Claims: , Description:FIELD OF THE INVENTION:

This invention relates to a system for adjusting tension of a belt or chain drive such as used in a drive system for transmitting drive from a power source to a component connected to the power source.

BACKGROUND TO THE INVENTION:

A belt or a chain drive is commonly used to transmit tractive force from a power source, such as an electric motor, to a different component which is driven using the power received from the power source. The rotary motion/ torque/ power of the power source is transmitted to the other component which is distal from the power source using a drive such as a chain/ belt drive. Tension in the chain/belt drive plays an important role in power transmission efficiency since if the chain/belt drive is loose then it slips which reduces the transmission efficiency. During operation the tension in the belt or chain reduces due to various factors such as vibrations hence, it is important to maintain/ adjust the desirable tension in the belt drive at regular intervals to achieve maximum transmission efficiency. Also, the tension in the belt/ chain drive should not exceed a certain limit as such over-tension could cause failure of the belt/chain drive due to undue stresses.

For example, in the case of electric vehicles, the power produced by a power source – i.e. electric motor, is transmitted to wheel(s) of the vehicle conveniently using a belt/ chain drive. The belt/ chain needs to have sufficient tension to achieve maximum power transmission efficiency. Therefore, the belt or chain drive requires adjustment to its tension to ensure efficient operation. In case of an internal combustion (IC) engine, the power sources may be engine operated using gasoline and/or gaseous fuel.

A strong trend to electric vehicle manufacture and use is now becoming evident as concerns with climate change and availability of fossil fuels become evident. Electric vehicles include a number of batteries including a large number of electric cells. The number of batteries required for an application is driven largely by the required vehicle range. At the present time, readily available batteries remain bulky and this may limit their use particularly where desired vehicle range conflicts with small vehicle size. Conventionally, two/ three/four wheeled vehicles operated electrically or using engines have a rear wheel drive in which the power source, i.e. engine or battery, motor-transmission and differential assembly, is mounted on a rear side of the vehicle. In such vehicles, the passenger also sits on the rear side of the vehicle concentrating weight on the vehicle rear side. Typically, this requires a more rigid rear suspension arrangement which increases the overall cost of the vehicle.

In addition, because many vehicle components are packed on the rear side where little space is available once power source, passenger and other load issues are taken into account, space constraints are a major challenge in such vehicles. Since the drive is typically provided to the two rear wheels, a differential and left and right side drive shafts have to be used which increases complexity as well as cost.

The Applicant’s co-pending Indian Patent Application No., the contents of which are hereby incorporated herein by reference, discloses a front wheel drive electric vehicle which is more efficient than the rear wheel drive configuration. The front wheel drive needs a belt or chain drive to transmit tractive force from the electric motor through a transmission system to the front wheel. The belt or chain drive requires adjustment to its tension to ensure efficient operation.

SUMMARY OF THE INVENTION:

It is an object of the present invention to provide an efficient system for adjusting chain or belt drive tension.
With this object in view, the present invention provides a system for adjusting belt or chain drive tension comprising:
a drive assembly comprising a power source;
a chain or belt drive co-operating with the power source; and
at least a component connected to the power source through the belt or chain drive
wherein a portion of the drive assembly is connected to a mounting bracket assembly configured to adjust position of the portion of the drive assembly for tension adjustment of the belt or chain drive.

In one embodiment of the invention, an electric vehicle is provided with the drive assembly, the power source is an electric motor and the component is a wheel, preferably the front wheel, of the vehicle. The electric motor is connected to the wheel through a belt or chain drive also connected to a transmission system. In a preferred arrangement, the drive assembly is mounted above the front wheel of vehicle, preferably to the suspension system, for example on the front forks of a suspension system for the electric vehicle.

The mounting bracket assembly conveniently enables adjustment of the position and/or orientation of a drive assembly comprising a combination of the electric motor and transmission system, this typically being the most advantageous portion of the drive assembly from the perspective of packaging and ease of system implementation. The mounting bracket assembly conveniently provides a pivotable mount for adjusting the position of the electric motor – transmission system assembly. This allows position of the electric motor – transmission system to be adjusted while maintaining tension in the belt or chain drive at an efficient level.

