PIVOT STEERING SHAFT

FIELD OF THE INVENTION

[0001] The present subject matter relates generally to a steering column, and more particularly, to a pivot steering shaft of a straddle type vehicle having swinging power unit.

BACKGROUND OF THE INVENTION

[0002] Generally, a front portion of a vehicle having a swinging power unit has a steering column used to steer the vehicle. The steering column comprises of a sleeve welded or brazed in a hollow head pipe of the vehicle body structure and in which a centrally located pivot steering shaft is journaled by bearings. A handle bar is connected to the upper end of the pivot steering shaft. The pivot steering shaft is manually operated with the help of the handle bar and is rotatable within the head pipe to steer a front wheel and to turn the vehicle in different directions.

[0003] The lower distal end of the pivot steering shaft is connected to a lower bracket comprising two rotatable front fork rods placed on either side of the lower bracket and angularly disposed to the pivot steering shaft. Configurations with fork or shock absorber on one side only are also feasible. The lower bracket connects the front wheel to the vehicle body structure through the aforementioned fork rods. The front wheel is rotatably supported on a lower end of the two front fork rods and partially covered with a front wheel cover.

[0004] Ordinarily, the entire pivot steering shaft of the vehicle with the swinging power unit is of solid rod type. When the vehicle encounters a bump or a pothole, a strong impact load is felt at the interface of the pivot steering shaft and the lower bracket which may develop bending stress. The lower bracket transfers this load from the front wheel to the front portion of the vehicle body structure. The upper end of the steering shaft also made up of solid rod, does not feel strong impact load compared to the lower end and hence adds to unnecessary weight and cost of the vehicle. The lower end thus necessitates more strength. This requires more material to be added at the lower end.

[0005] Alternatively, the weight and strength requirements can be met by use of high strength tube material which is expensive and suffer from limitation of availability of such special high strength tubes. One could also employ a low cost tube combined with heat treatment process to increase the strength of the tube either locally or in totality. However, both of the above would result in significant cost increase in addition to special requirement of raw material processing of tube to meet strength requirements. There is thus a need to develop an improved, light weight, pivot steering shaft which is capable to withstand high impact loads and variable field loads without compromising its functionality.

[0006] Hence, the present subject matter is directed to overcome one or more problems as set forth above. It is therefore an object of the present invention to provide an improved, cost effective and light weight pivot steering shaft for a vehicle with a swinging power unit capable to withstand bending stresses when such a vehicle is subjected to impact loads or shock loads. It is another object of the present invention to provide a locally strengthened pivot steering shaft through a rod means which can readily be adapted to fit different sizes and shapes of the shaft. It is a further object of the present invention to restrain the cost and weight of the pivot steering shaft without attenuating its functionality. Yet another object of the present invention is to disclose a pivot steering shaft combining the best properties of rod and tube configurations, where a hollow tubular shaft is having a rod insert to strengthen the pivot steering shaft.

SUMMARY OF THE INVENTION

[0007] To this end, the present subject matter discloses a steering column assembly for a two wheeled straddle type vehicle with a swinging power unit comprising a pivot steering shaft substantially perpendicular to a lower bracket and swingably supporting a front wheel, the said pivot steering shaft having an upper and a lower end, the lower end being connected to the lower bracket and the upper end being connected to a handle bar assembly wherein the said pivot steering shaft further comprises a hollow tube, preferably of circular cross section and made of steel alloy forming the length of the pivot steering shaft, and a rod means present inwardly to the hollow tube, towards the lower end of the pivot steering shaft, and press fitted to the said hollow tube.

[0008] According to an aspect of the present invention, a bottom edge at the lower most end of the rod means comprises a chamfer so as to ensure proper seating and weld penetration. The pivot steering shaft is locally stiffened by the rod means and length of the said rod means does not cover the entire length of the pivot steering shaft.

[0009] 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

[00010] 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 shows a side view of a vehicle with a swinging power unit capable to accommodate the present subject matter.

FIG. 2 shows a detailed side view of an anterior portion of the vehicle of FIG. 1.

FIG. 3 shows a left sectional view of a pivot steering shaft disposed in an anterior portion of the vehicle with styling parts removed.

FIG. 4 shows an enlarged left sectional view of a pivot steering shaft of FIG. 3

FIG. 5 shows a perspective view of the complete assembly of the pivot steering shaft.

DETAILED DESCRIPTION OF THE INVENTION

[00011] The subject matter described herein relates to a steering column assembly for a vehicle with a swinging power unit. 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, wherever referred to, 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 assembly 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.

