Vehicle body movements experience pitch, roll, and yaw which are usually the result of suspension reacting to turns, braking, accelerations, and road conditions. The primary load-bearing elements on a suspension system is the strut itself which is mounted on the wheel axle at the bottom and to the vehicle body on the top using a Strut Mount (also called Top Mount) to avoid transfer of any vertical knocks into the body. The Front and Rear Strut Suspensions (Strut and Spring) along with individual mounting components (Strut Mounts, Strut Bearing, Spring Isolators and Spring seats) must be harmonized to get the precise ride comfort and safe handling. Sigma offers a wide coverage of complete ready to install Strut Super Kits which are designed to fit & function precisely with the OE and OE equivalent Struts and Springs. Our Super kits are designed to offer the right harmony needed for the vehicle occupants to feel safe and comfortable. Individual mounting kit components are also available. For the right product to match your Vehicle Make, Model and Year please click on our E-Catalogue.

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Suspension Strut Bearings

Proven competence and experience is required in the design, analysis, and manufacture of suspension strut bearings. Suspension strut bearings play a very critical role in the harmonized functioning of the complete suspension strut assembly and its components.

Bearings absorb radial and axial forces and ensures low-friction and distortion-free movement of the shock absorber spring during steering and deflection enabling the spring to operate without self-aligning torque. Certain designs are used to also locate the shock-absorber spring and form a support surface for full deflection of the shock absorber and can be used with coupled and uncoupled suspension struts . This helps to isolate the body from road noise. These usually have a compact design that has been optimized for limited mounting space and are supplied as a sealed unit.

SIGMA Strut bearings undergo extensive testing using special test rigs and defined test standards, as well as stringent process and function controls to ensure that all customer requirements are met. Suspension strut bearings from SIGMA represent a chassis component that contribute substantially to the comfortable, safe, reliable, and economical operation of your vehicle Strut Assemblies.

MCU/NR Jounce Bumpers or Bump Stops

Micro Cellular Urethane (MCU) is a highly engineered, semi-closed cell, ester-based foamed Urethane. MCU jounce bumpers offer particular advantages in durability, vibration, isolation, noise reduction and suspension energy management. It has a superior tear and abrasion resistance and offers more constant spring rate than rubber across a wide range of temperatures . Specific application includes suspension jounce bumpers and coil seat insulators in suspension strut assemblies.

Jounce bumpers are typically 50-120 mm in length and their primary function is to limit suspension travel and protect shocks and strut valves from suspension over travel and absorb maximum jounce loads. SIGMA offers both MCU and NR(Natural Rubber ) Jounce bumpers to meet or exceed OE design , stiffness and performance.

Suspension Spring Seats and Spring Seat Isolators

The coil spring is located around the shock absorber and it extends between an upper spring seat which is part of the top mount assembly for the strut assembly and lower spring seat which is attached typically by welding to the shock absorber of the strut assembly.

The spring seats of the strut assembly have several functions for the suspension system. The spring seats support and maintain the correct position of the spring and support the loading on the spring under all driving conditions of the vehicle for the entire life of the vehicle. The spring seats are mechanically resistant during the life of the vehicle. They resist braking loads, deformations, wear, abrasion, changing loads and hits by stones and other debris. The spring seat is environmental and corrosion resistant to different temperatures, different moisture levels, aggressive liquids and gasses. The spring seats ensure proper fixing of the components of the strut assembly and easy assembly of the strut assembly into the vehicle. With the other components of the strut assembly the spring seats resist any unwanted displacements and/or rotations. The design of the spring seats also ensure that the spring to spring seat contact does not promote or accelerate corrosion of the spring or the spring seat.

SIGMA Spring seats and Isolators are made from high tensile steel, aluminum, glass filled nylon, and right combination of such metals with NR (Natural Rubber) and MCU (micro cellular urethane) to meet or exceed OE design, stiffness and performance.

Strut Boots / Dust Covers

Strut suspension is comprised of a shock absorber and a coil spring positioned around the shock absorber. To protect the shock absorber against dust and muddy water, a dust cover is provided to extend around the shock absorber such that it covers the shock absorber over an area spanning from a piston rod portion to a body portion thereof with a given clearance between an outer periphery of the shock absorber and the dust cover. The dust cover has a bellows-like portion and is thus capable of telescopic action so that it can follow the telescopic action of the shock absorber. The coil spring and dust cover are interrelated such that they form a predetermined clearance between the dust cover and coil spring by the dust cover becoming larger in outer diameter when contracted. Whereas for miniaturization of automobiles such a clearance between the coil spring and dust cover should be kept to a minimum.

