GB2494648A - A method for controlling an engine stop-start system - Google Patents

Abstract

A method for controlling the operation of an engine idle stop-start system is disclosed in which, if the time taken to start an engine controlled by the engine stop-start system exceeds a predefined limit, operation of the engine stop-start system is inhibited so that normal stop-start operation does not occur during at least the current drive cycle. This prevents excessive use of a starting system for the engine which can result in premature failure of the starting system and also reduces negative reactions from a user of the motor vehicle due to the slow or delayed engine starting time.

Description

A Method for Controlling an Engine Stop-Start System.

This invention relates to a motor vehicle having an engine stop-start system to automatically stop and start an internal combustion engine of the motor vehicle and in particular to a method for controlling such an engine stop-start system.

It is known to provide a motor vehicle with an engine stop-start system for automatically stopping and starting the engine whenever it is determined from driver actions that there is an opportunity to do so in order to improve fuel consumption and reduce emissions from the engine.

It is a problem with such engine stop-start systems that they significantly increase the wear and/ or deterioration of components associated with a starting system for the engine such as for example a starter motor and a battery.

It is a further problem that if the time taken to restart the engine following a stop is excessive due to malfunction of the starting system or for any other reason this further increases the wear/ and or deterioration of the starting system components and also often leads to dissatisfaction in a user of the motor vehicle and may also result in actual use problems due to the driver engaging the clutch fully before the engine has fully restarted thereby resulting in an engine stall.

It is an object of this invention to provide a method for controlling the operation of an engine stop-start system in order to minimise the problems associated with the prior art.

According to a first aspect of the invention there is provided a method for controlling an engine stop-start system of a motor vehicle wherein the method comprises measuring the time taken for an engine controlled by the engine stop-start system to start and controlling the operation of the engine stop-start system based upon the result of the measuring step.

If the time taken for the engine to start is greater than the predefined limit the operation of the engine stop-start system may be controlled so as to inhibit stop-start operation.

The method may further comprise only inhibiting stop-start operation if the predefined limit has been exceeded more than a pre-defined number of times.

If the time taken for the engine to start is less than a predefined limit the operation of the engine stop-start system may be controlled so as to permit normal stop-start operation.

Each start time may be combined with an average of previous start times to produce a rolling average start time that is compared with the pre-defined limit.

If the time taken for the engine to start is greater than a second predefined limit that is higher than the predefined limit the operation of the engine stop-start system may be controlled so as to deactivate stop-start operation.

The method may further comprise alerting a user of the engine if operation of the engine stop-start system is one of inhibited and deactivated.

The time to start the engine may be measured for a period commencing when a command to restart the engine is produced to a point in time where a pre-determined criterion has been met.

The criterion may be the attainment by the engine of a pre-defined rotational speed.

According to a second aspect of the invention there is provided an engine stop-start system for a motor vehicle having an electronic processor arranged to automatically stop and start an engine based upon predefined criteria wherein the electronic processor is operable to measure the time taken for the engine to start following a command for an engine start and control the operation of the engine stop-start system based upon the result of the measuring step.

If the time taken for the engine to start is greater than the predefined limit the electronic processor may be operable to inhibit stop-start operation.

If the time taken to start is greater than a second predefined limit that is greater than the predefined limit the electronic processor may be operable to deactivate stop-start operation.

If operation of the engine stop-start system is one of inhibited and deactivated, the electronic processor may be further operable to activate a warning device so as to alert a user of the engine.

According to a third aspect of the invention there is provided a motor vehicle having an engine stop-start system constructed in accordance with said second 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 representation of a motor vehicle having an engine stop-start system according to a second aspect of the invention; Fig.2 is a high level flow chart showing the actions performed by the engine stop-start system including steps forming a first embodiment of a method for controlling the engine stop-start system according to a first aspect of the invention; and Fig.3 is a high level flow chart showing the actions performed by the engine stop-start system including steps forming a second embodiment of a method for controlling the engine stop-start system according to the first aspect of the invention.

With reference to Fig.1 there is shown a motor vehicle having an engine 10 driving a multi-speed transmission 11.

