STEERING COLUMN

FIELD OF THE INVENTION

[0001] The present subject matter relates generally, to a steering column and more particularly, pertains to a variable cross section hydro-formed single fork steering column tube for a three wheeled vehicle.

BACKGROUND OF THE INVENTION

[0002] In many countries of the world, motor vehicle specially a three wheeled motor vehicle is a significant mode of public transportation. It is vastly used as a point to point mode of transport in rural and urban areas. Though such vehicle is designed to bear the load of four people, generally it is overloaded and is operated intermittently for 12 to 14 hours a day to enable the driver to maximize his earnings.

[0003] The three wheeled passenger carrier motor vehicle generally includes a front fork steering column for a single front wheel, an integral tubular frame extending from the fork to a rear axle which spans the rear end thereof and is powered by a conventional power unit propelling a pair of rear wheels thereon. Such a three wheeled vehicle is often driven over pot holed roads in urban areas and rugged, rough, unmetalled roads in rural areas. Operating on this type of terrain coupled with excess load causes high stress on some areas (the bent areas) of the steering column tube of the vehicle. As a result, it may buckle which might lead to vehicle failure. The vehicle would be stranded without being operated for some time as the vehicle would not receive immediate servicing and maintenance support due to its likelihood of being operated in a relatively inaccessible location. This may also cause monetary loss to the driver.

[0004] Therefore, the steering column tube needs to be stiffened in order to support the variable field loads. There is manufacturing feasibility issue while stiffening the tube at these areas. Moreover, correction of the tube to achieve final dimension causes deformation after the tube is stiffened. Further, to minimize the stress acting on various areas of the steering column tube, conventionally either stiffeners or gussets are added to increase the moment of inertia and thereby to prevent bending. However there is a pressing need to develop a steering column tube with better stiffness while eliminating additional stiffeners and gussets in the single steering column in a three wheeled vehicle.

[0005] The present subject matter is directed to overcome one or more problems as set forth above and obviate the lacunae in the prior art. Therefore it is an object of the present invention to disclose a steering column tube for a three wheeled vehicle sufficiently stiffened at high stress areas to prevent its bending and increase its ability to effectively counter variable field loads without the need for additional stiffeners or gussets. It is another object of the present invention to disclose a cost effective steering column tube with a variable section modulus so as to achieve the desired stiffness. It is yet another object of the present invention to provide a steering column tube for a three wheeled vehicle without the need for conversion and which can withstand high load conditions despite less mass.

SUMMARY OF THE INVENTION

[0006] To this end, the present subject matter discloses a steering column assembly in an anterior portion of a three wheeled vehicle comprising a steering column tube, the said steering column tube comprising a variable cross section, the variable cross section including a circular cross section at a top and a bottom end and a rectangular cross section sandwiched in between the circular cross section at the top and the bottom end to stiffen a plurality of high stress areas of the steering column tube in such a way that the circular cross section converges towards the lower end of the steering column tube.

[0007] According to an aspect of the present subject matter, the steering column tube is fabricated by hydroforming.

[0008] The foregoing objectives and summary provide only a brief introduction to the present subject matter. To fully appreciate these and other objects of the present subject matter as well as the subject matter itself, all of which will become apparent to those skilled in the art, the ensuing detailed description of the subject matter and the claims should be read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The above and other features, aspects, and advantages of the subject matter will be better understood with regard to the following description, appended claims and accompanying drawings where:

FIG. 1 illustrates the perspective view of a concerned three wheeled passenger carrier vehicle.

FIG. 2 shows a front view of the three wheeled passenger carrier with the styling parts and the covering removed.

FIG. 3 depicts a right side view of the said vehicle according to the present invention.

FIG. 4 shows a front view of a steering column tube as per the present invention.

FIG. 5 illustrates a top perspective view of the steering column tube according to the present invention.

FIG. 6 is a table showing comparison between a hydro-formed steering column tube according to the present invention and that in prior art.

DETAILED DESCRIPTION OF THE INVENTION

[00010] The subject matter described herein relates to a steering column tube with variable section modulus which is capable of connecting a handle bar to a front wheel in a three wheeled vehicle used mainly, but not solely as a passenger carrier. It is to be noted that "front" and "rear", and "left" and "right" wherever referred to in the ensuing description, refer to front and rear, and left and right directions as seen in a state of being seated on a seat of the vehicle. Furthermore, a longitudinal axis refers to a front to rear axis relative to the vehicle, while a lateral axis refers generally to a side to side, or left to right axis relative to the vehicle. Various other features of the steering column according to the present subject matter here will be discernible from the following further description thereof, set out hereunder. The detailed explanation of the constitution of parts other than the subject matter which constitutes an essential part has been omitted at suitable places.

[00011] FIG. 1 describes a side view of a concerned three wheeled passenger carrier vehicle, referenced by the numeral 100, driven by an internal combustion engine. It has a front cowl 101 along with a windscreen 102. The lower portion of the front cowl 101 is connected to a front wheel 104 with a wheel cover 103 stationed in between. A handle bar assembly 109 is present behind the front cowl 101 which is used to operate the said three wheeled vehicle 100. In this view, a steering tube assembly is not visible to an onlooker of the vehicle. The vehicle is laterally divided into two halves, along the line X-Y, an anterior portion A having the driver's seat 107 while a posterior portion P has a long passenger seat 108 with a seating capacity of minimum three passengers. The rear panel (also known as cabin) 106 along with the second half of the vehicle containing the passenger seat 108 is supported on a pair of rear wheels 105 located on either side of the longitudinal axis of the vehicle 100. Below the passenger seat 108, an internal combustion engine (not shown) is located used to power the vehicle.

