TRAILING ARM SUSPENSION RECESSION CONTROL

Abstract: An independent wheel suspension system for a motor vehicle includes a trailing arm (70) mounted for pivotal resilient movement through pivotal connecting members (72, 74), carried in the vehicle chassis (78). Resilient pivotal connection to a strut assembly (10) is effected through ball stud (56). The configuration and positioning of the trailing arm (70) and its mountings (72, 74, 56) elevates the vehicle roll center and reduces toe-out of the vehicle wheels during recession.

Description: TRAILING ARM SUSPENSION RECESSION CONTROL Technical F ield The present invention relates generally to wheel suspension systems for motor vehicles and , more particu¬ larly, to such systems which include pivotally mounted trail ing arms as an element of the wheel support in conj unction with a strut assembly at a common ball joint and which provide some means for cushioning the otion of the wheels of the vehicle during recession. Background Art It is known in the vehicle suspension arts to provide an independent wheel suspens ion fo r the front wheels of the vehicle which incorporates a pair of tra iling arms mounted to a portion of the chassis of the vehicle. Exemplary of such independent wheel suspension systems is that disclosed in appl icant ' s U. S. patent 2 , 760 ,787 assigned to the assignee of the present invention . Such systems provide the advantageous vehicle des ign capability of providing for anti-brake dive force and attitude control of the vehicle during braking . Such systems do, however , define a low roll center for the vehicle about its longi¬ tudinal vertical plane of symmetry . This has necessitated the provision of transversely extending roll bars which detract fro the true independent nature of the vehicle wheel suspension system and add to vehicle weight and cost or relatively high rate suspens ion spr ings wh ich, while increasing roll, control , detract from the r iding comfort of the vehicle. It is also known in the pr ior art to provide spring biasing or resilient members wh ich effect resistance to wheel recession or which control wheel recession, that is, generally rearward wheel movement in response to the imposition of a frontal impact. Exemplary of sys tems which employ such devices are those disclosed in U .S. patent 3 , 083 ,032 to Cuskie ? 3, 151 ,877 to Bajer ; and 3 ,195 ,878 to Rosky et al . The def iciency in attempting to apply such technology to a trailing arm suspension of the type of interest here is that the wheel motion occu ing during recession with such cushioning structures tends to produce toe out between the front wheels of the vehicle wheel which is disadvantageous in terms of vehicle steering capability and which increases tire wear . Disclosure of the Invention The suspension system descr ibed herein provides a trailing arm suspension system . The tr ailing arm is mounted to the vehicle chassis through a pair of pivotal connections, at least one of which is preferably resilient which define an axis for pivotal movement of the trailing arm which is canted upwardly toward the vertical plane of symmetry of the vehicle and in wh ich a connection from the trailing arm to a suspension strut assembly mounted between the vehicle wheel and the body is positioned at a point above and to the rear of the pivotal axis of the trail ing arm. This positioning of the chassis and strut connections of the suspens ion system yields a trailing arm suspension system which makes use of the anti-dive teaching of U .S. patent 2 , 760 ,787 while def ining a roll center for the vehicle that is elevated above the low roll center defined by the system disclosed in that patent for roll res istance due to suspension geometry, thereby eleminating the need for a roll bar and/or high rate suspens ion spr ings . This advantageously arranged system is identically descr ibed and is claimed in appl icant ' s concurrently filed appl ication entitled "ELEVATED ROLL CENTER TRAILING ARM SUSPENSION FOR MOTOR VEHICLES" . Responsive to the def iciencies of the pr ior art, OMPI WIPO the invention suspension system of the present invention fur ther provides resil ient mounting of the outboard pivotal connection of the trailing arm to provide for measurable longitud inal and rearward movement of the wheel , thus inducing wheel recession that may occur dur ing wheel forward rolling motion over pavement irreg ular ities. S ince connection of the tra iling arm to the strut assembly is effected thr ough a bal l jo int connect ion and steering movement of the wheel is effected through another ball joint connection to the strut assembly, the toe out tendency of the wheel d ur ing recession is counteracted by the imposition of the steering load on the strut on the one hand and the freedom of pivoting movement afforded at the steering arm ball joint connect ion and the outboard res ilient mount of the trailing arm on the other hand . The economical ly and structural ly advantageous construction of portions of the strut assembly employed in the suspens ion system disclosed herein is claimed in the concurrently f iled application of applicant and B. K . Chance entitled "STAMPED STRUT AND SPINDLE SUPPORT" . Br ief Description of the Drawings The present invention can be understood by reading the following descr iption of the best mode for carrying out the invention with reference to the accompanying sheets of drawings in which . Figure 1 is a partial ly exploded perspect ive view of the strut assembly of the suspension system of the present invention; Figure 2 is an exploded perspective view fro another angle of the strut assembly il lustrating the connec tion of the trail ing arm