GB2302578A

GB2302578A - Vehicle nudge bar and energy-absorbing mounting device

Info

Publication number: GB2302578A
Application number: GB9512797A
Authority: GB
Inventors: Eric Raymond Clark
Original assignee: R G MANUFACTURING Ltd
Current assignee: R G MANUFACTURING Ltd
Priority date: 1995-06-23
Filing date: 1995-06-23
Publication date: 1997-01-22
Anticipated expiration: 2015-06-23
Also published as: GB2302578B; GB9512797D0

Abstract

A nudge bar (1) for a vehicle includes a plurality of brackets (2-5) for mounting the nudge bar on a vehicle. At least one of said brackets (2-5) includes an energy absorbing device (6). In one embodiment, the energy absorbing device (6) comprises a tube (18) and a piston (15) arranged to be driven into the tube. The external dimensions of the piston (15) are greater than the internal dimensions of the tube (18) and driving the piston into the tube thereby causes deformation of the tube.

Description

Nudge bar and energy absorbing device The present invention relates to a nudge bar for a vehicle.

The invention also relates to an energy absorbing device for use in particular, although not exclusively, with a nudge bar.

Nudge bars (also known as bull bars or brush guards) are grill-like constructions made of bent and welded tubular steel that fit over the front of a vehicle to protect the vehicle from being damaged by minor collisions with undergrowth during cross-country driving.

It has been reported by various road safety organisations that fitting a nudge bar to a vehicle can increase the risk of injury to a pedestrian in the event of a collision.

This is because nudge bars tend to be very heavy and rigid and do not give as readily as the bodywork of vehicle when struck. The peak impact forces transferred to the pedestrian in an accident can therefore be higher if a nudge bar is fitted to the vehicle. This danger is particularly acute if the pedestrian is a young child, as nudge bars often extend to the height of the child's head.

It has been proposed that the risk of injury could be reduced if the nudge bar included some form of energy absorption, to reduce the peak forces transferred to the pedestrian. However, it is difficult to find a suitable energy absorbing device. Some of the requirements for such a device include that it should be capable of resisting exposure to all weather conditions for perhaps twenty years or longer without any significant loss of reliability, it should be able to withstand the vibrations and operational forces occurring during normal use of the vehicle, including minor collisions with other vehicles during parking operations, it should have sufficient strength to support the nudge bar securely, it should be small and relatively inexpensive and, most importantly, it should be efficient and reliable in operation. Meeting these requirements has proven to be rather difficult.

It is an object of the present invention to provide a nudge bar that mitigates at least some of these disadvantages.

A further object of the invention is to provide an energy absorbing device that is small and cheap enough for use with a nudge bar and that is reliable and efficient in operation.

According to the present invention there is provided an energy absorbing device comprising a tube and a piston arranged to be driven into the tube, the external dimensions of at least a portion of the piston being greater than the internal dimensions of at least a corresponding portion of the tube.

The piston cannot be driven into the tube without either deforming the tube or cutting away at least a portion of the internal surface of the tube. Energy is required to drive the piston into the tube and the device can thus be used to absorb the energy of a collision.

Advantageously, the tube and the piston are substantially circular in cross-section and the outside diameter of the piston is greater than the internal diameter of the tube.

In this form, both the tube and the piston are easily manufactured, which reduces the cost of the device.

The outside diameter of the piston may be 1-5%, and advantageously 1.5-3%, and preferably approximately 2% greater than the internal diameter of the tube. For example, if the tube has a nominal internal diameter of 26mum, the diameter of the piston may be 26.50mum, to a tolerance of +O.OOmm, -0.05mm.

Advantageously, the tube is made of aluminium. This has been found in tests to perform consistently and reliably across a wide range of temperatures, it is relatively cheap and easy to manufacture and is resistant corrosion and deterioration.

Advantageously, the piston includes a portion having an interference fit in the tube. The piston may thus be secured to the tube in the correct position to be driven into the tube.

Advantageously, the device includes means for guiding the piston into the tube, so ensuring that the piston enters the tube correctly. The guiding means preferably comprises a guide member that extends substantially axially through the device and is slidable relative to the piston and/or the sleeve. For example, the guiding means may comprise an elongate member that extends with a sliding fit through an axial bore in the piston. Alternatively, the member may extend with a sliding fit through an axial bore in a seating member for the tube.

Advantageously, the device includes means for releasably preventing sliding of the guide member relative to the piston and/or the sleeve. For example, an adhesive may be applied to the contacting surfaces of the relatively slidable parts. This prevents sliding of the parts unless the applied force is sufficient to break the adhesive bond.

The device may include fixing means for securing the device to two relatively movable members. Advantageously, the fixing means comprises a bolt that extends substantially axially through the device. Preferably, the fixing means includes means for preventing excessive compressive forces being transmitted to the piston and tube. This prevents the piston being driven into the tube by over-tightening of the fixing means.

