GB2444941A

GB2444941A - A method of controlling engine speed during a manual gearshift

Info

Publication number: GB2444941A
Application number: GB0623846A
Authority: GB
Inventors: Nicholas Dashwood Crisp; Peter Douglas Devonport; Jonathan Willey
Original assignee: Ford Global Technologies LLC
Current assignee: Ford Global Technologies LLC
Priority date: 2006-11-30
Filing date: 2006-11-30
Publication date: 2008-06-25
Also published as: GB0722829D0; GB2445062B; GB2445062A; GB2445062A8; GB2445062B8; DE102007057526A1; GB0623846D0; DE102007057526B4

Abstract

An engine (10, fig 1) of a motor vehicle (5) is connected to a manual gearbox (11) by a manual clutch (18). A Method of controlling the engine during a manual gearshift comprises in step 10 monitoring a state of, for example, an ignition switch (17), in step 20 it is determined by a position of a clutch pedal (25) whether a gear change has been initiated, in step 30 the type of gear change is established by using output from an accelerator pedal (24) in combination with a gear position sensor (12), in step 40 a target engine speed NTGT is determined, in step 50 it is ascertained whether the target engine speed NTGT is greater than an engine speed NDEM demanded by a driver, if yes the method moves to step 60 where the engine speed NDEM is driven towards the target engine speed NTGT and in step 70 with the engine speed NDEM at the target engine speed NTGT where it is held until confirmed that a selected gear is engaged. The method uses an electronic controller to assist the driver with gear changes which may be of different types such as accelerating upshift/down shifts and/or decelerating upshifts/downshifts.

Description

A Method for Controlling an Engine This invention relates to a motor

vehicle having a manual gearbox and a manually operable clutch to driveably connect the gearbox to an engine of the motor vehicle and in particular to a method for controlling the speed of the engine during a gear change.

It is well known to provide a motor vehicle with a manual gearbox and a manually operable clutch to driveably connect the gearbox to an engine. It is a problem with such an arrangement that it requires considerable skill and experience in order to effect a gear change without producing lurching of the motor vehicle or excessive slip in the clutch.

It is an object of the invention to provide a method that permits such a motor vehicle to be driven more easily.

According to a first aspect of the invention there is provided a method for controlling an engine of a motor vehicle having a manual gearbox and a manually operated clutch during a gear change the method comprising determining a target engine speed based upon the type of gear change taking place and controlling the engine during the gear change to drive the engine speed towards the target engine speed.

If the type of gear change is an accelerating downshift, the target engine speed may be greater than a predicted input speed of the gearbox at the end of the change in gear.

Alternatively, if the type of gear change is a decelerating downshift, the target engine speed may be less than a predicted input speed of the gearbox at the end of the change in gear.

As yet a further alternative, if the type of gear change is one of a decelerating upshift, a substantially constant road speed upshift and a substantially constant road speed downshift, the target engine speed may be substantially equal to a predicted input speed of the gearbox at the end of the change in gear.

As yet one more alternative, if the type of gear change is an accelerating upshift, the target engine speed may be greater than a predicted input speed of the gearbox at the end of the change in gear.

The engine speed may be driven to one of the greater of the target engine speed and an engine speed demanded by a driver of the motor vehicle using a driver controlled engine demand device and an engine torque demand equivalent to the target engine speed and an engine torque demanded by a driver of the motor vehicle using a driver controlled engine demand device.

The method may further comprise predicting the type of gear change from the position of a driver controlled engine demand device.

The driver controlled engine demand device may be an accelerator pedal.

The type of gear change may be predicted by combining the position of the driver controlled engine demand device and a sensed change in selected gear.

The sensed change in selected gear may be sensed by a gear selector sensor.

The method may further comprise at least one of determining the road speed of the motor vehicle, determining when the clutch is moved from an engaged to a disengaged position, measuring the speed of the engine and determining starting and ending gears for the change in gear.

