Exhaust System Temperature Estimation Device

Abstract

To improve energy saving performance of an exhaust system temperature estimation device while keeping accuracy in the estimation of an exhaust system temperature.SOLUTION: An exhaust system temperature estimation device comprises: temperature detection means 11 which is installed on an exhaust system of an engine 2 and detects a temperature TUP of an installation location; and state detection means 12 which detects a parameter λ indicating a combustion state of the engine 2. The exhaust system temperature estimation device also has calculation means 10 which executes: first calculation to calculate a first estimated temperature T1 of the exhaust system, while the engine 2 is in operation, at a location different from the installation location by referring to the temperature TUP and the parameter λ; and second calculation to calculate a second estimated temperature T2 of the exhaust system, while the engine 2 is stopped, by referring not to the parameter λ but to the temperature TUP. The calculation means 10 reduces calculation frequency or calculation time of the second calculation in a state where the engine 2 is stopped as a condition to restart the engine 2 gets severer.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an exhaust system temperature estimation device for estimating the temperature of an exhaust system of an engine (internal combustion engine).

Background Art

[0002] Conventionally, a technique for estimating the exhaust system temperature using the detection value of a sensor provided in the exhaust system of an engine is known. For example, when estimating the temperature of a catalyst interposed in an exhaust passage, a method of estimating the catalyst temperature using a heat balance model of the catalyst and the measured temperature on the downstream side of the catalyst is known. In addition, techniques for estimating the temperature of exhaust gas using the element temperature or impedance of an air-fuel ratio sensor are also known (see, for example, Patent Documents 1 to 3).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0004] The exhaust system temperature during engine operation changes according to, for example, the combustion state of the engine and the reaction state of the catalyst. On the other hand, the exhaust system temperature during engine stoppage gradually decreases according to the elapsed time since the engine stopped and is not affected by the combustion state of the engine or the reaction state of the catalyst. Therefore, it is conceivable to estimate the exhaust system temperature using different methods during engine operation and stoppage.

[0005] However, while the engine is stopped, since it is not necessary to control the combustion temperature or the catalyst temperature of the engine, depending on the accuracy of the estimation calculation, power and computing power may be wasted and become useless. On the other hand, if the estimation of the exhaust system temperature during engine stoppage is simply prohibited, the exhaust system temperature immediately after the engine restarts cannot be correctly grasped, and the controllability of the engine and the catalyst deteriorates.

[0006] One of the objectives of this case was devised in view of the above problems, and is to provide an exhaust system temperature estimation device that can improve energy-saving performance while maintaining the estimation accuracy of the exhaust system temperature. Note that, not limited to this objective, the operational effects derived from each configuration shown in the "Mode for Carrying Out the Invention" described later, which are operational effects not obtainable by the conventional technology, can also be positioned as other objectives of this case.

Means for Solving the Problems

[0007] This case can be realized as the aspects or application examples disclosed below. The disclosed exhaust system temperature estimation device solves at least a part of the above problems. The disclosed exhaust system temperature estimation device is provided in the exhaust system of the engine, and includes temperature detection means for detecting the temperature at the installation location, state detection means for detecting a parameter representing the combustion state of the engine, and calculation means for executing a first calculation for calculating a first estimated temperature of the exhaust system at a position different from the installation location with reference to the temperature and the parameter when the engine is operating, and executing a second calculation for calculating a second estimated temperature of the exhaust system with reference to the temperature without referring to the parameter when the engine is stopped. The calculation means reduces the calculation frequency or calculation time of the second calculation as the conditions for restarting the engine become stricter when the engine is in a stopped state.

Effects of the Invention

[0008] According to the disclosed exhaust system temperature estimation device, the energy saving performance can be improved while maintaining the estimation accuracy of the exhaust system temperature.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Mode for Carrying Out the Invention

[0010] [1. Vehicle] The exhaust system temperature estimation device as an example is applied to the vehicle 1 shown in FIG. 1. This vehicle 1 is a plug-in hybrid vehicle that can run using the engine 2 and the motor 3 as drive sources. The engine 2 is an internal combustion engine such as a gasoline engine or a diesel engine, and drives a rotating shaft by burning a mixture of fuel and air in a combustion chamber. The driving force generated by the engine 2 is used to drive the drive wheels of the vehicle 1, and can also be used to generate electric power by a generator (not shown). The generated electric power of the generator is charged to the battery 7 described later.

[0011] The motor 3 is a motor generator (an electric motor and a generator combined) that has a function of driving drive wheels with the power of the battery 7 and a function of charging the battery 7 with regenerative power generated by using the inertial rotation of the drive wheels. The battery 7 is a secondary battery such as a lithium-ion secondary battery or a nickel-metal hydride battery, and can also be charged by an external charging facility (external charging). The operating states of the engine 2, the motor 3, and the generator are selectively used or used in combination according to, for example, the driving state of the vehicle 1 or the operation of the driver. Information regarding the operating states of the engine 2 and the motor 3 is transmitted to the arithmetic unit 10. Further, the charge rate (SOC, State Of Charge) of the battery 7 is calculated by, for example, a battery management device built into the battery 7, and the information is transmitted to the arithmetic unit 10.

