Rear lower control arm for motor vehicle

Abstract

Rear lower control arm (5) for a motor vehicle comprising a top part (5t) and a bottom part (5b) defining together a hollow volume (5h), said top and bottom parts (5t, 5b) each comprising respectively a top and bottom first hole (17t, 17b) and a top and bottom second hole (19t, 19b), wherein said top and bottom parts (5t, 5b) are joined together by securing together at least part of said top and bottom horizontal surface outer peripheries (5tho, 5bho), at least part of said top and bottom first hole side walls outer peripheries (17tso, 17bso), at least part of said top and bottom second hole side walls outer peripheries (19tso, 19bso).

Description

The present invention relates to a rear lower control arm for a motor vehicle. Inparticular, it relates to a rear lower control arm for a vehicle having a rear wheeldrive propulsion or a four-wheel drive system or an electrical or hybrid powertrain.The rear suspension assembly of such types of vehicles are submitted to high forcesassociated to the torque applied by the rear propulsion and carry an importantweight associated to one or several of the following elements according to the typeof vehicle: the electrical motor, the battery, the internal combustion engine, the four-wheel drive management device, etc.This combination of high torque and load exerted on the rear suspension results inchallenging conditions for the structural elements linking the rear wheels to the restof the vehicle, prevalent among them being the rear lower control arms which arearguably the most important structural parts linking the rear wheels to the body ofthe vehicle.Alongside the above-mentioned structural requirements of the rear lower controlarm, there is also a push to bring down the weight of the rear lower control arm.Indeed, automotive manufacturers are constantly looking for weight saving solutionsin general to address environmental concerns associated with the gas consumptionof internal combustion engine vehicles and to provide ever longer driving autonomyin the case of electrical or hybrid vehicles. In the specific case of the rear lowercontrol arm, the mass of the part is particularly critical because it is included in whatis known as the unsprung mass of the vehicle. This unsprung mass corresponds toall the elements which are not supported by the suspension springs of the vehicle.It includes the wheels and the lower control arms. Reducing the unsprung mass ofthe vehicle is a key factor to improve vehicle handling and overall passengercomfort.Hollow rear lower control arms design, also known as clamshell designs, haveappeared on the market to address the weight lightning challenge and to enable toproduce rear lower control arms using sheet metal stamping rather than casting, thelatter being generally more expensive and less productive. Such designs, such asdisclosed for example by KR20170079400, include a top and bottom part which arejoined together around their edges and a hole to house the spring mount. While thisconcept is indeed successful in bringing down the weight of the part, it is generallynot satisfactory in vibratory performance because of the large generally flat surfacesof the top and bottom parts which resonate and exhibit poor performance in panelmode. It is also not satisfactory in stiffness because of the large generally flatsurfaces which will tend to deform under bending or torsional loads.The object of the present invention is to remedy the shortcomings of the currentclamshell designs by providing a rear lower control arm having a clamshell designwhich remains industrially manufacturable and which has improved vibratory andstiffness performance and also provides additional weight lightning.To this end the present invention relates to:A rear lower control arm for a motor vehicle comprising a top part and a bottom partdefining together a hollow volume, said top and bottom parts each comprisingrespectively-a top and bottom horizontal surface, delimited respectively by a top andbottom horizontal surface outer periphery,- top and bottom side walls extending in a general direction of at least 45°compared to the horizontal plane along at least part of the top and bottomhorizontal surface outer periphery, said top and bottom side walls beingdelimited by a top and bottom side wall outer periphery,- a top and bottom first hole, comprising respectively top and bottom firsthole side walls extending in a general direction of at least 45° comparedto the horizontal plane, said top and bottom first hole side walls beingdelimited by top and bottom first hole side walls outer peripheries,- a top and bottom second hole, comprising respectively top and bottomsecond hole side walls, extending in a general direction of at least 45°compared to the horizontal plane, said top and bottom second hole sidewalls being delimited by top and bottom second hole side walls outerperipheries,wherein said top and bottom parts are joined together-by securing together at least part of said top and bottom horizontal surfaceouter peripheries,-by securing together at least part of said top and bottom first