SE538550C2

SE538550C2 - An electric system of a motor vehicle and a method for controlling such an electric system

Info

Publication number: SE538550C2
Application number: SE1451103A
Authority: SE
Inventors: Ledfelt Gunnar
Original assignee: Scania Cv Ab
Priority date: 2014-09-19
Filing date: 2014-09-19
Publication date: 2016-09-13
Also published as: BR102015020213B1; SE1451103A1; DE102015010528A1; BR102015020213A2

Abstract

22 ABSTRACT An electric system is configured to be arranged in a motorvehicle and comprises a power battery (2), a start battery (8)connected in parallel with the power battery, a generator (5) aswell as consumers (6) of electric energy comprising a start motor(18). A switch (10) is arranged to enable disconnection of thestart battery from said consumers. A device is configured tocheck and determine the ability of the power battery (2) to deliverelectric energy to said consumers (6), and means (17) isconfigured to close said switch when receiving information abouta disappearing of the ability of the power battery to deliverelectric energy to said consumers for providing a current path between the start battery (8) and said consumers (6). (Pig. 1)

Description

The present invention relates to an electric system configured tobe arranged in a motor vehicle and a method for controlling suchan electric system according to the preambles of the appendedindependent claims directed to such a system and a method, respectively.

The invention is not restricted to a special type of motor vehicles,although the invention is particularly applicable to wheeled motorvehicles, especially utility vehicles, such as trucks or lorries andbusses, and the invention will for that sake hereinafter primarilybe discussed for that field of use for illuminating the invention but accordingly not in any way restrict it thereto.

An electric system of this type is usually called dual batterysystem, since it has two battery packs connected in parallel, onewith one or several such said power batteries functioning asservice batteries and one with one or more said start batteries.Each such battery pack may have only one power battery andone start battery, respectively, even if they each have usuallytwo or more batteries connected in series, such as usually two12V batteries connected in series in trucks. The object of thestart battery is to ensure that the start motor gets sufficientpower through current from the start battery for being able tostart the combustion engine of the motor vehicle also if the power battery of the electric system would be entirely discharged. lt is for that reason important to maintain a high charging state of thestart battery independently of the charging state of the powerbattery. This is the reason for arranging the start battery of suchan electric system on the opposite side of the power battery withrespect to the generator and the consumers of electric energy ofthe vehicle and arranging a switch between one pole of thepower battery and the start battery. This means that the startbattery may be disconnected from said consumer side, i.e. therest of the electric system, in connection with a turning off of themotor of the vehicle, and the start battery may then be connectedto the electric system again in connection with a following start ofthe motor.

The good function of motor vehicles of today is increasinglydepending upon the supply of electric energy to a number ofconsumers of such energy. These consumers are for instanceheadlamp bulbs, clutch actuators, servo-unit pumps and differentmicroprocessors for controlling the operation of the vehicle. Saidgenerator is normally used for generating electric energy and oneor more said power batteries for storing electric energy. Thecapacity of the generator to supply current is when starting themotor of the motor vehicle in general sufficient to both chargesaid power batteries and supply electric energy to the electricenergy consumers of the vehicle. ln the case that the generatoris overloaded, i.e. said consumers need more electric power thanthe generator is able to alone provide, the power batteries willassist said generator so that enough current (electric power) willbe provided to said consumers. However, would a mal-function ofthe power batteries or the cabling thereof occur, so that the power batteries are not able to deliver electric energy to said consumers the generator has to alone take care of this. This isnormally no problem for the generator. However, if the loadapplied on the electric system by said consumers exceeds thecapacity of the generator and the power batteries have droppedout the system voltage will decrease rapidly, which may result infailure of the function of some of said consumers and occurrenceof dangerous situations. Especially when headlamp bulbs and/orother bulbs of the vehicle are turned on or powerful electricactuators are activated such high needs of supply of electricpower may suddenly occur that the generator will not be able tokeep the system voltage at a normal level but it may sink belowcritical levels resulting in failure of components of said electricsystem. This is particularly critical if it happens during driving of the vehicle in darkness.

