Method for avoiding a runaway condition of an internal combustion engine

Abstract

In a method for avoiding a runaway condition of an internal combustion engine that includes a cylinder, an operational characteristic of the engine, presumed to be caused by an unrequested introduction of hydrocarbon into the cylinder, is detected and the engine is derated in dependence of the detection, and, while the engine is derated, a test procedure is performed to detect an unrequested introduction of hydrocarbon into the cylinder.

Claims

1. A method for avoiding a runaway condition of an internal combustion engine comprising a cylinder, comprising detecting an operational characteristic of the engine, presumed to be caused by an unrequested introduction of hydrocarbon into the cylinder, derating the engine in dependence of the detection, performing while the engine is derated a test procedure to detect an unrequested introduction of hydrocarbon into the cylinder, the engine comprising an inlet guide for guiding air to the cylinder, and the cylinder comprising a piston connected to a crankshaft, the engine further comprising a crankcase for housing the crankshaft, wherein the engine comprises a crankcase ventilation system which is arranged to assume an open condition in which a fluid in the crankcase is guided to the atmosphere, and a closed condition in which a fluid in the crankcase is guided to the inlet guide, determining a first value of an operating parameter while the engine is operated in a first predetermined operating condition with the crankcase ventilation system in the closed condition, determining a second value (n2) of the operating parameter while the engine is operated in the first predetermined operating condition with the crankcase ventilation system in the open condition, and determining, based at least partly on the first and second operating parameter values, whether or not there is an unrequested introduction of hydrocarbon into the cylinder.

2. A method according to claim 1, wherein the test procedure is initiated in dependence on the detection and/or the derating.

3. A method according to claim 1, wherein derating the engine comprises reducing a maximum torque of the engine.

4. A method according to claim 1, wherein detecting an operational characteristic of the engine comprises determining during operation of the engine a first value of an engine system parameter, and comparing the first value to a first predetermined threshold value.

5. A method according to claim 4, wherein the engine system parameter is a difference between the temperature of exhaust gases produced by the engine and an expected temperature of exhaust gases produced by the engine.

6. A method according to claim 4, wherein derating the engine in dependence of the detection comprises derating the engine in dependence of the comparison of the first engine system parameter value to the first predetermined threshold value.

7. A method according to claim 4, wherein derating the engine in dependence of the detection comprises derating the engine if the first engine system parameter value exceeds the first predetermined threshold value.

8. A method according to claim 1, where the engine is provided in a vehicle, comprising issuing in dependence on the detection of the operational characteristic of the engine an instruction to a driver of the vehicle to allow the engine to idle.

9. A method according to claim 1, comprising determining, if the difference between the first and second operating parameter values is larger than a predetermined value difference, that there is an unrequested introduction of hydrocarbon into the cylinder.

10. A method according to claim 1, wherein the first predetermined operating condition is engine idling.

11. A method according to claim 1, wherein the operating parameter is the engine rotational speed.

12. A method according to claim 1, comprising, if the difference between the first and second operating parameter values is larger than a predetermined value difference, controlling the crankcase ventilation system so as to assume the open condition.

13. A method according to claim 1, comprising, if the difference between the first and second operating parameter values is larger than a predetermined value difference, stopping the engine.

14. A method according to claim 4, comprising determining while the engine is derated a second value of the engine system parameter, and comparing the second value to a second predetermined threshold value.

15. A method according to claim 14, wherein the initiation of the test procedure is dependent on the comparison of the second engine system parameter value to the second predetermined threshold value.

16. A method according to claim 14, comprising determining to initiate the test procedure if the second engine system parameter value is lower than the second predetermined threshold value.

17. A method according to claim 14, comprising, if the second engine system parameter value exceeds the second predetermined threshold value, derating the engine further.

18. A method according to claim 17, wherein derating the engine further comprises operating the engine in a limp-home mode.

