Claims:We claim:
1. A simple, cost effective, silent chain drive (130) for power output drive (POD) transmission system with reduced noise level and shift resistance, eliminating the need of idler gear, comprising of: atleast a drive sprocket (131), wherein said drive sprocket (131) is in communication with the rear transmission assembly (221); atleast a driven sprocket (132), wherein said driven sprocket (132) is coupled to the propeller shaft (230) via the said POD output shaft (229), wherein the said propeller shaft (230) transmits power to the front axle (223); atleast a silent chain (133), wherein said silent chain (133) is trained around the said drive sprocket (131) and the said driven sprocket (132); and a housing (224), accommodating the said POD system, wherein the said drive sprocket (131) and the driven sprocket (132) is placed with a controlled centre distance.

2. A silent chain drive (130) for power output drive (POD) transmission system, as claimed in claim 1, wherein said silent chain (133) is an endless track chain.

3. A silent chain drive (130) for power output drive (POD) transmission system, as claimed in claim 1, wherein said silent chain (133), comprises of: plates (134a,134b); and pins (135).

4. A silent chain drive (130) for power output drive (POD) transmission system, as claimed in claim 1 & claim 3, wherein said plates are selected from link plates (134a), guide plates (134b) and/or combinations thereof.

5. A silent chain drive (130) for power output drive (POD) transmission system, as claimed in claim 1 & claim 4, wherein said link plates (134a) is provided with a notch for engaging the said drive sprocket (131) and the said driven sprocket (132).

6. A silent chain drive (130) for power output drive (POD) transmission system, as claimed in claim 1 & claim 3, wherein said pins (135) connects the said link plates (134a) and the said guide plates (134b).

7. A silent chain drive (130) for power output drive (POD) transmission system, as claimed in claim 1, wherein said housing (224) lodging the said drive sprocket (131) and the driven sprocket (132) with controlled centre distance is provided with a minimum chain slackness.

8. A silent chain drive (130) for power output drive (POD) transmission system, as claimed in claim 1, wherein said housing (224) is provided with a bottom portion (138) having a better clearance between silent chain (133) and the said bottom portion (138) with respect to the silent chain sag on the coast side.

