GB2274628A

GB2274628A - Additional energy-absorbing system for a motor vehicle steering column

Info

Publication number: GB2274628A
Application number: GB9402014A
Authority: GB
Inventors: Philippe Corfa
Original assignee: Nacam SA
Current assignee: Robert Bosch Automotive Steering Vendome SAS
Priority date: 1993-02-02
Filing date: 1994-02-02
Publication date: 1994-08-03
Anticipated expiration: 2014-02-02
Also published as: GB2274628B; FR2701000B1; GB9402014D0; ES1027883Y; ES1027883U; FR2701000A1

Abstract

The said steering column comprises a shaft 1 mounted in a tubular casing 2. An inner ring 3 is mounted between the casing and the shaft. The shaft has a large-diameter part 5 on the steering wheel side and a small-diameter pant 6 on the steering box side. The hole 4 in the inner ring has a larger diameter than part 6, and a smaller diameter than part 5 of the shaft, so that in the event of an impact part 5 pushes inner ring 3 to displace it over a predetermined distance within casing 2, the resulting clamping effect absorbing energy in order to protect the head of the driver. <IMAGE>

Description

ADDITIONAL ENERGY-ABSORBING SYSTEM FOR A STEERING COLUMN OF A MOTOR VEHICLE The invention relates to a steering column of a motor vehicle and more particularly to an additional energy-absorbing system adapted to protect the driver's head in the event of an impact.

Numerous protection systems exist which are based on utilisation of energy and which have to comply with safety standards determined by a "driver body check test", better known as the "BBT test". Many devices have been suggested to satisfy this type of test, particularly devices which use wave tubes. In order to comply with more and more exacting safety demands, one standard provides for the protection of the driver's head, that is to say a standard embracing the shock of impact on the head of the driver, better known as the "HIC test". To meet these requirements, motor vehicle steering columns have to comprise a safety system which passes the HIC test in terms of shock of impact on the driver's head before the safety system which has to meet the BBT or driver's body check test comes into operation.

The object of the present invention is to suggest a supplementary safety system which satisfies the HIC test and which cuts in before the safety device which satisfies the driver's body check or BBT test, this system being installed without difficulty in existing steering columns in order not to alter the overall bulk of the column in relation to the environment in the motor vehicle.

According to the invention, the additional energy absorption system of a motor vehicle steering column for protecting the head of the driver relates to a steering column comprising a steering control shaft installed in a casing tube. This system comprises an inner ring mounted in the casing tube and having a hole through which the steering control shaft can pass. The steering control shaft has two parts of different diameters: a large diameter part at the steering wheel end and a small diameter part at the steering box end.According to the invention, the hole in the inner ring has a larger diameter than the small diameter part of the steering control shaft and a smaller diameter than the large diameter part of the said steering control shaft so that in the event of an impact, the large diameter part pushes the inner ring so that the said inner ring is displaced within the housing tube over a predetermined length of travel, with the desired instantaneous locking-up or clamping effect in order to absorb the energy required over a total contact surface area to protect the driver's head in accordance with the HIC test.

Advantageously, one embodiment of the invention includes an intermediate ring which is disposed inside the tubular casing between the said casing and the inner ring, this intermediate ring being rigid with the casing tube.

In order to allow a more progressive response from the additional energy absorption system, the inner ring has a chamfer disposed on its periphery and on the same side as the steering box. Furthermore, the hole in the inner ring has a conical entrance which is disposed on the steering wheel side and which cooperates with a conical transition provided on the steering control shaft between the small diameter part and the large diameter part.

In accordance with the invention, the inner ring is preferably of metal and the intermediate ring is of a material of the plastic type, with flutes made on its outer surface.

According to an alternative embodiment of the invention, the plastic intermediate ring comprises a metal sleeve mounted on the outside of the plastic intermediate ring, said metal sleeve likewise having flutes on its outer surface.

Advantageously, according to the invention, the means of axially retaining the intermediate ring consist of deformations inside the tubular casing. More precisely, the interior deformations in the tubular casing consist of two circular sets of interior deformations which are disposed opposite each of the ends of the intermediate ring. One series of interior deformations is disposed at the end of the tubular casing, on the same side as the steering box, in order to secure the end of the intermediate ring. Each of these interior deformations is made on the basis of a single cut-out. A second series of interior deformations inside the tubular casing and adapted to secure the other end of the intermediate ring is made on a basis of two cut-outs.

The additional energy-absorbing system for a motor vehicle steering column according to the invention thus has the advantage that it can be easily disposed in existing steering columns and absorbing the energy by extrusion in order to comply with the HIC driver's head impact shock test before the energy absorption in line with the driver's body check or BBT test comes into action.

