SE539061C2

SE539061C2 - A method for checking the function of a compression release brake system

Info

Publication number: SE539061C2
Application number: SE1451500A
Authority: SE
Inventors: Mörner Fredrik; Rönnqvist Patrik
Original assignee: Scania Cv Ab
Priority date: 2014-12-09
Filing date: 2014-12-09
Publication date: 2017-04-04
Also published as: SE1451500A1

Abstract

19 ABSTRACT The function of a compression release brake system of a com-pression ignited engine with a plurality of cylinders (10) in a mo-tor vehicle is checked by driving a crank shaft (14) of the engineto rotate at a constant speed without injection of fuel into the cyl-inders while for each cylinder, for the compression release brakesystem in an inactive state and then in an active state or in theopposite order, measuring the torque to be applied for maintain-ing said speed in a position of said crank shaft where the torquewould be influenced by the behaviour of that cylinder by a cor-rectly functioning action of said compression release brake sys-tem in an active state thereof. The torque values obtained foreach cylinder for the compression release brake system in inac-tive and active state are then compared, and the function of thecompression release brake system for each individual cylinder ofthe engine is determined based upon the result of this compari- SOn. (Fig 2).

Description

The present invention relates to a method for checking the func-tion of a compression release brake system of a compression ig-nited engine with a plurality of cylinders in a motor vehicle, saidsystem comprising an arrangement configured, in an active stateof said system, to influence opening of an exhaust valve of eachsaid cylinder so as to obtain a braking action upon a crank shaftof the engine by influencing gas compression inside the cylin-ders.

The invention is not restricted to a special type of motor vehicles,although the invention is particularly applicable to heavy wheeledmotor vehicles, such as trucks or lorries and buses, and the in-vention will for that sake hereinafter primarily be discussed forthat field of use for illuminating the invention but accordingly notin any way restrict it thereto.

The fuel used in such an engine may be of any conceivable typeand diesel and ethanol may be mentioned as examples. Such acompression ignited engine may offer poor possibilities to useengine braking when braking a motor vehicle. This is the reasonto providing especially heavy motor vehicles with a compressionrelease brake system for providing additional braking of the vehi-cle in particular when driving downhill. A compression releasebrake system causes braking by opening exhaust valves of the engine at positions of the operation cycle of the cylinders result- ing in a modified compression in the cylinders and by that a brak-ing action upon a crank shaft of the engine with respect to nosuch opening of the exhaust valves. Such exhaust valves open-ing may especially be carried out in connection with reaching thetop dead centre TDC of the piston in the cylinder after the com-pression cycle, so that air trapped in the cylinder is released andthe piston will not receive any force from any gas pushing it down when moving away from said top dead centre.

However, the function of such a compression release brake sys-tem may of course for different reasons be degraded, which mayfor instance be due to a malfunction related to only one or a fewof the cylinders of the engine, such as an incorrectly functioningvalve rocker arm for the exhaust valve of such a cylinder whichmay depend upon an obstruction in an hydraulic line to a cham-ber to be filled with hydraulic fluid for triggering modified openingof the exhaust valve or a malfunction of an hydraulic valve con-trolling the supply of hydraulic fluid to a said chamber. The driverof the vehicle may then bring the vehicle to a workshop andcomplain about the deteriorated braking effect of the compres-sion release brake system. However, the workshop will then nothave any possibility to check the function of the compression re-lease brake system, since it is only possible to activate this sys-tem when the engine is running and the system has the requiredhydraulic fluid pressure making it mostly impossible to point outfor which of the cylinders the valve rocker arm associated withthe exhaust valve does not function correctly when activating thecompression release brake system. This may then result in a re-placement of said valve rocker arms for all the cylinders and a considerable unnecessary cost although perhaps only one valve rocker arm functions incorrectly when activating the compressionrelease brake system. lt is even possible that the replacement ofall valve rocker arms will not result in a compression releasebrake system functioning perfectly would a malfunction for any ofsaid valve rocker arms be dependent upon an obstruction of a said hydraulic fluid line.

BACKGROUND ART US 2003/0115944 A1 discloses a method for checking the func-tion of a compression release brake system, in which this systemis activated and deactivated and differences in a response of theengine are compared with expected such WO2013/125439 A1 discloses another method for checking the func- tion of a compression release brake system, in which the number FGSDOHSGS. of revolutions of an engine versus time is examined with thecompression release brake system in an active state and in aninactive state. However, the methods disclosed in these docu-ments have the problem just mentioned with respect to pointingout for which of the cylinders the compression release brake sys-tem does not function would it be determined that the compres- sion release brake system as a whole has a degraded function.

