GB2414056A

GB2414056A - A hydraulic chain tensioner having a pressure regulator

Info

Publication number: GB2414056A
Application number: GB0410569A
Authority: GB
Inventors: Ian Pegg; Michael James Watts
Original assignee: Ford Global Technologies LLC
Current assignee: Ford Global Technologies LLC
Priority date: 2004-05-12
Filing date: 2004-05-12
Publication date: 2005-11-16
Also published as: GB0410569D0; GB2414057B; GB0509169D0; GB2414057A

Abstract

A hydraulic chain tensioner system for an engine 10 is disclosed in which the system includes a pressure regulator 14 interposed between an oil supply system of an engine 10 of the motor vehicle 5 and a hydraulic chain tensioner 15. The pressure regulator 14 is operable to prevent the oil pressure supplied to the hydraulic chain tensioner 15 exceeding a predetermined maximum pressure.

Description

24 14056

A HYDRAULIC CHAIN TENSIONER SYSTEM FOR AN ENGINE

This invention relates to internal combustion engines and in particular to a hydraulic chain tensioner system for an engine.

Known designs of hydraulic chain tensioner for internal combustion engines depend on general engine oil pressure to dictate the tension applied to chain. In practice a minimum lo oil feed pressure is required to provide adequate dynamic performance of the chain drive system. When pressures higher than this minimum value are used this can give rise to the following problems, an increase in parasitic loss through friction leading to worse fuel consumption and increased wear in the chain drive components.

A further problem with known designs is the variation of load with oil pressure. This makes the system more difficult to optimise for NVH and also makes the system less durable. This is because in current tensioner designs oil is fed directly to the tensioner normally from the main oil gallery of the engine. As will be appreciated by those skilled in the art, the oil pressure in the gallery will vary with engine speed and with oil viscosity.

It is a further problem with known hydraulic chain tensioners that they are affected by the actual build of the engine and also by wear during use. That is to say, variations in bearing clearances from engine to engine due to component tolerances will affect the actual pressure produced in the oil supply system for a given engine speed and operating temperature and, when the bearings wear, the bearing clearances will increase so that the pressure in the oil supply system will tend to be lower for the same engine speed and operating temperature than when the engine was new.

Such an arrangement therefore leads to a large range of tension applied to the chain and, in practice, the applied tension will exceed the maximum required for acceptable drive system performance over a large percentage of the engine operating cycle. This often results in increased power absorption due to increased frictional losses, increased tendency to wear due higher tensions than required and increased guide rubbing noise and wear.

lo It is an object of this invention to provide an improved hydraulic chain tensioner system for an engine.

According to a first aspect of the invention there is provided a hydraulic chain tensioner system for an internal combustion comprising a first fluid connection to a high pressure part of an oil supply system of the engine, a fluid pressure regulator to receive oil at pressure from the first fluid connection and supply it to a hydraulic chain tensioner acting against a drive chain so as to maintain tension in the drive chain wherein the pressure regulator is operable to limit the pressure of the oil supplied to the hydraulic chain tensioner to a predetermined maximum pressure.

The oil pressure supplied to the hydraulic chain tensioner from the pressure regulator may increase with the speed of the engine from zero engine speed until the predetermined maximum pressure is reached after which the pressure supplied to the hydraulic chain tensioner may remain substantially constant.

If the pressure supplied to the pressure regulator is greater than the predetermined maximum pressure, then excess pressure may be bled back from the pressure regulator to a low pressure part of the oil supply system of the engine.

The system may further comprise a second fluid connection to return oil from the pressure regulator to the low pressure part of the oil supply system of the engine.

The engine may have an oil sump and the low pressure part of the oil supply system of the engine may be the oil sump.

The oil supply system of the engine may include an oil lo pump having a low pressure inlet and a high pressure outlet and the high pressure part of the oil supply system of the engine may be a part of the oil supply system of the engine located on the high pressure outlet side of the oil pump.

In which case, the low pressure part of the oil supply system of the engine may be a part of the oil supply system located on the low pressure inlet side of the oil pump.

The system may further include an orifice to restrict the flow of oil from the oil supply system through the pressure regulator.

The orifice may be interposed between the pressure regulator and the oil supply system of the engine to restrict the flow of oil from the engine oil supply system to the pressure regulator.

The orifice may be located in the first fluid connection to the pressure regulator.

The drive chain may be a camshaft drive chain.

According to a second aspect of the invention there is provided a motor vehicle having an internal combustion engine, the engine having a drive chain wherein tension of the drive chain is controlled by a hydraulic chain tensioner system in accordance with said first aspect of the invention.

The invention will now be described by way of example with reference to the accompanying drawing of which: Fig.1 is a schematic diagram of a motor vehicle having a hydraulic chain tensioner system according to the invention; Fig.2 is a diagram showing the relationship between pressure and engine speed for an oil supply system of an engine; and Fig.3 is a diagram showing the relationship between pressure supplied to a hydraulic chain tensioner and engine speed in accordance with the invention.

