FIELD OF THE INVENTION

The present invention relates to a method at compression braking and a device adapted for diagnosis and control of compression braking of a vehicle.

The invention also relates to a computer program and a computer program product comprising computer program code for the implementation of a method according to the invention, and an electronic control device and a motor vehicle.

BACKGROUND

Compression braking refers to braking that occurs in the absence of fuel supply to the cylinder in the combustion engine, by way of opening one of the valves through which the gas mixture is supplied into and out of, respectively, the cylinder's combustion chamber, during the cylinder's compression stroke and/or expansion stroke. One version of compression braking entails that the cylinder's exhaust valve is opened at the end of the cylinder's compression stroke or just at the beginning of its expansion stroke, that is to say when the cylinder's piston is in the vicinity of its top dead centre, which leads to a rapid pressure drop in the cylinder. Another version of compression braking entails that the cylinder's inlet valve opens during the compression stroke's initial stage, which results in the pressure building up in the cylinder becoming considerably less than in case where the valve is kept closed. By closing the valve at the top dead centre, the piston will create a negative pressure in the cylinder during the expansion stroke, resulting in a mild braking effect. In both versions, the amount of energy transmitted via the cylinder's piston in the form of torque to the vehicle's operation is reduced, so that the vehicle decelerates. US 2003/01 15944 describes a method to test the functionality of a compression brake in a vehicle operated by a multi-cylinder combustion engine. The method comprises selective compression deceleration of only one cylinder, while at the same time supplying a specific amount of fuel to the other cylinders, while the engine's engine speed is measured and compared to an expected engine speed. Based on this comparison, conclusions are reached relating to the functionality of the compression brake. This method is not, however, adapted for use during normal operation of the vehicle, but to test the compression brake's performance during one testing occasion.

SUMMARY OF THE INVENTION

One objective of the present invention is to achieve a manner of assessing, during normal operation of a vehicle which is decelerated with a compression brake, the braking torque obtained via the compression brake. Another objective is to obtain a measured value, in a cost effective manner, of the braking action that may be obtained via compression braking of a vehicle, in order to then use such measured value at the control of the compression brake in combination with other braking mechanisms in the vehicle.

These objectives are achieved according to the invention through the method and the device according to the enclosed claims. According to a first aspect, a method is achieved at compression braking of a vehicle comprising a combustion engine with at least one cylinder. The method comprises

during one working cycle of the combustion engine when compression braking occurs, detecting movements of a cylinder head belonging to said cylinder or of parts adjacent thereto in the engine, which movements have been generated by the compression braking, and

based on said detected movements, determining or estimating a braking torque caused by the compression braking.

Surprisingly, at compression braking of a cylinder in a combustion engine of a vehicle, it is possible to detect movements caused by the compression braking in the cylinder's cylinder head and in adjacent parts of the engine, and thus, by way of analysis of these movements, to determine or estimate a braking torque. The movements arise partly as a consequence of pressure changes in the cylinder, and partly as a consequence of opening and closing of the valves controlling the compression braking. By detecting and interpreting these movements, a large amount of information relating to the compression braking may be obtained, and such information may be used to determine or estimate the braking torque caused by the compression braking. Since the method may be carried out at normal operation of the combustion engine when compression braking is applied, the calculated or estimated braking torque may be used to provide feedback to the vehicle's control system, and be the basis of control of compression braking during subsequent working-cycles of the combustion engine. The method according to the invention may thus also be used to ensure that the compression braking is not used under the conditions where this would be harmful to the engine, for example because of over pressure and overheating.

