Abstract:
A collapsible steering column assembly comprising a mounting structure, the mounting structure comprising a first part for connecting to the body of a vehicle and a second part for connecting to part of a steering mechanism, the first and second parts being interconnected to permit relative movement therebetween as the assembly collapses, wherein: one of the first or second parts comprises a slot, the slot comprising a pocket and a channel defined by two opposing sidewalls, each sidewall being the outer edge of a deformable structure; the other of the first or second parts comprises a lug, the lug extending into the pocket when the assembly is in a non-collapsed state and being configured to be driven through the channel to cause plastic deformation of the deformable structure as the assembly collapses; and the assembly comprises a re-enforcement that limits the plastic deformation of the deformable structure during the collapsing stroke to regions of the deformable structure adjacent to regions of the channel through which the lug has passed.

Description:
FIELD OF THE DISCLOSURE 
     This invention relates to a collapsible steering column assembly. 
     BACKGROUND 
     Many vehicles are provided with a steering control such as a wheel or yoke which allows the driver to control the vehicle&#39;s direction. Taking a conventional automobile as an example, it is typically equipped with a steering wheel which is located in front of the driver. A control linkage extends forwards from the steering wheel to a mechanism such as a steering rack that converts rotation of the steering wheel to an appropriate motion of the automobile&#39;s steering wheels. The control linkage, together possibly with any cosmetic or support structures associated with it is known as a steering column. In addition to automobiles, similar structures exist in other vehicles, such as trucks, motor boats and aircraft. 
     The steering column typically extends away from the driver&#39;s position, most normally forward of the driver. If the vehicle is involved in a collision the driver&#39;s body might hit the steering column. It is therefore desirable for the steering column to be able to deform, particularly by collapsing in the direction along its axis, so as to absorb energy and reduce injury to the driver. 
     Several techniques are known for absorbing kinetic energy in a steering column. In one class of techniques a shaft of the steering column is capable of telescoping axially, a first part of the column being in the form of a tube into which a second part of the column can slide. Relative motion of the first part relative to the second part is resisted by means of a frictional clamping arrangement. When the column is subjected to an axial compression force that is high enough to overcome the friction of the clamp the two parts can collapse telescopically. One problem with this arrangement is that it is difficult to design the clamp so that energy is absorbed evenly as the column collapses. Once the frictional force of the clamp has been overcome the collapse of the steering column assembly can sometimes occur with minimal resistive force. 
     In a typical implementation of a steering column assembly in a vehicle, the assembly is secured to a support structure by means of a support bracket. The support structure may form part of the vehicle chassis or be some other structural component of the vehicle. In another class of energy absorption techniques energy is absorbed due to work done in the plastic deformation of the support bracket, or of other intermediary structures linking the steering column to the structure of the vehicle. 
     EP 0,479,455 B1 (Melotik) is an example of such a steering column assembly. In Melotik a support bracket connects a steering column assembly to a support structure.  FIG. 1  is a diagram of the support bracket. The right-hand portion of  FIG. 1  shows the bracket in its-non-collapsed state (i.e. before a substantial impact) and the left-hand portion of  FIG. 1  shows it in its collapsed state. The support bracket is broadly U-shaped in plan-view, and contains a base portion  54  and two side members  56  and  58 . The support bracket is designed to fit around the steering column such that the side members  56  and  58  are located on respective sides of the steering column. The base portion contains a bore  62  through which a steering shaft passes. Each side member contains a guide slot  92  which has at its rearward end a pocket  94 . When the assembly is in a non-collapsed state (on the right-hand side of  FIG. 1 ) a bolt  70 , which connects the support bracket to the structure of the vehicle, sits in the pocket  94 . Forward of the pocket the guide slot diminishes in width to be narrower than the diameter of the bolt  70 . The guide slot divides the side member into a guide rail  96  and a deformable rail  98 . The guide rail is thicker than the deformable rail. 