19. A method for avoiding a runaway condition of an internal combustion engine comprising a cylinder, where the engine comprises an inlet guide for guiding air to the cylinder, and the cylinder comprises a piston connected to a crankshaft, the engine further comprising a crankcase for housing the crankshaft and a crankcase ventilation system which is arranged to assume an open condition in which a fluid in the crankcase is guided to the atmosphere, and a closed condition in which a fluid in the crankcase is guided to the inlet guide, the method comprising detecting an operational characteristic of the engine, presumed to be caused by an unrequested introduction of hydrocarbon into the cylinder, wherein detecting an operational characteristic of the engine comprises determining during operation of the engine a first value of an engine system parameter, and comparing the first value to a first predetermined threshold value, derating the engine in dependence of the detection, performing while the engine is derated a test procedure to detect an unrequested introduction of hydrocarbon into the cylinder, determining while the engine is derated a second value of the engine system parameter, comparing the second value to a second predetermined threshold value, and, upon detecting that the second engine system parameter value exceeds the second predetermined threshold value, controlling the crankcase ventilation system so as to assume the open condition.

20. A method according to claim 14, comprising, if the second engine system parameter value exceeds the second predetermined threshold value, stopping the engine.

21. A method for avoiding a runaway condition of an internal combustion engine comprising a cylinder, comprising detecting an operational characteristic of the engine, presumed to be caused by an unrequested introduction of hydrocarbon into the cylinder, derating the engine in dependence of the detection, and performing while the engine is derated a test procedure to detect an unrequested introduction of hydrocarbon into the cylinder, wherein the engine comprises a fuel system for injecting fuel into the cylinder, determining a value of an engine operation parameter, and comparing the determined engine operation parameter value to a stored value of the engine operation parameter, wherein the determination of the engine operation parameter value is done while the engine is operated in a predetermined operating condition, and the stored value of the engine operation parameter is associated with the predetermined engine condition, determining based at least partly on the comparison whether or not there is an indication of an unrequested introduction of hydrocarbon into the cylinder.

22. A method according to claim 21, wherein the engine operation parameter value is a demanded fuel amount to be injected.

23. A method according to claim 21, wherein the engine operation parameter value is a rotational speed of the engine.

24. A method according to claim 21, wherein the predetermined operating condition is engine idling.

25. A method according to claim 21, wherein a determination is made that there is an indication of an unrequested introduction of hydrocarbon into the cylinder if the difference between the determined engine operation parameter value and the stored engine operation parameter value is larger than a predetermined threshold value.

26. A computer comprising a computer program for performing the steps of claim 1 when the program is run on the computer.

27. A non-transitory computer readable medium carrying a computer program for performing the steps of claim 1 when the program product is run on a computer.

28. A control unit configured to perform the steps of the method according to claim 1.

29. An engine system comprising a control unit according to claim 28.

30. A vehicle comprising an engine system according to claim 29.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) With reference to the appended drawings, below follows a more detailed description of embodiments of the invention cited as examples.

(2) In the drawings:

(3) FIG. 1 is a side view of a vehicle in the form of a truck.

(4) FIG. 2 is a schematic view of an engine system in the vehicle in FIG. 1.

(5) FIG. 3 is a block diagram depicting steps in a method according to an embodiment of the invention.

(6) FIG. 4 is a block diagram depicting steps in a method according to a further embodiment of the invention.

(7) FIG. 5 is a diagram illustrating a step in the method depicted in FIG. 4.

(8) FIG. 6 is a block diagram depicting further steps in the method depicted in FIG. 4.

DETAILED DESCRIPTION

(9) FIG. 1 shows a vehicle in the form of a truck, or a tractor for a semitrailer. It should be noted that the vehicle can be of a variety of alternative types, e.g. it may be a car, a bus, or a working machine such as a wheel loader. The vehicle comprises an internal combustion engine system with an internal combustion engine 1 with a plurality of cylinders. It should be noted that the invention is applicable to engines with any number of cylinders, even with a single cylinder. Also, the invention is applicable to engines with any cylinder configuration, e.g. an in-line configuration or a V-configuration.

(10) Reference is made to FIG. 2, which illustrates an engine system according to an example embodiment of the present invention. The engine system comprises the internal combustion engine 1 which has a plurality of cylinders, in this example four cylinders 220 indicated with broken lines in FIG. 2, and a crankcase 217 housing a crankshaft (not shown) connected to pistons (not shown) in the cylinders 220 via respective connecting rods. The crankcase 217 is arranged to hold a hydrocarbon lubricant of a lubrication system of the engine 1 as is known per se. In this embodiment, the engine is a diesel engine, i.e. an engine adapted for a diesel cycle.

