SE526638C2 - Monitoring of coolant temperature sensors - Google Patents

Abstract

The method for the monitoring of coolant temperature in an engine of a vehicle entails verifying that the outside air temperature is sufficiently high, ensuring that the engine is supplied with a sufficient amount of power during a predetermined time interval, and measuring the coolant temperature if the conditions according to the aforesaid stages during the predetermined time interval are met. The measured temperature is then compared with a predetermined lower threshold value and an alarm is triggered if the measured coolant temperature is lower than the threshold value. - Independent claims are also included for the following: - (A) a computer programme for the monitoring of a coolant temperature transmitter in a motor vehicle in which a coding component which is effective during the operating procedure of a control unit; - (B) a control unit comprising at least one memory unit which includes a computer programme; and - (C) a motor vehicle equipped with the aforesaid control unit for coolant temperature monitoring.

Description

, 20 not to meet the new legal requirements, where it is also specified that the test conditions must be selected in such a way that the monitoring takes place under operating conditions, ie usually while driving.

OBJECTS AND MOST IMPORTANT FEATURES OF THE INVENTION It is an object of the present invention to provide a method for testing and monitoring the coolant temperature sensor under operating conditions. More specifically, it is an object of the present invention to provide a method for checking that the coolant temperature sensor in a motor vehicle does not show too little or is stuck at too low a value.

These and other objects are achieved in accordance with the present invention by a method defined in claim 1.

According to the present invention, the above-mentioned objects are achieved by ensuring that certain conditions, such as sufficiently high external temperature and sufficient energy supplied to the engine, are fulfilled for a limited period of time. These conditions mean that the engine water temperature has risen to a sufficiently high level to be able to measure the coolant temperature using the coolant temperature sensor and compare the result with the expected lowest value.

An advantage of the present invention is that one can continuously during operation monitor the function of the coolant temperature sensor and get an indication of when it does not show a correct value.

Another advantage is that no additional hardware has to be implemented in the motor because all the necessary sensors already exist, and in addition the function of the control unit can be built into an already present control unit. Only software needs to be added. 72523 _4100; 2004-02-25 lO 15 526 638 u n o. En ao un: n o 0 o o n q o u v v o 0 o 0 I I II 'n n .uno c o o u o 0 I s u o n n n n n e a o; nu: uu nu anno-o s n n n se anno: c oo ou p u o Further advantages are achieved through various aspects of the invention and will be apparent from the following detailed description.

Brief description of the drawings Pig. 1a shows a schematic view of a vehicle comprising an OBD and a control unit in which the present invention can be implemented.

Fig. 1b shows a system for monitoring a temperature sensor according to the invention.

Pig. 2 shows a flow chart illustrating the method according to the invention.

Pig. 3 shows graphs illustrating the method according to the invention.

Detailed Description of Preferred Embodiments Figure 1 shows an example of a vehicle 1 in which the present invention may be implemented. According to future legal requirements, certain vehicles must include an on-board diagnostic (OBD) system.

Figure 1b shows a system 2 according to the present invention for monitoring the coolant temperature sensor. The system 2 comprises a control unit 3, a motor 4, an external temperature sensor 5 and a coolant temperature sensor 6. The control unit 3 collects necessary information from the system to be able to carry out the method according to the invention, including signals from the external temperature sensor 5 and the coolant temperature sensor 6.

These temperature sensors 5 and 6 are connected to the control unit 3 via lines 7 and 8, respectively. The control unit 3 also receives information about the vehicle's fuel consumption, the pressure of injected fuel to the engine and several other variables. 72523 .d0C; 2004-02-25 10 15 20 526 638 The control unit comprises at least one computer program product, preferably in the form of a memory M, such as a ROM (Read Only Memory), PROM (Programmable ROM), EPROM (Erasable PROM), EEPROM (Electrically EPROM) , flash memory, SRAM (Static Random Access Memory), etc. In the memory M there is a computer program 10 stored, which when executed enables the control unit to perform the method. Furthermore, there is a microprocessor pP that executes the computer program. The system 2 of course comprises other parts (not shown) such as radiator, engine fan, turbo etc., which parts are obvious to a person skilled in the art.

In short, the method according to the invention for monitoring a coolant temperature sensor is based on the idea and realization that if a sufficient amount of energy is supplied to an engine within a certain period of time, while the engine is operating under normal operating conditions regarding outside temperature Tmm, it is known that the coolant temperature is above a certain limit . If the measured coolant temperature is nevertheless below the specified limit, it is known that a malfunction of the coolant temperature sensor can be ascertained, ie. the temperature sensor shows a value that is too low. This applies provided that there are no errors in any other values used in the test. If, for example, the device for measuring the supplied fuel quantity (which as an example can be performed by a flow meter or the pressure sensor for the fuel, but which can also be estimated values for different speeds of the engine stored in tabular form) or the external temperature sensor shows incorrect values, this naturally affects present test.