hole sidewalls outer peripheries,-and by securing together at least part of said top and bottom second holeside walls outer peripheries.The inventors have found that introducing an additional hole compared to the state-of-the-art design surprisingly allows for increased vibration and stiffnessperformance. The inventors have also found that it is possible to manufacture sucha part using an industrially viable process.According to other optional features of the rear lower control arm according to theinvention, considered alone or according to any possible technical combination:-the top and bottom parts are joined together by welding-the top and bottom first hole side walls outer peripheries are joined together by theintermediary of a first intermediate part, wherein the top first hole side walls outerperiphery is attached to the first intermediate part along a top first hole assemblyperimeter, the bottom first hole side walls outer periphery is attached to the firstintermediate part along a bottom first hole assembly perimeter and wherein said topfirst hole assembly perimeter is located higher than said bottom first hole assemblyperimeter in the elevation direction-the top and bottom second hole side walls outer peripheries are joined together bythe intermediary of a second intermediate part, wherein the top second hole sidewalls outer periphery is attached to the second intermediate part along a top secondhole assembly perimeter, the bottom second hole side walls outer periphery isattached to the second intermediate part along a bottom second hole assemblyperimeter and wherein said top second hole assembly perimeter is located higherin the elevation direction than said bottom second hole assembly perimeter-The rear lower control arm comprises four attachment points for chassis elementsof the vehicle, said four attachment points being equipped with bushings comprisinga vibration damping material.-The top and bottom side walls do not extend around the entire length of respectivelythe top and bottom horizontal surface outer periphery, the areas in which the topand bottom side walls do not extend being called respectively top and bottom sidewall apertures and wherein the bushings are located in between at least part of saidtop and bottom side wall apertures-The top and bottom parts are made of steel having an ultimate tensile strengthabove 780MPa, as measured according to ISO standard ISO 6892-1, published inOctober 2009.The present invention further concerns a method for producing a rear lower controlarm as described above, comprising the steps of:a / providing a first a second flat sheetb / forming said first and second flat sheet, in order to produce a top part and abottom part comprising respectively a top and bottom horizontal surface, top andbottom side walls a top and bottom horizontal surface outer periphery, a top andbottom side wall outer periphery, further comprising respectively a top and bottomfirst hole, said first holes comprising respectively top and bottom first hole side walls,and top and bottom first hole side walls outer peripheries, and further comprisingrespectively a top and bottom second hole, said second holes comprisingrespectively top and bottom second hole side walls, and top and bottom second holeside walls outer peripheriesc / joining together said top and bottom parts by securing them together along atleast part of the top and bottom side wall outer periphery, by securing them togetheralong at least part of the top and bottom first hole side walls outer peripheries, andby securing them together along at least part of the top and bottom second hole sidewalls outer peripheries.According to other optional features of the rear lower control arm production methodaccording to the invention, considered alone or according to any possible technicalcombination, the method further comprises the steps of:-providing a first intermediate part and joining the top and bottom first hole side wallsouter peripheries to said first intermediate part to form a top and bottom first holeassembly perimeter-providing a second intermediate part and joining the top and bottom second holeside walls outer peripheries to said second intermediate part to form a top andbottom second hole assembly perimeter-providing bushings comprising a vibration damping material and positioning saidbushings in between previously arranged top side wall apertures and bottom sidewall aperturesOther aspects and advantages of the invention will appear upon reading thefollowing description, given by way of example, and made in reference to theappended drawings, wherein:-Fig 1 is an overall perspective view of a vehicle according to the invention-Fig 2 is an overall perspective view of a rear suspension train according to theinvention-Fig 3 is a perspective view of a rear cradle and rear lower control arms assemblyaccording to the invention-Fig 4 is a side perspective view of a wheel and rear lower control arm assemblyaccording to the invention-Fig 5 is a perspective view of a rear lower control arm according to the invention-Fig 6 is an exploded view of a rear lower control arm according to the invention.