GB2436604A

GB2436604A - Dynamic tensioning system for a belt or chain in an engine

Info

Publication number: GB2436604A
Application number: GB0606358A
Authority: GB
Inventors: Ian Graham Pegg; Brian Stanley Cumming
Original assignee: Ford Global Technologies LLC
Current assignee: Ford Global Technologies LLC
Priority date: 2006-03-30
Filing date: 2006-03-30
Publication date: 2007-10-03
Also published as: GB0606358D0

Abstract

A tensioning system for use in an internal combustion engine to tension a belt or chain drive 20, the tensioner 10 comprising means for varying the tension dynamically in direct/indirect dependence on prevailing engine operating conditions. The tension may be varied in dependence on engine speed, or the operating state of components driven by the engine, such as the alternator 16, fuel pump 18 or air conditioning compressor 14. The control system 12 may operate on an open loop system wherein the appropriate tension is looked up from a table, or a closed loop system which receives feedback from a sensor 22. The sensor 22 may be an optical sensor which monitors slap, or a sound sensor which detects emitted noise. The tensioner itself may be of a mechanical, pneumatic, hydraulic or electrical kind.

Description

TENSIONING SYSTEM

Field of the invention

The present invention relates to a tensioning system for use in an internal combustion engine to take up slack in a belt or chain drive. Such tensioning systems are needed to maintain a positive drive at all times and to reduce noise vibration and harshness (NVH)

Background of the invention

Belt and chain drives in engines usually suffer from dynamic excitations. These drives often have natural frequencies within the operating range of the engine, which often occur at or near the engine idling speed. The peak dynamic tension in the belt or chain may therefore vary considerably with the engine operating conditions.

The load on a belt or chain drive is affected not only by dynamic excitation but also by the operating state of certain components, such as an air conditioning compressor, a fuel pump or an alternator and by inertial effects during acceleration and deceleration.

Currently, belt or chain drive tension is maintained constant tension regardless of the peak dynamic loads prevailing at any one time. As the tension has to be set to cope with the worst case scenario, this necessarily means that the tension is often unnecessarily high for the prevailing dynamic peak loads. Excessive tension can cause drive losses of the order of 2% to 4% when the tensioning system is operating with a light dynamic load, and there is evidence to suggest that these losses are even greater when the chain or belt drive is under higher load.

Summary of the invention

With a view to mitigating the foregoing disadvantage, the present invention provides a tensioning system for use in an internal combustion engine to tension a belt or chain drive, which comprises means for varying the tension dynamically in dependence upon prevailing engine operating conditions.

In the present invention, the tension of a belt or chain drive is set at a level suited to the prevailing peak loads. Consequently, at any given time, the tension is sufficient to avoid slipping and NVH problems. However, when the peak loads are low, unnecessarily high tension is avoided. This results in a reduction in wear as well as in avoiding the drop in efficiency caused by excessive tension.

The tension in the belt or chain drive is preferably varied in accordance with the prevailing engine speed.

The belt tension may further be varied in dependence upon the loading applied by components, such as an air conditioning compressor, an alternator or a fuel pump.

Belt and chain drive tensioning systems currently in use operate hydraulically or mechanically and either type may be used in implementing the invention. In the case of a hydraulic tensioning system, the pressure may be varied as required while in a mechanical system, the point of anchoring of a spring acting to tension the belt or chain may be varied, for example by means of an electric motor, to vary the tension.

The control system serving to set the tension may be open loop or closed loop. In an open loop control system, the desired tension may be determined from a look-up table, or calculated from a suitable algorithm, and a command signal may be issued to set the tension accordingly. In a closed loop system, a feedback sensor, for example an optical sensor, is provided to monitor a parameter, such as slap along a run of the belt or chain, which varies with the tension and the tension is increased or decreased to maintain the tension at the desired level.

Brief description of the drawings

The invention will now be described further, by way of example, with reference to the accompanying drawing, which is a schematic block diagram of an embodiment of the invention.

Detailed description of the preferred embodiment

The drawing shows a variable tensioner 10 which is set by any control system 12. The control system 12 receives inputs from ancillary equipment driven by a chain or belt drive 20, the components shown in the drawing, by way of example, being an air conditioning compressor 14, an alternator 16 and a fuel pump 18.

