Single fastener strut top mount and method of optimizing same

A strut top mount is optimized to provide a resilient response to jounce and rebound load rates that is symmetrical and linear over a predetermined range of travel. An annular tower is formed of the body structure. A central bracket has adhered thereto an outer resilient element that abuts the tower, and has adhered oppositely thereto an inner resilient element. A bearing is supported by the central bracket, and a spring seat is supported by the bearing. A sleeve is received by a strut shaft and adhered to the inner resilient element A lower washer abuts a lower end of the inner resilient element. An upper washer abuts an upper end of the inner resilient element. A retention washer is mounted onto the strut shaft, wherein a periphery thereof has a retention washer resilient element. The components are collectively tuned to provide the optimization.

TECHNICAL FIELD

The present invention relates to MacPherson strut-type motor vehicle suspension systems, and particularly to single fastener MacPherson strut top mounts.

BACKGROUND OF THE INVENTION

Motor vehicle suspension systems are configured so that the wheels are able to follow elevational changes in the road surface as the vehicle travels therealong. When a rise in the road surface is encountered, the suspension responds in “jounce” in which the wheel is able to move upwardly relative to the frame of the vehicle. On the other hand, when a dip in the road surface is encountered, the suspension responds in “rebound” in which the wheel is able to move downwardly relative to the integrated body/frame structure of the vehicle. In either jounce or rebound, a spring (i.e., coil, leaf, torsion, etc.) is incorporated with the body structure in order to provide a resilient response to the respective vertical movements of the wheel with regard to the vehicle body structure. However, in order to prevent wheel bouncing and excessive vehicle body motion, a shock absorber or strut is placed at the wheel to dampen wheel and body motion. An example of a MacPherson strut is disclosed in U.S. Pat. No. 5,467,971.

Of interest is a prior art single fastener strut top mount for a MacPherson strut which is manufactured by Adam Opel GmbH, a division of General Motors Corporation, Detroit, Mich., and is shown generally at10inFIG. 1. This prior art strut top mount10interfaces with a broad, annular strut tower12which at its lower end (not shown) is connected to the body structure of the motor vehicle. This prior art strut top mount10features an annular tapered dome14that is open downward nestingly within the tower12, and is welded thereto at a conjoining16(the taper being smallest adjacent the conjoining, and largest distant from the conjoining). An annular outer rubber element18has an inclined outer surface18awhich abuts the dome14. An annular metal insert20is preferably provided, for stiffening, within the outer rubber element18adjacent the dome14. An annular stamped metal support shell22is adhered to the outer rubber element18in nested (i.e., in cross-section being oppositely disposed) relation to the dome14; and an annular inner rubber element24is nested within and adhered to the support shell22in cross-section being in opposite disposition with respect to the outer rubber element18, wherein the aforementioned adherences result from the molding process of the inner and outer rubber elements.

At an annular shelf22aof the support shell22, within an upper polymer housing26c, is an upper race26aof an annular bearing26. The lower race26bof the bearing26, within a lower polymer housing26d, is located at an annular spring bracket28, wherein the upper and lower polymer housings mutually have a conventional labyrinthine seal interfacing, and wherein the spring bracket locates and handles loads from both the coil spring32and the jounce bumper34. At an outer periphery28aof the spring bracket28, wherein the spring bracket has a diameter less than that of the strut tower12, but exceeding the diameter of the dome14, is formed a spring seat30having a rubber insulator30aupon which abuts the coil spring32. At an inner periphery28bof the spring bracket28, adjacent the bearing26, is a connection28cto the jounce bumper34. A strut shaft36is reciprocally interfaced to a strut housing (not shown) in a conventional manner so as to provide damping as it reciprocates in relation thereto in response to jounce and rebound. A tubular metal sleeve35receives the strut shaft36at a shoulder36athereof, wherein the sleeve is adhered (as a result of the aformentioned molding process) to the inner rubber element24. At the shoulder36aof the strut shaft36is a lower washer38which abuts a lower end24aof the inner rubber element24and a lower end of the sleeve35. Abutting an upper end of the sleeve35is an upper washer40which also abuts an upper end24bof the inner rubber element24, wherein the upper washer is held in place by a first nut42that is threaded onto the strut shaft36. A retention washer44is mounted onto the strut shaft36, and is held in place between the first nut and a second nut46, which is also threaded onto the strut shaft. At the periphery of the retention washer44is a retention washer rubber element48.

