GB2412448A

GB2412448A - Power train control system

Info

Publication number: GB2412448A
Application number: GB0406374A
Authority: GB
Inventors: Jan Pieter Prins; Derek Leslie Jones; Tim Slaney; Nicholas John Moore; Andrew Cotta
Original assignee: Ford Global Technologies LLC
Current assignee: Ford Global Technologies LLC
Priority date: 2004-03-22
Filing date: 2004-03-22
Publication date: 2005-09-28
Anticipated expiration: 2024-03-22
Also published as: DE102005012863A1; DE102005012863B4; GB0406374D0; GB2412448B

Abstract

A control device for a vehicle power train includes a means for varying a power output of the power train and a control means for generating a control signal for the power output varying means. The control means generates the control signal in response to a power demand signal, and in accordance with one of a number of selectable characteristics. The control means effects a gradual changeover from a first selected characteristic to a second selected characteristic, in a manner dependent upon the magnitude of the power demand signal, such that the changeover is smooth. The power output varying means may be controlled to alter power output by a fixed amount per unit of time, or to alter power output over a fixed time period. The selectable characteristics, such as sport, mud, grass and tarmac modes, may be selected in response to a signal from a driver operated switch 11 or vehicle mounted sensor 12.

Description

24 1 2448 Powertrain Control Systems This invention relates to powertrain

control systems for motor vehicles.

It is common to eliminate the traditional direct link (usually a mechanical linkage such as Bowden cable) between the driver-operated accelerator pedal of a motor vehicle and the fuelling system of its engine. It is replaced with electrical control of the engine fuelling, normally in the form of an engine management system running closed loop feedback control. Such systems are commonly known in the art as "drive-bywire." "Drive-by-wire" systems usually employ a pedal demand potentiometer connected to the driver-operated accelerator pedal to provide a signal of demanded power to the engine management system. The engine management system controls the supply of fuel and air to the engine in response to the pedal demand signal.

When a vehicle is to be used off-road, in conditions where the surface over which it is travailing is rough or uneven, there is a requirement for a low sensitivity in the accelerator pedal, at least over the initial range of pedal travel. (i.e. a high pedal displacement is required for a large power increase). This is because there is generally a lot of vibration which makes the vehicle hard to control if the accelerator is too sensitive. On the other hand, for on-road driving, where the driving surface is relatively smooth, a more sensitive accelerator pedal is usually preferable to give a more powerful feel to the vehicle. (i.e. a low pedal displacement gives a large power increase).

GB 2154763 and FR 2483012 each disclose a system having different throttle characteristics which are selectable by the driver to give the driving characteristics required, such as a sporty feel or economy of fuel.

WO 97/27388 discloses a powertrain control system which detects whether the vehicle is in an on-road or an off-road driving condition, and selects one of two throttle - 2 - characteristics, selection of a first characteristic providing a more sensitive accelerator pedal response for driving on-road, and selection of a second characteristic having a coarser response being made when the vehicle is in the off-road condition. Detection of the on or off-road condition may operate by detecting driver selection of a high (for on- road driving) or a low (for off-road driving) range of gear ratios.

In these known systems, the difference between two throttle characteristics, say on- road and off-road, for example, can be such that for the same accelerator pedal position, there is a large difference in engine power output. Hence, when changing from one characteristic to another, whilst the vehicle is in motion, the driver must release the accelerator pedal in order to avoid any jerkiness in the vehicle's motion. This jerkiness is brought about by the instant increase (or decrease) in engine power (or torque) when changing between two throttle characteristics; for example going from on-road to off-road, or sporty to economy. This is uncomfortable and disconcerting for the driver. However, it not always convenient to release the accelerator pedal at such times, as this leads to a loss in momentum which might result in the vehicle getting stuck when negotiating a steep hill or muddy terrain, for example.

Hence it would be advantageous to provide a system for effecting a change of throttle characteristic while a vehicle is on the move and without requiring the driver to lift his / her foot off the accelerator pedal whilst the change was taking place.

In a first aspect, the present invention consists of a device for controlling a motor vehicle powertrain, the vehicle being provided with a power output varying means for varying the power output of the vehicle powertrain, and a driver operated power demand means for providing a power demand signal, wherein the device comprises; - 3 a control means for generating a control output signal operative to control said varying means in response to said power demand signal and in accordance with one of a plurality of selectable control characteristics, wherein said control means is adapted to effect a gradual changeover from a first selected control characteristic to a second selected control characteristic in a manner dependent upon the magnitude of the power demand signal.

In a second aspect, the invention consists of a method for controlling the powertrain of a motor vehicle having a powertrain varying means, the method including the steps of; producing a power demand signal, storing a plurality of selectable control characteristics, generating a control output signal in response to said power demand signal and in accordance with one of said control characteristics, applying the generated control output signal to the powertrain varying means, and effecting a gradual changeover from a first selected control characteristic to a second selected control characteristic in a manner dependent upon the magnitude of the power demand signal.