The variable tensioner 10 acts on the belt or chain drive 20 to set the tension at a level determined by the control system 12. The drawing also shows an optional feedback sensor 22 which senses a parameter that varies with the belt tension and sends back a signal to the control system 12.

The principle upon which the present invention operates is that the tension in the belt or chain drive 20 is not set at a constant level for all possible operating conditions but is varied dynamically by the variable tensioner 10. In this way, the tension is set at a level that is only sufficient to cope with the peak loads prevailing at any one time, thereby avoiding unnecessarily high tensions when they are not essential. By reducing the tension in this manner, it is possible to reduce wear and avoid unnecessary parasitic losses which reduce the operating efficiency of the engine.

The variable tensioner 10 can operate mechanically, pneumatically, electrically or hydraulically, the type of system adopted not being crucial to the present invention.

In the case of a tensioner powered by fluid pressure or electrically, the drive tension can readily be varied on demand. In the case of a mechanical tensioner, it is possible to vary the position at which a tensioning spring is anchored to modify the tension in the belt or chain drive and such movements can be brought about electrically or by use of a pressurised fluid.

The control system 12 operates electrically to determine a suitable tension in the drive 20 in dependence upon the prevailing engine operating conditions which affect the peak loads in the belt or chain. The control system 12, in setting the desired tension, therefore takes account of such parameters as engine speed and the operating state of the loads driven by the belt or chain.

The variable tensioning system 10 may operate in an open loop configuration obviating the need for a feedback sensor. The illustrated embodiment does however show an optional feedback sensor 22 providing a feedback signal to the control system 12 to confirm that the tension in the belt or chain 20 has been set correctly by the variable tensioner 10 to the desired level.

The feedback sensor 22 may detect any parameter that is indicative of the tension in the drive 20. It may for example optically monitor the slap (side to side oscillation) of a run of the belt or it may sense noise or vibration emitted from the chain or belt drive 20.

When a feedback sensor is present, it is possible to dispense with inputs to the control system 12 to indicate the operating state of components driven by the belt or chain drive 20. In the latter case, the control system will simply set the variable tensioning system 10 to maintain an acceptable amplitude of slap or output sound level. When using a system relying on sound, it is possible for the control system to determine whether the belt or chain is too slack or too taut by the nature of the sound that is emitted. When the belt tension is excessive, the drive tends to whine, whereas, when it is too low, the drive tends to rattle.

It is stressed that the manner in which the variable tension in the belt or chain is set is not fundamental to the present invention. The novelty and advantages of the invention stem from the fact that the tension in the belt or chain 20 is dynamically varied to avoid excessive tension when a lower tension is sufficient to cope with the prevailing peak loads.

Claims

CLAIMS

1. A tensioning system for use in an internal combustion engine to tension a belt or chain drive, which comprises means for varying the tension dynamically in dependence upon prevailing engine operating conditions.

2. A tensioning system as claimed in claim 1, wherein the tension in the belt or chain drive is varied in accordance with the prevailing engine speed.

3. A tensioning system as claimed in claim 1 or 2, wherein the tension in the belt or chain drive is varied in dependence upon the operating state of components driven by the drive.

4. A tensioning system as claimed in any preceding claim, wherein a spring is provided to tension the chain or belt drive and the means for varying the tension dynamically are operative to vary the anchoring point of the spring.

5. A tensioning system as claimed in any preceding claim, having a variable tensioner connected to a control system in any open loop, the control system sending a command signal to the variable tensioner to set the tension at a level determined by the control system.

6. A tensioning system as claimed in any of claims 1 to 4, having a variable tensioner connected in a closed control loop to a control system which receives a feedback signal from a sensor detecting a parameter related to the tension in the bet or chain drive.

7. A tensioning system as claimed in claim 6, wherein the feedback sensor is an optical sensor monitoring slap in a run of the belt or chain.

8. A tensioning system as claimed in claim 6, wherein the feedback sensor is a sound sensor monitoring noise emitted from the belt or chain.

9. A tensioning system for use in an internal combustion engine to tension a belt or chain drive, constructed substantially as herein described with reference to and as illustrated in the accompanying drawing.