(11) The engine system comprises a fuel container 201 for hydrocarbon fuel. In this embodiment the fuel container 201 is arranged to hold dimethyl ether (DME). However, in alternative embodiments the fuel container 201 may be arranged to contain any fuel that is suitable for the specific engine type. Hence, the fuel container 201 may be arranged to hold diesel fuel, liquefied natural gas (LNG), etc. It should be noted that the invention is equally applicable to engines adapted for an Otto cycle. Thereby, the fuel container may be arranged to hold fuel suitable for Otto engines, such as petrol or again LNG. The engine system further comprises an injector 231 at each cylinder. The engine system further comprises, between the fuel container 201 and the injectors 231, a pump 232. The pump 232 is arranged to deliver fuel from the fuel container 201 to injectors 231, via a fuel conduit 234. The injectors 231 are arranged to be controlled by a control unit 211.

(12) The engine system comprises a crankcase ventilation system 206, which will be described in detail below, and a turbo unit comprising a turbine 221 and a compressor 222. More specifically, a conduit 209 connects the crankcase ventilation system 206 to an air intake 203 of the engine 1, upstream of the compressor 222. An intake manifold 212 is arranged to guide charge air from the compressor 222 to the cylinders of the engine 1. The air intake 203 and the intake manifold 212 are herein collectively referred to as an inlet guide.

(13) The control unit 211 is arranged to control the engine 1 so as to operate with a normal rating, in which the engine may produce a first maximum torque. As described below, the control unit 211 is also arranged to derate the engine 1 under certain conditions, whereby the engine may produce a second maximum torque which is lower than the first maximum torque. The control unit 211 is also arranged to derate the engine further under further conditions described below, whereby the engine may produce a third maximum torque which is lower than the second maximum torque. The normal rating and the derated modes are obtained by suitable control of the injectors 231.

(14) The crankcase ventilation system 206 in the non-limiting example depicted in FIG. 2 is similar to a system described in WO2015124160A1, incorporated herein by reference. The crankcase ventilation system 206 comprises an oil mist separator 204, a relief valve 208, and a control valve 210 electrically connected to the control unit 211. The oil mist separator 204 is connected to an oil trap 214 via a blow-by path 205. The oil trap 214 is connected to the crankcase 217. Thus, the oil mist separator 204 is arranged downstream of the crankcase 217 and is arranged to receive a fluid from the crankcase. The oil mist separator 210 is adapted to separate oil from the fluid received from the crankcase 217, and provides a return path (not shown) to the crankcase 217 for the separated oil.

(15) The relief valve 208 is arranged downstream the oil mist separator 204 and is arranged to be in fluid communication with the oil mist separator 204. The relief valve 208 is arranged to enter into a state in which a communication is provided between the oil mist separator 204 and an ambient environment of the engine 1, i.e. the atmosphere, when relief valve 208 is exposed to a pressure exceeding a predefined pressure limit.

(16) The control valve 210 is arranged downstream the oil mist separator 204 and the relief valve 208. The control valve 210 is arranged to selectively, by control of the control unit 211, provide a fluid communication between the oil mist separator 204 and the intake 203 of the engine 1. The control valve 210 may, for example, be a two-way valve.

(17) When there is fluid leakage formed in the crankcase 217 from e.g. the combustion process of the internal combustion engine, this crankcase fluid leakage is directed out from the crankcase through the blow-by path 205 and directed into the oil mist separator 204. In the oil mist separator 204 the leaked crankcase fluid is subjected to a separation process such that the fluid leaving the oil mist separator 204 is free, or relatively free, from particles that may negatively affect the environment.

(18) When the control valve 210 is open, the fluid may be transported from the crankcase 217 via the oil mist separator 204 to the air intake 203. Thereby the crankcase ventilation system 206 is in what is herein referred to as a closed condition. By closing the control valve 210, such a transportation is prevented. Thereby the crankcase ventilation system 206 is in what is herein referred to as an open condition. In the open condition, a pressure might build up upstream of the relief valve 208. When such a pressure builds up and exceeds the predefined pressure limit, the relief valve 208 opens so as to allow the fluid from the oil mist separator 204 to be released to the atmosphere.