[0012] In the exhaust system of the engine 2, an exhaust manifold 4 (exhaust manifold), a catalyst 5, and a filter 6 are provided in order from the upstream side. The exhaust manifold 4 is an exhaust pipe that connects between the engine 2 and the catalyst 5. When the engine 2 has a plurality of cylinders built therein, it is formed in a shape (manifold shape) that merges the exhaust gases discharged from each cylinder. The catalyst 5 is a device including a catalyst for purifying exhaust gas, and is, for example, an oxidation catalyst device, a three-way catalyst device, a trap catalyst device, or the like. The filter 6 is a device that filters particulate matter contained in the exhaust gas, and is, for example, a DPF (diesel particulate filter) or a GPF (gasoline particulate filter). The filtered particulate matter can be incinerated inside the filter 6 according to the temperature and components of the exhaust gas.

[0013] A temperature sensor 11 is installed in the exhaust flow path connecting the catalyst 5 and the filter 6. The temperature sensor 11 is installed in the exhaust system of the engine 2 and is one of the temperature detection means for detecting the temperature of the installation location. Such temperature detection means may be provided, for example, in an exhaust flow path upstream of the catalyst 5 or in an exhaust flow path downstream of the filter 6. The temperature sensor 11 of the present embodiment detects the upstream temperature T of the filter, which is the temperature of the exhaust gas flowing into the filter 6, and transmits the information to the arithmetic unit 10. UP

[0014] The air-fuel ratio sensor 12 for detecting the air-fuel ratio λ, which is a parameter corresponding to the air-fuel ratio of the air-fuel mixture introduced into the cylinder of the engine 2, is provided in the ekimani 4. The air-fuel ratio sensor 12 is one of the state detection means for detecting the parameter λ representing the combustion state of the engine 2. Further, an air flow sensor 13 for acquiring information on the flow rate F (mass flow rate) of the exhaust gas discharged from the engine 2 is provided in the intake system or the exhaust system of the engine 2.

[0015] The air-fuel ratio sensor 12 detects, as physical quantities corresponding to the air-fuel ratio of the air-fuel mixture introduced into the cylinder of the engine 2, for example, the amount of oxygen and the amount of carbon dioxide contained in the exhaust gas, and outputs signals corresponding thereto. The air-fuel ratio sensor 12 of the present embodiment is a linear air-fuel ratio sensor (LAFS) and has a structure in which a solid electrolyte is coated with a porous material (rate-determining layer) that rate-determines the diffusion of the exhaust gas. In the air-fuel ratio sensor 12, the electromotive force generated by the movement of oxygen ions in the solid electrolyte is measured, and a predetermined process is performed so that the value of the electromotive force has a linear relationship with the air-fuel ratio and is output. If the air-fuel ratio corresponding to the electromotive force measured here is defined as the "measured air-fuel ratio", the air excess ratio λ of the engine 2 corresponds to the value obtained by dividing the measured air-fuel ratio by the theoretical air-fuel ratio. The air-fuel ratio sensor 12 of the present embodiment executes such an operation internally to output the air excess ratio λ and transmits the information to the arithmetic unit 10.

[0016] Inside the air-fuel ratio sensor 12, a heater 15 (warming-up means) for maintaining the temperature of the sensor element within a predetermined active temperature range (for example, 700 to 800 °C) is built in. The energizing current of the heater 15 is adjusted by PWM (Pulse Width Modulation) control. For example, when it is desired to quickly raise the temperature of the sensor element, the duty ratio of the energizing current is set to a large value. On the other hand, after the temperature of the sensor element has risen to a certain extent and it is desired to maintain that temperature, the duty ratio of the energizing current is set to a small value.

[0017] The air flow sensor 13 shown in FIG. 1 is installed in the intake system of the engine 2 to measure the flow velocity, temperature, and pressure of the intake air. Based on these parameters, the intake air flow rate is calculated. Further, the exhaust gas flow rate F is calculated by adding the fuel addition amount to the intake air flow rate. When the air flow sensor 13 is installed in the exhaust system, the exhaust gas flow rate F can be directly calculated based on the flow velocity, temperature, and pressure of the exhaust gas. Note that the value of the flow rate F may be calculated inside the air flow sensor 13 or by the arithmetic unit 10. In addition, the vehicle 1 is provided with a vehicle speed sensor 14 that outputs a parameter corresponding to the vehicle speed V. The vehicle speed sensor 14 calculates the vehicle speed V based on, for example, the angular velocity of the wheels. The information on the vehicle speed V is transmitted to the arithmetic unit 10. Note that the value of the vehicle speed V may be calculated by the arithmetic unit 10.

[0018] [2. Arithmetic Unit] The arithmetic unit 10 (arithmetic means) is a computer (ECU, Electronic Control Unit) having a function of estimating the temperature of the exhaust system at a position different from at least the installation location of the temperature sensor 11. The arithmetic unit 10 incorporates a processor (central processing unit), a memory (main memory), a storage device (storage), an interface device, etc., not shown, and these are connected to each other via an internal bus so as to be communicable. The content of the determination and control performed by the arithmetic unit 10 is recorded and stored in the memory as firmware or an application program. When the program is executed, the content of the program is expanded in the memory space and executed by the processor.

