CN107762653B - Temperature control system of diesel oxidation catalyst - Google Patents

Abstract

The invention provides a temperature control system of a diesel oxidation catalyst, which comprises: oxidation catalyst, throttle valve, ECU; the ECU increases the exhaust temperature of the diesel engine through exhaust temperature control so as to enable the temperature of the oxidation catalyst to reach the ignition temperature; the exhaust temperature control includes: firstly, the exhaust temperature of the diesel engine is increased by delaying main injection; secondly, the near-rear oil injection quantity and the air inflow regulating quantity are controlled in a feedback mode according to the actual temperature of the inlet of the oxidation catalyst measured by the temperature sensor of the inlet of the oxidation catalyst, when the actual temperature of the inlet of the oxidation catalyst is lower than the target temperature of the inlet of the oxidation catalyst, the air inflow is preferably reduced, and when the actual temperature of the inlet of the oxidation catalyst is higher than the target temperature of the inlet of the oxidation catalyst, the near-rear oil injection quantity is preferably reduced; and (III) finally, controlling the opening of the throttle valve through a throttle valve model to realize the control of the air inflow. The invention can effectively control the exhaust temperature of the engine and reduce the fuel consumption at the same time.

Description

Diesel Engine Oxidation Catalyst Temperature Control System

technical field

The invention relates to the field of diesel engine aftertreatment control, in particular to a temperature control system of an oxidation catalyst DOC.

Background technique

Chinese patent CN103883380A discloses a method for increasing the temperature of the regenerated exhaust gas of the continuous regeneration type diesel particulate filter device. The method is to add a bypass passage connecting the engine intake pipe and the engine cylinder in parallel with the intercooler after the turbocharger, and install a bypass valve at the bypass passage and the branch port of the intercooler to control the intake air of the engine. The direction of the intake air in the pipe. When the DPF is regenerated, the ECU adjusts the opening of the bypass valve according to the upstream temperature of the DOC, and part of the supercharged intake air enters the cylinder without cooling, which increases the intake air temperature, thereby increasing the engine exhaust temperature.

The method for increasing the exhaust temperature of the engine not only increases the complexity of the structure, but also increases the temperature of the intake air when increasing the exhaust temperature. Excessive intake air temperature will affect the cooling effect of the intake air on the engine parts, thereby affecting the engine performance.

The exhaust gas heating method disclosed in Chinese patent CN103883380A is to divide the temperature of the engine into two stages. When the temperature is low, white smoke can be generated and the first stage of heating is carried out. The exhaust temperature is increased by increasing the rear spray to prevent the generation of white smoke. When the temperature exceeds the threshold, a new post injection is added to control the exhaust temperature.

The heating measures used in this patent are all methods recognized in the literature and patents, and the patent does not consider the coupling problem between these heating methods.

SUMMARY OF THE INVENTION

The object of the present invention overcomes the deficiencies in the prior art, and provides a temperature control system for a diesel engine oxidation catalyst, which can effectively solve the coupling problem of different engine heating measures during regeneration, and reduce the fuel consumption while effectively controlling the engine exhaust temperature. , which ensures the regeneration of the diesel particulate filter and improves the fuel economy. The technical scheme adopted in the present invention is:

A temperature control system for an oxidation catalyst of a diesel engine, comprising: an oxidation catalyst, a throttle valve, and an ECU; the throttle valve is connected to the intake port of the diesel engine through an intake manifold, and the exhaust port of the diesel engine is connected to the oxidation catalyst through an exhaust pipe; the ECU is connected to The temperature sensor set at the inlet of the oxidation catalyst; the ECU connects and controls the throttle valve;

The ECU increases the exhaust temperature of the diesel engine through exhaust temperature control, so that the temperature of the oxidation catalyst reaches the light-off temperature;

Exhaust temperature control includes:

(1) First, increase the exhaust temperature of the diesel engine by delaying the main injection;

(2) Then, according to the actual temperature at the entrance of the oxidation catalyst measured by the temperature sensor at the entrance of the oxidation catalyst, the amount of fuel injection and the amount of intake air is controlled by feedback, and when the actual temperature at the entrance of the oxidation catalyst is less than the target temperature at the entrance of the oxidation catalyst, Priority is given to reducing the intake air amount, and when the actual temperature of the oxidation catalyst inlet is greater than the target temperature of the oxidation catalyst inlet, the priority is to reduce the fuel injection amount near the rear;

(3) Finally, the control of the intake air volume is realized by controlling the opening degree of the throttle valve through the throttle valve model.

