U.S. patent application number 16/037792 was filed with the patent office on 2018-11-15 for hybrid electric vehicle controller and method.
The applicant listed for this patent is Jaguar Land Rover Limited. Invention is credited to Matthew HANCOCK, Geoff HANNIS, Manoj LAO, Steve LIGGINS, Simon MESSAGE.
Application Number | 20180326970 16/037792 |
Document ID | / |
Family ID | 49302033 |
Filed Date | 2018-11-15 |
United States Patent
Application |
20180326970 |
Kind Code |
A1 |
HANCOCK; Matthew ; et
al. |
November 15, 2018 |
HYBRID ELECTRIC VEHICLE CONTROLLER AND METHOD
Abstract
Embodiments of the present invention provide a controller for a
hybrid electric vehicle having an engine, electric propulsion means
powered by energy storage means and electric generator means
operable to be driven by the engine to recharge the energy storage
means, the controller being operable to: receive a signal
indicative of a required hybrid driving mode; receive a signal
indicative of a state of charge of the energy storage means;
determine which of a plurality of powertrain operating modes is
appropriate for vehicle operation at a given moment, the powertrain
operating modes including an engine charging mode in which the
engine drives the generator means to recharge the energy storage
means and an electric vehicle (EV) mode in which the engine is
switched off and the electric propulsion means is operable to
develop drive torque to drive the vehicle; and cause the powertrain
to assume the appropriate powertrain operating mode and the
required hybrid driving mode, wherein the controller is operable to
determine which of the plurality of powertrain operating modes is
appropriate for vehicle operation in dependence at least in part on
the signal indicative of the instant state of charge of the energy
storage means and a reference value of state of charge, the
controller being operable to set the reference value of state of
charge to one of a plurality of different respective values in
dependence on the signal indicative of the required hybrid driving
mode.
Inventors: |
HANCOCK; Matthew; (Whitley,
GB) ; LIGGINS; Steve; (Whitley, GB) ; MESSAGE;
Simon; (Whitley, GB) ; LAO; Manoj; (Whitley,
GB) ; HANNIS; Geoff; (Whitley, GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Jaguar Land Rover Limited |
Whitley |
|
GB |
|
|
Family ID: |
49302033 |
Appl. No.: |
16/037792 |
Filed: |
July 17, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14910814 |
Feb 8, 2016 |
10053081 |
|
|
PCT/EP2014/067752 |
Aug 20, 2014 |
|
|
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16037792 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B60W 20/13 20160101;
B60W 20/16 20160101; B60W 2540/00 20130101; Y02T 10/84 20130101;
Y10S 903/93 20130101; B60W 20/17 20160101; B60K 6/48 20130101; Y02T
10/6221 20130101; Y02T 10/62 20130101; B60W 10/06 20130101; Y02T
10/7258 20130101; B60W 20/20 20130101; B60W 2710/083 20130101; B60W
50/082 20130101; Y02T 10/56 20130101; B60W 2510/244 20130101; Y02T
10/6265 20130101; B60W 10/08 20130101; B60K 6/52 20130101; B60W
20/11 20160101; B60W 2540/215 20200201; B60W 10/26 20130101; B60W
2710/0666 20130101; Y02T 10/40 20130101; Y02T 10/72 20130101 |
International
Class: |
B60W 20/13 20060101
B60W020/13; B60W 20/17 20060101 B60W020/17; B60W 20/16 20060101
B60W020/16; B60W 20/11 20060101 B60W020/11; B60K 6/52 20060101
B60K006/52; B60K 6/48 20060101 B60K006/48 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 21, 2013 |
GB |
1314990.1 |
Claims
1. A controller for a hybrid electric vehicle having a powertrain
comprising an engine, an electric propulsion motor powered by a
battery, and an electric generator operable to be driven by the
engine to recharge the battery, the controller configured to:
receive a signal indicative of a required hybrid operating mode of
the vehicle; determine which of a plurality of powertrain modes is
appropriate for vehicle operation at a given moment, the powertrain
modes including at least one powertrain mode in which the engine is
switched on and an electric vehicle (EV) powertrain mode in which
the engine is switched off and the electric propulsion motor is
operable to develop drive torque to drive the vehicle; and cause
the powertrain to assume the appropriate powertrain mode according
to the required hybrid operating mode, wherein hybrid operating
modes include a first hybrid operating mode favoring prolonged
operation in the EV powertrain mode by promoting charging of the
battery to a higher state of charge, and a second hybrid operating
mode favoring a reduction in fuel consumption, wherein the
controller is operable to cause the engine to switch on when
vehicle speed exceeds a prescribed value, wherein the prescribed
value when the vehicle is operating in the first hybrid operating
mode is set to a value exceeding that of a prevailing speed limit
of a road which the vehicle is driving on.
2. The controller of claim 1, configured to receive a signal
indicative of the required hybrid operating mode from a user.
3. The controller of claim 1, wherein the prescribed value is
higher when the vehicle is operating in the first hybrid operating
mode relative to the second hybrid operating mode.
4. The controller of claim 3, wherein the prescribed value in the
first hybrid operating mode is 35 mph and the prescribed value in
the second hybrid operating mode is 30 mph, the prevailing speed
limit being 30 mph.
5. The controller of claim 3, wherein the prescribed value in the
first hybrid operating mode is 40 mph and the prescribed value in
the second hybrid operating mode is 35 mph, the prevailing speed
limit being 35 mph.
6. The controller of claim 1, wherein the controller is configured
to receive a signal indicative of a state of charge of the battery;
wherein the powertrain modes include an engine charging mode in
which the engine drives the electrical generator to recharge the
battery; wherein the first hybrid operating mode favors prolonged
operation in the EV powertrain mode by promoting charging of the
battery to a higher state of charge when the powertrain is in the
engine charging mode; and wherein the controller is operable for
determining which of the plurality of powertrain modes is
appropriate for vehicle operation in dependence at least in part on
a signal indicative of an instant state of charge of the battery
and a reference value of state of charge, the reference value in
the first hybrid operating mode being higher than that in the
second hybrid operating mode, and the controller being operable to
set the reference value of state of charge to one of a plurality of
defined respective values in dependence on the signal indicative of
the required hybrid operating mode and additionally in dependence
on a selected transmission mode, the selected transmission mode
being one of a plurality of selectable transmission modes.
7. The controller of claim 6, configured to determine the
appropriate powertrain mode in dependence on a deviation of the
signal indicative of the instant state of charge from the reference
value of state of charge.