Advantageously, the energy absorbing device is encased in a sleeve of rubber or plastics material, to protect the device against corrosion.

According to the present invention there is further provided a nudge bar including a plurality of brackets for mounting the nudge bar on a vehicle, at least one of said brackets including an energy absorbing device.

Advantageously, at least one of said brackets is arranged to permit pivoting of the nudge bar, the mass of the nudge bar is no more than llkg and the nudge bar is designed to have a height when fitted to a vehicle of no more than 950mm.

Advantageously, the nudge bar includes an energy absorbing device as described in the preceding paragraphs.

Alternatively, the nudge bar may include an energy absorbing device comprising a resilient body member and at each end thereof a fixing element.

The body member of the energy absorbing device may be made substantially or wholly of rubber and preferably is substantially cylindrical and has a pinched waist portion.

Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, of which: - FIGURE 1 is a perspective view of a nudge bar showing the mounting brackets; FIGURE 2 is a side view of a first form of energy absorbing device; FIGURE 3 is an end view of the energy absorbing device shown in Figure 2; FIGURE 4 is a side view in cross-section of a second form of energy absorbing device; FIGURE 5 is a side view in cross-section of a plunger, comprising a part of the second form of energy absorbing device; FIGURE 6 is an end view of the plunger; FIGURE 7 is an end view of a seat; FIGURE 8 is a side view of the seat in cross-section; FIGURE 9 is a side view in cross-section of a sleeve; and FIGURE 10 is an end view of the sleeve.

Figure 1 shows a nudge bar (also known as a brush guard) for fitting to a vehicle. The nudge bar fits over the front of the vehicle to protect the vehicle from being damaged by minor collisions with undergrowth during cross country driving.

The nudge bar 1 is fabricated in a conventional manner from bent and welded tubular steel. The nudge bar is, however, designed to have a lower mass than is normal in conventional nudge bars. For example, the nudge bar may have a mass of approximately llkg. The height of the nudge bar is also less than usual and in particular is less than 950mm. These factors both help to reduce the risk of injury to a pedestrian, and especially to a child, in the event of a collision.

The nudge bar 1 has a pair of lower fixing points 2 that may be pivotally attached to lower mounting brackets 3.

The lower mounting brackets 3 are secured to the vehicle.

A pair of upper fixing points 4 may be secured to upper mounting brackets 5 by means of energy absorbing devices 6.

A first form of energy absorbing device is shown in Figures 2 and 3. The energy absorbing device comprises a rubber body 10 that is circular in cross-section and has a pinched waist. The overall shape of the rubber body 10 is similar to that of a bobbin. A circular steel washer 11 having a threaded bolt 12 secured thereto is bonded to each end of the rubber body 10. The two threaded bolts 12 are aligned substantially with each other and with the longitudinal axis of the rubber body 10.

When a pair of energy absorbing devices are mounted between the upper mounting brackets 5 and the upper mounting points 4, a certain amount of movement of the nudge bar 1 is possible, owing to the compressibility of the rubber body 10 and the pivoting arrangement of the lower mounts 2, 3.

In the event of a minor collision, the energy absorbing devices 6 are compressed, thereby reducing the peak force applied to the object involved in the collision. The risk of causing serious injury to a pedestrian in an accident is thereby reduced.

A second form of energy absorbing device is shown in Figures 4 to 10. Referring to Figure 4, the energy absorbing device 6 comprises a plunger 15, a seat 16, a sleeve 17, an aluminium tube 18 and a mounting bolt 19.

The plunger 15, which is shown in more detail in Figures 5 and 6, comprises a substantially cylindrical body 20 having a cylindrical bore 21 that extends longitudinally through the body. The curved outer surface of the body 20 is divided longitudinally into three portions of different diameters, those being a first portion 22 of diameter D1, a second portion 23 of diameter D2 and a third portion 24 of diameter D3, where D2 > D1 > D3. The diameter of D1 of the first portion 22 is selected so that the first portion 22 has an interference fit in the tube 18. For example, in the case of tubing having a nominal internal diameter of 26mm, the diameter Dl of the first portion may be 26.20mm, to a tolerance of +O.OOmm, -0.05mm.

The diameter D2 of the second portion 23 is sufficiently larger than the internal diameter of the tube 18 that it cannot enter the tube without deforming the tube. For example, the diameter D2 may be 26.50mm, to a tolerance of +O.OOmm, -0.05mm. The diameter D3 of the third portion 24 is not particularly critical, but may for example be approximately 25mm. As shown in Figure 5, the step 25 between the first portion 22 and the second portion 23 is bevelled at an angle of approximately 450. The leading edge of the first portion 22 and both ends of the bore 21 are chamfered at an angle of approximately 450.