The transmission 11 is driveably connected to the engine 10 by a clutch (not shown) which is manually engaged or released by a driver of the motor vehicle 5 and has a gear selector (not shown) . The gear selector is moveable between several positions including at least one position where a gear forming part of the multi-speed transmission is selected and a neutral position in which no gears of the multi-speed transmission are selected. When the gear selector is moved to the neutral position the multi-speed transmission 11 is said to be in a neutral state in which drive cannot be transmitted by the multi-speed transmission and when the gear selector is moved to an in gear position the multi-speed transmission II is said to be in an in gear state in which drive can be transmitted by the multi-speed transmission.

An engine starter in the form of an integrated starter-generator 13 is driveably connected to the engine 10 and in this case is connected by a flexible drive in the form of a drive belt or chain drive 14 to a crankshaft of the engine 10. The starter-generator 13 is connected to a source of electrical energy in the form of a battery 15 and is used to start the engine 10 and which is recharged by the starter-generator when it is operating as an electrical generator.

The invention is not limited to the use of a starter-generator 13 and the starter-generator 13 could be replaced by a starter motor for starting the engine 10.

is It will be appreciated that during starting of the engine 10 the starter-generator 13 drives the crankshaft of the engine 10 and that at other times the starter-generator is driven by the engine 10 to generate electrical power.

A driver operable on-off device in the form of a key operable ignition switch (not shown) is used to control the overall operation of the engine 10. That is to say, when the engine 10 is running the ignition switch is in a key-on' position and when the ignition switch is in a key-off' position the engine 10 is not able to run. The ignition switch also includes a third momentary position used to manually start the engine 10. It will be appreciated that other devices may be used to provide this functionality and that the invention is not limited to the use of an ignition switch.

An electronic control unit 16 is connected to the starter-generator 13, to the engine 10, to a gear selector sensor 12 used to monitor whether the transmission 11 is in neutral or in gear, to an engine speed sensor 21 used to measure the rotational speed of a crankshaft 20 of the engine 10, to a brake pedal position sensor 24 used to monitor the position of a brake pedal 23, to an clutch pedal position sensor 26 used to monitor the position of a clutch pedal 25 and to a throttle position sensor 19 used to monitor the position of an accelerator pedal 18. The accelerator pedal 18 provides a driver input of required power output from the engine 10. If the accelerator pedal 18 has been moved from a rest position it is said to be in a pressed position or in a pressed state.

It will be appreciated that the term gear selector sensor is not limited to a sensor that monitors the position of the gear selector but rather is any device which can provide a feedback of whether the transmission 11 is in gear or in neutral.

Similarly, the term brake pedal sensor is not limited to a sensor that monitors the position of the brake pedal but rather is any device that provides feedback of whether an operator of the motor vehicle 5 has applied pressure to the brake pedal 23 to apply the brakes of the motor vehicle 5. For example the brake pedal sensor could monitor the pressure of the fluid in one or more brake lines. When the brake pedal 23 has been pressed sufficiently to apply the brakes it is said to be in a pressed state or in a pressed position.

In this case the clutch pedal position sensor comprises of first and second switches SW1 and SW2 (not shown) which are arranged to give an indication when the clutch pedal 25 is towards either end of its travel. This is achieved by opening or closing the switches SWl and SW2 when the clutch pedal 25 reaches certain positions. If the travel of the clutch pedal 25 is said to be zero percent when it is not being operated that is to say when it is an un-pressed state and one hundred percent when it is pressed to the limit of its travel that is to say when it is in a pressed state then the switch positions may correspond in one example to travel percentages of 10% for the first switch and 75% for the second switch. When the clutch pedal 25 is at 10% or less than 10% of its travel the first switch will be closed (SW1 = 1 and a high side signal will be sent to the electronic control unit 16 confirming this and when the clutch pedal 25 is at 75% or more than 75% of its travel the second switch will be closed SW2 =1 and a low side signal will be sent to the electronic control unit 16 confirming this. When the clutch pedal 25 is between 10% and 75% of its travel no signal will be sent by either switch SW1 and SW 2 = 0. When the clutch pedal is in the pressed state it is said to be in a pressed position and the clutch is disengaged and when it is in the un-pressed state it is said to be released or in an un-pressed position and the clutch is engaged.

Note that when the SW = 1 signal is sent from the first switch the clutch will definitely be engaged and when the signal 5W2 =1 is sent from the second switch the clutch will definitely be disengaged.

