EP2864172A1 - Method and system for control of a regenerative braking system in a vehicle - Google Patents

Method and system for control of a regenerative braking system in a vehicle

Info

Publication number
EP2864172A1
EP2864172A1 EP13810710.7A EP13810710A EP2864172A1 EP 2864172 A1 EP2864172 A1 EP 2864172A1 EP 13810710 A EP13810710 A EP 13810710A EP 2864172 A1 EP2864172 A1 EP 2864172A1
Authority
EP
European Patent Office
Prior art keywords
speed
vehicle
max
road
section
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP13810710.7A
Other languages
German (de)
French (fr)
Other versions
EP2864172A4 (en
Inventor
Fredrik Roos
Johan FALKHÄLL
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Scania CV AB
Original Assignee
Scania CV AB
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Scania CV AB filed Critical Scania CV AB
Publication of EP2864172A1 publication Critical patent/EP2864172A1/en
Publication of EP2864172A4 publication Critical patent/EP2864172A4/en
Withdrawn legal-status Critical Current

Links

Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60W—CONJOINT CONTROL OF VEHICLE SUB-UNITS OF DIFFERENT TYPE OR DIFFERENT FUNCTION; CONTROL SYSTEMS SPECIALLY ADAPTED FOR HYBRID VEHICLES; ROAD VEHICLE DRIVE CONTROL SYSTEMS FOR PURPOSES NOT RELATED TO THE CONTROL OF A PARTICULAR SUB-UNIT
    • B60W30/00—Purposes of road vehicle drive control systems not related to the control of a particular sub-unit, e.g. of systems using conjoint control of vehicle sub-units
    • B60W30/18—Propelling the vehicle
    • B60W30/18009—Propelling the vehicle related to particular drive situations
    • B60W30/18109—Braking
    • B60W30/18127—Regenerative braking
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60T—VEHICLE BRAKE CONTROL SYSTEMS OR PARTS THEREOF; BRAKE CONTROL SYSTEMS OR PARTS THEREOF, IN GENERAL; ARRANGEMENT OF BRAKING ELEMENTS ON VEHICLES IN GENERAL; PORTABLE DEVICES FOR PREVENTING UNWANTED MOVEMENT OF VEHICLES; VEHICLE MODIFICATIONS TO FACILITATE COOLING OF BRAKES
    • B60T1/00—Arrangements of braking elements, i.e. of those parts where braking effect occurs specially for vehicles
    • B60T1/02—Arrangements of braking elements, i.e. of those parts where braking effect occurs specially for vehicles acting by retarding wheels
    • B60T1/10—Arrangements of braking elements, i.e. of those parts where braking effect occurs specially for vehicles acting by retarding wheels by utilising wheel movement for accumulating energy, e.g. driving air compressors
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60W—CONJOINT CONTROL OF VEHICLE SUB-UNITS OF DIFFERENT TYPE OR DIFFERENT FUNCTION; CONTROL SYSTEMS SPECIALLY ADAPTED FOR HYBRID VEHICLES; ROAD VEHICLE DRIVE CONTROL SYSTEMS FOR PURPOSES NOT RELATED TO THE CONTROL OF A PARTICULAR SUB-UNIT
    • B60W30/00—Purposes of road vehicle drive control systems not related to the control of a particular sub-unit, e.g. of systems using conjoint control of vehicle sub-units
    • B60W30/14—Adaptive cruise control
    • B60W30/143—Speed control
    • B60W30/146—Speed limiting
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60W—CONJOINT CONTROL OF VEHICLE SUB-UNITS OF DIFFERENT TYPE OR DIFFERENT FUNCTION; CONTROL SYSTEMS SPECIALLY ADAPTED FOR HYBRID VEHICLES; ROAD VEHICLE DRIVE CONTROL SYSTEMS FOR PURPOSES NOT RELATED TO THE CONTROL OF A PARTICULAR SUB-UNIT
    • B60W50/00—Details of control systems for road vehicle drive control not related to the control of a particular sub-unit, e.g. process diagnostic or vehicle driver interfaces
    • B60W50/0097—Predicting future conditions
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60K—ARRANGEMENT OR MOUNTING OF PROPULSION UNITS OR OF TRANSMISSIONS IN VEHICLES; ARRANGEMENT OR MOUNTING OF PLURAL DIVERSE PRIME-MOVERS IN VEHICLES; AUXILIARY DRIVES FOR VEHICLES; INSTRUMENTATION OR DASHBOARDS FOR VEHICLES; ARRANGEMENTS IN CONNECTION WITH COOLING, AIR INTAKE, GAS EXHAUST OR FUEL SUPPLY OF PROPULSION UNITS IN VEHICLES
    • B60K31/00—Vehicle fittings, acting on a single sub-unit only, for automatically controlling vehicle speed, i.e. preventing speed from exceeding an arbitrarily established velocity or maintaining speed at a particular velocity, as selected by the vehicle operator
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60T—VEHICLE BRAKE CONTROL SYSTEMS OR PARTS THEREOF; BRAKE CONTROL SYSTEMS OR PARTS THEREOF, IN GENERAL; ARRANGEMENT OF BRAKING ELEMENTS ON VEHICLES IN GENERAL; PORTABLE DEVICES FOR PREVENTING UNWANTED MOVEMENT OF VEHICLES; VEHICLE MODIFICATIONS TO FACILITATE COOLING OF BRAKES
    • B60T2201/00—Particular use of vehicle brake systems; Special systems using also the brakes; Special software modules within the brake system controller
    • B60T2201/04—Hill descent control
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60T—VEHICLE BRAKE CONTROL SYSTEMS OR PARTS THEREOF; BRAKE CONTROL SYSTEMS OR PARTS THEREOF, IN GENERAL; ARRANGEMENT OF BRAKING ELEMENTS ON VEHICLES IN GENERAL; PORTABLE DEVICES FOR PREVENTING UNWANTED MOVEMENT OF VEHICLES; VEHICLE MODIFICATIONS TO FACILITATE COOLING OF BRAKES
    • B60T2210/00—Detection or estimation of road or environment conditions; Detection or estimation of road shapes
    • B60T2210/30—Environment conditions or position therewithin
    • B60T2210/36—Global Positioning System [GPS]
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60T—VEHICLE BRAKE CONTROL SYSTEMS OR PARTS THEREOF; BRAKE CONTROL SYSTEMS OR PARTS THEREOF, IN GENERAL; ARRANGEMENT OF BRAKING ELEMENTS ON VEHICLES IN GENERAL; PORTABLE DEVICES FOR PREVENTING UNWANTED MOVEMENT OF VEHICLES; VEHICLE MODIFICATIONS TO FACILITATE COOLING OF BRAKES
    • B60T2270/00—Further aspects of brake control systems not otherwise provided for
    • B60T2270/60—Regenerative braking
    • B60T2270/604—Merging friction therewith; Adjusting their repartition
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60T—VEHICLE BRAKE CONTROL SYSTEMS OR PARTS THEREOF; BRAKE CONTROL SYSTEMS OR PARTS THEREOF, IN GENERAL; ARRANGEMENT OF BRAKING ELEMENTS ON VEHICLES IN GENERAL; PORTABLE DEVICES FOR PREVENTING UNWANTED MOVEMENT OF VEHICLES; VEHICLE MODIFICATIONS TO FACILITATE COOLING OF BRAKES
    • B60T7/00—Brake-action initiating means
    • B60T7/12—Brake-action initiating means for automatic initiation; for initiation not subject to will of driver or passenger
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60W—CONJOINT CONTROL OF VEHICLE SUB-UNITS OF DIFFERENT TYPE OR DIFFERENT FUNCTION; CONTROL SYSTEMS SPECIALLY ADAPTED FOR HYBRID VEHICLES; ROAD VEHICLE DRIVE CONTROL SYSTEMS FOR PURPOSES NOT RELATED TO THE CONTROL OF A PARTICULAR SUB-UNIT
    • B60W2300/00—Indexing codes relating to the type of vehicle
    • B60W2300/12—Trucks; Load vehicles
    • B60W2300/125—Heavy duty trucks
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60W—CONJOINT CONTROL OF VEHICLE SUB-UNITS OF DIFFERENT TYPE OR DIFFERENT FUNCTION; CONTROL SYSTEMS SPECIALLY ADAPTED FOR HYBRID VEHICLES; ROAD VEHICLE DRIVE CONTROL SYSTEMS FOR PURPOSES NOT RELATED TO THE CONTROL OF A PARTICULAR SUB-UNIT
    • B60W2520/00—Input parameters relating to overall vehicle dynamics
    • B60W2520/10—Longitudinal speed
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60W—CONJOINT CONTROL OF VEHICLE SUB-UNITS OF DIFFERENT TYPE OR DIFFERENT FUNCTION; CONTROL SYSTEMS SPECIALLY ADAPTED FOR HYBRID VEHICLES; ROAD VEHICLE DRIVE CONTROL SYSTEMS FOR PURPOSES NOT RELATED TO THE CONTROL OF A PARTICULAR SUB-UNIT
    • B60W2552/00—Input parameters relating to infrastructure
    • B60W2552/15—Road slope, i.e. the inclination of a road segment in the longitudinal direction
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60W—CONJOINT CONTROL OF VEHICLE SUB-UNITS OF DIFFERENT TYPE OR DIFFERENT FUNCTION; CONTROL SYSTEMS SPECIALLY ADAPTED FOR HYBRID VEHICLES; ROAD VEHICLE DRIVE CONTROL SYSTEMS FOR PURPOSES NOT RELATED TO THE CONTROL OF A PARTICULAR SUB-UNIT
    • B60W2552/00—Input parameters relating to infrastructure
    • B60W2552/20—Road profile, i.e. the change in elevation or curvature of a plurality of continuous road segments
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60W—CONJOINT CONTROL OF VEHICLE SUB-UNITS OF DIFFERENT TYPE OR DIFFERENT FUNCTION; CONTROL SYSTEMS SPECIALLY ADAPTED FOR HYBRID VEHICLES; ROAD VEHICLE DRIVE CONTROL SYSTEMS FOR PURPOSES NOT RELATED TO THE CONTROL OF A PARTICULAR SUB-UNIT
    • B60W2552/00—Input parameters relating to infrastructure
    • B60W2552/30—Road curve radius
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60W—CONJOINT CONTROL OF VEHICLE SUB-UNITS OF DIFFERENT TYPE OR DIFFERENT FUNCTION; CONTROL SYSTEMS SPECIALLY ADAPTED FOR HYBRID VEHICLES; ROAD VEHICLE DRIVE CONTROL SYSTEMS FOR PURPOSES NOT RELATED TO THE CONTROL OF A PARTICULAR SUB-UNIT
    • B60W2555/00—Input parameters relating to exterior conditions, not covered by groups B60W2552/00, B60W2554/00
    • B60W2555/60—Traffic rules, e.g. speed limits or right of way
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60W—CONJOINT CONTROL OF VEHICLE SUB-UNITS OF DIFFERENT TYPE OR DIFFERENT FUNCTION; CONTROL SYSTEMS SPECIALLY ADAPTED FOR HYBRID VEHICLES; ROAD VEHICLE DRIVE CONTROL SYSTEMS FOR PURPOSES NOT RELATED TO THE CONTROL OF A PARTICULAR SUB-UNIT
    • B60W2556/00—Input parameters relating to data
    • B60W2556/45—External transmission of data to or from the vehicle
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60W—CONJOINT CONTROL OF VEHICLE SUB-UNITS OF DIFFERENT TYPE OR DIFFERENT FUNCTION; CONTROL SYSTEMS SPECIALLY ADAPTED FOR HYBRID VEHICLES; ROAD VEHICLE DRIVE CONTROL SYSTEMS FOR PURPOSES NOT RELATED TO THE CONTROL OF A PARTICULAR SUB-UNIT
    • B60W2556/00—Input parameters relating to data
    • B60W2556/45—External transmission of data to or from the vehicle
    • B60W2556/50—External transmission of data to or from the vehicle of positioning data, e.g. GPS [Global Positioning System] data