BACKGROUND ART lt is for that sake desired to be able to improve the capacity ofbatteries and generators of such a system to reliably provide saidconsumers with electric energy. US 2011/0260544 A1 describesan electric system of this type enabling the use of a small powerbattery available to a low cost by providing the possibility to usea start battery to assist the generator in keeping a systemvoltage on a certain level while at the same time disconnecting the power battery from the consumer side.

SUMMARY OF THE INVENTION The object of the present invention is to provide an electric system and a method of the type defined in the introduction being improved in at least some aspect with respect to such electric systems and methods already known.

This object is with respect to the electric system obtained by providing such a system with the features listed in the characterizing part of appended patent claim 1.

By checking and determining the ability of the power battery todeliver electric energy to said consumers and if a disappearanceof this ability is determined connect the start battery to saidconsumer side of the electric system the risk of failure of thefunction of some of said consumers and occurrence of dangeroussituations is eliminated. lt would then be recommended to informthe driver of the vehicle about this measure, so that the driverdoes not unnecessarily stop and turn off the engine, since it mayafter that possibly not be started again due to a at least partiallydischarged start battery. An advantage of such an electricis that application of any tools for checking and determining the ability system functioning in this way it does not requireof the power battery to deliver electric energy to said consumersand no new control units or the like have to be arranged in thevehicle for realizing the features of the electric system accordingto the invention. Furthermore, said checking and determining andpossibly switching in of said start battery may be carried outautomatically without any involvement of the driver of the vehicle.According to an embodiment of the invention said devicecomprises a member configured to measure a parameter of saidpower battery on which said ability is depending. Such a parameter may be any parameter describing the condition of the battery, such as charging degree of the battery, chemical features thereof or the like.

According to another embodiment of the invention said electricsystem is of the type that further comprises a unit configured tocontrol said generator to deliver a system voltage to saidconsumers according to a voltage reference value and meansconfigured to measure said system voltage, and said devicecomprises o an arrangement configured, during operation of the motor ofsaid vehicle, to gradually lower said voltage reference valuedelivered to said unit towards a limit value lower than anexpected voltage level of said power battery, o means configured to compare the value of the system voltagemeasured with said voltage reference value during saidlowering of the latter, and o an apparatus configured to derive information about the abilityof said power battery to deliver electric energy to saidconsumers on the basis of the result of said comparison.

By lowering the voltage reference value used for controlling the generator in this way reliable information about the ability of the power battery to deliver electric energy to said consumers maybe efficiently obtained, since when said voltage reference valuegets lower than the actual value of the power battery voltage thepower battery will take over the entire feeding of said consumerswith electric energy if the power battery is able to do this. lf thisis not the case it may be due to a mal-function of said power battery or the cabling thereof.

According to another embodiment of the invention said device isconfigured to determine that the ability of the power battery todeliver electric energy to said consumers has disappeared if saidcomparison of the value of the system voltage measured and thevoltage reference value during said lowering of the latter showsthat a difference thereof remains lower than a predeterminedvalue. This predetermined value is then chosen so that adifference lower than that indicates that the system voltage valuefollows the voltage reference value of the generator, whichmeans that said power battery is not able to deliver any electricenergy to said consumers. And the switch will then be closed forproviding a current path between the start battery and said COnSUmefS.

According to another embodiment of the invention said device isconfigured to determine that the ability of the power battery todeliver electric energy to said consumers has disappeared if saidcomparison of the value of the system voltage measured andsaid voltage reference value during said lowering of the lattertowards said limit value at a certain rate shows that the value ofthe system voltage measured remains to decrease at the samerate until said limit value is reached. Reliable information aboutthe disappearance of the ability of the power battery to deliverelectric energy to said consumers is by this obtained.

According to another embodiment of the invention saidarrangement is configured to carry out said lowering of saidvoltage reference value at a rate so as to reach said limit valuewithin 10s-60s or 10s-40s. lowering of the voltage reference value by the arrangement is This speed of carrying out said suitable. lf the speed is too high lamps of the vehicle may start totwinkle and if the speed is to low the power battery will beunnecessarily much discharged.