[00012] FIG. 1 illustrates a side view of a concerned vehicle with a swinging power unit. Typically such a vehicle includes a body frame assembly made up of several tubes welded together which usually supports the body of the said vehicle. The vehicle has a steerable anterior wheel 110 and a driven rear wheel 111 driven by driving force generated by the power unit. The body frame assembly 101 of the vehicle is an elongated structure, which typically extends from a forward end to a rearward end of the vehicle. It is generally convex in shape, as viewed from a side elevational view. The body frame assembly 101 includes a head pipe 600 and a down pipe that extends downward from the head pipe 600, and is covered by a plurality of vehicle body covers including a front panel 115, a leg shield 116, an under seat cover 117 and a side panel 112. The head pipe 600 is provided at the anterior end of the body frame 101.

[00013] A handlebar assembly 105 and a seat assembly 106 are supported at opposing ends of the frame assembly and a generally open area is defined there between known as floorboard 107 which functions as a step through space. A fuel tank (not shown) that stores fuel supplied to the engine is disposed at the rear end of the vehicle above the rear wheel 111. It is present on the upper side of the power unit along with a fuel tank cap. The seat for a driver and a pillion is placed forward to the fuel tank and rearwardly of the floorboard 107. A muffler is provided to the right side of the rear wheel, and connects to the engine. A side stand fixed to the left side of the body frame supports the vehicle such that vehicle inclines to the left side without falling.

[00014] typically, a front suspension assembly 103 is operatively positioned between the anterior wheel 110 and the frame assembly. Similarly a rear suspension assembly 114 is operatively positioned between the rear wheel 111 and the frame assembly. The front suspension assembly 103 commonly is a telescopic fork arrangement while the rear suspension assembly 114 is a hydraulic damped arrangement.

[00015] In the said vehicle, the rear suspension swing arm typically supports the power unit which is configured to drive the rear wheel 111 of the vehicle. The power unit is structured such that an engine 102 and a swing case 108, which are well known for this form of straddle type vehicle, are integrally constructed. In an embodiment of the present invention, the engine is a four stroke single cylinder internal combustion engine and the swing case 108 is connected to a left side surface of a crankcase of the engine 102 so as to extend forward.

[00016] It is disposed on the vehicle frame with one end of the swing case 108 attached to the rear wheel hub in such a way that the power unit is substantially angularly disposed to the ground. The engine 102 is arranged horizontally, that is, its crankshaft is placed perpendicularly to the longitudinal direction of the vehicle body. Since the basic construction of an engine is known to those versed in the art, the details have been omitted. The said power unit is surrounded by a shroud (not shown) with a fan to enhance forced cooling of the power unit. The shroud present over the power unit is also known as cooling cowl and may be made of plastic resin or the likes.

[00017] The present invention, in accordance with one embodiment thereof, involves an improved pivot steering shaft with tubular cross section and a rod insert- for the vehicle with the swinging power unit. FIG. 2 depicts the detailed view of the anterior portion of the concerned vehicle. A front fork 500 for rotatably supporting the anterior (front) wheel 110 is operably supported by the head pipe 600. The front fork 500 is connected to a lower bracket 200 and turnably supported on the head pipe 600. A pivot steering shaft 11 is positioned behind a front panel 115 of the said vehicle and not visible to an onlooker on the road. It is partially engulfed along its length and is operably supported by the head pipe 600.

[00018] A handle bar assembly 105 contains a hand grip which is used by an operator of the said vehicle to steer the vehicle. The lower bracket 200 connects the front wheel 110 to the vehicle frame through a pair of front forks 500 on either side of the longitudinal axis of the vehicle. The front fork 500 rotatably supports the front wheel 110 and is operably supported by the head pipe 600. Further, the anterior wheel 110 is partially covered with a wheel cover 113. The wheel cover 113 has a largely curved front portion 113a, a flat middle portion 113b and a rearmost curved portion 113c covering the anterior wheel 110. The wheel cover 113 is disposed in such a way so as to allow the motion of the wheel cover 113 accompanied by the steering operation of the front fork 500. The wheel cover 113 is connected to the lower bracket 200 through a wheel cover mounting structure 400 with the help of fasteners and is held below the lower bracket 200. Apart from load transfer the lower bracket 200 withstands shock, impact, torsion and clamping loads and also facilitates steering of the vehicle.

[00019] A cross sectional view of the proposed pivot steering shaft 11 is depicted in FIG. 3. The pivot steering shaft 11 has two ends, an upper end 15 and a lower end 16. The upper end 15 of the pivot steering shaft 11 is connected to the handle bar assembly 105. The lower end 16 of the pivot steering shaft 11 culminates into the lower bracket 200. The pivot steering shaft 11, in accordance with one embodiment thereof, is made of a hollow tube 12 made of alloy steel with a solid rod means 13 inserted into it. The hollow tube 12 has a circular cross section and is hollow for more than half of its length. According to a preferred embodiment of the present invention, the hollow tube is a cold drawn electrically welded (CEW) tube.

[00020] The lower end 16 of the pivot steering shaft 11 comprises of a rod means 13. The rod means is solid in nature and is present inner to the hollow tube 12. The lower end of the rod means 13 is in contact with a bearing in the lower bracket 200 in which the lower end of the pivot steering shaft 11 is journaled. The lower end of the pivot steering shaft 11 is welded to the lower bracket 200.