According to one embodiment of the invention, the detected movements comprise movements generated by pressure changes arising in the cylinder's combustion chamber during the compression braking. By detecting such movements, the pressure changes arising in the cylinder during the compression braking may be indirectly detected. Thus, the development over time of the gas pressure in the cylinder during a working cycle may be reliably derived. The movements, which in this manner may be detected and which are generated by pressure changes in a combustion chamber of the cylinder, may for example be vibrations, noise, i.e. gas movements, various types of shape changes, such as protrusions, in said cylinder head or in adjacent parts in the engine. These may also be movements in the form of strains in screws in the engine which are detected, such as screws in main bearings or connecting rod bearings, and in cylinder head bolts. The appearance of such movements depends on pressure changes in the combustion chamber, and may for example be detected by applying strain-sensors on such screws. Since the pressure changes may be detected indirectly outside the combustion chamber itself, advantageously no cylinder pressure sensor needs to be fitted inside the combustion chamber. Accordingly, a more cost effective determination of the gas pressure in the cylinder is obtained, and the disruptions which a cylinder pressure sensor may give rise to are avoided.

According to one embodiment of the invention the said movements which have a frequency of ≤ 250 Hz, 0.5 Hz-250 Hz or 0.5 Hz-200 Hz which is detected. Thus, movements occurring with relatively low frequency are detected, and the basic frequency of variations in the gas pressure inside said cylinder lies within these intervals, which is the same as the combustion engine's engine speed, which e.g. may typically be 60 revolutions per minute (1 Hz) for a marine diesel engine and as high as 12 000 revolutions per minute (approximately 200 Hz) for an otto engine in a motorcycle. According to one embodiment of the invention, the movements that are detected comprise movements generated by activation and/or deactivation of the compression braking. By detecting such movements, among others information about the duration of the compression braking may be extracted, which may be useful in estimating the braking torque based on a model, without preparing a gas pressure curve for the cylinder. For example, a measured value of the cylinder's charge air pressure may be used, in order to via an inlet channel to the cylinder estimate, together with the duration of the compression braking, the compression pressure at compression braking, and this value may then be compared with an expected value for the compression pressure during one working cycle without compression braking. Saved information regarding the compression braking's performance and the control parameters used to activate and deactivate the compression braking may be used to be able to adjust the control parameters, and thus to be able to improve the control of the compression braking to a desired braking torque. In this manner, control errors may be minimised. According to one embodiment of the invention, the detected movements comprise movements generated by a change of position, such as opening and closing, of at least one valve that controls compression braking. Opening and closing of valves gives rise movements with a higher frequency than the movements arising as a consequence of pressure changes in the cylinder, and may therefore easily be distinguished from these. By detecting opening and closing of one or several valves that control compression braking, the start and duration of compression braking may be determined with great accuracy. Detection of opening and closing of the one or several valves controlling the compression braking may be combined with detection of movements caused by pressure changes in the cylinder, but may also be used without simultaneously preparing a pressure curve. In the latter case, the duration of the compression braking may be used in order to make a simpler estimate, with the help of a model, of the braking torque caused by the compression braking as described above. According to one embodiment of the invention, information extracted by way of detection of said movements, generated through activation and/or deactivation of compression braking, is used in order to estimate, with the use of a model, the braking torque caused by the compression braking. In this embodiment, a simpler estimate of the braking torque may be made, without preparing a gas pressure curve.

According to another embodiment of the invention, the braking torque caused by the compression braking is determined by way of, based on said detected movements generated by pressure changes arising during compression braking, calculating said pressure changes in the cylinder, comparing the calculated pressure changes with stored data relating to pressure changes during an equivalent part of a working cycle of the cylinder in the absence of compression braking, and based on such comparison, to calculate said braking torque. By thus starting from the pressure changes in the cylinder and using these in determining the braking torque, a reliable value of the braking torque caused by the compression braking may be calculated, without using other signals than those obtained through the detection of the pressure changes caused by the compression braking in the cylinder. By comparing the gas pressure measured over time with a corresponding gas pressure curve in the absence of compression braking, the braking torque caused by the compression braking may be determined with great accuracy.

According to one embodiment of the invention, the method also comprises detecting the engine's engine speed at activation and/or deactivation of compression braking and/or at active compression braking, and, based on the engine speed and the determined or estimated braking torque, to determine or estimate the braking effect of the compression braking. The braking effect may then be used at the control of the compression brake and a brake interacting with the compression brake, for example a so- called retarder, where there is a desire to control the deceleration based on the braking effect, which the respective brakes are able to provide.

