Control device for internal combustion engines
The control device for internal combustion engines addresses the challenge of maintaining NOx purification and engine output by implementing output limiting and relaxation processes, effectively managing catalyst temperature to ensure efficient NOx reduction and engine performance.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- TOYOTA JIDOSHA KK
- Filing Date
- 2024-11-07
- Publication Date
- 2026-05-19
AI Technical Summary
Existing internal combustion engines face a challenge in maintaining both NOx purification performance and engine output performance when the selective reduction type catalyst exceeds its optimal temperature, leading to decreased NOx purification rates due to ammonia oxidation.
A control device that implements output limiting and relaxation processes based on catalyst temperature, adjusting engine output to prevent excessive heating and maintain catalyst effectiveness.
The control device achieves balanced NOx purification and engine output performance by dynamically managing engine output to prevent catalyst overheating, ensuring efficient NOx reduction even during high demand scenarios.
Smart Images
Figure 2026082374000001_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to a control device for an internal combustion engine.
Background Art
[0002] As described in Patent Document 1, an internal combustion engine provided with a selective reduction type catalyst for purifying nitrogen oxides (NOx) in exhaust gas in an exhaust passage is known. The selective reduction type catalyst adsorbs ammonia generated from the aqueous urea added to the exhaust gas. Then, the adsorbed ammonia reduces NOx.
Prior Art Documents
Patent Documents
[0003]
Patent Document 1
Summary of the Invention
Problems to be Solved by the Invention
[0004] When the temperature of the selective reduction type catalyst becomes higher than the optimum purification temperature, ammonia is oxidized, resulting in a decrease in the NOx purification rate. Therefore, it is desirable to implement an output limit during high output requirements of the internal combustion engine to suppress excessive high temperature of the selective reduction type catalyst.
[0005] However, when such an output limit is implemented, it becomes difficult to ensure the output performance according to the driver's request. Therefore, it is desired to achieve both NOx purification performance and engine output performance.
Means for Solving the Problems
[0006] The control device for an internal combustion engine that solves the above problems is applied to an internal combustion engine equipped with multiple exhaust purification members, including a selective reduction catalyst, in the exhaust passage. The control device performs output limiting processing and output limiting relaxation processing. The output limiting processing is a process that limits the output of the internal combustion engine when the requested output of the internal combustion engine is greater than or equal to a predetermined determination value, and when the selective reduction catalyst located downstream of the exhaust passage is used as a downstream catalyst, the output limiting relaxation processing is a process that relaxes the output limit imposed by the output limiting processing when the temperature of the downstream catalyst is less than or equal to a predetermined determination value. [Effects of the Invention]
[0007] This internal combustion engine control system can achieve both NOx purification performance and engine output performance. [Brief explanation of the drawing]
[0008] [Figure 1] Figure 1 is a schematic diagram showing the exhaust system of an internal combustion engine in one embodiment. [Figure 2] Figure 2 is a flowchart showing the procedure of processing performed by the control device of the same embodiment. [Modes for carrying out the invention]
[0009] Below, an embodiment in which a control device for an internal combustion engine is applied to a diesel engine mounted on a vehicle will be described with reference to Figures 1 and 2. <Configuration of the exhaust system of an internal combustion engine> As shown in Figure 1, the internal combustion engine 10 is a well-known diesel engine, and the engine output is adjusted by adjusting the amount of fuel supplied to the cylinders.
[0010] Multiple exhaust purification components are provided in the exhaust passage 26 of the internal combustion engine 10 to purify the exhaust gas. More specifically, in the exhaust passage 26, an oxidation catalyst 30 (labeled DOC in Figure 1), a filter 50, a first selective reducing catalyst 41 (labeled SCR1 in Figure 1), and a second selective reducing catalyst 42 (labeled SCR2 in Figure 1) are arranged in series in the direction of the exhaust gas flow. Hereafter, the selective reducing catalyst will be referred to as SCR (Selective Catalytic Reduction). The first selective reducing catalyst 41 will be referred to as the first SCR41, and the second selective reducing catalyst 42 will be referred to as the second SCR42.
[0011] A urea addition valve 230 for adding urea solution to the exhaust gas is provided in the exhaust passage 26 between the filter 50 and the first SCR 41. The oxidation catalyst 30 raises the temperature of the exhaust gas by oxidizing the hydrocarbons contained in the exhaust gas.
[0012] The filter 50 collects particulate matter contained in the exhaust. The first SCR41 and second SCR42 reduce and purify NOx contained in the exhaust gas using a reducing agent. Urea water added from the urea addition valve 230 is converted to ammonia by hydrolysis using the heat of the exhaust gas and is adsorbed onto the first SCR41 and second SCR42. The ammonia adsorbed onto the first SCR41 and second SCR42 then acts as a reducing agent, reducing and purifying the NOx.
[0013] The control device 100 includes a processing circuit 110. The processing circuit 110 includes a CPU that executes processing according to a program and a ROM in which the program is stored. Various controls are performed by the CPU executing the program stored in the ROM.