Definitions

  • the present invention relates to a method for controlling a regenerative brake system according to the preamble of claim 1 and a control unit according to the preamble of claim 28.
  • the present invention relates also to a computer programme and a computer programme product which implement the method according to the invention.
  • Vehicles may vary in speed when travelling on a section of road. These speed variations may for example be due to changes in torque demanded from an engine of the vehicle or to the vehicle accelerating or decelerating because of a gradient on the section of road. Vehicles, particularly heavy vehicles such as trucks, buses or any other heavy vehicles, are
  • v max typically accelerated on downhill runs by their great train weight M, which conversely often decelerates them on uphill runs .
  • M great train weight
  • v max the maximum speed which the vehicle should not exceed.
  • This maximum speed v max may be used to prevent the vehicle reaching too high a speed, e.g. a speed exceeding the speed limit for the section of road or exceeding a maximum permissible speed for the vehicle.
  • the maximum speed v max may thus be a speed limit which the driver does not wish to exceed, e.g. to avoid risk of being accused of speeding.
  • the driver typically brakes, e.g. by using a brake pedal, if the vehicle exceeds
  • Vmax ⁇ Many motor vehicles today are equipped with cruise control.
  • One object of cruise control is to achieve a predetermined uniform speed.
  • Cruise control is often conducted in vehicles by two interacting systems, viz. a cruise control system which demands torque from an engine system, and a downhill speed control system which prevents the vehicle from developing excessive speed, particularly on downhill runs.
  • the cruise control tries to adjust the engine torque in order to avoid deceleration, or avoid applying brake action, on downhill runs where the vehicle is accelerated by its own weight.
  • a general object of the cruise control is to provide the vehicle driver with easier driving and greater comfort by making it unnecessary for him/her to apply acceleration in order to maintain a set speed v set chosen by him/her.
  • the set speed v set is the speed set by the driver which he/she wishes to maintain on level roads.
  • the cruise control then provides an engine system of the vehicle with the set speed v set for control of the engine system.
  • the set speed v se t is often related to a speed limit for a section of road on which the vehicle is at the time.
  • a traditional downhill speed control brakes the vehicle automatically when a downhill control speed v dhsc is reached.
  • the downhill speed control thus for example regulates the speed of heavy vehicles on downhill runs on which they are accelerated by their own weight.
  • the regulation by the downhill speed control uses auxiliary brakes, e.g. a retarder, an exhaust brake and a four-stage electromagnetic brake
  • downhill speed control braking or driver-controlled braking usually represents a complete loss.
  • Downhill speed control braking and driver-control braking are often related to the aforesaid maximum speed v max .
  • recoverable depends inter alia on the magnitude of the brake energy and/or the brake energy, and on other parameters specific to the regenerative brake system.
  • Braking on a downhill run is one example of such a situation.
  • the present invention may be employed on substantially all types of vehicles which have a regenerative brake system, comprising inter alia hybridised vehicles and totally electric vehicles .
  • a regenerative brake system may be an integral part of a vehicle's power train, as in a hybridised vehicle in which an electrical machine is run in generator mode during braking so that at least some of the brake energy is utilised.
  • Regenerative brake systems may comprise one or more from among a battery, a supercapacitor , a flywheel, a spring, a hydraulic pump cooperating with an accumulator, a pneumatic compressor cooperating with a pressure tank, and a device for conveying energy to a consumer on board the vehicle. These devices recover or transfer the energy which is braked away by the brake system. When the energy is conveyed to consumers on board the vehicle, loads may be caused to consume it at times when braking takes place. In favourable conditions, a
  • previous known downhill speed controls waste energy through it being braked away at such high power that not all of this brake energy can be utilised by the regenerative brake system, making it necessary to also use traditional brake systems.
  • the level of the power which can be utilised by the regenerative brake system in previous known systems is thus not optimum for regeneration.
  • controlling a regenerative brake system according to the characterising part of claim 1. It is also achieved by the aforesaid control unit according to the characterising part of claim 28, and by the aforesaid computer programme and computer programme product.
  • the present invention controls when, i.e. at what
  • the regenerative brake system has to be
  • the invention chooses this time/location earlier than in previous known systems, which means that the braking can take place over a longer period of time, thereby reducing the mean power of the braking, since the energy to be braked away is spread over a longer period of time. This means that the regeneration takes place at a lower mean power, making it possible for more of the brake energy to be utilised by the regenerative brake system than in previous known systems.
  • the control of the braking will thus be adjusted to the
  • the regeneration is optimised on the basis of the regenerative brake system' s regeneration
  • Using a lower brake power i.e. by braking over a longer time according to the invention, means that more of the braking can be conducted with the regenerative brake system than in previous known braking at higher brake power. This is
  • the present invention thus makes it possible to capture and use more of the total brake energy by means of the
  • the efficiency of the regenerative brake system may increase if the present invention is employed. A larger proportion of the brake energy is thus recovered by using the present invention, at brake powers both above and below the maximum capacity.
  • the time/location for activation of brake action may in favourable circumstances be chosen such that the regenerative brake system can utilise substantially all of the brake energy. This means that substantially no energy is wasted by being simply braked away, since substantially no traditional brake systems are used to lower the vehicle's speed.
  • a lowered average speed which arises from a lengthening of the braking period according to the invention also has the affect of reducing the air resistance to the vehicle. This means that less energy is braked away by the air resistance, making it possible for more energy to be braked away by the
  • the present invention thus makes it possible for some of the energy previously braked by the air resistance to be recovered by the
  • FIG. 1 is a flowchart of the method according to the present invention
  • Figure 2 illustrates an example of a driving situation
  • Figure 3 illustrates an example of a driving situation
  • Figure 4 illustrates an example of a driving situation
  • Figure 5 depicts a control unit.
  • Figure 1 is a flowchart of the method according to the present invention.
  • a first step 101 of the method determines at least one predicted speed v pred which the vehicle is predicted to follow along a section of road.
  • the at least one predicted speed v pre ci is thus here determined for a period of time which the vehicle will spend on the section of road.
  • the section of road is that immediately ahead of the vehicle and may for example have here a length L of 1000 metres or any suitable length.
  • the at least one predicted speed v pred may here be determined in various ways and on the basis of various
  • a second step 102 of the method according to the present invention activates a regenerative brake system of the vehicle if the at least one predicted speed v pred exceeds the maximum speed v max along the section of road, and the
  • a third step 103 of the method recovers brake energy in the regenerative brake system when brake action is applied.
  • the second method step 102 therefore analyses whether the at least one predicted speed v pred determined in the first step will exceed the maximum speed v max along the section of road. If such is the case, the actual speed v act at which the vehicle is travelling and the maximum speed v max are compared to determine when the vehicle's actual speed v act will reach v max . The regenerative brake system is then activated before v act reaches v max . In previous known systems, only the actual speed v act was compared with the maximum speed v max , and the braking was activated when v act exceeded v max .
  • the present invention instead identifies first whether braking will be appropriate on the basis of the predicted speed v pre d- It then uses this knowledge to activate the regenerative brake system earlier than in previous known systems, i.e. to choose an activation location P re gen which is reached before v act reaches v max . This results in braking over a longer period of time and a
  • the present invention determines the at least one predicted speed v pred for the section of road ahead of the vehicle. It then analyses the predicted speed v p r e ci to see whether it will exceed maximum speed v max if no braking takes place. In this example v pred would exceed v max at the second location P2 if no braking was effected. According to the invention the braking will therefore be activated at an activation location P reg en which is before the second location P2 at which the actual speed v act according to the invention would have reached the maximum speed v max if no braking was effected. The invention applies brake action until the third location P3 is reached. At a merging location P CO mmon situated after the second location P2, the actual speed v act according to the invention coincides with the previous known actual speed v act _ re g U iar ⁇
