GB2442557A

GB2442557A - A Method For Determining Degradation Of A Lubricating Oil

Info

Publication number: GB2442557A
Application number: GB0718253A
Authority: GB
Inventors: Andrew Gary Scarisbrick; Keith William Barter
Original assignee: Ford Global Technologies LLC
Current assignee: Ford Global Technologies LLC
Priority date: 2006-10-05
Filing date: 2007-09-19
Publication date: 2008-04-09
Anticipated expiration: 2027-09-19
Also published as: GB2442557B; DE102007045837B4; GB0718253D0; GB0619689D0; DE102007045837A1; GB2442490A

Abstract

A method is disclosed which uses a condition monitoring apparatus 10 having a device 1, 20, 30, 40 and 50 for monitoring the condition of an oil lubricated component of an engine 100. The device 1, 20, 30, 40 and 50 includes a sacrificial component 4, 24a, 24b, 34, 44a, 44b and 54 that deteriorates in a manner that mimics the actual wear of the oil lubricated component. The method comprises using the output from the device 1, 20, 30, 40 and 50 to determine the actual wear of the sacrificial component 4, 24a, 24b, 34, 44a, 44b and 54 and providing an estimated life of the oil based upon the rate of wear. If the rate of wear exceeds a pre-determined rate then a user of the engine 100 can be notified by means of a warning device 11.

Description

A Method for Determining Degradation of a Lubricating Oil This

invention relates to the monitoring of the condition of the oil in an internal combustion engine.

The introduction of lower emission regulations such as EU Stage IV and Stage V has lead to the adoption of different approaches to combustion and exhaust treatment systems. It is known that NOx levels can be lowered by reducing the temperature of combustion which can be achieved through later injection timing and higher levels of exhaust gas recirculation. Lean NOx traps used to reduce NOx emissions have to be regularly regenerated and this is achieved by generating rich conditions in the combustion chamber. All of these techniques result in higher levels of particulate matter and in the fuel being induced past the piston and into the oil sump. Once in the oil system, this fuel and soot can have a dramatic effect on the rate at which metal contact points such as the cam followers and chain will wear and so it is essential to determine when the condition of the oil has degraded to such an extent the rapid wear of engine components is likely to be occurring.

It is known to use a sensor that is able to detect a number of important components including soot, oil, water, acids as well as other properties that are known to effect the rate at which wear occurs.

There are two problems with such an approach, firstly, the current ability of such a sensor to measure all of the important parameters accurately for different oil types does not allow an accurate indication of oil quality to be obtained and secondly, the relationship between soot levels, fuel levels in the oil and the wear rate of components is very complicated and so it is difficult to predict based solely on an analysis of the oil when high levels of wear are likely to be occurring. The wear rate is also a function of operating conditions including temperature, load, speed, and oil type and so, even if precise measurements of soot and fuel levels in the oil can be obtained, an accurate indication of wear rate which is the parameter of interest in riot easy to obtain.

An alternative technique to using a sensor of the type previously described is to use an algorithm. The algorithm is developed to estimate the level of fuel and soot in the oil and historical levels of soot and fuel determined from experimental work are then set as limits. When these limits are exceeded, the driver is warned of the danger. These algorithms are prone to the same issues described above with reference to known sensors and are calibrated using information from a range of operating conditions that is likely to be more limited than the customers will experience during normal running.

It is an object of this invention to provide a method of determining the condition of the oil that is more accurately able to determine when the degradation of the oil has become such that it is likely to increase the wear of a component.

According to a first aspect of the invention there is provided method for determining an expected life of a lubricating oil in a machine having at least one oil lubricated component wherein the method comprises using a condition monitoring apparatus having a device including a sacrificial component located on the machine in the same environment as the oil lubricated component so as to wear in a similar manner to the oil lubricated component, and a sensor to measure the actual wear of the sacrificial component, using the measured wear to determine a wear parameter and using the wear parameter to provide an expected life of the oil.

The wear parameter may be a wear rate value indicative of the current wear rate.

The method may further comprise comparing the wear rate value with a predicted wear rate value.

The predicted wear rate value may be based upon experimental data relating machine running time and wear rate stored in the form of a look up table.

