CONTROL OF KINETIC ENERGY RECOVERY SYSTEMS

Abstract

The present invention relates to methods of controlling kinetic energy recovery systems (KERS), to controllers, KERS, drivetrains and vehicles including the KERS and controllers. The KERS comprises an energy storage system. In an embodiment, a vehicle is provided with a first vehicle operating mode wherein the energy storage system has a first target state of charge, and with a second vehicle operating mode wherein the energy storage system has a second target state of charge. The first or second vehicle operating mode is selected and energy is transferred between the energy storage system and the vehicle in order to achieve the target state of charge associated with the selected vehicle operating mode. In other embodiments, the KERS includes a variable power transmission device adapted to transfer energy to and from the energy storage system. The energy storage system is maintained at suitable energy levels for the vehicle's driving conditions.

Claims

1-10. (canceled)

11. A method of controlling a kinetic energy recovery system (KERS) for a vehicle, the KERS comprising an energy storage system having a pre-determined maximum operating energy storage capacity and a variable power transmission device adapted to transfer energy to and from the energy storage system, the method comprising: (i) determining an instantaneous available inertial energy of the vehicle; (ii) determining an instantaneous state of charge of the energy storage system; (iii) in dependence upon the maximum energy storage capacity and the instantaneous state of charge, determining an instantaneous state of charge headroom; and, (iv) transferring energy to or from the energy storage system using the variable power transmission device, such that the instantaneous state of charge headroom is substantially equal to or greater than the instantaneous available inertial energy of the vehicle.

12. A method according to claim 11, wherein the maximum operating energy storage capacity is a fixed limit of the energy storage system, or is a fixed or variable limit based on durability or energy loss requirements.

13. A method according to claim 11, wherein the calculation of the instantaneous available inertial energy of the vehicle takes account of one or more of: power losses due to efficiency () effects of the variable power transmission device; vehicle drag effects; anticipated energy dissipation due to the application of foundation brakes; and engine braking.

14. (canceled)

15. (canceled)

16. (canceled)

17. A method according to claim 11, wherein the variable power transmission device is adapted to transfer energy to or from the vehicle and the energy storage system.

18. A method according to claim 11, wherein the variable power transmission device is adapted to transfer energy to or from an engine of the vehicle and the energy storage system.

19. A method of controlling a kinetic energy recovery system (KERS) for a vehicle, the KERS comprising an energy storage system having a pre-determined minimum state of charge and a variable power transmission device adapted to transfer energy to and from the energy storage system, the method comprising: (i) determining an instantaneous inertial energy of the vehicle; (ii) determining a vehicle maximum operating inertial energy; (iii) determining a vehicle maximum required inertial energy in dependence upon the vehicle maximum operating inertial energy and the vehicle instantaneous inertial energy; (iv) determining an instantaneous state of charge of the energy storage system; (v) determining an available storage energy in dependence upon the instantaneous state of charge of the energy storage system and the minimum state of charge of the energy storage system; (vi) transferring energy to or from the energy storage system using the variable power transmission device, such that the available storage energy in the energy storage system is substantially equal to or greater than the vehicle maximum required inertial energy.

20. A method according to claim 19, wherein the pre-determined minimum state of charge is a fixed limit for the energy storage system.

21. A method according to claim 19, wherein the pre-determined minimum state of charge is a fixed or variable limit based on durability or energy loss requirements.

22. A method according to claim 19, wherein the determining of the vehicle maximum required inertial energy takes account one or more of: of power losses due to efficiency () effects of the variable power transmission device; vehicle drag effects; anticipated energy dissipation due to the application of foundation brakes; and engine braking.

23. (canceled)

24. (canceled)

25. (canceled)

26. A method according to claim 19, wherein the variable power transmission device is adapted to transfer energy one or more of: to or from the vehicle and the energy storage system; and to or from an engine of the vehicle and the energy storage system.

27. A method according to claim 11, wherein braking of the vehicle may be accomplished by a blend of foundation brakes of the vehicle and the KERS.

28. A method according to claim 11, wherein during supply of KERS braking torque to the vehicle the KERS braking torque is reduced, optionally to zero, as the state of charge of the energy storage system approaches a predetermined limit.

29. A method according to claim 28, wherein a driver can compensate for reduction in KERS braking by applying additional effort to a brake pedal.

30. A method according to claim 11, wherein a controller is configured to detect activation of a vehicle anti-lock braking system and to de-activate KERS braking, optionally by ceasing to perform energy transfer to the energy storage system using the variable power transmission device.

31. A method according to claim 11, wherein the energy storage system comprises one or more of: a flywheel; and an electrical capacitor.