  • the actual speed v act according to the present invention is below the actual speed v act _ reg uiar according to previous known solutions from the activation location P reg en to the merging location Pcommon which means that the average actual speed v act according to the present
  • the present invention is lower than the actual speed v act regular according to previous known solutions.
  • the present invention applies brake action from the activation location P reg en to the third location P3, thereby lengthening the braking time by the space between the activation location P re gen and the second location P2 as compared with prior art.
  • the brake power may thus be regulated to a level which is more favourable for regeneration with the regenerative brake system, making it possible for more of the brake energy to be utilised by the regenerative brake system than in previous known systems.
  • locations such as PI, P2, P3, P4, Pregen and Pcommon, but one skilled in the art will appreciate that these locations correspond to respective points in time.
  • the magnitude of the maximum speed v max may be determined in various different ways. If the vehicle is equipped with a cruise control whereby the driver sets for example a desired set speed v set , the maximum speed v max may have a magnitude related to the set speed v set . In one embodiment of the invention the maximum speed v max may exceed the set speed v se t
  • the maximum speed v max is related to a downhill control speed d hsc of a downhill speed control on board the vehicle.
  • This embodiment thus provides a connection to the downhill speed control and its use on downhill runs.
  • the magnitude of the maximum speed v max is related to the nature of the section of road and/or the traffic on it.
  • the magnitude of v max is therefore decided by one or more characteristics of the section of road, e.g. a speed limit or a road curvature.
  • the characteristics may also comprise the presence or absence of one or more speed cameras and the traffic situation on the section of road, e.g. whether there is any queuing or not.
  • radar may be used to determine a speed of, and/or a distance from, a vehicle in front.
  • the maximum speed v max may then be determined in such a way that there will be no risk of running into, or coming too close to, the vehicle in front.
  • Radar is used inter alia by adaptive cruise controls (ACC) , which mean that radar information is available on board vehicles equipped with such adaptive cruise controls. The extra complexity will therefore be modest in this
  • the magnitude of the maximum speed v max may vary along said section of road.
  • v max is dynamic. Its magnitude may for example here be a function of time or locations on the section of road. It may then for example take the form of a vector with possibly different values pertaining to different
  • the predicted speed v pred is determined on the basis of knowledge of the section of road. This knowledge may be based on one or more from among positioning information, e.g. GPS (global positioning system) information, map information, topography information, weather reports, information communicated between vehicles and
  • positioning information e.g. GPS (global positioning system) information, map information, topography information, weather reports, information communicated between vehicles and
  • FIG. 3 depicts a non-limitative example of using knowledge of the section of road in the same driving situation as in Figure 2.
  • the actual speed v act _ reg uiar and the braking in prior art are as described above as in relation to Figure 2.
  • the determination of the at least one predicted speed v pre d takes this knowledge into account.
  • the predicted speed v pre d largely corresponds in the diagrams to the curve of the actual speed v act regu iar in prior art.
  • a very exact determination of v pre d may be made.
  • This very exact predicted speed v pred may serve as a basis for determining the braking in such a way that the energy recovery for the regeneration in the regenerative brake system is maximised while at the same time the vehicle maintains a suitable actual speed v act at the end of the downhill run.
  • the braking may also be commenced earlier, since the control unit can with great certainty predict that v act will exceed v max if no braking takes place.
  • the at least one predicted speed v pre d for the section of road ahead of the vehicle is determined and analysed to see whether it will exceed the maximum speed v max if no braking takes place.
  • the predicted speed v pred corresponds here largely to the curve of the actual speed v act regular according to prior art. As the control unit knows that predicted speed v pred is reliable, it can already apply brake action at the
  • the second location P2 is in fact also where previous known solutions would have begun to apply brake action.
  • brake action may therefore be applied immediately when the vehicle begins to accelerate on the downhill run, since on the basis of knowledge of the section of road this acceleration can easily be predicted to reach v max .
  • the invention applies brake action until the third location P3 is reached.
  • the actual speed v act according to the present invention is below the actual speed v act regular according to previous known solutions for a relatively long time, from the activation location Pregen to the merging location P C ommon.
  • the average actual speed v act according to the present invention will thus be below the average actual speed v act _ re guiar according to previous known solutions over the same period beginning at the first location PI and ending at the third location P3.
  • the present invention applies brake action from the activation location P re gen to the third location P3, thereby lengthening the braking distance/time by the space between the first time location PI and the second location P2 as compared with prior art. This means that the braking takes place over a longer period of time and at a consequently lower brake power, making it possible for more of the brake energy to be utilised than in previous known solutions.
  • the braking may also be
  • One embodiment of the present invention determines a speed profile v prof which extends from an actual speed v act , e.g. the actual speed v act at the first location PI, to the maximum speed v max , e.g. at the third location P3.
  • the speed profile v prof might then correspond to the broken line for the actual speed v act according to the present invention between the first position PI and the third position P3.
  • the appropriate speed profile v prof may here first be determined in order to serve as a basis for activation of the regenerative brake system.
  • the appropriate shape of the speed profile v p!:0f may depend on which parameter is to be optimised, e.g. fuel saving, regeneration, acceptability to drivers, acceptability to other road users and/or driver comfort.
  • the speed profile v prof is determined such that the resulting brake power is within a favourable range for the regenerative brake system's regeneration.
  • a certain brake system may here have a maximum regeneration capacity corresponding to a first brake power limit value, in which case the speed profile v pr0f in this embodiment is determined such that the resulting brake power is below this limit value.
  • LACCs look-ahead cruise controls
  • v ref the reference speed v ref is allowed, within a certain range, to differ from the set speed v set chosen by the driver, in order to achieve a more fuel-saving way of driving based on the knowledge.
  • LACCs may use the various forms of knowledge in a variety of different ways. Knowledge of for example a speed limit on the road ahead may be used to effect fuel-efficient lowerings of speed before a coming lower speed limit. Similarly, knowledge of for example a roundabout or intersection ahead may also be used as a basis for fuel-efficient braking before reaching them.
  • An LACC does for example allow the reference speed v ref to be raised before a steep uphill run to above the set speed v set , since the vehicle may be assumed to lose speed uphill because of its high train weight relative to engine performance.
  • LACCs similarly allow the reference speed v ref to drop to below the set speed v set before a steep downhill run, since the vehicle may be assumed to be accelerated downhill by its high train weight.
  • the concept here is that greater fuel economy is achieved by making use of the vehicle's acceleration caused by its own weight downhill than by first accelerating before the downhill run and then braking downhill. LACCs may thus reduce fuel consumption with hardly any effect upon journey time .
  • Figure 4 illustrates a non-limitative example of how an embodiment of the present invention may interact with an LACC.
  • the actual speed v act regu l ar and the braking in prior art are as described in relation to Figures 2 and 3 above.
  • the invention may be employed not only in the downhill situation depicted in Figure 4 but also in the context of other speed changes initiated by LACCs.
  • the determination of the predicted speed v pred takes into account the knowledge which the LACC possesses.
  • the LACC lowers the reference speed v re f to below the set speed v set , e.g. before a downhill run, since this reduces the need for conventional braking and is efficient in terms of fuel economy.
  • brake action may, as depicted in Figure 4, be applied already at an activation location P re gen before the downhill run begins at the first location PI. Regeneration may thus be conducted by the regenerative brake system when the lowering of the actual speed v act takes place before the downhill run, resulting in a further lengthening of braking time.
  • the actual speed v act according to the present invention is below the actual speed v act reg uiar according to previous known solutions for a long time, from the first location PI to the merging location P com mon- This results in the average actual speed v act , and also the brake power, according to the present invention being below the average actual speed v act _ regu i ar according to previous known solutions over the same period.
  • Regeneration may also be conducted from the actual speed v act according to LACC being allowed to be below the set speed v set at the activation location P re gen , which occurs before the downhill run begins at the first location PI.