In a third aspect, the invention provides a vehicle incorporating the device according to said first aspect of the invention.

The device may further incorporate a memory for storing said plurality of selectable control characteristics. - 4

The control means may be arranged to select a characteristic in response to a signal generated by a driver-operated driving-mode selection switch. Alternatively, selection may be brought about by a signal from an onboard sensor.

Preferably each of the control characteristics is applicable over substantially the full range of operable conditions of the power output varying means.

Preferably, over said range of conditions of the power demand means, for any specific condition within that range, the condition of the power output varying means produced by the one characteristic corresponds to a different power output than that produced by the other characteristics.

The control characteristics may converge at their upper ends so that the maximum power available is substantially the same for each characteristic. The control characteristics may also converge at their lower ends so that the minimum power available is substantially the same for each characteristic.

The on-board sensor may comprise a vibration detection means for detecting vibrations in the vehicle, thereby inferring that the vehicle is being driven off-road.

The power demand means may comprise an accelerator pedal and the power demand signal may be dependent on the position of the accelerator pedal such that, when a first characteristic is selected, the power output varying means is more sensitive to changes in position of the accelerator pedal than when a second characteristic is subsequently selected. The pedal demand signal may vary over the total range of travel of the accelerator pedal.

In a first example, the control means is adapted to effect the changeover by generating a control output signal which causes the power output varying means to alter the power output by a constant amount per unit time. - 5

In a second example, the control means is adapted to effect the changeover by generating a control output signal which causes the power output varying means to alter the power output over a fixed time period.

In a third example, the control means is adapted to effect the changeover during a fixed time period by generating a control output signal which causes the power output varying means to alter the power output at a variable rate dependent upon the magnitudes of power demand signals measured at discrete time intervals during the changeover period.

The invention will now be described, by way of example only, with reference to the drawings off which; Figure 1 is a schematic block diagram of a system according to an embodiment of the invention, and Figures 2 and 3 are graphical representations of the power output characteristics used by the system of figure 1.

Referring to figure 1, the power output of an engine of a motor vehicle (not shown) is controlled by a power output varying means 1 in the form of a DC motor 2 bi-directionally driving a throttle shaft 3 on which is held a throttle butterfly 4 which controls the airflow entering the engine. The DC motor 2 operates off a nominal 12 volt DC supply controlled by a control means 5 in the form of an electronic control unit (ECU) 6 in communication with a memory 7. The ECU 6 receives an input from a power demand means 8 in the form of a pedal demand potentiometer 9 which is arranged to produce a pedal demand signal which is dependent on the position of the accelerator pedal 10. The pedal demand signal varies over the total range of accelerator pedal travel and is a continuously variable voltage rising from 0.5 volts DC for zero pedal displacement to 5 volts DC for wide / full pedal displacement. A second input to the ECU 6 is provided by a mode selection switch 11. - 6

This input is indicative of the terrain over which the vehicle is travelling or intending to travel, or of a driving mode. Typical switch settings which are selectable are "sport", "mud", "grass" and "tarmac".

Additional or alternative modes are possible but just these four are shown for illustrative purposes. Each setting has associated with it a control characteristic which dictates the amount of power demanded from the engine for a given pedal position. Each of these four associated characteristics is stored in the memory 7.

A third input to the ECU 6 is provided by a driving condition sensing means 12 comprising a suspension controller 13 and four suspension potentiometers 14 for indicating the vertical position of a wheel of the vehicle.

The ECU 6 produces a control signal on line 15 which is coupled to the motor 2 for controlling the amount of throttle butterfly 4 opening.

Figure 2 illustrates two power output characteristics in the form of a "tarmac" characteristic 16 and a "mud" characteristic 17. The characteristics 16, 17 relate a throttle opening (vertical axis) produced by the DC motor 2 to a pedal demand signal (horizontal axis) derived from the pedal demand potentiometer 9. The characteristics 16, 17 are selected by the ECU 6 depending on inputs from either the switch 11 or the suspension controller 13.

The characteristics 16, 17 both start at the same point giving zero throttle opening for a pedal demand signal corresponding to zero pedal travel. For low accelerator pedal displacement, i.e. low pedal demand signals, the "tarmac" characteristic 16 is steeper than the "mud" characteristic 17, giving greater throttle opening for the same amount of pedal movement. At high pedal displacements, i.e. high pedal demand signals, the "tarmac" characteristic 16 becomes less steep and the "mud" characteristic 17 becomes more steep.

In this region the "tarmac" characteristic 16 therefore gives less change in throttle opening for a given amount of pedal movement than the "mud" characteristic 17. Characteristics 16, 17 therefore converge towards their upper ends and meet at a point where full accelerator pedal depression produces a wide open throttle.