     When a significant impact occurs, the bolt  70  is driven forwards from its initial position in pocket  70 . As the bolt moves through the guide slot  92  the energy absorbing side rail undergoes plastic deformation. Once the bolt reaches the end position, as illustrated on the left-hand side of  FIG. 1 , the guide slot will have been deformed to a slot of uniform width. Energy is absorbed by the support bracket as the deformable rails are pushed sideways. Although in theory it might be possible to design the deformable rails so that energy can be absorbed uniformly along the travel of the bolt, in practice this would be expected to be difficult. The reason for this is that when the bolt is part way through its travel parts of the deformable rails will already have moved sideways, and that movement will significantly affect the force needed to advance the bolt further into the slot. 
     EP 2,377,743 (Olgren) discloses a further method of absorbing the kinetic energy of an impact onto the steering column by means of plastic deformation. The steering assembly of Olgren comprises a steering shaft housed in a jacket. A support bracket attaches the assembly to the vehicle.  FIG. 2   a  is a diagram of the support bracket  30 . The bracket contains a substantially horizontal base plate  54  and two vertical panels  56  and  58  which project downwards from the base plate. Each vertical panel contains a first slot  60 , the slot extending horizontally. 
     In one structure disclosed by Olgren a carriage is attached rigidly to the jacket of the steering shaft, the carriage being supported by the bracket  30 .  FIG. 2   b  is a diagram of the carriage  32 . The carriage is generally U-shaped when viewed in cross-section and contains two vertical walls  64  and  66 . Each vertical wall contains a guide slot  68  which has at its one end a hole  100 . The width of the guide slot is uniform along its length and less than the diameter of the hole  100 . A bolt is used to assemble the carriage to the bracket  32 . When the carriage is assembled to the bracket  32  and the steering column assembly is in a non-collapsed state the bolt is threaded through the holes  100  of the carriage and slots  60  of the support bracket  30 . The diameter of the bolt is greater than the width of the guide slot  68 . During the collapse of the assembly the bolt travels from the hole  100  through the guide slot  68  to an end position  106 . Because the diameter of the bolt is greater than the width of the guide slot, the bolt causes the vertical walls  64  and  66  to plastically deform. The work done in plastically deforming the vertical walls absorbs a portion of the impact energy of the driver onto the steering column assembly. 
     In another structure disclosed by Olgren energy is absorbed through the plastic deformation of the support bracket itself. In this embodiment the slots of the support bracket are contoured in the same fashion as the guide slots  68  of the carriage in the first embodiment.  FIG. 3  is a diagram of the support bracket according to the second embodiment. A bracket  230  comprises a substantially horizontal base plate and two vertical panels that extend vertically downwards from the base plate. Each panel has a guide slot  260 , with a hole at its one end. The guide slots have uniform width which is less than the diameter of the hole. When the bracket is in its initial assembled position a bolt  280  threads both holes. The diameter of the bolt is greater than the width of the guide slots. In the event of a substantial impact the bolt is driven along the slot  260 . Energy is absorbed by the plastic deformation of the bracket  230 . 
     There is thus a need for an improved method of absorbing kinetic energy during the collapse of a steering column. 
     According to the present invention there is provided a collapsible steering column assembly comprising a mounting structure, the mounting structure comprising a first part for connecting to the body of a vehicle and a second part for connecting to part of a steering mechanism, the first and second parts being interconnected to permit relative movement therebetween as the assembly collapses, wherein: one of the first or second parts comprises a slot, the slot comprising a pocket and a channel defined by two opposing sidewalls, each sidewall being the outer edge of a deformable structure; the other of the first or second parts comprises a lug, the lug extending into the pocket when the assembly is in a non-collapsed state and being configured to be driven through the channel to cause plastic deformation of the deformable structure as the assembly collapses; and the assembly comprises a re-enforcement that limits the plastic deformation of the deformable structure during the collapsing stroke to regions of the deformable structure adjacent to regions of the channel through which the lug has passed. 
     Suitably the deformable structure comprises a relatively strong portion running longitudinally with the channel and a relatively weak portion running longitudinally with the channel and located between the relatively strong portion and the channel. 
     Suitably the relatively strong portion of the sidewall is thicker than the relatively weak portion of the sidewall when viewed in cross-section in a plane perpendicular to the longitudinal direction of the slot. 