membe r to the strut assembly ; F ig ure 3 is a diagrammatic cross-sectional view of the suspension system of the pr esent invention; OMPI Fig ure 3A is an enlarged cross-sectional view of the resil ient pivotal mounting of one end of the trailing arm; Figure 4 is a diagrammatic side view of the inven- tiσn suspension system; Figure 5 is a diag rammatic top view of the suspen¬ sion system of the present invention; and Figure 6 is a diagrammatic presentation of the definition of the roll center of the suspension system of the present invention. Description of the Preferred Embodiments Turning now to the drawings, in particular Fig ures 1 and 2 thereof , the vehicle wheel suspens ion of the present invention is illustrated as consisting essentially of a strut assembly indicated general ly at 10 that is opera ively disposed between the body (not shown ) , of the vehicle and a front driven wheel assembly 12 of the vehicle. It is to be understood that an essentially identical assembly is symmetr ically arrayed on the other side of the vehicle . The strut assembly 10 includes an upper mounting portion 14 to provide for attachment to the vehicle body and. further includes a telescoping piston and cylinder assembly 16 which may be chosen from many such assemblies available . The assembly 16 essentially includes a tubular portion 18 which is fixedly secured to a support member 20 which will be later described in greater detail . A stamped spr ing support membe r 22 is secured to the upper portion of the support portion 20 and provides a lower seat 24 for receiv ing a spr ing 26 carried in sur rounding relationship about the piston and cylinder assembly 16. The upper mount portion 14 includes an upper spr ing seat 28 for receiving the upper end of the spr ing 26. Also provided with the spr ing suppo rt portion 22 is an integral, radially outwardly extending arm portion 30 having a pocket 32 formed therein for receiving an output portion 34 of the steering assembly of the vehicle as shown in exploded view to the left of Figure 1. This output pottion 34 includes a ball stud member 31 mounted through a bushing assembly 33 in the pocket 32 for conventional attachment to the arm portion 30. A fixed length link or the rod 35 operatively connects the stud member 31 to the vehicle rack and pinion steering gear system (not shown). Considering now in more detail support portion 20, it is illustrated in Figure 1 as comprising a wheel or spindle support member 36 and a strut support member 38. The two members are arranged in abutting relationship and define a conventional mounting base for the wheel 12 providing a cavity 40 through which a drive unit such as a front wheel drive half shaft assembly 42 may be oper ' atively connected to the wheel 12. The strut support member 38 includes an upstanding arm portion 44 defining a channel 46 for receiving the tube 18 of the piston and cylinder assembly 16. A plurality of apertures 48, as may best be seen in Figure 2, are formed through the arm portion 44 for permitting welding attachment as indicated at 50 of the strut assembly to .the spindle support 20. A generally hemispherical depression 52 is formed on the inner face of the spindle support member 36 at a position below the center line of the wheel 12. A ball stud 54 having an elastomeric cushion formed about its ball end 56 is inserted into the depression 52 and retained in place by a retaining plate 58 secured by suitable fasteners (not shown) as through the apertures indicated at 60 in the plate 58. The stud portion 62 of the ball stud 54 is received through a cross hole 64 formed through a clamping bushing 66 carried by a portion of a trailing arm 70. The trailing arm 70 is pivotably mounted on a OMPI generally transversely extending portion of the chassis of the vehicle by operation of two transversely spaced stud members 72, 74. It is to be understood, however, that for vehicle configurations using different structural orienta- tions, the mountings here described as being effected at body or chassis positions may be functionally duplicated by connections effected in frames, subframes and unit body components without departing from the present teaching _. As may best be seen in Figures 3, 4* and 5, the stud members 72, 74 define an axis of rotation upwardly canted toward the center line of the vehicle and the ball stud 56 is positioned upwardly and rearwardly of that axis of rota¬ tion. The inboard stud member 72 is of preferably a conventional pivotally mounted construction while the outboard stud member 74 is resiliently mounted. In the embodiment illustrated in Figure 2, the outboard mounting stud 74 includes a stud member carried in a resiliently mounted bushing 75 having a rotational axis transverse to the longitudinal axis of the vehicle. The stud 76 extends forwardly through a portion 78 of the vehicle chassis and includes an enlarged head portion 80 to capture a spring 82 between the stud 76 and the chassis portion 78. A more preferred configuration for the outboard pivotal connection 74 is illustrated in Figure 3a. In this embodiment a stud member 84 includes an eye portion 86 for receiving an elastomeric bushing 88 by which the stud member 84 is resiliently mounted on a transversely extend¬ ing cross-bolts 90 carried in the outboard portions 73 of the trailing arm 70. A forwardly extending generally cylindrical shaft portion 92 of the stud member 84 is resiliently mounted in another elastomeric bushing 94 which may slidingly engage the stud member 84 or may fixedly engage it in shear and which is carried in an aperture 96 formed through the chassis portion 78 of the vehicle. Forward movement of the stud 84 is cushioned by a cushion