According to a second aspect of the invention there is provided a motor vehicle having a manual gearbox, an engine, a manually operated clutch to selectively driveably connect the engine to the gearbox and an electronic controller to assist with gear changes wherein the electronic controller lo is operable to determine a target engine speed based upon the type of gear change taking place and control the engine during the change in gear to drive the engine speed towards the target engine speed.

If the type of gear change is an accelerating downshift, the controller may be operable to drive the engine to a target engine speed that is greater than a predicted input speed of the gearbox at the end of the change in gear.

Alternatively, if the type of gear change is a decelerating downshift, the controller may be operable to drive the engine to a target engine speed that is less than a predicted input speed of the gearbox at the end of the change in gear.

As a further alternative, if the type of gear change is an accelerating upshift, the controller may be operable to drive the engine to a target engine speed that is greater than a predicted input speed of the gearbox at the end of the change in gear.

As yet a further alternative, if the type of gear change is one of a decelerating upshift, a substantially constant road speed upshift and a substantially constant road speed downshift, the controller may be operable to drive the engine to a target engine speed that is substantially equal to a predicted input speed of the gearbox at the end of the change in gear.

The engine speed may be driven to the greater of the target engine speed and an engine speed demanded by a driver of the motor vehicle using a driver controlled engine demand device.

The motor vehicle may further comprise predicting the type of gear change from the position of a driver controlled engine demand device.

The driver controlled engine demand device may be an accelerator pedal.

The motor vehicle further comprises at least one of a means for determining the road speed of the motor vehicle, a means for determining when the clutch is moved from an engaged to a disengaged position, a means for measuring the speed of the engine and a means for determining starting and ending gears for the change in gear.

The invention will now be described by way of example with reference to the accompanying drawing of which:-Fig.l is a schematic diagram of a motor vehicle according to the invention; Fig.2 is a look-up table containing values of speed offset for various types of gear change; Fig.3 is a chart showing various sensor combinations suitable for use with the invention; Fig.4 is a flow chart of one embodiment of a method according to the invention; Fig.5 is a chart showing various variables during an assisted gear change of an accelerating downshift type; Fig.6 is a chart showing various variables during an assisted gear change of a decelerating downshift type; and Fig.7 is a chart showing various variables during an assisted gear change of a non-accelerating upshift type.

With reference to Fig.l there is shown a motor vehicle having an engine 10 driving a multi-speed transmission 11 via disengageable manually operable clutch 18. 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. 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 can if required be driven by the engine 10 to generate electrical power. The starter-generator 13 is connected to an electrical load which in this case is in the form of a battery 15. The battery is used to start the engine 10 by powering the starter-generator 13 and is recharged by the starter-generator 13 when the starter-generator 13 is operating as an electrical generator. It will be appreciated that other means such as a starter motor could be used to start the engine and an alternator could be used to generate electricity to recharge the battery.

It will be appreciated that other electrical loads could be connected to the starter-generator 13 by any known means.

A driver operable on-off device in the form of a key operable ignition switch 17 is used to control the overall operation of the engine 10. That is to say, when the engine is running the ignition switch 17 is in an on' position and when the ignition switch 17 is in an off' position the engine 10 is not able to run. The ignition switch 17 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 determine which gear has been selected, to a road speed sensor 21 used to measure the rotational speed of a road wheel 20 of the vehicle 5, to an accelerator pedal is position sensor 24 used to monitor the position of an accelerator pedal 23 and to a clutch pedal position sensor 26 used to monitor the position of a clutch pedal 25. This arrangement of sensors is referred to as option 1 in Fig.3.

It will be appreciated that other means for obtaining the road speed could be used and that the invention is not limited to the use of a road speed sensor that senses road wheel speed.

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 an engine speed sensor 27 and sends various signals to the engine 10 used to control operation of the engine 10.

During normal engine running the electronic control unit 16 is operable to control the engine 10 to produce the engine torque desired by the driver. it will be appreciated that various means are used to control engine output depending upon the type of engine used and that the invention is not limited to any specific means.