According to another embodiment of the invention thearrangement is configured to carry out said lowering of thevoltage reference value towards a said limit value of 70%-95% or80%-90% of the expected voltage level of said power battery.Said limit value has to be set so that it will by said lowering ofthe voltage reference value be determined whether the powerbattery is able to deliver electric energy to said consumers ornot. But a system voltage being at said limit value, which will bethe case for a disappearance of said ability, may not jeopardizethe function of any equipment of the vehicle connected to saidelectric system of the motor vehicle. lf for instance said expectedvoltage level in a truck is 26V some such equipment mayautomatically drop out if the system voltage gets lower than 2OV.lt would in such a case be suitable to have said limit value to be not lower than 21V.

According to another embodiment of the invention said device isconfigured to check and determine said ability of the powerbattery when the load of said generator is less than 80% of themaximum generator load. This means that the electric system isprepared to meet possible sudden load increases that may occur.This also means that the device shall not carry out said checkingand determining when the driver has a high need of light, such as when driving in darkness.

According to another embodiment of the invention said device isconfigured to check and determine said ability during operationof the motor in a state in which said switch is open and by thatthe start battery disconnected from said consumer side. Thisnormally means that the start battery is fully charged and thenready to be connected to said consumers for providing them withelectric energy would the checking and determining of said ability of the power battery require this.

According to another embodiment of the invention said device isconfigured to check and determine said ability of the powerbattery at least once each day said vehicle is driven. This is asuitable interval for carrying out said checking and determining,since the good function of said power battery electric energydelivering capacity will then be checked each day the vehicle isdriven. lf an existence of a disappearance of said ability isdetermined this information should as mentioned above bedelivered to the driver so that the driver then knows that if the motor is turned off it may not be started again.

The object of the present invention is with respect to the methodfor controlling an electric system of a motor vehicle obtained byproviding a method according to the independent method claim.The advantages of such a method and embodiments thereofappear clearly from the above discussion of an electric system according to the invention and the embodiments thereof.

The invention also relates to a computer programme having the features of claim 13, a computer programme product having the features of claim 14, an electronic control unit having the features of claim 15 and a motor vehicle according to claim 16.

Other advantageous features as well as advantages of the present invention appear from the description following below.

BRIEF DESCRIPTION OF THE DRAWINGS With specific description of an embodiment of the invention cited as reference to the appended drawings, below follows a an example. ln the drawings: Fig.1 illustrates very schematically an electric system according to an embodiment of the invention,Fig. 2 is a graph illustrating a possible development over timeof the system voltage for an electric system according toFig. 1 when a method according to an embodiment ofthe present invention is carried out,Fig. 3 is a graph corresponding to Fig. 2 illustrating whathappens if a method according to an embodiment of theinvention is carried out and it is determined that thepower battery of the electric system shown in Fig. 1 isnot able to deliver electric energy to the consumers of said system, Fig. 4 is a flow chart illustrating the steps carried out in amethod according to an embodiment of the invention,and Fig 5 is a schematic view illustrating an electronic control unit for implementing a method according to the invention.