  • the braking in this embodiment therefore takes place over a longer distance and time and results in a lower brake power, making it possible for the regenerative brake system to utilise a larger proportion of the brake energy than in previous known solutions.
  • the gradient along the section of road is substantially the same as where the vehicle is at the time when the determination takes place.
  • the vehicle there is no need for the vehicle to have access to map information, positioning information and/or topography information, since the road gradient where the vehicle is at the time may be determined in other ways, e.g. on the basis of an accelerometer or a force equation.
  • the gradient where the vehicle is may also be available on board, since it is used by other systems, e.g. systems for gear choice or the like. This embodiment therefore often involves the vehicle in a limited amount of complexity.
  • the determination of the predicted speed v pred is based on the actual speed v act and an actual acceleration a ac t of the vehicle. This is followed by analysing how close the vehicle' s actual speed v act is to the maximum speed v max and how quickly the vehicle is approaching it. The activation location P regen is then also determined on the basis of a difference between the vehicle's actual speed v act and maximum speed v max and on the basis of an actual
  • acceleration a act of the vehicle. It may for example be deemed appropriate to apply brake action if v act is relatively close to, and also quickly approaching, v max .
  • the determination of the at least one predicted speed v pre d is based on an assumption that the fuel supply to the engine is throttled for the whole or parts of the section of road.
  • the predicted speed v pre d is here based on an engine brake simulation whereby the engine torque is based on a dragging of the engine, i.e. on a drag torque curve for the engine.
  • the determination of the at least one predicted speed v pred is based on an assumption that the vehicle freewheels for the whole or part of the section of road.
  • the simulation of the predicted speed v pred is here based on a freewheeling simulation whereby the vehicle rolls freely with open clutch and/or in neutral gear. When the vehicle is freewheeling no power is transmitted from the engine to the tractive wheels.
  • the power train torque i.e. the vehicle's propulsive torque
  • a vehicle speed regulator which receives speed set-point values from the cruise control logic.
  • the set speed v 3et serves as such a set-point value.
  • the reference speed v ref serves as this set-point value.
  • the determination of the at least one predicted speed v pred is based on a cruise control simulation which is conducted on board the vehicle on the basis of a vehicle speed set-point value. In cases where the vehicle travels with the cruise control operating, the speed set-point value in the simulation may then be based on the cruise control's set speed v se t-
  • the set-point value may also be based on the vehicle's current actual speed v ac t or an estimation of a driver' s desired actual speed v act . This embodiment achieves an accurate estimate of the at least one predicted speed v pre d even when cruise control driving is not employed, i.e. during accelerator pedal
  • the activation location Pregen is determined to a location where the vehicle accelerates and where it is found that the predicted speed v pred will exceed the maximum speed v max .
  • An example of such an activation location P reg en is depicted in Figure 2, in which the vehicle is on a downhill run and is accelerated by its train weight, while at the same time it may be found that v pre d will exceed
  • the activation location P re gen i.e. the location where the regenerative brake system is activated, is determined to the location where the vehicle has a power surplus and where it is found that v pre d will exceed v max .
  • a vehicle is assumed here and throughout this specification to have a power surplus if it accelerates without fuel supply to the engine.
  • An example of such an activation location P re gen is depicted in Figure 2, where the vehicle is on a downhill run and is accelerated by its train weight .
  • Pregen is determined to a location from which it is calculated that the maximum speed v max may be reached along the section of road by using a brake energy which may be provided with the regenerative brake system.
  • An example of such an activation location P re gen is depicted in Figure 3, where it may be found at the first location PI that the speed profile v prof can be achieved by braking with the regenerative brake system so that v max is reached along the section of road, e.g. at the third location P3.
  • This dynamically variable brake energy serves as a basis for calculating adaptively the brake action to be applied in order to brake away this brake energy.
  • the adaptive algorithm may here be based on at least one prediction of a braking process v pred brake of the vehicle.
  • a braking process v p red _ bra k e denotes here how the actual speed v act will be altered by the appropriate brake action determined.
  • the braking process v pred b ra ke is determined on the basis of the current brake action, i.e. the brake action applied at the time when the prediction of v p re d brake is made.
  • the prediction of v pred brake changes dynamically during the braking.
  • v pred _brake is determined on the basis of a brake action which is pre- calculated on the basis of an appropriate brake action to be applied, its appropriateness being assessed on the basis of a brake energy which needs to be braked away. If the prediction of the braking process v p re d brake s i.e. the prediction of how the actual speed v act of said vehicle will be altered by the appropriate brake action determined, will reach the maximum speed v max , the brake action, i.e. the brake torque/brake power, is increased. If conversely the prediction of the braking process v p re d brake s i.e. the prediction of how the actual speed v act of said vehicle will be altered by the appropriate brake
  • v pred _ b ra k e shows that v act will not reach v max , the brake action, i.e. the brake torque/brake power, is decreased.
  • the increase and/or decrease in brake action may here be determined on the basis of how close to the maximum speed v max the prediction of the braking process v pred brake comes.
  • the result is a regulation which just reaches v max at the end of the downhill run.
  • a method for controlling a regenerative brake system may also be implemented in a computer programme which, when executed in a computer, causes the computer to conduct the method.
  • the programme usually takes the form of a computer programme product 503 (depicted in Figure 5) stored on a digital storage medium and is contained in a computer-readable medium of the computer programme product.
  • Said computer-readable medium comprises a suitable memory, e.g. ROM (read-only memory), PROM (programmable readonly memory) , EPROM (erasable PROM) , flash memory, EEPROM (electrically erasable PROM), a hard disc unit, etc.
  • FIG. 5 depicts schematically a control unit 500 comprising a calculation unit 501 which may take the form of substantially any suitable kind of processor or microcomputer, e.g. a circuit for digital signal processing (digital signal
  • the calculation unit is connected to a memory unit 502 which is situated in the control unit 500 and which provides the calculation unit with, for example, the stored programme code and/or the stored data which the calculation unit needs to enable it to perform calculations.
  • the calculation unit is also adapted to storing partial or final results of
  • the control unit 500 is further provided with respective devices 511, 512, 513, 514 for receiving and sending input and output signals.
  • These input and output signals may comprise waveforms, pulses or other attributes which the input signal receiving devices 511, 513 can detect as information and which can be converted to signals processable by the calculation unit 501. These signals are then conveyed to the calculation unit.
  • the output signal sending devices 512, 514 are arranged to convert signals received from the calculation unit in order, e.g. by modulating them, to create output signals which can be conveyed to other parts of the vehicle.
  • receiving and sending input and output signals may take the form of one or more from among a cable, a data bus, e.g. a CAN (controller area network) bus, a MOST (media oriented systems transport) bus or some other bus configuration, or a wireless connection .
  • a data bus e.g. a CAN (controller area network) bus, a MOST (media oriented systems transport) bus or some other bus configuration, or a wireless connection .
  • One aspect of the invention proposes a system comprising a control unit adapted to controlling a regenerative brake system in a vehicle.
  • the control unit comprises a prediction unit adapted to determining at least one predicted speed v pred for the vehicle on a section of road. This determination may be conducted in various different ways in the embodiments described above of the method, to which end the prediction unit is adapted to being able to make the predictions
  • the control unit comprises also an activation unit adapted to activating the regenerative brake system before an actual speed v act of the vehicle reaches the maximum speed v max if the at least one predicted speed v pred exceeds v max along the section of road.
  • control unit and consequently the system, according to the present invention have the same advantages as indicated above for the methods according to the invention.
  • the aforesaid computer may take the form of the calculation unit 501 and that the aforesaid memory may take the form of the memory unit 502.
  • the invention relates also to a motor vehicle 1, e.g. a truck or a bus, provided with at least one control unit for controlling a regenerative brake system according to the invention.
  • a motor vehicle e.g. a truck or a bus
  • the present invention is not restricted to the invention' s embodiments described above but relates to and comprises all embodiments within the protective scope of the attached independent claims.