The predicted wear rate value may be calculated using an algorithm based upon a relationship between machine running time and wear rate.

The method may further comprise using the wear rate comparison to determine the expected life of the oil.

The method may further comprise providing an indication of expected oil life to a user of the machine.

The wear parameter may be a rate of change of a wear rate value.

The method may further comprise comparing the rate of change of wear rate value with a predicted rate of change of wear rate value.

The predicted rate of change of wear rate value may be based upon experimental data relating machine running time and wear rate stored in the form of a look up table.

The predicted rate of change of wear rate value may be calculated using an algorithm based upon a relationship between machine running time and wear rate.

The method may further comprise using the rate of change of wear rate comparison to determine the expected life of the oil.

The method may further comprise providing an indication of the expected oil life to a user of the machine.

The method may further comprise comparing the wear rate value with a pre-determined wear rate value and providing an indication to the user of the machine that the oil requires replacing when the wear rate value is greater than the pre-determined wear value.

The machine may be an internal combustion engine.

The invention will now be described by way of example with reference to the accompanying drawing of which:-Fig.1 is a line diagram of a machine having a condition monitoring apparatus; Fig.2 is a line diagram of a first monitoring device forming part of a first embodiment of a monitoring apparatus; Fig.3 is an outline diagram of a second embodiment of a monitoring device forming part of the monitoring apparatus shown in Fig.1; Fig.4 is an outline diagram of a third embodiment of a monitoring device forming part of the monitoring apparatus shown in Fig.l; Fig.5 is a partial cross-sectional view through a fourth embodiment of a monitoring device forming part of the monitoring apparatus shown in Fig.l; Fig.6 is a view along the line X-X on Fig.5; Fig.7 is a partial cross-sectional view through a fifth embodiment of a monitoring device forming part of the monitoring apparatus shown in Fig.l; Fig.8 is a flow chart of a first embodiment of a method for determining oil degradation; Fig.9 is a flow chart showing a second embodiment of a method for determining oil degradation; and Fig.10 is a chart showing a relationship between wear in micrometers and running time for a sacrificial component of a condition monitoring apparatus.

With reference to Fig.l there is shown a machine in the form of an internal combustion engine 100 having a cylinder block and cylinder head assembly 101, an oil reservoir in the form of a sump 103, a rocker or cam box cover 102 and an oil pump 105 to circulate oil from the sump 103 through the cylinder block and cylinder head to lubricate components associated therewith. The engine 100 is provided with a condition monitoring apparatus to monitor the condition of one or more components within the engine 100.

The condition monitoring apparatus in this case comprises of five separate monitoring devices 1, 20, 30, 40 and 50, an electronic unit 6 and a warning device in the form of a lamp 11. It will however be appreciated that the condition monitoring apparatus could have only one monitoring device and that alternative warning devices could be provided instead of or in addition to the warning lamp 11 such as an audible warning device or a display device.

All of the monitoring devices 1, 20, 30, 40 and 50 have a sacrificial component 4, 24a, 24b, 34, 44a, 44b and 54 which wears in a manner that can be measured and used as an indication of the actual wear of one or more components of the engine 1.

The first monitoring device 1 is a unique component fitted to the cam cover 102 to provide and indication of camshaft wear and is shown in greater detail in Fig.2.

The second monitoring device 20 is formed as part of an oil level dipstick and is used to provide an indication of the wear of a component subject to abrasive wear such as for example a piston of the engine 1 that has oil jet cooling.

The monitoring device 20 is shown in greater detail in Fig.3.

The third monitoring device 30 is formed as part of an oil filter used to filter out particulate matter from the oil and is used to monitor the corrosive effects of the oil on a soft metal bearing material such as that used in the big end bearing caps of the engine 100. The monitoring device 30 is shown in greater detail in Fig.4.

The fourth monitoring device 40 is formed as part of an oil drain or sump plug and is used to provide an indication of timing chain wear. The monitoring device 40 is shown in greater detail in Figs.5 and 6.

The fifth monitoring device 50 is formed as part of an oil filler cap and is used to provide an indication of camshaft rocker wear. The monitoring device 50 is shown in greater detail in Fig.7.