The electronic control unit 16 is further operable to control the rotational speed of the engine 10 during a gear change so as to improve the quality of the gear change by either increasing the engine 10 speed or reducing the engine speed. In addition, the electronic control unit 16 is operable to increase the load on the starter-generator 13 by switching in more electrical load if the rate of slowing of the engine 10 due to friction alone is insufficient.

It will be appreciated that the input speed to the gearbox can be determined based upon road speed and the gear selected and that a sensor measuring this speed is not essential.

In alternative embodiments the gear selector sensor 12 could be used to monitor only whether the transmission 11 is in neutral, a clutch operation switch 19 could be used to provide a signal when the clutch 18 is disengaged or moved from the fully engaged position instead of monitoring the position of the clutch pedal 25 and a sensor 28 could be provided to measure directly the rotational speed of the input shaft of the gearbox 11. Fig.3 shows various sensor combinations that could be used.

The electronic control unit 16 is programmed to execute a method according to this invention as shown in Fig.4 The method starts at step 10 which corresponds to a switching on of the ignition switch 17. The state of the ignition switch 17 is merely used as an indication the the motor vehicle 5 is being driven and various alternative means of making this determination could be used.

The method then proceeds to step 20 where it is determined whether a gear change has been initiated. In this case this is facilitated by monitoring the position of the clutch pedal 25 using the signal received from the clutch pedal sensor 26 in combination with the road speed sensor 21. The signal from the road speed sensor 21 is used to confirm whether the motor vehicle 10 is moving above a predetermined speed so as to distinguish a gear change event from a launch event.

If the output from the clutch pedal sensor 26 indicates that the clutch 18 is being disengaged and the vehicle 5 is moving above the pre-determined speed then it is assumed that a gear change event has been initiated and the method advances to step 30.

If at step 20 it is determined that a gear change event has not been initiated then the method cycles around step 20 until such an event occurs.

At step 30 the type of gear change event is established. This is achieved in this case by using the output from the accelerator pedal sensor 24 in combination with the gear position sensor 12. The controller 16 uses the gear position sensor 12 to determine whether the gear change is an upshift or a downshift so as to fully establish the type of gear change occurring.

If the output from the accelerator position sensor 24 indicates that the accelerator pedal position is less than say 5% open and a higher gear has been selected then it is assumed that a decelerating or constant speed upshift event is occurring. If the accelerator position is determined to be more than 5% open and a higher gear has been selected then it is assumed that an accelerating upshift is being performed. The variations of type of gear change used in this embodiment of the invention are described in greater below with respect to Fig.2. The term constant speed' as meant herein means that the motor vehicle 5 is cruising or operating under substantially steady state speed conditions.

Once the type of gear change has been established a compensation value is retrieved from, in this case, a look up table stored in a memory of the electronic control unit 16 of the type shown in Fig.2. It will be appreciated that the compensation value could be calculated or derived in some other manner and that the use of a look up table is only one way of producing this compensation value.

As can be seen in Fig.2, the type of gear change is determined to be one of nine variations, although there could be more or less variations depending upon the specific implementation of the invention. In this case the variations are:-three variations for the situation where no gear change actually occurs and for which the compensation value is zero Rpm; a decelerating or a constant speed upshift, for which the compensation value is zero Rpm; an accelerating upshift with an accelerator pedal position of between 5 and 20% open, for which the compensation value is +100 Rpm; a strongly accelerating upshift with an accelerator pedal position of more than 20% open, for which the compensation value is +500 Rpm; a decelerating downshift where the accelerator pedal position is less than 5% open, for which the compensation value is -100 RPM; a constant speed downshift with an accelerator pedal position of between 5 and 20% open, for which the compensation value is zero Rpm; and an accelerating downshift with an accelerator pedal position of more than 20% open, for which the compensation value is +500 Rpm.

