Engine control unit

Abstract

To suppress the deterioration of emissions to the extent that it does not cause a lack of driving force in the vehicle. [Solution] An electronic control unit 20 applied to an engine 10 mounted on a vehicle 1 and equipped with an exhaust purification catalyst 18 in the exhaust passage 12 performs output limit control to control the engine output so that it remains below an output limit value during the period until the exhaust purification catalyst 18 has finished warming up. In doing so, the unit calculates an estimated vehicle speed, which is an estimated value of the vehicle speed assuming that the driving resistance is of a predetermined magnitude, based on the engine output. Furthermore, if the actual vehicle speed is lower than the estimated vehicle speed and the discrepancy between the actual vehicle speed and the estimated vehicle speed is large, the unit sets the output limit value to be larger than in other cases.

Description

Technical Field

[0006] ,

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

Background Art

[0002] The engine control device described in Patent Document 1 is configured to suppress deterioration of emissions by restricting the output of the engine during a period until warm-up of an exhaust purification catalyst installed in an exhaust passage is completed.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] When the above output restriction is applied to an engine mounted on a vehicle, there is a risk that the driving force of the vehicle will be insufficient during the output restriction when the vehicle has a large load or is climbing a slope.

Means for Solving the Problems

[0005] The engine control device for solving the above problems is a control device applied to an engine mounted on a vehicle and having an exhaust purification catalyst installed in an exhaust passage, and includes calculating an estimated vehicle speed, which is an estimated value of the vehicle speed when assuming that the running resistance is a predetermined magnitude, based on the engine output; setting an output restriction value to be a larger value when the actual vehicle speed is lower than the estimated vehicle speed and the deviation between the actual vehicle speed and the estimated vehicle speed is large than when not; and controlling the engine output to be below the output restriction value during a period until warm-up of the exhaust purification catalyst is completed.

[0006] Another engine control device that solves the above problems is a control device applied to an engine mounted on a vehicle and equipped with an exhaust purification catalyst in the exhaust passage, and is configured to: calculate an estimated acceleration, which is an estimated value of the vehicle's acceleration assuming that the driving resistance is of a predetermined magnitude, based on the engine output; set an output limit value such that it is greater than the value when the actual acceleration of the vehicle is lower than the estimated acceleration and the discrepancy between the actual acceleration and the estimated acceleration is large; and control the engine output so that it is less than or equal to the output limit value for the period until the exhaust purification catalyst has finished warming up. [Effects of the Invention]

[0007] The above-mentioned engine control device has the effect of suppressing the deterioration of emissions to the extent that it does not cause a shortage of driving force in the vehicle. [Brief explanation of the drawing]

[0008] [Figure 1] This diagram schematically shows the configuration of the engine control device of the first embodiment. [Figure 2] Figure 1 is a flowchart of the output limit setting routine executed by the engine control unit. [Figure 3] Figure 1 is a time chart showing the changes in (a) the cumulative air volume M, (b) the engine output Pe, (c) the actual vehicle speed Vt and estimated vehicle speed Ve, and (d) the deviation rate during cold starting of an engine to which the engine control device shown in Figure 1 is applied. [Figure 4] This is a flowchart of the output limit setting routine executed by the engine control device of the second embodiment. [Modes for carrying out the invention]

[0009] (First Embodiment) The following describes a first embodiment of the engine control device. <Engine control system configuration> First, the configuration of the engine control device of this embodiment will be described with reference to Figure 1. The engine 10 to which the control device of this embodiment is applied is mounted in vehicle 1.

[0010] The engine 10 comprises a combustion chamber 11 for burning the air-fuel mixture, an intake passage 12 which is the path for introducing air into the combustion chamber 11, and an exhaust passage 13 which is the path for discharging exhaust gas from the combustion chamber 11. The intake passage 12 is equipped with an airflow meter 14 for detecting the intake air volume Ga and a throttle valve 15 for adjusting the intake air volume Ga. The engine 10 also comprises an injector 16 for injecting fuel and an ignition device 17 for igniting the air-fuel mixture in the combustion chamber 11 by spark discharge. Furthermore, the exhaust passage 13 of the engine 10 is equipped with an exhaust gas purification catalyst 18 for purifying the exhaust gas produced by combustion in the combustion chamber 11.

