Engine control method and engine control device

Abstract

Provided is an engine control method for controlling an engine which includes a water temperature sensor that detects the temperature of engine cooling water and an oil temperature sensor that detects the temperature of engine oil, wherein it is determined whether or not the water temperature sensor has failed and, if the water temperature sensor has failed, the output of the engine is restricted to be lower when the detection value of the oil temperature sensor is higher.

Description

Engine control method and engine control device

[0001] The present invention relates to an engine control method and an engine control device.

[0002] A known vehicle control method is to switch to a limp-home mode, which limits engine output and vehicle speed so that the vehicle can drive to a service station when a fault diagnosis determines that there is a fault. JP 5760734B discloses a control method that determines whether to execute the limp-home mode or stop the engine depending on the results of a fault diagnosis of each part of the vehicle.

[0003] The control described in the above document will either activate limp home mode or shut down the engine if any type of failure occurs. The control described in the above document, which immediately activates limp home mode or shuts down the engine, is effective in the event of a failure in a device directly related to engine operation, such as a fuel injection system or ignition system. However, there are some failures that do not require limiting the vehicle speed to an extremely low level or shutting down the engine, as is the case with limp home mode. For example, a water temperature sensor that detects the engine coolant temperature may fail even though the engine coolant temperature is at an appropriate temperature. In such a case, if the engine coolant temperature can be maintained at an appropriate temperature, there is no need to switch to limp home mode. However, the control described in the above document will switch to limp home mode and significantly limit the vehicle speed.

[0004] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a control that allows a vehicle to travel without limiting its speed more than necessary even if a water temperature sensor that detects the engine coolant temperature has failed.

[0005] According to one aspect of the present invention, there is provided an engine control method for controlling an engine equipped with a water temperature sensor for detecting the temperature of engine coolant and an oil temperature sensor for detecting the temperature of engine oil, in which it is determined whether the water temperature sensor is malfunctioning, and if so, the engine output is restricted to a lower value as the detected value of the oil temperature sensor increases.

[0006] FIG. 1 is a schematic diagram of an engine cooling circuit. FIG. 2 is a time chart showing an example of changes in water temperature and oil temperature after a cold start. FIG. 3 is a diagram showing the relationship between water temperature and oil temperature. FIG. 4 is a torque-speed map of the engine. FIG. 5 is a flowchart showing a control routine for limiting engine output. FIG. 6A is an example of a time chart showing a case where a water temperature sensor malfunctions during constant-speed driving and the control of the comparative example is executed. FIG. 6B is an example of a time chart showing a case where a water temperature sensor malfunctions during constant-speed driving and the output limitation according to the embodiment is executed. FIG. 7A is an example of a time chart showing a case where a water temperature sensor malfunctions while driving on an uphill road and the control of the comparative example is executed. FIG. 7B is an example of a time chart showing a case where a water temperature sensor malfunctions while driving on an uphill road and the control of the embodiment is executed. FIG. 8A is another example of a time chart showing a case where a water temperature sensor malfunctions while driving on an uphill road and the control of the comparative example is executed. FIG. 8B is another example of a time chart showing a case where a water temperature sensor malfunctions while driving on an uphill road and the control of the comparative example is executed. 9A and 9B are example time charts showing the control according to the comparative example and the control according to the embodiment, respectively, when the vehicle starts from a stopped state with a malfunction of the water temperature sensor.

[0007] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0008] FIG. 1 is a schematic diagram of a cooling circuit 100 of an engine 2 to which control according to an embodiment of the present invention is applied.

[0009] The engine 2 is a water-cooled internal combustion engine that uses engine coolant (hereinafter simply referred to as "coolant") for cooling, and includes a water jacket (not shown) through which the coolant flows, and an oil jacket (not shown) through which engine oil (hereinafter simply referred to as "oil") for lubrication and the like flows. The engine 2 also includes a water temperature sensor 7 that detects the temperature of the coolant (hereinafter also referred to as "water temperature"), and an oil temperature sensor 8 that detects the temperature of the oil (hereinafter also referred to as "oil temperature"). The detected values ​​of the water temperature sensor 7 and the oil temperature sensor 8 are output to a controller 1 (described later).

