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A New Bushing Chain with no Chordal Action, no Polygon Effect

Summary text

Contents

1. Introduction
2. A new chain with no polygon effect
3. Theory in short
4. Abutments of chain plate
5. Analytical model in Matlab
6. Multi-body dynamics simulation AVL-Tycon
7. Advantages of SmartChain
8. Conclusions

Chain drives in combustion engines frequently induce a disturbing noise, so-called whine noise. Basically, this noise is caused by the chordal action or polygon effect that originates from the periodically changing effective radius of the sprockets. Smartchain B.V. presents a new roller chain or bushing chain that entirely avoids the disturbing polygon effect. The concept was evaluated by AVL List GmbH, Austria, using the multi-body dynamics software Tycon.

 

1. INTRODUCTION


The polygon effect is one of the main causes of the relatively high noise and vibration level of roller chains and bushing chains. Besides the excitation of longitudinal and transversal vibrations of the chain spans, meshing impacts between the chain links and the sprocket mesh occur. The noise excitation induced by the polygon effect usually occurs dominantly at the meshing frequency of the chain drive (=polygon frequency). If this frequency coincides with a natural frequency of the structure of the engine, resonance occurs which leads to an additional increase in the level of structure borne noise. The resulting disturbing noise is known as whine noise.
Silent chains have more favourable acoustic properties than roller chains or bushing chains but their cost price is at least twice as high. Synchronous belts generally show a very good acoustic behaviour but their life-time is unacceptably short, in particular if used in diesel engines.
Therefore, there is a real need for a durable, low-noise, low-cost roller chain drive or bushing chain drive without a disturbing polygon effect.

 

2. A NEW CHAIN WITH NO POLYGON EFFECT


The new chain of SmartChain B.V. is a durable, low-cost roller chain or bushing chain that does not show a polygon effect. Meshing impacts between chain and sprocket no longer occur and the transmission ratio is totally constant. From a theoretical point of view, it is expected that the noise and vibration level of the new chain is at least as favourable as that of the silent chain. The new ideas of SmartChain B.V. have been protected by international patent applications. The new chain may be applied, for instance, in the (timing) chain drive of the camshaft(s), injector pump, balancer shaft or oil pump of an internal combustion engine, but of course also in any roller chain or bushing chain drive.



3. THEORY IN SHORT


The theory behind the “zero polygon effect” of this new innovative chain is surprisingly simple. It is based on elementary kinematic principles and is therefore considered to be conclusive.
The zero polygon effect is realized by guiding the chain in such a way that near the engagement and the disengagement region of the sprocket, the centres of the pins of the chain follow a specific theoretical path B in the fixed plane, Figure 4. This theoretical path is calculated such that at a presumed constant rotational speed of the sprocket, the velocity of the chain at the straight section of the theoretical path is constant. As a consequence, the rotational speed of the other sprocket is also constant. In addition, the meshing impacts between the chain links and the sprocket mesh no longer occur.

Chain


    Figure 4 The new chain guided by the stationary and rotating guide



4. ABUTMENTS OF CHAIN PLATES COOPERATING WITH GUIDE RINGS OF SPROCKET


The most effective technique to force the centres of the pins to follow the theoretical path is to guide the chain simply in the rotating plane. This is realized by modifying the chain plates of the chain, Figure 3. The chain plates, originally consisting of an approximately “figure of eight” contour, are supplied with two precisely shaped abutments n at one side of the chain plate. At each side of the sprocket a ring 10B, which serves as a rotating guide for the abutments is mounted. The contours of the abutments have been calculated in such a way that the centres of the pins follow the theoretical path B. The chain plate with the abutment works together with the rotating guide ring and functions as a lever.
It is remarked that it is possible to guide the centres of the pins additionally by a straight stationary guide. This will lead to slightly better results but also to higher costs. Therefore, in most cases, this stationary guide is not necessary.

 

chain-plate

Figure 3 The new chain with two abutments per chain plate



5. ANALYTICAL MODEL IN MATLAB


The practical feasibility of the new chain concept must be proven by means of elaborate experimental tests. However, a good first assessment of the feasibility of the new chain may also be acquired by means of a simplified kineto-static model of the SmartChain concept. For this purpose, an analytical model has been generated in MATLAB. This model is used to calculate the required geometry of the abutments of the chain plates and the guide systems. In addition, the kinematics and the mechanical equilibrium conditions, including the effect of friction between the chain links and the stationary guide and the rotating guide, are considered. The model calculates specific mechanical parameters such as Hertz contact stresses at the contact area of the abutments, elasto-hydrodynamic oil film thicknesses, and mechanical efficiencies. The numerical results are very convincing and do not present an obstacle for the technical implementation of the new concept.