9. A silent chain drive (130) for power output drive (POD) transmission system, as claimed in claim 1, wherein said housing (224) is provided with side clearance to accommodate the said silent chain (133) with varying width.
, Description:SILENT CHAIN DRIVE FOR POWER OUTPUT DEVICE TRANSMISSION
FILED OF THE INVENTION
The present invention generally relates to power transmission system, More particularly the present invention is related to implementation of silent chain drive in power output drive (POD) system for attenuating the shift resistance and noise from the POD system.
BACKGROUND OF THE INVENTION
Vehicles while operating in four wheel drive mode uses power output device transmission to power its front wheels, during such operation gearbox transfers drive to front transmission via POD transmission arrangement consisting of drive and driven gears, idler gears and shafts. The rotational irregularity of the engine may cause a frequent engaging and disengaging of the tooth flanks of the gear tooth system located between the engine sided drive unit and the transmission input shaft. This generates noises known as “engine idle knock”. In addition to this when the POD system gets loaded there exists a whining noise from the POD system.
During the four wheeled mode operation, a coupler is engage POD output shaft to POD gear train which consists of drive gear, idler and driven gear. The POD output shaft connected to propeller shafts transmits power to front axle, thereby transmitting the torque to all wheels. Gears used in such POD transmission are heavy and are of higher module to take care of load and torque requirements. Each meshed gear interaction includes a backlash, i.e., a clearance that occurs between mating components of the gears. Backlash has no effect when the gears are transferring torque but may manifest itself in audible noise, e.g., as a rattle or clunk. Excessive backlash is known to affect gear durability and cause torque transfer delays as the clearance between the mating components of the gears is taken up during a torque transition. Audible noise associated with backlash during torque transition may be noticeable and objectionable. The presence of idler gears in the drive train also posse a main source of noise.
In conventional power transmitting mechanism, the engine drive shaft, idler gear and the transmission shaft i.e. the driven output shaft are each equipped with one sprocket. A chain is trained around these sprockets including the idler gear for transmitting power from a drive shaft to the driven shaft. During such operations high rattle and whine noise is generated mainly because of the collision between the chain and the teeth of the sprockets lifting away from another and then striking each other as a result of high frequency torque fluctuations with unequal meshing forces, known as backlash. This sound can be greatly amplified if the components forming the sound are excited at their resonant frequencies causing a resonance sound by periodic collision with high meshing stiffness. This high variation in meshing stiffness also leads to transmission error, which also acts as a source of noise in the system.
Another reason for noise generation is the low contact ratio between the chain and the sprocket meshing, which can be moderated by increasing the contact ratio. But the possibility of increasing the contact ratio is hindered due to the packaging, assembly and serviceability constraints. Overall in track-type vehicles, the undercarriage, such as, track assemblies, drive sprockets, idlers, track rollers, are the major contributors to the overall noise. In order to suppress such noises, various designs and technologies have been adapted and implemented in the direction of mechanical modifications. However, such mechanical solutions are complicated and expensive during production and implementation, therefore there exists a strong demand for reduction of noise level in the POD transmission system.
US patent 5419743 provides a low noise chain drive which include toothed sprockets and an endless silent chain having sets of link plates successively connected for articulation by means of connecting members. The link plate teeth are defined by an outside flank and an inside flank. The sprocket has sprocket teeth defined by a sprocket tooth flank. The link plate teeth stay in sliding contact at their outside flanks with the sprocket teeth from the beginning of their engaging process through its completion to thereby ease engagement impacts and noises.
US patent 6413180 discloses a power transmitting mechanism which includes a first silent chain trained around teeth of a first driving sprocket and a teeth of first driven sprocket, and a second silent chain trained around teeth of a second driving sprocket and teeth of a second driven sprocket. The pitch of the driving sprockets is a random pitch which varies in a random pattern along the circumference of the sprockets. The silent chains have a single pitch. By thus phasing the two driving sprocket, periodic meshing impact sounds emitted from the respective silent chains are cancelled out or offset each other.
US patent 4082372 relates to a noise reducing device for a track chain arrangement which includes a pair of annular supporting brackets secured to the opposite sides of the sprocket, a plurality of resilient members secured to the radial outer surfaces of the said pair of annular supporting brackets, and a pair of resilient metal hoops secured to the resilient members in concentric relation to the sprocket. The metal hoops are elastically deformed when the track chains engage the sprocket teeth thereby mitigating the generated noise due to meshing action.
Japanese patent Application 55-119281, provides a crawler belt with rotatable buffer members of cylindrical shape between laterally spaced rows of endlessly connected track links alternately with connecting members, in such a way that, as the crawler belt is driven to turn around, the buffer members are brought into abutting engagement with the drive sprocket prior to the connecting members to reduce their striking noises.
All of the cited prior-art documents provides a means for suppressing the noise generation in transmission systems. Several of the cited documents used a kind of additional arrangement such as link plates, guide plates, rubber/elastic enclosures, buffer members, annular brackets and pitch position rearrangement etc., to mitigate the noise generation. All of these increases the design complexity and weight of the transmission system as a whole, this subsequently affects the vehicle performance. The present invention provides a silent chain system which are used in place of gear train system in POD transmission enabling a considerable reduction in noise level from the POD system. The present invention by way of implementing silent chain in power output drive (POD) system attenuates the shift resistance in four wheel drive vehicle, thereby achieving a smooth shifting between two wheel mode and four wheel mode of operation.