As an alternative to this arrangement the actual position of the clutch pedal can be monitored using a single sensor such as a rotary potentiometer and the determination of when the clutch is engaged or disengaged can then be performed by the electronic control unit 16 using the signal received from the position sensor. In this case the high and low side clutch signals representing positions of the clutch pedal 25 where it is known the clutch will be engaged or disengaged would be determined by the electronic control unit 16 based upon the signal received from the clutch pedal position sensor.

The electronic control unit 16 receives several signals from the engine 10 including a signal indicative of the rotational speed of the engine 10 from the engine speed sensor 21 and sends signals to the engine 10 used to control shutdown and start-up of the engine 10. In this case the engine 10 is a spark ignited engine 10 and the signals sent from the electronic control unit 16 are used to control a fuel supply system (not shown) for the engine 10 and an ignition system (not shown) for the engine 10. If the engine 10 were to be a diesel engine then only the fuel supply to the engine would be controlled.

The electronic control unit 16 comprises of various components including a central processing unit, memory devices, one or more electronic processors, timers and signal processing devices to convert the signals from the sensors connected to the electronic control unit 16 into data which is used by the electronic control unit 16 to control the operation and in particular the automatic stopping and starting of the engine 10.

The electronic control unit 16 is also connected to a driver warning device which in this case is in the form of a human machine interface 17 located on a control panel of the motor vehicle 5.

During normal engine running the electronic control unit 16 is operable to control the fuel supplied to the engine 10 and to adjust the ignition system so that sparks are supplied to the engine 10 from spark plugs at the correct timing to produce the desired engine torgue.

The electronic control unit 16 controls the operation of the engine 10 which is operable in two modes, a first or stop-start running mode and a second or continuous running mode. However, it will be appreciated that one or more separate electronic controllers could be used to control the normal running of the engine 10 and the electronic controller 16 may only control the switching of the engine 10 between the two modes of operation and the automatic stopping and starting of the engine 10.

All of the components used to stop and start the engine in response to driver actions form in combination the engine stop start system of which the electronic control unit 16 is a major component.

One factor used in the case of a conventional engine stop-start system to determine whether the engine 10 is operated in the second mode or in the first mode is whether the motor vehicle 5 is moving. If the motor vehicle 5 is moving the engine is operated in the second mode and the engine 10 will be run continuously and, if the motor vehicle is not moving, the engine 10 will normally be run in the first mode in which automatic stop-start operation of the engine will occur. However, the electronic control unit 16 in accordance with this invention is further operable to determine whether it is appropriate to run the engine 10 in the first mode by checking one or more engine operating parameters such as the time taken to start the engine 10 before permitting operation in the first mode, as discussed in more detail hereinafter with respect to Figs.2 and 3.

In the first or stop-start mode the engine 10 is selectively stopped and started by the electronic control unit 16 without driver intervention when one or more predetermined engine stop and start conditions exist. These stop and start conditions are based upon the actions of the driver as provided by the signals received by the electronic control unit 16 from the throttle sensor 19, the brake sensor 24, the clutch sensor 26 and the gear selector sensor 12. The position or state of the clutch pedal 25, the accelerator pedal 18, the brake pedal 23 and the transmission 11 are all different motor vehicle variables which can be used to control the operation of the engine 10.

The specific conditions used for the purpose of this example are that the engine 10 is stopped when the transmission 11 is in neutral and the clutch pedal 25 is not -1O -being depressed OWl =1 and is started when the clutch pedal is depressed SW2 =1. such a system is often referred to as a stop in neutral system. It will however be appreciated by those skilled in the art that various other combinations of driver action could be used to control stopping and starting of the engine.

The sequence of events for an engine stop-start cycle are the state of switch Owl changes from SWl= 1 to Owl = 0 and the status of switch 5W2 changes from 5W2 = 0 to sW2 = 1 in response to the driver pressing the clutch pedal 25, a neutral position is then selected in the transmission 11.

The driver will then release the clutch pedal 25 so that the status of the switch OWl changes from Owl = 0 to Owl = 1 and the status of switch 0W2 changes from 0W2 = 1 to SW2 = 0 and the engine 10 is stopped when neutral is detected a OWl = 1.