[0014] The control device 100 receives detection values from various sensors. For example, the control device 100 receives the detection signal from the crank angle sensor 21, which detects the rotation angle of the crankshaft in order to calculate the engine rotation speed NE. The control device 100 receives the detection signal from the intake air volume GA, which is detected by the air flow meter 22. The control device 100 receives the detection signal from the exhaust temperature TH, which is detected by the exhaust temperature sensor 23, which is located upstream of the oxidation catalyst 30. The control device 100 receives the detection signal from the accelerator pedal operation amount sensor 24, which detects the accelerator pedal operation amount ACCP, which is the amount of operation of the accelerator pedal that adjusts the output of the internal combustion engine 10. The control device 100 receives the detection signal from the vehicle speed sensor 25, which detects the vehicle speed SPD.
[0015] The control device 100 calculates the requested output based on the accelerator pedal input amount (ACCP) and vehicle speed (SPD). The control device 100 then controls the engine rotational speed (NE) and engine torque of the internal combustion engine 10 to obtain the requested output.
[0016] <Processing performed by the control unit> Figure 2 shows the procedure of processing performed by the processing circuit 110 of the control device 100. The processing shown in Figure 2 is repeatedly executed at predetermined execution cycles. In the following, the step number of each process is represented by a number preceded by "S".
[0017] When this process is started, the control device 100 determines whether the current requested output is equal to or greater than the steady-state maximum output (S100). The steady-state maximum output is the upper limit of the engine output during steady-state operation and is variably set based on, for example, the engine rotational speed NE and engine torque. More specifically, if the temperature of the SCR becomes excessively high, exceeding the optimal purification temperature (for example, around 400°C), the NOx purification rate decreases due to the oxidation of ammonia. Here, when the internal combustion engine 10 is required to produce high output, the exhaust temperature becomes high, which may cause the SCR to become excessively hot. Therefore, the upper limit of the engine output that can suppress such excessive temperature increases of the SCR is set in advance as the steady-state maximum output.
[0018] In the process of S100, when it is determined that the current required output is greater than or equal to the steady-state maximum output (S100: YES), the control device 100 determines whether the temperature of the downstream SCR is less than or equal to a predetermined determination value A (S110). The temperature of the downstream SCR is the temperature of the downstream catalyst when the SCR arranged downstream of the exhaust passage 26 is used as the downstream catalyst. In the present embodiment, the second SCR 42 arranged at the most downstream of the exhaust passage 26 is used as the downstream catalyst. In the present embodiment, the temperature of the downstream SCR is estimated, but it may also be detected by a sensor. Further, in the determination value A, for example, the maximum temperature of the downstream SCR temperature that can tolerate a decrease in the NOx purification rate due to the high temperature of the SCR is preset.
[0019] In the process of S110, when it is determined that the temperature of the downstream SCR is less than or equal to the determination value A (S110: YES), the control device 100 calculates an output limit relaxation amount (S120). The output limit relaxation amount is a value for changing the value of the steady-state maximum output described above to the side where the engine output increases. For example, by adding the output limit relaxation amount to the steady-state maximum output, the steady-state maximum output is changed to the side where it increases. The output limit relaxation amount is set based on, for example, the temperatures of the first SCR 41 and the second SCR 42, the predicted NOx purification amount, the predicted NOx emission amount from the internal combustion engine 10, and the like.
[0020] Next, the control device 100 executes an output limit relaxation process (S130). In the process of S130, the control device 100 controls the output of the internal combustion engine 10 so as not to exceed the steady-state maximum output changed by the output limit relaxation amount.
[0021] Next, the control device 100 calculates a constraint temperature arrival time (S140). The constraint temperature arrival time is the time from the start of the process of S130 until the temperature of the downstream SCR reaches the determination value A. The control device 100 calculates the constraint temperature arrival time based on, for example, the engine output and the temperature of the downstream SCR.
[0022] Next, the control device 100 determines whether the execution time of the output limit relaxation process is equal to or longer than the restricted temperature arrival time (S150). Then, the control device 100 repeatedly executes the process of S150 until it determines that the execution time of the output limit relaxation process is equal to or longer than the restricted temperature arrival time.
[0023] In the process of S150, when it is determined that the execution time of the output limit relaxation process is equal to or longer than the restricted temperature arrival time (S150: YES), the control device 100 ends the output limit relaxation process (S160). In the process of S160, the control device 100 ends the output limit relaxation process by returning the steady-state maximum output changed by the output limit relaxation amount to the value before the change. When returning the steady-state maximum output to the value before the change, it is preferable to perform a process of gradually returning the steady-state maximum output to the value before the change in order to suppress a sudden change in torque.
[0024] When a negative determination is made in the process of S110 described above, the control device 100 executes an output limit process (S170). The output limit process in the process of S170 is a process of restricting the output of the internal combustion engine 10 so that it does not exceed the steady-state maximum output when the required output of the internal combustion engine 10 is equal to or higher than the steady-state maximum output which is a predetermined determination value. When the process of S170 is executed, the calculation of the output limit relaxation amount described above is not performed. Therefore, in the output limit process in the process of S170, the output of the internal combustion engine 10 is restricted by the value of the steady-state maximum output before being changed by the output limit relaxation amount.