The reason why one can use the measure of sufficient amount of energy to ensure that the engine has been run in such a way that one can verify a misleading coolant temperature sensor is the following reasoning. 72523 .dOC; 2004'02-25 lO 526 638. .a a. oo ono- o o o v o o u u uno. n o o o a o a o o nu nano øooo oas Assume that you set up a control volume, where the whole engine is this control volume and that you also assume that: Qkylvau / um = Qkyzvaß / mu (1) where Q stands for heat flow, ie. added energy per unit of time, then according to the first law of thermodynamics you can write: Qbrvlnsle _ Qomgivning _ Qavgaszr _ Qnytfígenergí = at) where / áf is the change in the inner energy, which can be further expressed as follows: âWà = mQaQ © á “mQö% WÜáæâ % MÜá (3 where m is the mass of the engine, CV is the specific heat capacity at a certain constant volume (V), Tämä is the temperature of the goods and Tywyümm is the temperature of the refrigerant. In equation (3) we assume that Tgod is approximately equal to Tkylvâtska.

In other words, it is the change in the internal energy that determines how quickly the coolant temperature changes, assuming that no heat is supplied to the coolant outside the control volume because a thermostat in the cooling system is switched off at low temperatures. This means that no cooling of the coolant takes place except for the negligible losses that occur in the pipes. It can in itself heat the coolant outside the control volume, but this only means that more energy is added to the control volume and the heating is faster. 72523 .dOC, '2004-02-25 10 15 526 638 en no oøaø o n n n n o n n nno n u n I n n o man; nnnn nun Now assume that the heat radiation to the surroundings is relatively constant, but that Qwwm, çhw flfl and Qßwßßw vary greatly depending on how you run the engine, e.g. if driving at idle or at maximum load on a steep uphill slope. When these three quantities are relatively small, ie. at idle, the external temperature affects the heating process a lot (ie.

Qwwwm), which means that it is very slow to warm up the engine. In the case where these quantities are large (in case of strong variations and high load), the external temperature Tæm will have a smaller effect on the heating process. Thus, in order to obtain a sufficiently fast heating process, Qmmt, Qwuw and Qwnwm fi must be large enough at the same time: as QMgfw-w; is small enough.

The first condition is verified by determining whether enough fuel has been injected in a sufficiently short time, which can be verified by over time either integrating the amount of injected fuel into the engine or integrating the pressure of injected fuel into the engine. It turns out that as the amount of fuel injected into pulp per unit time increases, Qwwk will increase. The increase is not entirely proportional to the amount of fuel injected in pulp per unit time, but decreases somewhat at high values of the amount of fuel injected. However, the relationship between Qwww and the amount of fuel injected can be assumed to be approximately proportional.

The second condition is verified by checking that the outside temperature is higher than a certain limit, preferably in the range 0 ° C to, more preferably 4 ° C to 6 ° C. 72523 .dOC; 2004-02-25 lO 15 20 526 638 ooo ooo oo oo o oo oo oo oo oo oo IIOO oooooooooooooooooooooooooooo ooo ooo ooooo I oooo oooooo I oooooooooooo I oooooo oo oooo oooo ooo The conditions that apply under normal operating conditions include the following criteria: - external temperature: ° C - 30 ° C - atmospheric pressure: <2000 masl (meters above sea level) - coolant temperature: 60 ° C - 100 ° CI and since the external temperature sensor 5 can measure a slightly misleading temperature, it is preferred that a slightly lower temperature, than those stated normal operating conditions, is used as a limit to determine whether the second condition is met.

Figure 2 shows a flow chart illustrating the method according to the invention, where the flow starts in step 20. In step 21 the parameters used by the method are set, ie. Thw which is the limit which the outside temperature must exceed in a later step in the method, Tgæt is the limit which is measured by the coolant temperature sensor must be exceeded, Qnmü which is the amount of supplied energy which must be supplied to the engine during a certain time period, and tmm which indicates the upper limit of the time period .

Once these parameters have been set, the flow proceeds to step 22 where a counter R1 is reset. Further in step 23 an integrator is to be reset which is to integrate the supplied energy Q, i.e. the heat flow, during the time period in which counter R1 is active.

The flow continues to step 24 where the supplied energy Q is determined, either as a function of measured amount of injected fuel or as a function of measured pressure of the injected fuel. Then Q. 72523 _1306 is integrated; 2004-02-25 10 15 20 526 638 In the subsequent step 25, the counter R1 is counted up and then tested if the outside temperature Tæm exceeds the limit Tum in step 26. If this is the case, the flow proceeds to step 27, otherwise the flow is fed back to step 22, where counter R1 is reset.