The bellows-like portion of such a conventional dust cover is comprised of a series of alternating ridges and grooves, the ridges being spaced apart at an equal pitch and having the same height. When blow molded the dust cover having such a complex portion, it is difficult to render it uniform in thickness at all portions thereof. Thus, the resulting dust cover may have weak and strong portions due to the thickness irregularities and is thus liable to experience buckling wherein the dust cover, when contracted, deforms to partially project laterally. This may give rise to such instances that when a coil spring extending around an outer periphery of the dust cover is compressed, the dust cover is pinched between adjacent two spirals of the coil spring, thus damaging the dust cover.

SIGMA Dust covers are made of both Rubber and Plastic and are designed strictly as per OEM design to ensure 100% effectiveness and functionality when installed on your vehicle.

Rubber to Metal Strut Mounts absorb bumps and isolate vibrations:

The damping force of the shock absorber is a function of the speed with which the piston rod is forced into the unit. If the spring needs to be compressed a considerable distance as the wheel travels over a obstacle, the shock absorber acts as a rigid connection between the hub carrier and the body.

The vehicle occupants thus feel a hard bump rubber to metal elements between the shock absorber and the body(“Top Mounts”) which are compressed at a considerable distance into the stops, absorbing peak forces. Without this elastic connection to the body i.e a Top Mount /Strut Mount, the shock absorber would transmit wheel noises to the body as a growling sound, acting in the same way as a rigid rod.

Rubber to Metal Strut Mounts offer ride comfort & safe handling.

It is difficult to give a clear definition of “ safe handling “ than it is to define “ride comfort” since there as many technical parameters of a vehicle that are relevant for safe handling including wheelase and track, position of center of gravity, tire properties, chassis mounts, suspension design and tuning. Chassis tuning is always dependent on the vehicle manufacturers own philosophy. SIGMA rubber to metal Strut Mounts are therefore reversed engineered strictly to match the OEM design and specifications using the same material to suit specific vehicle tuning.

SIGMA Strut Assembly Components (Front & Rear Suspension)

The wheel suspension has the task of ensuring maximum driving safety and ride quality while providing accurate steering. It must also transfer tire-road contact forces to the vehicle frame and isolate the body from road noise, while being as lightweight as possible.

To accomplish these objectives, the components in the suspension system must be correctly matched to one another, which requires close cooperation between the suspension or chassis manufacturer and the system supplier.

Elastomeric compounds for Strut Mounts and Kits:

At SIGMA we take pride in producing our own rubber compounds and ensuring our strut mounts incorporate the key criteria while developing elastomeric compounds for our suspension kits:

  • Dynamic Hardening
  • Fatigue Strength
  • Tear Propagation resistance
  • Temperature resistance
  • Creep & Relaxation
  • Ozone Resistance
  • Oil Resistance
  • Bonding
  • Break Load
  • Compatibility with Hydro fluids and Grease.
  • Solubility of Substances: Elastomeric compounds must not release chemicals that interfere with metal parts and other mating components of the Strut Assemblies.

Bonding technology & Material Selection

Metals: “Substrates” are the surfaces to which the elastomers are to be bonded. These are mainly steel sheets, aluminum die cast, extrusions, deep drawn parts, tubes, castings. Our product development and design teams decide on the materials to be used in each case after a thorough review of the OEM design and materials. Initially all the parts need to be protected against corrosion. For the rubber to be effectively bonded to the metal part, all these substances need to be completely removed, leaving no residue.

Plastics:  Plastics are increasingly becoming the substrate of choice in vehicle production. They are light, can be molded quickly and easily and therefore represent a low cost alternative to metal components. Plastics however also need to be treated to ensure optimum preparation for the elastomer and materials selected depending on the kind of application. In strut mounts and strut assemblies the main applications of plastics are spring seats and bearings. Incase the material is not selected correctly shrinkage and breakages are common resulting in failure of the strut assembly or cracking noise which can be irritating.

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