It will be appreciated that these compensation values are provided by way of example and that the invention is not limited to these values or to accelerator pedal positions.

-10 -For example, and without limitation, a driver demand torque variable could be used or other types of driver demand source could be used.

The method then advances to step 40 where a target engine speed Ntqt is determined.

In this case this is determined using the formula:-Ntgt = N1 + Ncf where:-Ni is the expected rotational speed of an input shaft to the gearbox 11 after the gear change has taken place and NCf is the compensation value.

It will be appreciated that alternative methods for calculating the target engine speed can be used such as the use of a state machine or alternative forms of calculation such as Ntgt N1 X Ncfd.

where:-Ni is the expected rotational speed of the input shaft to the gearbox 11 after the gear change has taken place and NCfd is the compensation value.

In this latter case the compensation values stored in the look up table would be decimal fraction values such as, for example, 1.0; +1.1; +1.25 and 0.90 After establishing the appropriate target engine speed Ntgt the method advances to step 50 where it is determined whether the determined target engine speed Ntqt is greater than an actual engine speed Ndem demand by the driver as sensed by the accelerator pedal sensor 24.

It will be appreciated that, in practice, the position of the accelerator pedal 25 is normally interpreted as a torque demand rather than a specific engine speed. However, -11 -by using a map of engine torque verses accelerator pedal position either an equivalent torque demand value can be derived for the target engine speed Ntgt which can then be compared to the driver torque demand or the torque demand from the driver can be converted into a theoretical engine speed which can then be compared with the target engine speed Ngt. It will also be appreciated that other methods of comparing driver demand with the target engine speed Ntgt could also be used.

In the situation where maximum acceleration is being demanded by the driver this is likely to result in an engine speed at the point of clutch engagement that is larger than that determined for the target engine speed Ntgt. In such situations the change assist method is abandoned and the method advances through step 100 where the driver demanded engine output is used to step 200 where the method ends.

It will be appreciated that the motor vehicle could be provided with a switch to allow step 50 to be bypassed if required so as to always use the target engine speed Ntgt, such an arrangement would be useful for novice or inexperienced drivers. Alternatively, step 50 could normally be skipped unless a switch is activated to activate a driver override.

If the target engine speed Ntgt is greater than the engine speed Ndeni demanded by the driver, the method advances to step 60 where the electronic control unit 16 is operable to drive the engine speed towards the target engine speed Ntgt. In the case where the engine speed has to be driven down this may require the application of an additional load to the engine 10 if it is predicted that the engine deceleration due to the reduced fuelling and friction losses will not be sufficient to reduce the engine speed to the target engine speed Ntgt in the desired time period. In this case the starter-generator 13 can be used as an additional -12 -load to increase the deceleration of the engine 10 by switching on or connecting one or more electrical loads to the starter-generator 13.

The method then advances to step 70 with the engine speed at the target engine speed Ntgt where it is held until it is confirmed that the selected gear has been engaged and the clutch 18 has been re-engaged at which point the gear is considered to be fully engaged and the method terminates as indicated in step 200.

If the gear is not confirmed to be engaged after a predetermined period of time, the method can include an additional step to terminate the method and return the engine speed to an idle speed or to the actual speed being demanded by the driver as in such a situations it is likely that a normal gear change is not taking place. The motor vehicle 5 may, for example, be coasting.

With reference to Fig.5 there is shown the results for an assisted gear change from third gear to second gear of the accelerating downshift type for a motor vehicle utilising an engine speed control method according to the invention.

It will be noted that the target engine speed Ntgt has been set for 500 Rpm above the predicted gearbox input shaft speed N at the end of the gear change in order to produce additional acceleration at the moment of engagement. In this case the predicted input shaft speed N1 is 4000 Rpm and the target engine speed Ntgt is 4500 Rpm. It will be noted that the engine speed never actually reaches the target engine speed Ntgt because before it can do so the clutch has engaged sufficiently to drag the engine speed to the input shaft speed N1.