[0019] As shown in FIG. 1, an engine 2, a motor 3, a battery 7, a temperature sensor 11, an air-fuel ratio sensor 12, an air flow sensor 13, and a vehicle speed sensor 14 are connected to the arithmetic unit 10 of the present embodiment. Based on the information transmitted from these various devices, the arithmetic unit 10 estimates the exhaust system temperature of the engine 2 (for example, the temperature of the exhaust gas discharged from the engine 2, the temperature of the exhaust gas at various locations in the exhaust system, the temperature of various components installed in the exhaust system, etc.). The arithmetic unit 10 of the present embodiment estimates the catalyst temperature and the ekimani temperature (exhaust system temperature) using different methods during the operation and stop of the engine 2.

[0020] When the engine 2 is operating, the arithmetic unit 10 executes a first calculation to calculate first estimated temperatures T1 and T3 for each of the catalyst temperature and the ekimani temperature. The first calculation is a calculation that refers to both the filter upstream temperature T detected by the temperature sensor 11 and the air excess ratio λ detected by the air-fuel ratio sensor 12 when calculating the first estimated temperatures T1 and T3. The values of the air excess ratio λ representing the combustion state of the engine 2 are reflected in the first estimated temperatures T1 and T3 calculated by the first calculation. UP On the other hand, when the engine 2 is stopped, the arithmetic unit 10 executes a second calculation to calculate second estimated temperatures T2 and T4 for each of the catalyst temperature and the ekimani temperature. The second calculation is a calculation that refers to the filter upstream temperature T detected by the temperature sensor 11 without referring to the air excess ratio λ detected by the air-fuel ratio sensor 12 when calculating the second estimated temperatures T2 and T4. Since the second calculation is executed when the engine 2 is stopped, the value of the air excess ratio λ representing the combustion state of the engine 2 is not reflected in the second estimated temperatures T2 and T4. However, the period during which the second calculation is performed is up to when the second estimated temperatures T2 and T4 and the filter upstream temperature T become almost equal (until the difference between the second estimated temperatures T2 and T4 and the filter upstream temperature T becomes equal to or less than a predetermined value). The second calculation ends when the second estimated temperatures T2 and T4 and the filter upstream temperature T become almost equal.

[0021] When the engine 2 is stopped, the arithmetic unit 10 executes a second calculation to calculate second estimated temperatures T2 and T4 for each of the catalyst temperature and the ekimani temperature. The second calculation is a calculation that refers to the filter upstream temperature T detected by the temperature sensor 11 without referring to the air excess ratio λ detected by the air-fuel ratio sensor 12 when calculating the second estimated temperatures T2 and T4. UP Since the second calculation is executed when the engine 2 is stopped, the value of the air excess ratio λ representing the combustion state of the engine 2 is not reflected in the second estimated temperatures T2 and T4. However, the period during which the second calculation is performed is up to when the second estimated temperatures T2 and T4 and the filter upstream temperature T become almost equal (until the difference between the second estimated temperatures T2 and T4 and the filter upstream temperature T becomes equal to or less than a predetermined value). The second calculation ends when the second estimated temperatures T2 and T4 and the filter upstream temperature T become almost equal. UP When the engine 2 is stopped, the arithmetic unit 10 executes a second calculation to calculate second estimated temperatures T2 and T4 for each of the catalyst temperature and the ekimani temperature. The second calculation is a calculation that refers to the filter upstream temperature T detected by the temperature sensor 11 without referring to the air excess ratio λ detected by the air-fuel ratio sensor 12 when calculating the second estimated temperatures T2 and T4. UP Since the second calculation is executed when the engine 2 is stopped, the value of the air excess ratio λ representing the combustion state of the engine 2 is not reflected in the second estimated temperatures T2 and T4. However, the period during which the second calculation is performed is up to when the second estimated temperatures T2 and T4 and the filter upstream temperature T become almost equal (until the difference between the second estimated temperatures T2 and T4 and the filter upstream temperature T becomes equal to or less than a predetermined value). The second calculation ends when the second estimated temperatures T2 and T4 and the filter upstream temperature T become almost equal. UP When the second estimated temperatures T2 and T4 and the filter upstream temperature T become almost equal, the second calculation ends.

[0022] In the "during operation of engine 2" in this embodiment, it includes an engine running mode in which vehicle 1 is driven using only engine 2, and an engine combined mode (parallel mode, series mode) in which vehicle 1 is driven using both engine 2 and motor 3. Also, in the "during stop of engine 2" in this embodiment, it includes an EV mode in which vehicle 1 is driven using only motor 3, and a stopped state in which the main power supply of vehicle 1 is cut off. Note that the EV mode of this embodiment includes an EV normal mode and an EV priority mode. The EV priority mode is a mode configured such that the start of engine 2 is suppressed compared to the EV normal mode (that is, it is difficult for engine 2 to start). These EV normal mode and EV priority mode will be described later.

