Oil temperature control method and device for internal combustion engine

Abstract

To suppress an increase in oil temperature when a state where a vehicle-side required output is great, such as uphill driving, continues in a series hybrid vehicle.SOLUTION: In a series hybrid vehicle, when a vehicle-side required output is great, the vehicle operates in an HEV mode in which it travels while generating electric power through combustion operation of an internal combustion engine. On the basis of an SOC of a battery, a target rotational speed is switched between a first rotational speed N1 and a second rotational speed N2. When an oil temperature of lubricating oil becomes equal to or greater than a predetermined threshold SL that is close to an allowable upper limit temperature (time t1), the target rotational speed is limited by a regulated rotational speed N3 set from the viewpoint of oil temperature. Consequently, an increase in oil temperature can be suppressed while continuing uphill driving at a constant vehicle speed.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to oil temperature control of lubricating oil in an internal combustion engine, and more particularly to oil temperature control of an internal combustion engine for generating electricity that drives a generator in a series hybrid vehicle. [Background technology]

[0002] In series hybrid vehicles that generate electricity using an internal combustion engine and run on a motor, in many cases, when the required output from the vehicle is high, such as when climbing a slope or towing, the vehicle will operate in so-called HEV mode, even if the battery SOC is at a relatively high level. Note that running on the traction motor with battery power while the internal combustion engine is stopped is called "EV running," and running on the traction motor while generating electricity using the internal combustion engine is called "HEV running."

[0003] For example, the steeper the gradient of an uphill road, the higher the generator output required, which increases the rotational speed of the internal combustion engine that drives the generator. If the internal combustion engine continues to operate at a high rotational speed, the temperature of the lubricating oil that lubricates various parts of the internal combustion engine will rise and may approach the upper limit of the allowable temperature.

[0004] Patent Document 1 discloses that when the engine oil temperature or coolant temperature exceeds an allowable value due to prolonged revving while the vehicle is stopped, the amount of fuel supplied is adjusted to limit the engine speed to a certain value or below. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 4-143438 Summary of the Invention [Problem to be solved by the invention]

[0006] The technology in Patent Document 1 addresses abnormal increases in oil or water temperature caused by revving the vehicle while stopped, when the vehicle does not require the output of the internal combustion engine to run, and does not take into account increases in oil temperature while driving uphill, for example. In a vehicle that runs on the output of an internal combustion engine, adjusting the amount of fuel supplied to limit the engine speed to a low level makes it difficult to run at the desired vehicle speed. [Means for solving the problem]

[0007] The present invention relates to an internal combustion engine for generating electricity that drives a generator in a series hybrid vehicle, comparing the oil temperature of the internal combustion engine with a predetermined threshold value close to an upper allowable temperature limit; If the oil temperature is equal to or higher than the threshold value, the high rotation speed of the internal combustion engine is limited to a regulated rotation speed.

[0008] In series hybrid vehicles, when the vehicle's required output is high, such as when climbing a slope or towing, the vehicle operates in HEV mode, generating electricity with the generator. If the oil temperature exceeds a threshold during HEV operation, the engine speed is limited to a regulated speed, preventing the oil temperature from rising or causing the oil temperature to tend to decrease. In this case, the generator continues to generate electricity, allowing the vehicle to continue driving. [Effects of the Invention]

[0009] According to the present invention, when the oil temperature of the internal combustion engine for generating electricity in a series hybrid vehicle approaches the upper allowable temperature limit, the oil temperature can be reduced or prevented from increasing while the vehicle continues to run. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is an explanatory diagram of the configuration of a series hybrid vehicle. [Figure 2] 4 is a flowchart showing a process flow of oil temperature control according to an embodiment. [Figure 3] 4 is a time chart showing an example of an operation when traveling uphill. [Figure 4]10 is a time chart showing another example of the operation when traveling uphill. [Figure 5] FIG. 10 is an explanatory diagram of an embodiment having a plurality of stages of rotation speed regulation. DETAILED DESCRIPTION OF THE INVENTION

[0011] An embodiment of the present invention will now be described in detail with reference to the drawings. First, a series hybrid vehicle, on which the present invention is based, will be described. FIG. 1 schematically shows the configuration of a series hybrid vehicle according to one embodiment. The series hybrid vehicle includes a power-generating motor-generator 1 that operates primarily as a generator, an internal combustion engine 2 used as a power-generating internal combustion engine that drives the power-generating motor-generator 1 in response to power demands, a traction motor-generator 4 that operates primarily as a motor to drive drive wheels 3, and a battery 5 that stores the generated power. Electric power obtained by the internal combustion engine 2 driving the power-generating motor-generator 1 is stored in the battery 5 via an inverter device (not shown). The traction motor-generator 4 is driven and controlled using the power from the battery 5. Electric power generated by the traction motor-generator 4 during regeneration is stored in the battery 5 via an inverter device (not shown).

