Hybrid electric vehicle controller and method of controlling a hybrid electric vehicle

Abstract

Embodiments of the invention provide a controller for a hybrid electric vehicle (HEV) having an engine and an electric machine, the controller being configured upon start-up to control an electric machine to provide torque to drive a vehicle with an engine off if a state of charge (SoC) of an energy storage device is above an EV-start SoC threshold and to start an engine if a SoC of an energy storage device is below the EV-start SoC threshold, wherein the EV-start SoC threshold is determined to be one selected from amongst a value sufficient to allow a vehicle to travel a prescribed distance before a SoC falls below a SoC minimum level at which an engine is started and a value sufficient to allow a vehicle to operate for a prescribed time period before a SoC falls below the SoC minimum level.

Claims

1. A controller for a hybrid electric vehicle (HEV) having an engine and an electric machine and an energy storage device, the controller being configured to start the engine if a state of charge (SoC) of the energy storage device is below a SoC minimum level (SoCmin), the controller being further configured, upon initial start-up of the vehicle in which the vehicle is controlled to transition from a not ready state to a ready state, to determine whether the SoC of the energy storage device is below an EV-start SoC threshold (SoCEV-start) instead of SoCmin; if the SoC of the energy storage device is below an EV-start SoC threshold the vehicle is controlled to start the engine, and if the SoC of the energy storage device is not below an EV-start SoC threshold the vehicle is controlled to start in EV mode, wherein SoC EV-start is greater than SoCmin and comprises at least one of: a value sufficient to allow the vehicle to travel a prescribed distance before the SoC falls below SoCmin; and a value sufficient to allow the vehicle to operate for a prescribed time period before the SoC falls below SoCmin.

2. A controller as claimed in claim 1 wherein a prescribed SoC threshold is set to a value sufficiently high to protect the energy storage device from becoming damaged due to excessive draining of charge from the energy storage device.

3. A controller as claimed in claim 2 wherein the prescribed SoC threshold is set to a value of around 10%, from around 10% to around 20%, from around 20% to around 30%, from around 30% to around 40% and from around 40% to around 50% of an upper limit to an amount of charge the energy storage device is capable of storing.

4. A controller as claimed in claim 1 wherein a prescribed SoC threshold is set to a value sufficient to allow the vehicle to travel the prescribed distance provided a value of driver demanded torque does not exceed a prescribed threshold value.

5. A controller as claimed in claim 1 further arranged upon start-up to control the vehicle to start the engine if an ambient temperature is below a prescribed temperature threshold.

6. A controller as claimed in claim 1 further arranged upon start-up to control the vehicle to start the engine if an ambient temperature is above a prescribed temperature threshold.

7. A hybrid electric vehicle comprising an engine, an electric machine and a controller as claimed in claim 1.

8. A hybrid electric vehicle as claimed in claim 7 wherein the vehicle is operable by the controller to operate in a parallel mode in which the engine provides torque to propel the vehicle and an electric vehicle (EV) mode in which the electric machine provides torque to propel the vehicle and the engine is switched off, the controller being arranged to start the engine if the state of charge (SoC) of the energy storage device is below a SoC minimum level (SoCmin), the controller being further configured, upon initial startup of the vehicle in which the vehicle is controlled to transition from a not ready state to a ready state, to determine whether the SoC of the energy storage device is below an EV-start SoC threshold (SoCEV-start) instead of SoCmin; if the SoC of the energy storage device is below an EV-start SoC threshold the vehicle is controlled to start the engine, and if the SoC of the energy storage device is not below an EV-start SoC threshold the vehicle is controlled to start in EV mode, wherein SoC EV-start is greater than SoCmin and comprises at least one of: a value sufficient to allow the vehicle to travel the prescribed distance before the SoC fails below SoCmin; and a value sufficient to allow the vehicle to operate for a prescribed time period before the SoC falls below SoCmin.

9. A vehicle as claimed in claim 8 wherein in the parallel mode the electric machine is operable as an electric motor to provide torque to drive the vehicle.

10. A vehicle as claimed in claim 8 wherein in the parallel mode the electric machine is operable as an electric generator to charge the energy storage device.

11. A vehicle as claimed in claim 7 wherein the vehicle is a series-type hybrid electric vehicle.

12. A method of controlling a hybrid electric vehicle having an engine and an electric machine, the method comprising: upon initial start-up of the vehicle in which the vehicle is controlled to transition from a not ready state to a ready state, determining whether a SoC of an energy storage device of the vehicle is below an EV-start SoC threshold (SoCEV-start) instead of a SoC minimum level (SoCmin); if the SoC of the energy storage device is below the EV-start SoC threshold, controlling the vehicle to start the engine, and if the SoC of the energy storage device is not below the EV-start SoC threshold, controlling the vehicle to start in EV mode, wherein SoC EV-start is greater than SoCmin and comprises at least one of: a value sufficient to allow the vehicle to travel a prescribed distance before the SoC falls below SoCmin; and a value sufficient to allow the vehicle to operate for a prescribed time period before the SoC falls below SoCmin.