Further, in the above (2), when the actual temperature at the inlet of the oxidation catalyst is less than the target temperature at the inlet of the oxidation catalyst, and the exhaust temperature of the diesel engine needs to be increased, the target intake air amount is first reduced, and when the target intake air amount is adjusted to the minimum After the limit value, increase the fuel injection amount near the rear.

Further, in the above (2), when the actual temperature at the inlet of the oxidation catalyst is greater than the target temperature at the inlet of the oxidation catalyst, and the exhaust temperature of the diesel engine needs to be reduced, the fuel injection amount near the rear is first reduced, and when the fuel injection amount near the rear is reduced After reaching the minimum limit, increase the target intake air volume.

Further, the adjustment of the intake air volume and the adjustment of the fuel injection volume are carried out within their respective adjustment ranges. Oil volume adjustment range.

Further, the throttle valve model includes a throttle valve model pressure drop model and a throttle valve flow model;

The gas pressure before the throttle valve is calculated through the throttle valve pressure drop model, which includes:

a.) First calculate the target pressure after the throttle valve is obtained;

b.) Then query the resistance coefficient MAP of the throttle valve according to the opening degree of the throttle valve to obtain the resistance coefficient at the throttle valve, and then calculate the pressure of the gas flowing through the throttle valve from the gas flow rate, gas temperature, and target pressure after the throttle valve The gas pressure before the last throttle valve is equal to the pressure drop of the gas flowing through the throttle valve plus the target pressure after the throttle valve; the calculation formula is as follows:

The throttle valve opening is calculated by the throttle valve flow model;

c.) According to the target intake air volume multiplied by the target intake air volume feedback coefficient, the actual required intake air volume through the throttle valve is obtained, and then the throttle valve is calculated according to the gas pressure before the throttle valve and the target pressure after the throttle valve calculated above. The pressure ratio before and after the valve is obtained by querying the correction coefficient MAP of the pressure ratio before and after the throttle valve to obtain the correction coefficient of the pressure ratio before and after the throttle valve; according to the pressure before the throttle valve and the gas temperature, the density correction coefficient corresponding to the standard working condition is obtained;

The required intake air volume is then corrected by the density correction and the pressure ratio correction before and after the throttle valve to obtain the maximum gas flow through the throttle valve;

The maximum gas flow through the throttle valve = the required intake air volume ÷ the throttle valve intake air density correction coefficient ÷ the throttle valve front and rear pressure ratio correction coefficient;

Then according to the maximum gas flow through the throttle valve, query the maximum flow position MAP of the throttle valve pre-calibrated under the standard operating conditions, and obtain the throttle valve opening degree.

Furthermore, the target pressure after the throttle valve = the target intake air amount * 287.1 * intake manifold temperature / (charging efficiency * diesel engine displacement).

Furthermore, the maximum flow position MAP of the throttle valve is obtained by measuring the relationship between the maximum gas flow rate of the throttle valve and the opening degree of the throttle valve under standard operating conditions.

The advantages of the present invention are: by using the present invention, the coupling problem of different engine temperature-raising measures during regeneration can be effectively solved, the fuel consumption can be reduced while the exhaust temperature of the engine is effectively controlled, and the regeneration of the diesel particulate filter is ensured and improved. fuel economy.

Description of drawings

FIG. 1 is a schematic diagram of a diesel engine exhaust gas purification system of the present invention.

FIG. 2 is a schematic diagram of the exhaust gas treatment temperature control system of the present invention.

FIG. 3 is a schematic diagram of the temperature rise adjustment parameters of the diesel engine according to the present invention.

FIG. 4 is a schematic diagram of the control flow of the exhaust gas temperature of the diesel engine according to the present invention.

FIG. 5 is a schematic diagram of calculating the target pressure after the throttle valve of the present invention.

6 is a schematic diagram of a throttle valve pressure drop model of the present invention.