DETAILED DESCRIPTION OF AN EMBODIMENT OF THEINVENTION Fig. 1 illustrates schematically the general structure of an electricsystem according to the invention configured to be arranged in amotor vehicle 1 schematically indicated and which have twopower or service batteries 2 connected in series _ The powerbatteries are for example 12V-batteries, so that a service oroperation voltage between the two poles 3, 4 of the powerbatteries 2 is approximately 24V. A generator 5 and consumers 6of electric energy are both connected to opposite poles 3, 4 ofthe power batteries 2 on a consumer side 7 thereof. The box 6represents an amount of components of the motor vehicle to besupplied with electric energy by the generator 5 and/or the powerbatteries 2 and does also include a start motor 18. Two startbatteries 8 connected in series are connected to opposite poles3, 4 of the power battery pack on a side 9 thereof opposite tosaid consumer side 7 and a switch 10 is arranged between onepole 3 of the power battery pack and the start batteries 8 forenabling disconnecting and connecting of the start batteries with respect to said consumer side 7. 11 An engine management system for controlling components of theelectric system is schematically indicated by the box 11. Thissystem 11 may include functions to be carried out by differentparts of the electric system according to the present invention,and such parts have for that sake been shown to be included inthe box 11 and belong to a device 25 configured to check anddetermine the ability of the power batteries 2 to deliver electricenergy to the consumers 6. One such part is a unit 12 configuredto control the generator 5 to deliver a system voltage Usys to theconsumers 6 according to a voltage reference value. Means 13are configured to measure said system voltage. An arrangement14 is configured to provide the unit 12 with said voltagereference value and when carrying out a method for obtaininginformation about the ability of the power batteries to deliverelectric energy to the consumers during operation of the motor ofthe vehicle 1 gradually lower said voltage reference valuetowards a limit value lower than an expected voltage level of thepower batteries 2. Means 15 are configured to compare the valueof the system voltage measured by the means 13 with saidvoltage reference value during the lowering of the latter. Anapparatus 16 is configured to derive information about the abilityof said power batteries to deliver electric energy to saidconsumers on the basis of the result of said comparison. lt isillustrated in Fig. 1 by arrows how the system current lsys forsupplyingcomposed by the currents lb from the power batteries 2 and a the consumers 6 with electric energy may be current lg from the generator 5. However, once the motor of thevehicle has been started the capacity of the generator is ingeneral high enough for both charging the power batteries 2 and supplying said consumer 6 with electric energy. The power 12 batteries 2 will then only assist the generator to deliver electricenergy to the system would the generator be overloaded. lt isindicated in Fig 1 that said device as an alternative may have amember 26 configured to measure a parameter of the power batteries 2 on which said ability is depending.

A method according to an embodiment of the invention will nowbe described while making reference to the graphs of Figs. 2 and3. The method is carried out when the load of the generator is sothat the power batteries 2 are not participating in providing theconsumers with electric energy and the switch 10 is open and bythat the start batteries 8 disconnected from the consumer side ofthe electric system, which will then indicate that they are fullycharged. The system voltage Usys is then higher than theexpected battery voltage Ubex. The solid line in the figures showsthe system voltage and the dashed line the voltage referencevalue delivered to the generator. The method is started at thetime to by gradually lowering the voltage reference value towardsa limit value Ulm Fig. 2 illustrates what happens if the powerbatteries 2 are able to deliver electric energy to said consumers,which means that the power batteries will define the systemvoltage and take over the feeding of electric energy to theconsumers as soon as the voltage reference value delivered tothe unit 12 will be lower than the voltage of the power batteries2. This happens at the time t1, and the lowering of the voltagereference value is continued a short time after that, perhaps inthe order of a couple of seconds, so that a sufficient difference Abetween the system voltage measured and the voltage referencevalue is obtained for being able to reliably state that the power batteries are able to deliver electric energy to said consumers. 13 The method is then terminated and said voltage reference valueraised so that the generator will feed the consumers again and also charge the power batteries when needed.

Fig. 3 shows what happens if the power batteries are not able todeliver electric energy to said consumers. This means that thedevelopment of the system voltage will follow the development ofthe voltage reference value all the way to said voltage limit valueUmm. The lowering of said voltage reference value is terminatedwhen the system voltage measured reaches said limit value fornot jeopardizing the function of any components of the vehicledepending upon supply of electric energy by said electric system.The electric system comprises means 17 configured to close theswitch 10 when receiving information about the disappearing ofthe ability of the power battery to deliver electric energy to saidconsumers for then providing a current path between the startbatteries 8 and said consumers 6. The start batteries will thentake over the task of the power batteries for avoiding that anycomponents of the electric system will fail. Said information isthen delivered to the driver, so that the driver then knows that itmay most probably not be possible to start the motor of the vehicle again would it be stopped.

There are a number of circumstances influencing the expectedvoltage level of the power batteries 2, and some of thesecircumstances may be considered when selecting said expectedlevel and by that possibly also said limit value. The charginglevel of said power batteries, the size of the batteries and theoverall condition of the batteries are elements influencing saidlevel. The is another such expected voltage temperature 14 element, and said expected voltage level will be lowered with a falling temperature.

