GB2568295A

GB2568295A - Vehicle control system and method of controlling a vehicle

Info

Publication number: GB2568295A
Application number: GB1718696.6A
Authority: GB
Inventors: Mourre Thomas; James Green Christopher; Marsden Paul
Original assignee: Jaguar Land Rover Ltd
Current assignee: Jaguar Land Rover Ltd
Priority date: 2017-11-13
Filing date: 2017-11-13
Publication date: 2019-05-15
Anticipated expiration: 2037-11-13
Also published as: GB201718696D0; DE102018218104A1; GB2568295B

Abstract

A control system for controlling at least a portion of a powertrain of a motor vehicle 100 is provided. The control system is configured to cause a transmission 131 of the powertrain 120 to assume a predetermined gear ratio in dependence at least in part on vehicle speed in accordance with one of an engine connected relationship and a connection relationship. The control system is also configured to: cause the powertrain 120 to assume a coasting configuration in which the transmission 131 is disconnected from an engine 121 of the vehicle or an engine connected configuration in which the transmission 131 is connected to the engine 121; and cause the transmission 131 to assume a gear ratio in accordance with the engine connected relationship when the powertrain 120 is in the engine connected configuration. When the powertrain 120 is in the coasting configuration, the gear ratio of the transmission 131 is set, prior to reconnection, to a gear ratio determined in accordance with the connection relationship. A corresponding method of controlling a vehicle, a vehicle including the control system, and a computer readable program/medium are also disclosed.

Description

VEHICLE CONTROL SYSTEM AND METHOD OF CONTROLLING A VEHICLE

TECHNICAL FIELD

This invention relates to a control system for controlling at least a portion of a powertrain of a vehicle and to a method of controlling at least a portion of a powertrain. In particular, but not exclusively, embodiments of the present invention relate to the control of powertrains of vehicles having an engine that may be switched off and restarted whilst the vehicle is moving. Aspects of the invention relate to a method, to a control system, to a vehicle, to a non-transitory computer readable carrier medium carrying computer readable code, to a computer program product, to a non-transitory computer readable medium and to a processor.

BACKGROUND

It is known to provide a vehicle having engine ‘stop/start’ capability in which, when the vehicle is held stationary by a braking system and the accelerator pedal not depressed, the engine is switched off to conserve fuel. The engine may be restarted when the brake is released or the accelerator pedal depressed.

In so-called ‘mild hybrid electric vehicles’ (MHEVs), an internal combustion (IC) engine is provided with an electric machine in the form of a motor/generator. The electric machine is operable as a motor to provide additional torque to provide torque assist for the engine to drive a driveline via a transmission and may also be used for starting the engine. The electric machine may also be operated as a generator to recharge a battery of the vehicle.

During coasting in which the IC engine remains connected to a driveline of the vehicle via a transmission, the vehicle is allowed to roll, without application of the accelerator pedal. In this condition fuel may be cut-off (so-called ‘deceleration fuel shut-off’) and the vehicle allowed to slowly decelerate due to engine braking (‘engine over-run’) and other external factors. Such coasting may be referred to as ‘engine-connected coasting’. During engineconnected coasting IC engine speed is a function of the speed of the vehicle and the gear ratio of the transmission.

It is an aim of embodiments of the present invention to provide a method of vehicle control that enables reduced fuel consumption and/or enhanced drivability in a vehicle, optionally in an MHEV vehicle.

SUMMARY OF THE INVENTION

In one aspect of the present invention for which protection is sought there is provided a control system for controlling at least a portion of a powertrain of a motor vehicle, the system being configured to cause a transmission of the powertrain to assume a predetermined gear ratio in dependence at least in part on vehicle speed in accordance with one of an engine connected relationship and a connection relationship, the control system being configured to: cause the powertrain to assume a coasting configuration in which the transmission is disconnected from an engine of the vehicle or an engine connected configuration in which the transmission is connected to the engine, and cause the transmission to assume a gear ratio in accordance with the engine connected relationship when the powertrain is in the engine connected configuration; wherein when the powertrain is in the coasting configuration, the gear ratio of the transmission is set, prior to reconnection, to a gear ratio determined in accordance with the corresponding connection relationship.

