PASSIVE SHOCK ABSORBERS AND STRUTS

Description

BWI Group passive dampers are derived from a century-long heritage of suspension technology development and manufacture carried out first by Delco Products Division of General Motors Corporation, later by Delphi Automotive, and now by BWI Group. Product portfolio ranges from dampers for all sizes of passenger cars through performance and luxury cars to heavy SUV’s and delivery vans.

 

BWI Group manufactures passive dampers for OEM market in Europe, Asia and North America, developing the core technology in one major technical center in Europe (Kracow, Poland) and working on applications in customer regions.

BWI Groups product development capabilities include:

  • Full CAE capability at vehicle/suspension/component level with FEA-based sizing of structural components and simulation of damper performance (fluid dynamics and valve mechanics),
  • Prototyping capability following manufacturing processes intended for serial production,
  • Expertise in Vehicle Road Load Data analysis and definition of accelerated tests,
  • Full range of validation testing to replicate vehicle operating conditions (labs and experimental vehicles).
  • Ride Development capability with ride vans and tuning personnel in all regions.

Technology

BWI Group passive dampers technology is based on a Bill of Design (BoD) and Bill of Process (BoP) principle combined with continuous improvement and an innovative approach to new product functionalities.

BoD/BoP collects all proven technologies and lessons learned throughout years of manufacture into a set of standardized, reliable and economical design and process solutions.

BWI Group delivers the whole range of passive damper design variants: shock absorbers, coil-over-shock absorbers and McPherson struts in twin- and monotube execution. Piston rod size for twintube dampers ranges from 10 to 28 mm, while main valve sizes extend from 20 to 40 mm. For monotube dampers, piston rod sizes range from 11 mm to 18 mm combined with 36 mm or 46 mm valves. Standard solutions may also incorporate rebound energy management devices like steel or plastic rebound springs and bumpers.

BWI Group focuses on refining damper performance in terms of NVH behaviour and friction reduction. As a result, BoD is regularly updated with noise-reducing features and low friction solutions.

Apart from standard passive damper technology, BWI Group offers innovative solutions to address or exceed evolving market expectations:

  • Weight reduction by means of:
    • Lightweight materials (composites, aluminum)
    • Tailored component shape and properties (hollow rod, variable wall thickness for outer tube, one piece clevis bracket)
    • Damper downsizing (monotube with base valve to achieve twintube performance in smaller monotube package)
  • Special hydraulic functions
    • End of rebound stroke energy management system (Hydraulic Rebound Stop, or HRS)
    • End of compression stroke energy management system (Hydraulic Compression Stop, or HCS)
    • Special valves (SuperProgressive, SuperDigressive)

Benefits

BWI dampers are appreciated by vehicle manufacturers for:

  • Wide tuning range to ensure superb ride, handling and comfort thanks to several families of highly tunable, durable and versatile valve systems;
  • Robust packaging ensured by a wide range of piston rod and main valve sizes together with vehicle-customized envelope and attachments;
  • Durability to address most demanding customer requirements;
  • Repeatability of damper performance in serial production due to use of precision components as well as optimized valve assembly process.
  • High quality of the final product due to highly automated and statistically controlled manufacturing and assembly processes.
Special Passive Valves

SuperDigressive

Design aimed at reduction of maximum force transmitted to vehicle body in compression stroke and improvement of vehicle comfort on severe impacts without deterioration of body control and handling. Built into the compression side of the piston valve. Ensures practically flat force-velocity curve in compression for piston rod speeds over 0.7 m/s.

 

SuperProgressive

Design ensures steep increase of damping forces in compression stroke for piston rod velocities exceeding 1,5 m/s. Features adjustable switching point, damping force gain and rate. Can be added to base valve, piston valve or both valves.

Ensures additional protection of other suspensions components at high compression impacts (bad roads) by dissipating excess of impact energy inside the damper. Contributes to improved vehicle handling in off-road conditions.

 

Monotube damper with additional compression valve

Monotube damper with additional compression valve between piston and gas cup helps reduce internal gas pressure and achieve twintube performance in monotube packaging. Potential 30%  damper weight reduction and enhanced performance (combining advantages of twin and monotubes).

 


Hydraulic Rebound Stop (HRS) for end of rebound stroke energy management system

The aim of the Hydraulic Rebound Stop is to improve ride quality throughout the damper stroke while eliminating the impact and topping noise at fully extended position. End of stroke damping generated in HRS dissipates the energy which normally appears as a spike of energy when transferred through conventional rebound stops.