8. The controller of claim 6, configured to determine which of the
powertrain modes is appropriate at a given moment in time according
to a value of a cost function for each powertrain mode, the value
of the cost function being determined by reference to the signal
indicative of the instant state of charge and the reference value
of state of charge of the respective powertrain modes.
9. The controller of claim 6, wherein the value of the cost
function of each powertrain mode is determined in further
dependence on at least one selected from amongst a rate of fuel
consumption of the vehicle, a rate of emission of a gas by the
vehicle and an amount of noise generated by the vehicle, and
wherein the controller is configured to determine a required
powertrain mode according to a feedback Stackelberg equilibrium
control optimization methodology.
10. The controller of claim 6, wherein, when the powertrain is in
the EV powertrain mode, the controller is operable to cause the
powertrain to assume the engine charging powertrain mode in
dependence on driver torque demand, wherein when the first hybrid
operating mode is selected the controller is configured to cause
the vehicle to assume the engine charging powertrain mode only at
higher values of driver torque demand than when the second hybrid
operating mode is selected.
11. The controller of claim 6, wherein, when the powertrain is in
the engine charging operating mode, the controller is configured to
cause the electric generator to apply a greater charging load to
the engine when the vehicle is in the first hybrid operating mode
compared with the second hybrid operating mode.
12. The controller of claim 6, wherein the controller is configured
to command the powertrain to assume the engine charging mode when
the second hybrid operating mode is selected and the state of
charge of the battery is below a prescribed soft minimum value
state of charge, the soft minimum value state of charge being
greater than a prescribed absolute minimum value state of charge,
wherein the controller is configured to determine whether it is
appropriate for the powertrain to assume the engine charging
powertrain mode or the EV powertrain mode when the vehicle is
operating in the first hybrid operating mode or upon vehicle
initialization and the state of charge is below the prescribed soft
minimum value state of charge, wherein a magnitude of an interval
from the prescribed absolute minimum value state of charge to the
prescribed soft minimum value state of charge is approximately 10%
of the magnitude of the interval from the prescribed absolute
minimum value state of charge to a prescribed absolute maximum
value state of charge.
13. The controller of claim 6, wherein if the state of charge
reaches a value below a prescribed engine start value of the state
of charge, the controller commands the engine to start and the
powertrain to assume the engine charging mode until the state of
charge exceeds a prescribed minimum engine stop value of the state
of charge, wherein once the state of charge exceeds the minimum
engine stop value of the state of charge the powertrain may resume
operation in the EV powertrain mode if the controller determines
this is the optimum powertrain mode according to an energy
optimization strategy; and wherein if the powertrain resumes
operation in the EV powertrain mode once the state of charge
exceeds the prescribed minimum engine stop value of the state of
charge following an engine start due to the state of charge falling
below the engine start value of the state of charge causing the
powertrain to assume the engine charging mode, the minimum engine
stop value of the state of charge is incremented by a prescribed
increment amount.
14. A hybrid electric vehicle, comprising: a powertrain comprising
an engine, an electric propulsion motor powered by a battery, an
electric generator operable to be driven by the engine to recharge
the battery, and a controller; wherein the controller is configured
to: receive a signal indicative of a required hybrid operating mode
of the vehicle; determine which of a plurality of powertrain modes
is appropriate for vehicle operation at a given moment, the
powertrain modes including at least one powertrain mode in which
the engine is switched on and an electric vehicle (EV) powertrain
mode in which the engine is switched off and the electric
propulsion motor is operable to develop drive torque to drive the
vehicle; cause the powertrain to assume the appropriate powertrain
mode according to the required hybrid operating mode, wherein
hybrid operating modes include a first hybrid operating mode
favoring prolonged operation in the EV powertrain mode by promoting
charging of the battery to a higher state of charge, and a second
hybrid operating mode favoring a reduction in fuel consumption; and
cause the engine to switch on when vehicle speed exceeds a
prescribed value, wherein the prescribed value when the vehicle is
operating in the first hybrid operating mode is set to a value
exceeding that of a prevailing speed limit of a road which the
vehicle is driving on.
15. The vehicle of claim 14, wherein the electric generator and the
electric propulsion motor are each provided by an electric machine,
and wherein the controller is further configured to cause the
electric machine to be operated as the electric propulsion motor or
as the electric generator.
16. The vehicle of claim 14, wherein the electric generator and
electric propulsion motor are provided by respective different
electric machines.
17. The vehicle of claim 14, further configured to operate in a
parallel mode in which the engine delivers drive torque to the
powertrain.
18. The vehicle of claim 14, further configured to operate in a
series mode in which the engine drives the electric generator to
develop charge to recharge the battery or power the electric
propulsion motor while the electric propulsion motor delivers drive
torque to the powertrain.
19. A method of controlling a hybrid electric vehicle having a
powertrain comprising an engine, an electric propulsion motor
powered by a battery, and an electric generator configured to be
driven by the engine to recharge the battery, the method
comprising: receiving a signal indicative of a required hybrid
operating mode; determining which of a plurality of powertrain
operating modes is appropriate for vehicle operation at a given
moment, the powertrain operating modes including at least one
powertrain mode in which the engine is switched on and an electric
vehicle (EV) mode in which the engine is switched off and the
electric propulsion motor is configured to develop drive torque to
drive the vehicle; causing the powertrain to assume the appropriate
powertrain operating mode and the required hybrid operating mode,
wherein hybrid operating modes include a first hybrid operating
mode favoring prolonged operation in the EV powertrain mode by
promoting charging of the battery to a higher state of charge, and
a second hybrid operating mode favoring a reduction in fuel
consumption; and causing the engine to switch on when vehicle speed
exceeds a prescribed value, wherein the prescribed value when the
vehicle is operating in the first hybrid operating mode is set to a
value exceeding that of a prevailing speed limit of a road which
the vehicle is driving on.
20. A computer readable medium carrying computer program code for
controlling a vehicle to carry out the method of claim 19.
Description
RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 14/910,814, filed Feb. 8, 2016, which itself
is a 35 U.S.C. .sctn. 371 national stage application of PCT
Application No. PCT/EP2014/067752, filed on Aug. 20, 2014, which
claims priority from Great Britain Patent Application No. 1314990.1
filed on Aug. 21, 2013, the contents of which are incorporated
herein by reference in their entireties. The above-referenced PCT
International Application was published in the English language as
International Publication No. WO 2015/024971 A2 on Feb. 26,
2015.