Some embodiments of the present invention have the advantage that the transmission speed/gear ratio assumed by the transmission upon initial connection of the transmission to the engine when switching from the coasting to the engine connected configuration whilst the vehicle is moving may be set to a value providing improved vehicle response to driver demand for drive torque. It is to be understood that the engine connected relationship, which may also be referred to as an engine connected speed/gear ratio relationship, employed whilst the powertrain is in the engine connected configuration, whilst providing a suitable transmission speed/gear ratio in the engine connected configuration, may be such that the engine speed required in order to permit reconnection to the transmission at the prescribed transmission speed/gear ratio following coasting may take an unacceptably long period for the engine to achieve, delaying the delivery of drive torque from the engine to wheels of the vehicle. Accordingly, the connection relationship, which may also be referred to as a connection speed/gear ratio relationship, may be arranged to prescribe a higher transmission gear for a given vehicle speed, over at least certain speed ranges, compared with the value provided by the engine connected map, in order to reduce the time required for the engine to spin up to the required speed for reconnection.

In an embodiment where the transmission is a dual clutch transmission (DCT), the transmission is considered to be disconnected from an engine of the vehicle when both dual clutches are driveably disconnected simultaneously. In this embodiment the transmission of the powertrain is considered to assume a predetermined gear ratio when said gear ratio is engaged to driveably connect an input shaft with the transmission output shaft. An input shaft being a shaft providing torque into the transmission which may be directly driven by one of the dual clutches.

In an embodiment where the transmission is a planetary automatic transmission, the transmission is disconnected from an engine of the vehicle when a clutch provided within the transmission which would be required to transmit drive in the currently selected gear ratio from the input to the output is driveably disconnected. In this embodiment the transmission of the powertrain is considered to assume a predetermined gear ratio when the remaining clutches which would be required to transmit drive in the currently selected gear ratio from the input to the output are driveably connected.

In an embodiment where the transmission is a hybrid transmission, the transmission is disconnected from an engine of the vehicle when an engine disconnect clutch provided between the transmission and the engine is driveably disconnected or one of the above disconnection methods are used dependent on the transmission configuration. In this embodiment the transmission of the powertrain is considered to assume a predetermined gear ratio when a drive path through the transmission relating to said predetermined gear ratio is driveably disconnected by a clutch.

It is to be understood that some known control systems may have more than one engine connected relationship, selectable by the control system when required. For example, the control system may have one engine connected relationship for use when driving in a ‘normal’ driving mode and another engine connected relationship for driving in a ‘sports’ or ‘dynamic’ driving mode in which the powertrain and optionally one or more other vehicle systems such as a suspension system, steering system and/or braking system are configured in such a manner as to provide improved handling when the vehicle is driven in a more dynamic manner. However, it is not known to provide a separate relationship for reconnection of an engine and transmission following coasting.

The engine connected relationship may also be referred to as a drive relationship.

Optionally, the control system may be configured, when the powertrain is in the coasting configuration, to determine a value of required gear ratio and to cause the transmission to assume the required ratio substantially only when it is determined that a transition from the coasting configuration to the engine connected configuration is to be made.

In some alternative embodiments, the control system may be configured, substantially throughout the period for which the powertrain is in the coasting configuration, to determine a value of required gear ratio according to the connection relationship and to cause the transmission to assume the required ratio if the transmission is not already in the required ratio.

Optionally, the control system is configured to receive a signal indicative of the position of an accelerator control.

The accelerator control may be an accelerator pedal control. The signal indicative of the position of the control may provide an indication of the position of the control with respect to a range of movement or travel of the control. The position may be expressed as a percentage of the allowable range of movement or travel of the control.

Optionally, the control system is configured, when the powertrain is in the engine connected configuration, to determine a value of required gear ratio as a function of vehicle speed and accelerator control position according to the engine connected relationship and to cause the transmission to assume the required ratio.

Alternatively, the control system may be configured, when the powertrain is in the coasting configuration, to determine, according to the connection relationship, a value of required gear ratio as a function of vehicle speed and not accelerator control position, and to cause the transmission to assume the required ratio.

Optionally, the control system is configured, when the powertrain is in the coasting configuration, to determine a value of required gear ratio as a function of vehicle speed and accelerator control position at least according to the connection relationship and to cause the transmission to assume the required ratio.

Optionally, the connection relationship corresponds substantially to the engine connected relationship at a substantially fixed, predetermined accelerator control position.

Thus it is to be understood that the connection relationship may be a special case of the drive relationship, i.e. the case where the accelerator control position is a predetermined position such as 40%, 50%, 60% or any other suitable position.