It will appreciated that these combinations of monitoring device and engine components are only provided as examples and that other combinations could be used. The common feature of all of these monitoring devices 1, 20, 30, and 50 is that they are all attached to the engine 100 such that they can be easily removed without disassembling the engine 100. This is important because they may need to be removed at regular intervals to be replaced if they are designed to deteriorate or wear at a faster rate than the component that they are provided to mimic. That is to say it is desirable to use a material that is more sensitive to degradation of the oil than the actual component so that as soon as the oil is degraded the monitoring apparatus will be able to measure a change and warn a user of the engine 100.

With reference to Fig.2 there is shown in greater detail the first monitoring device 1 which is fitted to the cam cover 102 to provide an indication of camshaft wear.

The monitoring device 1 comprises of a sacrificial component 4 which is slidingly supported and is urged into contact with a camshaft 2 of the engine 100 by a spring 7. A sensor in the form of a piezo-electric device 5 is interposed between the spring 7 and the sacrificial component 4. A number of signals are sent to the electronic unit 6 by means of a cable 9. These signals may include a measurement of temperature of the sensor 5, an output signal from the sensor 5 and a measurement of the total acid number of the oil.

The sacrificial component 4 is made from a material that has been tested under laboratory conditions and proven to wear faster than the lobes of the camshaft 2 that it is intended to mimic when the properties of the oil used to lubricate the camshaft 2 begin to degrade. It will be appreciated that the sacrificial component 4 could be made from more than one material so as to replicate the wear of more than one oil lubricated component of the engine 100.

Therefore when the oil begins to degrade the sacrificial component 4 will begin to wear rapidly. As the sacrificial component 4 wears the load on the spring 7 reduces and this reduction in load is sensed by the piezo-electric sensor 5. The signal from the piezo-electric sensor 5 which sent to the electronic unit 6 will then indicate that rapid wear is occurring and the electronic unit 6 can either be arranged to illuminate the lamp 11 when the measured load on the piezo-electric sensor 5 falls below a predetermined value or when the rate of change of load on the piezo-electric sensor 5 increases above a pre-determined rate.

With reference to Fig.3 there is shown in greater detail the second monitoring device 20 which is used to provide an indication of piston abrasion. The monitoring device 20 comprises of a first sacrificial component 24a which is fastened to a stem 24b of the dipstick which forms a second sacrificial component. The first sacrificial component 24a is arranged such that a high pressure jet of oil from a nozzle 28a impinges directly against it. The second sacrificial component 24b is arranged such that a second jet of oil from a nozzle 28b impinges directly against it. The pressure of the jet of oil from the second nozzle 28b may be different than that from the first nozzle 28a to replicate different abrasive conditions.

Electromagnetic wave measuring devices (not shown) are directed onto the first and second sacrificial components 24a and 24b at the positions where the two jets impinge against them. The electromagnetic wave measuring devices measuring the wear of the first and second sacrificial components 24a and 24b and transmit signal to a receiver located in the upper end of the dipstick. These signals are sent to the electronic unit 6 by means of a cable 29 attached to the dipstick. Other signals such as a measurement of the temperature of the oil and a measurement of the total acid number of the oil may also be sent to the electronic unit 6 via the cable 29.

The first and second sacrificial components 24a and 24b are made from different materials that have been tested under laboratory conditions and proven to wear faster than the piston that it is intended to mimic when the properties of the oil used to cool the piston begin to degrade.

Therefore when the oil begins to degrade the sacrificial components 24a, 24b will begin to wear rapidly.

As the sacrificial components 24a, 24b wear the electromagnetic wave measuring devices will send signals to the electronic unit 6 which can be used to determine when it is necessary to change the oil. The signals from the electromagnetic wave measuring sensors can be used by the electronic unit 6 for comparison purposes or independently to determine when rapid wear is occurring and the electronic unit 6 can either be arranged to illuminate the lamp 11 when the measured wear is greater than a predetermined value or when the rate of change of wear on one or both of the sacrificial components 24a, 24b increases above a pre-determined rate.