In step 27 it is tested whether the integrated value of the supplied energy Qi, i.e. the energy content of the engine fuel supplied to the engine is higher than the amount of energy supplied Qnmü which must be supplied to the engine 4 in order to verify the function of the coolant temperature sensor, an example of Qnmü is a value in the range 2 to 8 kg of fuel, preferably 5 kg fuel. In the case where the integrated value of the supplied energy is lower than Qnnu, the flow is fed back to step 24, where a further determination and integration of Q is performed. Otherwise, the flow proceeds to step 28.

In step 28, it is determined whether the time that has elapsed since counter R1 was reset, which took place in step 22, is sufficiently short.

This is done by comparing the value on counter R1 with the upper limit nmx for the determined time period. In the event that the time period has been exceeded, ie. counter R1 has been counted up to a value exceeding tmu, then no test is performed by the coolant temperature sensor but the flow is fed back to step 22, where counter R1 is reset. Otherwise, the flow proceeds to step 29.

Since the test conditions are met to verify the lower limit of the coolant temperature sensor, a value of the coolant temperature Tm is measured in step 29 and then in step 30 the measured value I is determined; is above the set level Tüßc. If so, the flow is terminated in step 31, but in the case where Tm is lower than Igeü, the flow proceeds to step 32 and an alarm is issued to the driver of the vehicle. 72523 .d0C; 2004-02-25 526 638 The method according to Figure 2 is preferably implemented in a software in a loop, where the flow is reconnected from step 31 to step 22, unless there are some parameters. adjusted, which is done in step 2l. The method can e.g. implemented in a 10 msec loop in a real-time software. The program is installed and run in the control unit 3 using the memory M and the microprocessor pP. The program can also be stored on a carrier such as a CD-ROM, magnetic tape, floppy disk, hard disk, etc.

Figure 3 shows three graphs with different variables (Tmm, Qi, Tm) as a function of time t which illustrate how the method according to the invention works. The time axis, i.e. The X-axis is divided into minutes, and for each Y-axis the division for the two temperature axes is divided into ° C and the axis for integrated input energy is divided into kg of fuel. In the top graph, which shows Tæm as a function of t, there is a curve 40 illustrating the temperature measured by an external temperature sensor 5 from a time 0. The top graph illustrates the first condition for verification of the coolant temperature sensor to be performed. The lowest permissible temperature limit Tkw is shown as a dashed line and in this example is set to 6 ° C.

In the middle graph, which shows Qi as a function of t, there are several sub-curves 41, 42, 43 and 44 illustrated which show an integrated value of supplied energy to the engine 4. The middle graph illustrates the second condition for verification of the coolant temperature sensor to be able to implemented. When the value of the integrated supplied energy Qi reaches a certain value Qnmü, provided that the condition illustrated in the top graph, a value of the coolant temperature can be read. Qumk is shown as a dashed line and in this example is set to 5 kg. If Qi reaches Qnmk within a predetermined time period (0-tmu) determined by 72523 .dOC; 2004-02-25 ..._____....... ~ _-___.. __ .., 10 15 20 526 638 oooo ooo 10 the time of the beginning of the integration of Q and the time when Qumk is reached then enough energy has been supplied to the motor 4 under normal operating conditions and fast enough.

The time period can e.g. set in the range of 10-30 minutes, preferably 15-20 minutes.

In the lower graph, which shows Tm as a function of t, there is a curve 45 illustrating the temperature measured by a coolant temperature sensor 6 from a time 0. At time 0 the vehicle starts and the coolant temperature increases initially, and should finally end up in an area 60 -10 ° C under normal operating conditions. The coolant temperature varies over time. At the time when the first and second conditions for Tum and Qi, respectively, are met, T is measured; and compared with a predetermined value Test, e.g. the lowest temperature that the coolant has under normal operating conditions, ie. 60 ° C in this example.

Four times tl, tg, t3 and t4 have been marked with four dotted lines in all graphs. The X-axis in all graphs starts at the time t = 0 (e.g.

Within the time period to-tl, the condition for Tum is met and Qi when Q fi nü at tl, see curve 41. Assume that the maximum allowed time period is set to 20 minutes, ie. mmx = 20 minutes.

Then a measurement of Tm is made at the time tl in the case where t1 tmm = 20 minutes. The conditions are met and the temperature measured by the coolant temperature sensor 6 at tl is about 65 ° C which is higher than Ttäm. The coolant temperature sensor thus works.

At time t1, the integrator begins to re-form Qi until time tz, see curve 42, when the condition for Tæm does not 72523 .d0C; 2004-02-25 10 15 ll longer is met and the integrator is reset again. As long as Tum is lower than Tum, the integrator will be reset, see curve 43, ie. all the way to time t3.