[0023] When engine 2 is in a stopped state, the arithmetic unit 10 is configured to reduce the arithmetic frequency or arithmetic time of the second arithmetic as the conditions for restarting engine 2 become stricter. Conversely, when engine 2 is in a stopped state, the arithmetic frequency or arithmetic time of the second arithmetic is increased as the conditions for restarting engine 2 become looser. For example, when the SOC of battery 7 at the time of stop of engine 2 is high, it is considered that the possibility of subsequently requiring a restart of engine 2 is lower compared to when the SOC is low (that is, there is a high possibility that engine 2 will remain stopped for some time). Therefore, the arithmetic unit 10 reduces the arithmetic frequency of the second arithmetic or ends the second arithmetic early to suppress waste of power and arithmetic capabilities. Conversely, when the SOC of battery 7 at the time of stop of engine 2 is low, since there is a high possibility that engine 2 will restart subsequently, the arithmetic frequency of the second arithmetic is increased or the second arithmetic is continued as long as possible to ensure the temperature estimation accuracy immediately after engine 2 restarts.

[0024] Specific numerical values are given as follows. Assume that the operation frequency of the first operation is, for example, the frequency at which it is executed at a cycle of 100 [ms] (the number of operations per unit time is 10 [times / s]). In contrast, the operation frequency of the second operation is controlled to be the frequency at which it is executed at a cycle of at least 100 [ms] or more, and the stricter the conditions for restarting the engine 2 are, the longer the cycle (for example, at a cycle of 100 to 1000 [ms]) it is executed. Also, when reducing the operation time of the second operation, a predetermined value (the threshold value of the difference between the second estimated temperatures T2, T4 and the filter upstream temperature T) related to the end condition of the second operation may be increased. UP And the difference threshold).

[0025] Examples of the above "conditions for restarting the engine 2" include the SOC of the battery 7, as well as conditions such as the driving mode of the vehicle 1, vehicle speed V, battery temperature, and the frequency of accelerator and brake operations by the driver. For example, in existing hybrid vehicles, there is a known technology that enables the selection of the engine 2 restart conditions in the EV mode (the mode of traveling only with the driving force of the motor 3) from among a plurality of types of conditions. Specifically, there is a known hybrid vehicle in which the occupant can select either the EV normal mode or the EV priority mode as the EV mode.

[0026] In the EV priority mode, as shown in FIG. 2, compared with the EV normal mode, the conditions for vehicle speed V and load (for example, physical quantities set according to required torque, intake air volume, accelerator opening, etc.) for restarting the engine 2 are set more strictly. In FIG. 2, the area below the left of the solid line represents the driving area where the EV normal mode is maintained, and the area below the left of the broken line represents the driving area where the EV priority mode is maintained. The solid line means the boundary between the EV normal mode and the engine combined mode (parallel mode, series mode), and the broken line means the EV priority mode andIt means the boundary with the engine combined mode (parallel mode, series mode). Here, the area below the solid line is included in the area below the dashed line. That is, in the EV priority mode, engine 2 is less likely to be used in combination than in the EV normal mode, and there is a high possibility that engine 2 remains stopped. Therefore, when the driving mode of vehicle 1 is the EV priority mode, the operation frequency of the second operation is reduced, or the second operation is terminated early to suppress waste of power and computing power.

[0027] Further, the arithmetic unit 10 is such that the smaller the deviation between the upstream filter temperature T UP and the first estimated temperatures T1 and T3, the smaller the operation frequency or operation time of the second operation. This is because if the deviation between the upstream filter temperature T UP at the time when engine 2 stops and the first estimated temperatures T1 and T3 is small, the period until the second estimated temperatures T2 and T4 and the upstream filter temperature T UP become almost the same value is shortened. As a result, power and computing power are easily conserved, and the energy saving performance is improved.

[0028] The first operation related to the estimation of the catalyst temperature is executed based on the following formula 1. The subscript (n) in formula 1 represents the current value of the repeatedly executed operation, and the subscript (n-1) represents the previous value. Also, A in formula 1 is a temperature correction value, which is set according to the air excess ratio λ detected by the air-fuel ratio sensor 12. B in formula 1 is a running wind correction value, which is set based on the flow rate F derived from the detection value of the air flow sensor 13 and the vehicle speed V derived from the detection value of the vehicle speed sensor 14. In this embodiment, the product of the first correction coefficient B1 set according to the flow rate F and the second correction coefficient B2 set according to the vehicle speed V is set as the running wind correction value B. The first correction coefficient B1 and the second correction coefficient B2 will be described later. The current value T 1(n) of the first estimated temperature T1 is the previous value T UP of the upstream filter temperature T UP(n-1) and the previous value A (n-1) of the air-fuel ratio correction value A (in other words, the previous value λ (n-1)From the sum with the air-fuel ratio correction value A set from (n-1) (In other words, the previous value of the flow rate F and It is calculated as a value obtained by subtracting the running wind correction value B) set from the previous value of the vehicle speed V.

[0029]

Number

[0030] The second calculation related to the estimation of the catalyst temperature is executed based on the following formula 2. B' in formula 2 is the running wind correction value at the time of engine stop, and is set based on the temperature decrease rate that changes with the passage of time and the vehicle speed V detected by the vehicle speed sensor 14. The current value T of the second estimated temperature T2 2(n) is the catalyst temperature T when the engine 2 stops 1(m) (m: the timing when the engine 2 stops) as the initial value, and the second estimated temperature T 2 the previous value T 2(n-1) From the previous value B' of the running wind correction value B' at the time of engine stop (n-1) (In other words, the temperature decrease rate and It is calculated as a value obtained by subtracting the running wind correction value B') set from the previous value of the vehicle speed V. In this embodiment, the product of the third correction coefficient B3 set according to the passage of time and the second correction coefficient B2 set according to the vehicle speed V is set as the running wind correction value B' at the time of engine stop.