With reference to Fig.4 there is shown in greater detail the third monitoring device 20 which is used to monitor the corrosive effects of the oil on a soft metal bearing material such as that used in the big end bearing caps of the engine 100. The monitoring device 30 comprises of a sacrificial component 34 which is fastened in a flow of oil "OF" entering the third monitoring device 30 through a port 31. A sensor in the form of a capacitance sensor 35 is attached to one end of the sacrificial component 34.

A number of signals are sent to the electronic unit 6 by means of a cable 39. These signals may include a measurement of temperature of the sensor 35, an output signal from the sensor 35 and a measurement of the total acid number of the oil.

The first sacrificial components 35 is made from a material that has been tested under laboratory conditions -10 -and proven to corrode faster than the soft bearing material that it is intended to mimic when the properties of the oil begin to degrade and for which the capacitance changes considerably as the material corrodes.

Therefore when the oil begins to degrade the sacrificial component 34 will begin to corrode rapidly. As the sacrificial component 34 corrodes the capacitance sensor sends a signal to the electronic unit 6 which can be used to determine when it is necessary to change the oil. The signal from the capacitance sensor can be used by the electronic unit 6 to illuminate the lamp 11 when the measured corrosion is greater than a predetermined value or when the rate of change of corrosion increases above a pre-determined rate.

With reference to Figs.5 and 6 there is shown in greater detail the fourth monitoring device 40 which is used to provide an indication of timing chain wear.

The monitoring device 40 comprises of two sacrificial components 44a, 44b which are slidingly supported in a rotor 47 of an electric motor 42 fastened to a hexagonal head 41.

An outer surface of a casing of the motor 42 has a threaded form so as to permit the monitoring device 40 to be secured in an oil drain hole in the sump 103 of the engine 100.

The sacrificial components 44a, 44b are each urged into contact with a bore formed in an end portion 43 of the casing of the electric motor 42 by respective springs and a sensor in the form of a piezo-electric device 45 is interposed between each of the springs and the sacrificial component 44a, 44b with which it cooperates. A number of signals are sent to the electronic unit 6 by means of a cable 49. These signals may include a measurement of -11 -temperature of the sensor 45 for temperature compensation purposes, an output signal from the sensor 45 and a measurement of the total acid number of the oil.

The sacrificial components 44a and 44b are in this case made from the same material that has been tested under laboratory conditions and is proven to wear faster than the links of the timing chain that it is intended to mimic when the properties of the oil used to lubricate the chain begin to degrade.

Therefore when the oil begins to degrade the sacrificial components 44a and 44b will begin to wear rapidly. As the sacrificial components 44a and 44b wear the load on each spring reduces and this reduction in load is sensed by the piezo-electric sensor 45. Because the piezo-electric sensor 45 is interposed between the two springs the change in load is double that it would be if it were to be interposed between only one spring and a fixed abutment which further increases the sensitivity to wear.

The signal from the piezo-electric sensor 45 which is sent to the electronic unit 6 will then indicate that rapid wear is occurring and the electronic unit 6 can either be arranged to illuminate the lamp 11 when the measured load on the piezo-electric sensor 45 falls below a predetermined value or when the rate of change of load on the piezo-electric sensor 45 increases above a pre-determined rate.

With reference to Fig.7 there is shown a fifth monitoring device 50 which is used to provide an indication of camshaft rocker wear.

The monitoring device 50 includes an electric motor 54 having an output shaft fitted with an eccentric drive that is used to reciprocate a plate 56 having a wear surface formed thereon. The plate 56 is slidingly supported by a -12 -body 53 in which is formed a cavity defining guides for the plate 56.

A sacrificial component in the form of a wear block 54 is urged into contact with the wear surface on the plate 56 by a leaf spring 57. One end of the leaf spring 57 rests upon a piezo-electric device forming a load sensor 55. A number of signals may be sent from the sensor 55 to the electronic unit 6, these signals may include a measurement of temperature of the sensor 55 for temperature compensation purposes, an output signal from the sensor 55 and a measurement of the total acid number of the oil.

