of a hydraulic cylinder with a piston inside.
- Struts are a structural component of the suspension system that combines a shock absorber and a coil spring in a single unit. The strut assembly includes the shock absorber, coil spring, spring seat, and upper mount.
Functionality
- Shocks are solely responsible for damping the up-and-down motion of the suspension. They absorb the energy from bumps and dissipate it, preventing excessive bouncing.
- Struts not only dampen the up-and-down motion but also provide structural support for the vehicle’s suspension and bear some of the vehicle’s weight . They act as a structural link between the body and the wheel.
Design and Components
- Shocks have a simpler design with a hydraulic cylinder and piston .
- Struts have a more complex design with additional components like a coil spring, spring seat, and upper mount . They often incorporate features like a bearing plate, jounce bumper, and dust shield.
- Struts may include additional components like a strut mount with vibration isolation features , a filtration assembly , and a rotary abutment for improved performance.
Installation and Replacement
- Shocks are typically easier to replace as they are individual components.
- Replacing struts often requires disassembling more components and may involve additional parts like a spring compressor.
Performance and Ride Quality
- Both shocks and struts contribute to ride quality, but struts have a more significant impact due to their structural role in the suspension system.
- Struts aim to provide better handling and stability, especially during cornering and braking, as they support the vehicle’s weight.
- Advanced strut designs may incorporate features like adjustable damping or magnetorheological fluid for improved performance and adaptability.
How to Maintain Your Shocks and Struts
Servicing and Maintenance
Over time, gas and oil can leak, degrading performance. Servicing involves:
- Deflating the strut and compressing it fully
- Charging with oil under pressure to minimize trapped air
- Extending the piston to a predetermined stroke
- Charging with gas to the specified pressure
This “weight-off-wheels” servicing process eliminates variations from trapped air, ensuring that gas and oil levels remain within the design envelope for proper functionality. Temperature should also be measured to adjust gas pressure accordingly.
Monitoring and Testing
Monitoring systems can detect oil/gas loss by analyzing transient pressure coefficients and temperature-adjusted pressures during landings. Dynamic testing, like drop tests or rolling tests, evaluates impact loads and force-time curves, which can be influenced by factors like wing flexibility. Modeling and simulation tools aid in optimizing designs and servicing procedures.
Applications of Shocks and Struts
Automotive Applications
Shocks and struts are critical components in automotive suspension systems, absorbing impacts and vibrations from the road. Their primary applications include:
- Vehicle Suspension: Shocks and struts are essential for maintaining vehicle stability, handling, and ride comfort by damping the oscillations of the springs. They help keep the tires in contact with the road surface and prevent excessive bouncing or swaying.
- Shock Absorption: During sudden impacts or collisions, shocks, and struts absorb the kinetic energy and dissipate it, protecting the vehicle’s chassis and occupants from severe jolts. This is particularly important in crash scenarios.
- Adjustable Ride Height: Some strut designs allow for adjustable ride height, enabling customization for different driving conditions or vehicle loads.
Aircraft and Aerospace Applications
Shocks and struts play a crucial role in aircraft landing gear systems, where they must withstand high impact forces during landing and taxiing:
- Landing Gear Struts: Aircraft landing gear frequently uses oleopneumatic shock struts to cushion impact forces during touchdown and provide a smooth landing. Their design is crucial for passenger safety and the structural integrity of the aircraft.
- Shock Absorption for Components: Shock absorbers protect sensitive aerospace components from vibrations and shocks during flight and landing.
Other Applications
Beyond automotive and aerospace, shocks and struts find applications in various industries where impact absorption and vibration damping are required:
- Industrial Machinery: Shock absorbers reduce vibrations in industrial machines like presses and textile machines, extending equipment life.
- Protective Structures: Shock absorbers are integrated into bumpers, barriers, and safety systems to absorb impact forces and prevent damage.
- Sporting Goods: Shock absorbers are used in equipment like shoes and protective gear to cushion impacts and improve comfort.