According to one embodiment of the invention, the method also comprises the steps: when a braking torque is requested during a later working cycle, following said working cycle in the combustion engine, control the compression braking during the later working cycle based on the determined or estimated braking torque for the previous working cycle, so that the requested braking torque is achieved.

In this embodiment, the calculated or estimated braking torque during one working cycle is thus used in order to control the compression braking in the subsequent working cycle. Thus, a direct feedback is provided to a control system of the engine and the control system may, any time during operation, continuously adjust the control of the compression braking, based on the previous working cycle. According to one embodiment of the invention, the compression braking is controlled during the later working cycle at least partly by adjusting the duration of the compression braking. In this manner, a simple way of controlling the braking torque caused by the compression braking is achieved.

According to one embodiment of the invention, the compression braking is controlled during the later working cycle at least partly through control of the timing for the activation of the compression braking. This is an alternative way of achieving a control of the braking torque caused by the compression braking.

According to one embodiment of the invention, the compression braking is controlled during the later working cycle by way of controlling the opening and/or closing of at least one valve that controls the compression braking. This may occur by adjusting the duration of the compression braking, but also by adjusting the degree of opening of the one or several valves controlling the compression braking. Thanks to this embodiment, the compression braking of a multi-cylinder engine may be controlled jointly for all cylinders. Opening and closing of the valves may be controlled for example mechanically, hydraulically or electromagnetically.

According to one embodiment of the invention, the method is carried out for a vehicle comprising a combustion engine with at least two cylinders, and the compression braking is controlled during the later working cycle at least partly by controlling the number of cylinders, to which compression braking is applied.

This is an alternative way of controlling the compression braking, so that the desired braking torque is achieved, and naturally may be used separately or in combination with also controlling the duration of the compression braking.

According to one embodiment of the invention, the detection of said movements is carried out separately for the respective cylinders in the combustion engine. By detecting movements separately for each cylinder, the signal treatment, which is required to obtain interpretable data from the detected movements, is facilitated. This is especially applicable in multi- cylinder combustion engines, where each cylinder has a separate cylinder head. For multi-cylinder combustion engines, where several cylinders share one common cylinder head, the detection may occur either separately or jointly, but with a joint detection, information about compression braking in individual cylinders is lost. According to a second aspect of the invention, the above mentioned objectives are achieved through a device, adapted for diagnosis and control of compression braking in a vehicle comprising a combustion engine with at least one cylinder, which device comprises at least one sensor element, adapted to be arranged separately from the cylinder's combustion chamber on a part of a cylinder head belonging to the cylinder or on adjacent parts of the engine, and adapted to detect movements of said cylinder head or said adjacent parts in the engine, which movements were generated by compression braking, and through it also comprising a device adapted, based on the detected movements, to calculate or estimate a braking torque caused by the compression braking in the cylinder. The function of such a device and embodiments thereof are defined in non-independent claims, and the possibilities which they offer, are explained in the discussion above of the innovative method.

The invention also relates to a computer program, a computer program product, an electronic control device, and a motor vehicle, which function as set out above

The invention is not limited to any specific type of combustion engine, but encompasses otto engines as well as compression ignited engines, nor to any specific fuel, non-exhaustive examples of which may comprise fuel in the form of petrol, ethanol, diesel and gas.

Likewise, the invention comprises combustion engines intended for all types of motor vehicles, wheeled motor vehicles as well as trucks, buses, passenger cars and motorcycles, boats and crawlers or similar vehicles.