TECHNICAL FIELD
[0002] The present invention relates to controllers for hybrid
electric vehicles. In particular embodiments of the invention
relate to controllers for hybrid electric vehicles operable in a
parallel mode.
BACKGROUND
[0003] It is known to provide a hybrid electric vehicle having an
internal combustion engine operable to provide drive torque to
drive the vehicle and an electrical propulsion motor operable to
provide drive torque when the vehicle is operated in an electric
vehicle (EV) mode. A vehicle control system determines when to
switch the internal combustion engine on or off, and when to open
or close a clutch KO between the engine and a transmission. In some
vehicles the electric propulsion motor is integrated into the
transmission.
[0004] It is also known to provide an electric machine as a starter
for cranking the engine when an engine start is required. Known
starters include belt-integrated starter/generators. Such devices
are operable as electrical generators driven by the engine as well
as a starter. The vehicle may include a belt integrated starter
generator in addition to a starter for starting the engine, in some
embodiments.
SUMMARY OF THE INVENTION
[0005] Embodiments of the invention may be understood with
reference to the appended claims.
[0006] Aspects of the present invention provide a control system, a
vehicle and a method.
[0007] In one aspect of the invention for which protection is
sought there is provided a controller for a hybrid electric vehicle
having an engine, electric propulsion means powered by energy
storage means and electric generator means operable to be driven by
the engine to recharge the energy storage means, the controller
being operable to: [0008] receive a signal indicative of a required
hybrid driving mode; [0009] receive a signal indicative of a state
of charge of the energy storage means; [0010] determine which of a
plurality of powertrain operating modes is appropriate for vehicle
operation at a given moment, the powertrain operating modes
including an engine charging mode in which the engine drives the
generator means to recharge the energy storage means and an
electric vehicle (EV) mode in which the engine is switched off and
the electric propulsion means is operable to develop drive torque
to drive the vehicle; and cause the powertrain to assume the
appropriate powertrain operating mode and the required hybrid
driving mode, wherein the controller is operable to determine which
of the plurality of powertrain operating modes is appropriate for
vehicle operation in dependence at least in part on the signal
indicative of the instant state of charge of the energy storage
means and a reference value of state of charge, the controller
being operable to set the reference value of state of charge to one
of a plurality of different respective values in dependence on the
signal indicative of the required hybrid driving mode.
[0011] Embodiments of the present invention have the advantage that
the operating mode of the powertrain at a given moment in time may
be influenced by adjustment of the reference value of the state of
charge depending on the selected hybrid driving mode. Thus, in some
embodiments the controller may be configured to favour operation of
the powertrain in the EV mode when a particular driving mode is
selected. Thus if a user wishes to enjoy vehicle operation in EV
mode more than a mode in which the engine is switched on, the user
may select a corresponding hybrid driving mode.
[0012] It is to be understood that reference to an instant state of
charge is to be understood to mean a prevailing or current state of
charge of the energy storage means. The instant state of charge may
be the most recently available measured value of state of charge of
the energy storage means in some embodiments.
[0013] The engine may be an internal combustion engine. The engine
may be petrol fired or diesel fired. Other arrangements are also
useful.
[0014] The controller may be operable to determine the appropriate
powertrain operating mode in dependence at least in part on a
deviation of the signal indicative of the instant state of charge
from the reference value of state of charge.
[0015] It is to be understood that in some embodiments the
controller may be arranged to promote charging of the energy
storage means to a higher state of charge when the powertrain is in
the engine charging mode, thus favouring operation of the
powertrain in the EV mode for longer periods when the engine is
switched off.
[0016] The controller may be operable to determine which of the
powertrain operating modes is appropriate at a given moment in time
according to a value of a cost function for each powertrain
operating mode, the value of the cost function being determined at
least in part by reference to the signal indicative of the instant
state of charge and the reference value of state of charge of the
respective powertrain operating modes.
[0017] Optionally, the value of the cost function of each
powertrain operating mode is determined at least in part in further
dependence on at least one selected from amongst a rate of fuel
consumption of the vehicle, a rate of emission of a gas by the
vehicle and an amount of noise generated by the vehicle.
[0018] The controller may be configured to determine the required
powertrain operating mode according to a feedback Stackelberg
equilibrium control optimisation methodology.
[0019] Such a methodology is known, and may be understood for
example by reference to UK patent application GB1115248.5.
[0020] In some embodiments, the cost function is responsive at
least in part to a rate of fuel consumption of the vehicle, a rate
of emission of a gas by the vehicle and/or a deviation of a state
of charge of the energy storage means from the reference value.
[0021] The controller may be arranged to receive a signal
indicative of the required hybrid driving mode from a user.
[0022] That is, the user may input a signal indicative of the
required hybrid driving mode.
[0023] Optionally, the hybrid driving modes include a first driving
mode favouring prolonged operation in EV mode, and a second driving
mode favouring a reduction in fuel consumption, wherein the value
of reference state of charge in the first driving mode is higher
than that in the second driving mode.
[0024] The first mode may correspond to a selectable electric
vehicle (SEV) mode. The second mode may correspond to a general or
default hybrid electric vehicle (HEV) driving mode. In embodiments,
other modes may be available and/or useful.
[0025] Advantageously, when the powertrain is in the EV powertrain
mode the controller may be operable to cause the powertrain to
assume the engine charging powertrain mode in dependence at least
in part on driver torque demand. If the vehicle is in the first
mode and the powertrain is in the EV powertrain mode, the
controller may be arranged to cause the powertrain to switch from
the EV mode to the engine charging powertrain mode only above a
threshold value of driver torque demand that is higher than that
when the vehicle is operating in the second mode.
[0026] Advantageously, when the powertrain is in the engine
charging operating mode the controller may be configured to cause
the generator means to apply a greater charging load to the engine
when the vehicle is in the first driving mode compared with the
second driving mode.
[0027] This feature has the advantage that, because the energy
storage means is charged more aggressively in the first mode, the
state of charge increases more quickly, enabling the vehicle to
spend a greater amount of time in the EV powertrain operating
mode.
[0028] Optionally when the powertrain is in the EV operating mode
the controller is operable to cause the engine to switch on when
vehicle speed exceeds a prescribed value, the prescribed value
being higher when the vehicle is operating in the first mode
relative to the second mode.