[0010] The cooling circuit 100 includes a first coolant passage 9 , a second coolant passage 10 , a third coolant passage 11 , and an oil cooling passage 12 .

[0011] In the first coolant passage 9, a flow path switching valve (hereinafter also referred to as MCV) 4, a radiator 5, and a water pump 3 are arranged in this order from the outlet side.

[0012] A first coolant passage 9, a second coolant passage 10, and a third coolant passage 11 are connected as outlets to the MCV 4. The MCV 4 is equipped with a valve mechanism that can selectively open and close the openings of each passage. The valve mechanism is controlled by a controller 1, which will be described later.

[0013] The radiator 5 is a heat exchanger that cools the coolant by exchanging heat with the atmosphere. The radiator 5 also includes an electric fan 13 for increasing the amount of air passing through the radiator 5. The on / off state of the electric fan 13 is controlled by a controller 1, which will be described later.

[0014] The water pump 3 is driven by the driving force of the engine 2 or by the power of a battery (not shown), and has the function of circulating the cooling water.

[0015] The second coolant passage 10 has one end connected to the MCV 4 and the other end connected to the water pump 3 .

[0016] The third coolant passage 11 has one end connected to the MCV 4 and the other end connected to the water pump 3, and passes through the engine oil cooler 6 on the way.

[0017] The oil cooling passage 12 communicates between the oil jacket outlet and the oil jacket inlet of the engine 2, and an engine oil cooler 6 is interposed therebetween.

[0018] The engine oil cooler 6 is a heat exchanger that cools or heats the oil by exchanging heat with cooling water. An oil pump (not shown) circulates the oil between the engine 2 and the engine oil cooler 6. The oil pump is driven by the driving force of the engine 2 or by power from a battery (not shown).

[0019] The controller 1 controls the output of the engine 2. The controller 1 also functions as a malfunction determination unit and an output control unit to limit the engine output, which will be described later.

[0020] The controller 1 is configured by a microcomputer equipped with a central processing unit (CPU), a read-only memory (ROM), a random access memory (RAM), and an input / output interface (I / O interface). The controller 1 can also be configured by multiple microcomputers.

[0021] In the above-described cooling circuit 100, the controller 1 switches the cooling water path in accordance with the cooling water temperature as follows.

[0022] During a cold engine start, coolant flows from the MCV 4 through the second coolant passage 10 and the third coolant passage 11, and the flow to the first coolant passage 9 is blocked. This eliminates heat dissipation from the radiator 5, promoting an increase in noise. Furthermore, heat dissipation to the oil in the engine oil cooler 6 suppresses an increase in water temperature, but has the effect of promoting an increase in oil temperature. Therefore, when the cooling circuit 100 is viewed as a whole, an increase in water temperature and oil temperature is promoted.

[0023] Even after warm-up is complete, coolant basically flows from the MCV 4 through the second coolant passage 10 and the third coolant passage 11, and flow to the first coolant passage 9 is blocked. However, if the water temperature exceeds a predetermined temperature (e.g., 95°C), flow to the second coolant passage 10 is blocked, and coolant flows through the first coolant passage 9 and the third coolant passage 11. This is to cool the coolant in the radiator 5. The electric fan 13 operates when the temperature rises above the predetermined temperature or when the vehicle speed decreases.

[0024] 2 is a time chart showing an example of changes in water temperature and oil temperature after cold starting of the engine 2. In the figure, the solid line indicates the oil temperature, and the dashed line indicates the water temperature.

[0025] When the engine is cold and stopped, the water temperature and oil temperature are almost equal. When the engine is started at timing T1, the water temperature rises faster than the oil temperature. This is due to the difference in the heat quantity of the heat source. That is, the coolant absorbs the combustion heat of the engine 2 in the water jacket provided around the piston, while the oil absorbs the frictional heat of the sliding parts of the engine 2. Furthermore, the heat of combustion is far greater in quantity than the frictional heat.

[0026] As described above, heat is dissipated from the coolant to the oil in the engine oil cooler 6 while the water temperature is greater than the oil temperature. The reason the water temperature becomes constant from time T2 is because the heat balance is achieved through heat dissipation from the radiator 5. In contrast, the oil temperature continues to rise and becomes higher than the water temperature from time T3 onwards. Therefore, from time T3 onwards, heat is dissipated from the oil to the coolant in the engine oil cooler 6. Then, from time T4 onwards, the heat absorption from the engine 2 and the heat dissipation to the coolant are balanced, resulting in a constant temperature.