member such as the 0 ring depicted at 98 and rearward movement is limited by provision of an enlargement 100 formed on the forward end of the stud portion 94. Elasto- metic buttons 102 or other cushioning means such as an "0" ring may be provided on the rear face 104 of the enlarge¬ ment. Operation of the vehicle suspension system in the present invention may be better understood by reference to the schematic representations of the system depicted diagrammatically in Figures 3-6. It can be seen in these Figures that the suspen¬ sion system of the present invention makes use of the teaching of applicant's previously mentioned U.S. patent 2,760,787, which is incorporated herein by reference, by defining wheel suspension geometry which provides for an anti-brake feature dive. As can best be seen in Figure 4, ball stud 56, through which connection is made between the spindle support member 20 and the chassis mounted trailing arm 70, is positioned above and to the rear of trailing arm pivot connections 72, 74. Line A of Figure 4 indicates the plane of the trailing arm 70 through which vehicle braking forces must act. Therefore, upon application of a horizon¬ tal braking force on the wheel W, represented by the vector. B in Figure 4, that braking force is resolved into a compo¬ nent C acting generally rearwardly along the trailing arm 70 and a component D acting generally downwardly through the wheel W to the ground . The reaction to the component D through the ball stud 56 tends to pivot the trailing arm 70 upwardly, opposing the tendency of the vehicle to dive in response to the horizontal weight transfer resulting from vehicle deceleration due to application of braking force. It will be noted, however, that while the general anti-dive effect above described is as provided by the prior art system of U.S. patent 2,760,787, the suspension system of the present invention differs from the prior art system in certain advantageous respects * One such differ¬ ence, best illustrated in Fig ure 6, is the provision of an elevated roll center for the suspension system . In Figure 6, ' schematic point M represents the center of the body mounting portion 14 of strut assembly 10. The line X-Y therefrom extending through the drive center CV of the half shaf t assembly 42 , the strut steering connector 34 , and the ball - joint connection 56 to the point R at the center of the wheel represents the plane in which connections between the body, wheel , strut and road are effected . As is well known in the suspension arts Point 0, the instan¬ taneous suspension center is established by projecting perpendicularly from the point M to the point of inter- section with the plane defined by pivotal mounts 72 , 74 of trailing arm 70 through which connection to the vehicle chassis is effected . Projecting from this point O to the point R at the intersection of the wheel center and the ground yields a roll center at intersection point RC with the vehicle center line which is elevated above the ground for this suspension system. It has been established that such elevation of the roll center can eliminate the need for a transversely extending roll bar or higher rate suspension spr ings or a combination of both. Thus, a truly independent front suspension can be provided at reduced cost and without sacrifice of riding comfort. Another advantageous difference from the prior art system , best illustrated in Figures 3A and 5 , is th resilient recession control afforded by the configuration of the trailing arm outboard pivotal connection 74. Rearward ( rightward as indicated at R in Figure 5) movemen of the wheel W in response to the frontal impact is resiliently resisted by the outboard pivotal connection 7 as may be appreciated by the descr iption of the alternativ constructions of pivotal mounting 74 illustrated in Figure 2 and 3 A. In Figure 5, the movement of pivotal mount 74, which is preferably accαnmodated by mounting inboard pivotal mount 72 for limited angular movement is diagram- atically illustrated. Were the steering arm portion 30 of strut assembly not restrained from rotative movement by the fixed length steering link 35 (whose length is chosen to minimize angular variation of steering arm position with respect to the vehicle's vertical plane of symmetry as the wheel and strut move vertically during ride), this movement of trailing arm 70 would cause the wheel W to toe out as ball stud 56, and consequently the wheel W would shift arcuately counterclockwise as viewed in Figure 5. However, because the fixed length rod 35 does not permit rotative movement of the arm 30, the wheel W is constrained to move straight backward and inward as the spindle support 20 effectively rotates about the ball stud 56. It can be appreciated that a slight change in wheel tread path occurs during this motion. Perfect parallel displacement of the wheel W can be obtained at a given vehicle riding height by proper selection of angular position, as perceived in the plan vie of Figure 5, of the theoretical steering arm axis at its connection to the fixed length steering linkage 35 and the theoretical king pin axis. While only certain variations from the disclosed embodiment have been described or suggested, others may be possible without departing from the scope of the appended claims. Such variations include, inter alia, choosing the angle made by the steering arm portion 30 with the vehicle's vertical longitudinal plane of symmetry to provide initially as the wheel is turned from the straight position a measure of toe-in (oversteer), and as steering movement increases a further measure of toe-out (under- steer) as may be desirable for certain vehicle applica¬ tions.