The mounting bracket assembly further conveniently comprises a pair of first mounting brackets, which as described above, are conveniently connected to the suspension system. Each first mounting bracket provides bearing points for the front wheel drive assembly portion. The first mounting brackets are connected to the outer tube of each front fork in a conventional manner which connects the two front forks. One of the first mounting brackets conveniently connects the two front forks at the front side while the other member of the pair of first mounting brackets connects the front forks at the rear side.

Suitable first mounting brackets can be welded on the fork or formed integrally with a front fork, more preferably with an outer tube of a front fork. The first mounting brackets are conveniently provided with, or provide, mounting or base member(s) to form a platform, cradle or surface for mounting the front wheel drive assembly portion. To this end, first mounting brackets conveniently comprise a plate. At least one of the first mounting brackets may include or be connected, directly or indirectly, to the adjustable mounting bracket assembly. For example, the adjustable mounting bracket assembly may have a portion which though movable and engageable with the first mounting bracket(s), in a required position (with belt or chain drive having required tension) by suitable fasteners to form a joint. One end of the front wheel drive assembly portion is pivotably fixed to the first mounting bracket on one side, for example the rear side, of the front forks while the other end of the front wheel drive assembly portion is connected to the adjustable mounting bracket on other side of the front forks. Alternatively, the position of pivot point and adjustable mounting bracket may be interchanged.

The movable portion of the adjustable mounting bracket assembly conveniently consists of two integrally formed parts. The first part or chain tension adjuster body may have a U or C shape structure having a pair of arms. Each arm may include a fixing means for fixing the electric motor – transmission assembly onto the chain tension adjuster body at the required position. The pair of arms are integrally formed with a downwardly extending threaded bolt portion forming a second part of the movable portion mounting bracket assembly. The adjustable mounting bracket may be moved upward or downward, conveniently in linear manner. Such movement enables the pivoting movement of the electric motor - transmission assembly in linear direction, causing the centre distance between the drive means, , and the driven means, to change together with the tension of the chain drive. The drive means and driven means may be a sprocket.

The first mounting bracket is provided with a hole for inserting the threaded bolt portion of the movable portion of the adjustable mounting bracket assembly. The movable portion of the adjustable mounting bracket assembly is secured in the required position corresponding with required front wheel drive assembly portion position and belt or chain drive tension by suitable fasteners. Preferably, nutswhich engage against the threaded bolt portion of the adjustable mounting bracket assembly. Two nuts are conveniently provided such that one is provided on the upper surface of the first mounting bracket which preferably enables drive assembly portion position adjustment. The other nut is mounted below the first mounting bracket and is used as locking nut to lock and unlock the position of the movable portion of the adjustable mounting bracket assembly.

The engagement of adjustable mounting bracket to a first mounting bracket, and the configuration of the above mentioned joint, is selected such that the friction plane is perpendicular to the direction of vibration i.e. vibrations are produced in a vertical direction while the friction plane which is a friction between the surface of first mounting bracket and the surface of nut. This avoids the direct vibration load coming in line with the friction surfaces of the joint (formed by the clamping of adjustable mounting bracket to the first mounting bracket).

Weight is an important consideration and so it will be understood that the first mounting brackets are of relatively small thickness and correspondent relatively high stiffness. A potential consequence is lesser deflection of a first mounting bracket under clamping load, which may lead to loosening of the above described joint between first mounting bracket and adjustable mounting bracket with external loading, for example through vibration and other forces acting during vehicle operation.

In another aspect, the present invention provides an adjustable mounting bracket for adjusting belt/chain drive tension consisting of:
a chain tension adjuster body having a pair of arms, each arm including a fixing means for connecting the adjustable mounting bracket, either directly or indirectly, to the belt drive; and
a downwardly extending threaded bolt portion integrally formed with the chain adjuster body.

The adjustable mounting bracket may include a scale, for example of, or related to, centre distance, to facilitate chain tension adjustment. Such a scale can be included within the threaded bolt portion of the above described preferred adjustable mounting bracket. Use of the scale also avoids the possibility of over tension in the belt or chain as over tension creates undue stresses and can lead to failure of belt or chain. Hence over tension should be avoided. Accordingly, the first mounting bracket should be fabricated from a material with deflection that accommodates the expected external loadings from vibration and other forces during vehicle operation. For example, aluminium may be selected in preference to steel.