BRIEF DESCRIPTION OF THE DRAWINGS

Below are descriptions of example embodiments of the invention, with reference to the enclosed drawings, in which:

Fig. 1 a is a schematic view illustrating a part of a combustion engine, in which a device according to one embodiment of the invention is arranged, shows a possible location of a sensor element,

Fig. 2 is a diagram, which schematically illustrates the gas pressure in a cylinder in a combustion engine as a function of time, during a part of a working cycle of the cylinder with and without compression braking, according to one first version of compression braking, Fig. 3 is a diagram, which schematically shows the gas pressure in a cylinder in a combustion engine as a function of time, during a part of a working cycle of the cylinder with and without compression braking, according to a second version of compression braking,

Fig. 4 is a flow chart showing a method according to an embodiment of the invention,

Fig. 5 is a flow chart showing a method according to another embodiment of the invention, and Fig. 6 is a diagram of an electronic control device for the implementation of a method according to the invention.

DETAILED DESCRIPTION OF EMBODIMENTS ACCORDING TO THE INVENTION

Fig. 1 a illustrates very schematically a combustion engine 1 , in which a device adapted for diagnosis and control of compression braking according to one embodiment of the invention is arranged. The combustion engine is arranged in an implied motor vehicle 2, for example a truck. The engine 1 is equipped with a device 3, indicated with a dashed line, adapted to detect operating conditions in the engine, and such device has a schematically drawn device 4, which is adapted to detect among others the pressure in the combustion chambers 5 of the combustion engine's cylinders 6, of which there are six in this case, but of which there may be any number. Each cylinder 6 comprises a piston 14, arranged to operate a crank shaft 12, an inlet valve 10, controlling the gas in-flow from an inlet channel 15 to the cylinder's combustion chamber 5, and an exhaust valve 1 1 , controlling the outflow of exhausts via an exhaust channel 16. In the inlet channel 15, a pressure sensor 17 is arranged. A pressure sensor (not displayed) may also be arranged inside the exhaust channel 16.

The device 4 has, in order to be able to detect said pressure in the combustion chambers 5, one sensor element 7 per cylinder 6, and this is arranged separately from the associated combustion chamber 5 on the respective cylinders' cylinder heads 8. The sensor elements 7 in this case are piezo resistive sensors, adapted to detect, in the form of vibrations, movements propagated in the cylinder head 8, generated by pressure changes in the relevant combustion chambers 5. The sensor element 7 is also adapted to detect movements generated by opening and closing of the inlet valve 10 and the exhaust valve 1 1 , which movements propagate in the cylinder head 8 and in parts adjacent thereto in the engine. The device 3 also comprises a unit 9, which may consist of the vehicle's electronic control device, adapted to receive information about the detected movements from the sensor elements 7, and to compare such information, or information calculated based on such sensor information, with values stored in relation to the desired operating conditions in the engine.

Fig. 1 b shows another placement of the sensor element 7. The sensor element is here placed on a section adjacent to the cylinder head. In this example, the sensor element is placed on the engine, specifically on the engine block. The sensor elements/sensors 7 may be of a suitable type, e.g. piezo resistive or piezo electrical elements or optical sensors. The sensor element may here be placed on the engine, in an area adjacent to the outlet of the exhaust channel from a cylinder. For example on a surface on the engine block next to the outlet, on the engine, of the exhaust channel from a cylinder on the engine. The surface where the sensor 7 is placed may be substantially vertical. The sensor may be arranged to detect movements, which are perpendicular to the movements of the piston. The sensor may also be arranged to detect movements, which are perpendicular both in relation to the piston's direction of movement and in relation to the engine's longitudinal direction. In one embodiment, the sensor is located on the engine's long side. The sensor may be arranged to detect movements in a direction, which is perpendicular in relation to the surface on which it is placed.

In another embodiment (not displayed) the sensor element 7 may be placed in a corresponding manner as when placed on the engine at the outlet of the exhaust channel from a cylinder, but instead placed in a corresponding location on the engine, at the suction channel's inlet to a cylinder.