(19) Other valve arrangements are possible for the crankcase ventilation system 206. For example, the relief valve 208 and the control valve 210 may be replaced by a single valve controllable by the control unit 211 so as to selectively provide a communication between the oil mist separator 204 and the air intake 203 and a communication between the oil mist separator 204 and the atmosphere.

(20) The control unit 211 is also arranged to receive signals from a temperature sensor 215 arranged to detect the temperature of exhaust gases produced by the engine. The temperature sensor is located in an exhaust guide downstream of the turbine 221. The control unit 211 is also arranged to receive signals from a rotational speed sensor 216 arranged to detect the rotational speed of the engine 1. The control unit 211 is further arranged to receive signals from an air flow sensor 218 arranged to detect the air flow in the air intake 203 as is known per se.

(21) FIG. 3 is a block diagram depicting steps in a method for avoiding a runaway condition of the engine 1 according to an embodiment of the invention. The method comprises detecting S1, S2 an operational characteristic of the engine 1, presumed to be caused by an unrequested introduction of hydrocarbon into the cylinders 220. An unrequested introduction of hydrocarbon into the cylinders may have any of a number of causes, e.g. a mixture of excess fuel and oil may be vented from the crankcase 217 into the air intake 203 via the crankcase ventilation system 206. The excess fuel may enter the crankcase 217 e.g. due to leakage from the fuel conduit 234, or from the cylinders 220.

(22) The method further comprises derating S3 the engine 1 in dependence of the detection. The derating provides a quick response to reduce a risk of the engine entering a runaway condition or suffering damage due to overload etc. in case the detected operational characteristic of the engine is caused by unrequested introduction of hydrocarbon into the cylinders 220. However, the detected operational characteristic may have causes other than such unrequested hydrocarbon cylinder introduction. Since the cause of the detection cannot be established with a high degree of certainty, the derating is executed instead of an engine shutdown which may in itself cause a safety risk, e.g. where the vehicle is moving on a busy road.

(23) The method also comprises performing while the engine is derated a test procedure S6 to detect an unrequested introduction of hydrocarbon into the cylinders 4. By such a test procedure, it may be established with a relatively high degree of certainty, after the detection of the operational characteristic of the engine, whether or not there is an unrequested introduction of hydrocarbon into the cylinders 220.

(24) FIG. 4 is a block diagram depicting steps in a method for avoiding a runaway condition of the engine 1 according to a further embodiment of the invention. The method comprises detecting S1, S2 an operational characteristic of the engine 1, presumed to be caused by an unrequested introduction of hydrocarbon into the cylinder. The detection comprises determining S1 during operation of the engine 1 a first value DT1 of an engine system parameter, and comparing S2 the first value to a first predetermined threshold value DTlim1. This detection is done under normal operation of the engine system, with the crankcase ventilation system 206 in the closed condition.

(25) An example of the detection S1, S2 of the operational characteristic of the engine 1 is illustrated in FIG. 5 showing a graph of the exhaust temperature T as a function of time t. It should be noted that the depicted graph in FIG. 5 showing the exhaust temperature variation over time when the vehicle is running only serves as an example.

(26) The control unit 211 determines repetitively at a series of points in time the expected exhaust temperature, preferably the expected maximum temperature. A series of expected exhaust temperatures is illustrated in FIG. 5 with the line 306. More specifically the control unit 211 has access to a model which calculates the expected exhaust temperature based on current values of operational parameters including the amount of fuel injected by the injectors 231, the rotational speed of the engine 1 as obtained from the rotational speed sensor 216, and the air flow as detected by the air flow sensor 218. As the operational conditions change, the expected exhaust temperature changes as can be seen by the line 306.