Then when the driver presses the clutch pedal 25 to engage a gear the status of switch OWl changes from SW1= 1 to swi = 0 and the state of switch 0W2 changes from 0W2 = 0 to 5W2 = 1 the changing of the status of the switch 0W2 from 0W2 =0 to 8W2 = 1 is used as an indication that a start is required.

It will be appreciated that time reguired for the driver to press the clutch pedal 25 and engage a driving gear while the switch SW2 status remains at 5W2 = 1 is when the engine 10 is ideally restarted because during this period of time there is no additional drag upon the engine 10. Therefore by the time the status of the switch 0W2 changes to 0W2 =0 the engine 10 should preferably be restarted and running if this is not the case then an invalid start will result and in some cases stalling of the engine 10 could occur. For a normal restart the time period during which the clutch pedal 25 is pressed sufficiently to keep the clutch disengaged (SW2 status remains at 5W2 = 1) is in the region of 2 seconds and so the engine 10 must -11 -start in less than this amount of time if problems are to be avoided.

When the engine 10 is operating in the second mode it is run continuously so long as the ignition switch remains in the on' position.

The measurement of motor vehicle speed may be via the use of a road wheel sensor or any other convenient means.

A first embodiment of a method according to the invention will now be described with reference to Fig.2.

The method starts at box 100 which is a key-on event. is

Then in step 110 the method checks whether the engine stop start system is currently deactivated' or inhibited' The term deactivated' as meant herein is that normal operation of the engine stop-start system has been terminated so that the engine will be permanently operated in the second mode of operation until external intervention has occurred such as for example the resetting of the engine stop-start system.

The term inhibited' as meant herein is that normal operation of the engine stop-start system has been temporarily terminated so that the engine will be operated during the current operating cycle in the second mode of operation. However, the engine stop-start system in this case is reset by a key-off event and so will revert to normal operation (engine operating in first mode) when the next key-on event occurs.

The test in box 110 may therefore comprise:-Check value of two flags Fl and F2; -12 -if Fl and F2 <1 then use normal (first) mode; if Fl = 1 then inhibit operation; and if F2 = 1 then deactivate operation.

other tests could be used and the invention is not limited to the use of such a test.

Therefore if the test result from box 110 is such that the engine stop-start system is to be inhibited or deactivated no further action is taken and the method advances via box 115 to box 280 to check whether a key-off event has occurred, if it has, the method ends at box 300 by saving values for the two flags Fl and F2 after setting flag Fl equal to zero and keeping flag F2 at its current value.

If it there has not been a key-off event in box 280, the method returns to box 110 where the flags Fl and F2 are read again and where the engine system has been deactivated will cycle continuously through the boxes 110, 115 and 280 until the flag F2 is reset to zero by outside intervention.

In the case where there has not been a key-off event in box 280 and the engine stop start system has been inhibited the method will as before cycle continuously through the boxes 110, 115 and 280 but in this case the flag Fl will eventually be reset to zero when a key-off event as indicated in box 300 occurs.

If the test result from box 110 indicates that the engine stop-start system is not currently deactivated or inhibited the method advances to box 120 which is a test to determine whether the engine 10 is to be automatically stopped. If the engine 10 is not to be stopped the method advances from box 120 to box 280 to check whether a key-off event has occurred, if it has, the method ends at box 300 and, if it has not, the method returns to box 110.

-13 -Returning now to box 120 if the conditions for an engine stop are present the method advances to step 130 and the engine 10 is stopped.

Then in box 140 the engine restart conditions are checked for and this process will continue until a positive result is reached at which point the method advances to box 150. In this case the engine restart conditions are a single condition namely that the clutch pedal 25 is pressed.

The generation of an engine start request in box 150 simultaneously starts a timer running in the electronic control unit 16 to measure the time taken for the engine to start as indicated in box 200 and this starts the key steps is of the method which also include the steps indicated in boxes 210 to 275.

In the case of this example, the time taken to start is the time from the point when the engine start signal is produced to a time where the engine 10 has reached a pre-defined speed, which in this case, is 700RPM but could be another speed for different engine types. When the engine reaches this speed, as indicated by the engine speed sensor 21, the timer in the electronic control unit 16 is stopped and the elapsed time (Ts) is saved in memory.

The method then advances to box 210 where the validity of the time measurement is checked. For example, starts interfered with by driver are ignored (e.g. if clutch is brought up too quickly before the engine has started) . If the start is not a valid one the method moves from box 210 to box 280 to check whether a key-off event has occurred, if it has, the method ends at box 300 as discussed above otherwise it returns to box 110.