[0031]

Number

[0032] The first calculation related to the estimation of the exhaust manifold temperature is executed based on the following Equation 3. D in Equation 3 is the running wind correction value. The current value T of the first estimated temperature T3 3(n) is calculated by subtracting the previous value D of the running wind correction value D from the previous value T of the filter upstream temperature T UP (in other words, UP(n-1) the running wind correction value D set from the previous value V of the vehicle speed V (n-1) ). the previous value of the flow rate F and The previous value V of the vehicle speed V (n-1)

[0033]

Equation

[0034] The second calculation related to the estimation of the ekimani temperature is executed based on the following Equation 4. The current value T of the second estimated temperature T4 4(n) is the ekimani temperature T when the engine 2 stops 3(m) (m: the timing when the engine 2 stops) as the initial value, and the second estimated temperature T 4 the previous value T 4(n-1) from of the previous value D’ of the running wind correction value D’ (D’ is the product of the third correction coefficient D3 and the second correction coefficient D 2, which is set according to the passage of time) and (n-1) (in other words,[[]] the passage of time and the previous value V of the vehicle speed V (n-1) is calculated as a value obtained by subtracting the set running wind correction value D’). Note that the third correction coefficient D3 has a characteristic of decreasing as the time t elapses.

[0035]

Equation

[0036] Also, when the engine 2 is stopped, the arithmetic unit 10 has a function of PWM - controlling the heater 15 to warm up the air - fuel ratio sensor 12 before the condition for restarting the engine 2 is satisfied. For example, assume that during the stop of the engine 2, the SOC of the battery 7 gradually decreases and approaches a predetermined charge rate (lower - limit SOC) for restarting the engine 2. The arithmetic unit 10 calculates the difference between the SOC of the battery 7 and the predetermined charge rate, and when this difference becomes less than the predetermined charge - rate difference, it energizes the heater 15 at a predetermined duty ratio to heat the sensor element of the air - fuel ratio sensor 12.

[0037] At this time, when the elapsed time since the engine 2 stopped is less than the predetermined time, the possibility that the air - fuel ratio sensor 12 is wetted is low. Therefore, compared with the case where the elapsed time is longer than the predetermined time, the duty ratio for heating is increased. As a result, it is possible to quickly reach the active - temperature range of the sensor element without the risk of damaging the sensor element. Note that such a control function of the heater 15 may be realized by incorporating control means (for example, a processor and a memory) in the heater 15 itself.

[0038] [3. Function] [A. Estimation of Catalyst Temperature] Fig. 5 is a graph showing the temporal changes in the upstream temperature T of the filter UP (detected value) and the catalyst temperature (estimated value). Before time t1, the engine 2 is operating, and the driving mode of the vehicle 1 is, for example, the parallel mode or the series mode. At this time, the upstream temperature T of the filter UP is gradually rising. In the arithmetic unit 10, a first calculation related to the estimation of the catalyst temperature is executed, and a first estimated temperature T1 is estimated based on Equation 1. The first estimated temperature T1 is estimated to be a temperature higher than the upstream temperature T of the filter UP .

[0039] At time t1, the engine 2 stops. The engine 2 stops when a predetermined stop condition is satisfied (for example, when the SOC has risen sufficiently or the vehicle speed V has decreased to a predetermined speed or less), or when the occupant disconnects the main power supply of the vehicle 1. At this time, in the arithmetic unit 10, the first calculation is switched to a second calculation, and a second estimated temperature T2 is estimated based on Equation 2. Further, the arithmetic unit 10 determines the degree of strictness of the conditions for restarting the engine 2 when the engine 2 stops.

[0040] For example, it is determined whether the SOC of the battery 7 at time t1 (or around that time) is equal to or higher than a predetermined SOC. If it is equal to or higher than the predetermined SOC, it is determined that "the conditions for restarting the engine 2 are strict (that is, the situation where the restart of the engine 2 is less likely to be required)". On the other hand, if the SOC of the battery 7 is less than the predetermined SOC, it is determined that "the conditions for restarting the engine 2 are loose (that is, the situation where the restart of the engine 2 is more likely to be required)".

[0041] Alternatively, it is determined whether the driving mode of vehicle 1 after time t1 is the EV priority mode or the EV normal mode. If it is the EV priority mode, it is determined that "the conditions for restarting engine 2 are strict (that is, it is a situation where the possibility of restarting engine 2 is low)". On the other hand, if the driving mode of vehicle 1 is the EV normal mode, it is determined that "the conditions for restarting engine 2 are loose (that is, it is a situation where the possibility of restarting engine 2 is high)".

[0042] When the conditions for restarting engine 2 are strict, the arithmetic unit 10 reduces the arithmetic frequency and arithmetic time of the second arithmetic, and suppresses the waste of power and arithmetic ability. On the other hand, when the conditions for restarting engine 2 are loose, the arithmetic frequency and arithmetic time of the second arithmetic are increased compared to the case where it is not so, and the temperature estimation accuracy is ensured. Also, the arithmetic unit 10 at the time when the engine 2 stops (time t 1 ) The deviation between the upstream filter temperature T UP and the first estimated temperature T1 is smaller, the arithmetic frequency or arithmetic time of the second arithmetic is reduced.