At time tg, the integrator begins to form Qi again, see curve 44, until Qnmü is reached, which occurs at time t4. The time period during which Q is integrated, ie. ti-tg, is 60-3l = 29 minutes, which is longer than the allowable time period of 20 minutes as above. Which means that no alarm is sounded even though I; at time t4 is lower than Tgät.

In the event that the permitted time period is set to 30 minutes, an alarm will be issued to the driver of the vehicle.

The method described above assumes that the engine efficiency and fuel efficiency are constant. However, the method can be developed by also taking into account variations in these efficiencies in connection with the supplied energy per unit of time Q being calculated for each measurement of either the amount of fuel supplied or the pressure of the supplied fuel.

A co-pending patent application entitled "Monitoring the engine coolant temperature sensor" with the same applicant describes a method for checking that the coolant temperature sensor in a motor vehicle does not show too much or is stuck at too high a value. In an embodiment of the present invention, the method described in said application may be performed at the same time as the method of the present invention is performed. A combination of these would thus mean that the function of the coolant temperature sensor regarding both an upper and a lower limit can be performed simultaneously.

Both methods for monitoring the coolant temperature sensor depend on the external temperature sensor functioning properly and a co-pending patent application, entitled "Method and control unit for monitoring a temperature sensor", with the same applicant, describes how the function of the external temperature sensor can be monitored. In an embodiment of the present invention, the method described in said application can be used to periodically check that the external temperature sensor shows a correct value. Should the test of the external temperature sensor give the result that it is out of order, this can be noticed in the present test and a warning light, for example, illuminates, which indicates that the result may be incorrect due to a broken external temperature sensor. 72523 .dOC; 2004-02-25

Claims (14)

10 15 20 25 30 526 638 13 New Patent Claims A method for monitoring the temperature of the coolant in a vehicle's engine (4), wherein the engine (4) is provided with a coolant temperature sensor (6) which provides a control unit (3) with information on measured coolant temperature (Ty), and that a external temperature sensor (5) also provides the control unit (3) with information about measured external temperature (Tam), characterized in that the method comprises the following steps: a) to verify that the external temperature (Tam) is higher than a temperature limit value (Inch), b) to ensure that the energy (Q) supplied to the engine (4) for a predetermined period of time is higher than an energy limit value (Qnmn), c) that when steps a) and b) have been fulfilled during the predetermined time period, measure the coolant temperature (Tm), and d ) to compare the measured coolant temperature (15) with - a predetermined lower limit value (ïïæt), where an alarm _ is issued when the measured coolant temperature (Tg) is lower than said limit value (Tnwg. The method according to claim 1, wherein the verification of the external temperature in step a) comprises the steps of measuring the external temperature (Inch) with the external temperature sensor (5) and comparing it with the temperature limit value (Tnw) corresponding to the lowest determined limit for normal operating conditions. The method according to claim 2, wherein the lowest determined limit for normal operating conditions is set to a value in the range 0 ° C to 6 ° C, preferably 4 ° C to 6 ° C. The method according to any one of claims 1-3, wherein the supplied energy (Q) in step b) is derived from the energy content of the engine fuel. 72523 new requirementsxloc; 2004-11-22 lO 15 20 25 526 638 14 The method according to claim 4, wherein the efficiency of the engine and / or the fuel is taken into account in connection with the supplied energy being calculated. The method according to any one of claims 4-5, wherein the amount of energy supplied (Q) is determined by a fuel flow meter by: bl) measuring the amount of fuel injected into the engine (4) with a flow meter, or b2) measuring the pressure on with a pressure sensor injected fuel into the engine (4). The method according to any one of claims 4-6, wherein the supplied energy (Q) during the time period corresponds to 2 to 8 kg of fuel, and preferably 5 kg of fuel. The method according to any one of claims 1-7, wherein the time period in step b) is chosen to be in the range 10 to 30 minutes, preferably in the range 15 to 20 minutes. The method according to any one of claims 1-8, wherein the limit value (ïgæt) in step d) is selected to be the lowest temperature that the motor water has under normal operating conditions. The method according to claim 9, wherein the temperature of the coolant under normal operating conditions is allowed to fluctuate between 60 ° C and 100 ° C. A computer program for monitoring a coolant temperature sensor (6) in a vehicle engine (4), characterized in that coding means which when driven in a control unit (3) cause the control unit (3) to perform the method according to any one of claims 1-10. 72523 new RIaVJSOC; 2005-02-22 10 526 638 15 A computer program product comprising a computer readable medium and a computer program according to claim 11, wherein the computer program is included in the computer readable medium. A control unit for monitoring the temperature of the coolant in a vehicle engine (4), characterized in that the control unit comprises at least one storage unit (M) comprising a computer program according to claim 11. Vehicle (1) comprising an external temperature sensor (5) for measuring the external temperature (TW), characterized in that the vehicle (1) is further equipped with a control unit (3) according to claim 13. 72523 new requirementsxloc; 2004-11-22