In use the electric motor 54 causes the plate 56 to be reciprocated relative to the wear block 54 causing the wear block 54 to wear. When the oil begins to degrade the sacrificial component 54 will begin to wear rapidly. As the sacrificial component 54 wears the load on the spring 57 reduces and this reduction in load is sensed by the piezo-electric sensor 55. The signal from the piezo-electric sensor 55 which is sent to the electronic unit 6 will then indicate that rapid wear is occurring and the electronic unit 6 can either be arranged to illuminate the lamp 11 when the measured load on the piezo-electric sensor 55 falls below a predetermined value or when the rate of change of load on the piezo-electric sensor 55 increases above a pre-determined rate.

Therefore in summary several new and inventive

proposals have been formulated by the inventors these can be summarised as the provision of a sacrificial sensor.

The basic implementation provides a separate wear sensor that is specifically designed to wear at a rate that is far quicker than critical engine components. In this way problems with oil quality can be identified very quickly and the driver alerted or the engine operating condition -13 -restricted. The sensor might need to be replaced regularly and would therefore ideally be located in a serviceable location such as within the oil filter, near or as part of the oil drain plug, near or as part of the oil filler cap, as part of the oil dip stick.

In one implementation the wear sensor is constructed from a material that would be worn by the action of the sensor interacting with a component within the engine and lubricated by the engine oil supply. The sensor is designed with a known wear rate, as the lubricating oil is degraded the wear rate of the sensor will change triggering the actions described elsewhere such as sending a signal to the electronic unit 6.

Various lubrication regimes such as boundary, hydrodynamic and mixed could be simulated by different oil delivery methods to the wear interface.

Another implementation provides a wear sensor that is a self-contained unit that uses the oil flow around it, or be independently powered to mimic the wear behaviour of the critical components. Electrical signals from the electronic unit 6 could be used via actuators to reproduce the engine speed and load. The advantage of this is that it has no effect on existing components.

A further implementation uses a wear sensor that is constructed from a material that is worn by the action of the oil passing over its surface such as being placed within a high flow section of the lubrication system.

In another implementation, an oil jet is directed onto part of the sensor so that the oil jet impingement wears the sensor. By measuring wear under different flow regimes, wear due to different wear mechanisms can be identified.

-14 -An advantage of this type of sensor is that it interacts with the lubricating oil only and therefore has no direct impact on existing components.

Significant wear takes place while an engine is stationary such as corrosive or adhesive wear. Such a wear mechanism can also be simulated.

Various methods of collecting and processing the signal from the monitoring device and distributing to the required devices could be used such as a wired or wireless system.

If the monitoring device is part of the oil filter, which is a consumable item, the same wireless communication could be used to demonstrate to a customer the condition of the oil and the oil filter.

The change in dimension of the sacrificial component could be measured by many techniques including, but not limited to, Ultrasonic sensing, electromagnetic wave measuring, reluctance sensing, capacitance sensing, electrical resistance sensing and piezo-electric sensing.

The wear sensor could also include the function of other types of sensor including, but not limited to, oil temperature sensing, oil level sensing, oil acidity sensing, oil viscosity sensing, crankshaft speed sensing, camshaft speed sensing, engine Torque sensing.

The monitoring device could be designed to replicate at least one or more of the following wear mechanisms, Abrasion, Adhesion, Corrosion and Fatigue.

It is also proposed that a number of monitoring devices be designed whereby they would simulate a range of materials present in the engine. The wear of one or more of these materials could be monitored by a single monitoring device.

-15 -It will be appreciated that this could apply to relative motions including but not limited to rotating and sliding interfaces.

The electronic control unit 6 could be programmed to control a monitoring device to carry out engine load simulation by varying the speed and load on the sacrificial component by various means including but not limited to electrical actuation or hydraulic pressure to simulate the actual operating conditions of the engine.

With reference to Fig.8 there is shown a method for determining the degradation of a lubricating oil of an internal combustion engine of a motor vehicle using a condition monitoring apparatus as described above or any other condition monitoring apparatus that includes a sensor capable of measuring actual wear of a component.

The method starts at step 10 where the system is initialised and at step 20 an initial or datum value Mi of output from a sensor of the condition monitoring apparatus is stored in a memory representing the unworn condition of the sacrificial component of the condition monitoring apparatus being used.

