Calculation jounce and rebound damping
Jounce and Rebound. • Jounce is the upward movement or compression of suspension components. • Rebound is the downward movement or. without the author's prior written permission. date. Ingi Níels Karlsson. Master of .. used to define the mass and properties of each part in the Adams model 21 .. Usable travel of at least 50 mm with 25 mm rebound and 25 mm jounce. Thread: Calculation jounce and rebound damping Join Date: Nov ; Location: Yogyakarta, Indonesia; Posts: 31 However the best way to learn this is to read through the examples and then do it. There are no shortcuts.
As a result, a major automobile manufacturer requested the design of several alternatives to its current rebound bumper and expressed a need for a spring with a soft entry and a longer travel. Consequently, this invention is primarily related to the problems of the strut assemblies of automobiles.
Related Art Rebound bumpers for strut assemblies are conventionally formed of urethane elastomers.
US5192057A - Elastomer rebound, jounce and related compression springs - Google Patents
Their purpose is merely to soften and dampen the rebound impact when the strut of the suspension assembly is extended its maximum length as the wheel assembly drops into a depression relative to the vehicle body.
Presently, such bumpers comprise small urethane washers surrounding the piston of the strut and have such a limited thickness as to cushion the vehicle only upon the last 2 to 3 millimeters of rebound. Moreover, they have a constant, high spring rate that does little to attenuate the noise, vibration or impact forces. Present jounce bumpers for strut assemblies have undesirable characteristics similar to those of the rebound bumpers.
Some improvement in these bumpers has been obtained through the use of micro-cellular urethane. Illustrative of this prior art are U.E46 M3 Front Suspension Animation - Jounce/Rebound Travel
Anderson relate to compression springs that have a primary application in railroad car draft gears and other energy absorption devices. These applications involve a very high spring rate to absorb the impact forces generated by railroad cars weighing as much aspounds. Such compression springs do not solve the problems faced by today's automobiles which demand a very soft ride in a light weight vehicle. It is an elongated hollow body formed of an elastomer whose ratio of plastic deformation to its elastic deformation is greater than 1.
Preferably, the elastomer is a copolyester polymer elastomer such as that manufactured and sold by E. The hollow body, preferably, takes the shape of an elongated bellows unit which may be placed over the piston rod of a strut. The bellows is formed of side walls and connecting sections whose dimensions vary along the length of the bellows so as to provide for a predetermined, variable spring rate.
It depicts an automotive strut assembly 10 whose top end 12 is adapted for attachment to a vehicle body not shown and whose lower end 14 includes a mounting plate 16 adapted for connection not shown to an associated wheel and tire assembly Affixed to and extending upward from the mounting plate 16 are inner and outer cylinders 20 and Interposed between the top of these cylinders 20 and 22 is an annular cup 24 which has a central aperture 26 to receive, seal and provide a bearing surface.
Extending through this aperture 26 is a piston rod 28 which carries a piston 30 at its lower end.
- Member comments
- Dammed Ping Calculus
- Other Languages:
The piston 30 may include metering orifices not shown to restrict the flow of fluid between upper and lower chambers 32 and 34 defined by the inner cylinder 20 and the piston The top end 12 of the strut assembly includes a piston mounting nut 36 which clamps a spacer 38 and a downward opening retaining cup 40 on a reduced diameter of the piston rod Surrounding the spacer 38 is an annular mounting cup 42 filled with an elastomer This cup 42 is affixed to the vehicle body not shown.
Often, the coil spring of the suspension system is mounted around this strut assembly. This conventional strut assembly 10 receives and benefits from our invention which is incorporated as a rebound bumper 50 into the upper chamber 32 between the annular cup 24 and an annular abutment 25 that is affixed to the piston rod Our invention is also incorporated into the strut assembly 10 as a jounce bumper 52 by insertion into the retaining cup 40 to extend downward and cushion upward movement of the strut assembly These compression spring bumpers 50 and 52 have the purpose of attenuating the noise, vibration and impact forces through soft entry, long travel and a variable spring rate.