-13 -With reference to Fig.6 there is shown the results for an assisted gear change from third gear to second gear of the decelerating downshift type for a motor vehicle utilising an engine speed control method according to the invention.

It will be noted that the target engine speed Ntqt has been set for 100 rpm below the predicted gearbox input shaft speed N1 at the end of the gear change. In this case the predicted input shaft speed N1 is 3900 Rpm and the target engine speed Ntgt is 3800 Rpm. It will be noted that the engine speed actually exceeds the target engine speed Ntgt during the gear change because the clutch has engaged sufficiently to drag the engine speed to the input shaft speed N1 before the time at which full engagement was expected to occur. However, compared to the engine speed for the unassisted case shown on the chart, the engine speed in the assisted case is far better matched to the input shaft speed N1 and so a smoother change will result. In addition, clutch wear will be reduced for the assisted gear change because the energy generated in the clutch as it slips to drag up the engine speed in the unassisted case is greatly reduced in the assisted case.

With reference to Fig.7 there is shown the results for an assisted gear change from third gear to fourth gear of the constant speed upshift type for a motor vehicle utilising an engine speed control method according to the invention.

This type of gear change is the type normally made during general use and although the term constant speed' is used it will be appreciated that there may be a small amount of acceleration or deceleration with this type of upshift.

It will be noted that the target engine speed Ntqt has been set for the same Rpm as the predicted gearbox input -14 -shaft speed N at the end of the gear change. In this case the predicted input shaft speed N is 2000 Rpm and the target engine speed Nrgt is therefore also 2000 Rpm. It will be noted that the engine speed follows the desired deceleration to the target engine speed Ngt during the gear change fairly accurately although there is a slight offset during the change because the braking effect on the engine 10 is not perfectly matched to the theoretical deceleration.

However, compared to the engine speed for the unassisted case shown on the chart, the engine speed in the assisted case is far better matched to the input shaft speed N1 and so a smoother change will result. Note the significant engine speed oscillations that occur after clutch engagement in the unassisted case. In addition, clutch wear will be reduced for the assisted gear change because the energy generated in the clutch as it slips to drag up the engine speed in the unassisted case is virtually eliminated in the assisted case because the engine speed is synchronised with the input shaft speed N1 before the clutch is engaged.

Although the invention has been described with reference to one embodiment using the sensor combination referred to as option 1 in Fig.3 it will be appreciated that it can also be achieved using one of the other sensor options indicated in Fig.3 or other sensor combinations not shown in Fig.3.

For example, in the case of sensor option 6 the type of gear change can be inferred from the accelerator position and even though there is no direct measurement of gear position or input speed these can also be derived or inferred. For example, the current gear can be determined from a combination of current road speed and engine speed and whether an up shift or downshift is going to take place can be predicted based upon the vehicle activity prior to -15 -the gear change commencing. For example, a rising road speed with a small percentage open accelerator pedal position indicates that a constant speed up change is the most likely. The target speed can then be calculated based upon the predicted gearbox input speed if an upshift were to occur. If, however the road speed is falling this might indicate a downshift is more likely. Therefore it can be seen that the type of gear change likely could be inferred and an appropriate engine target speed Ntgt could then be determined.

Therefore in summary the invention provides a method to assist a driver with a gear change in a motor vehicle such as an automobile, SUV, MPV, truck, van or motor cycle having a manual gearbox and a manually operable clutch that seeks to drive the engine speed to the most suitable speed for the type of gear change taking place. In some cases the engine speed is driven to a rotational speed that is the same as the input speed of the gearbox but in other cases it is driven to a higher speed or to a lower speed.