In another aspect of present invention, the drive assembly may include an internal combustion (IC) engine driven using gasoline and/or gaseous fuel instead of an electric motor. Other power sources are possible.
The vehicle as described above includes a simple and cost effective adjustable mounting bracket for adjusting belt drive tension.

SHORT DESCRIPTION OF THE DRAWINGS:

The system for adjusting belt or chain drive tension of the present invention may be more fully understood from the following description of preferred embodiments thereof, made with reference to the accompanying drawings in which:

Fig. 1 is a partial first front isometric view of an electric vehicle according to one embodiment of the present invention.
Fig. 2 is a partial second front isometric view of an electric vehicle according to one embodiment of the present invention.
Fig. 3 is a side view of the front wheel and front wheel drive assembly for the electric vehicle of Fig. 2.
Fig. 4 is a rear isometric section view of the front wheel and front wheel drive assembly of Fig 3.
Fig. 5 is a side view of the front wheel and front wheel drive assembly of Figs. 3 and 4.
Fig. 6 is a front view showing the relative disposition of electric motor-transmission assembly and chain drive for the vehicle of Figs. 1 and 2.
Fig. 7 is a first schematic view showing the relative disposition of output shaft of electric motor-transmission assembly and wheel axel using a chain drive for the vehicle of Figs. 1 and 2
Fig. 8 is a second schematic view showing disposition of output shaft of electric motor-transmission assembly for the vehicle of Figs. 1 and 2
Fig. 9 is a side partial cutaway view of the electric motor-transmission assembly and chain drive for the vehicle of Figs. 1 and 2.
Fig. 10 is a rear partial cutaway view of the electric motor-transmission assembly and chain drive for the vehicle of Figs. 1 and 2.
Fig. 10A is a rear isometric partial cutaway view of the electric motor-transmission assembly and chain drive for the vehicle of Figs. 1 and 2.
Fig. 10B is a cutaway view of the electric motor-transmission assembly and chain drive for the vehicle of Figs. 1 and 2 showing a movable portion of the adjustable mounting bracket assembly for adjusting tension (or chain tensioner) of the chain drive of Figs. 7 to 10A.
Fig. 10C is a schematic view of the chain tensioner shown in Figs. 8 to 10B.
Fig. 11 is a side view of the body of the chain tensioner for the chain drive of the vehicle shown in Figs. 1 and 2.
Fig. 12 is a front view of the body of the chain tensioner for the chain drive of the vehicle shown in Figs. 1 and 2.
Fig. 13 is a partial rear view of the front wheel drive assembly showing the chain tensioner in position for tensioning the drive chain of the vehicle of Figs. 1 and 2.
Fig. 14 is a front isometric view of a two wheeler electric vehicle according to a second embodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS:

Referring now to Figs. 1 and 2, there is shown the front portion of a three wheeler electric vehicle 10. A driver sits at the front of the electric vehicle 10 on front seat 12 and rear seats 13 and 14 are available for seating of passengers, rear seat 13 being rear facing in passenger compartment 188 with weather protection being provided by roof 88A. A target number of passengers is 2 or 3. A further passenger could join the driver on the front seat 12. Both seats 12 and 14 are of bench style though other configurations could be adopted if required. The driver steers electric vehicle 10 through handlebar (Not Shown) connected, through steering rod 15a, to the front forks and axle of front wheel 84. The front of electric vehicle 10 is substantially formed by body panel 210 including a windscreen 215 for driver visibility. Body panel 210 is connected to roof 88A of the electric vehicle.

The electric vehicle 10 includes a frame and chassis 11 with a front portion of the vehicle frame including a pair of upwardly extending telescopic forks of conventional design comprising sliders 90 and outer tubes 92 in the conventional manner for three wheeler vehicles of internal combustion engine type as known in the art. Sliders 90 include coil springs/dampers to absorb surface irregularities and consequential noise and vibration

Electric vehicle 10 includes a front wheel drive assembly 110, comprising as a key portion, the electric motor 20 as power source and transmission system 80 for converting electrical energy from the electric battery module (Not Shown) into tractive force from the electric motor 20 and transmission system 80 for the front wheel 84 as driven component and its associated rubber tyre 85 to which electric motor 20 and transmission system 80 are connected. Electric motor 20 has a rating of 7kW to 10 kW (though this rating is dictated by application) and is controlled by vehicle control unit (VCU). Further description of the front wheel drive assembly 110 as well as electric vehicle 10 is provided in the Applicant’s co-pending Indian Patent Application No. , the contents of which are hereby incorporated herein by reference.