Claims: CIAIMS What is claimed is : 1. An independent wheel suspension system for the steerable wheels of a vehicle of the type wherein a resiliently telescoping strut assembly is interposed between the wheel and a portion of the vehicle body at each wheel and a trailing arm member is pivotally mounted to the wheel and strut assembly and is pivotally mounted to the vehicle chassis forwardly of the wheel , characterized in that the trailing arm is mounted to the chassis by a pair of transversely spaced, axial ly aligned pivotal connecting members, that member remotely spaced from the longitudinal vertical plane of symmetry of the vehicle being resil iently mounted to permit certain rearward movement of the remotely spaced member . 2. An independent wheel suspension system as defined in Claim 1, further characterized ia that the other connecting member is mounted for limited multi-directional movement in the plane of the trailing arm member . 3. An independent wheel suspension system as defined in Claim 1 , further characterized in that means for pivotally mounting the trailing arm member to the vehicle chassis are provided which include: A. an inboard connecting stud member hav ing an elongated axially extending stud portion fixed to the chassis and being resiliently pivotally mounted to the trailing arm member, B. an outboard connecting stud member trans- versely spaced outwardly from the inboard connecting stud member and having an elongated ax i al ly extending stud por tion securable to the vehicle chassis and being res iliently pivotally mounted to the trailing arm member; ■ and C. means for resiliently mounting the outboard connecting stud member stud portion to the vehicle chassis to permit limited generally rearward movement of the trailing arm member . 4. An independent wheel suspens ion system as defined in Claim 3 , further characterized in that the outboard stud portion is received in a long itudinally extending aperture formed in a portion of the veh icle chassis and cylindrical resilient bushing means is carried in the aperture in surrounding relationship about the stud portion. 5. An independent wheel suspension system as defined in Claim 4 , further characterized in that the cylindrical resilient bushing is fixedly secured to engage the outboard stud portion in shear . 6. An independent wheel suspens ion system for the steerable wheels of a vehicle of the type wherein a resiliently telescoping strut assembly is interposed between the wheel and a portion of the vehicle body at each wheel and a trailing arm member is pivotally mounted to the wheel and strut assembly and is pivotally mounted to the vehicle chassis forwardly of the wheel , characterized in that the strut assembly is operatively connected to a f ixed length steering link for effecting rotative steering move- ment in response to transverse movement of the link with respect to the vehicle and the means for pivotally mounting the trailing arm member to the vehicle chassis include resil ient mounting means operative to permit limited rearward axial movement of the trailing arm member in response to the imposition of certain rearwardly directed fofce on the vehicle wheel in forward motion whereby rotative toe-out movement of the wheel is resisted by the fixed link and rearward movement of the wheel with respect to the vehicle results in pivotal movement of the trailing arm with respect to the wheel and strut assembly dur ing the ' limited axial movement of the trail ing arm . 7. An independent viieal suspens ion system as defined in Claim 6 , wherein the length of the fixed length steering link is chosen to minimize angular var iation of the strut assembly operative connection with respect to the vehicle vertical plane of symmetry during r ide motion.

Inventors: MULLER GEORGE H, MULLER, GEORGE, H.
Applicants: FORD FRANCE, FORD MOTOR CO, FORD WERKE AG, FORD FRANCE S.A., FORD MOTOR COMPANY, FORD MOTOR COMPANY LIMITED, FORD-WERKE AKTIENGESELLSCHAFT
Application year: 1983
Main classification: B60G15
IPC codes: B60G3, B60G15