-14 -If in box 210 the start is oonfirmed to be a valid one, then the method advances to box 220 to perform a comparison of the measured start time with a predefined maximum time (Ts Max) Is Max is a period of time that is much longer than it would normally take to start the engine 10 and which is indicative that a serious problem exists preventing efficient starting of the engine 10. For example and without limitation, if the expected time to start the engine when all components are in a new or fully functioning condition is 0.6 seconds then Ts Max could be set to 2.0 seconds.

is If the time taken to start the engine 10 exceeds Ts Max then the method advances to box 230 where operation of the engine stop start system is deactivated (second mode selected) and then in box 235 the flag F2 is set to 1 and saved in memory for reading in box 110 when box 110 is next entered. The method then continues from box 235 to box 270 where a driver is alerted of the deactivation via the human machine interface 17 under the control of the electronic control unit 16 and then advances to box 275 where it advances to box 280. Control options for box 280 are described above and will not be described again.

On the other hand, if in box 220 the engine start time Ts is not greater than Ts Max, then the method advances to box 240 where the current value of start time is added to an existing average start time for the current engine operating cycle.

This may be a simple averaging of an existing average value Ts Avg with the new value Ts such as [ (Ts Avg + Ts) /2] or may be based upon an eguation such as the equation:- -15 -Is Avg = Is Avg0ld + [(Ts -Is Avg0-d)/ NI Where: -Is Avg0JCI = existing value of average start time; I5ew = new acquired value of start time; and N = a number equal to or greater than 1.

For example, if Ts Avg!-j = 0.65 5, Tsew = 0.67 s and N= 5 Then Is Avg = 0.65 + [(0.67 -0.65)/SI = 0.654 seconds Compared to a result of 0.66 seconds if simple averaging is used. is

The use of such an equation reduces the risk of system error if a rogue value of I5rpw is produced.

The method then advances from box 240 to box 250 where the IS Avg value is compared with a predefined limit which in this case is a value much closer to the expected start time and which defines a start time that will produce wear or degradation of the starting system for the engine or create significant driver dissatisfaction.

For example the test may be is Is Avg > 0.85 using the data referred to above for a start.

If the value of Ts Avg exceeds the limit Ts Avg Max then the method advances to box 260 where operation of the engine stop-start system is inhibited by operating the engine in the second mode of operation for the rest of the current operating cycle. That is to say, operation of the engine stop-start system is inhibited until there has been a key-off' and subsequent key-on' event. This achieved by setting in box 260 the flag Fl to a value of 1 and resetting in box 300 the flag Fl = 0.

-16 -The flag Fl value is read whenever the method returns to box 110 therefore resulting in this case in the method looping through the boxes 110, 115 and 280 for the current operating cycle once the flag Fl has been set to equal unity until a key-off event occurs in box 280.

Returning to box 260 after completing the inhibiting of the engine stop-start system the method advances to box 270 where the driver is alerted of the inhibiting of operation via the human machine interface 17 under the control of the electronic control unit 16 and then advances to box 275 and from there to box 280 the control options of which are described above.

It will be appreciated that the alert provided in box 270 may be different for a deactivation event and a inhibiting event.

A second embodiment of a method according to the invention will now be described with reference to Fig.3.

The second embodiment is identical to that described with respect to the first embodiment described above with respect to boxes 100, 115, 120, 130, 140, 150, 200, 210 and 280 but in this case only inhibiting of the engine stop start system occurs there is no deactivation with the disclosed method although this could be added if required.

The same reference numerals have been used for these boxes and the operations performed in these boxes are not described again in detail.

The method starts in box 100 which is a key-on event and advances to box 1110 which is equivalent to box 110 previously described and in step 1110 the method checks whether the engine stop start system is currently inhibited' -17 -The term inhibited' has the same meaning as described above -The test in box 1110 therefore comprises the checking of the value of the flag Fl and, if Fl < 1, using the normal stop-start mode of operation for the engine stop-start system. Conversely, if Fl = 1, then operation of the engine stop-start system is inhibited.

Other tests could be used and the invention is not limited to the use of such a test.