[0027] Figure 3 is a graph showing the results of a thermal evaluation test in which the relationship between oil temperature and water temperature was examined while varying the load on the engine 2 after the engine 2 had warmed up. The horizontal axis represents water temperature, and the vertical axis represents oil temperature. Figure 3 shows that the oil temperature is always higher than the water temperature in the high oil and water temperature range.

[0028] The controller 1 uses various parameters detected by sensors (not shown) to control the output of the engine 2. For example, an accelerator opening sensor detects the accelerator opening, and a crank angle sensor detects the engine speed, and based on these, the required output is calculated and the fuel injection amount, ignition timing, etc. are set according to the required output. If the engine 2 is equipped with a variable valve mechanism, the controller 1 also sets the valve timing, etc., along with the fuel injection amount and ignition timing. The controller 1 also limits the output in response to an increase in water temperature to prevent the water temperature from becoming excessively high.

[0029] That is, the ability to detect various parameters is a prerequisite for controlling the output of the engine 2. For this reason, the controller 1 also performs fault diagnosis in parallel with output control. If a fault is diagnosed, the controller 1 may switch to a limp-home mode that limits engine output and vehicle speed so that the vehicle can be driven to a repair shop, or may stop the engine.

[0030] However, even if a fault is diagnosed in the fault diagnosis, there may be cases where it is not actually necessary to limit the output. For example, if the water temperature sensor 7 is faulty due to a broken wire or poor contact, the fault diagnosis will diagnose a fault, but if the water temperature is normal, there is no need to limit the output. However, in order to drive without limiting the output, it is necessary to somehow confirm that the water temperature is normal.

[0031] Therefore, in this embodiment, when the water temperature sensor 7 fails, the oil temperature is used as an alternative characteristic to the water temperature based on the relationship between the oil temperature and the water temperature described above, and the output of the engine 2 is limited based on the oil temperature.

[0032] 4 is a torque-rotation speed map used for output control when the water temperature sensor 7 fails, with the horizontal axis representing engine rotation speed and the vertical axis representing engine torque. This map is pre-stored in the controller 1. In the figure, the solid line represents the maximum torque line, the one-dot chain line represents a first limit line (to be described later), the two-dot chain line represents a second limit line (to be described later), and the dashed line represents a third limit line (to be described later).

[0033] The maximum torque line is the torque line when the accelerator is fully open.

[0034] The second limit line may be, for example, an iso-oil temperature line created using an oil temperature corresponding to the upper limit water temperature in the engine design. The upper limit water temperature and the corresponding oil temperature may be set based on the relationship shown in Figure 3, and in this embodiment, the upper limit water temperature is set to, for example, 110°C.

[0035] The first limit line is, for example, a line connecting the midpoint between the value on the maximum torque line and the value on the second limit line.

[0036] The third limit line is a limit line for limiting the vehicle speed to a predetermined vehicle speed (for example, about 35 km / h) or less, and in this embodiment, the third limit line is a line for limiting the engine speed to Ne1, for example. Note that the restriction by the third limit line is not essential.

[0037] Using the torque-rotation speed map, the controller 1 limits the engine torque to a first limit line or less if the oil temperature exceeds 100°C, and limits the engine torque to a second limit line or less if the oil temperature exceeds 105°C.Then, if the oil temperature exceeds 110°C, the controller 1 limits the engine rotation speed according to the third limit line.The purpose of both limits is to suppress an increase in water temperature.

[0038] When limiting based on the first limit line is initiated, the driver may be notified that output is being limited, for example, by lighting up a caution lamp or by using text information. Furthermore, when limiting based on the second limit line is initiated, the driver may be notified that output is being further limited by lighting up a caution lamp in a color different from that used when limiting based on the first limit line or by using text information. When limiting engine speed based on the third limit line is initiated, the driver may be notified that engine speed is being limited by lighting up a caution lamp in a color different from that used when limiting output.