[0011] Vehicle 1 is equipped with an electronic control unit 20, which serves as an engine control device for controlling the engine 10. The electronic control unit 20 comprises a processing circuit 21 that performs various processes for engine control, and a storage device 22 that stores programs and data for engine control. The electronic control unit 20 receives detection results from various sensors installed in various parts of Vehicle 1, including the engine 10. In addition to the detection result of the intake air volume Ga from the airflow meter 14 mentioned above, the detection results of the sensors received by the electronic control unit 20 also include engine water temperature Thw, crank angle θc, accelerator opening Acc, and actual vehicle speed Vt. Engine water temperature Thw represents the temperature of the coolant in the engine 10, and crank angle θc represents the rotation angle of the crankshaft, which is the output shaft of the engine 10. Accelerator opening Acc represents the amount the driver operates the accelerator pedal, and actual vehicle speed Vt represents the driving speed of Vehicle 1. The electronic control unit 20 determines the amount of control for the engine 10 based on these detection results, and controls the engine by operating the actuators of the engine 10 according to the determined amount of control. Examples of the amount of control for the engine 10 include the opening degree of the throttle valve 15, the amount of fuel injected by the injector 16, and the ignition timing of the air-fuel mixture by the ignition device 17.

[0012] <Power limiting control during cold starts> During a cold start of the engine 10, the electronic control unit 20 performs output limit control to control the engine output Pe so that it remains below the output limit value LM until the exhaust purification catalyst 18 has finished warming up. In this embodiment, the electronic control unit 20 determines whether the start is a cold start or a warm start based on the engine water temperature Thw at the time of starting the engine 10. If the electronic control unit 20 determines that it is a cold start, it starts output limit control. The electronic control unit 20 continues output limit control until the exhaust purification catalyst 18 has finished warming up. In this embodiment, the electronic control unit 20 determines that the exhaust purification catalyst 18 has finished warming up when the accumulated air amount M is equal to or greater than a preset warm-up determination value Mx. The accumulated air amount M represents the total amount of air used for combustion in the combustion chamber 11 after the engine 10 has started. The electronic control unit 20 calculates the accumulated air amount M by integrating the intake air amount Ga detected by the air flow meter 14.

[0013] Figure 2 shows a flowchart of the output limit setting routine executed by the electronic control unit 20 to set the output limit value LM in output limit control. The electronic control unit 20 repeatedly executes this routine at predetermined control cycles while output limit control is being performed.

[0014] When the electronic control unit 20 starts this routine, it first acquires the total air volume M, engine output Pe, and actual vehicle speed Vt in step S100. The electronic control unit 20 also calculates the engine rotational speed Ne from the detected crank angle θc, and determines the engine output Pe based on the engine rotational speed Ne and the intake air volume Ga.

[0015] Next, in step S120, the electronic control unit 20 sets the value of the standard output limit value LM0 based on the accumulated air volume M. The electronic control unit 20 sets the standard output limit value LM0 such that its value increases as the accumulated air volume M approaches the warm-up judgment value Mx.

[0016] In the subsequent step S130, the electronic control unit 20 calculates an estimated vehicle speed Ve based on the engine output Pe. The estimated vehicle speed Ve represents an estimated value of the vehicle speed when traveling at the current engine output Pe assuming that the running resistance is of a predetermined magnitude. In the storage device 22 of the electronic control unit 20, a map showing the relationship between the engine output Pe and the estimated vehicle speed Ve obtained through experiments or the like is stored. The electronic control unit 20 calculates the estimated vehicle speed Ve by referring to that map.

[0017] The state where the running resistance here is of a predetermined magnitude represents a state where the load weight of the vehicle 1 is a predetermined weight and the vehicle 1 is traveling steadily on a flat road. In the case of this embodiment, for example, a weight slightly heavier than the weight of the maximum number of passengers of the vehicle 1 is set as the predetermined weight.