The relationship between the front wheel drive assembly 110 and front wheel 84 is conveniently shown in Figs. 1 and 2 and, in greater detail, in Figs. 3 to 12 and described further below. The same principles would also apply to a two wheeler vehicle.

The front wheel drive assembly 110 is mounted above and close to the front wheel 84 and its associated tyre 85 and mudguard 89 in what is a limited space to provide a compact arrangement. This close positioning reduces or avoids transmission losses.

The front wheel drive assembly 110 is mounted to the outer tubes 92 using a pair of first mounting brackets 117 and 117A which also connect the outer tubes 92. Mounting bracket 117A is mounted on the rear side of the outer tubes 92. Mounting bracket 117 is mounted on the front side of the outer tubes 92. During vehicle running conditions, mounting of the front wheel drive assembly 110 to outer tubes 92 causes the front wheel drive assembly 110 to move along with the sliders 90. That is, when sliders 90 move by distance x the front wheel drive assembly 110 also advantageously moves by the same distance x in the same direction. That is, the front wheel drive assembly forms part of the unsprung mass of the vehicle 10. In this way, the wheel 84 to electric motor – transmission output shaft centre distance always remains constant even when the sliders 90 move.

Mounting bracket 117 is formed integrally with the outer tubes 92 and further description of the features of the mounting bracket 117 is provided in the Applicant’s co-pending Indian Patent Application No. , the contents of which are incorporated herein by reference. Mounting bracket 117A, with the exceptions discussed below, is of similar configuration to mounting bracket 117.

The electric motor and transmission assembly 20, 80 mounting is shown in further detail in Figs. 3 to 6 and 9 to 10B. To this end, the electric motor 20 and transmission system 80, is mounted horizontally when viewed from the front of the vehicle 10 as shown in Figs. 3 to 6. An assembly comprising the electric motor 20 and transmission system 80 forming one essential portion of front wheel drive assembly 110, makes such placement easier. An output shaft 800 of the transmission assembly 80 is connected to the axle 86 of the front wheel 84 by a chain drive 25 as typically used in motorcycles. A drive in the form of chain drive 25 is accommodated within, and protected by, chain case 25A which is connected to the output shaft of transmission 80 and extends at a downward inclination therefrom. Other forms of belt drive could be used as known in the art. The output shaft of the electric motor 20 is connected to the output sprocket 802 of transmission system 80 through a single or double speed reduction gear drive comprising meshing helical gears 80A which have higher contact surface and smooth operation which help in noise reduction and have higher transmission efficiency. Output sprocket 802 is fixed and rotates with transmission system output shaft 800. As sprocket 802 rotates, the chain drive 25 also moves transmitting torque to axle 86 and front wheel 84.

As known in the art, any force is composed from its horizontal and vertical force components. In case of chain drive 25, the tension side 25B carries the power i.e. force which can be divided into vertical and horizontal components. The horizontal force component acting around the front wheel centre 184 creates torque and causes the front wheel 84 to rotate. The vertical force component is desirably in line with an outer tube 90 and slider 92 so that these fork components can completely take up this vertical force. If the vertical force component is not in line with the fork components 90, 92 then it can cause unbalanced forces acting on the front wheel 84 which can result in drift or tilt in the vehicle 10. Therefore, the chain tension side 25B is provided parallel, more desirably exactly parallel, to the fork components 90, 92 – as shown in Figs. 3 to 11 – in order to avoid unbalanced forces acting on the front wheel 84. From the foregoing discussion, it will also be understood that chain drive 25 tension is an important consideration and tension must be adjusted to ensure efficient operation.

Referring further to tension adjustment for chain drive 25, the chain drive 25 is connected to an adjustable mounting bracket 125 which includes a movable Centre Distance (CD) adjustment mechanism or chain tensioner 125A for adjusting the tension in chain 25 by adjusting the CD between drive sprocket 802 and driven sprocket 186 of transmission system 80 as schematically shown in Figs. 7 and 8.