-Fig 7 is a cross-section view of a rear lower control arm according to the inventionfollowing the I-1 cross section plane defined on Fig 5-Fig 8 is a cross-section view of a rear lower control arm according to the inventionfollowing the I-11 cross section plane defined on Fig 5In the following description, the terms "upper", "lower", "front", "rear", "transverse"and "longitudinal" are defined according to the usual directions of a mounted vehicle.More particularly, the terms "upper" and "lower", are defined according to theelevation direction of the vehicle, the terms "front", "rear" and "longitudinal" aredefined according to the front / rear direction of the vehicle and the term "transverse"is defined according to the width of the vehicle. The term "height" refers to thedistance between two points, lines, surfaces or volumes as measured in thehorizontal direction.The yield strength, the ultimate tensile strength and the uniform and total elongationare measured according to ISO standard ISO 6892-1, published in October 2009.By average thickness of a part, or of a portion of a part, it is meant the overallaverage thickness of the material making up the part after it has been formed into a3-dimensional part from an initially flat sheet.Referring to Fig 1, 2 and 3, the rear suspension 3 of a motor vehicle 1 comprises forexample a rear cradle 4, two rear lower control arms 5, two vibration dampers 7, twowheels 9 and elements to link the wheels 9 to said rear lower control arms 5, suchas for example knuckles 11 and integral links 13.The rear cradle 4 hosts a rear internal combustion engine or a rear electrical motoror the rear four-wheel drive management system (these elements are not depictedin the figures). The rear cradle 4 is attached to the body of the vehicle 1 for exampleby securing rear suspension horns 6 to rear members (the rear members are notdepicted in the figures).The rear cradle 4 is further attached to rear lower control arms 5, present on theright and the left side of the vehicle. Said rear lower control arms 5 are the structurallink between the body of the vehicle, to which the rear cradle 4 is attached and thewheels 9.The vibration damper 7 is attached to the rear lower control arm 5. The vibrationdamper is for example a coil spring, as depicted on fig 2. A gas spring cylinder orhydraulic spring cylinder can also be used as vibration damper 7. Thanks to thepresence of the vibration damper 7, the wheels can move up and downindependently from the body of the vehicle, allowing for a comfortable ride even ona bumpy road. Furthermore, thanks to this suspension system, all four wheels of thevehicle stay on the road during driving, which is an essential element for goodvehicle handling and overall safety. The suspension system is tuned in order toafford the best compromise between vehicle comfort and vehicle handling.The rear lower control arm 5 is equipped with bushings 15, which serve to housethe attachment points to the elements to which the rear lower control arm 5 isattached to. The bushings 15 are made for example of a steel cylinder shell housinga vibration damping material, for example rubber like material, in order to absorb thevibrations coming from the interaction between the wheels, the tires and the road.Referring to figure 4, which shows an example of the fixation of the rear lower controlarm 5 to the wheel 9, the rear lower control arm 5 is attached to a knuckle 11, itselfconnected to the wheel hub 10, and to an integral link 13, which is itself connectedto the knuckle 11.Referring to figure 3, the other two bushings in the depicted particular embodimentare attached to fixation points on the rear cradle 4.Referring to figures 5 and 6, the rear lower control arm 5 consists of a top part 5tand a bottom part 5b defining between them a hollow volume 5h.The top part 5t comprises a top horizontal surface 5th and top side walls 5ts. Thetop horizontal surface 5th is delimited by a top horizontal surface outer periphery5tho. The top side walls 5ts, are delimited by a top side wall outer periphery 5tso.The top horizontal surface 5th extends in a substantially horizontal plane and formsthe main surface of the top part 5t. The top side walls 5ts extend along at least apart of the top horizontal surface outer periphery 5tho. The top side walls 5ts extendin a general direction which is at least inclined at 45° compared to the horizontaldirection. In a particular embodiment, the top side walls 5ts do not extend aroundthe entire length of the top horizontal surface outer periphery 5tho, as depicted onfigure 6. The areas of discontinuity of the top side walls 5ts are referred to as topside wall apertures 5tsa. Advantageously, the presence of such apertures 5tsaallows to house bushings 15 in the corners of the rear lower control arm 5. Saidbushings 15 serve to connect the rear lower control arm 5 to other elements suchas the rear cradle 4 and elements linking the rear lower control arm 5 to the wheel9. Furthermore, the presence of top side wall apertures 5tsa in the corners of thetop part 5t makes it easier to manufacture the top part 5t by stamping a flat