[0029] The prescribed vehicle speed for engine start may be
gradient dependent. That is, the threshold may be greater when the
vehicle is descending a hill compared with travel over flat
terrain, or uphill. The speed may increase with increasing downhill
gradient steepness.
[0030] The engine may be switched on to provide drive torque in the
case of a parallel hybrid vehicle, or so that the powertrain can
assume the engine charging mode in the case of a parallel hybrid
electric vehicle or a series hybrid electric vehicle.
[0031] Optionally, when the controller causes the vehicle to
operate in the first mode or the second mode the controller causes
the engine to turn on in dependence at least in part on an amount
by which an accelerator pedal is depressed.
[0032] If the accelerator pedal is not depressed, or depressed by
less than a threshold amount, the controller may cause the
powertrain to remain in the EV mode. Thus if a vehicle speed
increases above a turn-on threshold due to coasting downhill, the
vehicle may remain in the EV mode.
[0033] Optionally the state of charge of the energy storage means
is permitted to take a value from a prescribed absolute minimum
state of charge to a prescribed soft minimum value greater than the
prescribed absolute minimum state of charge only when the vehicle
is operating in the first hybrid operating mode or upon vehicle
initialisation.
[0034] The magnitude of the interval from the prescribed absolute
minimum state of charge to the prescribed soft minimum value may be
approximately 10% of the magnitude of the interval from the
prescribed absolute minimum state of charge to a prescribed
absolute maximum state of charge.
[0035] This has the benefit that the powertrain is more likely to
operate in the EV mode when the driver selects the first mode
because the interval of state of charge values below the soft
minimum value (that is, in the so-called `reserved` interval) will
normally be available for use. The reserved interval may be used
automatically upon vehicle initialisation thus providing a smooth
vehicle departure from rest. Once the vehicle has operated in the
reserved interval, the controller may subsequently inhibit vehicle
operation in said reserved interval when the state of charge value
increases above the prescribed soft minimum value. This helps to
some extent to ensure that the driver does not experience prolonged
periods when the engine is on and/or periods where a greater
charging load to the engine is applied when the vehicle is no
longer operating in the first mode.
[0036] The controller may be operable to cause the engine to be
drivably coupled to one or more wheels of the vehicle in addition
to the electric propulsion means.
[0037] Thus the controller may be suitable for controlling a
parallel hybrid vehicle.
[0038] The controller may be operable to cause the engine to
deliver drive torque when the powertrain is operated in the engine
charging mode.
[0039] The controller may be operable to cause the powertrain to
operate in a parallel boost mode in which the engine delivers drive
torque in addition to the electric propulsion means.
[0040] In a further aspect of the invention for which protection is
sought there is provided a hybrid electric vehicle powertrain
comprising a controller according to a preceding aspect.
[0041] Optionally, the electric generator means and the electric
propulsion means are each provided by an electric machine.
[0042] The controller may be operable to cause the electric machine
to be operated as a propulsion motor or a generator.
[0043] The generator means may comprise an electric generator and
the electric propulsion means may comprise a propulsion motor.
[0044] In a further aspect of the invention there is provided a
hybrid electric vehicle comprising a controller or a powertrain
according to a preceding aspect.
[0045] The vehicle may be operable in a parallel mode in which the
engine delivers drive torque to the powertrain.
[0046] The vehicle may be operable in a series mode in which the
engine drives the generator means to develop charge to recharge the
battery or power the propulsion motor whilst the propulsion motor
delivers drive torque to the powertrain.
[0047] In a further aspect of the invention for which protection is
sought there is provided a method of controlling a hybrid electric
vehicle having an engine, electric propulsion means powered by
energy storage means and electric generator means operable to be
driven by the engine to recharge the energy storage means, the
method comprising: [0048] receiving a signal indicative of a
required hybrid driving mode; [0049] receiving a signal indicative
of a state of charge of the energy storage means; [0050]
determining which of a plurality of powertrain operating modes is
appropriate for vehicle operation at a given moment, the powertrain
operating modes including an engine charging mode in which the
engine drives the generator means to recharge the energy storage
means and an electric vehicle (EV) mode in which the engine is
switched off and the electric propulsion means is operable to
develop drive torque to drive the vehicle; and causing the
powertrain to assume the appropriate powertrain operating mode and
the required hybrid driving mode, [0051] the method comprising
determining which of the plurality of powertrain operating modes is
appropriate for vehicle operation in dependence at least in part on
the signal indicative of the instant state of charge of the energy
storage means and a reference value of state of charge, and setting
the reference value of state of charge to one of a plurality of
different respective values in dependence on the signal indicative
of the required hybrid driving mode.
[0052] In one aspect of the invention for which protection is
sought there is provided a computer readable medium carrying
computer program code for controlling a vehicle to carry out a
method according to a preceding aspect.
[0053] Within the scope of this application it is envisaged that
the various aspects, embodiments, examples, features and
alternatives set out in the preceding paragraphs, in the claims
and/or in the following description and drawings may be taken
independently or in any combination. Features described with
reference to one embodiment are applicable to all embodiments,
unless there is incompatibility of features.
[0054] For the avoidance of doubt, it is to be understood that
features described with respect to one aspect of the invention may
be included within any other aspect of the invention, alone or in
appropriate combination with one or more other features.
BRIEF DESCRIPTION OF THE DRAWINGS
[0055] Embodiments of the invention will now be described with
reference to the accompanying figures in which:
[0056] FIG. 1 is a schematic illustration of a hybrid electric
vehicle according to an embodiment of the present invention;
and
[0057] FIG. 2 illustrates operation of the vehicle of FIG. 1 in a
general hybrid electric vehicle (HEV) driving mode;
[0058] FIG. 3 illustrates operation of the vehicle of FIG. 1 in a
selectable electric vehicle (SEV) driving mode; and
[0059] FIG. 4 is a table illustrating changes in vehicle behaviour
when operating in the SEV mode compared with operation in the HEV
mode.
DETAILED DESCRIPTION
[0060] In one embodiment of the invention a hybrid electric vehicle
100 is provided as shown in FIG. 1. The vehicle 100 has an engine
121 coupled to a belt integrated starter generator (BISG) 123B. The
BISG 123B may also be referred to as a belt integrated (or belt
mounted) motor generator and is operable to crank the engine 121
when starting is required. In addition or instead, a dedicated
starter motor may be provided. In some embodiments therefore, a
BISG may be provided but a separate starter motor is employed for
starting the engine 121. The engine 121 is coupled in turn to a
crankshaft-integrated starter/generator (CIMG) 123C by means of a
clutch 122. The clutch 122 may also be referred to as a KO clutch
122.