OBJECTIVES OF THE INVENTION
The main object of the present invention is to provide a silent chain drive in power output drive (POD) transmission system.
Another object of the present invention is to provide a silent chain drive in replacement of the idler gear and heavy gear drive system in power output drive (POD) transmission system for reducing the noise levels.
Still another objective of the present invention is to provide a silent chain drive in power output drive (POD) transmission system for attenuating the shift resistance.
Yet another objective of the present invention is to reduce the movable parts and eliminate the cumulative errors and misalignment in the transmission system thereby enabling noise reduction in the system.
Final objective of the present invention is to provide a cost effective silent chain drive in power output drive (POD) transmission system with reduced number of operating parts.
SUMMARY OF THE INVENTION
Heavy duty vehicles provided with four wheel drive option uses power output device (POD) transmission to power front wheels, the rear transmission (221) transfers drive to front transmission via POD transmission (222) arrangement. During such operation presence of heavy gear drive system with idler gears generates huge rattling noise associated with the meshing and collision action of the gear drive. The present invention provides a silent chain drive (130) for power output drive (POD) transmission system which replaces the heavy gear drive system in POD system that generates huge rattling noise associated with the meshing and collision action of the gear drive. The present invention provides a silent chain drive POD system with reduced noise level and shift resistance, eliminating the need of idler gear. The power output drive (POD) transmission system with silent chain drive (130) according to the present invention, comprises of: atleast a drive sprocket (131); atleast a driven sprocket (132); atleast a silent chain (133) trained around the said drive sprocket (131) and the said driven sprocket (132); and a housing (224), accommodating the POD components. The silent chain comprising of link plates (134a) and guide plates (134b) strike the said drive sprocket (131) and the driven sprocket (132) at an angle which reduces the impact and noise generation resulting from the meshing and collision action between the chain and the sprockets. The said housing (224) is provided with drive sprocket mounting centre (136) and the driven sprocket mounting centre (137) distance to have a minimum coast side chain slackness. This controlled centre distance between the drive and the driven sprocket eliminates the need of idler gear in-between them thus reducing the gear mesh contact. This further reduces the associated whistling or humming noise and also results in zero tooth flank backlash mitigating the noise generation at source. Thus the silent chain drive POD transmission system (130) of the present invention eliminates the heavy gear drive and its corresponding assembly parts. This reduces the overall movable components of the system thereby eliminating the cumulative errors and misalignment of the transmission system. This also reduces the overall weight and cost of the system. Further the present invention provides a space-saving silent chain drive POD transmission system with attenuated shift resistance enabling smooth shift transition between two wheel drive mode and four wheel drive mode with larger permissible tolerances.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 depicts the conventional power output drive (POD) transmission system in four wheel drive vehicle.
Figure 2 shows the existing state of the art POD transmission system with gear train arrangement including an idler gear.
Figure 3 represents the POD transmission system with silent chain drive according to the present invention.
Figure 4 shows the silent chain with link plates, guide plates and pins according to the present invention.
Figure 5 provides the front view of the housing for POD transmission system with silent chain drive according to the present invention.
Figure 6 shows the perspective view of the housing for POD transmission system with silent chain drive according to the present invention.
Figure 7 represents the comparison graph for noise level (NVH) measurement for tractors with gear driven POD system and with silent chain drive POD system.
While the invention is amenable to various modifications and alternative forms, specifics thereof have been shown by way of example in the drawings and will be described in detail. It should be understood, however, that the intention is not to limit the invention to the particular embodiments described. On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.
DETAILED DESCRIPTION OF THE DRAWINGS
The present invention as embodied by an "Silent chain drive for power output device transmission" succinctly fulfils the above-mentioned need(s) in the art. The present invention has objective(s) arising as a result of the above-mentioned need(s), said objective(s) being enumerated below. In as much as the objective(s) of the present invention are enumerated, it will be obvious to a person skilled in the art that, the enumerated objective(s) are not exhaustive of the present invention in its entirety, and are enclosed solely for the purpose of illustration. Further, the present invention encloses within its scope and purview, any structural alternative(s) and/or any functional equivalent(s) even though, such structural alternative(s) and/or any functional equivalent(s) are not mentioned explicitly herein or elsewhere, in the present disclosure. The present invention therefore encompasses also, any improvisation(s)/modification(s) applied to the structural alternative(s)/functional alternative(s) within its scope and purview. The present invention may be embodied in other specific form(s) without departing from the spirit or essential attributes thereof.
Throughout this specification, the use of the word "comprise" and variations such as "comprises" and "comprising" may imply the inclusion of an element or elements not specifically recited.
Heavy duty vehicles such as tractor are provided with four wheel drive option to cater high torque application requirements. These vehicle uses power output device (POD) transmission to power front wheels, the gearbox (225) transfers drive to front transmission via POD transmission (222) arrangement. The present invention uses a unique side drive front axle (223) unlike centre drive vehicles. Separate spacer housing (224) coupled to gearbox (225) and rear transmission (221), accommodates POD transmission in these four wheeled drive vehicles.