     Alternatively the relatively weak portion could have a tapered profile when viewed in cross-section in a plane perpendicular to the longitudinal direction of the slot. 
     The relatively strong portion may have a higher material hardness than the relatively weak portion. The relatively strong portion may have a greater cross-sectional area than the relatively weak portion. The relatively strong portion could be configured with strengthening structures, such as ribs, which contribute to it being more resistant to deformation than the relatively weak portion. The relatively weak portion could be configured with zones of weakness, such as grooves, notches or perforations, which contribute to it being less resistant to deformation than the relatively strong portion. 
     Preferably the re-enforcement is the relatively strong portion. 
     Preferably the relatively strong portion is configured such that plastic deformation of the deformable structure is limited to the relatively weak portions. 
     Suitably the total width of the channel and the relatively weak portions is at least as great as the width of the lug. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The present disclosure will now be described by way of example with reference to the following drawings. In the drawings: 
         FIG. 1  is a plan view of a prior art steering column assembly mounting bracket before and after an impact. 
         FIG. 2   a  is a side view of a prior art bracket of an adjustable steering column assembly. 
         FIG. 2   b  is a side view of a prior art carriage of an adjustable steering column assembly to be used in conjunction with the bracket of  FIG. 2   a.    
         FIG. 3  is an exploded view of a prior art steering column assembly. 
         FIG. 4  is a view of a steering column assembly according to an embodiment of the present invention. 
         FIG. 5  is a plan view of a steering column assembly according to an embodiment of the present invention. 
         FIG. 6  is plan view of the underside of a steering column assembly according to an embodiment of the present invention. 
         FIG. 7  is a cross-sectional view of a steering column assembly in a non-collapsed state according to an embodiment of the present invention. 
         FIG. 8  is a cross-sectional view of the mounting block of  FIG. 7  after collapse, with the shape of the mounting block before collapse indicated by dashed lines. 
     
    
    
     DETAILED DESCRIPTION 
     The apparatus described below provides a means of permitting a steering column assembly to collapse, absorbing energy. In a preferred embodiment the steering column is mounted to a vehicle by means of a bracket that includes a slot. A relatively stiff lug is located in the slot. One of the bracket and the lug is connected to the body of the vehicle and the other is connected to the distal end of the steering column so that when the steering column collapses the lug moves in the slot. The width of the slot is smaller than the dimension of the lug that extends transversely to the slot. As a result the lug deforms the slot when it slides in the slot. The slot is defined by two opposing sidewalls. At least one of the sidewalls comprises a relatively strong portion running longitudinally with the slot and a relatively soft portion located between the relatively strong portion and the slot. The relatively soft portion defines one of the side walls of the slot. The relative strength of the strong and soft portions is selected such that when the lug ploughs through the slot, deformation of the said one of the sidewalls is restricted to the relatively soft portion and the relatively strong portion remains substantially undeformed. Thus the relatively strong portion prevents the sidewall itself from bowing out, meaning that the deformation of the soft portion sidewall can absorb energy along a substantial portion of the track of the lug in the slot, and meaning that the energy absorbed by deformation of the soft portion may be more predictable than in some prior designs. 
       FIGS. 4 to 8  illustrate a steering column assembly embodying the present invention. 
     A steering shaft  401  interconnects a steering wheel (not shown) to a steering mechanism such as a steering rack (not shown). The steering shaft comprises two elongate parts that are rotationally fast with each other about their axis. The two parts of the steering shaft can telescope together. To that end, one of the parts could be a splined sliding fit inside the other; or one part could be a tube inside which the other part fits, and one of the parts could have a keyway that runs axially and is engaged by a projecting key on the other part. At the forward end of the steering shaft there is a universal joint  402 . When the structure shown in  FIG. 4  is mounted in a vehicle the universal joint allows the steering shaft to swing about a horizontal axis that passes through the universal joint, whilst still transmitting rotation to the steering mechanism. 
     The steering shaft runs inside a locating tube  403 . The locating tube holds the steering shaft in a set orientation as will be described in more detail below. A mechanism for fore and aft adjustment of the steering wheel (not shown) can be attached to the rearward end of the locating tube. 