FIGS. 1A and 1Bare graphs showing what is believed to be the response of the prior art strut top mount10to jounce and rebound. In this regard,FIG. 1Ashows a graph50of load force versus displacement in which plot52indicates the believed response of the outer rubber element18to jounce; andFIG. 1Bshows a graph60of load force versus displacement in which plot62indicates the believed response of the prior art strut top mount10to jounce and rebound.

FromFIGS. 1A and 1B, several conclusions can be drawn with respect to the prior art strut top mount10. Asymmetry is seen in the jounce to rebound rate ratio. Over-travel of the prior art strut top mount10can occur if the jounce bumper forces are routed through the inner rubber element, wherein the prior art strut top mount would have an unacceptably large amount of travel in jounce; and is likely why the jounce bumper forces are instead routed through the spring loadpath. The latter loadpath arrangement does not enable use of monotube struts (monotube struts route the jounce bumper loads up through the strut rod and, therefore, the strut top mount thereof requires an appropriately high load capacity in the damper rod load-path to handle them, whereby this is possible only for a single path strut top mount or a dual path strut top mount with the bumper and damper loads combined into the same path). The rebound rate changes abruptly as the retention washer rubber element engages the strut tower. The outer rubber element axial rate cannot be used to tune the prior art strut top mount10axial rate range, and the inner rubber element has little authority over overall axial rate, wherein the outer rubber element axial rate is determined by the inherent deflection requirement for retention (the retention objective is to ensure that the prior art strut top mount maintains contact with the underside of the strut tower at all times, and the outer rubber element compliancy allows for the retention washer to separate from the strut tower and thereby create freedom of mount movement during operation). With respect to the radial rate range of the prior art strut top mount10, the large outer rubber element acts in series with the inner rubber element and is relatively soft in the radial direction. Additionally, the design height position of the prior art strut top mount10, when loaded under vehicle curb weight, varies with vehicle mass, making it difficult to use this design on multiple vehicle applications (i.e., differing rubber chemistry or durometer of each of the inner and outer rubber elements is required, wherein the outer rubber element is adjusted to vehicle mass to provide a desired retention washer gap with respect to the strut tower, and the inner rubber element is tuned to adjust, somewhat, the mount rate).

Accordingly, what remains needed in the art is a single fastener, compact strut top mount which has an optimized resilient response to jounce and rebound.

SUMMARY OF THE INVENTION

The present invention is a single fastener, compact strut top mount which is optimized in that its resilient response to jounce and rebound load rates is symmetrical and linear over a predetermined range of travel, is stiff radially, is tunable for various vehicle applications and provides excellent vibration isolation.

The strut top mount according to the present invention is configured to interface with a narrow, annular strut tower which, at its lower end, is connected to the body structure of the motor vehicle. The strut top mount includes an annular central bracket. At one side of the central bracket, is an annular outer resilient element, and at the other side of the central bracket is an annular inner resilient element, wherein the inner and outer resilient elements are adhered to the central bracket as a result of the molding process of the inner and outer resilient elements. The outer resilient element abuts the strut tower without adherence thereto. A series of ramp-shaped convolutes are integrally formed at the outer peripheral side and top surfaces of the outer resilient element.