(27) The dotted line 308 in FIG. 5 illustrates a series of exhaust temperatures as determined by means of the temperature sensor 215. Repetitively the difference between the respective exhaust temperature 308 as determined by means of the temperature sensor 215 and the expected temperature 306 is determined, this difference forming in this example the first value DT1 of the engine system parameter. In the example in FIG. 5, after following the expected exhaust temperature, the exhaust temperatures 308 as determined by means of the temperature sensor 215 become larger than the corresponding expected temperature. The first predetermined threshold value DTlim1 is in this example formed by a maximum allowable difference between on one hand the respective exhaust temperature 308 as determined by means of the temperature sensor 215 and on the other hand the temperature 306 expected, as mentioned above, at the operational conditions in which the exhaust temperature 308 is determined.

(28) Reference is made again to FIG. 4. If the first value DT1 of the engine system parameter exceeds the first predetermined threshold value DTlim1, the engine is derated S3 and thereby limited to producing the second maximum torque which as mentioned is lower than the first maximum torque providing a limitation during normal operation. The second maximum torque may be e.g. 85% of the first maximum torque.

(29) In addition, if the first value DT1 of the engine system parameter exceeds the first predetermined threshold value DTlim1, an instruction is issued S4 to a driver of the vehicle to allow the engine to idle. This instruction may be provided by visual means, e.g. by a message on a dashboard of the vehicle, and/or by audible means.

(30) In this embodiment, the method comprises determining by means of the temperature sensor 215, while the engine is derated, a second value of the engine system parameter, and comparing S5 the second value DT2 to a second predetermined threshold value DTlim2. Similarly to the first value DT1 of the engine system parameter, the second value DT2 is formed by the difference between the exhaust temperature as determined by means of the temperature sensor 215 and the expected temperature 306.

(31) If the second engine system parameter value DT2 exceeds S5 the second predetermined threshold value DTlim2, the engine is derated further S10, and thereby limited to producing the third maximum torque which as mentioned is lower than the second maximum torque. Such a further derating of the engine may comprise operating the engine in a limp-home mode, which may involve limitations on one or more additional engine and/or vehicle control parameters. If the second engine system parameter value DT2 exceeds S5 the second predetermined threshold value DTlim2 while the engine is derated, the further derating provides a quick response to reduce a risk of the engine entering a runaway condition and/or suffering serious damage.

(32) Further, if the second engine system parameter value DT2 exceeds S5 the second predetermined threshold value DTlim2, the control valve 210 is controlled S7 so as for the crankcase ventilation system 206 to assume the open condition. This will reduce the risk of any further unrequested hydrocarbon entering the cylinders 220 via the air intake 203. In addition, the method may comprise instructing S9 the driver of the vehicle to stop the engine if the second engine system parameter value DT2 exceeds S5 the second predetermined threshold value DTlim2.

(33) In this embodiment, if on the other hand the second engine system parameter value DT is lower S5 than the second predetermined threshold value DTlim, it is determined to initiate a test procedure S6 while the engine is derated. By such a test procedure, it may be established with a relatively high degree of certainty, after the detection of the operational characteristic of the engine, whether or not there is an unrequested introduction of hydrocarbon into the cylinders 220 that originates from the crankcase.

(34) Reference is made to FIG. 6. The test procedure comprises, following said instruction S4 to the driver, determining S601 whether the engine is operated in a first predetermined operating condition, in this example whether the engine is idling. If it is determined that the engine is idling, a first value n1 of an operating parameter in the form of the engine rotational speed is determined S602 by means of the rotational speed sensor 216. The rotational speed determination S602 is performed with the crankcase ventilation system 206 in the closed condition, i.e. with the control valve 210 (FIG. 2) in the open state allowing a communication between the oil mist separator 204 and the air intake 203.

(35) Subsequently, the status of the crankcase ventilation system 206 is changed S603 to the open condition, i.e. with the control valve 210 (FIG. 2) in the closed state allowing a communication between the oil mist separator 204 and the atmosphere via the relief valve 208. With the crankcase ventilation system 206 in the open condition a second value n2 of the engine rotational speed is determined S604 while the engine is idling.

(36) Subsequently it is determined S605, based on the first and second operating engine rotational speed values n1, n2, whether or not there is an unrequested introduction of hydrocarbon into the cylinders 220. If the difference between the first and second engine rotational speed values n1, n2 is larger than a predetermined value difference, it is determined that there is an unrequested introduction of hydrocarbon into the cylinders 220, and the control valve 210 is controlled S7 so as for the crankcase ventilation system 206 to assume the open condition, (FIG. 4). This will reduce the risk of any further unrequested hydrocarbon entering the cylinders 220 via the air intake 203.