[0039] From the viewpoint of engine protection, output limitation according to the first limit line is not essential. However, when output limitation according to the first limit line begins, the driver can recognize that the water temperature is approaching the upper limit temperature. If the driver then makes an effort to drive in a way that prevents the water temperature from rising any further, there is a good chance that output limitation according to the second limit line can be avoided.

[0040] 5 is a flowchart showing an example of a control routine for limiting the output of the engine 2, executed by the controller 1. This control routine is pre-programmed in the controller 1 and is repeatedly executed at predetermined intervals (e.g., several milliseconds). In parallel with this control routine, the controller 1 also performs fault diagnosis on devices other than the water temperature sensor 7 and the oil temperature sensor 8, such as the fuel injection device and the ignition device. If this fault diagnosis indicates the presence of a fault, the controller 1 limits the output of the engine 2 or stops the engine, depending on the nature of the fault, as in known fault control.

[0041] In step S100, the controller 1 determines whether the water temperature sensor 7 has failed, and if it has failed, the process of step S110 is executed, and if it has not failed, the current routine is terminated. The determination of whether the water temperature sensor 7 has failed may be performed using a method generally used for failure determination. For example, if no signal is input from the water temperature sensor 7, or if extreme outlier values ​​are continuously input, the controller 1 determines that the water temperature sensor 7 has failed.

[0042] In step S110, the controller 1 determines whether the oil temperature sensor 8 is normal. If it is normal, the process of step S120 is executed. If it is not normal, the current routine is terminated. The determination in this step may be performed using a method generally used for malfunction determination. The reason for terminating the current routine if the oil temperature sensor 8 is not normal is that if an accurate oil temperature cannot be obtained, the oil temperature cannot be used as an alternative characteristic for the water temperature.

[0043] In step S120, the controller 1 changes the flow path of the coolant and operates the electric fan 13 to dissipate heat in the radiator 5. Changing the flow path means controlling the MCV 4 so that the coolant flows through the first coolant passage 9. It is desirable to operate the electric fan 13 at its maximum rotation speed, which can suppress an increase in the coolant temperature.

[0044] In addition, in step S120, in addition to the above processing, the gear position of the automatic transmission (not shown) may be fixed and the lock-up clutch may be disengaged. Shifting to a lower gear position depending on the vehicle speed increases the engine speed, which can easily cause the water temperature to rise. However, this can be prevented by fixing the gear position. Furthermore, as the engine speed increases, changes in accelerator pedal position can cause vehicle behavior to become more pronounced, impairing drivability. However, fixing the gear position can prevent this. Furthermore, disengaging the lock-up clutch allows power transmission from the engine 2 to the automatic transmission via fluid, which can further reduce vehicle behavior caused by changes in accelerator pedal position.

[0045] In step S130, the controller 1 determines whether the oil temperature is equal to or higher than a threshold value Tth [°C]. If the oil temperature is equal to or higher than the threshold value Tth, the controller 1 executes the process of step S140. If the oil temperature is not equal to or higher than the threshold value Tth, the controller 1 terminates the current routine. The threshold value Tth [°C] can be set arbitrarily from among oil temperatures at which the oil temperature can be said to be higher than the water temperature, and is set to 80 [°C], for example, based on FIG. 3. The reason why the controller 1 terminates the current routine if the oil temperature is lower than the threshold value Tth [°C] is that the oil temperature cannot be used as an alternative characteristic for the water temperature unless the relationship oil temperature ≥ water temperature holds.

[0046] In step S140, the controller 1 determines whether the oil temperature is higher than a first temperature. If it is higher, the controller 1 executes the process of step S150. If it is not higher, the controller 1 ends the current routine. The first temperature is a threshold value for determining whether or not to limit the output according to the first limit line described above, and may be set to 100°C, for example. If the oil temperature is equal to or lower than the first temperature, the controller 1 ends the current routine, and the output of the engine 2 is not limited.

[0047] In step S150, the controller 1 executes a first output limit. The first output limit is an output limit based on the first limit line described above. By implementing the first output limit, the increase in water temperature is suppressed, the driver is made aware of the increase in water temperature, and the vehicle can be driven at a higher speed than in the conventional limp-home mode.