As shown in fig.2, the existing state of the art POD Transmission system consists of a drive gear (226); a Idler gear (227); and a driven gear (228) to receive and transmit power to the front axle when the vehicle is operated in two wheel drive mode, the power is transmitted from the drive gear (226) to the driven gear (228) via the said idler gear (227). The said POD driven gear (228) is supported by its POD output shaft (229) by means of a bush, therefore the output shaft does not receive power during the vehicle operation in two wheel drive mode. When the vehicle operates in four wheel drive mode, a coupler engages the said POD driven gear (228) and the said POD output shaft (229) via the rotating idler gear (227) and the drive gear (226). POD output shaft (229) which is connected to propeller shaft (230) transmits power to front axle (223), thereby transmitting the required torque to front wheel assembly. This step down gear ratios makes outer gear to rotate at higher rpm than the input. Also the presence of idler gear (227) in this drive train is the main source of noise generation. Further gear system used in these type of POD transmission systems are heavy and are of higher module to take care of high load and torque requirements.
The present invention provides a simple, cost effective, silent chain drive (130) for power output drive (POD) transmission system with reduced noise level and shift resistance, eliminating the need of idler gear, comprising of: atleast a drive sprocket (131), wherein said drive sprocket (131) is in communication with the gearbox assembly (225); atleast a driven sprocket (132), wherein said driven sprocket (132) is coupled to the propeller shaft (230) via the said POD output shaft (229), wherein the said propeller shaft (230) transmits the power to the front axle (223); atleast a silent chain (133), wherein said silent chain (133) is trained around the said drive sprocket (131) and the said driven sprocket (132); and a housing (224), accommodating the POD components, wherein the said drive sprocket (131) and the driven sprocket (132) is placed with the controlled centre distance, wherein the said housing (224) which lodge the said drive sprocket (131) and the driven sprocket (132) is provided with a minimum chain slackness.
In the preferred embodiment of the present invention, wherein said silent chain (133) is an endless track chain, wherein the said silent chain (133) comprises of: plates (134a,134b); and pins (135), wherein the said plates are selected from link plates (134a), guide plates (134b) and/or combinations thereof. The link plate (134a) receives tension and is provided with a notch for engaging the drive and driven sprockets. The guide plates (134b) act as guides for the said drive and driven sprockets and are not provided with notch. The pins (135) connects the said link plate and the guide plate, wherein the shape of the said pins (135) is selected from round, spherical, elliptical, hexagonal, trapezoidal, D-shaped and/or combinations thereof. All the silent chain components share the tension and possess higher capacity than the roller chains.
The said link plates of the silent chain strike the said drive and driven sprocket at an angle which reduces the impact and the noise generation resulting from the meshing and collision action between the chain and the sprockets. This makes the said chain a silent one. The silent chain runs at higher speed than the roller chain without generating considerable noise, higher the chain speed greater is the difference seen from that of the roller chains.
In the preferred embodiment, wherein the said housing (224) is provided with drive sprocket mounting centre (136) and the driven sprocket mounting centre (137) distance to have a minimum coast side chain slackness, shown in fig.4. This controlled centre distance between the drive and the driven sprocket eliminates the need of idler gear in-between them reducing the gear mesh contact, this in turn reduces the generation of noise level at the source. Wherein the said housing (224) is provided with a bottom portion (138) having a better clearance between silent chain and the bottom portion of the housing with respect to the silent chain sag on the coast side. Wherein the said housing is also provided with side clearance to accommodate the said silent chain with varying width (Fig.5).
The silent chain drive POD transmission system (130) of the present invention eliminates the heavy drive (226), idler (227) and driven (228) gears and its corresponding assembly parts. This reduces the overall movable components of the system thereby eliminating the cumulative errors and misalignment of the transmission system. The elimination of idler and associated gears reduces the noise generation in the system. Further to add on this the overall system weight and cost is reduced, due to elimination of heavy and expensive components.
The present invention by way of providing silent chain in POD transmission system (130) reduces loads and vibration damping. The system further eliminates the need for intermediate sprockets (idler gear), this reduces the whistling or humming noise and also results in zero tooth flank backlash. Further the present invention provides a space-saving POD transmission system with attenuated shift resistance enabling smooth shift transition between two wheel drive mode and four wheel drive mode with larger permissible tolerances.
EXAMPLE 1
To ascertain the level of noise reduction in the present POD transmission system with silent chain drive (130), a comparison experiment with test results are established. A heavy duty vehicle having drive, idler and driven gear with roller chain POD system is compared with NVH measurement of another heavy duty vehicle with silent chain drive POD transmission system. As per the standard both the vehicles are made to run at speed from idle to 30kmph in 4 wheeled drive mode and the generated noise is measured close to driver ear. Results were mapped and recorded for both the POD transmission system with idler gear train and silent chain drive and the comparison results were plotted as graph (Fig.6) with frequency in x-axis and measured noise level in y-axis. The measured noise level reflects a reduction on an average of 0.6dB(A) in POD system with silent chain drive system (139) when compared to POD system with gear drive system (140).
It will be apparent to a person skilled in the art that the above description is for illustrative purposes only and should not be considered as limiting. Various modifications, additions, alterations, and improvements without deviating from the spirit and the scope of the invention may be made by a person skilled in the art.

LIST OF REFERENCE NUMERALS
221 - Rear transmission
222 - POD transmission
223 - Front axle
224 - Housing (POD spacer Housing)
225 - Transmission
226 - Drive gear
227 - Idler gear
228 - Driven gear
229 – POD output shaft
230 - Propeller shaft
130- Power output drive (POD) transmission system with silent chain drive
131 - Drive sprocket
132 - Driven sprocket
133 - silent chain
134a - Link plate
134b - Guide plate
135 - silent chain pin
136 - drive sprocket mounting center
137 - driven sprocket mounting center
138 - Housing bottom portion
139 - NVH measurement of POD system with silent chain drive system
140 - NVH measurement of POD system with gear drive system