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

This object is obtained by providing such a method with the fea- tures listed in the characterizing part of appended patent claim 1.

Accordingly, the crank shaft is in a step a) driven without injec-tion of fuel and the torque to be applied thereto for maintaining aconstant speed thereof is measured in an active and an inactivestate of the compression release brake system. The torque val-ues so obtained for each cylinder are then in a step b) comparedand the function of said system for each individual cylinder is in astep c) determined based upon the result of this comparison.Thus, by the quite new approach to drive the engine without sup-ply of fuel and carry out a so-called compression test then possi-ble with the compression release brake system in an active andin an inactive state and comparing the results of the compressiontest for each cylinder in these states it will be possible to detectany malfunction of one or more cylinders with respect to thefunction of the compression release brake system. This is due tothe fact that the compression in a cylinder is changed if the com-pression release brake system is activated and functions correct-ly with respect to that cylinder. This means that it may be avoid-ed to replace a valve rocker arm or take any other measures forrepairing the compression release brake system for a cylinder forwhich it in fact functions correctly. Furthermore, the method ac-cording to the invention will be easy to carry out in a short time and by that to a low cost also with respect to time consumption.

According to an embodiment of the invention in step b) for eachcylinder the torque value obtained in an inactive state of the sys-tem is compared with the torque value obtained in an active state of the system, and it is determined that if the torque value in said active state exceeds the torque value in said inactive state by atleast a predetermined level said compression release brake sys-tem functions correctly for that cylinder. By carrying out such acomparison of said torque values of said active and inactivestates of the compression release brake system for each cylinderit may reliably be determined which cylinder or cylinders have acorrect function with respect to the compression release brake system.

According to another embodiment of the invention it is deter-mined that if for a cylinder the torque value in said active statedeviates by less than a predetermined value from the torque val-ue in said inactive state a malfunction of said compression re-lease brake system exists for that cylinder. This malfunction maythen be due to that the compression release brake system willnot function at all for that cylinder, i.e. not be active for that cyl-inder in the active state of said system, or the compression re-lease brake system will be active all the time for that cylinder andthen also have a braking action upon the engine by that cylinderwhen the compression release brake system is in an inactive state.

According to another embodiment of the invention when it hasbeen determined that a said malfunction of the compression re-lease brake system exists for a cylinder a step of determiningaverage values of the torque values obtained for all cylinders insaid inactive state and said active state of the compression re-lease brake system is carried out, these two average values arecompared, and it is determined that a malfunction of said com- pression release brake system exists for all said cylinders if a difference of said two average values is less than a predeter-mined value. ln another embodiment of the invention said torquevalue in said active state of said system may for each cylinder becompared with said average value for the torque values in saidinactive state of the system, and it is determined that if the dif-ference of said torque value in said inactive state for a cylinderand said average torque value in said inactive state exceeds apredetermined level the compression release brake system ispermanently in an active state for that cylinder. Thus, this type ofmalfunction of the compression release brake system for a cylin- der may be detected in this way.

According to another embodiment of the invention said torquevalue in said active of said system is for each cylinder comparedwith said average value of the torque values obtained for all cyl-inders in said active state of the system, and it is determined thatsaid compression release brake system is permanently inactivefor a cylinder for which said average torque value in said activestate of said system exceeds said torque value for that cylinder in said active state by at least a predetermined value.

According to another embodiment of the invention a start motorof said engine is operated for driving said crank shaft in step a).lt is suitable to use the start motor of the engine for carrying outthe driving of the crank shaft of the engine without fuel supply tothe engine for checking the function of the compression release brake system in accordance with the invention.

According to another embodiment of the invention said crank shaft of the engine is in step a) driven by driving means separate from said engine, such as another engine, an electric motor, abelt driving wheels of a driven axle of said motor vehicle etc.These are other options for driving said crank shaft to rotate for carrying out the method according to the invention.

According to another embodiment of the invention said engine isstarted and driven with injection of fuel into said cylinders for ob-taining a constant temperature of the cylinders thereof substan-tially independent upon the environment before carrying out stepa). Substantially steady conditions when performing the method according to the invention may by this be obtained.