Further advantages will arise from the invention which will be more clearly understood from the ensuing description of particular examples of embodiment, with no implied limitation, reference being made therein to the appended drawings in which: Fig. 1 is a cross-sectional view of the additional energy absorption system for a steering column of a motor vehicle according to the invention; Fig. 1A is a view of a detail in Fig. 1; Fig. 2 is a graph showing the development of stress due to impact as a function of time in order to comply with the HIC and BBT tests; Fig. 3 is a cross-section through another embodiment of additional energy-absorbing system for a steering column according to the invention; Fig. 4 is a plan view according to IV in Fig. 3.

The various tests and measurements conducted by the Applicants have made it possible to establish the graph shown in Fig. 2 and which relates to fluctuations in impact stress as a function of time, in order to comply firstly with the HIC driver's head impact shock test standards and secondly to comply with the driver's body check test or BBT test. It can be seen that the value for impact stress is markedly lower in the HIC test zone than in BBT test zone. This impact stress value for the HIC test may easily be adapted by the system according to the invention which will be described hereinafter.

As can be seen from Fig. 1, the additional energy absorption system for a motor vehicle steering column for protecting the driver's head, in accordance with the invention, is mounted on a steering column which comprises a steering control shaft 1 which is mounted in a tubular casing 2. The additional energy-absorbing system according to the invention essentially comprises an inner ring 3 disposed between the tubular casing 2 and the steering control shaft 1. This inner ring 3 is mounted in the tubular casing 2 and has in it a hole 4 to allow passage of the steering control shaft 1. The steering control shaft 1 has two parts of different diameters: a large-diameter part 5 on the same side as the steering wheel and a small-diameter part 6 on the same side as the steering box. The hole 4 in the inner ring 3 has a diameter which is greater than the small-diameter part 6 of the steering control shaft 1 and a diameter which is smaller than the large-diameter part 5 of the said steering control shaft 1. In this way, a shoulder is obtained between the large-diameter part 5 and the small-diameter part 6 of the steering control shaft which pushes on the inner ring 3 in the event of an impact.

Thus, in the event of an impact, the large-diameter part 5 pushes the inner ring 3 so that the said inner ring 3 becomes displaced within the tubular casing 2 over a predetermined length of travel, with the desired instantaneous clamping action in order to absorb the energy over a total contact surface area to protect the head of the driver.

In the system shown in Fig. 1, an intermediate ring 7 is provided which is disposed within and is fixed to the tubular casing 2 so that the inner ring 3 slides inside this intermediate ring 7.

The intermediate ring 7 is of a plastics material and comprises on the outside a metal sleeve 8 the inner surface 20 of which is force-fitted onto the outer face 15 of the intermediate plastics ring 7.

The metal sleeve 8 comprises flutes 19 made on its outer surface 21 in order to make up for variations in finish on the inner surface 26 of the tubular casing 2.

Furthermore, means for axially securing the intermediate ring 7 make it possible to immobilise the said intermediate ring 7 in relation to displacement of the steering control shaft 1 in the event of an impact.

The inner ring 3 which is of metal in one form of embodiment comprises a chamfer 11 disposed at its periphery on the outer surface 13 in such a way as to improve the sliding movement of the inner ring 3 inside the intermediate ring 7 when there is an impact. The hole 4 in the inner ring 3 comprises a conical entry 12 which is disposed on the same side as the steering wheel. In the event of an impact, this conical entry 12 is pushed by a conical transition 9 which is made on the steering control shaft 1 between the small-diameter part 6 and the large-diameter part 5.

Thus, the tubular casing 2 has an interior surface 26 which is always smooth while the metal sleeve 8 of the intermediate ring 7 may be smooth or have flutes 19 which make it possible to make up for variations in the inner surface 26 of the tubular casing 2. According to the invention, there is still a clamping effect for the contact surface between the outer surface 13 of the inner ring 3 and the inner surface 14 of the intermediate ring 7. Upon assembly, there is an instantaneous contact surface between the inner ring 3 and the intermediate ring 7 which corresponds to the diameter of this inner ring 3 multiplied by the axial width of this inner ring 3.When the additional energy-absorbing system functions, there is a displacement of this inner ring 3 within the intermediate ring 7 over a predetermined distance in order to provide a total contact surface area which makes it possible to absorb the desired quantity of energy to be able to comply with the driver's head impact shock or HIC standards. The total contact surface area is therefore equal to the instantaneous contact surface area plus the surface area represented by the energy absorption stroke multiplied by the diameter of the inner ring 3. Therefore it is possible according to the additional energy-absorbing system of the invention to predetermine the desired amount of energy absorption by modifying or adapting the sliding stroke to match the sliding surface area and by adapting the clamping effect of the inner ring 3 in the intermediate ring 7.Furthermore, this clamping effect can be constant, variable or evolutive in order precisely to satisfy the demands imposed. Finally, another advantage of the invention resides in the choice of the type of chamfer 11 on the inner ring 3 and the condition of the contact surfaces 13 and 14 and the materials used for making the inner ring 3 and the intermediate ring 7.