In particular, the use of our compression spring as a rebound bumper provides measurable ride improvements over the existing urethane washers used for this purpose.
USA - Elastomer rebound, jounce and related compression springs - Google Patents
In part, the improvement is illustrated in FIG. The curve on the right illustrates the characteristics of an existing rebound bumper for a General Motors W-car. It is a urethane washer and has a total travel of approximately 2 millimeters in response to an applied static forces varying from 0 to Newtons.
The very short rebound travel and the high rebound force that occurs when the strut 10 is fully extended by a road surface condition results in the transmission of an impact like force to the body of the vehicle. Such rebound bumpers, transmit, rather than isolate the noise, vibration and impact forces from a road surface depression to the vehicle and its load.
In contrast to the urethane washer bumper, our invention can provide rebound travel in excess of 20 millimeters. As reflected by the left curve of FIG. When certain road conditions are encountered, the rebound bumper is engaged by a downward movement of the cylinders 20 and 22 relative to the piston Due to the variable spring rate of our invention, the initial engagement of the rebound bumper 50 is very soft.
As relative downward movement continues, the spring rate increases and the resilient force of the bumper spring opposes further movement at an increasing spring rate over a permitted compression of the spring of more than 20 millimeters. The result is elimination of transmission of most, if not all, of the noise, vibration and impact forces which are imposed on the strut assembly during rebound.
Significantly, the soft entry of the piston into the rebound bumper and its long travel also contributes to a very smooth ride. The jounce bumper 52 of our invention has compression spring characteristics similar to those of the curve of the rebound bumper graphically illustrated in FIG.
Similarly, it is also provided with a variable spring rate and provides for a soft entry and a substantial cushioning travel.
Eibach Suspension Glossary
The compression spring according to our invention is formed of an elastomer having tensile characteristics such that the ratio of plastic strain is greater than 1. One such elastomer is a copolyester polymer elastomer manufactured and sold by E.
It is reasonably inert to fluid in the strut assembly, and significantly, it is quite durable. Moreover, this elastomer is not subject to tearing or to crack propagation even when made in relatively thin cross sections as required by our invention.
For a more complete description of this elastomer, see Anderson U. Normally, the selected elastomer is purchased in pellet form, and, according to our invention, is injected or extruded into an annular mold to form a parison.
As shown in FIG. As a result, its wall thickness varies, being thinner at one end and thicker at the other. An annular male die member 68 of constant diameter is inserted centrally into the opening 67 of the mold 66 to define a cylindrical space for the parison Illustrative dimensions of a die used in forming a parison for a strut assembly included an internal diameter of mold 66 that varied from 1.
Eibach Suspension Glossary
These dimensions provide a parison having a variable wall thickness as shown in FIG. Preferably, the mold 66 is made in two semi-cylindrical sections that may be held together by bolts, or alternatively, by a press in a conventional manner. The blow mold 80 of FIG. It is sealed at the top and bottom by plates 84, one of which is removable to permit insertion of the parison.
The hat-shaped upper closure member 21 is formed with a cylindrical axially upstanding outer wall portion 51 concentrically disposed around the cup inner side wall 40 defining an annular space therebetween.
The upper closure member wall portion 51 has its lower end terminating in a radially outwardly extending attaching flanged brim The flanged brim 52 is removably fixed to a vehicle body strut receiving sheet metal panel or tower 55, as by bolts 56, extending through holes 57 upon the assembly 10 being positioned in panel circular opening The upper closure member 21 terminates at its upper end in a horizontal annular cap ring 64 forming a central access aperture The lower closure member 22 defines a circular base collar 70 having a central flanged opening defined by a downturned annular flange 72 concentrically disposed about the principal axis "A".
The collar 70 is shown boarded by an upwardly and outwardly diverging wall portion 73 having its upper terminus formed with a outwardly bowed annular seat portion The shoulder portion 74 terminates at its upper end in a radially outwardly extending terminal flange 76 in subjacent flatwise contact with the underside of the cover member flanged brim The collar 70 and its down-turned flange 72 is disposed above a subjacent upturned annular flange 78 and radially inwardly extending central base disc 79 of upper coil spring seat As a result an annular cavity is formed sized to snugly receive therein a circular ball bearing ring assembly 82 concentrically disposed about the axis "A".