With reference to Fig.1 there is shown a motor vehicle 5 having an engine 10. The engine 10 as shown has a single overhead camshaft (not shown) driven by a camshaft drive chain 19 engaged with a drive chain wheel 18 connected to a crankshaft (not shown) of the engine 10 and a camshaft drive wheel 20 connected to the camshaft. It will be appreciated that the invention is not limited to use with such an engine and can be used with any chain driven camshaft arrangement and is not limited to use with a camshaft drive chain.

To maintain tension in the camshaft drive chain 19 a hydraulic chain tensioner 15 is arranged to apply a force to the camshaft drive chain 19 via a pivotable slider or slipper 17. The hydraulic chain tensioner 15 is conventional in construction and has a piston 16 engaged in a bore (not shown) connected to a supply of hydraulic pressure. The hydraulic chain tensioner 15 further includes a spring (not shown) to provide a biasing force to the piston 16 holding it against the slipper 17 when no pressure is being supplied and a fallback prevention device in the form of a ratchet device (not shown) to prevent the piston 16 from fully retracting when no pressure is applied to it.

The engine 10 is provided with an oil supply system to supply lubricating oil to its various moving components.

The oil supply system includes various passages (not shown) formed within a cylinder block and cylinder head forming the engine 10 and an oil pump 12 to circulate oil through the lo oil supply passages. The oil pump 12 has a low pressure inlet connected to a supply of oil stored in a reservoir in the form of a sump 11 and a high pressure outlet to supply oil at high pressure to the engine 10. It will be appreciated that the engine 10 could alternatively use a dry sump oil supply system in which oil is returned from the oil supply system directly to the pump without the need for a sump.

The hydraulic chain tensioner 15 is supplied with oil ?0 at pressure from a pressure regulator 14 which is connected by a first fluid connection to a high pressure part of the oil supply system of the engine 10. In this case the first fluid connection is in the form of a hydraulic pipe connected at one end to a position in the oil supply system near to a high pressure outlet from the oil pump 12 and connected at the opposite end to the pressure regulator 14.

An orifice or restriction 13 is located in the first fluid connection to limit the flow of oil to the pressure regulator 14.

A second fluid connection in the form of a second hydraulic pipe is arranged to return or bleed oil to a low pressure part of the oil supply system of the engine 10 on a low pressure inlet side of the pump 12. In this case oil is bled from the pressure regulator 14 to the sump 11 when the pressure in the pressure regulator 14 exceeds a predetermined maximum pressure. It will be appreciated that the oil could be bled directly from the pressure regulator 14 to a chain housing and could then be returned to the sump or other low pressure part of the oil supply system. It will further be appreciated that the first and second fluid connections could also be formed as passageways in the engine or in the pump or in some other way and that the invention is not limited to the use of hydraulic pipes to connect the pressure regulator 14 to the oil supply system.

It will further be appreciated that if a suitable orifice or restrictor 13 is not fitted to the supply to the pressure regulator 14 or within the regulator 14 then, when excess pressure is bled back to the sump 12, a large quantity of oil will be extracted from the oil supply system thereby lowering the oil pressure in the oil supply system and reducing its effectiveness. That is to say, the function of the orifice is to prevent the hydraulic chain tensioner system from greatly interfering with the normal operation of the oil supply system of the engine. That is to say, without such an orifice, the flow to the pressure regulator could require the pump to work harder than would normally be required or significantly reduce the oil pressure downstream from the position where the oil supply to the pressure regulator is connected. In the latter case, such a significant reduction in oil pressure could result in insufficient lubrication of the components supplied by the oil supply system. It will be appreciated that the orifice could be formed as an integral part of the pressure regulator 14.

In its simplest form the pressure regulator comprises a passage or chamber (not shown) leading to a fluid supply connection to the hydraulic chain adjuster 15 and a spring loaded pressure relief valve (not shown) arranged to bleed hydraulic fluid into the second fluid connection when the l pressure in the passage or chamber reaches or exceeds a predetermined maximum pressure.

The predetermined maximum pressure is determined from the maximum load that it is required to apply to the camshaft drive chain 19 using the dimensions and geometry of the various components of the hydraulic chain tensioner 15 and the slipper 17. As will be understood by those skilled in the art when the pressure in the pressure regulator 14 lo reaches the predetermined maximum pressure the effect of this pressure upon the spring loaded pressure relief valve is sufficient to dislodge the valve from a complementary seat against the action of a spring used to bias it closed towards the seat.

It will be appreciated that the invention is not limited to the use of such a pressure regulator and that other types of pressure regulator could be used. For example, the pressure relief valve could be electronically controlled by an electronic control unit in response to a pressure signal supplied from a pressure sensor associated with the hydraulic chain tensioner 15 to prevent the pressure in the hydraulic chain tensioner 15 from exceeding the predetermined maximum pressure.

With reference to Fig. 2 there is shown a typical relationship between oil pressure and engine speed for an oil supply system of an internal combustion engine. The solid line represents the relationship when the oil is at its normal operating temperature and the dotted lines show the effect of temperature on the relationship with a higher pressure being produced for the same engine speed as the oil temperature is reduced due to increasing viscosity of the oil. It will be seen that increasing the speed of the engine will result in a corresponding increase in the pressure in the oil supply system. It will therefore be appreciated that the actual pressure produced depends upon the viscosity of the oil being pumped and so will be affected by the temperature of the oil being pumped.