[0018] In the next step S140, the electronic control unit 20 divides the actual vehicle speed Vt by the estimated vehicle speed Ve and calculates the divided value as the value of the deviation rate. Then, in the subsequent step S150, the electronic control unit 20 determines whether or not the deviation rate is less than or equal to the threshold value X. A positive value slightly smaller than 1 is set as the threshold value X.

[0019] Subsequently, when the electronic control unit 20 determines that the deviation rate exceeds the threshold value X (S150: NO), in step S160, it calculates the value of the standard output limit value LM0 as the value of the output limit value LM as it is. On the other hand, when the electronic control unit 20 determines that the deviation rate is less than or equal to the threshold value X (S150: YES), in step S170, it adds a predetermined additional amount U to the standard output limit value LM0 and calculates the added value as the value of the output limit value LM. Then, after calculating the output limit value LM in step S160 or step S170, the electronic control unit 20 ends the processing of this routine in the current control cycle.

[0020] <Operation of the First Embodiment> The exhaust purification catalyst 18 has a reduced exhaust purification rate until warm-up is completed. Therefore, after a cold start, if the engine 10 is operated at high power during the period until the warm-up of the exhaust purification catalyst 18 is completed and a large amount of exhaust flows into the exhaust purification catalyst 18, there is a risk that unpurified exhaust will be released to the outside air. The electronic control unit 20 executes output limit control during the period until the warm-up of the exhaust purification catalyst 18 is completed. And the electronic control unit 20 suppresses the deterioration of emissions at cold start by controlling the engine output Pe so that it becomes a value below the output limit value LM in this output limit control.

[0021] In the process of FIG. 2 for setting the output limit value LM, the electronic control unit 20 calculates an estimated vehicle speed Ve, which is an estimated value of the vehicle speed when assuming that the running resistance is a predetermined magnitude, based on the engine output Pe (S130). Further, the electronic control unit 20 obtains a deviation rate, which is the ratio of the actual vehicle speed Vt to the estimated vehicle speed Ve (S140). And when the deviation rate exceeds the threshold value X (S150: NO), the electronic control unit 20 sets the value of the standard output limit value LM0 as the value of the output limit value LM (S160). On the other hand, when the deviation rate is less than or equal to the threshold value X (S150: YES), the electronic control unit 20 sets the value obtained by adding the increase amount U to the standard output limit value LM0 as the value of the output limit value LM (S170). A positive value slightly smaller than 1 is set for the threshold value X. Therefore, the case where the deviation rate is less than or equal to the threshold value X means that the actual vehicle speed Vt is lower than the estimated vehicle speed Ve and the deviation between the actual vehicle speed Vt and the estimated vehicle speed Ve is large. Therefore, when the actual vehicle speed Vt is lower than the estimated vehicle speed Ve and the deviation between the actual vehicle speed Vt and the estimated vehicle speed Ve is large, the electronic control unit 20 sets the output limit value LM to be a larger value than in the case where it is not so.

[0022] Figure 3 shows an example of the control mode during cold start of the engine 10. Figure 3(a) shows the change in the cumulative air volume M, Figure 3(b) shows the change in the engine output Pe, Figure 3(c) shows the change in the actual vehicle speed Vt and estimated vehicle speed Ve, and Figure 3(d) shows the change in the deviation rate. In the case of Figure 3, the engine 10 starts at time t0. The electronic control unit 20 starts output limit control of the engine 10 from this time t0. At the following time t2, the cumulative air volume M reaches the warm-up determination value Mx. At this time t2, the electronic control unit 20 determines that the exhaust purification catalyst 18 has finished warming up and terminates the output limit control.

[0023] When vehicle 1 is heavily loaded or climbing a slope, the driving resistance is high, making it difficult to increase vehicle speed. The electronic control unit 20 calculates the estimated vehicle speed Ve, which is an estimated value of the vehicle speed assuming that the driving resistance is of a predetermined magnitude, based on the engine output Pe. When vehicle 1 is running under driving resistance exceeding the predetermined magnitude, the actual vehicle speed Vt will be lower than the estimated vehicle speed Ve. Therefore, if the actual vehicle speed Vt is lower than the estimated vehicle speed Ve, and the discrepancy between the actual vehicle speed Vt and the estimated vehicle speed Ve is large, it is considered that vehicle 1 is running under driving resistance exceeding the predetermined magnitude. In such cases, the driving force required for vehicle 1 to move will also be greater.