Application Cases
| Product/Project | Technical Outcomes | Application Scenarios |
|---|---|---|
| Adaptive Suspension Systems | Utilising real-time sensors and adjustable damping, these systems optimise ride comfort and handling by adapting to road conditions and driving styles. This results in improved traction, stability, and reduced body roll. | Luxury and performance vehicles, where a balance of comfort and dynamic handling is desired. |
| Semi-Active Suspension Struts | Employing magnetorheological or electrorheological fluids, these struts can rapidly adjust damping forces in response to sensor data, providing superior ride quality and handling compared to passive systems. | Sports cars, off-road vehicles, and other applications where precise suspension control is critical. |
| Air Suspension Systems | Using adjustable air springs instead of conventional coil springs, these systems can dynamically alter ride height and stiffness, improving load-carrying capacity, ride comfort, and handling characteristics. | Commercial vehicles, luxury cars, and off-road vehicles where variable load and terrain conditions are encountered. |
| Aircraft Landing Gear Struts | Designed to withstand extreme impact forces during landing and taxiing, these struts utilise advanced materials and oleo-pneumatic or gas-charged damping mechanisms to absorb shocks and protect the airframe. | Commercial and military aircraft, where safe and controlled landing is critical for passenger safety and structural integrity. |
| Motorcycle Suspension Systems | Employing specialised dampers and springs, these systems are optimised for the unique dynamics of motorcycles, providing enhanced stability, cornering performance, and rider comfort over various road surfaces. | High-performance motorcycles, off-road motorcycles, and touring bikes where precise suspension tuning is essential for handling and rider experience. |
Latest Innovations of Shocks and Struts
Shock Absorber Design Innovations
- Nonlinear Spring Shock Stops: Using nonlinear springs as shock stops instead of conventional hard stops can reduce impact force and enable wafer-level fabrication. Test devices with nonlinear springs showed an 88% shock survival rate compared to 4% for hard stops.
- Soft Coating Shock Stops: Applying a soft Parylene coating as a shock-stop material can absorb impact and improve the shock survival rate to 94%. Optimizing the design parameters of these soft shock springs further enhances protection.
- Multifunction Support: A single-piece multifunction support integrates filtration, shock absorption, and rotary stop housing, reducing complexity and improving the durability of struts.
- Strut with Elastic Body: Providing an elastic body in the strut design can absorb bending forces and prevent damage to the conductor member and penetrated member, improving durability for vehicles like motorcycles.
Strut-based Combustor Innovations
- Hydrogen Injection Wedge Strut: Strut geometries with ramps, grooves, and asymmetric designs can enhance mixing efficiency, combustion efficiency (up to 78.4%), and streamwise motion of fuel in scramjet combustors.
- Strut-assisted Liquid Fuel Injection: Injecting liquid fuel adjacent to a strut and cavity flame holder improves vaporization, lateral dispersion, and mixing efficiency in supersonic combustors compared to cavity-only injection.
- Shock-Vortex Interaction: Streamwise vortices induced by hypermixer struts can interact with shock waves, promoting supersonic combustion. Vortex breakdown near shock impingement enhances pressure rise and combustion.
Performance Optimization
- Transonic Strut-Braced Wing: Aerodynamic shape optimization of a strut-braced wing aircraft shows potential for 7.8% block fuel burn reduction over a conventional tube-and-wing design for single-aisle aircraft.
- Shock Strut Stroke Sensing: Providing an intermediate member with high magnetic permeability between the rod pipe and coil improves stroke sensor performance and durability in shock absorbers.
Technical Challenges
| Nonlinear Spring Shock Stops | Utilising nonlinear springs as shock stops instead of conventional hard stops to reduce impact force and enable wafer-level fabrication, improving shock survival rates. |
| Soft Coating Shock Stops | Applying a soft Parylene coating as a shock stop material to absorb impact and improve shock survival rates up to 94%. |
| Multifunction Support Integration | Integrating filtration, shock absorption, and rotary stop housing into a single-piece multifunction support to reduce complexity and improve strut durability. |
| Strut with Elastic Body | Providing an elastic body in the strut design to absorb bending forces and prevent damage to the conductor member and penetrated member, improving durability for vehicles like motorcycles. |
| Hydrogen Injection Wedge Strut | Utilising strut geometries with ramps, grooves, and asymmetric designs to enhance mixing efficiency, combustion efficiency (up to 78.4%), and streamwise motion of fuel in scramjet combustors. |
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