[0048] In step S160, the controller 1 determines whether the oil temperature is higher than a second temperature Tth2 [°C]. If it is higher, the controller 1 executes the process of step S170. If it is not higher, the controller 1 ends the current routine. The second temperature Tth2 [°C] is a threshold value for determining whether or not to limit the output according to the second limit line described above, and may be set to 105 [°C], for example. If the oil temperature is equal to or lower than the second temperature Tth2 [°C], the controller 1 ends the current routine, and the first output limit is maintained.

[0049] In step S170, the controller 1 executes the second output limit, which is the output limit according to the second limit line described above.

[0050] In step S180, the controller 1 determines whether the oil temperature is higher than a third temperature Tth3 [°C]. If it is higher, the process of step S190 is executed. If it is not higher, the current routine is terminated. The third temperature Tth3 [°C] is a threshold value for determining whether or not to limit the engine speed according to the above-mentioned third limit line, and may be set to 110 [°C], for example. If the oil temperature is equal to or lower than the third temperature Tth3 [°C], the current routine is terminated, and the state in which the second output limit is performed is maintained.

[0051] In step S190, the controller 1 executes the restriction of the engine speed according to the third restriction line described above, thereby restricting the vehicle speed to a low speed, but allowing the vehicle to travel to a repair shop or the like.

[0052] According to the above control routine, even if the water temperature sensor 7 fails, the output of the engine 2 is not immediately limited, and as long as the oil temperature is below the threshold value Tth0, the vehicle can continue to drive in the same way as if the sensor were not malfunctioning. This makes it possible to avoid a sudden decrease in vehicle speed, which could lead to a rear-end collision with a following vehicle. Even when the first output limit is initiated, the amount of output limit is small, so a speed decrease that would result in a rear-end collision with a following vehicle does not occur. Furthermore, because the output is limited in stages from the first output limit to the second output limit in response to an increase in oil temperature, the driver is made aware that the vehicle is not normal, and the driver's anxiety is reduced compared to when the output is suddenly reduced.

[0053] After the first output restriction, second output restriction, or rotation speed restriction is initiated by the above control routine, if it is determined in step S100 that there is no malfunction in the water temperature sensor 7, that is, if the function of the water temperature sensor 7 has been restored by repair or replacement, etc., the restriction in progress is released.

[0054] Next, cases where the control according to this embodiment is executed in various driving situations will be described.

[0055] [Driving at a constant speed on a highway] Figures 6A and 6B are time charts showing what happens when the water temperature sensor 7 fails while driving at a constant speed (e.g., 120 km / h). Figure 6A is a comparative example showing a case where a switch to a conventional limp-home mode is executed, while Figure 6B shows a case where control according to this embodiment, i.e., control using oil temperature as an alternative characteristic to water temperature, is executed. The conventional limp-home mode is a control that executes limiting of engine speed using a third control line. Here, the limit is set to 1100 rpm or less.

[0056] First, a comparative example will be described.

[0057] The vehicle conditions before the malfunction (before time 0) are as follows: engine speed: 2300 [rpm], engine torque: 200 [Nm], gear: 7th speed, lock-up clutch: locked up (L / U ON), MCV 4: blocking the flow path to the first coolant passage leading to radiator 5 (MCV Close), electric fan 13: operating at 1200 [rpm], oil temperature: 100 [°C], water temperature: 90 [°C].

[0058] If it is determined at time 0 that the water temperature sensor 7 has failed, the engine speed decreases, the lock-up clutch goes into a non-lock-up state (L / U OFF), the MCV 4 opens the flow path to the first coolant passage leading to the radiator 5 (MCV Open), and the electric fan 13 goes to its maximum speed (2700 rpm). This causes a decrease in engine torque, a shift to a lower gear, and a decrease in vehicle speed. Furthermore, the change in the coolant flow path and the increase in the rotation speed of the electric fan 13 cause the oil temperature and water temperature to begin to decrease.

[0059] Fuel cut is performed during deceleration, and when the engine speed drops to 1,100 rpm, fuel recovery is performed, but fuel cut is performed again due to the engine speed limit. As a result, fuel cut and fuel cut recovery are repeated. In particular, if the driver increases the accelerator pedal depression amount in response to the decrease in vehicle speed, fluctuations in engine speed and engine torque become large. Furthermore, because the gear has been downshifted to first gear, fluctuations in vehicle speed due to fluctuations in engine speed and engine torque also become large, making the vehicle speed unstable.