[0024] In the case of Figure 3, at time t1 while the output limiting process is being executed, the deviation rate is less than or equal to the threshold X. Up to this time t1, the electronic control unit 20 sets the value of the standard output limit value LM0 as the value of the output limit value LM. Then, from time t1 onward, the electronic control unit 20 sets the value of the output limit value LM as the value of the standard output limit value LM0 plus an additional amount U.

[0025] Figure 3(b) shows the change in engine output Pe when the standard output limit value LM0 is kept set to the output limit value LM even after time t1, indicated by a dotted line. In this case, the engine output Pe is controlled to be less than or equal to the standard output limit value LM0. The standard output limit value LM0 is set as a value that limits the engine output Pe so as to suppress the deterioration of emissions even when the exhaust purification catalyst 18 has not yet warmed up. Therefore, in this case, the driving force generated by the engine 10 to the vehicle 1 may be insufficient to overcome the driving resistance experienced by the vehicle 1.

[0026] On the other hand, Figure 3(b) shows the change in engine output Pe in this embodiment, indicated by a thick solid line. In this embodiment, even when output limit control is being executed, the occurrence of engine output Pe exceeding the standard output limit value LM0 is permitted from time t1 onward.

[0027] <Effects of the First Embodiment> The engine control device of this embodiment provides the following effects. The electronic control unit 20 performs output limit control, controlling the engine output Pe so that it remains below the output limit value LM until the exhaust purification catalyst 18 has finished warming up. Furthermore, the electronic control unit 20 calculates the estimated vehicle speed Ve, which is an estimated value of the vehicle speed assuming that the driving resistance is of a predetermined magnitude, based on the engine output Pe. The electronic control unit 20 then sets the output limit value LM to a larger value than usual when the actual vehicle speed Vt is lower than the estimated vehicle speed Ve, and the discrepancy between the actual vehicle speed Vt and the estimated vehicle speed Ve is large. As a result, when the vehicle 1 is running under high driving resistance, the upper limit of the engine output Pe that can be generated during output limit control is raised higher than usual. Therefore, the engine control device of this embodiment has the effect of suppressing the deterioration of emissions to the extent that it does not cause a shortage of driving force in the vehicle 1.

[0028] (Second Embodiment) Next, a second embodiment of the engine control device will be described. In this embodiment, components common to the above embodiment are denoted by the same reference numerals, and their detailed descriptions are omitted. The engine control devices of this embodiment and the first embodiment differ in the processing content of the output limit value setting routine.

[0029] Figure 4 shows a flowchart of the output limit value setting routine executed by the electronic control unit 20 of this embodiment. The electronic control unit 20 repeatedly executes this routine at predetermined control cycles while output limit control is being performed. The processing in steps S120, S150-S170 of this routine is the same as in the case of Figure 2.

[0030] In this embodiment, when the electronic control unit 20 starts this routine, in step S105 it obtains the accumulated air volume M, the engine output Pe, and the actual acceleration At of the vehicle 1. The actual acceleration At is obtained, for example, as the time derivative of the actual vehicle speed Vt. After that, the electronic control unit 20 performs the processing in step S120 as in the case of Figure 2, and then proceeds to step S135. In step S135, the electronic control unit 20 calculates the estimated acceleration Ae based on the engine output Pe. The estimated acceleration Ae represents the estimated acceleration of the vehicle 1 if it were to run at the current engine output Pe, assuming that the running resistance is of a predetermined magnitude. Then, in the next step S145, the electronic control unit 20 divides the actual acceleration At by the estimated acceleration Ae and calculates the resulting value as the deviation rate. After that, the electronic control unit 20 proceeds to step S150. The processing in the subsequent steps S150 to S170 is the same as in the case of Figure 2.