     A mounting block  404  provides for the attachment of the structure shown in  FIG. 4  to a vehicle. When the structure is in use the mounting block is firmly anchored to the body of the vehicle, for example to a bulkhead at the front of the passenger compartment, by means of bolts passing through holes  450 . A carriage  405  is attached to the mounting plate. The carriage comprises a base plate  406  and two sidewalls  407  which extend perpendicularly from the base plate. The sidewalls define arcuate slots  408  which describe a radius about the centre of the universal joint  402 . Pins  409  (see  FIG. 5 ) extend horizontally from the locating tube  403  and through the slots  408 . A clamp mechanism  410  can be operated to pull on at least one of the pins by bearing on the sidewall through which that pin runs, and thereby clamp the locating tube in a particular orientation relative to the carriage and hence to the vehicle. The clamp mechanism could be a cam attached to a lever which allows it to be operated by hand. When the clamp is released the locating tube is free to swing in the plane of the sidewalls about the centre of the universal joint. Since the steering shaft runs through the locating tube, this mechanism allows a driver to alter the rake of the steering shaft and then lock it in the desired orientation. 
     The base plate  406  of the carriage is flat and lies against a region of the mounting block  404  which is flat, whereby the base plate can slide against the mounting block. In  FIG. 4  the carriage is shown in its initial position. After sliding relative to the mounting block it can adopt the position shown by chain dotted lines at  451 . The base plate is located relative to the mounting block by bolts  411  which pass through holes in the mounting block and then through slots  412  in the base plate  406  of the carriage. The slots  412  run parallel with the steering shaft in the plane of the base plate. A nut is tightened on to each of the bolts to hold the base plate against the mounting block. A low-friction and/or compressible washer  413 , for example of a plastics material such as nylon, is located between the head of the bolt and the base plate to avoid the bolt excessively restricting motion of the base plate relative to the mounting block. 
     The mounting block defines a third slot  417 . The third slot is parallel with the first and second slots. The third slot lies along the projection of the steering shaft into the plane of the surface of the mounting block that faces the base plate  406 . The third slot is located adjacent to the base plate. A stud  418  is rigidly attached to the base plate and extends into the slot. The stud is constituted by a bolt  419  which passes through a hole  420  in the base plate. A collar  421  surrounds the part of the bolt that projects into the slot and a nut  452  is tightened to the bolt to clench the collar to the base plate. 
     The third slot  417  comprises a pocket  423  and a channel  422  (see  FIG. 6 ). The pocket is sized to receive the collar  421  comfortably. The channel  422  is parallel-sided. The channel can be deformed, as will be described in more detail below, but in its undeformed condition the channel is narrower than the stud. More precisely, the width of the channel is less than the width of the part of the stud that would pass between the walls of the channel if the carriage were to slide relative to the mounting block by movement of bolts  411  along slots  412 . In the example shown in the figures, due to the configuration of the slots  412  that sliding is a linear motion. Conveniently the exterior shape of the collar  421  is of constant cross-section in any plane perpendicular to the base plate. Most conveniently the exterior shape of collar  421  is a circular cylinder about an axis perpendicular to the base plate. 
     As will be described in more detail below, the mounting block is deformable in the region of the third slot  417  so that if sufficient force is applied the carriage can slide relative to the mounting block with the stud  418  ploughing through the channel  422 , enlarging the width of the channel so that the stud can pass along it. The steering column of  FIGS. 4 to 8  can be mounted in a vehicle. If that vehicle is involved in a collision, the driver may hit the steering wheel or an airbag connected to the steering wheel and push it forwards. The force applied by the driver&#39;s body can be passed via the locating tube  403  and the pins  409  to the rearward-facing walls of the arcuate slots  408 . Since the mounting block is anchored to the vehicle, this force pushes the carriage  405  forwards relative to the mounting block. If the force is sufficient, the stud  418  will be moved from pocked  423  and forced to plough through the channel  422  causing plastic deformation of the walls of the channel. The plastic deformation of the channel absorbs energy, reducing the peak impact of the driver&#39;s body on the steering wheel and contributing to the driver&#39;s safety. 