[0012] The operation of the motor generators 1 and 4, the charging and discharging of the battery 5, and the operation of the internal combustion engine 2 are controlled by a controller 6. The controller 6 is composed of multiple controllers connected to each other so that they can communicate with each other, such as a motor controller 7 that controls the motor generators 1 and 4, an engine controller 8 that controls the internal combustion engine 2, and a battery controller 9 that manages the battery 5. Information such as the accelerator pedal position and vehicle speed (not shown) is input to the controller 6. The battery controller 9 also calculates the SOC of the battery 5 based on the voltage and current of the battery 5. When the SOC drops to a predetermined lower limit, the internal combustion engine 2 is started via the engine controller 8 to generate electricity. The engine controller 8 is connected to various sensors typically required for controlling the internal combustion engine 2 (e.g., an air flow meter, a crank angle sensor, an air-fuel ratio sensor, a coolant temperature sensor, an atmospheric pressure sensor, an outside air temperature sensor, etc.). As described above, the driving modes of such a series hybrid vehicle include an EV mode in which the vehicle runs on power from the battery 5 without combustion operation of the internal combustion engine 2, and an HEV mode in which the vehicle runs while generating electricity through combustion operation of the internal combustion engine 2.

[0013] In one embodiment, the internal combustion engine 2 is a four-stroke cycle spark ignition internal combustion engine, a so-called gasoline engine. When the internal combustion engine 2 is operated to generate electricity, it is basically operated at a specific operating point (load and rotational speed) that provides the best thermal efficiency when the power generation request is due to a drop in the SOC of the battery 5. On the other hand, when power generation is required due to a large output required on the vehicle side, such as when climbing a slope or towing, the internal combustion engine 2 is operated with either the first rotational speed N1 or the second rotational speed N2 as the target rotational speed, depending on the SOC of the battery 5.

[0014] The first rotation speed N1 is set relatively higher than the second rotation speed N2 so as to perform forced charging while satisfying the output required by the vehicle, and is used until the SOC of the battery 5 reaches a relatively high first SOC threshold SOC1. The second rotation speed N2 is set relatively lower so as to satisfy the output required by the vehicle while allowing a decrease in the SOC of the battery 5. The second rotation speed N2 is used until the SOC reaches the first SOC threshold SOC1 and decreases to a relatively low second SOC threshold SOC2. When the SOC of the battery 5 decreases to the second SOC threshold SOC2, the target rotation speed is switched back to the first rotation speed N1. That is, the target rotation speed is switched between the first rotation speed N1 and the second rotation speed N2 depending on the SOC of the battery 5. The specific values ​​of the first rotation speed N1 and the second rotation speed N2 change depending on the magnitude of the output required by the vehicle, and the larger the required output, the higher the rotation speed becomes. For example, the first rotation speed N1 and the second rotation speed N2 are set by map search based on the vehicle operating conditions. In one embodiment, the second rotation speed N2 is approximately 2500 to 3000 rpm, and the first rotation speed N1 is approximately 4000 to 5000 rpm. This allows the vehicle to run in a situation requiring high output, such as uphill running, while maintaining the SOC of the battery 5 within an appropriate range.

[0015] The internal combustion engine 2 is equipped with an oil temperature sensor 10 that detects the temperature of the lubricating oil, and the detection signal is input to the engine controller 8. The engine controller 8 compares the oil temperature detected by the oil temperature sensor 10 with a predetermined threshold value SL, and if the oil temperature is equal to or higher than the threshold value SL, limits the rotation speed of the internal combustion engine 2 so as not to exceed a predetermined restricted rotation speed N3. The oil temperature threshold value SL is set to a temperature close to the allowable upper limit temperature of the lubricating oil (for example, a temperature several degrees Celsius lower than the allowable upper limit temperature) determined from the viewpoint of viscosity reduction, etc. The restricted rotation speed N3 is a fixed value that is unrelated to the vehicle operating conditions, i.e., the required output from the vehicle side. In other words, the restricted rotation speed N3 is determined from the viewpoint of oil temperature control, regardless of the power generation requirement. Conversely, the first rotation speed N1 and the second rotation speed N2 are determined from the viewpoint of power generation, and therefore may be set higher than the restricted rotation speed N3.