13. A method as claimed in claim 12 further comprising, when in a parallel mode, controlling the electric machine as an electric motor to provide torque to drive the vehicle.

14. A method as claimed in claim 12 further comprising, when in a parallel mode, controlling the electric machine as an electrical generator to charge the energy storage device.

15. A method as claimed in claim 12 further comprising controlling the vehicle to assume a parallel mode if a value of driver demanded torque exceeds a prescribed threshold value.

16. A method as claimed in claim 12 comprising controlling the vehicle to start the engine if an ambient temperature is below a prescribed temperature threshold.

17. A method as claimed in claim 12 further comprising controlling the vehicle to start the engine if an ambient temperature is above a prescribed temperature threshold.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Embodiments of the invention will now be described, by way of example only, with reference to the accompanying figures in which:

(2) FIG. 1 is a schematic illustration of a hybrid electric vehicle according to an embodiment of the invention; and

(3) FIG. 2 shows a relationship between parameters SoC(min) and SoC(offset).

DETAILED DESCRIPTION

(4) A hybrid electric vehicle (HEV) 100 according to an embodiment of the present invention is shown schematically in FIG. 1. The HEV 100 has an internal combustion engine 121 releasably coupled to a crankshaft integrated motor/generator (CIMG) 123 by means of a clutch 122. The CIMG 123 is in turn coupled to an automatic transmission 124. The transmission 124 is arranged to drive a pair of front wheels 111, 112 of the vehicle by means of a corresponding pair of front drive shafts 118. The vehicle 100 also has an auxiliary driveline 130 arranged to drive a pair of rear wheels 114, 115 by means of an auxiliary driveshaft 132 (or propshaft 132) and a rear differential 135.

(5) A battery 150 is provided that may be electrically coupled to the CIMG 123 in order to allow the CIMG 123 to generate torque when the CIMG 123 is operated as a motor. Alternatively the battery 150 may be electrically coupled to the CIMG 123 to receive charge from the CIMG 123 when the CIMG 123 is operated as a generator in order to recharge the battery 150.

(6) The vehicle 100 is configured to operate in a parallel mode or an electric vehicle (EV) mode.

(7) In the parallel mode of operation the clutch 122 is closed and the engine 121 is arranged to provide torque to the transmission 124 through the CIMG 123. In this mode the CIMG 123 may be operated either as a motor or as a generator.

(8) In the EV mode of operation the clutch 122 is opened and the engine 121 is turned off. Again, the CIMG 123 is then operated either as a propulsion motor or as a generator. The CIMG 123 may be operated as a motor in order to drive the vehicle or as a generator in order to effect regenerative braking of the vehicle 100.

(9) The vehicle 100 has a controller 140 arranged to control the vehicle 100 to transition between the parallel and EV modes depending on a variety of parameters associated with the vehicle 100 and driver actions that will not be discussed herein.

(10) It is to be understood that when an operator of the vehicle 100 initially starts the vehicle 100 the vehicle 100 is controlled to transition from a not ready state in which the vehicle 100 is not ready to move to a ready state in which the vehicle 100 is ready move. By ready to move is meant that if a driving mode of the transmission 124 is selected and an accelerator pedal 161 of the vehicle 100 is depressed the vehicle 100 may be driven.

(11) In the embodiment of FIG. 1 the vehicle 100 is operable to transition from the not ready state to the ready state by pressing a START button. It is to be understood that in a non-hybrid vehicle pressing a START button (or turning a key to a START position) typically results in starting of the engine.

(12) However in a HEV the engine 121 may not start immediately upon selecting START. For example in the case of a mild hybrid vehicle (being a stop-start vehicle not having an EV mode) pressing the START button may not result in an engine start until the accelerator pedal 161 is depressed.

(13) In a full hybrid electric vehicle 100 according to the present invention (a full HEV being a HEV having an EV mode in which the engine may be switched off) the controller 140 is arranged to determine whether to start the vehicle in EV mode or parallel mode upon the START button being pressed. In some embodiments the controller 140 determines whether to start in EV mode or parallel mode when a driving mode of the transmission 124 is selected. In some embodiments the controller 140 determines whether to start in EV mode or parallel mode when the accelerator pedal 161 is depressed.

(14) The controller 140 is arranged to determine the required mode responsive to the state of charge (SoC) of the battery 150, an ambient temperature of the environment in which the vehicle is operating and a determination whether the vehicle 100 is likely to be able to travel a prescribed distance in EV mode before requiring a transition to a parallel mode. In some alternative embodiments the controller 140 is arranged to determine the required mode responsive to a determination whether the vehicle 100 is likely to be able to operate for a prescribed time period in EV mode before requiring a transition to a parallel mode. By the term operate is included standing of the vehicle or travel of the vehicle.