At step 100 the engine is started and a timer forming part of the electronic unit 6 is set to zero.

At step 110 a first measurement of wear Mc is determined from the signal received by the electronic unit 6 from the sensor and at step 120 this value of wear Mc is stored in a memory of the electronic unit 6.

At step 130 the timer is started and at step 140 it is determined whether a predetermined period of time has elapsed by comparing a current timer value T with a test period value Tte. If the pre-determined time period has not -16 -elapsed then the method keeps rechecking the elapsed time until the time period has elapsed.

When at step 140 it is determined that the pre-determined time period has elapsed, the method proceeds to step 150 where a further measurement of wear M(c+1) is obtained from the signal sent by the sensor to the electronic unit 6.

Then at step 160 the rate of wear during the test period is determined by subtracting the latest wear measurement M(c+1) from the previous wear measurement Mc and dividing this by the period of time over which wear has been measured that is to say, the test time to produce a rate of wear value. Alternatively, the rate of wear can be produced by subtracting the previous wear measurement Mc from the latest wear measurement M(c+1) and dividing this by the period of time over which wear has been measured.

Then at step 170, the rate of wear value is compared to a predicted wear rate value. The predicted wear rate value can be based upon experimental data relating engine running time and wear rate stored in the form of a look up table or the predicted wear rate can be calculated using an algorithm based upon an experimentally determined relationship between engine running time and wear rate.

It will be appreciated, that as the oil deteriorates the rate of wear of the oil lubricated component and the sacrificial component of the condition monitoring apparatus will increase. A relationship between wear rate and time can be established by experimental work, Fig.10 shows an example of a wear/ time relationship for one type of condition monitoring apparatus.

By knowing the current rate of wear and comparing it with a predicted wear rate value it is possible to determine -17 -the expected life of the oil. That is to say, for example, if the current wear rate is 0.5 this value can be used to determine how long the oil was run in the experimental case to reach the same level of wear. In this example it can be seen that a measured wear rate of 0.5 corresponds to the position X on the chart shown in Fig.l0 which occurs when the oil was run experimentally.

It will be appreciated that there may be several relationships between time and wear depending upon the duty cycle experienced by the engine and so the actual engine running time could be used to determine which experimental wear/ time relationship best fits the actual operation of the engine. For example, if the engine has been run for 5300 hours and one wear/ time relationship indicates that the rate of 0.5 should be reached after 6000 hours of running and a second wear/ time relationship indicates that a wear rate of 0.5 should be reached after 5500 hours of running then the second relationship would be used as this best matches the actual running of the engine.

Using the selected relationship it is possible to predict when the wear rate will reach further higher rates of wear and so, if for example, a pre-determined wear rate of 2.0 is known to be a wear rate where the oil has degraded to such an extent that serious wear of any component lubricated by the oil is likely to be occurring thereby requiring the oilto be changed, then the predicted time for the oil to degrade from 0.5 to 2.0 using the selected relationship provides a value for the estimated remaining useful life of the oil. In the example shown in Fig.lO the pre-determined wear rate of 2.0 is indicated by the arrow Y and this rate of wear occurs after approximately 8400 hours of engine running. It can therefore be calculated that the remaining life of the oil is 8400-5600 = 2800 hours of actual engine running.

-18 -As shown in step 175 this expected oil life can then be provided to a user of the engine either in terms of time or can be converted into an approximate mileage based upon historical data of the actual running of the engine.

Alternatively, the expected oil life could be stored in a diagnostic unit for downloading by a service technician or could be sent via any suitable communication means to a service organisation so as to enable a service to be arranged with a user of the vehicle to which the engine is fitted when it has been predicted the oil will need to be changed.

The method then proceeds to step 180 where the rate of wear is compared to the pre-determined wear rate such as the 2.0 wear rate and, if the rate of wear is greater than the predetermined wear rate, the method will advance to step 190 where an oil change warning is issued indicating that the useful life of the oil has been reached but otherwise the method advances to step 200 where the current value of wear is saved as Mc ready for the next cycle.