[0060] As described above, in the conventional limp home mode, although increases in oil temperature and water temperature can be avoided, the vehicle speed is significantly limited and the vehicle becomes unstable.

[0061] Next, the control according to this embodiment will be described. The vehicle condition before the malfunction occurs is the same as in the comparative example.

[0062] If it is determined at time 0 that the water temperature sensor 7 has failed, the controller 1 puts the lock-up clutch into a non-lock-up state (L / U OFF), puts the MCV 4 into a state where the flow path to the first cooling water passage connected to the radiator 5 is open (MCV Open), sets the rotation speed of the electric fan 13 to the maximum (2700 rpm), and fixes the gear position.

[0063] At this point, the oil temperature is 100°C, so no output restriction is performed. Furthermore, since the oil temperature and water temperature have decreased by controlling the MCV 4 and the electric fan 13 as described above, no output restriction is performed thereafter.

[0064] Then, as the lockup state is changed to a non-lockup state, the engine speed increases and the engine torque decreases, and as a result, the vehicle speed is maintained at 120 km / h.

[0065] As described above, in the conventional limp home mode, the vehicle speed is limited and becomes unstable, whereas the control according to this embodiment makes it possible to maintain the vehicle speed at the time when the water temperature sensor 7 fails.

[0066] [Driving uphill under high load (oil temperature below 100°C when malfunction occurs)] Figures 7A and 7B are time charts showing what happens when the water temperature sensor 7 malfunctions while driving uphill under high load and with an oil temperature below 100°C. Figure 7A is a comparative example showing the case where a switch to the conventional limp home mode is executed, and Figure 7B shows the case where the control according to this embodiment is executed.

[0067] First, a comparative example will be described.

[0068] The vehicle conditions at the time when the malfunction occurred (time 0) were as follows: engine speed 3100 [rpm], engine torque 490 [Nm], gear position 4, lock-up clutch in lock-up state (L / U ON), MCV 4 with the flow path to the first coolant passage connected to radiator 5 open (MCV Open), electric fan 13 operating at maximum speed (2700 [rpm]), oil temperature 90 [°C], water temperature 75 [°C], and vehicle speed 85 [km / h].

[0069] If it is determined at time 0 that the water temperature sensor 7 has failed, the engine speed decreases and the lock-up clutch goes into a non-lock-up state (L / U OFF). This causes a decrease in engine torque, a shift to a lower gear, and a decrease in vehicle speed. Furthermore, the decrease in engine speed and engine torque causes the oil temperature and water temperature to begin to decrease.

[0070] The behavior of the engine speed, engine torque, and vehicle speed after time 0 is the same as that shown in Fig. 6A. In other words, in the conventional limp home mode, although increases in oil temperature and water temperature can be avoided, the vehicle speed is significantly limited and becomes unstable.

[0071] Next, the control according to this embodiment will be described. The vehicle condition before the malfunction occurs is the same as in the comparative example.

[0072] If it is determined at time 0 that the water temperature sensor 7 has failed, the controller 1 fixes the gear position. Although coolant is flowing through the radiator 5 and the electric fan 13 is operating at maximum speed, the oil temperature and water temperature continue to rise because the vehicle is running under high load.

[0073] When the oil temperature exceeds 100°C at time T1, the first output limit is implemented, reducing engine torque and vehicle speed. At time T2, the engine torque reaches the limit value imposed by the first output limit, and the vehicle speed drops to 55 km / h. This vehicle speed is maintained until time T3, when the oil temperature exceeds 105°C.

[0074] When the oil temperature exceeds 105°C at time T3, the second output limit is implemented, further reducing the engine torque and vehicle speed. Then, at time T4, the engine torque reaches the limit value imposed by the second output limit, and the vehicle speed becomes 35 km / h. This vehicle speed is maintained until the oil temperature exceeds 110°C and the engine speed limit is initiated.