[0061] The CIMG 123C is integrated into a housing of a transmission
124 which is in turn coupled to a driveline 130 of the vehicle 100
thereby to drive a pair of front wheels 111, 112 and a pair of rear
wheels 114, 115 of the vehicle 100. The driveline 130 in
combination with the transmission 124, CIMG 123C, clutch 122,
engine 121 and BISG 123B may be considered to form part of a
powertrain 131 of the vehicle 100. Wheels 111, 112, 114, 115
arranged to be driven by the driveline 130 may also be considered
to form part of the powertrain 131.
[0062] It is to be understood that other arrangements are also
useful. For example the driveline 130 may be arranged to drive the
pair of front wheels 111, 112 only or the pair of rear wheels 114,
115 only, or to be switchable between a two wheel drive mode in
which the front or rear wheels only are driven and a four wheel
drive mode in which the front and rear wheels are driven.
[0063] The BISG 123B and CIMG 123C are arranged to be electrically
coupled to a charge storage module 150 having a battery and an
inverter. The module 150 is operable to supply the BISG 123B and/or
CIMG 123C with electrical power when one or both are operated as
propulsion motors. Similarly, the module 150 may receive and store
electrical power generated by the BISG 123B and/or CIMG 123C when
one or both are operated as electrical generators. In some
embodiments, the CIMG 123C and BISG 123B may be configured to
generate different electrical potentials to one another.
Accordingly, in some embodiments each is connected to a respective
inverter adapted to operate at the corresponding potential of the
CIMG 123C or BISG 123B. Each inverter may have a respective battery
associated therewith. In some alternative embodiments the CIMG 123C
and BISG 123B may be coupled to a single inverter which is adapted
to receive charge from the CIMG 123C and BISG 123B at the
respective potentials and to store the charge in a single battery.
Other arrangements are also useful.
[0064] As noted above, the BISG 123B has an electric machine 123BM
that is drivably coupled to a crankshaft 121C of the engine 121 by
means of a belt 123BB. The BISG 123B is operable to provide torque
to the crankshaft 121C when it is required to start the engine 121
or when it is required to provide torque-assist to the driveline
130 as discussed in further detail below.
[0065] The vehicle 100 has a vehicle controller 140 operable to
command a powertrain controller 141PT to control the engine 121 to
switch on or off and to generate a required amount of torque. The
vehicle controller 140 is also operable to command the powertrain
controller 141PT to control the BISG 123B to apply a required value
of positive or negative torque (operating as a propulsion motor or
a generator) to the engine 121. Similarly, the vehicle controller
140 may command the CIMG 123C to apply a required value of positive
or negative torque (again operating as a propulsion motor or a
generator) to the driveline 130 via the transmission 124.
[0066] The vehicle has an accelerator pedal 171 and a brake pedal
172. The accelerator pedal 171 provides an output signal to the
vehicle controller 140 indicative of an amount by which the pedal
171 is depressed. The vehicle controller 140 is arranged to
determine the amount of driver demanded torque based on the
accelerator pedal position and one or more other vehicle parameters
including engine speed W.
[0067] The vehicle 100 of FIG. 1 is operable by the vehicle
controller 140 in an electric vehicle (EV) mode in which the clutch
122 is open and the crankshaft 121C is stationary. In EV mode the
CIMG 123C is operable to apply positive or negative torque to the
driveline 130 via the transmission 124. Negative torque may be
applied for example when regenerative braking is required under the
control of a brake controller 142B.
[0068] The powertrain 131 is operable in one of a plurality of
parallel modes in which the engine 121 is switched on and the
clutch 122 is closed. The parallel modes include a `parallel boost`
mode in which the CIMG 123C is operated as a motor to provide drive
torque to the driveline 130 in addition to the torque provided by
the engine 121. In the present embodiment the powertrain 131 is
operated in the parallel boost configuration when the amount of
driver demanded torque exceeds the maximum torque available from
the engine 121. The amount of additional torque available from the
CIMG 123C may be determined in dependence on the vehicle
configuration as described in more detail below. It is to be
understood that the feature of torque boost increases the available
drive torque beyond that which is available from the engine 121
alone.
[0069] The parallel modes also include a parallel torque filling
mode and a parallel torque assist mode. The parallel torque filling
mode is a mode in which the CIMG 123C delivers drive torque to the
driveline 130 in addition to the engine 121 in order to meet driver
demand for torque more quickly than if the engine 121 alone
delivers drive torque. Torque filling provides the benefit that
driver torque demand may be satisfied more quickly, improving a
responsiveness of the vehicle to an increase in torque demand.
[0070] In the present embodiment torque filling is implemented when
a rate of increase of driver torque demand relative to the amount
of torque delivered by the engine 121 exceeds a prescribed value.
Once driver torque demand has been satisfied, the amount of torque
delivered by the CIMG 123C decreases as the amount of torque
delivered by the engine 121 increases to meet driver demand
substantially entirely, without a requirement for additional torque
from the CIMG 123C.
[0071] In the torque-assist parallel mode the CIMG 123C provides
steady-state drive torque in addition to the engine 121 in order to
relieve loading on the engine 121. This may assist in reducing fuel
consumption. Torque-assist may be considered to be distinct from
`torque filling`, the latter being employed in a transient manner
when an increase in drive torque is required.
[0072] The powertrain 131 may alternatively be operated in a
parallel recharge mode in which the CIMG 123C is driven as a
generator by the engine 121 to recharge the charge storage module
150.
[0073] In the present embodiment, the vehicle 100 is also operable
in one of a plurality of hybrid operating modes. The hybrid
operating modes include a default hybrid electric vehicle (HEV)
operating mode and a user-selectable EV hybrid operating mode,
referred to herein as a `selectable EV operating mode` (SEV
operating mode). The SEV operating mode is selected by a user by
means of SEV selector button 145 accessible to a driver whilst
driving. When depressed, the SEV button 145 illuminates to confirm
the SEV operating mode has been selected.
[0074] In the present embodiment the vehicle 100 is also operable
in a selectable hybrid inhibit (SHI) hybrid operating mode in which
the controller 140 causes the engine 121 to latch in the on
condition, and in a command shift or `tip shift` (TIP) hybrid
operating mode.