sheet.Indeed, if the top side walls 5ts run along the entire top horizontal surface outerperiphery 5tho, including the corners of the top part 5t, the top part 5t would haveareas in which the deformation would extend in 3 different directions (the verticaldirection and two orthogonal horizontal directions). This type of deformation is verydifficult to achieve in the case of high strength materials, such as high strengthsteels. The presence of top side wall apertures 5Stsa therefore advantageouslyincreases the stamping feasibility of the top part 5t.Similar to the top part 5t, the bottom part 5b comprises a bottom horizontal surface5bh and bottom side walls 5bs. The bottom horizontal surface 5bh is delimited by abottom horizontal surface outer periphery 5bho. The bottom side walls 5bs, aredelimited by a bottom side wall outer periphery 5bso. The bottom horizontal surface5bh extends in a substantially horizontal plane and forms the main surface of thebottom part 5b. The bottom side walls 5bs extend along at least a part of the bottomhorizontal surface outer periphery 5bho. The bottom side walls 5bs extend in ageneral direction which is at least inclined at 45° compared to the horizontaldirection. In a particular embodiment, the bottom side walls 5bs do not extendaround the entire length of the bottom horizontal surface outer periphery 5bho, asdepicted on figure 6. The areas of discontinuity of the bottom side walls 5bs arereferred to as bottom side wall apertures 5bsa. Advantageously, the presence ofsuch apertures 5bsa allows to house bushings 15 in the corners of the rear lowercontrol arm 5. Said bushings 15 serve to connect the rear lower control arm 5 toother elements such as the rear cradle 4 and elements linking the rear lower controlarm 5 to the wheel 9. Furthermore, the presence of bottom side wall apertures 5bsain the corners of the bottom part 5b makes it easier to manufacture the bottom part5b by stamping a flat sheet. Indeed, if the bottom side walls 5bs run along the entirebottom horizontal surface outer periphery 5bho, including the corners of the bottompart 5b, the bottom part 5b would have areas in which the deformation would extendin 3 different directions (the vertical direction and two orthogonal horizontaldirections). This type of deformation is very difficult to achieve in the case of highstrength materials, such as high strength steels. The presence of bottom side wallapertures 5bsa therefore advantageously increases the stamping feasibility of thebottom part 5b.In a particular embodiment, the top and bottom side walls 5ts, 5bs do not extendaround respectively the entire length of the top and bottom horizontal surface outerperiphery 5tho, 5bho, as depicted on figure 6. The areas of discontinuity of the topside walls 5ts are referred to as top and bottom side wall apertures 5tsa, 5bsa.Advantageously, the presence of such apertures 5tsa, 5bsa allows to housebushings 15 in the corners of the rear lower control arm 5, as pictured on fig 5. Saidbushings 15 serve to connect the rear lower control arm 5 to other elements suchas the rear cradle 4 and elements linking the rear lower control arm 5 to the wheel9. Furthermore, the presence of side wall apertures 5tsa, 5bsa in the corners of thetop and bottom parts 5t, 5b makes it easier to manufacture the top and bottom parts5t, 5b by stamping a flat sheet. Indeed, if the side walls 5ts, 5bs run along the entirehorizontal surface outer periphery 5tho, 5bho including the corners of the parts 5t,5b, the parts 5t, Sb would have areas in which the stamping deformation wouldextend in 3 different directions (the vertical direction and two orthogonal horizontaldirections). This type of deformation is very difficult to achieve in the case of highstrength materials, such as high strength steels. The presence of side wall apertures5tsa, 5bsa therefore advantageously increases the stamping feasibility of the topand bottom parts 5t, 5b.The top and bottom parts 5t, 5b are assembled to form the rear lower control arm 5by securing them together along an assembly perimeter 5w. The assemblyperimeter 5w runs along at least part of the top and bottom side wall outerperipheries 5tso, 5bso. The assembly perimeter 5w is formed for example bywelding, more particularly for example by Metal Active Gas welding (MAG welding)or by laser welding. Because the top and bottom parts 5t, 5b include side walls 5ts,5bs, which are generally inclined compared to the horizontal direction by at least45°, the top and bottom horizontal surfaces 5ts, 5bs are spaced away at a distanceh from each other as measured in the vertical direction. The top and bottomhorizontal surfaces 5ts, 5bs thus define between them a hollow volume 5h. Thepresence of this hollow volume 5h confers rigidity to the rear lower control arm 5.The rear lower control arm 5 further comprises a first hole 17, designed to house abottom end of the vibration damper 7. The first hole 17 is formed by the assemblyof a top first hole 17t and a bottom first hole 17b respectively formed in the top andbottom parts 5t, 5b. Said top and bottom first holes 17t, 17b, comprise respectivelytop and