According to another embodiment of the invention said activestate of the compression release brake system is obtained bycontrolling said arrangement to open the exhaust valve of eachcylinder to be open after the return of a piston in the cylinder atthe top dead centre after compression stroke of said piston.Thus, this means that said position for measuring the torque willfor each cylinder be when the piston of that cylinder has reached said top dead centre and moves away therefrom.

The invention also relates to a computer program having the fea-tures of claim 12, a computer program product having the featuresof claim 13, and an electronic control unit having the features of claim 14.

Other advantageous features as well as advantages of the pre- sent invention appear from the description following below.

BRIEF DESCRIPTION OF THE DRAWINGS With reference to the appended drawings, below follows a specif- ic description of an embodiment of the invention cited as an ex- ample. ln the drawings: Fig 1 Fig 2 Fig 3 Fig 4 is a very schematic view illustrating a compression re-lease brake system to which a method for checkingthe function thereof according to the invention may be apphed, is a very schematic view of parts of an engine provid-ed with a compression release brake system accord-ing to Fig 1 used for explaining said method according to an embodiment of the invention, is a flow chart illustrating the steps carried out in amethod according to an embodiment of the invention, and is a schematic view illustrating an electronic unit for implementing a method according to the invention.

DETAILED DESCRIPTION OF AN EMBODIMENT OF THEINVENTION The general construction of a compression release brake system is schematically illustrated in Fig 1. This system may be activat- ed by an engine control unit 1 and is an hydraulic system with anhydraulic pump 2 supplying hydraulic fluid to a first solenoidvalve 3 connecting to an hydraulic line 4 branched into as manylines as cylinders of the engine, and only one 5 of these linesand components associated therewith is shown in Fig 1. This line5 is connected to a control valve 6 connected through a line 7 toa chamber 8 in connection with a rocker arm valve 9 forming anexhaust valve of a cylinder 10 of said engine. lt is illustrated howa cam 11 of a cam shaft 12 of the engine may upon rotation ofthe cam shaft push the rocker arm valve 9 downwardly as seen in Fig 1 for opening said exhaust valve.

The function of the compression release brake system is as fol-lows. When the driver of a motor vehicle provided with said en-gine activates the compression release brake system the enginecontrol unit 1 controls the first solenoid valve 3 to open and sup-ply hydraulic fluid to each said control valve 6 filling the chamber8 with hydraulic fluid, which results in an extension of the rockerarm so that this will be hit by said cam 11 in a position in whichthe cam would not hit that rocker arm in absence of hydraulic flu-id in the chamber 8. That will be a position when the piston be-longing to the cylinder 10 is near the top dead centre TDC, sothat air compressed in the cylinder is released and no energy isreturned to the crank shaft. Energy is instead absorbed and thetorque to rotate the crank shaft will increase and the enginebraked.

When the compression release brake system is not needed any-more the engine control unit 1 will control the first solenoid valve 3 to close and the control valve 6 to empty the chamber 8, so that the exhaust valve of the cylinder will not open in said posi- tion for such braking action any more. lt is shown how the compression release brake system has asecond part connecting the hydraulic pump 2 to a second sole-noid valve 13 also controlled by the engine control unit 1. Thisvalve 13 may control the cam 11 by turning the entire exhaustcam shaft 12 and is accordingly a so-called cam phaser. This re-sults in an additional influence upon braking of the engine by in-fluencing the exhaust valve of the respective cylinder. By carry-ing out such cam phasing the exhaust valve may be brought toopen earlier, so that it may be open during the expansion strokeand by that let an over pressure from the exhaust side into thecylinder. This earlier opening of the exhaust valve will then resultin an earlier closing of the valve during the exhaust stroke, whichresults in an additional compression stroke in the operation cycleof the piston and the braking of the engine increases.

The present invention is directed to checking the function of acompression release brake system of this type, but it is prefera-bly only directed to checking the function of the part of the sys-tem connected to the first solenoid valve 3 and resulting in acompression release by opening the exhaust valve and by thatletting gas out thereof close to said top dead centre of the piston,since a malfunction of the cam phasing part of the compressionrelease brake system may easier be obtained by suitable sen- SOFS.

A malfunction of the compression release brake system with re- spect to a cylinder of the engine may be due to an obstruction of 11 the line 7 from the control valve 6 to the Chamber 8 or that therocker arm valve 9 may not be acted upon for any other reason.The chamber 8 will then not be filled with oil for obtaining com-pression release and braking. A malfunction of the control valve6 may also prevent the chamber 8 from being emptied, so thatthe compression release braking action will remain for that cylin-der also when the engine control unit has controlled the com- pression release brake system to assume an inactive state.