Hydraulic Rebound Stop features:

  • Progressive and smooth increase end-of-travel load
  • Rapid damping function recovery between events
  • Performance depends on position & velocity (the system is switched on when given rebound position is achieved)
  • Additionally as peaks of energy are trimmed off, there is a reduction of maximum value of rebound end-of-travel load transmitted to the car body during extreme events. Hence same vehicle’s body is able to support higher rebound loads.

Hydraulic Rebound Stop is compatible with internal rebound springs.

First production implementation in 2011.

 

Hydraulic Compression Stop (HCS) for end of compression stroke energy management system

Hydraulic Compression Stop is an hydraulic system which replaces conventional hard bump stops with hydraulic cushion. The peak force transmitted to the vehicle body from the suspension can be reduced because energy will be dissipated as HCS damping. Because of this, the vehicle body structure can be lighter due to lower strength and stiffness requirements for the same standard of refinement and durability. Moreover, HCS is not only more tuneable than traditional bump stops, leading to better vehicle dynamic performance, but it also improves noise, vibration and harshness (NVH). HCS improves occupant comfort and chassis refinement while ensuring that a heavily laden vehicle that is more likely to bottom its suspension can do so without transmitting damaging loads into the body structure.

HCS features:

  • Reduces the maximum compression forces in the suspension during extreme events or vehicle overload
  • Dissipates peak of energy which is accumulated in jounce bumper by shock absorber
  • Provides progressive and smooth increase of end-of-travel load
  • Improves NVH
  • Rapidly recovers damping function between events
  • HCS damping force value depends on the damper position (system is activated when required position is reached) and velocity

Due to different expectations to the level of compression damping force increase in the HCS system, two solutions are available:

  • Hydraulic Compression Stop Low Damping (HCS LD)
    Maximum compression damping generated by the system is limited by damper tuning due to hydraulic balance – additional compression damping is produced by additional HCS piston valve while utilizing the standard base valve.
    System to be launched into the market in 2018.
  • Hydraulic Compression Stop High Damping (HCS HD)
    Maximum compression damping forces are not limited by damper tuning – additional damping is generated in a separate chamber
Special Materials and Processes

Lightweight materials

A direct way to reduce weight is to replace currently used materials (all grades of steel) with lightweight equivalents like aluminium or composite materials.

Potential applications:

  • Aluminium reservoir tube assembly (including spring seat and other vehicle interfaces) for twintube struts (first production implementation in 1997)
  • Aluminium tube for monotube dampers

Even greater weight saving may be achieved with composite materials. For structural elements, lower mechanical properties may be offset by complex plastic-molded geometry. Strength and stiffness is built through structural design instead of material properties.

Available composite material applications:

  • Strut spring seat (first production implementation in 2013)
  • Internal rebound spring (first production implementation in 2002)

Tailored component shape and properties

Objective: remove unnecessary material without loss of damper performance or fatigue life.

BWI Group offers these products in the area of tailored component shape and properties:

  • Hollow piston rod
  • One piece knuckle bracket
  • Reservoir tube with variable wall thickness

Hollow piston rod

Piston rod size is primarily determined based upon the expected level of lateral force (bending moments). The majority of the stresses are supported by extreme fibers of the rod, leading to the potential to replace the solid piston rod structure by a tube without significant loss of strength or stiffness. Production technology is available in a variety of diameters from 18mm to 25mm, along with various tube thicknesses.

One piece knuckle bracket

Conventional strut clevis bracket design assumes an insert and outer shell, resistance welded together. The optimized shape consists of a reinforced insert, providing significant weight reduction and better stiffness. First production implementation in 2002.

Reservoir tube with variable wall thickness

Strut applications are exposed to significant level of bending moments which are the highest at the mounting interface (knuckle). The conventional approach is to deliver a straight tube that fulfils the strength requirement but carries overdesign in the areas further away from the mounting. This novel approach is to deliver an outer tube where strain is equal along the tube’s length – tailored properties of the final tube deliver strength relevant to the stress level;

  • In the area of knuckle assembly, where bending moments are high, thicker wall thickness
  • In the area of spring seat / damper closure, where bending moments are lower, thinner wall thickness

Mass reduction up to 20% – depending on application (length of clamping area, diameter, wall thickness in clamp area).

Technology developed and implemented in-house, first production implementation in 2013.