Timing chains or belts?
Tests reveal which is more efficient.

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08.04.14 12:17

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Timing chains or belts?
Tests reveal which is more efficient
Timing chains or belts? The question seems as old as the automobile or internal
combustion engine itself. During the past few decades, several studies haveinvestigated which timing drive technology offers the best quality and performance.
To shed some light on which type of timing drive provides more efficiency,
BorgWarner conducted intensive belt and chain drive testing on a motored engine
friction test stand at its technical center in Ithaca, New York.
By Al Moster, Director Engineering, Borg Warner and John Goodrow, Senior Engineering Manager, BorgWarner

Evaluating performance

When it comes to timing drives for internal
combustion engines, engine designers focus
on durability, installation space in the engine
compartment, NVH (noise, vibration and harshness) and overall efficiency. With years ofcomparable experience on the road, chain drives offer several advantages over belts when
considering a broad range of criteria.
With durability lasting as long as the engine’slife, chain drives are most suitable for highpower engines. Advanced manufacturing finishes, materials and coatings improve chain
strength, durability, wear resistance and efficiency. Most belt drives, on the other hand, require replacement prior to end of vehicle life.
In engines with limited installation space,chains offer a more compact solution. Where
every millimeter of installation space counts,
modern engines strongly favor chain drives
over belt drives. In the cases explored in thisBorgWarner Knowledge Library 201 4

study, the benefit is as much as 8-1 0 mm.
However, comparing the efficiency performance between chain drives and belt drives can be
more challenging. When evaluating friction, it
has been claimed that belts have a natural advantage due to their design, i.e. a non-metallic
belt on a metallic pulley. In many recent applications, chain manufacturers have successfully
optimized chain systems to reduce friction by
employing low-friction materials, optimized linkgeometry, tensioner tuning and advanced manufacturing techniques.

Testing

BorgWarner engineers set out to quantify theefficiency of chain drives and belt drives bymeasuring torque-to-turn at the crankshaft. In
the course of the investigation, BorgWarner’sinverted tooth silent chain drive was comparedwith a conventional dry belt and to a wet belt
operating in oil.
BorgWarner’s motored engine friction test1

stand in Ithaca, New York, allows engineers tomeasure the friction of the entire timing system. It consists of a non-firing engine poweredby an electric motor in which the chain tensions
are induced by the camshaft torques.
The engines used for testing were modified to
avoid variables such as fuel pump and oilpump drag, so that the friction losses associated with belt vs. chain drive could be isolated
and highly repeatable. Front and rear crankseals were also removed, and the crankshaft
was neutrally balanced without the pistons androds.
BorgWarner acquired two belt driven engines,
a 1 .0-liter I3 engine as well as a 1 .6-liter I4 engine, and tested those engines with their original timing drives. BorgWarner then developed
a chain drive solution for each of these engines
using an 8.0 mm pitch inverted tooth silent
chain and a 6.35 mm pitch inverted tooth silent
chain respectively.

Results of comparative measurements

As part of the chain system design process,dynamic system simulation was performed toensure robust performance of the design. This
simulation indicated that both of BorgWarner’s
chain drives would be robust and will satisfy all
requirements concerning chain tension andcontrol. The test data output resulted in approximately equal timing drive torque losses between the chain drive and the wet belt drivewith a good repeatability of +/- 0.02 Nm.
The comparison of BorgWarner’s chain drivewith a dry belt drive resulted in higher efficiency
on the part of the chain system. This disadvantage of dry belts can be at least partially explained by the use of cam seals to keep thebeltdry.

The investigation was conducted according to
the “strip method.” In this procedure, the chainor belt drive was installed on the engine, andthe amount of torque needed to spin the engine at the crankshaft was measured. Then, thechain or belt was removed, and the amount of
torque needed to spin the crankshaft wasmeasured to determine the crankshaft torque.
Finally, the crankshaft torque was subtracted
from the total engine torque. The result revealed the timing drive and valve train torque.
Exhaustive build/rebuild testing was conductedto ensure test results could be repeated. Periodic retests of a baseline were also conducted.
The results showed test repeatability at lessthan 3%.

BorgWarner Knowledge Library 201 4

BorgWarner’s advanced chain drive system
reduces friction and weight to help improve fueleconomy.
2

Timing drive valve train torque (Nm) of a chain in comparison with a dry belt.

BorgWarner testing shows belts and chains offer similar efficiency performance. However,chains still feature many advantages overbelts, including compact packaging, durability
and better system control.

What does this mean for different
engine setups?

Based on BorgWarner’s test results, chain andbelt drives have the same or similar efficiency
when the timing system is optimized. However,when choosing between chain and belt drives,
the adaptability of timing drives to different engine setups is another key consideration forengine designers.
Due to the higher strength-to-width ratio, chain
systems featuring a hydraulic tensioner, tightstrand guide and slack strand tensioner arm
contain all the elements necessary for adapting
to additional engine variants with minimal modifications. For example, for one application,
BorgWarner covers six different variants with a
BorgWarner Knowledge Library 201 4

common chain and tensioner design.
Conversely, a common dry belt features astrength-to-width ratio of less than half that of asimilar chain application. When increasedpower engine variants demand higher systemrobustness, several factors can have a considerable effect on efficiency and engine packaging, including increased belt width, thepotential need for a tight strand guide or idler
pulley and increased preload due to higher
amplitude inputs.

Conclusion

BorgWarner’s testing reveals that optimized
chain and belt drives show similar efficiency.
While chain drives exhibit a measurable efficiency advantage over dry belt drives, chain
drives and wet belt drives perform similarly. As
a result, design decisions regarding timing drives should be made by considering a numberof different criteria.

3Timing drive valve train torque (Nm) of a chain in comparison with a wet belt.

Adaptability, low dynamic cam oscillation,
strength and best-in-class NVH performance
make BorgWarner’s chain drives the best solution. With proven long-term field durability,
BorgWarner’s chain drives offer compact
packaging, optimized efficiency and robustness
against dynamic instability.

Contact
Email: technology@borgwarner.com
For more information, please visit
borgwarner.com
BorgWarner Knowledge Library 201 44