[0043] The upstream filter temperature T after time t1 UP gradually decreases. Also, the second estimated temperature T2 calculated by the second arithmetic changes so as to approach the upstream filter temperature T UP . The second arithmetic continues until the above-mentioned arithmetic time elapses or the difference between the second estimated temperature T2 and the upstream filter temperature T UP becomes less than or equal to a predetermined value, based on the stop time of engine 2. After time t2 when the second arithmetic ends, only the detection of the upstream filter temperature T UP continues, and the second estimated temperature T2 is regarded as the same value as the upstream filter temperature T UP .

[0044] Then, at time t4, immediately before the conditions for restarting the engine 2 are satisfied, PWM control for warming up the air-fuel ratio sensor 12 is started, and the heater 15 is energized at a predetermined duty ratio. The timing at which the PWM control is started is, for example, the timing when the difference between the SOC of the battery 7 and a predetermined charge rate (lower limit SOC) becomes less than a predetermined charge rate difference. Alternatively, the PWM control may be started at the timing when a passenger gets into the parked vehicle 1. By warming up the air-fuel ratio sensor 12 at least before restarting the engine 2, the detection accuracy of the air-fuel ratio sensor 12 is improved, and consequently, the accuracy of the first calculation immediately after the start of the engine 2 is enhanced.

[0045] If the elapsed time from time t1 to time t4 is less than a predetermined time, not much time has passed since the engine 2 stopped, and there is a low possibility that the element of the air-fuel ratio sensor 12 is wet (waterlogged) by the condensed water of the exhaust gas. Therefore, compared with the case where the elapsed time is equal to or more than the predetermined time, the duty ratio of the current energized to the heater 15 is set to a larger value. Thereby, it becomes possible to reach the active temperature range of the sensor element temperature at an early stage without the risk of damaging the sensor element. Also, at time t5, the conditions for restarting the engine 2 are satisfied, and the engine 2 starts. After this, the filter upstream temperature T UP gradually rises. In the arithmetic unit 10, a first calculation related to the estimation of the catalyst temperature is executed, and a first estimated temperature T1 is estimated based on Equation 1.

[0046] [B. Estimation of Exhaust Manifold Temperature] FIG. 6 is a graph showing the temporal variations of the filter upstream temperature T UP (detected value) and the exhaust manifold temperature (estimated value). Before time t1 when the engine 2 is operating, in the arithmetic unit 10, a first calculation related to the estimation of the exhaust manifold temperature is executed, and a first estimated temperature T3 is estimated based on Equation 3. The first estimated temperature T3 is the filter upstream temperature T UPIt is estimated to be at a lower temperature than that. On the other hand, when the engine 2 stops at time t1, the first calculation is switched to the second calculation, and a second estimated temperature T4 is estimated based on Equation 4. Further, when the engine 2 stops, the arithmetic unit 10 determines the degree of strictness of the conditions for restarting the engine 2.

[0047] When the conditions for restarting the engine 2 are strict, the arithmetic unit 10 reduces the calculation frequency and calculation time of the second calculation to suppress waste of power and calculation ability. On the other hand, when the conditions for restarting the engine 2 are loose, the calculation frequency and calculation time of the second calculation are increased as compared with the case where the conditions are not so, to ensure temperature estimation accuracy. Further, the arithmetic unit 10 at the time when the engine 2 stops (time t 1 ) Filter upstream temperature T UP The smaller the deviation between the filter upstream temperature T and the first estimated temperature T3, the smaller the calculation frequency or calculation time of the second calculation.

[0048] The second estimated temperature T4 calculated by the second calculation changes so as to approach the filter upstream temperature T UP . The second calculation continues until the above calculation time elapses or the difference between the second estimated temperature T4 and the filter upstream temperature T UP becomes less than or equal to a predetermined value, based on the stop time of the engine 2. After the time t3 when the second calculation ends, only the detection of the filter upstream temperature T UP continues, and the second estimated temperature T4 is regarded as the same value as the filter upstream temperature T UP . Note that the time t3 when the second calculation of the exhaust manifold temperature ends does not necessarily coincide with the time t2 when the second calculation of the catalyst temperature ends. Also, at time t4, PWM control for warming up the air-fuel ratio sensor 12 is started, and the duty ratio of the current supplied to the heater 15 is controlled. Further, at time t5, the engine 2 restarts, and the filter upstream temperature T UP gradually rises. In the arithmetic unit 10, the first calculation related to the estimation of the exhaust manifold temperature is executed, and the first estimated temperature T3 is estimated based on Equation 3.

[0049] [4. Effects] (1) In the above embodiments, a temperature sensor 11 (temperature detection means), an air-fuel ratio sensor 12 (state detection means), and an arithmetic unit 10 (arithmetic means) are provided. When the engine 2 stops, the arithmetic unit 10 decreases the arithmetic frequency or arithmetic time of the second arithmetic as the conditions for restarting the engine 2 become stricter. On the other hand, as the conditions for restarting the engine 2 become looser, the arithmetic frequency or arithmetic time of the second arithmetic is increased. With such a configuration, it is possible to improve the energy-saving performance while maintaining the estimation accuracy of the exhaust system temperature.