[0075] Whether the vehicle is operating in the HEV hybrid operating
mode, the SEV hybrid operating mode, the SHI hybrid operating mode
or the TIP operating mode the controller 140 is configured to
determine in which available powertrain mode the powertrain 131
should be operated in dependence on an energy optimisation strategy
that employs game theory. It is to be understood that in the SHI
hybrid operating mode the EV mode is not available since the engine
121 is latched in the on condition. The controller 140 is
configured to take this factor into account in determining the
required powertrain mode, however in the present embodiment the
controller 140 still employs the same energy optimisation strategy.
Other arrangements are also useful.
[0076] The non-cooperative approach of game theory is applied by
considering a multi-stage game played by the following two players:
a) a first player, the driver, represented by a discrete set of
load sites (for example wheel torque, wheel speed and gear
selected), covering the powertrain capability, and b) a second
player, the powertrain, represented by a discrete set of operating
modes.
[0077] The first player is interested in minimizing a cost
functional while the second player is interested in maximizing the
cost functional. The cost functional is formed as a sum of
incremental cost values over a finite horizon.
[0078] In respect of the embodiment of FIG. 1 the cost functional
of the game is based on the following incremental cost function L
related to the control action, u, the state vector, x, and the
operating variable, w:
L(x,u,w)=.alpha..times.Fuel(u,
w)+.beta..times.NOx(u,w)+.mu..times.[SoC.sub.SetPoint-(x-.DELTA.SoC(u,w))-
].sup.2+.gamma..times.G(w)
where u.di-elect cons.U is the control action (U is the set of
powertrain modes in this case which include the parallel boost mode
and parallel recharge mode), x.di-elect cons.X is the state vector
(X is the set of discretised high voltage battery SoC (state of
charge) values in this case) and w.di-elect cons.W is the vector of
operating variables which is also referred to as the load site
(discretised wheel speed, wheel torque and gear selected in this
case). In the above equation, Fuel denotes engine fuel consumption,
NOx denotes engine NOx emission mass flow rate, SoC.sub.SetPoint
denotes the desired SoC set-point at the end of the cycle,
.DELTA.SoC(u, w) denotes the deviation of SoC resulting from a
defined control action at a given load site.
[0079] Here G denotes a positive Gaussian function with the centre
at the centre of mass of a defined drive cycle, introduced to focus
the optimization on specific load sites.
[0080] In the present embodiment, the value of SoC set-point (which
may be referred to also as a target value or a reference value) is
changed in dependence on whether the vehicle 100 is operated in the
SEV mode, the HEV mode or the TIP mode. The SoC set-point may also
be changed in dependence on transmission operating mode. The value
of SoC set-point is set to a higher value for operation in the SEV
mode, TIP mode and transmission sport operating mode (when in the
HEV mode) compared with operation in the HEV mode in the drive
transmission operating mode in order to promote charging of the
charge storage module 150. In the present embodiment, if the
vehicle 100 is operated in the SEV mode, TIP mode or if the
transmission 124 is operated in the sport mode whilst in HEV mode,
the value of SoC set-point (that is, Game Theory setpoint, also
referred to as target value or reference value) is set to 65%
(other values are also useful) whilst if the vehicle 100 is
operated in the HEV mode (with the transmission in the drive mode)
the value of SoC set-point is set to 52%. Other values are also
useful. Similarly, other values of SoC set-point whilst operating
in various hybrid and transmission operating modes are also useful.
The fact that the value of SoC set-point is set to a higher value
in the SEV mode causes the controller 140 to tend to charge the
charge storage module 150 to higher values of state of charge
(SoC). For operation in the SHI and TIP hybrid modes, the SoC
set-point may be set to the same value as the HEV mode, or to any
other suitable value.
[0081] FIG. 2 and FIG. 3 are graphical illustrations of the manner
in which the controller 140 causes the vehicle 100 to operate when
the HEV and SEV driving modes are selected, respectively. The
figures show state of charge of the charge storage module 150 along
a horizontal axis. The content of the figures will now be
discussed.
[0082] In order to promote operation of the vehicle 100 in the EV
mode when the vehicle is in the SEV mode, the controller 140 is
configured to implement the following measures: [0083] (a) When in
SEV mode, the rate of charging of the charge storage module 150
when the powertrain is in the parallel recharge mode is increased
relative to that employed in the HEV mode. The vehicle 100 is
therefore able to spend longer periods of time in the EV mode for a
given drivecycle, satisfying the user requirement to increase the
time in which the powertrain 131 spends in the EV powertrain mode.
[0084] (b) When in SEV mode, the engine 121 is forced to turn on at
a higher engine-on threshold vehicle speed compared with operation
in the HEV mode. In the present embodiment the engine 121 is forced
to turn on when vehicle speed exceeds 35 mph and the accelerator
pedal 171 is depressed, compared with 30 mph in the HEV mode. Other
values are also useful. This feature reduces the chances of the
engine 121 being switched on when a user is attempting to maintain
a speed of 30 mph, for example when driving on a road having a
speed limit of 30 mph. Thus the engine-on threshold speed may be
set to a value exceeding that of a prevailing speed limit. If the
accelerator pedal 171 is not depressed, the engine 121 may remain
off even though vehicle speed exceeds the engine-on threshold. This
is so as to avoid switching the engine 121 on unnecessarily when
the engine-on threshold is exceeded, for example when coasting
downhill. [0085] (c) If the engine 121 switches on whilst the
vehicle 100 is cornering in SEV mode, the controller 140 allows the
engine 121 to switch off if the energy optimisation strategy
determines this should be undertaken. In contrast, if the vehicle
is operating in the HEV mode and the engine 121 switches on during
cornering, the engine 121 is latched in the on state until the
corner has been negotiated and the value of lateral acceleration
falls below a prescribed value, indicative that the vehicle is no
longer cornering, for a prescribed period of time, such as 5 s or
more. [0086] (d) If the transmission 124 of the vehicle 100 is
placed in the park or neutral mode and a minimum allowable state of
charge of the charge storage module 150 has been reached or is
reached, the energy storage module 150 is charged at the maximum
allowable rate of charge whenever the engine 121 develops
sufficient power (or operates at a sufficiently high speed) to
enable the CIMG 123C to be driven as a generator.