If this oil pressure is used to directly power the hydraulic valve tensioner then the pressure applied to the camshaft drive chain will vary greatly depending upon engine speed and oil viscosity. In addition, at high engine operating speeds a much higher load will be applied to the drive chain than at low engine operating speeds.

With reference to Fig.3 there is shown the relationship between pressure supplied to the hydraulic chain adjuster 15 and engine speed in accordance with this invention. The solid line represents the relationship when the oil is at its normal operating temperature and the dotted lines represent the relationship when the oil is at a lower temperature and hence higher viscosity.

It will be seen that when the engine 10 is started the pressure supplied will rise with engine speed until the predetermined maximum pressure PMaX is reached which, if the oil is at its normal running temperature, will occur at an engine speed N. Above this engine speed there is substantially no further increase in pressure supplied to the hydraulic chain adjuster 15 because the excess pressure is bled back to the sump 12 by the pressure regulator 14.

Therefore by designing the hydraulic chain adjuster 15 such that it produces the maximum required force upon the camshaft drive chain 19 when this maximum pressure is supplied to it, the range of force applied to the camshaft drive chain 19 is greatly reduced. In addition, because excessive load is not applied to the camshaft drive chain 19 when the engine is operating at high speed, chain wear, noise and friction are all reduced and as a consequence engine fuel efficiency, durability and refinement are increased. Furthermore, a system according to the invention is not affected by engine build or by bearing wear and, because the maximum load applied to the drive chain is lower than it would otherwise be, it is possible to design the components frictionally engaged with the chain such as the slipper and any chain guides in such a manner that they are cheaper to manufacture. That is to say, these components could be made smaller and/or be made from less expensive materials.

lo It will be appreciated by those skilled in the art that although the invention has been described by way of example with reference to a number of specific embodiments it is not limited to these embodiments and that various alternative embodiments or modifications to the disclosed embodiments could be made without departing from the scope of the invention.

For example, although the invention has been described with reference to its use for providing tension to a camshaft drive chain, it will be appreciated that it could be used for any engine driven chain such as for example, and without limitation, a chain driven balancer shaft, a chain driven oil pump or a chain driven fuel pump. It will be further appreciated that the invention is not limited to use in a motor vehicle.

Claims

Claims 1. A hydraulic chain tensioner system for an internal combustion

engine comprising a first fluid connection to a high pressure part of an oil supply system of the engine, a fluid pressure regulator to receive oil at pressure from the first fluid connection and supply it to a hydraulic chain tensioner acting against a drive chain so as to maintain tension in the drive chain wherein the pressure regulator is lo operable to limit the pressure of the oil supplied to the hydraulic chain tensioner to a predetermined maximum pressure.
2. A system as claimed in claim 1 wherein the oil pressure supplied to the hydraulic chain tensioner from the pressure regulator increases with the speed of the engine from zero engine speed until the predetermined maximum pressure is reached after which the pressure supplied to the hydraulic chain tensioner remains substantially constant.
3. A system as claimed in claim 1 or in claim 2 wherein if the pressure supplied to the pressure regulator is greater than the predetermined maximum pressure then excess pressure is bled back from the pressure regulator to a low pressure part of the oil supply system of the engine.
4. A system as claimed in claim 3 wherein the system further comprises a second fluid connection to return oil from the pressure regulator to the low pressure part of the oil supply system of the engine.
5. A system as claimed in claim 3 or in claim 4 wherein the engine has an oil sump and the low pressure part of the oil supply system of the engine is the oil sump.
6. A system as claimed in any of claims 1 to 5 wherein the oil supply system of the engine includes an oil pump having a low pressure inlet and a high pressure outlet and the high pressure part of the oil supply system of the engine is a part of the oil supply system of the engine located on the high pressure outlet side of the oil pump.
7. A system as claimed in claim 6 when dependent upon claim 3 or upon claim 4 wherein the low pressure part of the oil supply system of the engine is a part of the oil supply system located on the low pressure inlet side of the oil lo pump.
8. A system as claimed in any of claims 1 to 7 wherein the system further includes an orifice to restrict the flow of oil from the oil supply system through the pressure regulator.
9. A system as claimed in claim 8 wherein the orifice is interposed between the pressure regulator and the oil supply system of the engine to restrict the flow of oil from the engine oil supply system to the pressure regulator.
10. A system as claimed in claim 9 wherein the orifice is located in the first fluid connection to the pressure regulator.
11. A system as claimed in any of claims 1 to 10 wherein the drive chain is a camshaft drive chain.
12. A motor vehicle having an internal combustion engine, the engine having a drive chain wherein tension of the drive chain is controlled by a hydraulic chain tensioner system as claimed in any of claims 1 to 11.
13. A hydraulic chain tensioner system substantially as described herein with reference to the accompanying drawing.
14. A motor vehicle substantially as described herein with reference to the accompanying drawing.