Alternatively, the connection relationship may be a substantially separate relationship not defined or determined by reference to the drive relationship. In some embodiments the connection relationship may be predetermined empirically via calibration. The connection relationship may be provided in the form of a look-up table, optionally with only two variables - vehicle speed and required gear ratio - and not including accelerator pedal position.

Other arrangements may be useful in some embodiments.

Optionally, the control system is configured to store information defining the engine connected relationship in the form of an engine connected map.

Optionally, the control system is configured to employ the engine connected map at the predetermined value of accelerator control position in order to determine the required transmission gear ratio according to the connection relationship.

Optionally, the control system is configured to cause the powertrain to assume the coasting configuration when a predetermined one or more coasting configuration entry conditions are met, the one or more coasting configuration entry conditions including the condition that the accelerator control position corresponds to substantially zero.

Optionally, the one or more coasting configuration entry conditions further include the condition that a braking system has not been actuated and vehicle speed exceeds a predetermined minimum coasting configuration entry speed.

The value of the predetermined minimum off coasting entry speed may be any suitable value, such as 20kph, 15kph, 25kph or any other suitable speed.

Optionally, in the coasting configuration the engine is disconnected from the transmission and the engine is switched off.

The control system may comprise an electronic controller, the controller comprising processing means, wherein the processing means comprises an electronic processor having an electronic memory device electrically coupled to the electronic processor and having instructions stored therein, wherein the processor is configured to access the memory device and execute the instructions stored therein such that it is operable to cause the powertrain to assume a coasting configuration in which the transmission is disconnected from an engine of the vehicle or an engine connected configuration in which the transmission is connected to the engine, wherein when the powertrain is in the engine connected configuration the controller causes the transmission to assume a gear ratio in accordance with the engine connected relationship, and when the powertrain is in the coasting configuration and a transition to the engine connected configuration is required in which the transmission is reconnected to the engine, the controller causes the transmission to assume, prior to reconnection, a gear ratio determined in accordance with the connection relationship.

In a further aspect of the invention for which protection is sought there is provided a vehicle comprising a control system according to another aspect.

In a still further aspect of the invention for which protection is sought there is provided a method of controlling at least a portion of a powertrain of a motor vehicle, the method comprising causing a transmission of the powertrain to assume a predetermined transmission gear ratio in dependence at least in part on vehicle speed in accordance with one of an engine connected relationship and a corresponding connection relationship, the method comprising causing the powertrain to assume a coasting configuration in which the transmission is disconnected from an engine of the vehicle or an engine connected configuration in which the transmission is connected to the engine, whereby when the powertrain is in the engine connected configuration the method comprises causing the transmission to assume a gear ratio in accordance with the engine connected relationship, and when the powertrain is in the coasting configuration and a transition to the engine connected configuration is required in which the transmission is reconnected to the engine, the method comprises setting the gear ratio of the transmission, prior to reconnection, to a gear ratio determined in accordance with the connection relationship.

In one aspect of the invention for which protection is sought there is provided a method of controlling at least a portion of a powertrain of a motor vehicle, the method comprising causing a transmission of the powertrain to assume a predetermined transmission gear ratio in dependence on vehicle speed in accordance with one of an engine connected map and a connection map, the method comprising causing the powertrain to assume a coasting configuration in which the transmission is disconnected from an engine of the vehicle or an engine connected configuration in which the transmission is connected to the engine, whereby when the powertrain is in the engine connected configuration the method comprises causing the transmission to assume a gear ratio in accordance with the engine connected map, and when the powertrain is in the coasting configuration and a transition to the engine connected configuration is required in which the transmission is reconnected to the engine, the method comprises, prior to reconnection, setting the speed/gear ratio of the transmission to a gear ratio determined in accordance with the connection map.

In one aspect of the invention for which protection is sought there is provided a nontransitory computer readable carrier medium carrying computer readable code for controlling a vehicle to carry out the method of another aspect.

In another aspect of the invention for which protection is sought there is provided a computer program product executable on a processor so as to implement the method of another aspect.

In a further aspect of the invention for which protection is sought there is provided a nontransitory computer readable medium carrying computer readable code which when executed causes a vehicle to carry out the method of another aspect.

In an aspect of the invention for which protection is sought there is provided a processor arranged to implement the method of another aspect, or the computer program product of another aspect.