One (upper) side of a bearing is located at the central bracket, and a spring seat is located at the other (lower) side of the bearing, wherein the bearing and the spring seat are generally in vertical alignment with each other. A metal sleeve receives a strut shaft, wherein the sleeve is adhered to the inner resilient element (as a result of the aforementioned molding process). A lower washer abuts a lower end of the inner resilient element and a lower end of the sleeve. At an upper end of the sleeve is an upper rate washer which abuts an upper end of the inner resilient element, wherein the upper rate washer is held in place by a first nut that is threaded onto the strut shaft. A retention washer is mounted onto the strut shaft, and is held in place between the first nut and a second nut which is also threaded onto the strut shaft. At the periphery of the retention washer is a retention washer resilient element. The preferred resilient material of the inner and outer resilient elements and the retention washer resilient element is rubber.

In operation of the strut top mount according to the present invention, during jounce and rebound the outer and inner resilient elements stretch or compress, while the top convolute portion of the convolutes is rollingly interfaced with the tower (see below). The inner resilient element is primarily tuned to provide effective vibration isolation simultaneous with damper load reaction, while the outer resilient element provides additional isolation, and axial retention and load reaction while maintaining high radial stiffness. The configuration of the components and the composition of the outer and inner resilient elements are collectively tuned according to the method of the present invention to provide a symmetrical response of the strut top mount to jounce and rebound with a linear rate over a range of jounce and rebound motion. At the extreme of jounce, the central bracket provides an exponentially increasing reaction force of the outer resilient element against the strut tower. At the extreme of rebound motion, the retention washer resilient element abuts the tower with a high order exponential reaction force/deflection characteristic so as to keep mount travel within desired limits of rebound.

The method of optimizing the strut top mount according to the present invention encompasses the opposing objectives that exist for the axial load rates of the outer resilient element. A very soft axial load rate is needed to allow a gap to form between the retention washer and the vehicle body structure at the strut tower as vehicle weight is applied to the strut top mount, yet a very high axial load rate is needed to allow damper forces to be effectively reacted to the vehicle body structure. These objectives are simultaneously achieved by giving the outer resilient element an axial force deflection curve with a low rate over small deflections and thereafter a high order (fourth degree or higher) exponential shape.

A soft initial load rate characteristic of the outer resilient element provides a desirable strut top mount displacement when the vehicle corner sprung weight is applied to the strut top mount. A high load rate in the steep portion of the force deflection curve offers favorable damper reaction to the vehicle body. Because the outer and inner resilient elements react in series to loads applied to the strut top mount by the strut shaft, the axial compliance contribution from the outer resilient element is minimized to make the resultant axial load rate of the strut top mount from the outer and inner resilient elements sufficiently high. This is achieved by ensuring that the outer resilient element of the strut top mount is loaded into the steep portion of its force deflection curve under the vehicle's curb weight.

A specific arrangement of the strut tower and outer resilient element enable this desired load rate shape. The outer resilient element has a nearly vertical section positioned within a corresponding nearly vertical tower side wall. The column of resilient material thereof acts primarily in shear to axially applied forces and provides the low initial load rate, while reacting mostly in compression to radially applied forces for high radial stiffness. A top section of the outer resilient element located adjoining the substantially horizontal tower top wall reacts vertically against the tower with a rolling action and is ultimately mostly in compression for high durability and high load rate.

The top convolute portion of the convolutes provide a rolling engagement with the tower top wall, and at outer periphery of the outer resilient element acts primarily in shear to axially applied forces and provides a low initial load rate, while reacting mostly in compression to radially applied forces with respect to the tower side wall. This engagement feature provides a smooth, continuous transition between the soft shear and stiff compression sections of the outer resilient element and eliminates potential slapping noises by avoiding intermittent contact between flat surfaces. This outer resilient element geometric arrangement also enables a high radial load rate that adduces a favorable vehicle steering feel.

Several advantages of the strut top mount according to the present invention include: contact between the outer resilient element and the underside of the strut tower is provided between the extremes of jounce and rebound, thereby eliminating noise and providing high durability; a large gap between the retention washer and the strut tower of the vehicle body structure provides unimpeded damper isolation and sufficient freedom from contact with the strut tower during coning motion of the strut top mount during steering action of the vehicle suspension; a sufficiently high strut top mount axial rate for effective damper reaction (an overly high axial rate is undesirable for vibration isolation); and a high strut top mount radial rate for favorable vehicle steering feel. Further, since the strut top mount according to the present invention is quite insensitive to vehicle mass, it is suitable for use on a range of vehicle applications having differing vehicular masses.

