SUPPORTING BRIDGE FOR A STRADDLE TYPE VEHICLE

FIELD OF THE INVENTION

[0001] The present subject matter relates generally to a straddle type vehicle with a swinging power unit, and more particularly, to a supporting bridge connecting the anterior wheel to the frame of the vehicle.

BACKGROUND OF THE INVENTION

[0002] The anterior portion of a straddle type vehicle with a swinging power unit comprises of a supporting bridge to connect an anterior wheel to the frame of the vehicle through a fork assembly. The supporting bridge is a structural member of the vehicle which helps in load transfer from anterior wheel to frame. It withstands shock, impact, torsion and clamping loads as well as facilitates wheel cover mounting and steering control for better handling of the vehicle.

[0003] Each lateral end of the supporting bridge comprises of a bush usually fabricated from a sheet metal or through forging. Such bush is welded respectively at its upper and lower surface, to the upper and lower half brackets, of the supporting bridge thereby forming a complete supporting bridge. As shown in FIG. 3, the top portion of the bush has a flat surface (known as bolt side 211) and connected to the upper bracket of the supporting bridge whereas bottom portion of the bush (known as bore side 212) has a bore to insert an inner tube of the front fork assembly and connected to the lower bracket of the supporting bridge.

[0004] A side bolt clamp 210 is provided in the bush as a radial projection so that when the side bolt clamp is bolted, the bush tightens and clamps the inner tube of the front fork. The bush also has a plurality of partial slits, in horizontal and vertical plane, circumferencially spanning the bush surface to enable such clamping by aiding the radial movement of the bush. The dimensions of slits and their position affect the collapsibility of the bush during clamping as well as the strength of the joint. Generally, the vertical slit starts from the bore side and plunges along the long axis of the bush to a suitable height. This also enables avoiding any path for mud or water entry from the top. However the durability of the bush is limited for such design and can result in structural breakage. In a typical bush, the vertical slit is disposed between two horizontal slits. The width and height of both vertical and horizontal slits are optimized to get required strength and collapsibility. For fabricating the slits, a conventional cutting tool is used such that the cutter enters from one side of the bush and stops after crossing the horizontal slits. Thus one face of the bush has a slit to enable tool entry during machining.

[0005] Further, since the vertical slit is fabricated from the bore side to the bolt side, there is a discontinuity on the circumference of bush at the bore side. When the lower bracket is welded to the bush at bore side, discontinuity on the circumference of bush may lead to poor weld quality resulting in high stress concentration at the discontinuity of the bore. The high stress translates into poor strength of the supporting bridge and leads to its fatigue failure, especially that of lower bracket. Therefore the challenge is to increase the strength and durability of the lower bracket without compromising on the bush radial movement and its clamping potential and without addition of any undesirable weight.

[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 subject matter to disclose an improved supporting bridge for a straddle type vehicle with a swinging power unit by changing the slitting pattern of a connected bush for improved strength. Another object of the present invention is to increase the strength and durability of the lower bracket of the supporting bridge without attenuating its functionality while restraining the cost and weight of the vehicle.

SUMMARY OF THE INVENTION

[0007] To this end, the present subject matter discloses a supporting bridge for a straddle type vehicle connecting an anterior wheel to a main frame of the said vehicle, comprising a lower bracket present at a lower portion of the said supporting bridge, an upper bracket present at an upper portion of the said supporting bridge and mechanically connected to the lower bracket, at least one opening at each of the lateral end of the said supporting bridge, a bush ensconced in the said opening of the said supporting bridge, the bush having a bolt side and a bore side, wherein the bolt side having a partially open flat surface and bore side having a bore to receive an inner tube of a front fork, characterized in that, the said bush further comprises atleast two spaced horizontal slits in the horizontal plane and at least one vertical slit in the vertical plane in such a manner that the fabrication of the vertical slit is initiated from the bolt side of the bush, passing
through one of the horizontal slits and ending at the another horizontal slit, the vertical slit thereby spanning the space between the said horizontal slits.

[0008] According to an aspect of the present subject matter, each horizontal slit is approximately perpendicular to the bore axis and the vertical slit is approximately parallel to the bore axis.