[0016] FIG. 2 is a flowchart showing the flow of oil temperature control processing in one embodiment. Note that this processing is repeatedly executed while power generation is being performed due to a large required output on the vehicle side. In the first step 1, it is determined whether the oil temperature is equal to or higher than a threshold value SL. If it is equal to or higher than the threshold value SL, the process proceeds to step 2, where a restricted rotation speed N3 is set for rotation speed restriction. If the oil temperature is lower than the threshold value SL, step 2 is skipped. In this case, the restricted rotation speed N3 used for rotation speed comparison in steps 5 and 9, described below, remains at a sufficiently large default value. Note that an appropriate hysteresis is applied to the start and end of rotation speed restriction based on oil temperature determination. Once the oil temperature reaches or exceeds the threshold value SL and rotation speed restriction is initiated, the rotation speed restriction is released when the oil temperature falls below a restriction release threshold value SL2, which is a predetermined temperature (e.g., several degrees Celsius) lower than the threshold value SL.

[0017] In the next step 3, it is determined based on the SOC of the battery 5 whether forced charging is necessary. If the determination is YES, the process proceeds to step 4, where the first rotation speed N1 is selected as a temporary target rotation speed. In the next step 5, it is determined whether the first rotation speed N1 is lower than the restricted rotation speed N3. If the first rotation speed N1 is lower than the restricted rotation speed N3, the first rotation speed N1 is set as the final target rotation speed in step 6. If the first rotation speed N1 is equal to or higher than the restricted rotation speed N3, the restricted rotation speed N3 is set as the final target rotation speed in step 7. Note that if the oil temperature is below the threshold value SL in the oil temperature determination in step 1, the restricted rotation speed N3 is a sufficiently large default value, and therefore the determination in step 5 is always YES, and the first rotation speed N1 is used as the target rotation speed.

[0018] If it is determined in step 3 that forced charging is not necessary, the process proceeds from step 3 to step 8, where the second rotation speed N2 is selected as the temporary target rotation speed. In the next step 9, it is determined whether the second rotation speed N2 is lower than the restricted rotation speed N3. If the second rotation speed N2 is lower than the restricted rotation speed N3, the second rotation speed N2 is set as the final target rotation speed in step 10. If the second rotation speed N2 is equal to or higher than the restricted rotation speed N3, the restricted rotation speed N3 is set as the final target rotation speed in step 11. Note that if the oil temperature is lower than the threshold value SL in the oil temperature determination in step 1, the restricted rotation speed N3 becomes a sufficiently large default value, so the determination in step 9 is always YES, and the second rotation speed N2 is used as the target rotation speed.

[0019] FIG. 3 is a time chart showing an example of operation when traveling uphill. From top to bottom, the chart shows changes in (a) lubricant oil temperature, (b) engine speed, (c) torque of the engine 2, (d) SOC of the battery 5, and (e) vehicle speed. As shown in (e), this example shows traveling uphill at a constant vehicle speed of, for example, 50 to 70 km / h on a relatively steeply inclined road. As shown in (b) and (d), the target engine speed is alternately switched between a first engine speed N1 and a second engine speed N2 based on the SOC of the battery 5. Specifically, the target engine speed remains at the first engine speed N1 until the SOC reaches the first SOC threshold SOC1. Once the SOC reaches the first SOC threshold SOC1, the target engine speed is switched to the second engine speed N2. After that, once the SOC drops to the second SOC threshold SOC2, the target engine speed is switched back to the first engine speed N1. As shown in section (b), the torque of the internal combustion engine 2 is relatively high in the section of the first rotation speed N1 where forced charging is performed, and is relatively low in the section of the second rotation speed N2 where a decrease in the SOC is allowed.

[0020] During this uphill driving, the lubricant temperature rises and exceeds the threshold value SL at time t1. The target engine speed is then limited to a restricted engine speed N3, which is lower than the first engine speed N1. In the illustrated example, the restricted engine speed N3 is several hundred rpm lower than the first engine speed N1 but higher than the second engine speed N2. At this restricted engine speed N3, torque is maintained at a level comparable to that at the first engine speed N1. Because the first engine speed N1 is relatively high, even if the engine speed is reduced to a certain extent, it is possible to output torque close to the maximum torque of the internal combustion engine 2. Therefore, active charging continues, and the SOC continues to rise. Because the restricted engine speed N3 is higher than the second engine speed N2, when the target engine speed becomes the second engine speed N2 based on the SOC, the engine speed is not substantially limited, and the internal combustion engine 2 operates at the second engine speed N2.