[0075] As described above, even if the water temperature sensor 7 fails, output is not limited until time T1, and the vehicle speed before the failure can be maintained. Even if the oil temperature continues to rise, the output is limited in stages, using the first output limit and then the second output limit, so that a speed of 55 km / h or higher can be maintained until time T3, and from time T3 onwards, a speed of 35 km / h or higher can be maintained until the oil temperature exceeds 110°C. In other words, since the vehicle speed does not drop suddenly as in the comparative example, the possibility of being hit from behind by a following vehicle is reduced.

[0076] [Driving uphill under high load (oil temperature of 110°C or higher when malfunction is determined)] Figures 8A and 8B are time charts showing a case where the water temperature sensor 7 malfunctions while driving uphill under high load and with an oil temperature higher than 110°C. Figure 8A is a comparative example showing a case where a switch to the conventional limp home mode is executed, and Figure 8B shows a case where the control according to this embodiment is executed.

[0077] First, a comparative example will be described.

[0078] The vehicle conditions at the time when the malfunction occurred (time 0) were as follows: engine speed: 3100 [rpm], engine torque: 490 [Nm], gear: 4th speed, lock-up clutch: locked up (L / U ON), MCV 4: the flow path to the first coolant passage connected to radiator 5: open (MCV Open), electric fan 13: operating at maximum speed (2700 [rpm]), oil temperature: 130 [°C], water temperature: 115 [°C], and vehicle speed: 85 [km / h].

[0079] If the water temperature sensor 7 fails at time 0, the system switches to limp home mode. Except for the oil temperature and water temperature immediately before the switch, the behavior of each value after time 0 is the same as in Figure 7A. That is, the vehicle speed is limited to 10 km / h and becomes unstable around 10 km / h.

[0080] Next, the control according to this embodiment will be described. The vehicle condition before the malfunction occurs is the same as in the comparative example.

[0081] When the water temperature sensor 7 fails at time 0, the oil temperature is already 130°C, so the rotation speed is limited. Therefore, each value behaves in the same way as in Figure 8A, except that the gear position is fixed to fourth gear.

[0082] However, when the oil temperature reaches 100°C at time T2, the output limit is switched to the first output limit, engine torque increases, and vehicle speed increases accordingly. Then, when the oil temperature exceeds 105°C at time T3, the output limit is switched to the second output limit, engine torque decreases again, and vehicle speed also decreases. Then, at time T4, engine torque reaches the limit value set by the second output limit, and vehicle speed decreases to 35 km / h.

[0083] As described above, the controller 1 switches to the first output limit when the oil temperature drops due to the execution of the rotation speed limit, and switches to the second output limit if the oil temperature rises again after that. In other words, the output of the engine 2 is limited in accordance with the change in oil temperature, so the vehicle speed is not limited more than necessary.

[0084] 9A and 9B are time charts showing a case where the vehicle is stopped with the water temperature sensor 7 malfunctioning and then started moving. Fig. 9A shows a comparative example in which a conventional switch to the limp home mode is executed, and Fig. 9B shows a case in which the control according to the present embodiment is executed.

[0085] First, a comparative example will be described.

[0086] At time 0, engine 2 is started and the vehicle is set off. At this time, the oil temperature is 80°C and the water temperature is 70°C. Because the water temperature sensor 7 has failed at time 0, the engine enters limp home mode as soon as it starts. As a result, the engine speed becomes unstable between 1100 and 1300 rpm, and the vehicle speed also becomes unstable around 10 km / h. However, the rise in oil temperature and water temperature is kept to around 10°C each.

[0087] Next, the control according to this embodiment will be described. The vehicle state before the engine is started is the same as that shown in FIG.

[0088] When engine 2 is started at time 0 and the vehicle is started, the gear position is fixed at fourth gear, but the oil temperature is 80°C, so output is not limited. Therefore, the vehicle speed increases without being limited. Furthermore, as engine torque increases, the oil temperature and water temperature also increase, but output is not limited until the oil temperature exceeds 100°C.

[0089] As described above, if the oil temperature is equal to or lower than the first temperature, the same acceleration performance as when the water temperature sensor 7 is not malfunctioning can be obtained.