Embodiments of the invention may be implemented in any suitable manner, and may for example be incorporated in an electronic control unit of the motor or transmission, and operable in response to input signals of e.g. road speed, accelerator pedal position, motor speed, transmission speed and clutch pressure. The control unit may include a memory having thresholds and stored characteristics or algorithms, to ensure that motor speed is maintained at the lowest possible value during implementation of the strategy. Such characteristics can be determined empirically by suitably qualified staff to the intent that the strategy can be automatically enabled and disabled without affecting driveability of the vehicle or being otherwise noticeable to the vehicle driver.

Embodiments of the present invention are directed to improving one or more of vehicle drivability and fuel efficiency by providing separate relationships between vehicle speed and transmission gear depending on whether the vehicle powertrain is in an engine-connected mode (engine connected to the transmission) or about to reconnect the engine and transmission following a period of coasting with the engine disconnected from the transmission, optionally with the engine switched off (‘engine off coasting’). An ‘engine connected’ relationship may be employed during periods when the engine is connected to the transmission. A ‘connection’ relationship may be employed when it is required to reconnect the engine and transmission. By careful selection of required transmission gear as a function of vehicle speed (and optionally, further, as a function of accelerator pedal position) an improvement in vehicle drivability may be obtained, in terms of a trade-off between the time taken to cause the engine to attain the required speed for reconnection in the selected transmission gear, and the probability that a transmission gear downshift will be required immediately or shortly after reconnection of the engine and transmission.

It is to be understood that, the higher the transmission gear employed at the time of reconnection, the lower the engine speed and therefore lower the time required for the engine to attain the required speed from an off condition or an idle condition. However, the chances of a transmission gear downshift being required immediately or shortly after engine reconnection has been completed, in order to meet driver torque demand may be higher for higher gears. This can result in increased noise, vibration or harshness (NVH). In contrast, for lower gears, the chances of a transmission gear downshift being required immediately or shortly after engine reconnection has been completed, in order to meet driver torque demand, is lower for lower gears but the time taken for the engine to reach the required (higher) reconnection speed is correspondingly higher. Accordingly, some embodiments of the invention attempt to provide a connection relationship between transmission gear and vehicle speed (and optionally accelerator pedal position in addition) that reduces the risk of a downshift being required immediately or shortly after reconnection whist providing a gear for which the corresponding engine speed can be achieved within a reasonable time frame.

Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and/or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination . For example features disclosed in connection with one embodiment are applicable to all embodiments unless such features are incompatible.

BRIEF DESCRIPTION OF DRAWINGS

The present invention will now be described, by way of example only, with reference to the accompanying drawings in which:FIGURE 1 illustrates a mild hybrid electric vehicle (MHEV) according to an embodiment of the present invention having an engine, belt-integrated starter/generator (BISG) and transmission that may be disconnected from a driveline; and

FIGURE 2 illustrates schematically a map of required transmission gear as a function of accelerator pedal position P and vehicle speed employed by a control system of the vehicle of the embodiment of FIG. 1.

DETAILED DESCRIPTION

FIG. 1 is a schematic illustration of a mild hybrid electric vehicle (MHEV) 100 according to an embodiment of the present invention. The vehicle 100 has a conventional internal combustion (IC) engine 121 provided with a belt-integrated starter/generator (BISG) 125 and battery 126 for powering the BISG 126. The vehicle 100 has an automatic transmission 131 coupled to a driveline 150 that includes a power transfer unit (PTU) 141 and rear drive shaft 151. The engine 121 (including BISG 125), battery 126, transmission 131 and driveline 150 are collectively referred to as a powertrain 120 of the vehicle 100. It is to be understood that, whilst the present embodiment is an MHEV, embodiments of the invention are not limited to MHEVs and may be used in non-MHEVs including conventional vehicles, as well as in hybrid electric vehicles (HEVs).

In the present embodiment, the BISG is a 48V BISG and the battery is a 48V battery although other voltages may be useful in some embodiments such as 12V, 24V or any other suitable voltage.

The PTU 141 is operable in one of a 2 wheel drive configuration in which it is arranged to drive a pair of rear wheels 115 of the vehicle 100 only or a 4 wheel drive configuration in which it is arranged to drive the pair of rear wheels 115 and in addition a pair of front wheels 111. The automatic transmission 131 may be disconnected from the driveline 150 when required.

The vehicle 100 has an accelerator pedal 161 by means of which a driver can control engine torque demand and a brake pedal 163 by means of which a driver may control the amount of brake force generated by a braking system 170.