FIG. 7 is a schematic diagram of the throttle valve model position control of the present invention.

Detailed ways

The present invention will be further described below with reference to the specific drawings and embodiments.

FIG. 1 is a typical structural diagram of a diesel engine exhaust gas purification system in the present invention. The diesel engine 1 is provided with a particulate filter 2 (hereinafter referred to as DPF) and an oxidation catalyst 3 (hereinafter referred to as DOC) on the exhaust gas after-treatment system.

The main function of the particle filter 2 is to capture the amount of particles emitted by the diesel engine. When the captured amount reaches a certain level, the regeneration activities are carried out to burn the captured particles, and they are used repeatedly to reduce the impact of particle emissions on the atmosphere. Pollution.

The main function of the oxidation catalyst 3 is to further increase the exhaust gas temperature by oxidizing the diesel in the exhaust gas when its inlet temperature reaches its activation temperature (generally 230°C), so that the particle trap 2 can be regenerated.

By adjusting the variable supercharger 4, the throttle valve 5, and the exhaust gas recirculation system 6 to control the intake air amount, and by delaying the main injection and increasing the near post injection, etc., the exhaust temperature of the diesel engine is increased, so that the inlet temperature of the oxidation catalyst 3 reaches the starting temperature. ignition temperature.

Oxidation catalyst 3 inlet temperature sensor 10 is used for closed-loop control of oxidation catalyst 3 inlet temperature, particle trap 2 inlet temperature sensor 9, used for closed-loop control of particle trap 2 inlet temperature, particle trap 2 outlet temperature The sensor is used to predict the temperature inside the particle trap 2 .

In addition, the diesel engine exhaust gas purification system also includes a diesel engine control system ECU7, which is used to control the normal operation and regeneration of the diesel engine.

Figure 2 is a schematic diagram of the temperature control of the exhaust gas treatment temperature control system; it mainly includes three parts: DOC temperature control controls the inlet temperature of the oxidation catalyst 3 to reach the light-off temperature during regeneration by adjusting the intake air and increasing the near-post injection and other measures, so that HC can be oxidized in the oxidation catalyst 3 to increase the temperature at the outlet of the oxidation catalyst 3; DPF temperature control controls the inlet temperature of the particle trap 2 by increasing the far rear spray to realize the regeneration of soot particles in the particle trap 2; torque Compensation achieves the same torque in normal mode and regeneration mode by adjusting the amount of main injection during regeneration.

Figure 3 is a schematic diagram of the temperature rise adjustment parameters of the diesel engine. The inlet temperature of the oxidation catalyst 3 is controlled by adjusting the intake air amount and increasing the fuel injection amount near the rear to control the exhaust temperature of the diesel engine. The corresponding maximum and minimum values are obtained by looking up the table, so that when the intake air amount and the fuel injection amount are adjusted within the adjustment range, the stable operation of the diesel engine can be ensured and the temperature and temperature required for regeneration can be met. Oxygen content requirements.

FIG. 4 is a schematic diagram of a diesel engine exhaust gas temperature control process. Exhaust temperature is referred to as exhaust temperature in this article; the measures adopted to heat up the exhaust gas of diesel engine are mainly to delay the main injection, reduce the intake air volume, and increase the fuel injection volume near the rear. First, delay the main injection to increase the exhaust temperature of the diesel engine as much as possible while ensuring the stable operation of the diesel engine; then judge whether the actual temperature of the DOC inlet Tact is less than the target temperature of the DOC inlet Ttarget, if the actual temperature of the DOC inlet Tact is less than the target temperature of the DOC inlet Ttarget, then judge Whether the target intake air amount adjustment amount dmtarget is greater than the minimum intake air amount adjustment amount threshold dmmin, if the target intake air amount adjustment amount dmtarget is greater than the intake air amount minimum adjustment amount threshold dmmin, reduce the target intake air amount, otherwise increase the near post injection quantity;

If the actual temperature Tact at the DOC inlet is greater than the target temperature Ttarget at the DOC inlet, it is judged whether the adjustment amount of the fuel injection quantity Qcpost is greater than the minimum adjustment quantity threshold Qcpostmin of the near post injection, and if the adjustment quantity of the fuel injection quantity Qcpost is greater than the minimum adjustment quantity of the near post injection Qcpostmin, reduce the fuel injection amount near the rear, otherwise increase the target intake air amount. Finally, the DOC inlet temperature is controlled to reach the target temperature Ttarget.