[0031] When the vehicle is traveling under high rolling resistance, the acceleration of vehicle 1 becomes difficult to increase. Therefore, even if the actual acceleration At is lower than the estimated acceleration Ae calculated as described above, and the discrepancy between the actual acceleration At and the estimated acceleration Ae is large, it can be considered that vehicle 1 is traveling under rolling resistance exceeding a predetermined magnitude. For this reason, even if the discrepancy rate calculated as the ratio of the actual acceleration At to the estimated acceleration Ae is used in step S145 of Figure 4, the determination in step S150 can be made in the same way as in the case of Figure 2. Accordingly, the engine control device of this embodiment provides the same effects as in the first embodiment.

[0032] (Other embodiments) The above embodiment can be implemented with the following modifications. The above embodiment and the following modifications can be combined with each other to the extent that they do not contradict each other technically.

[0033] In the above embodiment, the standard output limit value LM0 is set as a value that increases as the accumulated air volume M approaches the warm-up determination value Mx, thereby easing the limit on engine output Pe in the output limit control as the exhaust purification catalyst 18 warms up. The manner in which the standard output limit value LM0 is set may be changed as appropriate. For example, the standard output limit value LM0 may be set to a fixed value.

[0034] In the above embodiment, the completion of warming up the exhaust gas purification catalyst 18 was determined based on the accumulated air volume M, but the same determination may be made by other means. For example, the completion of warming up the exhaust gas purification catalyst 18 may be determined based on the elapsed time since startup. Alternatively, the temperature of the exhaust gas purification catalyst 18 may be measured or estimated, and the same determination may be made based on the measured or estimated value.

[0035] In step S170 of Figures 2 and 4, the output limit value LM was calculated by adding an additional amount U to the standard output limit value LM0. However, the calculation of the output limit value LM in step S170 may be performed in a different manner as long as the calculated output limit value LM is greater than the standard output limit value LM0. For example, the process in step S170 may be performed by multiplying the standard output limit value LM0 by a coefficient set to a value greater than "1", and then setting the multiplied value as the value of the output limit value LM.

[0036] In step S150 of Figures 2 and 4, if it is determined that the deviation rate is less than or equal to the threshold X, the output limit of the engine 10 may be released. The state in which the output limit is released can be considered as a state in which the maximum output of the engine 10 is set as the value of the output limit LM and output limit control is being performed.

[0037] In the above embodiment, the determination in step S150 in Figures 2 and 4 was made using a deviation rate calculated as the ratio of the actual vehicle speed Vt to the estimated vehicle speed Ve, or the ratio of the actual acceleration At to the estimated acceleration Ae. This determination in step S150 may also be made using the difference between the estimated vehicle speed Ve and the actual vehicle speed Vt, or the difference between the estimated acceleration Ae and the actual acceleration At. [Explanation of symbols]

[0038] 1 vehicle 10 Engines 11 Combustion chamber 12 Intake passage 13 Exhaust passage 14. Airflow meter 15 Throttle valve 16 Injectors 17 Ignition system 18 Exhaust purifying catalyst 20 Electronic control unit 21 Processing Circuit 22 Storage device

Claims

1. A control device applicable to an engine mounted in a vehicle and equipped with an exhaust purification catalyst in the exhaust passage, The estimated vehicle speed, which is an estimated value of the vehicle speed assuming a predetermined magnitude of driving resistance, is calculated based on the engine output, and If the actual vehicle speed is lower than the estimated vehicle speed, and the discrepancy between the actual vehicle speed and the estimated vehicle speed is large, the output limit value shall be set to a larger value than in other cases. During the period until the exhaust gas purification catalyst has warmed up, the engine output is controlled to remain below the output limit value. An engine control device that performs this function.

2. A control device applicable to an engine mounted in a vehicle and equipped with an exhaust purification catalyst in the exhaust passage, The estimated acceleration, which is an estimated value of the vehicle's acceleration assuming a predetermined magnitude of driving resistance, is calculated based on the engine output. If the actual acceleration of the vehicle is lower than the estimated acceleration, and the discrepancy between the actual acceleration and the estimated acceleration is large, the output limit value shall be set to a larger value than in other cases. During the period until the exhaust gas purification catalyst has warmed up, the engine output is controlled to remain below the output limit value. An engine control device that performs this function.

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