The signal detected by the sensor element 7 may be treated in various ways. For example, the following signal treatment steps may be carried out. First the sensor's electrical signal is entered into a control device/signal treatment device. The signal is filtered with a bandpass filter in order to remove superfluous information, which does not belong to the frequency range around which information is required. The signal is evened out by way of filtering, averaging or by being replaced with one or several continuous function(s) with good likeness. Subsequently, the signal is scaled, e.g. with the help of the correlation between pressure and volume at compression. Subsequently, (a) suitable part(s) of the signal is/are transformed to the pressure domain. Supplemental modelling closes gaps in the signal's reliability, in order to form a pressure curve. The thus formed pressure curve is used to calculate different values at engine control. In some embodiments one or several of the steps above may be omitted. A first version of compression braking in a four stroke engine functions in such a manner that the exhaust valve 1 1 of the cylinder 6 opens at the end of the cylinder's 6 compression stroke, when the piston 14 moves from its bottom dead centre (BDC) to its top dead centre (TDC), or just at the beginning of its expansion stroke, when the piston 14 has turned around and is returning toward its bottom dead centre. This leads to a rapid pressure drop in the cylinder 6. The gas pressure in the cylinder 6 during such a compression braking is schematically illustrated with the diagram in Fig. 2, which shows a compression stroke and an expansion stroke in the cylinder 6.

A second version of the compression braking, schematically illustrated with the diagram in Fig. 3, entails that the inlet valve 10 of cylinder 6 opens during the initial stage of the compression stroke, when the piston 14 moves from its bottom dead centre (BDC) towards its top dead centre (TDC). Air then flows through the inlet valve 10, and the pressure building up in the cylinder becomes considerably smaller than in the case where the valve is kept closed. By closing the inlet valve 10 at the top dead centre, the piston creates a negative pressure in the cylinder 6 during the expansion stroke, which leads to a mildly braking effect. In both Fig. 2 and Fig. 3, the solid line A shows the gas pressure in the cylinder 6 at a working stroke with compression braking, and the dashed line B shows the gas pressure in the cylinder 6 during a corresponding working stroke without any compression braking. In none of these cases does any combustion take place in the cylinder 6 during the expansion stroke. The curves showing the gas pressure during compression braking also show a signal with a higher frequency, which is attributable to vibrations caused by opening and closing of the exhaust valve 1 1 and the inlet valve 10, respectively.

A method according to a first embodiment of the invention is schematically illustrated in Fig. 4. In step S1 , which is carried out continuously during the operation of the combustion engine, movements are detected which are generated partly by pressure changes in the combustion chamber 5, and partly by positional changes in the form of opening and closing of the exhaust valve 1 1 , which in this embodiment is used to control the compression braking. The movements are detected in the cylinder head 8 with the help of the sensor element 7. In step S2 the gas pressure in the combustion chamber 5 is calculated, based on the signal from the sensor element 7 in the unit 9, which calculation is carried out continuously during operation. In step S3 it is determined whether or not the compression braking is activated, based on the signal from the sensor element 7. In this embodiment, this is determined by detecting the signal, which is of a relatively high frequency compared to the signal generated by pressure changes in the cylinder, which is attributable to a positional change in the exhaust valve 1 1 . If the vehicle's driver has requested a braking torque and the compression braking has therefore been activated, then in step S4 a comparison is carried out between the gas pressure in the cylinder 6 during the current working cycle and data stored in the unit 9, relating to the gas pressure in the cylinder 6 during a working cycle without compression braking, but with otherwise similar operating conditions. Such stored data may, for example, be measured at a previous working cycle or obtained theoretically. Based on the comparison, in step S5, the braking torque to which the compression braking gives rise is calculated, specifically by way of integrating the pressure difference, to which the compression braking gives rise. In Figs. 2 and 3 the braking torque is represented by the area C between the curves A and B.

In order to determine the braking effect in addition to the braking torque, the calculation of the braking torque may be completed in step S6, by measuring the engine's engine speed at the activation and/or deactivation of the compression brake with the help of a speed sensor (not displayed). Based on the determined braking torque and the difference in engine speed, either between activation and deactivation in one and the same working cycle, or between activation alternatively deactivation in two consecutive working cycles, the braking effect may be determined in step S7.