[0087] In some embodiments charging may not be performed if the
engine is operating at idle speed, however if the engine speed is
subject to an increase in response to depression of an accelerator
pedal 171 by a driver the controller 140 takes the opportunity to
recharge the energy storage module 150 by means of the CIMG 123C at
as high a rate as can be achieved. In some embodiments the
controller 140 may cause a speed of the engine 121 to increase in
order to allow charging of the charge storage module 150. [0088]
(e) If the SoC of the charge storage module 150 falls below a first
prescribed value (which may be referred to as a minimum SoC or soft
minimum limit) when the vehicle is operating in the SEV hybrid
mode, the engine 121 is latched on and the CIMG 123C is operated as
a generator to recharge the charge storage module 150 at the
fastest allowable rate. In contrast, in the HEV hybrid mode the
controller 140 causes the CIMG 123C to recharge at a rate
determined in dependence on the energy optimisation strategy. The
controller 140 suspends application of game theory to determine the
preferred powertrain operating mode when the SoC falls below the
first prescribed value. In the present embodiment the first
prescribed value is around 39% although other values are also
useful.
[0089] It is to be understood that in known hybrid electric
vehicles and electric vehicles, a battery for storing charge is
only permitted to vary its SoC between prescribed values (which may
be referred to as hard limits) that lie within the absolute maximum
and minimum states of charge in order to prevent deterioration in
battery life due to excessively high and low charge states. In the
present embodiment the minimum allowable battery SoC is 35% whilst
the maximum allowable SoC is 70%. Other values are also useful.
[0090] (f) The vehicle 100 may not operate in the HEV hybrid mode
if the SoC falls below a second prescribed value (or prescribed
soft minimum value) which may be greater or less than the
abovementioned first prescribed value. The SoC interval from the
absolute minimum SoC to the second prescribed value is reserved
specifically for the SEV hybrid mode. This will enable vehicle
`pull-away` in the EV mode upon initialisation of the vehicle 100.
Specifically, the SoC is permitted to be less than the second
prescribed value if the SEV hybrid mode is selected by the driver
or the vehicle 100 has just been initialised. If the SoC assumes a
value that is less than the prescribed second value, the SoC is no
longer permitted to be less than said second prescribed value if
the SEV hybrid mode is not selected or deselected and the SoC
subsequently assumes a value greater than the second prescribed
value. The SoC interval from the absolute minimum SoC to the second
prescribed value may be approximately 10% of the permitted SoC
interval (that is, the interval from the absolute minimum SoC to
the absolute maximum SoC). Other values are also useful.
[0091] In the present embodiment, if the SoC of the charge storage
module 150 reaches a value below a prescribed engine start SoC
value, the controller 140 forces the powertrain to assume the
parallel recharge mode until the SoC of the charge storage module
150 exceeds a prescribed minimum engine stop SoC value. Once the
SoC exceeds the minimum engine stop SoC value the powertrain 131
may resume operation in the EV mode if the controller 140
determines this is the optimum mode according to the energy
optimisation strategy. If the powertrain 131 resumes operation in
the EV mode once the SoC exceeds the prescribed minimum engine stop
SoC value following an engine start due to the SoC falling below
the engine start SoC value, the minimum engine stop SoC value is
incremented by a prescribed increment amount. In the present
embodiment, the prescribed increment amount is higher when
operating in SEV mode compared with HEV mode although in some
embodiments the increment amounts may be substantially equal. This
feature has the effect that when the engine 121 is next started, it
must charge the energy storage module 150 to a higher SoC before
the engine 121 may be switched off, increasing the available charge
for operation in EV mode.
[0092] In the present embodiment, when operating in HEV mode the
prescribed increment amount is 2% each time the engine is stopped
as soon as the SoC reaches the minimum engine stop SoC value. When
operating in SEV mode the prescribed increment amount is 3%. Other
values are also useful.
[0093] Advantageously, the minimum engine stop SoC is higher when
operating in the SEV mode compared with the HEV mode. This allows
longer uninterrupted periods of operation in EV mode in a number of
situations. In the present embodiment the minimum engine stop SoC
is around 43% when operating in HEV mode and around 44.5% when
operating in SEV mode. Other values are also useful.
[0094] This feature has the advantage that a time period for which
the powertrain 131 operates in EV mode may be increased.
[0095] When the powertrain 131 is operated in a parallel mode, the
controller 140 is operable to assume the parallel torque boost mode
when an amount of driver torque demand exceeds that which may be
provided by the engine 121 alone at its maximum torque output. As
noted above, driver torque demand is related to accelerator pedal
position. In the SEV mode, the controller 140 limits provision of
torque boost to situations in which the accelerator pedal is
depressed more than a prescribed amount (which may be specified in
terms of a proportion of full travel in some embodiments). In the
present embodiment, when the vehicle is operated in the SEV mode
the parallel torque boost mode is only permitted when the
accelerator pedal 171 is depressed by more than 95%, corresponding
to movement of the pedal 171 beyond the `kick down` detent in the
present embodiment. Other arrangements are also useful. However,
this feature advantageously reduces draining of charge from charge
storage module 150 relative to operation in the HEV hybrid
operating mode.
[0096] In some embodiments the controller 140 may suspend provision
of torque boost in the SEV mode altogether.
[0097] Furthermore, the provision of torque filling is also
restricted when in the SEV mode compared with the HEV mode. In some
embodiments torque filling is not permitted in the SEV mode.
[0098] In some embodiments, energy overrun charging (i.e. use of
the engine to drive the CIMG 123C in order to slow the vehicle when
the engine 121 is switched on) is not permitted in the HEV mode,
but is permitted in the SEV mode. Other arrangements are also
useful.
[0099] It is to be understood that the controller 140 is configured
to store computer program code for causing one or more computing
devices of the controller 140 to perform the method of vehicle
control described herein. It is to be understood that a controller
according to an embodiment of the present invention may be provided
by a plurality of computing devices. The functionality described as
being performed by the controller may be performed by a plurality
of computing devices, control modules or the like, optionally at
different physical locations of a vehicle.