The vehicle 100 has a vehicle controller (VCU) 110 that is configured to run a software program that determines, at a given moment in time, the optimal operating state of the engine 121 (on or off), BISG 125 (acting as a motor, a generator, or neither), and transmission 131 (connected to the engine 121 or disconnected from the engine 121). An engine controller 121C controls operation of the engine 121, and is in communication with the VCU 110. The transmission controller 131C is also in communication with the VCU 110 and controls operation of the transmission 131, including causing the required transmission gear ratio to be assumed at a given moment in time by selection of the required transmission gear.

In the present embodiment, the VCU 110 is configured to cause the powertrain 120 to operate in one of two modes whilst the vehicle 100 is moving:

(a) Connected powertrain mode (transmission 131 connected to the engine 121); and (b) Off coasting powertrain mode (engine 121 off and transmission 131 disconnected from the engine 121).

The transmission controller 131C receives a signal from the VCU 110 indicating the required operating mode of the powertrain 120, i.e. whether the powertrain 120 is to be operated in the drive mode or the off coasting mode, and also a signal indicating the required mode of operation of the transmission 131. In the present embodiment the transmission 131 may be operated in a park mode P, in which the transmission is disconnected from the engine 121, a reverse mode R in which the transmission is connected to the engine 121 and a reverse gear is selected, a neutral mode N in which the transmission 131 is connected to the engine 121 but no engine torque is transmitted to the driveline 150, and a drive mode D in which the transmission is connected to the engine 121 and a forward gear is selected.

When the drive mode D of the transmission 131 is selected, and the VCU 110 indicates the powertrain is to be operated in the connected powertrain mode, the transmission 131 selects a gear ratio in dependence on vehicle speed and accelerator pedal position. In some embodiments, instead of the VCU providing the indication, a separate control module such as a gear shift module (GSM) may determine driver input and relay it to the relevant control unit such as the VCU 110 or transmission controller 131C.

In order for the Off coasting’ powertrain mode to be allowable, a set of Off coasting’ powertrain mode entry conditions must be met, which in the present embodiment are the following two conditions:

(1) neither one of the accelerator pedal 161 and brake pedal 163 are depressed; and (2) the vehicle speed exceeds a predetermined minimum off coasting entry speed, in the present embodiment 20kph.

In some embodiments of the present invention, the VCU 110 may be provided with information in respect of road layout ahead of the vehicle 100. If the VCU 110 determines that a bend in the road ahead exists within a predetermined distance or time the vehicle may inhibit the off coasting powertrain mode due to the expectation of acceleration in and/or out of the corner and possible braking beforehand.

Furthermore, it is to be understood that, in some alternative embodiments, the first off coasting powertrain mode entry condition noted above may include the condition that the accelerator pedal 161 is undepressed or depressed by an amount insufficient to result in the generation of positive powertrain torque. In some embodiments the first off coasting powertrain mode entry condition noted above may include the condition that the accelerator pedal 161 is undepressed or depressed by an amount that is no more than a predetermined amount such as 5%, 10%, 15% or any other suitable amount.

In use, in the event that the vehicle 100 is travelling with the powertrain 120 in the motoring mode the VCU 110 is configured repeatedly to determine whether the off coasting mode entry conditions are met. If the off coasting powertrain mode entry conditions noted above are met, the VCU 110 causes the powertrain 120 to assume the off coasting mode. If the VCU 110 subsequently detects depression of the accelerator pedal 161, the VCU 110 causes the powertrain to resume operation in the connected powertrain mode. In order to do so, the engine 121 must be restarted and connected to the transmission 131.

The amount of time required to reconnect the transmission 131 to the engine 121 and deliver a predetermined rate of acceleration of the vehicle following detection of depression of the accelerator pedal 161 is referred to as the ‘time to torque’. In the present embodiment the predetermined rate of acceleration is 0.07g and the time to torque is around 500ms. Other values may be useful, and achievable, in some embodiments. The actual value may depend at least in part on the type of engine 121 and transmission 131 employed by the vehicle 100.

In the present embodiment, when the powertrain is in the connected mode the transmission controller 131C is configured to cause the transmission 131 to assume a transmission gear ratio (by selection of the corresponding transmission gear) at a given moment in time that is determined by reference to an ‘engine connected’ relationship defined by an ‘engine connected map’ or ‘engine connected look-up table’ stored by the transmission controller 131C. This map or look-up table may be referred to as a ‘default’ map or look-up table and defines the relationship between vehicle speed, gear ratio, accelerator pedal position and engine speed when the transmission 131 is connected to the engine 121.