A first exemplary mode of operation will now be described with reference to figures 1 and 2. In this first example, the driver has pre-selected ''mud'' mode on the selector switch 11 and in response, the ECU 6 has selected the throttle response characteristic 17 from the memory 7 for control of the DC motor 2. Hence curve 17 will dictate the output control signal value on line 15 and so, the throttle opening. Say that the driver is pressing the pedal 10 by approximately one third of its full travel (i.e. the pedal demand signal is approximately 2 volts) so that the throttle opening is 10% i.e. the system is operating at point A on curve 17. Subsequently, the vehicle leaves the off-road terrain and moves onto a tarmac surface. So the driver moves the mode selection switch 11 from "mud" to "tarmac" whilst keeping the pedal position fixed. The ECU 6 detects this mode change and is now required to alter the throttle opening to a target value of 80% corresponding to point B on curve 16. In order to do this, the ECU 6 generates a control signal on line 15 for activating the motor so that the throttle opening increases at a fixed, predetermined rate per unit time. Hence, the driver will notice a gradual increase in power demand from the engine even though his foot is static on the pedal 10. When the ECU 6 detects that the throttle opening has reached the target value of 80% it maintains the throttle opening at that value until the driver changes the pedal position. Thereafter, the ECU 6 output on line is dictated by the "tarmac" curve 16 selected from the memory 7.

It will be appreciated that as the ECU 6 in this example operates to alter throttle opening at a fixed rate per unit time, it takes longer to reach the new selected mode curve starting from point A on curve 17 than it would starting from a point C, for example, where the pedal is depressed almost to its fullest extent.

A second alternative mode of operation will now be described, again with reference to figures 1 and 2. In this example, the driver has selected "tarmac" mode and is progressing with the pedal 10 at half of its full travel (i.e. the pedal demand signal is 2.25 volts). This corresponds to 90% throttle opening, the operating point shown as point D on curve 16, selected from the memory 7 by the ECU 6. The driver now proceeds off-road onto an uneven terrain, keeping the accelerator pedal 10 position constant but forgetting to change the mode selector switch 11 to "mud". A signal from the suspension controller 13 supplied to the ECU 6 is derived from the suspension potentiometers 12 and indicates that the vehicle is travailing under conditions equivalent to off-road use. In this example the vehicle is now travailing across a rough surface and so the suspension controller 13 sends a signal to the ECU 6. The ECU 6 is arranged to prioritise its inputs such that the signal from the suspension controller 13 will always override the mode selector switch 11. When the ECU 6 determines that the vehicle is no longer travailing off-road as a result of a signal from the suspension controller 13, it will reselect the power characteristic determined by the mode selector switch 11. In response to receiving the signal from the suspension controller 13 telling it that the "mud" characteristic is now required, the ECU 6 needs to decrease the throttle opening from its current 90% to 25% corresponding to point E on curve 17. In order to do this, the ECU 6 generates a control signal on line 15 for activating a motor 2 so that the throttle opening decreases linearly over a fixed, preset time period, say three seconds, until operating point E on curve 17 is reached. The driver will notice a gradual decrease in engine power during this three second period even though his foot is held static on the accelerator pedal 10. When the time period has elapsed and the throttle opening has diminished to the 25% target value, the ECU 6 maintains this throttle opening until the driver changes the accelerator pedal position. Thereafter, the ECU 6 output on line 12 is dictated by the "mud" curve 17 selected from the memory 7.

It will be appreciated in this second example, the time taken to move from any point on one curve (for example D or F) to the corresponding point on the other curve (E or G) is the same. - 9 -

A third alternative mode of operation will now be described with reference to figures 1 and 3. In this example, the driver has selected "mud" mode and is progressing with the accelerator pedal 10 depressed to one third of its full travel (i.e. the pedal demand signal is approximately 2 volts). In response to the signal from the selector switch 11, the ECU 6 has selected the appropriate characteristic curve 18 from the memory 7 for controlling the DC motor 2. The throttle opening is 10% at point A on curve 18, subsequently, the vehicle approaches uneven terrain and the driver moves the selector switch 11 to "tarmac." The ECU 6 detects the change of mode and so is required to alter the throttle opening to a target value of 80% corresponding to point B on curve 19. In this example, the ECU 6 is adapted to effect the changeover between curves 18 and 19 in a time period "T" set at three seconds and to measure the pedal demand signal during this period at preset time intervals "t", where t is equal to one second. So at time t,, when the changeover request is made, the pedal demand signal is 1.7 volts. The ECU 6 notes that it has to effect opening of the throttle from its current value of 10% to the target value of 80% in the space of three seconds. Therefore, it applies an appropriate signal to the DC motor 2 so that a throttle opening rate of 23% per second is effected. At time t2, one second later, the ECU 6 measures the pedal demand signal again. The throttle opening will at this point have reached 33%. However in this example, say that the driver wishes to accelerate and has depressed the accelerator pedal 10 to almost its fullest extent and at this time t2, the ECU measures the pedal demand signal to be 4.5 volts. A 4.5 volt pedal demand signal corresponds to a throttle opening of 98% on the "tarmac" curve 19. (Point B'). The offset now between measured throttle opening and target throttle opening is 55% percent. This difference has to be reduced to zero in the space of the remaining two seconds. Therefore, the ECU 6 adjusts its output control signal on line 15 so that a throttle opening rate of 27.5% per second is effected. After the three second time period has elapsed and the throttle opening has reached 98%, the ECU output is dictated by the "tarmac" curve 19.