A method for checking the function of this part of the compres-sion release brake system according to an embodiment of the in-vention will now be explained while at the same time making ref-erence to Fig 2. This engine is first of all started and driven withinjection of fuel into the cylinders thereof for obtaining a constanttemperature of the cylinders substantially independent upon theenvironment, such as by driving the engine in 10 minutes. Thecrank shaft 14 of the engine is then driven without injection offuel into the cylinders by the start motor of the engine. When thenumber of revolutions has been stabilized so that the crank shaftrotates with a constant speed the time it takes for two subse-quent marks 15, 16, such as holes, in a flywheel 17 of the engineto pass a sensor 18 when a piston 19 of a cylinder passes saidtop dead centre is measured. This is made both with the com-pression release brake system in an active and in an inactivestate. The time measured indicates how much the flywheel hasbeen braked or accelerated before and after the top dead centreof the piston of the cylinder. This corresponds to a torque meas-urement and the torques measured for that cylinder in said twodifferent states of the compression release brake system are then compared, and if the difference of these torque values ex- 12 ceeds a predetermined level it may be concluded that the com-pression release brake system functions correctly for that cylin-der. This procedure may then be repeated for each cylinder ofthe engine. Would for any of the cylinders the difference of saidtorque values be less than a predetermined value it may be con-cluded that the compression release brake system does not func-tion correctly for that cylinder. The malfunction may then eitherbe a constant braking action applied by said system or no suchbraking action applied even if the compression release brakesystem is in an active state. Comparison of the torque valuesmeasured for this cylinder with average of torque values meas-ured for all cylinders for the compression release brake system inan active and in an inactive state will then show which type of malfunctions exists for that cylinder.

Fig 3 illustrates a flowchart of a method according to an embodi-ment of the present invention carried out for checking the func-tion of a compression release brake system of a compression ig-nited engine with a plurality of cylinders in a motor vehicle. Themethod is started with a step S1 of driving the engine with injec-tion of fuel for obtaining a constant temperature of the cylindersof the engine. A start motor of the engine is then in a secondstep S2 activated to drive a crank shaft of the engine to rotate ata constant speed without injection of fuel into the cylinders. Withthe compression release brake system in an inactive state thetorque is measured for one of the cylinders when the pistonpasses the top dead centre by measuring time interval betweenmarks on a flywheel of the engine passing a sensor in a step S3.The compression release brake system is then in a step S4 trans- ferred to an active state, and in a step S5 the same measure- 13 ments as in step Se, is made. The torque values obtained for thecylinder for the compression release brake system in inactiveand active state are then compared in a step S6. The function ofthe compression release brake system is in a step S7 determinedfor the cylinder based upon the result of this comparison. Thequestion “Previous step carried out for all cylinders?” is thenasked in a Step S8. When the answer to this question is no thesteps Se, to S8 are then repeated until this has been done for all cylinders of the engine.

Computer program code for implementing a method according tothe invention is with advantage included in a computer programwhich can be read into the internal memory of a computer, e.g. theinternal memory of an electronic control unit of a motor vehicle.Such a computer program is with advantage provided via a comput-er program product comprising a data storage medium which can beread by a computer and which has the computer program stored onit. Said data storage medium is for example an optical data storagemedium in the form of a CD ROM disc, a DVD disc etc., a magneticdata storage medium in the form of a hard disc, a diskette, a cas-sette tape etc., or a flash memory or a memory of the ROM, PROM,EPROM or EEPROM type. Fig. 4 illustrates very schematically anelectronic control unit 20 comprising an execution means 21, e.g. acentral processor unit (CPU), for execution of computer software.The execution means 21 communicates with a memory 22, e.g. ofthe RAM type, via a data bus 23. The control unit 20 comprises alsoa non-transitory data storage medium 24, e.g. in the form of a flashmemory or a memory of the ROM, PROM, EPROM or EEPROMtype. The execution means 21 communicates with the data storage medium 24 via the data bus 23. A computer program comprising 14 computer program code for implementing a method according to theinvention, e.g. in accordance with the embodiment illustrated in Fig. 3, is stored on the data storage medium 24.

The invention is of course in no way restricted to the embodimentdescribed above, since many possibilities to modifications there-of are likely to be obvious to one skilled in the art without havingto deviate from the scope of invention defined in the appended claims.