Accordingly, it is an object of the present invention to provide a single fastener, compact strut top mount which has an optimized resilient response to jounce and rebound.

This and additional objects, features and advantages of the present invention will become clearer from the following specification of a preferred embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the Drawing,FIGS. 2 through 6depict views of the strut top mount according to the present invention,FIGS. 7 through 11depict graphs used, according to the present invention, for optimizing the strut top mount according to the present invention, the method for which being summarized atFIG. 12.

Referring firstly toFIGS. 2 through 4structural and functional aspects of the strut top mount100according to the present invention will be detailed.

A narrow, annular strut tower102is connected at its lower end (not shown) to structural members of the motor vehicle in a manner that is well known in the art. An annular outer resilient element104has a gently inclined outer surface104′ which abuts (without adherence) the strut tower102at a tower side wall102a. The outer resilient element104preferably has no metal insert (generally akin to20inFIG. 1), but this may be optionally included. An annular central bracket, having a U-shape in cross-section,106is defined by an outer bracket wall106a, a top bracket wall106band an inner bracket wall106c. A series of mutually spaced stiffening darts106dmay be provided in the central bracket106for strengthening. The outer bracket wall106ais adhered to the outer resilient element104as a result of the molding process of the outer resilient element. An annular inner resilient element108is adhered to the inner wall106cof the central bracket106as a result of the molding process of the inner resilient element. It is preferred for purposes of ease of manufacturing to form (mold) the inner and outer resilient elements108,104as a single piece, mutually interconnected by an upper resilient element115.

An annular bearing110has its upper race110aseated in an upper bearing polymer housing112that is, itself, nested at the top bracket wall106b. The lower race110bof the bearing110is seated in a lower bearing polymer housing114, having, in opposing disposition with respect to the lower race, a spring seat114atherebelow. It is to be noted that while not specifically illustrated in the drawing for the sake of clarity, the upper and lower bearing polymer housings112,114are mutually sealed by a conventional labyrinthine interface. A rubber coil spring insulator116is disposed at the spring seat114a, wherein a coil spring118is seated thereat. A strut shaft120is reciprocally interfaced in a conventional manner to a conventional strut housing (not shown) to provide wheel damping as it reciprocates in relation thereto in response to jounce and rebound.

A metal barrel sleeve122having a barrel shape selected to provide a desired radial stiffness, receives the strut shaft120at a shoulder120athereof, wherein the barrel sleeve is adhered to the inner resilient element108as a result of the molding process of the inner resilient element. At the shoulder120aof the strut shaft120is a lower washer124which abuts a lower end108aof the inner resilient element108and a lower end of the barrel sleeve122, and serves two purposes: firstly, transmission of loads into the lower portion of the inner resilient element, and secondly, a jounce bumper cup124afor location of a jounce bumper125. At an upper end of the barrel sleeve122is an upper rate washer126which abuts an upper end108bof the inner resilient element108, wherein the upper end is preferably in the form of a plurality of upstanding nibs108c. The upper rate washer126is held in place by a first nut128that is threaded onto the strut shaft120. A retention washer130is mounted onto the strut shaft120, and is held in place between the first nut and a second nut132that is threaded onto the strut shaft. At the periphery of the retention washer130is a retention washer resilient element134. The preferred resilient material of the inner and outer resilient elements and the retention washer resilient element is rubber.

The outer resilient element104has a vertical column104awhich abuts (without adherence) the tower side wall102a, wherein the tower side wall is nearly vertical. The vertical column104aacts primarily in shear to axially applied forces and provides a low initial load rate, while reacting mostly in compression to radially applied forces. A top section104bof the outer resilient element104abuts (without adherence) a tower top wall102bof the tower102, wherein the tower top wall is generally horizontal and the top section104breacts vertically against the tower top wall almost purely in compression for high durability and high load rate.