FIG. 5 is a schematic diagram of the calculation of the target pressure after the throttle valve. The target pressure after the throttle valve is calculated by the following formula: target pressure after the throttle valve = target intake air volume * 287.1 * intake manifold temperature / (charging efficiency * diesel engine displacement).

Figure 6 is a schematic diagram of a throttle valve pressure drop model. The gas pressure before the throttle is calculated from the throttle pressure drop model. When the gas flows through the throttle valve, there will be a pressure drop at the throttle valve, and its magnitude is related to the throttle valve opening, the gas flow rate, the gas temperature (which can be regarded as equal to the intake manifold temperature), and the target pressure after the throttle valve. First, query the throttle valve resistance coefficient MAP according to the throttle valve opening to obtain the resistance coefficient at the throttle valve, and then calculate the pressure drop of the gas flowing through the throttle valve from the gas flow rate, gas temperature, and target pressure after the throttle valve; finally The gas pressure before the throttle valve is equal to the pressure drop of the gas flowing through the throttle valve plus the target pressure after the throttle valve (that is, the pressure of the intake manifold); the calculation formula is as follows:

FIG. 7 is a schematic diagram of the throttle valve model position control. In general, the flow rate of the gas cannot exceed the speed of sound. The maximum gas mass flow corresponding to a given throttle opening position is the gas mass flow when the flow velocity is close to the speed of sound. Measure the relationship between the maximum gas flow rate of the throttle valve and the opening degree of the throttle valve under standard operating conditions, and obtain the maximum flow position MAP of the throttle valve. The gas flow can be measured by a flow sensor installed in the intake pipe before the throttle valve;

The actual gas flow through the throttle valve can be obtained by correcting the maximum throttle valve flow by using the density correction coefficient and the correction coefficient of the pressure ratio before and after the throttle valve according to the different working conditions and the standard working conditions when measuring the maximum gas flow rate of the throttle valve. Therefore, when the target intake air amount passing through the throttle valve is determined, the opening degree of the throttle valve can be calculated.

The specific method is to first multiply the target intake air amount by the target intake air amount feedback coefficient (the measured value of the intake air amount and the target intake air amount through the closed-loop control to obtain the target intake air amount feedback coefficient) to obtain the actual demand of the engine passing through the throttle valve. Gas volume, and then calculate the pressure ratio before and after the throttle valve according to the previously calculated gas pressure before the throttle valve and the target pressure after the throttle valve. According to the pressure ratio before and after the throttle valve, query the correction coefficient MAP of the pressure ratio before and after the throttle valve to obtain the pressure before and after the throttle valve. ratio correction coefficient; according to the pressure and gas temperature before the throttle valve, the density correction coefficient corresponding to the standard working condition is obtained;

The required intake air volume is then corrected by the density correction and the pressure ratio correction before and after the throttle valve to obtain the maximum gas flow through the throttle valve;

The maximum gas flow through the throttle valve = the required intake air volume ÷ the throttle valve intake air density correction coefficient ÷ the throttle valve front and rear pressure ratio correction coefficient;

Then according to the maximum gas flow through the throttle valve, query the maximum flow position MAP of the throttle valve pre-calibrated under the standard operating conditions, and obtain the throttle valve opening degree.

Claims (7)