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Abstract

The method and a control unit for controlling a regenerative brake system in a vehicle for which there is a defined maximum speed vmax which the vehicle should not exceed are presented. According to the present invention at least one predicted speed vpred for the vehicle on a section of road is determined. If the at least one predicted speed vpred exceeds the maximum speed vmax along the section of road, the regenerative brake system is then activated before an actual speed vact of the vehicle reaches the maximum speed vmax. The result is braking over more time and with less power than in previous known solutions, making it possible for the regenerative brake system to utilise more of the brake energy than in previous known systems.

Description

METHOD AND SYSTEM FOR CONTROL OF A REGENERATIVE BRAKING SYSTEM IN A VEHICLE
Technical field
The present invention relates to a method for controlling a regenerative brake system according to the preamble of claim 1 and a control unit according to the preamble of claim 28.
The present invention relates also to a computer programme and a computer programme product which implement the method according to the invention. Background
Vehicles may vary in speed when travelling on a section of road. These speed variations may for example be due to changes in torque demanded from an engine of the vehicle or to the vehicle accelerating or decelerating because of a gradient on the section of road. Vehicles, particularly heavy vehicles such as trucks, buses or any other heavy vehicles, are
typically accelerated on downhill runs by their great train weight M, which conversely often decelerates them on uphill runs . For many vehicles there is a defined maximum speed vmax which the vehicle should not exceed. This maximum speed vmax may be used to prevent the vehicle reaching too high a speed, e.g. a speed exceeding the speed limit for the section of road or exceeding a maximum permissible speed for the vehicle. On a given section of road the maximum speed vmax may thus be a speed limit which the driver does not wish to exceed, e.g. to avoid risk of being accused of speeding. The driver typically brakes, e.g. by using a brake pedal, if the vehicle exceeds
Vmax · Many motor vehicles today are equipped with cruise control. One object of cruise control is to achieve a predetermined uniform speed. Cruise control is often conducted in vehicles by two interacting systems, viz. a cruise control system which demands torque from an engine system, and a downhill speed control system which prevents the vehicle from developing excessive speed, particularly on downhill runs.
The cruise control tries to adjust the engine torque in order to avoid deceleration, or avoid applying brake action, on downhill runs where the vehicle is accelerated by its own weight. A general object of the cruise control is to provide the vehicle driver with easier driving and greater comfort by making it unnecessary for him/her to apply acceleration in order to maintain a set speed vset chosen by him/her. The set speed vset is the speed set by the driver which he/she wishes to maintain on level roads. The cruise control then provides an engine system of the vehicle with the set speed vset for control of the engine system. The set speed vset is often related to a speed limit for a section of road on which the vehicle is at the time.
A traditional downhill speed control brakes the vehicle automatically when a downhill control speed vdhsc is reached. The downhill control speed vdhsc is often related to the cruise control's set speed vset with an offset so that the downhill control speed vdhsc is equal to the set speed vset plus the offset speed v0f fSet r i.e. vdhsc = vset + v0ffSet - When a downhill speed control is used, the maximum speed vmax corresponds to the downhill control speed vdhsc, i.e. vmax = vdhsc.
The downhill speed control thus for example regulates the speed of heavy vehicles on downhill runs on which they are accelerated by their own weight. The regulation by the downhill speed control uses auxiliary brakes, e.g. a retarder, an exhaust brake and a four-stage electromagnetic brake
(Telnaa) , or a hybrid system comprising an electrical device which serves as a brake when used in a generator mode of the device. Other types of brakes may also be used by the
downhill speed control.
Brief description of the invention
On conventional vehicles, downhill speed control braking or driver-controlled braking, e.g. by using a brake pedal, usually represents a complete loss. Downhill speed control braking and driver-control braking are often related to the aforesaid maximum speed vmax.
On vehicles provided with a regenerative brake system, some of the total brake energy can be recovered. How much is
recoverable depends inter alia on the magnitude of the brake energy and/or the brake energy, and on other parameters specific to the regenerative brake system.
The invention will herein be mainly described in relation to downhill speed control braking, but one skilled in the art will appreciate that similar effects and problems to those which arise in downhill speed control braking may also arise in driver-controlled braking. The principles of the present invention may be applied in substantially all driving
situations which allow choice of when to apply brake action. If the exact time when braking of the vehicle is to commence is not critical from a safety perspective, in which case its timing may be controlled by the control unit according to the present invention, the present invention may be employed.
Braking on a downhill run is one example of such a situation. The present invention may be employed on substantially all types of vehicles which have a regenerative brake system, comprising inter alia hybridised vehicles and totally electric vehicles . A regenerative brake system may be an integral part of a vehicle's power train, as in a hybridised vehicle in which an electrical machine is run in generator mode during braking so that at least some of the brake energy is utilised.
Regenerative brake systems may comprise one or more from among a battery, a supercapacitor , a flywheel, a spring, a hydraulic pump cooperating with an accumulator, a pneumatic compressor cooperating with a pressure tank, and a device for conveying energy to a consumer on board the vehicle. These devices recover or transfer the energy which is braked away by the brake system. When the energy is conveyed to consumers on board the vehicle, loads may be caused to consume it at times when braking takes place. In favourable conditions, a
properly functioning regenerative brake system may recover a substantial proportion of the brake energy. Previous known downhill speed controls base their function on how an actual speed vact of the vehicle is related to the downhill control speed vdhsc, in such a way that brake action is applied when the downhill control speed vdhsc is reached. It then continues to be applied so that the downhill control speed vdh3C is maintained. Such braking often results in a relatively large amount of energy being braked away at high power, which is rarely optimum from a regeneration
perspective. In other words, previous known downhill speed controls waste energy through it being braked away at such high power that not all of this brake energy can be utilised by the regenerative brake system, making it necessary to also use traditional brake systems. The level of the power which can be utilised by the regenerative brake system in previous known systems is thus not optimum for regeneration.
There are two main reasons why high powers are not optimum during regeneration. One is that the regenerative brake system has a maximum capacity, which means that conventional brake systems have to be used if the brake power reguired is greater than this maximum capacity. Another reason is that the efficiency of the regeneration is lower at higher powers. All in all, today's known downhill speed control systems result in non-optimum regeneration in the brake system, since they take no account of regeneration-related characteristics of the power train and/or the brake system.
It is therefore an object of the present invention to propose a control which results in a more energy-efficient
regenerative brake system.
This object is achieved by the aforesaid method for
controlling a regenerative brake system according to the characterising part of claim 1. It is also achieved by the aforesaid control unit according to the characterising part of claim 28, and by the aforesaid computer programme and computer programme product.
The present invention controls when, i.e. at what
time/location, the regenerative brake system has to be
activated to result in advantageous regeneration in the power train. The invention chooses this time/location earlier than in previous known systems, which means that the braking can take place over a longer period of time, thereby reducing the mean power of the braking, since the energy to be braked away is spread over a longer period of time. This means that the regeneration takes place at a lower mean power, making it possible for more of the brake energy to be utilised by the regenerative brake system than in previous known systems. The control of the braking will thus be adjusted to the
regenerative brake system's capacity for recovering brake energy. In other words, the regeneration is optimised on the basis of the regenerative brake system' s regeneration
characteristics to make possible a higher proportion of energy recovery . Using a lower brake power, i.e. by braking over a longer time according to the invention, means that more of the braking can be conducted with the regenerative brake system than in previous known braking at higher brake power. This is
advantageous, since no energy is recovered when braking with traditional brake systems. The present invention also
achieves lower fuel consumption, since the energy recovered may for example be used subsequently to relieve for example the load upon the vehicle's combustion engine or to operate other consumers on board. The present invention thus makes it possible to capture and use more of the total brake energy by means of the
regenerative brake system than in previous known systems, since more of the brake power is within the regenerative brake system's maximum capacity. Even if the brake power in
previous known forms of brake control is below the
regenerative brake system's maximum capacity, the efficiency of the regenerative brake system may increase if the present invention is employed. A larger proportion of the brake energy is thus recovered by using the present invention, at brake powers both above and below the maximum capacity. The time/location for activation of brake action may in favourable circumstances be chosen such that the regenerative brake system can utilise substantially all of the brake energy. This means that substantially no energy is wasted by being simply braked away, since substantially no traditional brake systems are used to lower the vehicle's speed.
A lowered average speed which arises from a lengthening of the braking period according to the invention also has the affect of reducing the air resistance to the vehicle. This means that less energy is braked away by the air resistance, making it possible for more energy to be braked away by the
regenerative brake system. Thus more of the braking may be conducted by the regenerative brake system in situations where it is possible to recover the energy. The present invention thus makes it possible for some of the energy previously braked by the air resistance to be recovered by the
regenerative brake system.
Brief list of drawings
The invention is explained in more detail below with reference to the attached drawings, in which the same reference
notations are used for similar items,
Figure 1 is a flowchart of the method according to the present invention,
Figure 2 illustrates an example of a driving situation, Figure 3 illustrates an example of a driving situation,
Figure 4 illustrates an example of a driving situation, and Figure 5 depicts a control unit. Description of preferred embodiments Figure 1 is a flowchart of the method according to the present invention. A first step 101 of the method determines at least one predicted speed vpred which the vehicle is predicted to follow along a section of road. The at least one predicted speed vpreci is thus here determined for a period of time which the vehicle will spend on the section of road. The section of road is that immediately ahead of the vehicle and may for example have here a length L of 1000 metres or any suitable length. The at least one predicted speed vpred may here be determined in various ways and on the basis of various
parameters, as described in more detail below.
There is a defined maximum speed vmax which the vehicle should not exceed. A second step 102 of the method according to the present invention activates a regenerative brake system of the vehicle if the at least one predicted speed vpred exceeds the maximum speed vmax along the section of road, and the
activation of the regenerative brake system takes place according to the invention before an actual speed vact of the vehicle reaches the maximum speed vmax. A third step 103 of the method recovers brake energy in the regenerative brake system when brake action is applied.
The second method step 102 therefore analyses whether the at least one predicted speed vpred determined in the first step will exceed the maximum speed vmax along the section of road. If such is the case, the actual speed vact at which the vehicle is travelling and the maximum speed vmax are compared to determine when the vehicle's actual speed vact will reach vmax. The regenerative brake system is then activated before vact reaches vmax. In previous known systems, only the actual speed vact was compared with the maximum speed vmax, and the braking was activated when vact exceeded vmax. The present invention instead identifies first whether braking will be appropriate on the basis of the predicted speed vpred- It then uses this knowledge to activate the regenerative brake system earlier than in previous known systems, i.e. to choose an activation location Pregen which is reached before vact reaches vmax. This results in braking over a longer period of time and a