Electric motor 20 – transmission system 80 assembly is mounted at a plurality of mounting points respectively related to first mounting brackets 117 and 117A which form a platform and bearing surface for the assembly. At one mounting, the electric motor 20 – transmission assembly 80 is fixed to mounting bracket 117 to the adjustable mounting bracket assembly 125 enabling, when required, pivoting about pivot axis P, , enabling of the electric motor 20 – transmission assembly 80 about the pivot axis P during adjustment by the movable portion or chain tensioner 125A of mounting bracket assembly 125. At a further mounting, the electric motor 20 – transmission assembly 80 is indirectly fixed to rear mounting bracket 117A through chain tensioner 125, which together form adjustable mounting bracket 125 enabling the electric motor 20 to pivot about axis P and ultimately be fixed in a range of positions as measured by height above mounting bracket 117A which provides a mounting platform and bearing for the electric motor 20 – transmission system 80 portion of front wheel drive assembly 110. Such adjustment also changes the orientation, as measured by the angle of inclination, of the electric motor 20 – transmission system 80 assembly as well as the tension of chain drive 25.

The movable portion of adjustable mounting bracket assembly or chain tensioner 125A is bolted to the mounting bracket 117A by bolts 129A and 129B to form a joint. Upper bolt 129A is positioned immediately above mounting bracket 117A and lower bolt 129B is positioned immediately below mounting bracket 117A such that mounting bracket 117A is clamped, with frictional engagement, between the two bolts 129A, 129B.

Chain tensioner 125A consists of two integrally formed parts. The first part or chain tensioner body 125B has a U or C shape structure having a pair of arms 126. Each arm 126 has a bolt hole 126A for fixing the eledtric motor transmission assembly 80 onto the chain tensioner body 125 through bolt 128, the axis of which is pivot axis P. The chain adjuster arms 126 are integrally formed with a downwardly extending threaded bolt portion 127.

By rotating the above described nuts 129A, 129B in one direction or another, the bolt portion 127 of chain tensioner 125A can be moved linearly in either upward or downward direction. If the chain tensioner 125A is moved up and down, electric motor 20 – transmission system 80 assembly will pivot about axis P in either upward or downward direction. At the same time, such pivoting movement of the electric motor 20 - transmission assembly 80, will cause the centre distance between the drive sprocket 802 and the driven sprocket 186 to change together with the tension of the chain drive 25.

To enable such adjustment of the position of electric motor 20, the nuts 129A and 129B are rotated such that the chain tensioner 125 moves in upward or downward direction as required. The nut 129B mounted on the downward side of the platform formed by mounting bracket 117A acts as a locking nut while the nut 129A on the upward side of platform act as height adjustment nut. Whenever the position of adjustable mounting bracket 125 needs to be changed, locking nut 129B is first loosened and then the height adjustment nut 129A is rotated to cause the bolt portion 127 of the mounting bracket 125 to move in upward or downward direction. Since the chain tensioner 125A is bolted to the electric motor 20 – transmission system 80 by bolt 128, its angular movement is restricted; chain tensioner 125A may only move linearly.

Once the desired height adjustment of the chain tensioner 125A and electric motor 20- transmission assembly 80 is done, the locking nut 129B is again rotated to lock chain tensioner 125A at desired height thereby locking the electric motor 20-transmission system 80 at in position at the required height.

Therefore, when a user wishes to adjust the CD of chain drive 25, the nuts 129A and 129B are loosened to unclamp the chain tensioner 125A and enable the above described pivoting of the electric motor 20 – transmission system 80, whether in upward or downward direction, the required direction for electric motor 20 – transmission system 80 position adjustment being achieved by corresponding rotation of the adjustment nuts 129A, 129B. This adjustment of the electric motor 20 – transmission system 80 position by chain tensioner 125A changes the CD between driving sprocket 802 and driven sprocket 186 and the tension of the chain drive 25. If the chain drive 25 is required to be removed for any purpose such as maintenance, it is possible to first reduce the CD thereby allowing easy removal and insertion of chain drive 25 since the tension in the chain drive 25 is reduced upon reducing the CD. Similarly, when chain drive 25 tension is to be increased, the electric motor 20 – transmission system 80 position can be adjusted such that the CD of the chain drive 25 increases which induce more tension in the chain drive 25.