bottom first hole side walls 17ts, 17 bs, which are respectively delimited bytop and bottom first hole side walls outer peripheries 17tso, 17bso. Said top andbottom first hole side walls outer peripheries 17tso, 17bso are joined together forexample by welding, more particularly for example by MAG welding or laser welding.In a particular embodiment, said top and bottom first hole side wall outer peripheries17tso, 17bso are not joined directly together but through the intermediary of a firstintermediate part 17m, as depicted on fig 7. Optionally, said first intermediate part17m, often referred to as the spring mount, is provided with a substantially horizontallower part 17mh, on which the first end of the vibration damper 7 can rest. The topfirst hole side wall outer periphery 17tso is secured to the first intermediate part 17malong a top first hole assembly perimeter 17tw and the bottom first hole side wallouter periphery 17bso is secured to the first intermediate part 17m along a bottomfirst hole assembly perimeter 17bw, located lower in the elevation direction than thetop first hole assembly perimeter 17tw.The presence of said first intermediate part 17m allows for easier forming of the topand bottom parts 5t, 5b by stamping from a flat sheet. Indeed, in order to form thetop and bottom first hole side walls 17ts, 17bs, it is necessary to perform a flangingoperation whereby the side of a previously formed hole in the flat sheet is graduallydeformed in a direction substantially perpendicular to the plane of the sheet. As theflanging operation is performed, the more the sides of the hole are deformed, themore it becomes susceptible to crack formation. Such a phenomenon is well knownand the propensity of a material to resist to flanging deformations is known as thehole expansion ratio, which is defined by the normalized test ISO 16630. It isparticularly critical in the case of high strength materials, for example in the case ofhigh strength steels, for example in the case of steels having an ultimate tensilestrength above 590MPa. Thanks to the presence of the first intermediate part 17m,the sum of the heights of the top and bottom first side walls 17ts, 17bs can be lowerthan the total height h separating the top and bottom horizontal surfaces 5th and5bh. By thus limiting the heights of the top and bottom first side walls 17ts, 17bs, thepresence of the first intermediate part 17m allows to limit the risk of crack formationon the top and bottom first hole side walls outer peripheries 17tso, 17bso linked tothe flanging operation.The rear lower control arm 5 further comprises a second hole 19, designed toincrease the vibration and stiffness performance of the part and also designed tolower the weight of the part. Said second hole 19 is formed by the assembly of a topsecond hole 19t and a bottom second hole 19b. Said top and bottom second holes19t, 19b, comprise respectively top and bottom second hole side walls 19ts, 19 bs,which are respectively delimited by top and bottom second hole side walls outerperipheries 19tso, 19bso. Said top and bottom second hole side walls outerperipheries 19tso, 19bso are joined together for example by welding, moreparticularly for example by MAG welding or laser welding. In a particularembodiment, said top and bottom second hole side walls outer peripheries 19tso,19bso are not joined directly together but through the intermediary of a secondintermediate part 19m, as depicted on Fig 8. The top second hole side wall outerperiphery 19tso is secured to the second intermediate part 19m along a top secondhole assembly perimeter 19tw and the bottom second hole side wall outer periphery19bso is secured to the second intermediate part 19m along a bottom second holeassembly perimeter 19bw, located lower in the elevation direction than the topsecond hole assembly perimeter 19tw. As is the case with the first hole 17, the useof a second intermediate part improves the formability of the second hole bystamping by reducing the height of the second wall top and bottom side walls 19ts,19bs and therefore reducing the risk of crack formation around the top and bottomsecond wall side walls outer periphery 19tso, 19bso related to the flangingoperation.The inventors have found that surprisingly the introduction of the second hole 19greatly increases the vibration and stiffness performance of the rear lower controlarm 5 even though it also diminishes the total weight of the part. It is generalcommon sense that the vibration and stiffness performance of a part increase withthe weight of a part. For example, increasing the average thickness of a part whilekeeping the same overall design will necessarily result in better vibration andstiffness performance. However, in the current case it was possible to achieve animprovement in vibration and stiffness performance while lowering the weight of thepart.For example, for a lower control arm 5 made of top and bottom parts 5t, 5b made ofstamped parts produced by stamping steel sheets of 1,8mm average thickness andhaving an ultimate tensile strength higher than 780MPa, the inventors have foundthat the first vibration mode of the part