The controller also stores a ‘connection map’ for use only when determining in which gear the transmission 131 should be placed immediately prior to reconnecting the transmission 131 to the engine 121 when the powertrain is in the off coasting mode. The connection map defines the relationship between vehicle speed and required transmission gear ratio, and is independent of accelerator pedal position in the present embodiment.

The engine connected map stores values of vehicle speed at which a shift from one transmission gear to the next higher transmission gear is to be made (or said higher transmission gear to the gear below it), as a function of accelerator pedal position. Thus, the range of values of speed over which any given transmission gear is to be assumed, for a given accelerator pedal position, may be determined. In some embodiments separate engine connected maps may be provided for transmission gear upshifts and transmission gear downshifts, respectively. FIG. 2 illustrates an engine connected map for the vehicle of FIG. 1. The vertical axis of FIG. 2 corresponds to accelerator pedal position P whilst the horizontal axis corresponds to vehicle speed and engine speed. Traces ‘a’ to ‘g’ show transition points between successively higher gears, and represent values of vehicle speed and accelerator pedal position at which a transition from one gear to the next lower gear will occur, moving from right to left across a given trace. Trace (a) represents the transition from second gear to first, trace (b) represents the transition from third gear to second, and so forth.

The engine connected map is configured to provide a suitable transmission gear for a given vehicle speed and accelerator pedal position under a range of on-road driving conditions including urban and highway driving. In contrast, the connection map is configured to generate a gear number based on vehicle speed only, being independent of accelerator pedal position. The gear number generated provides a suitable compromise between the requirement to connect the engine 121 to the transmission 131 as quickly as possible when it is required for the powertrain 120 to transition from the off coasting mode to the engine connected mode (which in turn requires engine speed and transmission speed to be matched as quickly as possible, the engine 121 being spun up from a stationary condition by the BISG 125), and selecting a transmission gear that allows the powertrain 120 to meet driver torque demand without requiring an immediate transmission gear downshift upon reconnection of engine 121 and transmission 131.

It is to be understood that, the lower the gear in which the transmission 131 is configured to operate at the time of reconnection of the engine 121 and transmission 131, the lower the likelihood that a downshift will be required shortly after reconnection in order to meet driver torque demand. However, the lower the transmission gear at which reconnection takes place, the higher the engine speed required in order to reconnect the transmission 131, and therefore the longer the required time for reconnection.

In contrast, the higher the gear in which the transmission 131 is configured to operate at the time of reconnection, the lower the required engine speed and therefore the shorter the reconnection time. However, the higher the gear the greater the likelihood that a downshift will be required shortly after reconnection in order to meet driver torque demand. It is to be understood that a downshift shortly after a reconnection can be distracting to a driver. It may cause unwanted noise, vibration or harshness (NVH) and reduce driver enjoyment.

It is to be understood that, if, when the VCU 110 commands a transition from the off coasting mode to the engine connected mode, the engine 121 and transmission 131 were to be reconnected with the transmission 131 in the gear corresponding to that defined in the drive map for substantially zero accelerator pedal depression (see line ‘A’ of FIG. 2), the selected gear would be relatively high. The probability of a downshift occurring soon after reconnection would be correspondingly high since driver torque demand is likely to be relatively high following accelerator pedal tip-in with the powertrain 120 in the off coasting powertrain mode. If the engine 121 and transmission 131 were to be reconnected with the transmission 131 in the gear corresponding to that defined in the drive map for the instant value of accelerator pedal depression, the selected gear may be relatively low. For example, if the driver depresses the accelerator pedal by 80% of full travel, the required gear number for the transmission would be relatively low, see trace ‘C’ of FIG. 2. Thus the time taken for the vehicle 100 to assume the engine connected powertrain mode may be relatively long due at least in part to the requirement for a relatively high engine speed in order to match engine and transmission speeds.

Accordingly, in some embodiments, the connection map corresponds to the engine connected map for a single predetermined accelerator pedal position that is independent of the prevailing (instant) accelerator pedal position. In the present embodiment, the predetermined accelerator pedal position corresponds to substantially 50% accelerator pedal depression, represented by trace ‘B’ of FIG. 2, although other values may be useful in some alternative embodiments. Thus, in the present embodiment the connection map differs from the engine connected map in that the connection map stores information in respect of transmission gear as a function of speed for a single accelerator pedal position and not, in addition, as a function of accelerator pedal position.