As best be seen atFIGS. 3 and 4, a plurality of ramp-shaped convolutes140are integrally formed of the outer resilient element104, wherein a top convolute portion140t(including the corner140c) is located at the outer element top104t, and a side convolute portion140s(excluding the corner140c) is located at the outer element peripheral side104s. In this regard, the side convolute portion140sallows for manufacturing tolerances of the outer resilient element104with respect to the strut tower102, allowing the strut top mount (particularly the outer resilient element thereof) to be inserted with an interference fit into the strut tower using just a low insertion force. The top convolute portion140tof the convolutes140provide a rolling engagement with the tower top wall102b, and the outer periphery104pof the outer resilient element104acts primarily in shear to axially applied forces and provides a low initial load rate, while reacting mostly in compression to radially applied forces with respect to the tower side wall102a. This engagement feature provides a smooth, continuous transition between the soft shear and stiff compression sections of the outer resilient element104and eliminates potential slapping noises by avoiding intermittent contact between flat surfaces. This geometric arrangement of the outer resilient element104, wherein the high radial rate is related to minimal thickness sheer wall and the steepness thereof, also enables a high radial load rate that adduces a favorable vehicle steering feel.

Referring now additionally toFIGS. 5 and 6, operation of the strut top mount100will be detailed.

During jounce and rebound the inner and outer resilient elements108,104stretch or compress, while the top convolute portion140tof the convolutes140is rollingly interfaced with the tower102. The inner resilient element108is primarily tuned to provide effective vibration isolation simultaneous with damper load reaction, while the outer resilient element104provides additional isolation, and axial retention and load reaction while maintaining high radial stiffness. The configuration of the components and the composition of the outer and inner resilient elements are collectively tuned according to the method of the present invention to provide a symmetrical response of the strut top mount100to jounce and rebound with a linear rate over a selected range of jounce and rebound motion. At the extreme of rebound motion, as depicted atFIG. 5, the retention washer resilient element134abuts the tower102with a high order exponential reaction force/deflection characteristic so as to keep mount travel within desired limits of rebound. At the extreme of jounce, as depicted atFIG. 6, the central bracket106provides an exponentially increasing reaction force of the outer resilient element104against the strut tower102.

Turning attention now toFIGS. 7 through 12, the method of optimizing the strut top mount100will be detailed, wherein the method encompasses the opposing objectives that exist for the axial load rates of the outer resilient element. A very soft axial load rate is needed to allow a gap to form between the retention washer and the strut tower of the vehicle body structure as vehicle weight is applied to the strut top mount, yet a very high axial load rate is needed to allow damper forces to be effectively reacted to the vehicle body. These objectives can be accomplished by giving the outer resilient element an axial force deflection curve with a high order (fourth degree or higher) exponential shape.

A soft initial load rate characteristic of the inner and outer resilient elements provides a desirable strut top mount displacement when the vehicle corner sprung weight is applied to the strut top mount. A high load rate in the steep portion of the force deflection curve (seeFIG. 10) offers favorable damper reaction to the vehicle body. Because the outer and inner resilient elements react in series to loads applied to the strut top mount by the strut shaft, the axial compliance contribution from the outer resilient element is minimized to make the resultant axial load rate of the strut top mount from the outer and inner resilient elements sufficiently high. This is achieved by ensuring that the outer resilient element of the strut top mount is loaded into the steep portion of the force deflection curve under the vehicle's curb weight, perFIG. 10(soft initially, then a high order curve which provides high stiffness at the loaded condition).

According to the method of the present invention, per the flow chart600depicted atFIG. 12, a series of plots are prepared, selectively combined, compared and adjusted, if necessary, to synergistically achieve a desired optimization of the strut top mount100.