[0001] FIG. 2 illustrates a front view of the three wheeled vehicle with the panels and styling parts removed. The said three wheeled vehicle 100 is supported on a frame structure spanning from the anterior portion A to the posterior portion P of the vehicle. The anterior portion A comprises a steering column assembly connected to the front wheel 104, front suspension 203 and a trailing arm 204. The steering column assembly in turn comprises of a steering column tube 202, rotatably supporting the front wheel 104 and acting as a mechanical link between the handle bar 109 and the front wheel 104. The steering column tube 202 is engulfed by a head tube 205 on all sides and welded or secured to the head tube. The head tube 205, which is a part of vehicle chassis, usually houses bearings that allow the steering column tube 202 to turn freely. A clutch actuation lever 111 is pivotally mounted at a distal end of the handle bar 109 preferably on the left side thereof, such that the user may grip the handle bar 109 to change the gear ratio by retracting and releasing the clutch actuation lever 111.

[00012] FIG. 3 depicts the right side perspective view of the said three wheeled vehicle with all the coverings removed. Conventionally a steering column tube is generally a circular tube but bent towards the right side and connected to the front wheel. It may be made of steel or alloy steel. Generally all •• the road loads on the front wheel 104 are absorbed by the front suspension 203 which is strongly supported by the steering column tube 202. High stress areas, referenced by the numeral 206, can be identified at the bending points on a conventional steering column. To prevent deformation and increase load carrying capacity, these high stress areas 206 are generally stiffened by the use of additional aluminium casting which acts as a stiffener. However this adds to the cost of the vehicle. Additionally where a change in sectional requirement is there, conventionally two or three tubes are made and joined together to form the single part, which may result in loss of strength.

[00013] This problem can be avoided by increasing the section modulus of the particular stress area by increasing the sectional area without adding any stiffeners. It is possible to locally enlarge the section through hydroforming. Hence the steering column assembly in the present invention discloses a hydro-formed steering column tube with a variable cross section to ward off the stress. Locally the section of the steering column is increased wherever there is a need of decreasing the stress.

[00014] The structure of the present steering column tube, in accordance with an embodiment thereof, would now be described with the help of FIG. 4 and FIG. 5. FIG. 4 shows the front view of the steering column tube as per the present invention. The said steering column tube 202 comprises of a variable cross section comprising a circular cross section 301 and a rectangular cross section 302. The rectangular cross section is spread between the circular cross section on lower and upper portion of the steering column tube. At the lower end towards the front wheel axle, the said steering column tube has a converging circular cross section. FIG. 5 is the perspective view of the said steering column tube as per the present invention. The entire tube is made by hydroforming process which is a cost effective way of shaping malleable metals like aluminium into lightweight, structurally stiff and strong pieces.

Here a high pressure hydraulic fluid is used to press room temperature metal and obtain odd profiles. With hydroforming, a single tubular structure with variable cross section like the one in this invention can be produced without any joint. After the tube is made via hydroforming, it need not undergo correction to achieve the correct dimensions. Thus the tube will have least or no deformation to develop into the correct shape. Additionally several brackets 208 are separately attached to the said steering column tube like front wheel cover bracket, front suspension bracket and pivot bracket to mount the respective components over the said tube 202.

[00015] FIG. 6 carries a table showing the stress test comparison between the currently used constant cross section tube and the hydro-formed steering column tube during normal loading in the form of a bar graph. The table shows that the deflection of hydro-formed tube is 3.14 mm when compared with the conventional one whose deflection is 8.78 mm at normal load conditions in the X plane. The deflection of hydro-formed tube is 1.55 mm when compared with the conventional one whose deflection is 7.18 mm at normal load conditions in the Y plane. It is thus clear that the hydro-formed tube withstands more stress than the existing tube in normal load conditions and suffers about 200% fewer deflections. Additionally the section modulus for the proposed steering tube is also increased due to the hydroforming process coupled with variable cross section mainly at stress areas.

[00016] The present subject matter and its equivalent thereof offer many advantages, including those which have been described henceforth. The new hydro-formed steering column tube overcomes the process limitations of the conventional tube. It is capable to withstand worst load conditions with less mass. The variable cross section enables decrease in wobbling of handle bar while riding and better handling. The process of making the steering column tube is simplified and hence no additional correction is needed. The entire process is cost effective as the need for additional stiffeners is eliminated and process simplified.

[00017] The present subject matter is thus described. The description is not intended to be exhaustive nor is it intended to limit the invention to the precise form disclosed. It will be apparent to those skilled in the art that the disclosed embodiments may be modified in light of the above description. The embodiments described are chosen to provide an illustration of principles of the invention and its practical application to enable thereby one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. Therefore the forgoing description is to be considered exemplary, rather than limiting, and the true scope of the invention is that described in the appended claims.

We claim:

1. A steering column assembly in an anterior portion of a three wheeled vehicle comprising a steering column tube, the said steering column tube comprising a variable cross section, the variable cross section including a circular cross section at the top and the bottom end and a rectangular cross section sandwiched in between the circular cross section at the top and the bottom end to stiffen a plurality of high stress areas of the steering column tube in such a way that the circular cross section converges towards the lower end of the steering column tube.

2. The steering column assembly as claimed in claim 1 wherein the said steering column tube is fabricated by hydroforming.

3. A three wheeled vehicle comprising the said steering column assembly as claimed in any of the preceding claims

4. A steering column assembly substantially as herein described and
illustrated by the accompanying drawings.