The seat 16 is shown in more detail in Figures 7 and 8 and comprises a substantially cylindrical disc 26 having a cylindrical bore 27 that--extends axially through the seat.

The disc 26 includes a first portion 28 of diameter D4 and a second portion 29 of diameter D5, where D4 > D5. The diameter D5 of the second portion 29 is selected so that the second portion 29 has an interference fit in the tube 18. For example, the diameter D5 may be approximately 26.20mm, with a tolerance of +O.OOmm, -0.05mm. The leading edge 30 of the second portion 29 is chamfered. The diameter D4 of the first portion is substantially matched to the outside diameter of the tube 18 and may, for example, be approximately 29mm. The step 31 between the first portion 28 and the secdnd portion 29 is substantially perpendicular to the longitudinal axis of the energy absorbing device and abuts, in use, the end wall of the tube 18. The ends of the bore 27 are chamfered at an angle of approximately 450.

The sleeve 17 is shown in more detail in Figures 9 and 10 and comprises a metal tube having an outside diameter that is selected to provide a sliding fit in the bores 21 and 27 of the plunger 15 and the seat 16. For example, the sleeve may have an outside diameter of approximately llmm. The sleeve 17 has a longitudinal bore 32 through which, in use the mounting bolt 19 extends.

Preferably, the plunger 15 and the seat 16 are made of mild steel and are manufactured by machining. The sleeve 17 is also made of mild steel and is cut to the correct length from standard tube stock. The tube 18 is made of aluminium and is cut to length from standard stock.

When the energy absorbing device 6 is assembled, as shown in Figure 4, the first portion 22 of the plunger 15 is located in one end of the aluminium tube 18 with an end face of the aluminium tube 18 in engagement with the bevelled step 25. The second portion 29 of the seat 16 is similarly located in the other end of the aluminium tube 18, with the other end face of the tube 18 abutting the perpendicular wall 31 of the seat 16. The sleeve 17 extends through the cylindrical bores 21, 27 of the plunger 15 and the seat 16 respectively. All parts of the energy absorbing device 6 are secured to one another in this arrangement by means of an anaerobic adhesive. The entire assembled unit may be encased in a rubber or plastics sleeve (not shown).

In use, the energy absorbing device 6 is located between the mounting bracket 5 and the mounting point 4 of the nudge bar 1. First and second washers 35,36 are provided on either side of the mounting bracket 5, the internal diameter of outer washer 35 being matched substantially to the internal diameter of the sleeve 17 and the internal diameter of inner washer 36 being matched substantially to the internal diameter of the seat 16. The sleeve 17 is thus able to slide through the inner washer 36 but cannot pass through the outer washer 35.

The inner washer 36 may be a standard steel washer but is preferably made of a compliant material such as rubber or a synthetic elastomer. The compliant nature of the material allows the nudge bar to move very slightly in the initial stages of a collision, so reducing the very high load forces generated during the first two or three milliseconds of the collision. This significantly improves the performance of the device in preventing serious injury.

The length of the sleeve 17 is chosen so that when one end of the sleeve abuts the mounting point 4, the other end passes through the mounting bracket 5 and abuts the outer washer 35. The bolt 19 extends through the outer washer 35, the mounting bracket 5 and the sleeve 17 and engages a screw thread 37 in the mounting point 4.

When the bolt 19 is tightened to secure the nudge bar 1 to the mounting bracket 5, the compressive force exerted on the energy absorbing device 6 is carried entirely by the sleeve 17 and so is not transferred to the other parts of the energy absorbing device. This prevents the piston 15 being inadvertently driven into the tube 18 by overtightening of the bolt 17.

In the event of a collision, the force of the impact is transferred to the mounting bracket 5 through the piston 15, the tube 18 and the seat 16 rather than through the sleeve 17. This is because the sleeve 17 is able to slide through the mounting bracket 5. The piston 15 and the seat 16 thus exert a compressive force on the tube 18.

If the collision is a low level one, the force exerted by the piston 15 on the tube 18 is insufficient to drive the largest portion 23 into the tube 18 and the energy absorbing device 6 is not compressed. The nudge bar 1 is therefore maintained rigidly in position. Compression of the energy absorbing device is also resisted by the adhesive applied to the joint between the sleeve 17 and the seat 18, which prevents relative movement of those parts.

If the collision is a more severe one in which the force applied to the energy absorbing device 6 exceeds a predetermined limit, the piston 15 will be driven into the tube 18, swaging the tube outwards as it is forced along the length of the tube. This allows the nudge bar to pivot backwards and absorbs a great deal of the energy transferred to the nudge bar. The peak force transferred to the object that is in collision with the nudge bar is thereby limited, so greatly reducing the risk of injury to a pedestrian in an accident.