The embodiment shown in Figs. 3 and 4 comprises the same basic structure as that illustrated in Fig. 1, that is to say that it is disposed between the steering control shaft 1 and the tubular casing 2 of a motor vehicle steering column. This steering control shaft 1 is mounted in the tubular casing 2 by means of needle bearings 10. In the same way, the steering control shaft 1 comprises a large-diameter part 5 on the steering wheel side and a small-diameter part 6 on the steering box side. These parts 5 and 6 are connected to each other via a conical transition 9.

A metal inner ring 3 similar to that previously described comprises a hole 4 and a conical entry 12 which is disposed on the steering wheel side. Furthermore, this inner ring 3 is provided with a chamfer 11 disposed on its outer surface 13 on the steering box side.

An intermediate plastic ring 7 is mounted in the tubular casing 2 and it is provided on its outer surface 15 with flutes 16 to allow compensation for variations on the inner surface 26 of the tubular casing 2.

The intermediate ring 7 is fixed to the tubular casing 2 by axial securing means consisting of interior deformations in this tubular casing 2 which are disposed on each side of this intermediate ring 7. As can be seen particularly from the exterior view in Fig. 4 and in the sectional view in Fig. 3, the deformations inside the tubular casing 2 consist of two circular sets of interior deformations. These two circular sets of interior deformations are disposed opposite each of the ends 17 and 18 of the intermediate ring 7. The first series of interior deformations 22 is disposed at the end of the tubular casing 2 on the steering box side, in order to secure the end 17 of the intermediate ring 7. Each of these interior deformations 22 is made on the basis of a single cut-out 23. A second series of interior deformations 24 can be found inside the tubular casing 2 in order to secure the other end 18 of the intermediate ring 7. Each of these interior deformations 24 is based on two cut-outs 25.

The sole purpose of the reference indices inserted after the technical characteristics in the claims is to facilitate understanding of these claims without in any way restricting their scope.

Claims

PATENT CLAIMS

1. An additional energy-absorbing system for a motor vehicle steering column, for protecting the driver's head, the said steering column comprising a steering control shaft (1) which is installed in a tubular casing (2), characterised in that it comprises an inner ring (3) mounted in the tubular casing (2) and having a hole (4) to allow passage of the steering control shaft (1) which has two parts of different diameters, a large-diameter part (5) on the same side as the steering wheel and a small-diameter part (6) on the same side as the steering box, the hole (4) in the inner ring (3) having a larger diameter than the small-diameter part (6) of the steering control shaft (1) and a smaller diameter than the large-diameter part (5) of the said steering control shaft so that in the event of an impact the large-diameter part (5) pushes the inner ring (3) so that the said inner ring (3) is displaced within the tubular casing (2) by a predetermined travel with the desired instantaneous clamping action in order to absorb the energy required over a total contact surface area in order to protect the driver's head.

2. An additional system according to Claim 1, characterised in that it comprises an intermediate ring (7) disposed inside the tubular casing (2) between the tubular casing (2) and the inner ring (3) and fixed to the said tubular casing (2).

3. An additional system according to either of the preceding Claims, characterised in that the inner ring (3) comprises a chamfer (11) disposed on its periphery and on the same side as the steering box.

4. An additional system according to any one of the preceding Claims, characterised in that the hole (4) in the inner ring (3) comprises a conical entry (12) disposed on the steering wheel side and which cooperates with a conical transition (9) provided on the steering control shaft (1) between the small-diameter part (6) and the large-diameter part (5).

5. An additional system according to any one of the preceding Claims, characterised in that the inner ring (3) is of metal.

6. An additional system according to any one of Claims 2 to 5, characterised in that the intermediate ring (7) is of a plastic type of material.

7. An additional system according to Claim 6, characterised in that the intermediate plastic ring (7) comprises a metal sleeve (8) mounted on the outside of the said intermediate plastic ring (7).

8. An additional system according to Claim 6, characterised in that the intermediate plastic ring (7) comprises flutes (16) provided on its outer surface (15).

9. An additional system according to Claim 7, characterised in that the metal sleeve (8) has flutes (19) provided on its outer surface (20).

10. An additional system according to any one of Claims 2 to 9, characterised in that the means of axially securing the intermediate ring (7) consist of interior deformations in the tubular casing (2).

11. An additional system according to Claim 10, characterised in that the interior deformations in the tubular casing (2) consist of two circular sets of interior deformations disposed each of the ends (17, 18) of the intermediate ring (7), that is to say one set of interior deformations (22) disposed at the steering box end of the tubular casing (2) to grip the end (17) of the intermediate ring (7), each of these interior deformations being based on a single cut-out (23), a set of interior deformations (24) inside the tubular casing (2) to secure the other end (18) of the intermediate ring (7), each of these latter interior deformations (24) being based on two cut-outs (25).