Hence in this alternative third mode of operation, the system can accommodate a change in pedal position during the changeover from one throttle characteristic to another. -

The time period "T" and time intervals "t" may be set to values other than three seconds and one second respectively, as appropriate.

This third mode of operation can also be applied to the case where a change from tarmac to mud mode is required, i.e. decreasing the throttle opening over a fixed time period at a variable rate having regard to the magnitude of the measured pedal demand signals.

As a further refinement, the system of figure 1 may include feedback means in the form of a throttle position potentiometer (not shown) mounted on the throttle shaft 3. The throttle position potentiometer provides feedback to the ECU 6 of the position to which the DC motor 2 has driven the throttle butterfly 4 and the rate at which the throttle butterfly 4 is moving thereby providing for closed loop feedback control.

A communication means may also be provided in the form of an input / output port which is arranged to provide communications between the ECU 6 and an external device (not shown). The port provides the user with the opportunity to change any characteristics stored in the memory 7 and to perform tuning or diagnostic routines subject to suitable functionality being included in the ECU 6.

The system may be incorporated in a terrain optimization system such as that described in EP 1355209 where other vehicle systems such as transmission, brakes and suspension are optimised depending on the terrain being traversed.

The powertrain control system disclosed herein is not limited to controlling a throttle butterfly. Fuel injections systems for many current petrol and diesel engines have injectors or fuel pumps suitable for this kind of control. Modern transmissions such as continuously variable transmissions lend themselves to the manner of control disclosed herein, as does the supply of electrical power to a traction motor of an electrically-propelled vehicle. The demand means of the present invention is not limited to an accelerator pedal and may be in - 11 another form, such as a hand throttle or a twist-grip. The onboard sensor is not limited to a suspension control system and may be any device or system which includes automatic generation of an off-road signal when the vehicle is travailing over rough or uneven surfaces. One example of such another system is an anti-lock braking system which can include an adaptive algorithm to detect changes in road surface from the difference in speeds of the vehicle wheels. - 12

Claims

CLAIMS I

1. A device for controlling a motor vehicle powertrain, the vehicle being provided with a power output varying means for varying the power output of the vehicle powertrain, and a driver-operated power demand means for producing a power demand signal, wherein the device comprises; a control means for generating a control output signal operative to control said varying means in response to said power demand signals and in accordance with one of a plurality of selectable characteristics, wherein said control means is adapted to effect a gradual changeover from a first selected control characteristic to a second selected control characteristic in a manner dependent upon the magnitude of the power demand signal.

2. A device according to claim 1 in which the control means is adapted to effect the changeover by generating a control output signal which causes the power output varying means to alter the power output by a constant amount per unit time.

3. A device according to claim 1 in which the control means is adapted to effect the changeover by generating a control output signal which causes the power output varying means to alter the power output over a fixed time period.

4. A device according to claim 1 in which the control means is adapted to effect the changeover during a fixed time period by generating a control output signal which causes the power output varying means to alter the power output at a variable rate dependent upon the magnitudes of power demand signals measured at discrete time intervals during the changeover period.

5. A device according to any preceding claim and further including a memory for storing said plurality of selectable control characteristics. 13

6. A device according to any preceding claim in which the control means is arranged to select a control characteristic in response to a signal generated by a driver- operated switch.

7. A device according to any of claims 1 to 5 in which the control means is arranged to select a control characteristic in response to a signal generated by a vehicle- mounted sensor.

8. A method for controlling the powertrain of a motor vehicle having a powertrain varying means, the method including the steps of; producing a power demand signal, storing a plurality of selectable characteristics, generating a control output signal in response to said power demand signal and in accordance with one of said control characteristics, applying the generated control output signal to the powertrain varying means, and effecting a gradual changeover from a first selected control characteristic to a second selected control characteristic in a manner dependent upon the magnitude of the power demand signal.

9. A motor vehicle incorporating the device according to any of claims 1 to 7.

10.A device for controlling a motor vehicle powertrain, substantially as hereinbefore described with reference to the drawings.