The upper annular spring seat 80 is resiliently supported on the upper end coil of an helical suspension coil spring generally indicated at The coil spring 84 spirals around the shock outer support tube 14 and extends upwardly from an annular lower spring support seat member 86 axially positioned above the mounting bracket The member 86 has an upstanding neck portion 87 welded or otherwise secured to the support tube The upper one-piece sheet metal spring seat 80 is formed with an outer upwardly opening U-sectioned trough section defined by a radially extending lower bight wall 88 and an inner downwardly opening U-sectioned trough section defined by a radially extending upper bight wall It will be noted that the inner trough section bight wall 89 concentrically surrounds the ball bearing assembly 82 while the outer trough section bight wall 88 concentrically surrounds an upper portion of an elastomeric jounce bumper The jounce bumper 90 has an axial bore 91 receiving therethrough, in a press-fit manner, an upper portion of the shock piston rod A concentric vertically disposed cylindrical canister 94 has an upper open end sized to snugly encircle the spring seat upturned annular flange The canister 94 upper end terminates in an out-turned radial collar 96 adapted for flush attachment, as by spot welds, with an opposed underside of spring seat upper bight wall The canister 94, which is concentrically disposed about the strut axis "A", extends downwardly from the spring seat a predetermined dimension with a lower portion thereof formed with an integral inturned annular shoulder The shoulder 97 has depending therefrom a reduced diameter concentric ring 98 terminating in a return bent flanged hem 99 folded back upon the ring exterior surface.
The hem 99 free end is axially spaced a predetermined dimension from the shoulder 97 so as to form an external annular groove The groove is sized to receive therein an annular rib formed on the internal surface of upper neck portion provided on an elastomeric flexible accordion-like dust tube The dust tube encircles the upper portion of the strut cylinder 14 with the dust tube lower extremity shown contacting high surface of lower coil spring seat As viewed in FIG.
It will be seen that the concentric stopper ledge is in vertically spaced subjacent alignment with the annular folded upper stopper edge juncture of the canister Thus, as seen in FIG.
Such damage could occur with an un-shielded bumper wherein the shock axis is moved off-center during full jounce resulting in asymmetric outward radial bumper expansion causing the bumper to be sheared or cut by the canister lower extremity. It will be appreciated that, by virtue of the stopper ledge being off-set below the striker plate upper contact surfacethe bumper is axially spaced from the metal-to-metal jounce stop contact area between the lower stopper ledge and upper stopper juncture further insuring against damage to the bumper It will be further noted that the striker plate is formed with a frusto-conical shaped skirt adapted to provide a lead-in surface for the canister stopper juncture The lead-in skirt tends to correct for axial misalignment between the canister lower extremity and the jounce lower stopper ledge With reference to FIG.
The bumper 90 lower end face is shown axially spaced a predetermined dimension "X" from the striker plate upper opposed surface It will be noted that the dimension "X" defines the free vertical travel of the jounce bumper 90 prior to its lower end face contacting the striker plate upper surface The jounce bumper exterior is shown formed with a plurality of annular convolute portions about which the bumper folds when undergoing axial compression between the spring seat central disc 79 and opposed striker plate upper surface The dimension "Y" defines the potential or maximum axial jounce travel when the assembly 10 is in its design static mode.
It will be observed that with the assembly 10 in its full or maximum jounce mode of FIG. The dimension "Z" defines the vertical height of bumper chamber provided at the full jounce mode. By virtue of providing a metal-to-metal full jounce stop while limiting the degree of bumper compression to a predetermined applicant has greatly extended the service life of the bumper elastomeric material.
It will be further observed in FIG. As a result each bumper convoluteupon being bowed radially outwardly, is contained within the chamber thereby obviating damage thereto.