consequently lower brake power during the braking, making it possible for more of the brake energy to be utilised by the regenerative brake system than in previous known systems.
The prior art method and the method according to the present invention are illustrated schematically in the non-limitative example in Figure 2. A vehicle here embarks upon a downhill run at a first location PI. In prior art solutions the actual speed vact_reguiar would be increased on the downhill run by the vehicle's train weight M until it reached the defined maximum speed vmax at a second location P2. Only when the actual speed vact_reguiar reached the defined maximum speed vmax did previous solutions activate the braking. The actual speed vact regular then remained at the level of vmax until the downhill run ended at a third location P3 and the vehicle began to lose speed. The vehicle was finally back at the original speed at a fourth location P4. Prior art thus braked the vehicle between the second location P2 and the third location P3. The present invention determines the at least one predicted speed vpred for the section of road ahead of the vehicle. It then analyses the predicted speed vp r eci to see whether it will exceed maximum speed vmax if no braking takes place. In this example vpred would exceed vmax at the second location P2 if no braking was effected. According to the invention the braking will therefore be activated at an activation location Pregen which is before the second location P2 at which the actual speed vact according to the invention would have reached the maximum speed vmax if no braking was effected. The invention applies brake action until the third location P3 is reached. At a merging location PCOmmon situated after the second location P2, the actual speed vact according to the invention coincides with the previous known actual speed vact_regUiar ·
As may be seen in Figure 2, the actual speed vact according to the present invention is below the actual speed vact_reguiar according to previous known solutions from the activation location Pregen to the merging location Pcommon which means that the average actual speed vact according to the present
invention is lower than the actual speed vact regular according to previous known solutions. The present invention applies brake action from the activation location Pregen to the third location P3, thereby lengthening the braking time by the space between the activation location Pregen and the second location P2 as compared with prior art. This means that the braking takes place over a longer distance/time and at lower brake power than in previous known solutions. The brake power may thus be regulated to a level which is more favourable for regeneration with the regenerative brake system, making it possible for more of the brake energy to be utilised by the regenerative brake system than in previous known systems. Here and throughout this specification the invention is described in terms of locations such as PI, P2, P3, P4, Pregen and Pcommon, but one skilled in the art will appreciate that these locations correspond to respective points in time.
The magnitude of the maximum speed vmax may be determined in various different ways. If the vehicle is equipped with a cruise control whereby the driver sets for example a desired set speed vset, the maximum speed vmax may have a magnitude related to the set speed vset. In one embodiment of the invention the maximum speed vmax may exceed the set speed vset
x
by X percent, i.e. = vsgt * (1 +—) . Since the driver often chooses the set speed with respect to a speed limit for the section of road, the maximum speed vmax will often here be also indirectly related to a speed limit for the section of road.
In one embodiment of the invention the maximum speed vmax is related to a downhill control speed dhsc of a downhill speed control on board the vehicle. The maximum speed may here be set equal to the downhill control speed vdhsc, i.e. vmax = vdhsc. This embodiment thus provides a connection to the downhill speed control and its use on downhill runs.
The magnitude of the maximum speed vmax may also be related to how the driver behaves when driving the vehicle. If for example he/she often begins to brake at a certain driver- dependent speed vbrake driver on downhill runs, the system will learn to set the maximum speed vmax at this value, i.e. vmax = brake_driver · The system is thus here adjusted to the driver's behaviour, and if for example he/she begins to brake at a lower speed on downhill runs than previously, the value of the driver-dependent speed vbrake driver will decrease.
In one embodiment the magnitude of the maximum speed vmax is related to the nature of the section of road and/or the traffic on it. The magnitude of vmax is therefore decided by one or more characteristics of the section of road, e.g. a speed limit or a road curvature. The characteristics may also comprise the presence or absence of one or more speed cameras and the traffic situation on the section of road, e.g. whether there is any queuing or not. When the maximum speed vmax is related to surrounding traffic on the section of road, radar may be used to determine a speed of, and/or a distance from, a vehicle in front. The maximum speed vmax may then be determined in such a way that there will be no risk of running into, or coming too close to, the vehicle in front. Radar is used inter alia by adaptive cruise controls (ACC) , which mean that radar information is available on board vehicles equipped with such adaptive cruise controls. The extra complexity will therefore be modest in this
embodiment.
In one embodiment of the invention the magnitude of the maximum speed vmax may vary along said section of road. In other words, vmax is dynamic. Its magnitude may for example here be a function of time or locations on the section of road. It may then for example take the form of a vector with possibly different values pertaining to different
times/locations .
In one embodiment of the present invention the predicted speed vpred is determined on the basis of knowledge of the section of road. This knowledge may be based on one or more from among positioning information, e.g. GPS (global positioning system) information, map information, topography information, weather reports, information communicated between vehicles and
information communicated by radio, and may comprise knowledge of prevailing topography, road curvature, traffic situation, roadworks, traffic density and road surface states. It may comprise a speed limit for the section of road ahead and a traffic sign pertaining to the road. Many vehicles today are provided with systems, e.g. navigation systems and cruise control systems, which use such information. This embodiment may therefore be implemented with little additional complexity in vehicles where the information is already available. Figure 3 depicts a non-limitative example of using knowledge of the section of road in the same driving situation as in Figure 2. The actual speed vact_reguiar and the braking in prior art are as described above as in relation to Figure 2. In one embodiment of the present invention, where there is knowledge of the section of road, the determination of the at least one predicted speed vpred takes this knowledge into account. The predicted speed vpred largely corresponds in the diagrams to the curve of the actual speed vact reguiar in prior art. As the control unit which conducts the determination of Vpred then has very good knowledge of the nature of the section of road ahead, a very exact determination of vpred may be made. This very exact predicted speed vpred may serve as a basis for determining the braking in such a way that the energy recovery for the regeneration in the regenerative brake system is maximised while at the same time the vehicle maintains a suitable actual speed vact at the end of the downhill run. The braking may also be commenced earlier, since the control unit can with great certainty predict that vact will exceed vmax if no braking takes place.
This is illustrated in the example in Figure 3, in which the at least one predicted speed vpred for the section of road ahead of the vehicle is determined and analysed to see whether it will exceed the maximum speed vmax if no braking takes place. As mentioned above, the predicted speed vpred corresponds here largely to the curve of the actual speed vact regular according to prior art. As the control unit knows that predicted speed vpred is reliable, it can already apply brake action at the
beginning of the downhill run, i.e. at the first location PI. The activation location Pregen thus here coincides with the first location Pi, i.e. Pregen = PI, which is before the second location P2 at which the actual speed vact according to the invention would have reached the maximum speed vmax if no braking was effected. The second location P2 is in fact also where previous known solutions would have begun to apply brake action. In this embodiment, brake action may therefore be applied immediately when the vehicle begins to accelerate on the downhill run, since on the basis of knowledge of the section of road this acceleration can easily be predicted to reach vmax.
The invention applies brake action until the third location P3 is reached. In this example the third location P3 coincides with the merging location Pcoraraon, i.e. PCommon = P3, which is where the actual speed vact according to the invention and the previous known actual speed vact_reguiar again coincide.
As may be seen in Figure 3, the actual speed vact according to the present invention is below the actual speed vact regular according to previous known solutions for a relatively long time, from the activation location Pregen to the merging location PCommon. The average actual speed vact according to the present invention will thus be below the average actual speed vact_reguiar according to previous known solutions over the same period beginning at the first location PI and ending at the third location P3.
The present invention applies brake action from the activation location Pregen to the third location P3, thereby lengthening the braking distance/time by the space between the first time location PI and the second location P2 as compared with prior art. This means that the braking takes place over a longer period of time and at a consequently lower brake power, making it possible for more of the brake energy to be utilised than in previous known solutions. The braking may also be
controlled with great precision so that the maximum speed vmax is reached at precisely the end of the downhill run, in order to maximise the vehicle's fuel saving.
One embodiment of the present invention determines a speed profile vprof which extends from an actual speed vact, e.g. the actual speed vact at the first location PI, to the maximum speed vmax, e.g. at the third location P3. In the example in Figure 3 the speed profile vprof might then correspond to the broken line for the actual speed vact according to the present invention between the first position PI and the third position P3. Thus the appropriate speed profile vprof may here first be determined in order to serve as a basis for activation of the regenerative brake system. The appropriate shape of the speed profile vp!:0f may depend on which parameter is to be optimised, e.g. fuel saving, regeneration, acceptability to drivers, acceptability to other road users and/or driver comfort.
In one embodiment the speed profile vprof is determined such that the resulting brake power is within a favourable range for the regenerative brake system's regeneration. For
example, a certain brake system may here have a maximum regeneration capacity corresponding to a first brake power limit value, in which case the speed profile vpr0f in this embodiment is determined such that the resulting brake power is below this limit value.
There are strategic cruise controls, e.g. look-ahead cruise controls (LACCs), which use knowledge of road sections ahead, i.e. knowledge of the nature of the road ahead, to determine the configuration of a reference speed vre f which in such cruise controls is supplied to an engine system of the vehicle for control of a torque demand from the engine. In strategic cruise controls the reference speed vref is allowed, within a certain range, to differ from the set speed vset chosen by the driver, in order to achieve a more fuel-saving way of driving based on the knowledge.
LACCs may use the various forms of knowledge in a variety of different ways. Knowledge of for example a speed limit on the road ahead may be used to effect fuel-efficient lowerings of speed before a coming lower speed limit. Similarly, knowledge of for example a roundabout or intersection ahead may also be used as a basis for fuel-efficient braking before reaching them. An LACC does for example allow the reference speed vref to be raised before a steep uphill run to above the set speed vset, since the vehicle may be assumed to lose speed uphill because of its high train weight relative to engine performance.
LACCs similarly allow the reference speed vref to drop to below the set speed vset before a steep downhill run, since the vehicle may be assumed to be accelerated downhill by its high train weight. The concept here is that greater fuel economy is achieved by making use of the vehicle's acceleration caused by its own weight downhill than by first accelerating before the downhill run and then braking downhill. LACCs may thus reduce fuel consumption with hardly any effect upon journey time .