[0025] When the process of S160 or S170 ends, or when a negative determination is made in the process of S100 described above, the control device 100 ends the present process in the current execution cycle.
[0026] <Operations and Effects of the Present Embodiment> The optimum purification temperature of the SCR is lower than the optimum purification temperature of the three-way catalyst, and the reaction rate is slow, so it is necessary to increase the capacity. In addition, since a filter 50 with a large heat capacity is provided on the upstream side of the second SCR 42 which is a downstream catalyst, it also takes time for heat to be transmitted to the second SCR 42.
[0027] Therefore, when multiple exhaust purification members are provided in the exhaust passage 26, there is a time lag between when the engine output increases and when the temperature of the downstream catalyst rises. As a result, NOx purification by the downstream catalyst is possible with the output limit of the internal combustion engine 10 relaxed until the temperature of the downstream catalyst rises to a predetermined temperature.
[0028] Therefore, in this embodiment, even when the requested output of the internal combustion engine 10 is greater than or equal to the steady-state maximum output (S100:YES), the control device 100 executes the above output limit relaxation process (S130) if the temperature of the downstream catalyst is below a predetermined judgment value A (S110:YES). This output limit relaxation process is a process that relaxes the engine output limitation imposed by the output limiting process. Thus, it is possible to achieve both NOx purification performance and engine output performance.
[0029] <Example of changes> 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.
[0030] The process shown in Figure 2 may be performed in at least one of the following cases (a) to (f). (a): When the vehicle user intends to perform the action (e.g., by operating a switch).
[0031] (b): When the vehicle is towing. (c): When there is a large amount of luggage loaded onto the vehicle. (d): When there are many occupants in the vehicle.
[0032] (e): When the vehicle speed SPD is above a predetermined threshold value. (f): When it is detected that the vehicle is traveling on a highway. In the S110 determination process shown in Figure 2, the temperature of the subsequent SCR was determined. Alternatively, the determination process may be performed based on a value correlated with the subsequent SCR temperature. Examples of values correlated with the subsequent SCR temperature include the temperature of the exhaust gas flowing into the SCR and the temperature of the exhaust gas after passing through the SCR.
[0033] In the process shown in Figure 2, the output limit relaxation process terminated when its execution time reached the time required to reach the constraint temperature. Alternatively, the execution time for the output limit relaxation process may be predetermined. The output limit relaxation process may then be terminated once the predetermined execution time has elapsed.
[0034] Furthermore, the output limit relaxation process may be terminated when a value correlated with the downstream SCR temperature reaches a predetermined threshold. Examples of values correlated with the downstream SCR temperature include the temperature of the filter 50, the product of the engine load factor and operating time of the internal combustion engine 10, and the product of the intake air volume GA and exhaust temperature TH.
[0035] In the above embodiment, the second SCR42, located at the downstream end of the exhaust passage 26, was used as the downstream catalyst. However, the downstream catalyst is not necessarily limited to the SCR located at the downstream end of the exhaust passage 26; any SCR located downstream of the exhaust passage 26 is acceptable. For example, the first SCR41 may be used as the downstream catalyst. Alternatively, both the first SCR41 and the second SCR42 may be used as the downstream catalyst.
[0036] The exhaust system of the internal combustion engine 10 shown in Figure 1 is just one example, and other configurations are also possible. For example, an SCR may be supported on the filter 50, and urea solution may be added upstream of the filter 50. Alternatively, another SCR may be provided upstream of the first SCR 41, and urea solution may be added upstream of that additional SCR. The filter 50 may also be omitted. Another SCR may be provided downstream of the second SCR 42. Alternatively, one SCR may be provided downstream of the exhaust passage 26.
[0037] • Although urea solution was recommended, other reducing agents containing ammonia can also be used. [Explanation of symbols]
[0038] 10... Internal combustion engine 21... Crank angle sensor 22... Air flow meter 23... Exhaust temperature sensor 24…Accelerator pedal input sensor 25…Vehicle speed sensor 26... Exhaust passage 30… Oxidation catalyst 41…First-choice reduction catalyst 42…Second-selective reduction catalyst 50…filter 100...Control device 110… Processing circuit 230...Urea-adding valve
Claims
[Claim 1] A control device for an internal combustion engine, which includes a plurality of exhaust gas purification members, including a selective reduction catalyst, in the exhaust passage, The output limiting process and the output limiting relaxation process are executed. The output limiting process is a process that limits the output of the internal combustion engine when the requested output of the internal combustion engine is equal to or greater than a predetermined determination value. When the selective reduction catalyst located downstream of the exhaust passage is considered a downstream catalyst, the output limiting relaxation process is a process that relaxes the output limit imposed by the output limiting process when the temperature of the downstream catalyst is below a predetermined determination value. Control device for internal combustion engines.