could be shifted from 295Hz to 481Hz justthrough the introduction of the above described second hole 19. In other words, thefirst mode was increased by 39%. These results were obtained using numericalcalculations to simulate a free-free modal analysis. Such results could also beobtained by physically manufacturing the same part having the same overall design,one part having a first hole 17 only and the second part having a first hole 17 and asecond hole 19 as previously described and by measuring the responses tovibrations using for example laser doppler vibrometers to evaluate the vibrations.A modal analysis is performed to prevent issues in the field of NVH (Noise, vibration,and harshness). The idea is to have a sufficiently high first vibration mode, theprecise numerical value to be reached being case dependent, so that the rear lowercontrol arm 5 is stiff enough to have low transmissibility of the forces exerted on thewheel 9 to the rest of the body. By ensuing a sufficiently high first vibration mode,the rear lower control arm 5 will not be the weak link in the chain linking the wheelto the vehicle body and the passenger compartment.This is achieved by the formation of the second hole 19, which ensures a furtherconnection, outside the first hole 17, between the top horizontal surface 5th and thebottom horizontal surface 5tb. Thanks to the presence of this additional link it ispossible to overcome the limitation of clamshell designs which naturally have a largeflat panel in the top and bottom horizontal surfaces 5th,5tb, said large flat panelsbeing ideal candidates for vibration transmission.The first and second hole 17, 19 can be for example of circular shape or oval shape.In order to minimize stress concentration, which would have a negative effect on thefatigue performance of the part, it is preferable to design said holes using smoothcontours and to avoid any harsh angles in their shape.Thanks to the adjunction of the second hole 19, the vibration performance of thelower control arm 5 can be significantly improved. Because the second hole 19 alsoinvolves removing part of the material making up the top and bottom horizontalsurfaces 5th,5bh, the presence of said second hole 19 also allows to reduce theweight of the part. The inventors found that the above-mentioned improvement of39% of the vibration performance was associated with a weight reduction of the partof approximately 5%.The following process can be applied in order to manufacture a rear lower controlarm 5 according to the present invention:a / providing a first a second flat sheetb / forming said first and second flat sheet, for example by stamping, in orderto produce a top part 5t and a bottom part 5b comprising respectively a topand bottom horizontal surface 5th, 5bh, top and bottom side walls 5ts, 5bs atop and bottom horizontal surface outer periphery 5tho, 5bho, a top andbottom side wall outer periphery 5tso, 5bso, further comprising respectivelya top and bottom first hole 17t, 17b, comprising respectively top and bottomfirst hole side walls 17ts, 17bs, and top and bottom first hole side walls outerperipheries 17tso, 17bso, and further comprising respectively a top andbottom second hole 19t, 19b, comprising respectively top and bottom secondhole side walls 19ts, 19bs, and top and bottom second hole side walls outerperipheries 19tso, 19bsoc / joining together said top and bottom parts 5t, 5b by securing them togetheralong at least part of the top and bottom side wall outer periphery 5tso, 5bsoto form an assembly perimeter 5w, and by securing them together along atleast part of the top and bottom first hole side walls outer peripheries 17tso,17bso, and by securing them together along at least part of the top andbottom second hole side walls outer peripheries 19tso, 19bso.For example, the joining operation is performed by MAG welding or laser welding.In a specific embodiment, the assembly process also comprises the following steps:-providing a first intermediate part 17m-joining the top and bottom first hole side walls outer peripheries 17tso, 17bsoto said first intermediate part 17m to form a top and bottom first hole assemblyperimeter 17tw, 17bwIn a specific embodiment, the assembly process also comprises the following steps:-providing a second intermediate part 19m-joining the top and bottom second hole side walls outer peripheries 19tso,19bso to said second intermediate part 19m to form a top and bottom secondhole assembly perimeter 19tw, 19bwIn a specific embodiment, the assembly process can further comprise the followingsteps between step b and step c-providing bushings 15 comprising a vibration damping material-positioning the bushings in between previously arranged top side wallapertures 5tsa and bottom side wall apertures 5bsaAdvantageously, by positioning said bushings 15 in between said top and bottomside wall apertures 5tsa, 5bsa, the bushings will be naturally held into place inbetween the top and bottom horizonal surfaces 5th, 5bh.In a particular embodiment, said top and bottom side wall apertures 5tsa, 5bsa arelocated in the corners of the top and bottom horizontal surfaces 5th, 5bh.