The torque measurements may be carried out in other ways thandescribed above. lf for example an electric motor is used to drivethe crank shaft of the engine when carrying out the method ac-cording to the invention the current to that motor may be meas-ured as a measure of the torque instead of the acceleration of the flywheel.

Claims

1. A method for checking the function of a compression releasebrake system of a compression ignited engine with a pluralityof cylinders (10) in a motor vehicle, said system comprisingan arrangement configured, in an active state of said sys-tem, to influence opening of an exhaust valve (9) of eachsaid cylinder so as to obtain a braking action upon a crankshaft (14) of the engine by influencing gas compression in-side the cylinders, characterized by the steps: a) driving said crank shaft (14) to rotate at a constant speedwithout injection of fuel into said cylinders and for eachcylinder, for the compression release brake system in anactive state and then in an inactive state or in oppositeorder, measuring the torque to be applied for maintainingsaid speed in a position of said crank shaft where thetorque would be influenced by the behaviour of that cylin-der by a correctly functioning action of said compressionrelease brake system in an active state thereof, b) comparing the torque values obtained for each cylinder instep a) for said compression release brake system in saidinactive state and said active state, respectively, and c) determining the function of said compression releasebrake system for each individual cylinder of the engine based upon the result of said comparison.

2. A method according to claim 1, characterized in that in stepb) for each cylinder (10) said torque value obtained in an in- active state of said system is compared with the torque value 16 obtained in an active state of said system, and that it is de-termined that if the torque value in said active state exceedsthe torque value in said inactive state by at least a prede-termined level said compression release brake system func- tions correctly for that cylinder.

3. A method according to claim 2, characterized in that it isdetermined that if for a cylinder (10) the torque value in saidactive state deviates by less than a predetermined valuefrom the torque value in said inactive state a malfunction ofsaid compression release brake system exists for that cylin- der.

4. A method according to claim 3, characterized in that when ithas been determined that a said malfunction of the compres-sion release brake system exists for a cylinder (10) a step ofdetermining average values of the torque values obtained forall cylinders in said inactive state and said active state of thecompression release brake system is carried out, that thesetwo average values are compared, and that it is determinedthat a malfunction of said compression release brake systemexists for all said cylinders if a difference of said two aver- age values is less than a predetermined value.

5. A method according to claim 4, characterized in that foreach cylinder (10) said torque value in said inactive state ofsaid system is compared with said average value of thetorque values in said inactive state of the system, and that itis determined that if the difference of said torque value in said inactive state for a cylinder and said average torque 17 value in said inactive state exceeds a predetermined levelthe compression release brake system is permanently in an active state for that cylinder.

6. A method according to claim 4, characterized in that foreach cylinder (10) said torque value in said active state ofsaid system is compared with said average value of thetorque values obtained for all cylinders in said active state ofthe system, and that it is determined that said compressionrelease brake system is permanently inactive for a cylinderfor which said average torque value in said active state ofsaid system exceeds said torque value for that cylinder in said active state by at least a predetermined value.

7. A method according to any of the preceding claims, charac-terized in that a start motor of said engine is operated for driving said crank shaft (14) in step a).

8. A method according to any of claims 1-6, characterized inthat said crank shaft (14) of the engine is in step a) driven bydriving means separate from said engine, such as anotherengine, an electric motor, a belt driving wheels of a driven axle of said motor vehicle etc.

9. A method according to any of the preceding claims, charac-terized in that said engine is started and driven with injec-tion of fuel into said cylinders (10) for obtaining a constanttemperature of the cylinders thereof substantially independ- ent upon the environment before carrying out step a). 18

10. A method according to any of the preceding claims, charac-

11.

12.

13. terized in that said active state of the compression releasebrake system is obtained by controlling said arrangement toopen the exhaust valve (9) of each cylinder (10) to be openafter the return of a piston (19) in the cylinder at the top dead centre after a compression stroke of said piston. A computer program comprising a computer program code forcausing a computer to implement a method according to any ofclaims 1-10 when the computer program is executed in the computer. A computer program product comprising a data storage medi-um (24) which can be read by a computer and on which theprogram code of a computer program according to claim 11 is stored. An electronic control unit comprising an execution means(21), a memory (22) connected to the execution means and adata storage medium (24) which is connected to the executionmeans (21) and on which the computer program code of a computer program according to claim 11 is stored.