[0050] For example, during the stop of the engine 2, since it is not necessary to control the combustion temperature or catalyst temperature of the engine 2, power and computing power may be wasted by executing the second arithmetic. In particular, in a situation where it is presumed that the engine 2 has remained stopped for a long time, the exhaust system temperature converges to a temperature corresponding to the ambient temperature around it, so the second arithmetic itself may become wasted. On the other hand, by setting the arithmetic frequency and arithmetic time of the second arithmetic according to the "likelihood of the engine 2 restarting", it is possible to calculate the second estimated temperatures T2 and T4 while preventing unnecessary arithmetic. As a result, it becomes possible to accurately grasp the exhaust system temperature immediately after the engine 2 restarts, and the controllability of the engine 2 and the catalyst 5 can be improved.

[0051] (2) The arithmetic unit 10 according to the above embodiment decreases the arithmetic frequency or arithmetic time of the second arithmetic as the deviation between the filter upstream temperature T detected by the temperature sensor 11 when the engine 2 stops UP and the first estimated temperatures T1 and T3 becomes smaller. With such a configuration, power and computing power can be conserved, and the energy-saving performance can be improved. Conversely, when the deviation between the filter upstream temperature T UP and the first estimated temperatures T1 and T3 is large, by increasing the arithmetic frequency or arithmetic time of the second arithmetic, the second estimated temperature T 2 ,T the estimation accuracy of 4 can be improved.

[0052] (3) The arithmetic unit 10 according to the above embodiment has, at the longest, the second estimated temperatures T2 and T4 and the filter upstream temperature T detected by the temperature sensor 11UP The second operation is executed until they become equal. With such a configuration, unnecessary second operations after the second estimated temperatures T2 and T4 converge to the upstream filter temperature T can be prevented, and energy-saving performance can be improved. In particular, the power consumption (standby power) of the battery 7 when the vehicle 1 is stopped can be reduced. UP

[0053] (4) In the second operation, the arithmetic unit 10 according to the above embodiment calculates the second estimated temperatures T2 and T4 by correcting the upstream filter temperature T with the running wind correction value B which is a parameter according to the vehicle speed V. With such a configuration, the second estimated temperatures T2 and T4 with high accuracy can be calculated in consideration of the decrease in the exhaust system temperature due to the running wind. Therefore, the estimation accuracy of the second estimated temperatures T2 and T4 can be improved. UP

[0054] (5) The arithmetic unit 10 according to the above embodiment is applied to the vehicle 1 having an EV normal mode and an EV priority mode. When the EV priority mode is selected when the engine 2 stops, this arithmetic unit 10 reduces the operation frequency or operation time of the second operation as compared with the case when the EV normal mode is selected. Thus, in the EV priority mode in which the conditions for restarting the engine 2 are set strictly, by reducing the operation frequency and operation time of the second operation, waste of power and computing ability can be suppressed, and energy-saving performance can be improved. On the other hand, in the EV normal mode in which the conditions for restarting the engine 2 are relatively loose, by increasing the operation frequency and operation time of the second operation, the temperature estimation accuracy immediately after the engine 2 restarts can be ensured.

[0055] (6) The arithmetic unit 10 according to the above embodiment decreases the arithmetic frequency or arithmetic time of the second arithmetic as the SOC of the battery 7 is higher when the engine 2 stops. In this way, in a battery state where the engine 2 is less likely to restart, by reducing the arithmetic frequency and arithmetic time of the second arithmetic, waste of power and arithmetic capabilities can be suppressed, and energy-saving performance can be improved. On the other hand, in a battery state where the engine 2 is more likely to restart, by increasing the arithmetic frequency and arithmetic time of the second arithmetic, the estimation accuracy of the temperature immediately after the engine 2 restarts can be ensured.

[0056] (7) In the above embodiment, when the engine 2 is stopped, a heater 15 (warming-up means) for heating the air-fuel ratio sensor 12 is provided before the conditions for restarting the engine 2 are satisfied. With such a configuration, the sensor element built in the air-fuel ratio sensor 12 can be quickly heated up, and the estimation accuracy of the first estimated temperatures T1 and T3 immediately after the engine 2 starts can be improved.

[0057] (8) The heater 15 according to the above embodiment starts heating the air-fuel ratio sensor 12 when the SOC of the battery 7 approaches a predetermined charge rate (lower limit SOC) at which the engine 2 should be restarted. With such a configuration, the detection accuracy of the filter upstream temperature T UP used in the first arithmetic executed after the engine 2 restarts can be improved, and the estimation accuracy of the first estimated temperatures T1 and T3 can be improved.

[0058] (9) The heater 15 according to the above embodiment increases the duty ratio for heating the air-fuel ratio sensor 12 when the elapsed time since the engine 2 stopped is less than a predetermined time compared to when the elapsed time is equal to or more than the predetermined time. When the elapsed time since the engine 2 stopped is less than the predetermined time, the possibility that the air-fuel ratio sensor 12 is waterlogged is low, and even if the duty ratio is increased, there is almost no risk of damage (waterlogging crack) due to a sudden change in temperature. Therefore, the temperature of the sensor element can be quickly brought to the active temperature range without the risk of damage to the sensor element.