As discussed elsewhere herein, it is to be understood that in some embodiments a connection map may be provided for coasting reconnection that does not correspond to the engine connected map for a predetermined accelerator pedal position, but is a separately determined map providing a balance between engine spin up time and time to torque based on assumed pedal inputs at different vehicle speeds. The connection map may be a function of vehicle speed and not accelerator pedal position, i.e. configured to provide an indication of the required transmission gear that is dependent on vehicle speed and independent of accelerator pedal position. Alternatively, in some embodiments, the connection map may be arranged to provide an indication of the required transmission gear that is dependent on both vehicle speed and accelerator pedal position. In some alternative embodiments the connection map may be arranged to provide an indication of the required transmission gear that is dependent on vehicle speed, optionally accelerator pedal position, and in addition one or more other parameters such as terrain gradient or any other suitable parameter.

In the present embodiment, in use, when the VCU 110 requires the powertrain 120 to transition from the off coasting mode to the engine connected mode, the VCU 110 employs the connection map to determine the required transmission gear for the prevailing value of vehicle speed (by reference to a vehicle reference speed parameter). It is to be understood that by ‘prevailing’ is meant the current or instant accelerator control position. The VCU 110 then determines the required engine speed in order to allow matching of engine speed and transmission input speed so that the engine 121 and transmission 131 can be connected. The VCU 110 commands the transmission controller 131C to cause the transmission to assume the gear indicated by the connection map and commands the engine controller 121C to cause the engine to attain the required engine 121 speed. The VCU 110 causes the engine 121 to be connected to the transmission 131 as soon as the engine speed 121 is sufficiently closely matched to the transmission input speed, with the transmission 131 in the required gear.

In some embodiments, the VCU 110 calculates required engine speed based on a knowledge of vehicle speed and transmission gear ratio. In the present embodiment, the connection map is configured to output the required engine speed together with the value of required transmission gear, based on the vehicle reference speed input to the map. It is to be understood that the value of vehicle reference speed is generated by a brake controller 170C comprised by the braking system 170. It is to be understood that, in some embodiments, the transmission controller 131C may calculate required engine speed based on a knowledge of vehicle speed and transmission gear ratio, and instruct the engine controller 121C to cause the engine to set the engine target speed to the required engine speed. Other arrangements may be useful in some embodiments.

As noted above, in some alternative embodiments the connection map may store information in respect of transmission gear as a function of speed and, in addition, as a function of accelerator pedal position. However, it is to be understood that the required transmission gear output by the connection map will be typically different from that output by the engine connected map for similar values of vehicle speed.

In some embodiments, instead of consulting a separate connection map in order to obtain the required transmission gear ratio at the time of reconnection, the VCU 110 may refer to the engine connected map and apply the predetermined accelerator pedal position value, such as 50% in the present embodiment. Thus, instead of applying the actual prevailing value of accelerator pedal position P to the drive map, the substantially fixed, predetermined value is applied.

It is to be understood that embodiments of the present invention are applicable to scenarios in which an engine remains switched on during coasting, requiring the engine speed to be matched to transmission speed from an initial non-zero speed of rotation (such as in an engine-on coasting or On-coasting’ scenario), as well as embodiments in which the engine is started from a substantially zero initial speed (such as in an engine-off coasting or Offcoasting’ scenario).

It will be understood that the embodiments described above are given by way of example only and are not intended to limit the invention, the scope of which is defined in the appended claims.

Throughout the description and claims of this specification, the words “comprise” and “contain” and variations of the words, for example “comprising” and “comprises”, means “including but not limited to”, and is not intended to (and does not) exclude other moieties, additives, components, integers or steps.

Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

Features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith.

Claims

1. A control system for controlling at least a portion of a powertrain of a motor vehicle, the system being configured to cause a transmission of the powertrain to assume a predetermined gear ratio in dependence at least in part on vehicle speed in accordance with one of an engine connected relationship and a connection relationship, the control system being configured to: cause the powertrain to assume a coasting configuration in which the transmission is disconnected from an engine of the vehicle or an engine connected configuration in which the transmission is connected to the engine, and cause the transmission to assume a gear ratio in accordance with the engine connected relationship when the powertrain is in the engine connected configuration; wherein when the powertrain is in the coasting configuration, the gear ratio of the transmission is set, prior to reconnection, to a gear ratio determined in accordance with the connection relationship.