32. A controller for controlling a kinetic energy recovery system (KERS) for a vehicle, the KERS comprising an energy storage system and a variable power transmission device for transferring energy to or from the energy storage system, the controller being configured to implement a method according to claim 11.

33. A KERS in combination with a controller according to claim 32.

34. A drive system comprising a KERS adapted to be controlled by a controller according to claim 32.

35. A vehicle comprising a kinetic energy recovery system (KERS) and one or more of: a controller for controlling a kinetic energy recovery system (KERS) for a vehicle, the KERS comprising an energy storage system and a variable power transmission device for transferring energy to or from the energy storage system, the controller being configured to implement the method according to claim 11; and a drive system comprising the KERS adapted to be controlled by the controller.

36. A method of controlling a kinetic energy recovery system (KERS) for a vehicle, the KERS comprising an energy storage system having a pre-determined maximum operating energy storage capacity and a pre-determined minimum state of charge, the KERS further comprising a variable power transmission device adapted to transfer energy to and from the energy storage system, the method comprising: (i) determining a vehicle maximum operating inertial energy; (ii) determining an instantaneous state of charge of the energy storage system; (iii) in dependence upon the maximum energy storage capacity and the instantaneous state of charge, determining an instantaneous state of charge headroom; (iv) determining a vehicle maximum required inertial energy in dependence upon the vehicle maximum operating inertial energy and an instantaneous inertial energy of the vehicle; (v) determining an available storage energy in dependence upon the instantaneous state of charge of the energy storage system and the minimum state of charge of the energy storage system; and (vi) transferring energy to or from the energy storage system using the variable power transmission device, such that the instantaneous state of charge headroom is substantially equal to or greater than an instantaneous inertial energy of the vehicle and such that the available storage energy in the energy storage system is substantially equal to or greater than the vehicle maximum required inertial energy.

Description

SPECIFIC DESCRIPTION

[0058] The invention will now be described, purely by way of example, in connection with the accompanying drawings in which:

[0059] FIG. 1 is a schematic representation of a vehicle according to an embodiment of the present invention;

[0060] FIG. 2 is a graph schematically illustrating a vehicle's kinetic energy as a function of speed;

[0061] FIG. 3 is a graph schematically illustrating KERS energy as a function of vehicle speed;

[0062] FIG. 4 is a graph schematically illustrating maximum KERS power; and

[0063] FIGS. 5a, 5b and 5c represent a vehicle boost button for switching vehicle's operating mode and for providing visual information related to the KERS to a vehicle's driver.

[0064] FIG. 1 schematically illustrates a vehicle 101 according to an embodiment of the present invention. The vehicle 101 comprises a conventional engine 105 and foundation brakes 108, to control the vehicle's speed and, more generally, behaviour. The vehicle 101 also comprises a kinetic energy recovering system (KERS) 100 comprising an energy storage system (ESS) 102, which, in the described embodiment is in the form of a flywheel (not shown). The KERS also comprises a variable power transmission device (VPTD) 104. The engine 105 and KERS 100 are part of the drive system 107 of the vehicle 101, as shown in the Figure. The drive system may comprise one or more drives or drive components. Drives or drive components may be present, such as for example axels not connected to the drive system 107. Power and energy may thus flow to or from the KERS 100, in particular to or from its associated energy storage system 102, and, for example, exchanged between the energy storage system 102 and the engine 105 of the vehicle and/or between the energy storage system 102 and the vehicle 101. Such power and energy are exchanged via the variable power transmission device 104 of the KERS 100. A controller 106 is provided to govern the behaviour of the KERS 100, engine 105 and foundation brakes 108, as illustrated, particularly by controlling the energy levels of the energy storage system 102.

[0065] FIG. 2 shows a graph illustrating a relationship between vehicle speed and vehicle available kinetic (or inertial) energy. The line of increasing gradient reflects the fact that the vehicle kinetic energy is related to the square of vehicle speed, as KE=mv.sup.2. Excluding loss, drag and power transfer efficiency effects, the line also describes the preferable state of charge headroom 1 in the energy storage system 102. In the described embodiment of the invention, comprising the KERS 100 having the energy storage system 102 in the form of a flywheel, maintaining this headroom 1 allows the flywheel to absorb the kinetic energy of the vehicle 101 during all braking events such that the energy storage system 102 may not become saturated (full) under normal braking events. Thus braking performance may be consistent under all normal braking events even when predominantly using KERS braking alone.