(37) As can be seen in FIG. 4, the method may comprise instructing S9 the driver of the vehicle to stop the engine if the test procedure S6 indicates that there is an unrequested introduction of hydrocarbon into the cylinders 220.

(38) If on the other hand the test procedure S6 indicates that there is no unrequested introduction of hydrocarbon into the cylinders 220, i.e. if the difference between the first and second engine rotational speed values n1, n2 is smaller than the predetermined value difference (FIG. 5), a stored fuel amount value FAexp will be adjusted S20 as explained further below. In addition, the idling instruction dashboard message will be removed S8 and the engine will be controlled so as to exit S8 the derated condition.

(39) As can be seen in FIG. 4, if the first value DT1 of the engine system parameter does not exceed S2 the first predetermined threshold value DTlim1 it is determined S12 whether or not the engine is idling. If it is found that the engine is not idling, the determination whether or not the engine is idling is simply repeated, preferably after the lapse of a predetermined time interval. If it is determined that the engine is idling, an additional process S13-S15, described below, to establish whether there is an indication of an unrequested introduction of hydrocarbon into the cylinders 220, is executed. Thus, this process is carried out repeatedly during normal engine operation whenever a chance of it is given, i.e. whenever the engine is found to be idling. Once it has been determined S12 that the engine is idling, an engine operation parameter in the form of the engine rotational speed n is determined S13 by means of the rotational speed sensor 216. Further, the control unit 211 determines S14 a further engine operation parameter in the form of a demanded fuel amount FA to be injected by the injectors 231.

(40) Subsequently, the demanded fuel amount FA is compared S15 to a stored fuel amount value FAexp associated with a particular engine idling condition. Based on this comparison it is determined S15 whether or not there is an unrequested introduction of hydrocarbon into the cylinders 220. If the difference between the determined demanded fuel amount FA and the stored fuel amount value FAexp is larger than a predetermined threshold value, in this example 20% of the stored fuel amount value FAexp, it is determined that there is an unrequested introduction of hydrocarbon into the cylinders 220. More specifically, if the determined demanded fuel amount FA is smaller than 80% of the stored fuel amount value FAexp, it is determined that there is an unrequested introduction of hydrocarbon into the cylinders 220. Thereupon, similarly to step S4 described above, an instruction is issued S16 to a driver of the vehicle to allow the engine to idle, and the test procedure S6 described above is executed.

(41) The method also comprises comparing S15 the determined engine rotational speed n to a stored engine rotational speed value nexp associated with the engine idling condition. Based on this comparison it is determined S15 whether or not there is an unrequested introduction of hydrocarbon into the cylinders 220. If the difference between the determined engine rotational speed n and the stored engine rotational speed value nexp is larger than a predetermined threshold value, in this example 20% of the stored engine rotational speed value nexp, it is determined that there is an unrequested introduction of hydrocarbon into the cylinders 220. More specifically, if the determined engine rotational speed n is larger than 120% of the stored engine rotational speed value nexp, it is determined that there is an unrequested introduction of hydrocarbon into the cylinders 220. Again, thereupon the engine is derated S16 so as to allow a maximum torque of 80% of its normal maximum torque, and the test procedure S6 described above is executed.

(42) If the test procedure S6 indicates in contradiction to the indication provided by the determination in step S15 that there is no unrequested introduction of hydrocarbon into the cylinders 220, it is assumed that the stored fuel amount value FAexp, used in the determination in step S15, is incorrect, and this value if therefore adjusted S20.

(43) If on the other hand the determined demanded fuel amount FA is larger than 80% of the stored fuel amount value FAexp, and the determined engine rotational speed n is smaller than 120% of the stored engine rotational speed value nexp, it is determined that there is no unrequested introduction of hydrocarbon into the cylinders 220. Thereby, the idling instruction dashboard message will be removed S8 and the engine will be controlled so as to exit S8 the derated condition.

(44) It is to be understood that the present invention is not limited to the embodiments described above and illustrated in the drawings; rather, the skilled person will recognize that many changes and modifications may be made within the scope of the appended claims.