2. A control system according to claim 1 configured, when the powertrain is in the coasting configuration, to determine a value of required gear ratio and to cause the transmission to assume the required ratio substantially only when it is determined that a transition from the coasting configuration to the engine connected configuration is to be made.

3. A control system according to claim 1 configured, substantially throughout the period for which the powertrain is in the coasting configuration, to determine a value of required gear ratio and to cause the transmission to assume the required ratio if the transmission is not already in the required ratio.

4. A control system according to any preceding claim configured to receive a signal indicative of the position of an accelerator control.

5. A control system according to claim 4 configured, when the powertrain is in the engine connected configuration, to determine a value of required gear ratio as a function of vehicle speed and accelerator control position according to the engine connected relationship and to cause the transmission to assume the required ratio.

6. A control system according to any preceding claim configured, when the powertrain is in the coasting configuration, to determine a value of required gear ratio as a function of vehicle speed and not accelerator control position according to the connection relationship and to cause the transmission to assume the required ratio.

7. A control system according to claim 4 or claim 5 configured, when the powertrain is in the coasting configuration, to determine a value of required gear ratio as a function of vehicle speed and accelerator control position at least according to the connection relationship and to cause the transmission to assume the required ratio.

8. A control system according to any preceding claim wherein the connection relationship corresponds substantially to the engine connected relationship at a substantially fixed, predetermined accelerator control position.

9. A control system according to any preceding claim configured to store information defining the engine connected relationship in the form of an engine connected map.

10. A control system according to claim 9 as dependent on claim 8 configured to employ the engine connected map at the predetermined value of accelerator control position in order to determine the required transmission gear ratio according to the connection relationship.

11. A control system according to claim 4 or any of claims 5 to 10 depending through claim 4 configured to cause the powertrain to assume the coasting configuration when a predetermined one or more coasting configuration entry conditions are met, the one or more coasting configuration entry conditions including the condition that the accelerator control position corresponds to substantially zero.

12. A control system according to claim 11 wherein the one or more coasting configuration entry conditions further include the condition that a braking system has not been actuated and vehicle speed exceeds a predetermined minimum coasting configuration entry speed.

13. A control system according to any preceding claim wherein in the coasting configuration the engine is disconnected from the transmission and the engine is switched off.

14. A control system according to any preceding claim comprising an electronic controller, the controller comprising processing means, wherein the processing means comprises an electronic processor having an electronic memory device electrically coupled to the electronic processor and having instructions stored therein, wherein the processor is configured to access the memory device and execute the instructions stored therein such that it is operable to cause the powertrain to assume a coasting configuration in which the transmission is disconnected from an engine of the vehicle or an engine connected configuration in which the transmission is connected to the engine, wherein when the powertrain is in the engine connected configuration the controller causes the transmission to assume a gear ratio in accordance with the engine connected relationship, and when the powertrain is in the coasting configuration and a transition to the engine connected configuration is required in which the transmission is reconnected to the engine , the controller causes the transmission to assume, prior to reconnection, a gear ratio determined in accordance with the connection relationship.

15. A vehicle comprising a control system according to any preceding claim.

16. A method of controlling at least a portion of a powertrain of a motor vehicle, the method comprising causing a transmission of the powertrain to assume a predetermined transmission gear ratio in dependence at least in part on vehicle speed in accordance with one of an engine connected relationship and a connection relationship, the method comprising causing the powertrain to assume a coasting configuration in which the transmission is disconnected from an engine of the vehicle or an engine connected configuration in which the transmission is connected to the engine, whereby when the powertrain is in the engine connected configuration the method comprises causing the transmission to assume a gear ratio in accordance with the engine connected relationship, and when the powertrain is in the coasting configuration and a transition to the engine connected configuration is required in which the transmission is reconnected to the engine, the method comprises setting the gear ratio of the transmission, prior to reconnection, to a gear ratio determined in accordance with the connection relationship.

17. A non-transitory computer readable carrier medium carrying computer readable code for controlling a vehicle to carry out the method of claim 16.

18. A computer program product executable on a processor so as to implement the method of claim 16.

19. A non-transitory computer readable medium carrying computer readable code which when executed causes a vehicle to carry out the method of claim 16.

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20. A processor arranged to implement the method of claim 16, or the computer program product of claim 18.