[0009] According to another aspect of the present subject matter, the bore side of the bush is continuous and the bolt side of the bush is discontinuous.

[00010] 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

[00011] 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 concerned straddle type vehicle according to the present invention.

FIG. 2 depicts a diagrammatic illustration of an anterior portion of the said vehicle according to the present invention.

FIG. 3 illustrates front view and perspective view respectively of a bush present in a supporting bridge according to the prior art.

FIG. 4 depicts a perspective view of the supporting bridge according to the present invention.

FIG. 5 depicts a diagrammatic illustration of front view and perspective view respectively of a bush present in a supporting bridge according to the present invention.

FIG. 6 shows a front view of the supporting bridge according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[00012] The subject matter described herein relates to a supporting bridge with a bush in 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 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 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. In the ensuing exemplary embodiments, the vehicle is a straddle ride type vehicle. However it is contemplated that the concepts of the present invention may be applied to other types of vehicles within the spirit and scope of this invention including a scooter type motorcycle.

[00013] 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.

[00014] 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.

[00015] 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.

[00016] 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.

[00017] 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.

[00018] FIG. 2 depicts a diagrammatic illustration of an anterior portion of the said vehicle in detail according to the present invention. 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 supporting bridge 200 and turnably supported on the head pipe 600. The supporting bridge is a structural member of such a vehicle and connects the anterior wheel 110 to the vehicle frame thereby transferring load from anterior wheel to the frame. The head pipe 600 includes a rotatable steering shaft S steered by the handle bar 105 at the upper end. The rotatable steering shaft S is centrally connected to the supporting bridge 200 through steering bearings (not shown).

[00019] 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 has an upper surface facing the handlebar and a lower surface facing the ground. 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 provided above the anterior wheel 110 to avoid the said vehicle and its occupants from being splashed with mud, water and the like. The wheel cover 113 is attached to the supporting bridge 200 through a wheel cover mounting structure 400 by means of welding or fastening. The wheel cover mounting structure may be angularly disposed i.e. at an angle to the vehicle width axis. It is not visible to an onlooker as it is covered by the front panel 115. The wheel cover 113 is secured to the wheel cover mounting structure 400 in such a way that secured wheel cover 113 is placed below it.

[00020] FIG. 4 presents a diagrammatic illustration of a supporting bridge according to the present invention made up of at least two brackets of suitable form, namely a lower bracket 202 present at a lower portion of the supporting bridge and an upper bracket 201 present at an upper portion of the supporting bridge and mechanically connected to the lower bracket. In an embodiment, the upper bracket 201 is welded to the lower bracket 202 at their interface, generally at its lower portion. The lower bracket 202 is further connected to the front fork assembly whereas the upper bracket 201 of the supporting bridge 200 is connected to the main frame through the steering shaft S. The anterior surface of the supporting bridge 200 is attached to the wheel cover mounting structure 400 through which the wheel cover 113 is mounted to the supporting bridge 200.

[00021] Each lateral end of the supporting bridge 200 comprises of at least one bush 203 usually fabricated from a sheet metal or through forging and ensconced in an opening 204 provided at such lateral end of the supporting bridge. For the sake of simplicity, only one bush is explained in detail below. The other lateral end has an identical bush. The top portion of the bush is known as bolt side 211 whereas the bottom portion of the bush is known as bore side 212. The bolt side 211 has a partially open flat surface whereas the bore side 212 has a bore to receive the inner tube of the front fork 500 and hence is completely open.

[00022] FIG. 5 shows the front and perspective view of the bush 203 according to the present invention. The bush may be forged or made of sheet metal and is provided with a plurality of slits. The said slits are provided in two planes, horizontal and vertical.

[00023] According to an aspect, the bush 203 comprises of a plurality of horizontal slits 207a, 207b, in the horizontal plane, spaced with each other along the outer circumference of the bush and perpendicular to bore axis as shown to enable a partial radial section of the bush to tighten and clamp the inner tube of the front fork. In an embodiment, at least two spaced horizontal slits are provided in the bush in the horizontal plane. The bush is also provided with at least one vertical slit 208 in the vertical plane between the horizontal slits and parallel to the bore axis. The fabrication of vertical slit 208 initiates from the bolt side 211 and plunges along the bore axis passing the first horizontal slit 207a to a suitable length in such a way that the bolt side 211 has a slit on the top outer circumferential surface whereas the bore side 212 has none. Thus the bore side of bush is continuous and the bolt side is discontinuous.