[0066] The curved line on FIG. 3 shows an approximate relationship between vehicle speed and KERS energy target 2 that (excluding efficiency and loss effects) maintains the energy storage system state of charge headroom 1 as a function of vehicle speed. It can therefore be seen that at high vehicle speeds the storage state of charge target 2 approaches a zero or a minimum 3 whereas at low vehicle speeds the storage state of charge target 2 approaches a maximum level 4 which is, in this case, just below a storage limit 5. A further arrow 6 indicates that if the KERS energy storage state of charge 2 approaches the target line under braking (for example after a period of KERS braking on a long downhill slope) then the KERS braking effort may be roll(ed) off (that is, decreased gradually, potentially so that KERS braking approaches zero). Further braking of the vehicle 101 may be accomplished by a blend of the foundation brakes 108 and KERS braking such that the overall requested braking level indicated by the driver input such as the brake pedal position is achieved. In addition or alternatively, the driver may monitor the change in braking conditions that arise as the KERS braking effort is rolled off and compensate by applying additional effort at the brake pedal, this being termed driver in the loop feedback. If anti-lock braking system (ABS) becomes activated, then a control system may detect the activation of the ABS, for example by receiving a signal over a Control Area Network (CAN) of the vehicle, and may de-activate the KERS braking by ceasing to perform energy transfer to the energy storage system 102 using a power transmission device.

[0067] In FIG. 4, a graph shows an area 7 over which consistent required performance (that is, drive rather than braking) may be met using the KERS. The graph describes the KERS being maintained at high state of charge 8 when the vehicle has a low speed (that is, low kinetic energy) and the KERS being maintained at a low state of charge 9 when the vehicle has a high speed (that is, low kinetic energy). An example of a pre-determined maximum vehicle operating speed may be seen where the KERS energy approaches zero energy, and the line cuts the y-axis of the graph.

[0068] There are two options of (i) targeting a state of charge of the KERS 100 that ensures consistent performance (as described herein for example for a vehicle economy mode), or alternatively (ii) a selectable boost button as shown in FIGS. 5a, 5b and 5c may be depressed for driver selection of a performance mode. A hybrid mode in which engine power and hybrid power may be blended could also be provided. FIGS. 5a, 5b and 5c show a boost button 10 which may be depressed by the driver for the selection of performance mode. In response, the control system causes the flywheel (the storage system in the described embodiment) to be accelerated to an increased state of charge preferably to the maximum state of charge 5. The boost button 10 incorporates an illuminated annulus 11 that indicates when the storage system has approached the target increased state of charge (as shown in FIG. 5c), thus alerting the driver to the state of readiness of the KERS for a high performance manoeuvre such as overtaking. After a pre-determined period of time, the control system causes the flywheel to approach a reduced speed, corresponding to a reduced state of charge, commensurate with the economy mode, and the illuminated annulus 11 in the boost button 10 is caused to fade (as shown in FIG. 5b) such that it is no longer illuminated (as shown in FIG. 5a), and indicating to the driver that the flywheel is no longer charged to the level required for high performance. Thus the driver's enjoyment is enhanced, but fuel economy over a period of time may be achieved.

[0069] A telematics system may be provided in which a control system that receives from a database or interprets from an identified road signal information regarding terrain, traffic speed limits and other topographical information, determines from said information a forthcoming supplementary vehicle power requirement, determining a requirement to charge the energy storage system a pre-determined time before the increased vehicle power level is required to be deployed, and discharging the energy storage system when the increase in vehicle power is required.

[0070] Conversely, the KERS equipped vehicle may include a control system that receives from a database or interprets from an identified road signal information regarding terrain, traffic speed limits and other topographical information, determines from said information a forthcoming reduction in vehicle power requirement, determining a requirement to dis-charge the energy storage system a pre-determined time before the decreased vehicle power level is required, and charging the energy storage system when the requirement for the decrease in vehicle power is required.

[0071] Such systems may be enablers for enhanced reduction of emissions and fuel consumption. For example, if an efficient engine has been incorporated into a vehicle such that the engine displacement is reduced thus enabling higher fuel economy (as is well understood by those skilled in this technical field), then the control system may read information from a speed limit or from an information database that transmits said information regarding an increased forthcoming power requirement (for example, a hill or an increased speed limit that allows the vehicle speed to increase). Thus the control system may cause the energy storage system (for example a flywheel) to receive charge from the engine such that it is pre-charged ahead of the forthcoming requirement for increased power. In this way, the energy storage system may contain sufficient storage in order to supplement the available engine power such that sufficient energy is able to be transmitted to the vehicle in order to satisfy the transient increased power requirement (for example, climbing a hill).