[0021] The time chart in FIG. 4 shows another example of operation when traveling uphill. In this example, the oil temperature reaches or exceeds the threshold value SL at time t2. This time t2 roughly coincides with the timing when the target engine speed changes from the first engine speed N1 to the second engine speed N2. Therefore, the actual engine speed restriction begins the next time the target engine speed reaches the first engine speed N1, and the target engine speed is restricted to the restricted engine speed N3. Note that the oil temperature drops in the range of the second engine speed N2, which is lower than the restriction release threshold value SL2, which is set to have appropriate hysteresis, as described above.

[0022] By limiting the rotational speed of the internal combustion engine 2 to the regulated rotational speed N3 when the oil temperature exceeds the threshold value SL, the oil temperature is at least prevented from rising and does not exceed the allowable upper limit temperature. Furthermore, as a series hybrid vehicle, power generation continues even at the regulated rotational speed N3, so that the vehicle can be driven without a decrease in speed.

[0023] Next, a second embodiment will be described, which has multiple stages of restricted engine speeds depending on the oil temperature. In the previous embodiment, a single restricted engine speed N3 was set when the oil temperature reached or exceeded a threshold value SL. However, in the second embodiment, three stages of restricted engine speeds N31 to N33 are set. As shown in FIG. 5, when the oil temperature reaches or exceeds a first threshold value SL11, the engine speed is limited by a first restricted engine speed N31. When the oil temperature reaches or exceeds a second threshold value SL12, which is higher than the first threshold value SL11, the engine speed is limited by a second restricted engine speed N32, which is lower than the first restricted engine speed N31. When the oil temperature reaches or exceeds a third threshold value SL13, which is even higher, the engine speed is limited by a third restricted engine speed N33, which is lower than the second restricted engine speed N32.

[0024] As in the previous embodiment, the restriction release thresholds are set to have appropriate hysteresis in the direction of the decrease in oil temperature from, for example, the third threshold SL13. When the oil temperature falls below the restriction release threshold for each stage, the restriction is shifted to a relatively high restricted rotation speed.

[0025] By controlling in stages in this manner, it is possible to allow a higher rotation speed while reliably preventing the oil temperature from exceeding the allowable upper limit temperature.

[0026] Although an example of three stages is shown here, more stages may be used, or the restricted rotation speed may be changed in two stages.

[0027] Although one embodiment of the present invention has been described above, the present invention is not limited to the above embodiment and various modifications are possible. For example, the numerical values ​​such as the rotation speeds given in the above description are merely examples. [Explanation of symbols]

[0028] 1...Power generating motor generator 2...Internal combustion engine 4...Traction motor generator 5. Battery 8...Engine controller 10...Oil temperature sensor

Claims

1. In a series hybrid vehicle, an internal combustion engine for generating electricity drives a generator, comparing the oil temperature of the internal combustion engine with a predetermined threshold value close to an upper allowable temperature limit; If the oil temperature is equal to or higher than the threshold value, the high rotation speed of the internal combustion engine is limited by a regulated rotation speed. A method for controlling oil temperature in an internal combustion engine.

2. The target rotation speed of the internal combustion engine when the required output of the vehicle is large is switching, in accordance with the battery SOC, between a relatively high first rotation speed used until the battery SOC reaches a relatively high first SOC threshold and a relatively low second rotation speed used until the battery SOC drops to a relatively low second SOC threshold after reaching the first SOC threshold; 2. The oil temperature control method for an internal combustion engine according to claim 1.

3. When the oil temperature becomes equal to or lower than a restriction release threshold that is lower by a predetermined temperature than the threshold, the restriction imposed by the restricted rotation speed is released.

2. The oil temperature control method for an internal combustion engine according to claim 1.

4. The threshold value includes a plurality of threshold values, The restricted rotation speed is determined in stages for each threshold.

2. The oil temperature control method for an internal combustion engine according to claim 1.

5. an internal combustion engine for generating electricity that drives a generator in a series hybrid vehicle; an oil temperature sensor for detecting an oil temperature of the internal combustion engine; a controller that controls the rotation speed of the internal combustion engine so that it coincides with a target rotation speed; Equipped with The above controller is comparing the oil temperature of the internal combustion engine with a predetermined threshold value close to an upper allowable temperature limit; If the oil temperature is equal to or higher than the threshold value, the high rotation speed of the internal combustion engine is limited by a regulated rotation speed. Oil temperature control device for internal combustion engines.

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