Therefore if the test result from box 1110 is such that is the engine stop-start system is to be inhibited no further action is taken and the method advances via box 115 to box 280 to check whether a key-off event has occurred, if it has, the method ends at box 1300 by setting flag Fl and the counter N equal to zero.

If it there has not been a key-off event in box 280, the method returns to box 1110 where the flag Fl is read again and the method will cyole continuously through the boxes 1110, 115 and 280 until there is a key-off event at which time the flag Fl and the counter N are reset to zero as indicated in box 1300.

If the test result from box 1110 indicates that the engine stop-start system is not currently inhibited the method advances to box 120 which is a test to determine whether the engine 10 is to be automatically stopped. If the engine 10 is not to be stopped the method advances from box 120 to box 280 to check whether a key-off event has occurred, if it has, the method ends at box 1300 and, if it has not, the method returns to box 1110.

-18 -Returning now to box 120 if the conditions for an engine stop are present the method advances to step 130 and the engine 10 is stopped.

Then in box 140 the engine restart conditions (clutch pressed) are checked for and this process will continue until a positive result is reached at which point the method advances to box 150. The generation of an engine start reguest in box 150 simultaneously starts a timer running in the electronic control unit 16 to measure the time taken for the engine to start as indicated in box 200. As before, the time taken to start is the time from the point when the engine start signal is produced to a time where the engine has reached a pre-defined speed which in this case is 700RPM. The value of 700Rpm is a stable engine speed from which normal running of the engine 10 can be expected to result.

When the engine 10 reaches 700RPM, as indicated by the engine speed sensor 21, the timer in the electronic control unit 16 is stopped and the elapsed time (Is) is saved in memory.

In box 210 the validity of the time measurement is checked as before and if the start is not a valid one the method moves from box 210 to box 280 the control options of which have previously been discussed and, if in box 210 the start is confirmed to be a valid one, then the method advances to box 1220 to perform a comparison of the measured start time with a predefined time limit (IsLim) Tstim is a period of time that is longer than it would normally take to start the engine 10 and which is indicative that a problem exists preventing efficient starting of the engine 10. For example and without limitation, if the expected time to start the engine when all components are in -19 -a new or fully functioning condition is 0.6 seconds then TsLim may be set to 0.9 seconds.

If the time taken to start the engine 10 exceeds TsLim then the method advances to box 1230 where a counter is incremented by one (N = N + 1) . Then in box 1240 it is checked whether the counter has exceeded a predefined limit NLim.

For example NLim could be set to the value 2, therefore if the test at 1220 is met more than twice it is taken as an indication that an on-going degradation in starting performance is occurring and the method advances to box 1250 otherwise it returns from box 1240 to box 280 and if a key-off event has not occurred to box 1110 with a flag value of Fl = 0 so that operation is not inhibited and the steps from 1110 to 1240 will be repeated.

Conversely, if the test in box 1240 is met, the method advances from box 1240 to box 1250 where operation of the engine stop-start system is inhibited by operating the engine in the second mode of operation for the rest of the current operating cycle. That is to say, operation of the engine stop-start system is inhibited until there has been a key-off' and subsequent key-on' event. This achieved by setting in box 1250 the flag El to a value of 1 which will be read when the method returns via box 280 to box 1110 and by resetting in box 1300 the flag Fl and the counter N equal to zero following a key-off event in box 280.

When the flag Fl value is read in box 1110 it will result in the method looping through the boxes 1110, 115 and 280 for the current operating cycle once it has been set to Fl = 1, that is to say, until a key-off event occurs in box 280.

-20 -Returning to box 1250 after completing the inhibiting of the engine stop-start system the method advances to box 1260 where the driver is alerted of the inhibiting of operation via the human machine interface 17 under the control of the electronic control unit 16 and then advances to box 12805 and from there to box 280 the output options of which are described above.

It will be appreciated that if in box 1300 flag £1 is not set to zero and the counter N is not set to zero then the method could be used to provide deactivation of the engine stop-start system and the flag £1 and the counter N would need to be reset by external intervention such as resetting by a service operator, a user of the vehicle or the electronic control unit which could be a pcwertrain control module could monitor the manual keyed start times to see if these improve to a sufficient level and could then automatically reactivate the stop-start operation.

It will be appreciated that the steps described in the methods described above are provided by way of example and that a different sequence of steps or a combination of steps from the two methods could be used.