Fig. 4 illustrates a flow chart of a method according to anembodiment of the present invention carried out for an electricsystem of the type shown in Fig. 1. The method is started with astep S1 of asking if there is more than 5 minutes since motorstart. lf the answer to this question is yes it is in a second stepS2 asked if the load of the generator is less than 80% ofmaximum generator load. The steps S1 and S2 are repeated untilthe answers to both said questions are yes. A step Se, of loweringthe voltage reference value for the control of the generator andS4 of measuring a system voltage are then carried out in parallel.A comparison of system voltage measured and voltage referencevalue is at the same time carried out in step S5 and it is asked ina step S6 if it is possible to derive information about the ability ofthe power batteries to deliver electric energy. lf the answer tothis question is yes the method is stopped, but if the answer tothis question is no it is in a step S8 asked if the voltage referencevalue is higher than a limit value and if this is the case the stepsSs-Se are repeated. However, if the answer to this question is nosaid switch is in a step S8 closed for providing a current path between the start batteries and said consumers.

Computer programme code for implementing a method accordingto the programme which can be read into the internal memory of a invention is with advantage included in a computer computer, e.g. the internal memory of an electronic control unit of a motor vehicle. Such a computer programme is with advantage provided via a computer programme product comprising a data storage medium which can be read by acomputer and which has the computer programme stored on it.Said data storage medium is for example an optical data storagemedium in the form of a CD ROM disc, a DVD disc etc., amagnetic data storage medium in the form of a hard disc, adiskette, a cassette tape etc., or a flash memory or a memory ofthe ROM, PROM, EPROM or EEPROM type. Fig. 5 illustratesvery schematically an electronic control unit 11 comprising anexecution means 19, e.g. a central processor unit (CPU), forexecution of computer software. The execution means 19communicates with a memory 20, e.g. of the RAM type, via adata bus 21. The control unit 11 comprises also a non-transitorydata storage medium 22, e.g. in the form of a flash memory or amemory of the ROM, PROM, EPROM or EEPROM type. Theexecution means 19 communicates with the data storage medium22 via the data bus 21. A computer programme comprisingcomputer programme code for implementing a method accordingto the e.g. illustrated in Fig. 4 is stored on the data storage medium 22. invention, in accordance with the embodiment The embodiments described above, invention is of course in no way restricted to the since many possibilities formodifications thereof are likely to be obvious to one skilled in theart without having to derivate from the scope of invention defined in the appended claims.

Claims

Claims 16

1. An electric system configured to be arranged in a motor vehicle (1) and comprising a power battery (2),a start battery (8) connected in parallel with the powerbattery, a generator (5) as well as consumers (6) of electric(18) between opposite poles (3, 4) of the power battery on a energy comprising a start motor connectedconsumer side (7) thereof opposite to the side (9) forconnection of the power battery to the start battery, a switch (10) arranged between one pole (3) of thepower battery (2) and the start battery (8) so as toenable disconnection of the start battery from saidconsumer side (7), means (17) configured to control said switch (10) andto control the switch to be closed when activating thestart motor for starting the motor of the vehicle forproviding a current path between the start battery andthe consumer side of the power battery and by thatcurrent to the start motor, a device (25) configured to check and determine theability of the power battery (2) to deliver electric energyto said consumers (6) and send information thereaboutto said means (17), said means being configured toclose said switch (10) when receiving information abouta disappearing of the ability of the power battery (2) to deliver electric energy to said consumers for providing 17 a current path between the start battery (8) and saidconsumers (6), a unit (12) configured to control said generator (5) todeliver a system voltage to said consumers (6)according to a voltage reference value and means (13) configured to measure said system voltage, characterized in that said device comprises an arrangement (14) configured, during operation ofthe motor of said vehicle, to gradually lower saidvoltage reference value delivered to said unit (12)towards a limit value lower than an expected voltagelevel of said power battery (2), means (15) configured to compare the value of thesystem voltage measured with said voltage referencevalue during said lowering of the latter, and an apparatus (16) configured to derive informationabout the ability of said power battery (2) to deliverelectric energy to said consumers on the basis of the result of said comparison.