In a later working cycle, following said working cycle, during which a braking torque is requested by the vehicle's driver, the determined braking torque or the determined braking effect may be used to control the compression brake in step S9, so that this contributes, in a desirable manner, to the total braking of the vehicle. The control may be carried out by controlling the activation or deactivation of compression braking, for example by controlling the duration, during which the exhaust valve 1 1 is kept open, or by controlling the area of the opening to the exhaust channel 16, which is formed when the exhaust valve 1 1 opens completely or only partly. Another way of controlling the compression braking in a multi-cylinder engine is to activate the compression braking for one or several cylinders, depending on the braking effect requested and depending on the braking effect compression braking of the respective cylinder may be expected to contribute, based on the previously determined braking effect.

Steps S1 -S8 are repeated as long as the vehicle is in operation, in such a manner that as long as a braking torque is requested by the vehicle's driver, the braking torque and/or braking effect caused by compression braking is calculated for each working cycle, and used to control the compression braking during the subsequent working cycle. When a braking torque is no longer requested, the method may be interrupted and subsequently, the next time a braking torque is requested, be started again. A method according to a second embodiment of the invention is schematically illustrated in Fig. 5. In this embodiment, no curve for cylinder pressure over time is calculated, instead the braking torque caused by compression braking is estimated. In this embodiment, compression braking takes place by way of opening the inlet valve 10 during the compression stroke. In a first step S1', activation and deactivation of the compression brake is detected by detecting movements in the cylinder head 8, caused by the opening of the inlet valve 10 controlling the compression braking, in a similar manner as in the earlier embodiment described above. In step S2\ the gas pressure during the compression braking is measured in the inlet channel 15 with the help of the pressure sensor 17. When closing of the inlet valve 10, that is to say deactivation of the compression braking, is detected, the duration of the compression braking is calculated in step S3'. Thus, it may be determined how far up the piston 14 has moved in the cylinder's combustion chamber 5 during the compression braking. Through the assumption that the gas pressure in the inlet channel 15 during the compression braking is the same as in the cylinder's combustion chamber 5, and based on knowledge of the cylinder's geometry, the expected compression pressure may, during a working cycle with compression braking in the cylinder 6, thus be estimated. In a step S4' this expected compression pressure is compared with stored reference data, relating to the expected compression pressure during a working cycle in the absence of compression braking, and in the absence of combustion in the cylinder. In this manner, the braking torque is estimated in a step S5'. As in the above described embodiment, the engine's engine speed may be measured in a step S6' and a braking effect may be estimated in step S7', following which the compression braking may be controlling a subsequent working cycle in step S8'.

A computer program code for the implementation of a method according to the invention is suitably included in a computer program, loadable into the internal memory of a computer, such as the internal memory of an electronic control device of a combustion engine. Such a computer program is suitably provided via a computer program product, comprising a data storage medium readable by an electronic control device, which data storage medium has the computer program stored thereon. Said data storage medium is e.g. an optical data storage medium in the form of a CD-ROM, a DVD, etc., a magnetic data storage medium in the form of a hard disk drive, a diskette, a cassette, etc., or a Flash memory or a ROM, PROM, EPROM or EEPROM type memory. Fig. 6 very schematically illustrates an electronic control device 9 comprising execution means 20, such as a central processor unit (CPU), for the execution of computer software. The execution means 20 communicates with a memory 21 , e.g. a RAM memory, via a data bus 22. The control device 9 also comprises a data storage medium 23, e.g. in the form of a Flash memory or a ROM, PROM, EPROM or EEPROM type memory. The execution means 20 communicates with the data storage means 23 via the data bus 22. A computer program comprising computer program code for the implementation of a method according to the invention is stored on the data storage medium 23.

The invention is obviously not limited in any way to the embodiments described above, but numerous possible modifications thereof should be obvious to a person skilled in the area, without such person departing from the spirit of the invention as defined by the appended claims. For example, the method may be carried out for a two stroke engine as well as for a four stroke engine, as described above. It is of course also possible to apply the innovative method for any other type of compression braking than the versions described above, where either the inlet valve, the exhaust valve or both these valves are used to control the gas pressure in the cylinder during at least some part of the latter's compression stroke or expansion stroke.