[00021] The lower bracket 200 in the two wheeled straddle type vehicle with a swinging power unit is close to front wheel 110, the front wheel 110 of such a vehicle being smaller compared to a motorcycle. Consequently, the pivot steering shaft 11 in the present vehicle experience more shock loads at its lower end which affect the durability of the said shaft 11. Hence, rather than making the entire pivot steering tube of solid rod means and consequently of more weight and cost, it is proposed in the present invention that the said pivot steering shaft 11 be locally strengthened with the said solid rod means 13 inserted and located at the lower end 16 of the pivot steering shaft 11. The rod means 13 strengthens the pivot steering tube 11 and helps in warding off any shock loads experienced at the interface of the pivot steering shaft 11 and the lower bracket 200. The use of less than full shaft length of solid rod helps in keeping the steering inertia of the pivot steering shaft 11 as low as possible and at the same time meet the strength requirements.

[00022] The lower portion of the pivot steering shaft 11 is wider than the upper portion. The presence of more material at the bottom adds to strength of the said shaft 11. Furthermore, the height of the said solid rod means 13 is kept above the bearing plane to ensure sufficient overlap between the rod means and the lower bracket 200. If the gap between the rod means 13 and the hollow tube 12 is more, then the hollow tube 12 will take all the shock loads and will fail to distribute it to the rod means. Thus controlled tolerance is kept between the rod means and the hollow tube so as to ensure adequate load distribution to the frame and prevent the failure of the pivot steering shaft 11. The tolerance and fit between inner diameter of the hollow tube and outer diameter of the rod means may be optimised so as to use standard available rod size without additional machining operations on outer diameter of the rod means or inner diameter of hollow tube which further helps in keeping the costs low.

[00023] According to an aspect, the rod means 13 is press fitted to the hollow tube 12 from the lower end 16. The fit between the rod means 13 and the hollow tube 12 is optimized to meet strength requirement. Hence, adequate interference plays an important role in optimal working of the pivot steering shaft 11. FIG. 4 shows the sectional view of the said pivot steering shaft. A bottom edge at the lowermost end of the rod means 13 and the hollow tube is provided with a chamfer 14 to ensure sufficient weld penetration when it is welded to the lower bracket 200 and thereby avoid weld on weld, which may affect the strength requirements. FIG. 5 shows the complete assembled view of the pivot steering shaft 11 where the rod means 13 in not visible to the onlooker.

[00024] According to another aspect, the cross section of the pivot steering shaft is wider towards the lower end and narrower towards the upper end of the pivot steering shaft. Thus adequate thickness is maintained at the lower end of the pivot steering shaft which ensures good endurance against shocks whereas the less thicker upper end removes unnecessary material leading to reduction in weight and cost of the pivot steering shaft.

[00025] The present subject matter and its equivalent thereof offer many advantages, including those which have been described henceforth. The pivot steering shaft with the hollow tube and solid rod means leads to reduction in the weight of the pivot steering shaft without compromising its functionality. It helps to decrease the manufacturing cost of the vehicle. The reduced steering weight increases the ease of steering the vehicle by an operator of the vehicle. Moreover, the pivot steering shaft is locally strengthened at its lower end by the presence of solid rod means where the bending stresses and loads are maximum. It can thus withstand shock, impact and clamping loads. Both hollow tube as well as solid rod can be made of steel alloy.

[00026] The present subject matter is thus described. In this description, the terms "solid rod means" and "rod means" have been used interchangeably and both denote the same meaning. 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 for a two wheeled straddle type vehicle with a swinging power unit comprising a pivot steering shaft substantially perpendicular to a lower bracket and swingably supporting a front wheel, the said pivot steering shaft having an upper and a lower end, the lower end being connected to the lower bracket and the upper end being connected to a handle bar assembly, the said pivot steering shaft further comprising: a hollow tube, preferably of circular cross section and made of steel alloy forming the length of the pivot steering shaft, and a rod means present inwardly to the hollow tube, towards the lower end of the pivot steering shaft, and press fitted to the said hollow tube.

2. The steering column assembly as claimed in claim 1 wherein the said rod means of the pivot steering shaft is solid and made of steel alloy.

3. The steering column assembly as claimed in claim 1 or claim 2 wherein a bottom edge at the lower most end of the said rod means comprises a chamfer so as to ensure proper seating and weld penetration.

4. The steering column assembly as claimed in claim 1 wherein the pivot steering shaft is locally stiffened by the said rod means and length of the said rod means does not cover the entire length of the pivot steering shaft.

5. The steering column assembly as claimed in claim 1 wherein the cross section of the pivot steering shaft is wider towards the lower end and narrower towards the upper end of the pivot steering shaft.

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