At Block602a plot of the desired load rate characteristics of the strut top mount100is prepared by computer modeling, testing or other empirical methodology. For example,FIG. 7is a graph200of displacement versus load force of the strut top mount100, having a desired symmetric response to jounce and rebound load rates, as represented by plot202, wherein a reference plot204provides a1.25multiplied linear comparison. In this regard, where, for example a6mm linear range in each direction is desired, a linear interpolation over the first2mm of travel in each direction is provided. This interpolation is then multiplied by1.25, plotted and extended out to where it intersects the rate curve. The displacement at this intersection is defined as the range of linear rate characteristic for the given curve.

At Block604a plot of the desired load rate characteristics of the inner resilient element108is prepared by computer modeling, testing or other empirical methodology. For example,FIGS. 8 and 9are graphs300,300′ of displacement versus load force for the inner resilient element108of the strut top mount100. In order to optimize the inner resilient element108synergistically with respect to the remainder of the strut top mount100, the configuration and the composition (i.e., hardness of rubber) are selected in order to provide plot302, whereinFIG. 8depicts jounce andFIG. 9depicts rebound. At region A of plot302, compression is occurring at region A′ ofFIG. 6during jounce, causing a distinct increase in load rate for higher displacements. At region B of plot302, compression is occurring at region B′ ofFIG. 5during rebound, causing a distinct increase in load rate for higher displacements.

At Block606a plot of the desired load rate characteristics of the outer resilient element104is prepared by computer modeling, testing or other empirical methodology. For example,FIG. 10is a graph400of displacement versus load force of an outer resilient element104of the strut top mount100. In order to optimize the outer resilient element104synergistically with respect to the remainder of the strut top mount100, the configuration and the composition (i.e., hardness of rubber) are selected in order to provide plot402. At region C of plot402, compression is occurring at region C′ ofFIG. 6during jounce, causing a distinct increase in load rate for higher displacements. At region D, the response to displacement is linear.

At Block608a plot of the desired load rate characteristics of the retention washer element134is prepared by computer modeling, testing or other empirical methodology. For example,FIG. 11is a graph500of displacement versus load force of a retention washer resilient element134of the strut top mount100. In order to optimize the retention washer resilient element134synergistically with respect to the remainder of the strut top mount100, the configuration and the composition (i.e., hardness of rubber) are selected in order to provide plot502. At region E of plot502, compression is occurring at region E′ ofFIG. 5during rebound, causing a distinct increase in load rate for higher displacements in region G. At region F, the response to displacement is linear as there is a gap (see F′ inFIG. 2and F″ inFIG. 5).

At Block610the plots302,402and502are combined. At Block612the combined plots302,402,502are fitted to the optimal plot202for the strut top mount100. At decision Block614, inquiry is made whether the fit has been established. If the answer to the inquiry is no, then at Block616one or more of the resilient element plots302,402,502is adjusted, whereupon the combination, comparison and inquiry steps are repeated. If the answer to the inquiry is yes, then at Block618an optimized strut top mount has been designed and the plot parameters are used to fabricate the components of the strut top mount.

Several advantages of the strut top mount according to the present invention include: contact between the outer resilient element and the underside of the strut tower is provided between the extremes of jounce and rebound, thereby eliminating noise and providing high durability; a large gap between the retention washer and the strut tower of the vehicle body structure provides unimpeded damper isolation and sufficient freedom from contact with the strut tower during coning motion of the strut top mount during steering action of the vehicle suspension; a sufficiently high strut top mount axial rate for effective damper reaction (an overly high axial rate is undesirable for isolation); and a high strut top mount radial rate for favorable steering feel. Further, since the strut top mount according to the present invention is quite insensitive to vehicle mass, it is suitable for use on a range of vehicle applications having differing vehicular masses.

To those skilled in the art to which this invention appertains, the above described preferred embodiment may be subject to change or modification. Such change or modification can be carried out without departing from the scope of the invention, which is intended to be limited only by the scope of the appended claims.