[00024] According to another aspect of the present invention, the depth of each horizontal slit in the horizontal plane is in the range of 20% to 30% of inner diameter of the bush. However the width and height of the vertical slit and horizontal slit may be optimized to get required strength and collapsibility. More depth of the horizontal slit would loosen the clamp for holding the inner tube and decrease the strength. Such bush 203, after being ensconced in the opening 204, is welded along its circumference on the bolt side and bore side, to the upper and lower brackets at the upper and lower surface respectively of the supporting bridge to form a complete supporting bridge 200. Thus, at least one bush at each lateral end of the supporting bridge is used to connect the upper and lower bracket and also hold the inner tube of the front fork from its bore side. A fork clamping opening 210 is provided on the anterior surface of the supporting bridge 200 for securing the inner tube of the front fork with the bush 203.

[00025] FIG. 6 shows front view of the supporting bridge according to the present invention. The side bolt clamps 209 of the respective bushes present at the respective lateral ends of the supporting bridge 200 face each other and are not " ~ visible from outside due to the presence of the front panel 115. A bolt (not shown) or a known fastener is inserted into the side bolt clamp 209 of the bush 203 through the fork clamping opening 210 so as to hold the inner tube of the front fork inside the bore of the said bush 203, by tightly clamping the bush around the inner tube. Another bolt is inserted from bolt side to engage with threads on the inner tube to clamp the fork in vertical direction.

[00026] The load transfer from the wheel to the frame of the vehicle takes place through the supporting bridge 200 and first strikes at the bore side 212 of the bush 203. The removal of discontinuity on the bore side 212 of the bush due to improved vertical slit 208 enables the bush to take sufficient loads and respond to high stress concentration on the supporting bridge 200. This enables reduction in stress experienced by the lower bracket 202 of the supporting bridge 200 and the bush 203 by better distribution of loads coming from road and reduces stress on sharp corners. However, the vertical slit on bolt side 211 creates a path for water and mud entry into supporting bridge. This is closed by suitably using large size washer on the bolt side or large flanged bolt. Also the weld distribution due to slit is shifted from bottom to top i.e. from critical stress zone to less critical zone enabling reduction in stress levels on supporting bridge 200 and bush 203. Thus the strength and the durability of the lower bracket of the supporting bridge is increased according to the present invention without any cost or weight addition to the vehicle.

[00027] 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 supporting bridge for a straddle type vehicle connecting an anterior wheel to a main frame of the said vehicle, comprising:

a lower bracket present at a lower portion of the said supporting bridge,

an upper bracket present at an upper portion of the said supporting bridge and mechanically connected to the lower bracket,

at least one opening at each of the lateral end of the said supporting bridge,

a bush ensconced in the said opening of the said supporting bridge, the bush having a bolt side and a bore sider

wherein the bolt side having a partially open flat surface and bore side having a bore to receive an inner tube of a front fork,

characterized in that, the said bush further comprises atleast two spaced horizontal slits in the horizontal plane and at least one vertical slit in the vertical plane in such a manner that the fabrication of the vertical slit is initiated from the bolt side of the bush, passing through one of the horizontal slits and ending at the another horizontal slit, the vertical slit thereby spanning the space between the said horizontal slits.

2. The supporting bridge as claimed in claim 1, wherein each horizontal slit is approximately perpendicular to the bore axis and the vertical slit is approximately parallel to the bore axis.

3. The supporting bridge as claimed in claim 1, wherein the depth of each horizontal slit is in the range of 20% to 30% of inner diameter of the bush.

4. The supporting bridge as claimed in claim 1, wherein the bore side of the bush is continuous and the bolt side of the bush is discontinuous.

5. The supporting bridge as claimed in claim 1, wherein the straddle type vehicle includes a scooter type motorcycle.