Figure 4 illustrates a non-limitative example of how an embodiment of the present invention may interact with an LACC. The actual speed vact regular and the braking in prior art are as described in relation to Figures 2 and 3 above. One skilled in the art will appreciate that the invention may be employed not only in the downhill situation depicted in Figure 4 but also in the context of other speed changes initiated by LACCs. In one embodiment of the present invention, where there is knowledge of the section of road and there is interaction with an LACC the determination of the predicted speed vpred takes into account the knowledge which the LACC possesses. As mentioned above, in certain situations the LACC lowers the reference speed vref to below the set speed vset, e.g. before a downhill run, since this reduces the need for conventional braking and is efficient in terms of fuel economy.
If the LACC indicate that it intends to reduce the actual speed vact, e.g. before a downhill run, brake action may, as depicted in Figure 4, be applied already at an activation location Pregen before the downhill run begins at the first location PI. Regeneration may thus be conducted by the regenerative brake system when the lowering of the actual speed vact takes place before the downhill run, resulting in a further lengthening of braking time. Compared with previous known solutions, this embodiment of the invention here
increases the braking time and the braking distance by the space from the activation location Pregen to the second location P2 where the previous known solutions would have begun to brake . The regeneration may then proceed for the braking during substantially the whole downhill run until the actual speed vact according to the present invention reaches the maximum speed vmax and also coincides with the actual speed vact regular according to previous known solutions at the third location P3 at the end of the downhill run, where P3 = PCommon.
As may be seen in Figure 4, the actual speed vact according to the present invention is below the actual speed vact reguiar according to previous known solutions for a long time, from the first location PI to the merging location Pcommon- This results in the average actual speed vact, and also the brake power, according to the present invention being below the average actual speed vact_reguiar according to previous known solutions over the same period. Regeneration may also be conducted from the actual speed vact according to LACC being allowed to be below the set speed vset at the activation location Pregen , which occurs before the downhill run begins at the first location PI.
The braking in this embodiment therefore takes place over a longer distance and time and results in a lower brake power, making it possible for the regenerative brake system to utilise a larger proportion of the brake energy than in previous known solutions.
In one embodiment of the present invention it is assumed when determining the predicted speed vpred that the gradient along the section of road is substantially the same as where the vehicle is at the time when the determination takes place. In this embodiment there is no need for the vehicle to have access to map information, positioning information and/or topography information, since the road gradient where the vehicle is at the time may be determined in other ways, e.g. on the basis of an accelerometer or a force equation. The gradient where the vehicle is may also be available on board, since it is used by other systems, e.g. systems for gear choice or the like. This embodiment therefore often involves the vehicle in a limited amount of complexity. In one embodiment of the present invention the determination of the predicted speed vpred is based on the actual speed vact and an actual acceleration aact of the vehicle. This is followed by analysing how close the vehicle' s actual speed vact is to the maximum speed vmax and how quickly the vehicle is approaching it. The activation location Pregen is then also determined on the basis of a difference between the vehicle's actual speed vact and maximum speed vmax and on the basis of an actual
acceleration aact of the vehicle. It may for example be deemed appropriate to apply brake action if vact is relatively close to, and also quickly approaching, vmax.
In one embodiment of the present invention the determination of the at least one predicted speed vpred is based on an assumption that the fuel supply to the engine is throttled for the whole or parts of the section of road. The predicted speed vpred is here based on an engine brake simulation whereby the engine torque is based on a dragging of the engine, i.e. on a drag torque curve for the engine.
In one embodiment of the present invention the determination of the at least one predicted speed vpred is based on an assumption that the vehicle freewheels for the whole or part of the section of road. The simulation of the predicted speed vpred is here based on a freewheeling simulation whereby the vehicle rolls freely with open clutch and/or in neutral gear. When the vehicle is freewheeling no power is transmitted from the engine to the tractive wheels.
In cruise control driving the power train torque, i.e. the vehicle's propulsive torque, is regulated by a vehicle speed regulator which receives speed set-point values from the cruise control logic. In traditional cruise controls the set speed v3et serves as such a set-point value. In cruise
controls where the reference speed vref is allowed to deviate from the set speed vset r as in LACCs, the reference speed vref serves as this set-point value. In one embodiment of the present invention the determination of the at least one predicted speed vpred is based on a cruise control simulation which is conducted on board the vehicle on the basis of a vehicle speed set-point value. In cases where the vehicle travels with the cruise control operating, the speed set-point value in the simulation may then be based on the cruise control's set speed vset-
The set-point value may also be based on the vehicle's current actual speed vact or an estimation of a driver' s desired actual speed vact. This embodiment achieves an accurate estimate of the at least one predicted speed vpred even when cruise control driving is not employed, i.e. during accelerator pedal
driving .
In one embodiment of the invention the activation location Pregen is determined to a location where the vehicle accelerates and where it is found that the predicted speed vpred will exceed the maximum speed vmax. An example of such an activation location Pregen is depicted in Figure 2, in which the vehicle is on a downhill run and is accelerated by its train weight, while at the same time it may be found that vpred will exceed
Vmax · In one embodiment of the present invention the activation location Pregen, i.e. the location where the regenerative brake system is activated, is determined to the location where the vehicle has a power surplus and where it is found that vpred will exceed vmax. A vehicle is assumed here and throughout this specification to have a power surplus if it accelerates without fuel supply to the engine. An example of such an activation location Pregen is depicted in Figure 2, where the vehicle is on a downhill run and is accelerated by its train weight . In one embodiment of the invention the activation location
Pregen is determined to a location from which it is calculated that the maximum speed vmax may be reached along the section of road by using a brake energy which may be provided with the regenerative brake system. An example of such an activation location Pregen is depicted in Figure 3, where it may be found at the first location PI that the speed profile vprof can be achieved by braking with the regenerative brake system so that vmax is reached along the section of road, e.g. at the third location P3.
In one embodiment of the present invention the activation of the regenerative brake system is based on an adaptive
algorithm which analyses how much brake energy needs to be braked away, which brake energy changes dynamically while the vehicle is in motion, inter alia due to its speed and to road gradient. This dynamically variable brake energy then serves as a basis for calculating adaptively the brake action to be applied in order to brake away this brake energy.
The adaptive algorithm may here be based on at least one prediction of a braking process vpred brake of the vehicle. A braking process vp red_brake denotes here how the actual speed vact will be altered by the appropriate brake action determined.
In one embodiment the braking process vpred b rake is determined on the basis of the current brake action, i.e. the brake action applied at the time when the prediction of vp red brake is made. In another embodiment the prediction of vpred brake changes dynamically during the braking. In another embodiment vpred_brake is determined on the basis of a brake action which is pre- calculated on the basis of an appropriate brake action to be applied, its appropriateness being assessed on the basis of a brake energy which needs to be braked away. If the prediction of the braking process vp red brake s i.e. the prediction of how the actual speed vact of said vehicle will be altered by the appropriate brake action determined, will reach the maximum speed vmax, the brake action, i.e. the brake torque/brake power, is increased. If conversely the
prediction of vpred _brake shows that vact will not reach vmax, the brake action, i.e. the brake torque/brake power, is decreased.
The increase and/or decrease in brake action may here be determined on the basis of how close to the maximum speed vmax the prediction of the braking process vpred brake comes. The result is a regulation which just reaches vmax at the end of the downhill run.
These embodiments of the invention thus achieve during the braking a control of the brake system which results in a dynamic and more advantageous regeneration with the
regenerative brake system, since the brake power can be regulated to a level which is more favourable for
regeneration .
One skilled in the art will appreciate that a method for controlling a regenerative brake system according to the present invention may also be implemented in a computer programme which, when executed in a computer, causes the computer to conduct the method. The programme usually takes the form of a computer programme product 503 (depicted in Figure 5) stored on a digital storage medium and is contained in a computer-readable medium of the computer programme product. Said computer-readable medium comprises a suitable memory, e.g. ROM (read-only memory), PROM (programmable readonly memory) , EPROM (erasable PROM) , flash memory, EEPROM (electrically erasable PROM), a hard disc unit, etc.
Figure 5 depicts schematically a control unit 500 comprising a calculation unit 501 which may take the form of substantially any suitable kind of processor or microcomputer, e.g. a circuit for digital signal processing (digital signal
processor, DSP) , or a circuit with a predetermined specific function (application specific integrated circuit, ASIC) . The calculation unit is connected to a memory unit 502 which is situated in the control unit 500 and which provides the calculation unit with, for example, the stored programme code and/or the stored data which the calculation unit needs to enable it to perform calculations. The calculation unit is also adapted to storing partial or final results of
calculations in the memory unit 502.
The control unit 500 is further provided with respective devices 511, 512, 513, 514 for receiving and sending input and output signals. These input and output signals may comprise waveforms, pulses or other attributes which the input signal receiving devices 511, 513 can detect as information and which can be converted to signals processable by the calculation unit 501. These signals are then conveyed to the calculation unit. The output signal sending devices 512, 514 are arranged to convert signals received from the calculation unit in order, e.g. by modulating them, to create output signals which can be conveyed to other parts of the vehicle.
Each of the connections to the respective devices for
receiving and sending input and output signals may take the form of one or more from among a cable, a data bus, e.g. a CAN (controller area network) bus, a MOST (media oriented systems transport) bus or some other bus configuration, or a wireless connection .
One aspect of the invention proposes a system comprising a control unit adapted to controlling a regenerative brake system in a vehicle. The control unit comprises a prediction unit adapted to determining at least one predicted speed vpred for the vehicle on a section of road. This determination may be conducted in various different ways in the embodiments described above of the method, to which end the prediction unit is adapted to being able to make the predictions
according to the respective embodiment.
The control unit comprises also an activation unit adapted to activating the regenerative brake system before an actual speed vact of the vehicle reaches the maximum speed vmax if the at least one predicted speed vpred exceeds vmax along the section of road.
The control unit, and consequently the system, according to the present invention have the same advantages as indicated above for the methods according to the invention.
One skilled in the art will appreciate that the aforesaid computer may take the form of the calculation unit 501 and that the aforesaid memory may take the form of the memory unit 502.
One skilled in the art will also appreciate that the above system may be modified according to the various embodiments of the method according to the invention. The invention relates also to a motor vehicle 1, e.g. a truck or a bus, provided with at least one control unit for controlling a regenerative brake system according to the invention.
The present invention is not restricted to the invention' s embodiments described above but relates to and comprises all embodiments within the protective scope of the attached independent claims.