2. An electric system according to claim 1 characterized in that said device is configured to determine that the ability of the power battery (2) to deliver electric energy to said consumers (6) has disappeared if said comparison of the value of the system voltage measured and the voltage reference value during said lowering of the latter shows that a difference thereof remains lower than a predetermined value. 18

3. An electric system according to claim 1 or 2, characterized in that said device is configured to determine that the abilityof the power battery (2) to deliver electric energy to saidconsumers (6) has disappeared if said comparison of thevalue of the system voltage measured and said voltagereference value during said lowering of the latter towardssaid limit value at a certain rate shows that the value of thesystem voltage measured remains to decrease at the same rate until said limit value is reached.

4. An electric system according to any of the preceding claims,characterized in that said arrangement (14) is configured tocarry out said lowering of said voltage reference value at arate so as to reach said limit value within 10s-60s or 10s-40s.

5. An electric system according to any of the preceding claims,characterized in that said arrangement (14) is configured tocarry out said lowering of the voltage reference valuetowards a said limit value of 70%-95% or 80%-90% of the expected voltage level of said power battery (2).

6. An electric system according to any of the preceding claims,characterized in that said device is configured to check anddetermine said ability of the power battery (2) when the loadof said generator (5) is less than 80% of the maximum generator load.

7. An electric system according to any of the preceding claims,characterized in that said device is configured to check and 19 determine said ability during operation of the motor in a statein which said switch (10) is open and by that the start battery (8) disconnected from said consumer side (7).

8. An electric system according to any of the preceding claims,characterized in that said device is configured to check anddetermine said ability of the power battery (2) at least once each day said vehicle is driven.

9. A method for controlling an electric system of a motorvehicle, said system comprising a power battery (2), a startbattery (8) connected in parallel with the power battery, agenerator (5) as well as consumers (6) of electric energycomprising a start motor connected between opposite poles(3, 4) of the power battery (2) on a consumer side (7) thereofopposite to said connection of the power battery to the startbattery, a switch (10) arranged between one pole (3) of thepower battery and the start battery so as to enabledisconnection of the start battery from said consumer side,means (17) configured to control said switch (10) and tocontrol the switch to be closed when activating the startmotor for starting the motor of the vehicle for providing acurrent path between the start battery (8) and the consumerside (7) of the power battery (2) and by that current to thestart motor, a unit (12) configured to control said generatorto deliver a system voltage to said consumers according to avoltage reference value and means (13) configured tomeasure said system voltage, in which the methodcomprises the steps of, during operation of the motor of said vehicle, o check and determine the ability of the power battery (2)to deliver electric energy to said consumers (6) andsend information thereabout to said means (17), and o close said switch (10) when said means (17) receivesinformation about a disappearing of the ability of thepower battery (2) to deliver electric energy to saidconsumers (6) for providing a current path between thestart battery (8) and said consumers, characterized in that said step of checking and determiningcomprises the following sub-steps to o lower said voltage reference value gradually towards alimit value lower than an expected voltage level of saidpower battery (2), o compare the value of the system voltage measuredwith said voltage reference value during said loweringof the latter, and o derive information about the ability of said power battery (2) to deliver electric energy to said consumers (6) on the basis of the result of said comparison.

10. A computer program comprising computer program code for

11. causing a computer to implement a method according toclaim 9 when the computer program is executed in the computer. A computer program product comprising a non-transitorydata storage medium (22) which can be read by a computerand on which the program code of a computer program according to claim 10 is stored.

12.

13. 21 An electronic control unit of a motor vehicle comprising anexecution means (19), a memory (20) connected to theexecution means and a non-transitory data storage medium(22) which is connected to the execution means and onwhich the computer program code of a computer programaccording to claim 10 is stored. A motor vehicle, especially a wheeled vehicle such as ain that electronic control unit according to claim 12. truck or a bus, characterized it comprises an