[0072] Advantageously this may allow an internal combustion engine or other prime mover to be sized for a lower maximum capacity because the energy storage system may be capable of fulfilling transient increases in power requirement. Prime movers such as internal combustion engines that have a reduced displacement or size exhibit reduced friction characteristics relative to their useful power generation capability (known as indicated power) and therefore tend to exhibit improved efficiency, as well as reduced cost. Therefore, when combined with a control system that receives from a database or interprets from an identified road signal information regarding terrain, traffic speed limits and other topographical information into forthcoming supplementary power requirements, the KERS becomes an enabler not only for increased harvesting and reuse of vehicle kinetic energy, as previously described, but also becomes an enabler for reduced engine size and therefore enhanced reduction of emissions and fuel consumption.

[0073] In one embodiment there is a super-economy mode in which the storage system is kept at a low SOC, or is at a zero SOC so that boost to the vehicle from the storage system is not available. Fuel economy may be enhanced because losses in the storage system (such as a flywheel) may be minimised. In such an embodiment, selection of the performance mode by the driver or by a control system may cause the storage system to approach a target state of charge dependent upon the current speed and/or inertial and/or available inertial energy of the vehicle, as described earlier. Thus losses in the storage system (such as a flywheel) may be slightly higher on average than when in the super-economy mode, but boost to the vehicle is always available. This may, for example, always enable the vehicle to achieve a target speed, as described earlier.

[0074] Embodiments may also be applicable to commercial vehicles (including on-highway trucks) such as off-highway vehicles, including loaders such as back-hoe loaders and wheeled loaders, and excavators. However in these cases, a modified form of energy recovery system (ERS) may be employed, where the available energy for storage and reuse may be kinetic or gravitational energy or other forms of available energy of the vehicle.

[0075] Accordingly, further embodiments may provide a method of controlling an energy recovery system (ERS) for a vehicle (optionally an off-highway vehicle), the ERS comprising an energy storage system having a pre-determined maximum operating energy storage capacity and a variable power transmission device adapted for to transfer energy to and from the energy storage system and vehicle, the method comprising:

[0076] (i) determining an instantaneous available energy of the vehicle;

[0077] (ii) determining an instantaneous state of charge of the energy storage system;

[0078] (iii) determining a difference between the maximum energy storage capacity and the instantaneous state of charge to give an instantaneous state of charge headroom; and,

[0079] (iv) transferring energy to or from the energy storage system using the variable power transmission device, such that the instantaneous state of charge headroom is substantially equal to or greater than the instantaneous available energy of the vehicle.

[0080] Further embodiments may provide method of controlling an energy recovery system (ERS) for a vehicle (optionally an off-highway vehicle), the ERS comprising an energy storage system having a pre-determined minimum state of charge and a variable power transmission device adapted to transfer energy to and from the energy storage system, the method comprising:

[0081] (i) determining an instantaneous energy of the vehicle;

[0082] (ii) determining a vehicle maximum operating energy;

[0083] (iii) determining a vehicle maximum required energy as a difference between the vehicle maximum operating energy and the vehicle instantaneous energy;

[0084] (iv) determining an instantaneous state of charge of the energy storage system;

[0085] (v) determining an available storage energy as the instantaneous state of charge of the energy storage system minus the minimum state of charge of the energy storage system;

[0086] (vi) transferring energy to or from the energy storage system using the variable power transmission device, such that the available storage energy in the energy storage system is substantially equal to or greater than the vehicle maximum required energy.

[0087] Some vehicles may climb to different altitudes regularly the vehicle energy may be gravitational potential energy that may be stored and re-used. In such cases the gravitational energy is a function of the altitude of the vehicle. In loading vehicles, the vehicle energy may be gravitational energy from the loading boom or loading arm. In some vehicles the vehicle energy may be kinetic energy from a part of the vehicle that moves with respect to the vehicle chassis or ground engaging means (such as the cab); such vehicles include excavators. In each case, storage and reuse of the available energy of the vehicle system can reduce fuel consumption. In managing the SOC of the storage system, the engine may be reduced in size which can reduce fuel consumption further, as described earlier. Management of the SOC of the storage system may take account of vehicle aerodynamic losses, vehicle drag, efficiency effects in the power transmission device, engine braking and foundation braking as well as the kinetic or gravitational potential energy as described earlier for the examples that included KERS (i.e. where it is the vehicle's rolling kinetic energy is stored and reused). All other aspects of control that may be applied to the vehicle rolling kinetic energy applications (KERS) may be applied equally to these truck and off-highway applications

[0088] The invention has been above described with reference to one or more specific embodiments, purely as an example. The skilled person appreciates that additional and/or alternative embodiments are also encompassed by the invention within the scope defined by the appended claims.