Adjustment is facilitated if the bolt portion 127 of adjustable mounting bracket 125 is provided with a scale 127A as shown in Figs. 10C to 12. The scale 127A indicates the centre distance of the chain drive 25. The position of electric motor 20, transmission system 80 can then be adjusted to achieve the desired centre distance as visible and read on the scale 127A.

Adjustable mounting bracket assembly 125 also accommodates the substantial vibrations and forces acting on the joint during vehicle operation. If not allowed for, there would be a high possibility that during vehicle operation the nuts 129A, 129B would loosen, causing uncontrolled movement of the electric motor 20 – transmission system 80 position. This could lead to the reduction of chain drive 25 tension, thereby affecting the transmission efficiency. To prevent this, different sorts of locking nuts or other complex mechanisms could be employed increasing cost. In this case, suitable material or providing additional friction can be considered while manufacturing the mounting bracket 117A.

The configuration of the joint through disposition of adjustable mounting bracket 125 and first mounting bracket 117A is selected such that the friction plane F is perpendicular to the direction of vibration V as indicated in Fig. 13. This location avoids the direct vibration load acting on the friction surfaces of the joint (formed by the clamping of adjustable mounting bracket 125 to mounting bracket 117A by nuts 129A, 129B). If the face friction of the nuts 129A, 129B acting on bore portion 127 and mounting bracket 117A is maintained, the requisite reliable joint resistant to external loading during vehicle operation is achieved.

It will be understood that the portion of mounting bracket 117A clamped between the two nuts 129A, 129B is of relatively small thickness and correspondent relatively high stiffness. The result would be lesser deflection of the mounting bracket 117A under clamping load, which may lead to loosening of the nuts 129A, 129B with external loading. Aluminium and steel can be considered as materials for mounting bracket 117A. Both materials were tested for deflection under external load with the results presented in the table below.

Platform Made of Aluminium Platform made of Steel
Deflection of Bolt 0.013 mm 0.013 mm
Maximum Deflection of Platform 0.0005 mm 0.002 mm
Increase in the deflection due to external load 0.0004 mm 0.0002 mm

Bolt elongation and mounting bracket 117A compression under load were calculated. It was observed that a steel mounting bracket 117A has higher stiffness and produces lesser deflection for a given thickness of the plate portion of mounting bracket 117A. Hence the possibility of loosening of the joint under external load is greater if the mounting bracket 117A is made from steel. However, aluminium has comparatively lower stiffness and greater deflection which makes aluminium a preferred material for mounting bracket 117A because undesirable loosening of the joint is less probable. During clamping of adjustable mounting bracket 125, the bolt portion 127 is placed in tension (elongates) while the mounting bracket 117A is compressed by producing tension in locking nuts 129A, 129B.

In order to avoid the loosening of the joint, the deflection produced in the mounting bracket 117A due to external load must be less than the maximum deflection that can be produced in the mounting bracket 117A. In case of aluminium this condition is achieved whereas in case of steel the deflection capability is less and there is a high possibility of quickly loosening of the joint and uncontrolled pivoting of the electric motor 20 – transmission assembly 80.

The tension adjustment system is also applicable to a 2 wheeler vehicle. Referring to Fig. 14 there is shown a scooter 1010 provided with a front wheel drive assembly 110 as described above. Rider seat 1012 is located above the floor 1011 of the scooter. As with the 3 wheeler vehicle 10, the front wheel drive assembly 110 is mounted to outer tubes 92 of telescopic forks using a pair of mounting brackets 117 in the same manner as described above. It is equally true for scooter 1010 that, during vehicle running conditions, mounting of the front wheel drive assembly 110 to outer tubes 92 causes the front wheel drive assembly 110 to move along with the wheel 84 and sliders 90. That is, when sliders 90 move by distance x the front wheel drive assembly 110 also advantageously moves by the same distance x in the same direction. That is, the front wheel drive assembly 110 forms part of the unsprung mass of vehicle 1010. In this way, the wheel 84 to electric motor output shaft 202 centre distance always remains constant even when the sliders 90 move. Scooter 1010 also includes a chain drive for which tension may be adjusted using the same tension adjustment system as described above.

Modifications and variations to the electric vehicle described in the present specification may be apparent to skilled readers of this disclosure. Such modifications and variations are deemed within the scope of the present invention.