After step 200, the method advances to step 210 where it is determined whether the engine is still running. If the engine is not running then the method terminates at step 250 but if the engine is still running then the method advances to step 220 where the timer is reset to zero.

The method then advances back to step 130 and will cycle through steps 130 to 220 until the engine is stopped when it exits to step 250.

A modification of the method described comprises using a rate of change of wear rate value instead of a wear rate value and comparing the rate of change of wear rate with a predicted rate of change of wear rate value.

-19 -As before the predicted rate of change of wear rate value can be based upon experimental data relating engine running time and wear rate stored in the form of a look up table or can be calculated using an algorithm based upon a relationship between engine running time and wear rate.

In this case the method comprises using the rate of change of wear rate comparison to determine the expected life of the oil and once again would provide an indication of the expected oil life to a user of the engine and a warning of when the useful life of the oil has been reached.

With reference to Fig.9 there is shown a second embodiment method for determining the degradation of a lubricating oil using a condition monitoring apparatus as described above which is in many respects similar to that described above The method starts at step 10 where the system is initialised a timer is set to zero and a value of wear is set to zero and at step 20 an initial or datum value Ni produced from output from a sensor of the condition monitoring apparatus is stored in a memory representing the unworn condition of the sacrificial component of the condition monitoring apparatus.

At step 1000 the engine is started and this is sensed by monitoring the state of an engine run key switch in this case but other means could be used and in addition the timer is started (not shown on Fig.9) At step 1110 it is determined whether the value of Mc is greater than zero. For the very first operation of the engine it will not be and, in this case, the method proceeds to step 1115 where Mc is set to equal Ni. For all subsequent starts of the engine the value of Mc will be greater than zero and so in these cases a stored value of Mc -20 -is used which is the measurement of wear from the sensor when the timer was last zeroed.

At step 1140 it is determined whether a predetermined period of time over which wear is to be checked has elapsed by comparing the current timer value T with a pre-determined time value If the current timer value T is less than the pre-determined time value the system advances to step 1145 where the current timer value T is stored.

It is then determined at step 1148 whether the engine is still running and if it is running the method returns to step 1140 but if the engine is not running the method advances to step 1149 where the method terminates.

As soon as the pre-determined time value has elapsed so that T is greater than T1 the method advances to step 1150 where a current wear measurement M(1) is determined from the signal sent by the sensor of the condition monitoring apparatus and the method advances again to step 1160.

At step 1160 the rate of wear for the test period Ttei is determined. Note that in the case of this embodiment the test period may be many hours of engine running and that whenever the engine is turned off the timer value is stored so that upon re-starting the engine the timer can be restarted.

After the rate of wear is calculated it is used much as before to determine an estimated remaining useful life of the oil. That is to say, at step 1170 the wear rate value is compared with a predicted rate of wear value.

As before, the predicted wear rate value can be based upon experimental data relating engine running time and wear rate stored in the form of a look up table or can be calculated using an algorithm based upon a relationship -21 -between engine running time and wear rate. As before Fig.l0 shows an example of a wear/ time relationship for one type of condition monitoring apparatus which can either be stored in the form of the look up table or be represented by an algorithm and so by determining the current rate of wear and comparing it with a predicted wear rate value derived from the look up table or from the algorithm it is possible to determine the expected life of the oil.

One advantage of this embodiment over that shown in Fig.8, is that the rate of wear can be measured over a long period of time perhaps hundreds of hours and so minor fluctuations in wear are averaged and the magnitude of the wear is larger and so is easier to measure accurately. With the embodiment shown in Fig.8 the wear rate can only be determined when the engine is run long enough for the test period to have elapsed. Therefore, if the test period is one hour, the engine must be run for at least one hour for the value of wear rate to be calculated.

The expected remaining useful life of the oil is then indicated to a user of the engine as indicated in step 1175 or, as referred to above, could be made available to a service technician or service organisation.

The method then advances from step 1170 to step 1180 where a check is made to determine whether the rate of wear determined at step 1160 exceeds a pre-determined maximum wear rate R. This pre-determined maximum wear rate is determined by experimental work and is a rate of wear where the lubricating properties of the oil has been seriously degraded and where the oil is likely to be degrading at a high rate. If the rate of wear determined at step 1160 does exceed the pre-determined maximum wear rate R then the user is notified as indicated by the step 1190 that the oil needs to be changed as soon as possible. This warning could be done by any suitable means.