Claims

Claims
1. A method for controlling a regenerative brake system in a vehicle for which there is a defined maximum speed vmax which said vehicle should not exceed, characterised in that a control unit performs the steps of
- determining at least one predicted speed vpred for said vehicle on a section of road, and
- if said at least one predicted speed vpred exceeds said maximum speed vmax along said section of road, activating said regenerative brake system before an actual speed vact of said vehicle reaches said maximum speed vmax, the regeneration being optimised on the basis of the regenerative brake system' s regeneration characteristics.
2. A method according to claim 1, in which said section of road comprises a downhill run on which said vehicle is accelerated by a train weight M of the vehicle.
3. A method according to either of claims 1 and 2, in which said maximum speed vmax corresponds to a downhill control speed vdhsc, i.e. vmax = vdhsc, at which a system for downhill speed control brakes the vehicle.
4. A method according to either of claims 1 and 2, in which said maximum speed vmax is related to a set speed vset of a cruise control.
5. A method according to either of claims 1 and 2, in which said maximum speed vmax is related to a driver behaviour.
6. A method according to either of claims 1 and 2, in which said maximum speed vmax is related to surrounding traffic on said section of road.
7. A method according to either of claims 1 and 2, in which said maximum speed vraax is related to a characteristic of said section of road.
8. A method according to claim 7, in which said
characteristic comprises at least one out of
- a speed limit for said section of road,
- a curvature of said section of road,
- the presence of at least one speed camera on said section of road, and
- a traffic situation within said section of road.
9. A method according to any one of claims 1-8, in which said maximum speed vmax may change dynamically along said section of road.
10. A method according to any one of claims 1-9, in which said section of road is that nearest ahead of said vehicle.
11. A method according to any one of claims 1-10, in which knowledge of said section of road is used in said determination of said at least one predicted speed vpred.
12. A method according to claim 11, in which said
knowledge is based on at least one out of
- positioning information,
- map information, and
- topography information.
13. A method according to any one of claims 1-10, in which a road gradient affecting said vehicle at the time when said determination of said at least one predicted speed vpred is made is used in said determination of said at least one predicted speed vpred.
14. A method according to any one of claims 1-10, in which said determination of said at least one predicted speed Vpred is based on an actual speed vact of said vehicle and an actual acceleration aact of said vehicle.
15. A method according to any one of claims 1-14, in which said at least one predicted speed vpred is determined on the basis of an assumption that a fuel supply to an engine of said vehicle is throttled on at least part of said section of road .
16. A method according to any one of claims 1-15, in which said at least one predicted speed vpred is determined on the basis of an assumption that said vehicle freewheels along at least part of said section of road.
17. A method according to any one of claims 1-15, in which said at least one predicted speed vprect is determined on the basis of a cruise control simulation.
18. A method according to any one of claims 1-17, in which said activation of said regenerative brake system takes place at one of the following locations:
- an activation location Pregen at which it is found that said at least one predicted speed vpred will exceed said maximum speed vmax and at which said vehicle accelerates,
- an activation location Pregen at which it is found that said at least one predicted speed vpred will exceed said maximum speed vmax and at which said vehicle has a power surplus such that said vehicle accelerates without an engine of said vehicle being supplied with fuel, and
- an activation location Pregen from which it is calculated that said maximum speed vmax may be reached along said section of road by means of a brake energy which can be achieved with said regenerative brake system.
19. A method according to any one of claims 1-18, in which said activation of said regenerative brake system takes place on the basis of a speed profile vprof which extends from an actual speed vact of said vehicle to said maximum speed vmax
20. A method according to any one of claims 1-18, in which the activation of said regenerative brake system takes place on the basis of an adaptive algorithm which adaptively calculates an appropriate brake action to be applied on the basis of a brake energy which needs to be braked away.
21. A method according to claim 20, in which said adaptive algorithm comprises a prediction for said vehicle of a braking process vpred rake which depends on said appropriate brake action.
22. A method according to claim 21, in which said appropriate brake action increases if said prediction of said braking process vpred brake reaches said maximum speed vmax.
23. A method according to claim 21, in which said appropriate brake action decreases if said prediction of said braking process vpred brake is continually below said maximum speed vmax.
24. A method according to any one of claims 21-23, in which said predicted braking process vp red brake is based on any one out of
- a current brake action,
- a brake action which varies during braking, and
- a pre-calculated brake action based on an appropriate brake action to be applied, an assessment of whether said brake action is appropriate being based on a brake energy which needs to be braked away.
25. A method according to any one of claims 1-24, in which said regenerative brake system comprises at least one out of
- a battery,
- a supercapacitor,
- a flywheel,
- a spring,
- a hydraulic pump cooperating with an accumulator,
- a pneumatic compressor cooperating with a pressure tank, and - a device for conveying energy to consumers on board said vehicle .
26. A computer programme which comprises programme code and which when said programme code is executed in a computer causes said computer to conduct the method according to any one of claims 1-25.
27. A computer programme product comprising a computer- readable medium and a computer programme according to claim 26, which programme is contained in said medium.
28. A control unit adapted to controlling a regenerative brake system in a vehicle for which there is a defined maximum speed v which said vehicle should not exceed, characterised by
- a prediction unit adapted to determining at least one predicted speed vpred for said vehicle on a section of road, and - an activation unit adapted, if said at least one predicted speed v exceeds said maximum speed vmax along said section of road, to activating said regenerative brake system before an actual speed vact of said vehicle reaches said maximum speed vmax, the regeneration being optimised on the basis of the regenerative brake system's regeneration characteristics.
EP13810710.7A 2012-06-26 2013-06-20 Method and system for control of a regenerative braking system in a vehicle Withdrawn EP2864172A4 (en)

Applications Claiming Priority (2)

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SE1250681A SE538992C2 (en) 2012-06-26 2012-06-26 Method and control unit for controlling a regenerative braking system in a vehicle
PCT/SE2013/050738 WO2014003637A1 (en) 2012-06-26 2013-06-20 Method and system for control of a regenerative braking system in a vehicle

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EP2864172A4 (en) 2017-03-08

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