1. a diesel engine oxidation catalyst temperature control system, is characterized in that, comprises: oxidation catalyst, throttle valve, ECU; Throttle valve connects diesel engine air inlet by intake manifold, and diesel engine exhaust port is connected by exhaust pipe Oxidation catalyst; ECU is connected to the temperature sensor set at the inlet of the oxidation catalyst; ECU is connected to and controls the throttle valve; The ECU increases the exhaust temperature of the diesel engine through exhaust temperature control, so that the temperature of the oxidation catalyst reaches the light-off temperature; Exhaust temperature control includes: (1) First, increase the exhaust temperature of the diesel engine by delaying the main injection; (2) Then, according to the actual temperature at the entrance of the oxidation catalyst measured by the temperature sensor at the entrance of the oxidation catalyst, the amount of fuel injection and the amount of intake air is controlled by feedback, and when the actual temperature at the entrance of the oxidation catalyst is less than the target temperature at the entrance of the oxidation catalyst, Reduce the intake air amount, when the actual temperature at the inlet of the oxidation catalyst is greater than the target temperature at the inlet of the oxidation catalyst, reduce the amount of fuel injected near the rear; (3) Finally, the control of the intake air volume is realized by controlling the opening degree of the throttle valve through the throttle valve model. 2. The temperature control system of diesel engine oxidation catalyst as claimed in claim 1, characterized in that, In the above (2), when the actual temperature at the inlet of the oxidation catalyst is less than the target temperature at the inlet of the oxidation catalyst, and the exhaust temperature of the diesel engine needs to be increased, the target intake air volume is first reduced, and when the target intake air volume is adjusted to the minimum limit , and then increase the amount of fuel injection near the rear. 3. The temperature control system of diesel engine oxidation catalyst as claimed in claim 1, is characterized in that, In the above (2), when the actual temperature at the inlet of the oxidation catalyst is greater than the target temperature at the inlet of the oxidation catalyst, and the exhaust temperature of the diesel engine needs to be reduced, the fuel injection amount at the near and rear is first reduced, and when the near and rear fuel injection amount is reduced to the minimum limit. After the value is set, increase the target intake air volume. 4. The temperature control system of diesel engine oxidation catalyst as claimed in claim 2 or 3, characterized in that, Both the intake air volume adjustment and the near-rear fuel injection volume adjustment are carried out within their respective adjustment ranges; According to the current working conditions of the diesel engine, that is, the diesel engine speed and the circulating fuel injection quantity, the adjustment range of the intake air quantity and the fuel injection quantity adjustment range are obtained by looking up the table. 5. The temperature control system for a diesel engine oxidation catalyst as claimed in claim 1, 2 or 3, characterized in that, The throttle valve model includes the throttle valve model pressure drop model and the throttle valve flow model; The gas pressure before the throttle valve is calculated through the throttle valve pressure drop model, which includes: a.) First calculate the target pressure after the throttle valve is obtained; b.) Then query the resistance coefficient MAP of the throttle valve according to the opening degree of the throttle valve to obtain the resistance coefficient at the throttle valve, and then calculate the pressure of the gas flowing through the throttle valve from the gas flow rate, gas temperature, and target pressure after the throttle valve The gas pressure before the last throttle valve is equal to the pressure drop of the gas flowing through the throttle valve plus the target pressure after the throttle valve; the calculation formula is as follows:

The throttle valve opening is calculated by the throttle valve flow model; c.) According to the target intake air volume multiplied by the target intake air volume feedback coefficient, the actual required intake air volume through the throttle valve is obtained, and then the throttle valve is calculated according to the gas pressure before the throttle valve and the target pressure after the throttle valve calculated above. The pressure ratio before and after the valve is obtained by querying the correction coefficient MAP of the pressure ratio before and after the throttle valve to obtain the correction coefficient of the pressure ratio before and after the throttle valve; according to the pressure before the throttle valve and the gas temperature, the density correction coefficient corresponding to the standard working condition is obtained; The required intake air volume is then corrected by the density correction and the pressure ratio correction before and after the throttle valve to obtain the maximum gas flow through the throttle valve; The maximum gas flow through the throttle valve = the required intake air volume ÷ the throttle valve intake air density correction coefficient ÷ the throttle valve front and rear pressure ratio correction coefficient; Then according to the maximum gas flow through the throttle valve, query the maximum flow position MAP of the throttle valve pre-calibrated under the standard operating conditions, and obtain the throttle valve opening degree. 6. The temperature control system of diesel engine oxidation catalyst as claimed in claim 5, characterized in that, Target pressure after throttle = target intake air volume * 287.1 * intake manifold temperature / (charging efficiency * diesel engine displacement). 7. The temperature control system of diesel engine oxidation catalyst according to claim 5, wherein, The maximum flow position of the throttle valve, MAP, is obtained by measuring the relationship between the maximum gas flow rate of the throttle valve and the opening degree of the throttle valve under standard operating conditions.

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