Claims

1. Rear lower control arm (5) for a motor vehicle comprising a top part (5t) and a bottom part (5b) defining together a hollow volume (5h), said top and bottom parts (5t, 5b) each comprising respectively -a top and bottom horizontal surface (5th, 5bh), delimited respectively by a top and bottom horizontal surface outer periphery (5tho, 5bho), -top and bottom side walls (5ts, 5bs) extending in a general direction of at least 45° compared to the horizontal plane along at least part of the top and bottom horizontal surface outer periphery (5tho, 5bho), said top and bottom side walls (5ts, 5bs) being delimited by a top and bottom side wall outer periphery (5tso, 5bso), -a top and bottom first hole (17t, 17b), comprising respectively top and bottom first hole side walls (17ts, 17bs) extending in a general direction of at least 45° compared to the horizontal plane, said top and bottom first hole side walls (17ts, 17 bs) being delimited by top and bottom first hole side walls outer peripheries (17tso, 17bso), - a top and bottom second hole (19, 19b), comprising respectively top and bottom second hole side walls (19ts, 19bs), extending in a general direction of at least 45° compared to the horizontal plane, said top and bottom second hole side walls (19ts, 19bs) being delimited by top and bottom second hole side walls outer peripheries (19tso, 19bs0), wherein said top and bottom parts (5t, 5b) are joined together -by securing together at least part of said top and bottom horizontal surface outer peripheries (5tho, 5bho), -by securing together at least part of said top and bottom first hole side walls outer peripheries (17tso, 17bso), -and by securing together at least part of said top and bottom second hole side walls outer peripheries (19tso, 19bso).

2. Rear lower control arm (5) according to claim 1 wherein the top and bottom parts (5t, 5b) are joined together by welding.