[0100] Embodiments of the present invention may be understood by
reference to the following numbered paragraphs: [0101] 1. A
controller for a hybrid electric vehicle having an engine, an
electric propulsion motor powered by an energy storage device and
an electric generator operable to be driven by the engine to
recharge the energy storage device, the controller being operable
to: [0102] receive a signal indicative of a required hybrid
operating mode of the vehicle; [0103] receive a signal indicative
of a state of charge of the energy storage device; [0104] determine
which of a plurality of powertrain modes is appropriate for vehicle
operation at a given moment, the powertrain modes including an
engine charging mode in which the engine drives the generator to
recharge the energy storage device and an electric vehicle (EV)
mode in which the engine is switched off and the electric
propulsion motor is operable to develop drive torque to drive the
vehicle; and [0105] cause the powertrain to assume the appropriate
powertrain mode according to the required hybrid operating mode,
[0106] wherein the controller is operable to determine which of the
plurality of powertrain modes is appropriate for vehicle operation
in dependence at least in part on the signal indicative of the
instant state of charge of the energy storage device and a
reference value of state of charge, the controller being operable
to set the reference value of state of charge to one of a plurality
of different respective values in dependence on the signal
indicative of the required hybrid operating mode. [0107] 2. A
controller according to paragraph 1 operable to determine the
appropriate powertrain mode in dependence at least in part on a
deviation of the signal indicative of the instant state of charge
from the reference value of state of charge. [0108] 3. A controller
according to paragraph 1 operable to determine which of the
powertrain modes is appropriate at a given moment in time according
to a value of a cost function for each powertrain mode, the value
of the cost function being determined at least in part by reference
to the signal indicative of the instant state of charge and the
reference value of state of charge of the respective powertrain
modes. [0109] 4. A controller according to paragraph 3 wherein the
value of the cost function of each powertrain mode is determined at
least in part in further dependence on at least one selected from
amongst a rate of fuel consumption of the vehicle, a rate of
emission of a gas by the vehicle and an amount of noise generated
by the vehicle. [0110] 5. A controller according to paragraph 4
configured to determine the required powertrain mode according to a
feedback Stackelberg equilibrium control optimisation methodology.
[0111] 6. A controller according to paragraph 1 arranged to receive
a signal indicative of the required hybrid operating mode from a
user. [0112] 7. A controller according to paragraph 1 wherein the
hybrid operating modes include a first operating mode favouring
prolonged operation in EV mode, and a second operating mode
favouring a reduction in fuel consumption, wherein the value of
reference state of charge in the first operating mode is higher
than that in the second operating mode. [0113] 8. A controller
according to paragraph 7 wherein when the powertrain is in the EV
powertrain mode the controller is operable to cause the powertrain
to assume the engine charging powertrain mode in dependence at
least in part on driver torque demand, wherein when the first mode
is selected the controller is configured to cause the vehicle to
assume the engine charging powertrain mode only at higher values of
driver torque demand than when the second operating mode is
selected. [0114] 9. A controller according to paragraph 7 wherein
when the powertrain is in the engine charging operating mode the
controller is configured to cause the generator to apply a greater
charging load to the engine when the vehicle is in the first
operating mode compared with the second operating mode. [0115] 10.
A controller according to paragraph 7 wherein the controller is
operable to cause the engine to switch on when vehicle speed
exceeds a prescribed value, the prescribed value being higher when
the vehicle is operating in the first mode relative to the second
mode. [0116] 11. A controller according to paragraph 10 wherein
when the controller causes the vehicle to operate in the first
hybrid mode or the second hybrid mode, the controller is arranged
to cause the engine to turn on in dependence at least in part on an
amount by which an accelerator pedal is depressed. [0117] 12. A
controller according to paragraph 7 wherein the state of charge of
the energy storage means is permitted to take a value from a
prescribed absolute minimum state of charge to a prescribed soft
minimum value greater than the prescribed absolute minimum state of
charge only when the vehicle is operating in the first hybrid
operating mode or upon vehicle initialisation. [0118] 13. A
controller according to paragraph 12 wherein the magnitude of the
interval from the prescribed absolute minimum state of charge to
the prescribed soft minimum value is approximately 10% of the
magnitude of the interval from the prescribed absolute minimum
state of charge to a prescribed absolute maximum state of charge.
[0119] 14. A controller according to paragraph 1 operable to cause
the engine to be drivably coupled to one or more wheels of the
vehicle in addition to the electric propulsion motor. [0120] 15. A
controller according to paragraph 14 operable to cause the engine
to deliver drive torque when the powertrain is operated in the
engine charging mode. [0121] 16. A controller according to
paragraph 14 operable to cause the powertrain to operate in a
parallel mode in which the engine delivers drive torque to one or
more wheels in addition to the electric propulsion motor. [0122]
17. A hybrid electric vehicle powertrain comprising a controller
according to paragraph 1. [0123] 18. A powertrain according to
paragraph 17 wherein the electric generator and the electric
propulsion motor are each provided by an electric machine. [0124]
19. A powertrain according to paragraph 18 wherein the controller
is operable to cause the electric machine to be operated as a
propulsion motor or as a generator. Optionally, a single electric
machine may be provided, performing the functions of a generator or
a propulsion motor as required. [0125] 20. A powertrain according
to paragraph 17 wherein the generator and electric propulsion motor
are provided by respective different electric machines. [0126] 21.
A hybrid electric vehicle comprising a controller according to
paragraph 1 or a powertrain according to paragraph 15. [0127] 22. A
vehicle according to paragraph 21 operable in a parallel mode in
which the engine delivers drive torque to the powertrain. [0128]
23. A vehicle according to paragraph 21 operable in a series mode
in which the engine drives the generator to develop charge to
recharge the battery or power the propulsion motor whilst the
propulsion motor delivers drive torque to the powertrain. [0129]
24. A method of controlling a hybrid electric vehicle having an
engine, electric propulsion motor powered by an energy storage
device and an electric generator operable to be driven by the
engine to recharge the energy storage device, the method
comprising: [0130] receiving a signal indicative of a required
hybrid operating mode; [0131] receiving a signal indicative of a
state of charge of the energy storage device; [0132] determining
which of a plurality of powertrain operating modes is appropriate
for vehicle operation at a given moment, the powertrain operating
modes including an engine charging mode in which the engine drives
the generator to recharge the energy storage device and an electric
vehicle (EV) mode in which the engine is switched off and the
electric propulsion motor is operable to develop drive torque to
drive the vehicle; and [0133] causing the powertrain to assume the
appropriate powertrain operating mode and the required hybrid
operating mode, [0134] the method comprising determining which of
the plurality of powertrain operating modes is appropriate for
vehicle operation in dependence at least in part on the signal
indicative of the instant state of charge of the energy storage
device and a reference value of state of charge, and setting the
reference value of state of charge to one of a plurality of
different respective values in dependence on the signal indicative
of the required hybrid operating mode. [0135] 25. A computer
readable medium carrying computer program code for controlling a
vehicle to carry out the method of paragraph 24.
[0136] 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.
[0137] 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.
[0138] 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.
* * * * *