Therefore in summary, by using one of the methods

described above unnecessary wear or user dissatisfaction can be reduced or avoided by monitoring starting performance of the engine and preventing the operation of the engine 10 in the first (stop-start) mode of operation if the performance has dropped below a pre-defined level. The use of a simple time measurement eliminates the need for complex diagnostic routines or equipment that would otherwise be reguired to provide an indication of a degradation in starting performance.

It will be appreciated that many factors can cause such a degradation in performance such as low state of charge of -21 -the battery used to power the electric starting device (starter motor), a fault or problem with the operation of the starting device, ignition problems such as a faulty spark plug or incorrect ignition timing and fuelling problems such as a faulty fuel injector or erroneous fuel timing. The inventors have realised that instead of trying to analyse all of such potential problems involved with a degraded start performance it is advantageous to measure only the consequence of such problems in the manner described above.

It will be further appreciated that only the operational features of the engine stop-start system required to explain this invention are discussed in detail and that other factors may determine when operation in the first mode is permitted.

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.

Claims (1)

1. <claim-text>-22 -Claims 1. A method for controlling an engine stop-start system of a motor vehicle wherein the method comprises measuring the time taken for an engine controlled by the engine stop-start system to start and controlling the operation of the engine stop-start system based upon the result of the measuring step.</claim-text> <claim-text>2. A method as claimed in claim 1 wherein If the time taken for the engine to start is greater than a predefined limit the operation of the engine stop-start system is controlled so as to inhibit stop-start operation.</claim-text> <claim-text>3. A method as claimed in claim 2 wherein the method further comprises only inhibiting stop-start operation if the predefined limit has been exceeded more than a pre-defined number of times.</claim-text> <claim-text>4. A method as claimed in claim 2 or in claim 3 wherein if the time taken for the engine to start is less than the predefined limit the operation of the engine stop-start system is controlled so as to permit normal stop-start operation.</claim-text> <claim-text>5. A method as claimed in any of claims 2 to 4 wherein each start time is combined with an average of previous start times to produce a rolling average start time that is compared with the predefined limit.</claim-text> <claim-text>6. A method as claimed in any of claims 2 to 5 wherein if the time taken for the engine to start is greater than a second predefined limit that is higher than the predefined limit the operation of the engine stop-start system is controlled so as to deactivate stop-start operation.</claim-text> <claim-text>-23 - 7. A method as claimed in any of claims 1 to 6 wherein the method further comprises alerting a user of the engine if operation of the engine stop-start system is one of inhibited and deactivated.</claim-text> <claim-text>8. A method as claimed in any of claims 1 to 7 wherein the time to start the engine is measured for a period commencing when a command to restart the engine is produced to a point in time where a pre-determined criterion has been met.</claim-text> <claim-text>9. A method as claimed in claim 8 wherein the criterion is the attainment by the engine of a pre-defined rotational speed.</claim-text> <claim-text>10. An engine stop-start system for a motor vehicle having an electronic processor arranged to automatically stop and start an engine based upon predefined criteria wherein the electronic processor is operable to measure the time taken for the engine to start following a command for an engine start and control the operation of the engine stop-start system based upon the result of the measuring step.</claim-text> <claim-text>11. A system as claimed in claim 10 wherein if the time taken for the engine to start is greater than the predefined limit the electronic processor is operable to inhibit stop-start operation.</claim-text> <claim-text>12. A system as claimed in claim 11 wherein if the time taken to start is greater than a second predefined limit that is greater than the predefined limit the electronic processor is operable to deactivate stop-start operation.</claim-text> <claim-text>13. A system as claimed in claim 11 or in claim 12 wherein, if operation of the engine stop-start system is one -24 -of inhibited and deactivated, the electronic processor is further operable to activate a warning device so as to alert a user of the engine.</claim-text> <claim-text>14. A motor vehicle having an engine stop-start system as claimed in any of claims 10 to 13.</claim-text> <claim-text>15. A method for controlling an engine stop start system of a motor vehicle substantially as described herein with reference to the accompanying drawing.</claim-text> <claim-text>16. An engine stop-start system for a motor vehicle substantially as described herein with reference to the accompanying drawing.</claim-text> <claim-text>17. A motor vehicle substantially as described herein with reference to the accompanying drawing.</claim-text>