[0090] As described above, this embodiment provides an engine control method for controlling an engine 2 equipped with a water temperature sensor 7 that detects the temperature of engine coolant and an oil temperature sensor 8 that detects the temperature of engine oil. In this method, the controller 1 determines whether the water temperature sensor 7 has failed, and if so, limits the output of the engine 2 to a lower value the higher the detected value of the oil temperature sensor 8. This allows the vehicle to run without restricting the vehicle speed more than necessary, even if the water temperature sensor 7 has failed.

[0091] According to this embodiment, if the water temperature sensor 7 fails, the controller 1 causes engine coolant to flow into the radiator 5 and operates the electric fan 13 for the radiator 5. This makes it possible to suppress an increase in water temperature.

[0092] According to this embodiment, when the temperature detected by the oil temperature sensor 8 is higher than a first temperature Tth1 [°C], the controller 1 executes a first output limit to limit the output of the engine 2. Furthermore, when the detected value of the oil temperature sensor 8 exceeds a second temperature Tth2 [°C], which is higher than the first temperature Tth1 [°C], the controller 1 executes a second output limit to limit the output of the engine 2 to a value lower than the first output limit. The water temperature correlates with the vehicle's driving state, specifically, the load state of the engine 2. For example, when the vehicle is running at a low load, such as when traveling at a constant speed on a highway, more air passes through the radiator 5, maintaining the water temperature relatively low. Therefore, there is no need to significantly limit the engine output. In fact, switching from a high-speed driving state to a conventional limp-home mode increases the risk of being rear-ended by a following vehicle. On the other hand, when the engine 2 is running at a high load, the water temperature rises, so it is necessary to significantly limit the engine output to prevent the water temperature from rising. Furthermore, a high load state often occurs when the vehicle speed is low, such as during acceleration from a standstill. In such cases, even if engine output is significantly limited and the vehicle speed drops suddenly, the possibility of a rear-end collision is low and the driver is not made to feel uneasy. Therefore, the first output limit is set to a limit that allows a high vehicle speed to be maintained while suppressing an increase in water temperature, and the second output limit is set to a limit that prioritizes suppressing an increase in water temperature over maintaining vehicle speed, and the output is limited in stages according to the water temperature (actually, the oil temperature as an alternative characteristic). In this way, the output is limited according to the load state, making it possible to suppress an increase in water temperature while traveling at a vehicle speed that does not cause anxiety or dissatisfaction to the driver.

[0093] In this embodiment, when the controller 1 starts the first output limit or the second output limit, it continues the output limit until the function of the water temperature sensor 7 is restored. This makes it possible to prevent the water temperature from rising due to the output limit being released in a state where the water temperature sensor 7 has failed.

[0094] Although the embodiments of the present invention have been described above, the above embodiments merely illustrate some of the application examples of the present invention, and it is not intended that the technical scope of the present invention be limited to the specific configurations of the above embodiments.

Claims

1. An engine control method for controlling an engine equipped with a water temperature sensor that detects the temperature of engine coolant and an oil temperature sensor that detects the temperature of engine oil, the method determining whether the water temperature sensor has failed, and if so, limiting the output of the engine to a lower level the higher the detection value of the oil temperature sensor.

2. An engine control method as claimed in claim 1, further comprising the steps of: when the water temperature sensor fails, causing the engine cooling water to flow into a radiator and operating an electric fan for the radiator.

3. An engine control method according to claim 1, further comprising the step of: executing a first output restriction for restricting the output of the engine when the temperature detected by the oil temperature sensor is higher than a first temperature.

4. An engine control method as claimed in claim 3, further comprising the steps of: when the detection value of the oil temperature sensor exceeds a second temperature higher than the first temperature, a second output limit is implemented to limit the output of the engine to a value lower than the first output limit.

5. An engine control method as claimed in claim 4, wherein, when the first output restriction or the second output restriction is initiated, the output restriction is continued until the function of the water temperature sensor is restored.

6. An engine control device for controlling an engine equipped with a water temperature sensor for detecting the temperature of engine cooling water, and an oil temperature sensor for detecting the temperature of engine oil, the engine control device comprising: a failure determination unit for determining whether the water temperature sensor has failed, and an output control unit for limiting the output of the engine to a lower value the higher the detection value of the oil temperature sensor is if the water temperature sensor has failed.

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