3. Rear lower control arm (5) according to claim 1 or 2 wherein the top and bottom first hole side walls outer peripheries (17ts0, 17bso) are joined together by the intermediary of a first intermediate part (17m), wherein the top first hole side walls outer periphery (17tso) is attached to the first intermediate part (17m) along a top first hole assembly perimeter (17tw), the bottom first hole side walls outer periphery (17bso) is attached to the first intermediate part (17m) along a bottom first hole assembly perimeter (17bw) and wherein said top first hole assembly perimeter (17tw) is located higher than said bottom first hole assembly perimeter (17bw) in the elevation direction.

4. Rear lower control arm (5) according to any one of claims 1 to 3 wherein the top and bottom second hole side walls outer peripheries (19tso, 19bso) are joined together by the intermediary of a second intermediate part (19m), wherein the top second hole side walls outer periphery (19tso) is attached to the second intermediate part (19m) along a top second hole assembly perimeter (19tw), the bottom second hole side walls outer periphery (19bso) is attached to the second intermediate part (19m) along a bottom second hole assembly perimeter (19bw) and wherein said top second hole assembly perimeter (19tw) is located higher in the elevation direction than said bottom second hole assembly perimeter (19bw).

5. Rear lower control arm (5) according to any one of claims 1 to 4 comprising four attachment points for chassis elements of the vehicle, said four attachment points being equipped with bushings (15) comprising a vibration damping material.

6. Rear lower control arm (5) according to claim 5, wherein the top and bottom side walls (5ts, 5bs) do not extend around the entire length of respectively the top and bottom horizontal surface outer periphery (5tho, 5bho), the areas in which the top and bottom side walls (5ts, 5bs) do not extend being called respectively top and bottom side wall apertures (5tsa, 5bsa) and wherein the bushings (15) are located in between at least part of said top and bottom side wall apertures (5tsa, 5bsa).

7. Rear lower control arm (5) according to any one of claims 1 to 6 wherein the top and bottom parts (5t, 5b) are made of steel having an ultimate tensile strength above 780MPa, as measured according to ISO standard ISO 6892-1, published in October 2009.

8. Process for manufacturing a rear lower control arm according to any one of claims 1 to 7 comprising the steps of: a / providing a first a second flat sheet b / forming said first and second flat sheet, in order to produce a top part (5t) and a bottom part (5b) comprising respectively a top and bottom horizontal surface (5th, 5bh), top and bottom side walls (5ts, 5bs) a top and bottom horizontal surface outer periphery (5tho, 5bho), a top and bottom side wall outer periphery (5tso, 5bso), further comprising respectively a top and bottom first hole (17t, 17b), said first holes comprising respectively top and bottom first hole side walls (17ts, 17bs), and top and bottom first hole side walls outer peripheries (17tso, 17bso), and further comprising respectively a top and bottom second hole (19t, 19b), said second holes comprising respectively top and bottom second hole side walls (19ts, 19bs), and top and bottom second hole side walls outer peripheries (19tso, 19bso) c / joining together said top and bottom parts (5t, 5b) by securing them together along at least part of the top and bottom side wall outer periphery (5tso, 5bso), by securing them together along at least part of the top and bottom first hole side walls outer peripheries (17tso, 17bso), and by securing them together along at least part of the top and bottom second hole side walls outer peripheries (19tso, 19bs0).

9. Process according to claim 8 further comprising the steps of -providing a first intermediate part (17m) -joining the top and bottom first hole side walls outer peripheries (17tso, 17bso) to said first intermediate part (17m) to form a top and bottom first hole assembly perimeter (17tw, 17bw).

10. Process according to claim 8 or 9 further comprising the steps of -providing a second intermediate part (19m) -joining the top and bottom second hole side walls outer peripheries (19tso, 19bso) to said second intermediate part (19m) to form a top and bottom second hole assembly perimeter (19tw, 19bw).

11. Process according to any one of claims 8 to 10 further comprising the steps of: -providing bushings (15) comprising a vibration damping material -positioning the bushings (15) in between previously arranged top side wall apertures (5tsa) and bottom side wall apertures (5bsa).