(15) In the embodiment of FIG. 1 the controller 140 is arranged to determine how far the vehicle may travel in EV mode given the current SoC of the battery 150 and a likely charge drain on the battery 150 whilst driving. If the distance exceeds a prescribed distance and the ambient temperature is within a prescribed range (being above a lower threshold value and below an upper threshold value) the controller 140 is arranged to start the vehicle in EV mode. Thus, the engine 121 is not started when the START button is pressed or the accelerator pedal 161 is depressed.

(16) It is to be understood that the upper and lower temperature threshold values may be selected to bound a temperature range over which it is anticipated that an operator of the vehicle will not require activation of an engine-driven heating or air-conditioning system of the vehicle 100. In some embodiments the vehicle 100 is arranged to allow the operator to set values of the upper and lower temperature thresholds according to his or her preference.

(17) In determining the distance the vehicle 100 is likely to be able to travel, the vehicle is configured to check several vehicle state parameters indicative of a likely charge drain on the battery 150 whilst the vehicle 100 is operating. The state parameters include an operational state of one or more vehicle accessories such as an infotainment system, an operational state of one or more electrical heating elements such as a front or rear windscreen demist heating element, an ambient light level indicating a likelihood that one or more vehicle running lights may require to be activated, an operational state of one or more vehicle running lights (for example whether running lights are activated or not, and optionally a setting of the lights such as side lights only, side lights and headlights, or sidelights and full beam headlights), a vehicle loading and a determination whether a vehicle is towing a load. Data in respect of vehicle loading may be obtained by one of a variety of different means, for example by reference to a pitch angle of a vehicle, a vehicle suspension system or one or more other parameters or systems. Data in respect of whether a vehicle is towing a load may be obtained by reference to whether an electrical lighting board of a towed object such as a trailer has been connected to the vehicle 100 or one or more towing sensors.

(18) In some embodiments the controller 140 is configured to determine a value of a state of charge offset parameter SoC(offset) being a parameter indicative of an amount of charge the vehicle 100 is likely to draw from the battery 150 in order to travel the prescribed distance. This parameter is indicated in FIG. 2 which illustrates a relationship between a minimum allowable SoC of the battery, SoC(min), the value of SoC(offset) and a present value of SoC, SoC(present). If SoC(present) is greater than or equal to a sum of SoC(min) and SoC(offset), the vehicle 100 is configured to commence driving in EV mode. If SoC(present) is less than a sum of SoC(min) and SoC(offset) the vehicle 100 is configured to start the engine 121 and to operate in a parallel HEV mode or other mode in which the engine 121 is employed to drive the vehicle 100.

(19) Embodiments of the invention have the advantage that a more consistent start-up feel may be provided to an operator of the vehicle 100. This is because the vehicle 100 is arranged to launch (or initialise) in EV mode rather than parallel mode whenever conditions permit.

(20) In some embodiments of the invention the vehicle 100 is arranged to maintain at substantially all times a battery SoC sufficient for EV operation when required, and sufficient to meet the requirements discussed above for start-up in EV mode.

(21) Thus in some embodiments the vehicle 100 will typically be shut down (entering the not ready mode) at the end of a journey with a battery SoC that is sufficient to allow starting in EV mode and travel of the prescribed distance (or to operate for the prescribed time period) discussed above.

(22) However other arrangements are also useful.

(23) In some embodiments, the prescribed distance may itself be responsive to one or more parameters. In some embodiments the prescribed distance may be responsive to a geographical location of the vehicle 100. Thus if the vehicle 100 is located in an urban area the prescribed distance may differ from that in the case that the vehicle 100 is located away from an urban area. In some embodiments the prescribed distance may be lower in an urban area. In some embodiments the prescribed distance may be greater in an urban area.

(24) In some embodiments of the invention allowing recharging of the battery 150 from an external power source, it is to be understood that it may be necessary to recharge the battery 150 from the external power source in order to permit start-up in EV mode.

(25) It is to be understood that other arrangements are also useful.

(26) A specific embodiment of the invention has been described as implemented in the parallel-type hybrid electric vehicle of FIG. 1. It is to be understood that embodiments of the invention are equally applicable to hybrid vehicles operating in series mode in which the engine 121 does not provide driving torque to a driveline or wheels of the vehicle but rather drives a generator to charge the battery to allow a propulsion motor to drive the vehicle. In some HEVs the generator may be operable to provide electrical power directly to a propulsion motor providing driving torque to one or more wheels.

(27) 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.

(28) 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.

(29) 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.