-22 -If the wear rate determined at step 1160 is not greater than the pre-determined maximum wear rate R the method advances to step 1200 where the current value of wear M(1l) is saved as a new datum wear Mc. Then at step 1210 it is determined whether the engine is still running and, if it is running, the method advances to step 1240 where the timer is reset to zero before retuning to step 1110 whereas, if the engine is not running, the method terminates at step 1250.

A primary advantage of a method according to this method is that, unlike previous methods, it is not necessary to predict when changes to the composition of the oil are likely to affect wear. By directly measuring wear using the condition monitoring apparatus and determining when the wear actually is increasing at a certain rate, the oil can be changed when it actually has degraded rather than when it is predicted to have degraded.

Although the methods described above use the input from only one sensor it will be appreciated that more than one condition monitoring apparatus could be fitted to the engine and that the method may use the outputs from all of these to determine when the oil has degraded or to determine an estimated life of the oil.

It will also be appreciated that the methods described are only examples and the method steps could be performed in a different sequence to those shown and described. In addition it will be appreciated that other methods could be produced from those shown.

Therefore in summary, in accordance with this invention it is proposed to use a sensor that can directly measure the wear characteristics of the oil and so provide an accurate indication of the wear of one or more components in the -23 -engine to determine when the useful life of the oil has been reached.

It will be appreciated by those skilled in the art that although the invention has been described by way of example with reference to one or more embodiments it is not limited to the disclosed embodiments and that one or more modifications to the disclosed embodiments or alternative embodiments could be constructed without departing from the scope of the invention.

For example although the invention has been described with respect to its applications relating to an internal combustion engine it will be appreciated that it could be applied to other types of machines having lubricated components in which it is desirable to determine when the oil used to lubricate key components has degraded such as to cause excessive wear of one or more components such as for example the gears of a gearbox.

Claims

-24 -Claims 1. A method for determining an expected life of a

lubricating oil in a machine having at least one oil lubricated component, wherein the method comprises using a condition monitoring apparatus having a device including a sacrificial component located on the machine in the same environment as the oil lubricated component so as to wear in a similar manner to the oil lubricated component, and a sensor to measure the actual wear of the sacrificial component, using the measured wear to determine a wear parameter and using the wear parameter to provide an expected life of the oil.
2. A method as claimed in claim 1, wherein the wear parameter is a wear rate value indicative of the current wear rate.
3. A method as claimed in claim 2, wherein the method further comprises comparing the wear rate value with a predicted wear rate value to determine the expected life of the oil.
4. A method as claimed in claim 3, wherein the predicted wear rate value is based upon experimental data relating machine running time and wear rate stored in the form of a look up table.
5. A method as claimed in claim 3, wherein the predicted wear rate value is calculated using an algorithm based upon a relationship between machine running time and wear rate.
6. A method as claimed in claim 1, wherein the wear parameter is a rate of change of a wear rate value.

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7. A method as claimed in claim 6, wherein the method further comprises comparing the rate of change of wear rate value with a predicted rate of change of wear rate value to determine the expected life of the oil.
8. A method as claimed in claim 7, wherein the predicted rate of change of wear rate value is based upon experimental data relating machine running time and wear rate stored in the form of a look up table.
9. A method as claimed in claim 7, wherein the predicted rate of change of wear rate value is calculated using an algorithm based upon a relationship between machine running time and wear rate.
10. A method as claimed in any of claims 7 to 9, wherein the method further comprises providing an indication of the expected oil life to a user of the machine.
11. A method as claimed in claim 2, wherein the method further comprises comparing the wear rate value with a pre-determined wear rate value and providing an indication to the user of the machine that the oil requires replacing when the wear rate value is greater than the pre-determined wear value.
12. A method as claimed in any of claims 1 to 11, wherein the machine is an internal combustion engine.
13. A method for determining degradation of a lubricating oil in an engine substantially as described herein with reference to the accompanying drawings.