The initial force needed to drive the piston 15 into the tube 18 depends on the force needed to initiate swaging of the tube (i.e. the force needed to force the bevelled step 25 into the end of the tube 18) and the force needed to break the adhesive bond between the sleeve 17 and the seat 18. This force is greater than the force needed to drive the piston 15 further into the tube 18, after the initial resistance has been overcome: This is an important feature of the design as it helps to prevent compression of the energy absorbing device being caused by a minor, low level impact, which would otherwise reduce the subsequent effectiveness of the energy absorbing devices and cause the nudge bar to become loose on the mountings.

During compression of the energy absorbing device, the piston 15 is guided into the tube 18 by the sleeve 17, thereby ensuring that the piston enters the tube squarely.

This is important for reliable operation of the energy absorbing device at the predetermined force level. As the piston 15 is driven into the tube 18, the sleeve 17 slides through the mounting bracket 5. After a collision, the fact that the energy absorbing device has been compressed will be apparent from the fact that the upper mounting will then be loose, so indicating that new energy absorbing devices should be fitted.

In the event of a very severe collision, once the piston 15 has been driven the full length of the tube 18 and has come into contact with the seat 16, further energy is absorbed first by deformation of the mounting brackets, then by deformation of the nudge bar and finally by deformation of the vehicle body. The system of nudge bar, energy absorbing devices and mounting brackets is thus designed to collapse in a progressive manner with the aims that the maximum amount of energy should be absorbed and not transferred back to the object with which the vehicle collides, and that the cost of repairing the vehicle after a collision should be minimized.

Various modifications of the arrangement are possible. For example, a rubber washer maybe located between the energy absorbing device and the mounting bracket to add resilience to the mounting and to absorb vibrations. A washer may also be provided between the energy absorbing device and the nudge bar. The relative positions of the piston 15 and the seat 16 may also be reversed without affecting operation of the energy absorbing device.

It is further envisaged that the piston may have a roughened or knurled surface, to increase the force needed to drive the piston into the tube. Alternatively, the piston may be provided with one or more cutter elements arranged to cut grooves in the inner surface of the tube as the piston is driven into the tube, instead of or in addition to swaging the tube outwards.

Claims

1. An energy absorbing device comprising a tube and a piston arranged to be driven into the tube, the external dimensions of at least a portion of the piston being greater than the internal dimensions of at least a corresponding portion of the tube.

2. A device according to claim 1, wherein the tube and the piston are substantially circular in cross-section and the outside diameter of the piston is greater than the internal diameter of the tube.

3. A device according to claim 2, wherein the outside diameter of the piston is 1-5%, and advantageously 1.5-3%, and preferably approximately 2% greater than the internal diameter of the tube.

4. A device according to any one of the preceding claims, wherein the tube is made of aluminium.

5. A device according to any one of the preceding claims, wherein the piston includes a portion having an interference fit in the tube.

6. A device according to any one of the preceding claims, including means for guiding the piston into the tube.

7. A device according to claim 6, wherein the guiding means comprises a guide member that extends substantially axially through the device and is slidable relative to the piston and/or the sleeve.

8. A device according to claim 7, including means for releasably preventing sliding of the guide member relative to the piston and/or the sleeve.

9. A device according to any one of the preceding claims, including a seating member for the tube.

10. A device according to any one of the preceding claims, including fixing means for securing the device to two relatively movable members.

11. A device according to claim 10, wherein the fixing means comprises a bolt that extends substantially axially through the device.

12. A device according to claim 10 or claim 11, wherein the fixing means includes means for preventing excessive compressive forces being transmitted to the piston and tube.

13. A device according to any one of the preceding claims, wherein at least the piston and the tube are encased in a sleeve of rubber or plastics material.

14. An energy absorbing device substantially as described herein with reference to and as illustrated by Figs. 4 to 10 of the accompanying drawings.

15. A nudge bar including a plurality of brackets for mounting the nudge bar on a vehicle, at least one of said brackets including an energy absorbing device.

16. A nudge bar according to claim 15, wherein at least one of said brackets is arranged to permit pivoting of the nudge bar.

17. A nudge bar according to claim 15 or claim 16, the mass of the nudge bar being no more than llkg.

18. A nudge bar according to any one of claims 15 to 17, the nudge bar being designed to have a height when fitted to a vehicle of no more than 950mm.

19. A nudge bar according to any one of claims 15 to 18, including an energy absorbing device according to any one of claims 1 to 14.

20. A nudge bar according to any one of claims 15 to 18, including an energy absorbing device comprising a resilient body member and at each end thereof a fixing element.

21. A nudge bar according to claim 20, wherein the body member is made substantially or-wholly of rubber.

22. A nudge bar according to claim 20 or claim 21, wherein the body member is substantially cylindrical and has a pinched waist portion.

23. A nudge bar substantially as described herein with reference to and as illustrated by the accompanying drawings.