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

-16 -Claims 1. A method for controlling an engine of a motor vehicle

having a manual gearbox and a manually operated clutch during a gear change the method comprising determining a target engine speed based upon the type of gear change taking place and controlling the engine during the gear change to drive the engine speed towards the target engine speed.
2. A method as claimed in claim 1 wherein, if the type of gear change is an accelerating downshift, the target engine speed is greater than a predicted input speed of the gearbox at the end of the change in gear.
3. A method as claimed in claim 1 wherein, if the type of gear change is a decelerating downshift, the target engine speed is less than a predicted input speed of the gearbox at the end of the change in gear.
4. A method as claimed in claim 1 wherein, if the type of gear change is one of a decelerating upshift, a substantially constant road speed upshift and a substantially constant road speed downshift, the target engine speed is substantially equal to a predicted input speed of the gearbox at the end of the change in gear.
5. A method as claimed in claim 1 wherein, if the type of gear change is an accelerating upshift, the target engine speed is greater than a predicted input speed of the gearbox at the end of the change in gear.
6. A method as claimed in any of claims 1 to 5 wherein the engine speed is driven to one of the greater of the target engine speed and an engine speed demanded by a driver of the motor vehicle using a driver controlled engine demand device and an engine torque demand equivalent to the -17 -target engine speed and an engine torque demanded by a driver of the motor vehicle using a driver controlled engine demand device.
7. A method as claimed in any of claims 1 to 6 wherein the method further comprises predicting the type of gear change from the position of a driver controlled engine demand device.
8. A method as claimed in claim 7 wherein the type of gear change is predicted by combining the position of the driver controlled engine demand device and a sensed change in selected gear.
9. A method as claimed in any of claims 1 to 8 wherein the method further comprises at least one of determining the road speed of the motor vehicle, determining when the clutch is moved from an engaged to a disengaged position, measuring the speed of the engine and determining starting and ending gears for the change in gear.
10. A motor vehicle having a manual gearbox, an engine, a manually operated clutch to selectively driveably connect the engine to the gearbox and an electronic controller to assist with gear changes wherein the electronic controller is operable to determine a target engine speed based upon the type of gear change taking place and control the engine during the change in gear to drive the engine speed towards the target engine speed.
11. A motor vehicle as claimed in claim 10 wherein, if the type of gear change is an accelerating downshift, the controller is operable to drive the engine to a target engine speed that is greater than a predicted input speed of the gearbox at the end of the change in gear.

-18 -
12. A motor vehicle as claimed in claim 10 wherein, if the type of gear change is a decelerating downshift, the controller is operable to drive the engine to a target engine speed that is less than a predicted input speed of the gearbox at the end of the change in gear.
13. A motor vehicle as claimed in claim 10 wherein, if the type of gear change is an accelerating upshift, the controller is operable to drive the engine to a target engine speed that is greater than a predicted input speed of the gearbox at the end of the change in gear.
14. A motor vehicle as claimed in claim 10 wherein, if the type of gear change is one of a decelerating upshift, a substantially constant road speed upshift and a substantially constant road speed downshift, the controller is operable to drive the engine to a target engine speed that is substantially equal to a predicted input speed of the gearbox at the end of the change in gear.
15. A motor vehicle as claimed in any of claims 10 to 14 wherein the engine speed is driven to the greater of the target engine speed and an engine speed demanded by a driver of the motor vehicle using a driver controlled engine demand device.
16. A motor vehicle as claimed in any of claims 10 to wherein the motor vehicle further comprises predicting the type of gear change from the position of a driver controlled engine demand device.
17. A motor vehicle as claimed in claim 15 or in claim 16 wherein the driver controlled engine demand device is an accelerator pedal.
18. A motor vehicle as claimed in any of claims 10 to 17 wherein the motor vehicle further comprises at least one -19 -of a means for determining the road speed of the motor vehicle, a means for determining when the clutch is moved from an engaged to a disengaged position, a means for measuring the speed of the engine and a means for determining starting and ending gears for the change in gear.
19. A method of controlling an engine of a motor vehicle having a manual gearbox and a manually operated clutch during a change in gear substantially as described herein with reference to the accompanying drawing.
20. A motor vehicle substantially as described herein with reference to the accompanying drawing.