     With reference to  FIG. 7 , regions  455  of the mounting block run along the axis of the channel, i.e. along the axis along which the stud  418  moves relative to the mounting block when the assembly collapses. Regions  455  lie on either side of the channel. Between the channel and regions  455  are other regions  454 . Regions  454  and  455  are configured such that when the stud moves through the channel regions  454  are plastically deformed in at least the regions through which the stud has moved during collapse of the steering column, and regions  455  are undeformed along their entire length. The stud is configured so that it too is undeformed after collapse. 
       FIG. 7  shows the mounting block in cross-section prior to deformation of the channel. In regions  454  adjacent to the channel  417  the mounting block is relatively thin. In regions  455  further from the channel the mounting block is relatively thick. The total width of the channel plus both regions  454  and  455  is greater than the width of the stud  418 , as can be seen in  FIG. 7 . Due to the relative thickness of the mounting block in regions  454  and  455  the mounting block is more resistant to deformation in regions  455  than it is in regions  454 . The thickness of the mounting block in regions  454  is selected to be sufficiently small compared to its thickness in regions  455  that when the stud ploughs through the channel, plastically deforming the material of the mounting block, that deformation will be restricted to regions  454 , with regions  455  remaining substantially or entirely undeformed. This behaviour compels the stud to continue deforming region  454  throughout the whole of its travel along the channel, allowing energy to be absorbed progressively along the whole travel of the carriage and thus limiting the peak load on the driver. It also means that the energy expended in moving the stud through the channel can be predicted with reasonable accuracy by only considering the deformation of regions  454 . This makes that prediction easier than in some prior designs. 
       FIG. 8  shows the cross-section of a part of the mounting block after deformation. The regions  454  have been mushroomed by the passage of the stud between them. 
     The cross-sectional profile of the mounting block in the region of the channel could take any suitable form. There could be an abrupt change in thickness between regions  454  and  455 . Alternatively, there could be a tapered or curved region between the two as shown in  FIG. 8 . Each region could have a constant thickness or its thickness could vary over its width. The strength of each region could be controlled by means other than altering the thickness of the mounting block. For example, the material of the regions  454  could be softer than the material of regions  455 . Regions  455  could be defined by a separate component of softer material that is inserted into the remainder of the mounting block. Similarly, the mounting block could be reinforced by the attachment of a separate strengthening part at regions  455 . Regions  454  could be integral with regions  455  but the regions could have been subjected to different chemical or mechanical treatment regimes: for example regions  455  could have been subjected to strengthening treatment to which regions  454  have not been subjected. 
     In designing the profile of the mounting block, the following steps could, as an example, be followed. Assume the mounting block is to be formed of a single piece of material and the weaker regions  454  are to be defined by milling material from the mounting block. The thickness of the stud is determined and then the dimensions of the weaker regions  454  are determined in order to give the desired energy absorption from plastic deformation of the regions by motion of the stud. Finally the thickness of the stronger regions  455  is determined so as to be sufficient to ensure that they will not deform during the anticipated deformation of the weaker regions. Alternatively the dimensions of the weaker regions  454  are first determined, the thickness of the stronger regions being determined so as to be sufficient to ensure that they will not deform during deformation of the weaker regions. The thickness of the stud would then be determined to give the desired energy absorption from plastic deformation of the weaker regions by motion of the stud. 
     The mounting plate could, for example, be cast into shape, with the relatively weaker regions machined out if necessary. The mounting plate could, for example be formed of an aluminium alloy. The carriage could, for example be formed of steel plate. The collar  421  of the stud is preferably formed of a relatively hard material such as a hardened steel alloy so that it does not deform when it ploughs through the channel  417 . 
     The applicant hereby discloses in isolation each individual feature described herein and any combination of two or more such features, to the extent that such features or combinations are capable of being carried out based on the present specification as a whole in the light of the common general knowledge of a person skilled in the art, irrespective of whether such features or combinations of features solve any problems disclosed herein, and without limitation to the scope of the claims. The applicant indicates that aspects of the present invention may consist of any such individual feature or combination of features. In view of the foregoing description it will be evident to a person skilled in the art that various modifications may be made within the scope of the invention.