[0059] [5. Modification Example] The above embodiments are merely illustrative and are not intended to exclude various modifications and applications of technologies not explicitly stated in this embodiment. Each configuration of this embodiment can be implemented with various modifications without departing from their gist. Also, they can be selected as appropriate according to needs, or combined as appropriate.

[0060] In the above embodiment, the exhaust system temperature estimation device applied to the vehicle 1 was illustrated, but the application target of this case is not limited to the vehicle 1. As long as it is a system in which the exhaust system temperature is estimated at least when the engine 2 is stopped, the same control as the above embodiment can be applied. Specifically, ships, plants, power generation facilities, etc. equipped with the engine 2 can be the application targets of this case. Also in these application targets, when the engine 2 stops, the more stringent the conditions for restarting the engine 2 are, the more the calculation frequency or calculation time of the second calculation is reduced, thereby suppressing waste of power and calculation ability. Therefore, similar to the above embodiment, the energy-saving performance can be improved while maintaining the estimation accuracy of the exhaust system temperature.

[0061] In the above embodiment, the state detection means (air-fuel ratio sensor 12) for detecting the air excess ratio λ as a parameter representing the combustion state of the engine 2 was illustrated, but it is also possible to use an oxygen concentration sensor, a carbon dioxide concentration sensor, etc. as sensors having a similar function. Also, in the above embodiment, the temperature detection means (temperature sensor 11) interposed in the exhaust flow path connecting the catalyst 5 and the filter 6 was illustrated, but the installation location of the temperature sensor 11 may be set upstream of the catalyst 5 or downstream of the filter 6.

Explanation of Reference Numerals

[0062] 1 Vehicle 2 Engine 3 Motor 4 Exhaust Manifold 5 Catalyst 6 Filter 7 Battery 10 Arithmetic Unit (Arithmetic Means) 11 Temperature sensor (temperature detection means) 12 Air-fuel ratio sensor (condition detection means) 13 Airflow sensor 14 Vehicle speed sensor 15 Heater (warming-up means) T1 First estimated temperature T2 Second estimated temperature T3 First estimated temperature T4 Second estimated temperature T UP Upstream temperature of the filter λ Air excess ratio F Flow rate V Vehicle speed SOC State of charge A Air-fuel ratio correction value B Running wind correction value B1 First correction coefficient B2 Second correction coefficient B3 Third correction coefficient C Temperature correction value D Running wind correction value D1 First correction coefficient D2 Second correction coefficient D3 Third correction coefficient

Claims

1. Temperature detection means installed in the exhaust system of the engine for detecting the temperature at the installation location, State detection means for detecting a parameter representing the combustion state of the engine, When the engine is operating, a first calculation is executed to calculate a first estimated temperature of the exhaust system at a position different from the installation location with reference to the temperature and the parameter, and when the engine is stopped, a second calculation is executed to calculate a second estimated temperature of the exhaust system at the position different from the installation location with reference to the temperature without referring to the parameter over a predetermined calculation time, and calculation means for performing the second calculation, The calculation means reduces the calculation frequency or the calculation time of the second calculation as the condition for restarting the engine is stricter when the engine is stopped. An exhaust system temperature estimation device, characterized in that.

2. The calculation means reduces the calculation frequency or the calculation time of the second calculation as the deviation between the temperature detected by the temperature detection means and the first estimated temperature at the time when the engine is stopped is smaller. The exhaust system temperature estimation device according to claim 1, characterized in that.

3. The calculation means executes the second calculation until the second estimated temperature and the temperature detected by the temperature detection means become equal at the longest. The exhaust system temperature estimation device according to claim 1 or 2, characterized in that.

4. The calculation means calculates the second estimated temperature by correcting the temperature with a parameter according to the vehicle speed in the second calculation. The exhaust system temperature estimation device according to any one of claims 1 to 3, characterized in that.

5. An exhaust system temperature estimation device applied to a vehicle equipped with the engine and a motor, The driving modes of the vehicle include an EV normal mode in which the vehicle is driven by the motor with the engine stopped, and an EV priority mode in which conditions for restarting the engine are set more strictly compared to the EV normal mode. When the EV priority mode is selected when the engine stops, the arithmetic means reduces the arithmetic frequency or the arithmetic time compared to when the EV normal mode is selected. The exhaust system temperature estimation device according to any one of claims 1 to 4, characterized by the above.

6. The higher the charging rate of the battery in which electric power for driving the motor is stored, the more the arithmetic means reduces the arithmetic frequency or the arithmetic time. The exhaust system temperature estimation device according to claim 5, characterized by the above.

7. When the engine is stopped, a warm-up means for heating the state detection means is provided before the conditions for restarting the engine are satisfied. The exhaust system temperature estimation device according to any one of claims 1 to 6, characterized by the above.

8. The warm-up means starts the heating when the battery charging rate approaches a predetermined charging rate at which the engine should be restarted. The exhaust system temperature estimation device according to claim 7, characterized by the above.

9. The warm-up means increases the duty ratio for the heating when the elapsed time since the engine stopped is less than a predetermined time compared to when the elapsed time is equal to or more than the predetermined time. The exhaust system temperature estimation device according to claim 7 or 8, characterized by the above.

Images