6. MULTI-BODY DYNAMICS SIMULATION USING AVL-TYCON


6.1 MBD-model of the chain
In order to further increase the certainty about the practical feasibility of the new chain, AVL List GmbH, performed basic investigations by means of the method of multi body dynamics (MBD). The software Tycon was used for this purpose.
Based on a simple chain drive, comparative analyses with the common chain types bushing chain and silent chain were performed. The aim was a comparison of the dynamic properties of the new chain with those of known technical implementations.


6.2 Layout of Chain Drive
The simple drive, which was used as a basic configuration, had two sprockets (20/40 teeth, sprocket mesh according to DIN 8196) and a pitch of 8 mm. Guides were positioned in both free spans. The driving sprocket (20 teeth) has a prescribed constant rotational speed of 3000 rev/min. The driven sprocket is loaded by a constant moment of 20 Nm.


6.3 Comparison with a Bushing Chain and a Silent Chain
Figure 7 shows the dynamic fluctuation of the angular velocity of the driven sprocket, which is not constant due to the varying transmission ratio. This fluctuation is an indicator of the quality of the transmission behaviour of the chain drive. As expected, the bushing chain shows the highest amplitudes, whereas the silent chain shows a somewhat improved behaviour. The new chain concept (variant with stationary guides), however, shows a significant reduction of the respective amplitudes. If the results in the frequency domain are compared, all chain types clearly show the components of the polygon order (20th order of the driving sprocket). Considering the dominating polygon order, the new chain realizes a reduction by a factor of 8.6 compared to the bushing chain and by a factor of 6.3 compared to the silent chain.
If the stationary guides are omitted, all important parameters show only a minor deterioration. Considering the dominating polygon order, the new chain with no stationary guides is a significant factor 4.1 better than the bushing chain and even a factor 3 better than the silent chain.
The results allow the conclusion that the low-cost variant without stationary guides also behaves significantly better acoustically than the bushing chain and silent chain.



Fluctuation


    Figure 7 Fluctuation of angular velocity with the use of stationary
guides
                   compared to bushing chain and silent chain



7. OVERVIEW OF THE ADVANTAGES OF THE NEW CHAIN


In short, the expected technical and commercial advantages of the new chain are:
- potential reduction of the noise level
- acoustic quality at least equal to that of silent chains
- (theoretically) no polygon effect
- no meshing impact
- constant transmission ratio
- (theoretically) no chain vibration
- (theoretically) constant longitudinal chain force
- excellent behaviour even if stationary guides are omitted
- improved specifications (higher speed, higher maximum chain load)
- compact and reliable design
- suitable as a roller chain or a bushing chain
- suitable for mass production
- manufacturing price about equal to roller chains or bushing chains
- potential low-cost alternative for expensive silent chains
- high power density
- high mechanical efficiency
- reduced chain wear


It should be emphasized that, apart from some functional experimental tests, the new chain of SmartChain B.V. has mainly been investigated on a theoretical basis.



8. CONCLUSIONS


The new chain of SmartChain B.V. with no polygon effect is based on a surprisingly simple approach and has an acoustic quality that is at least equal to that of the silent chain. Its manufacturing price is not higher than that of a roller chain or a bushing chain. The new chain has the potential to penetrate and expand on the “low-noise” market of automotive silent chains and synchronous belts.


Acknowledgements

SmartChain B.V. is greatly indebted to AVL List GmbH and the Christian-Doppler-Laboratory for Engine and Vehicle Acoustics of the Institute for Internal Combustion Engines and Thermodynamics of the Graz University of Technology for performing the multi-body dynamics simulations with software Tycon.

 

The authors
Dipl.-Ing. Theo Korse (t.korse@smartchain.nl ) is director of SmartChain B.V., Zoetermeer, the Netherlands.
Dipl.-Ing. Martin Sopouch (martin.sopouch@avl.com ) is development engineer for the Software TYCON of AVL List GmbH und research assistent of the Christian-Doppler-Laboratorium für Motor- und Fahrzeugakustik am Institut für Verbrennungskraftmaschinen und Thermodynamik, TU-Graz, Austria.