CN114810302A

CN114810302A - Anti-dismantling diagnosis method for three-way catalytic converter of fuel gas heavy truck

Info

Publication number: CN114810302A
Application number: CN202210262494.5A
Authority: CN
Inventors: 陆静安; 储利民; 李朝阳; 李徐东; 任红云; 吴宇波; 吴昊; 包轶定
Original assignee: Shanghai New Power Automotive Technology Co ltd
Current assignee: Shanghai New Power Automotive Technology Co ltd
Priority date: 2022-03-17
Filing date: 2022-03-17
Publication date: 2022-07-29
Anticipated expiration: 2042-03-17
Also published as: CN114810302B

Abstract

The invention relates to a disassembly-preventing diagnosis method for a three-way catalyst of a fuel gas heavy truck, which is added in an on-board diagnosis system (OBD). in the process of carrying out lean-rich switching on a fuel-air ratio of an engine, rear and front oxygen concentration signals of a catalyst are collected, and according to the condition that the value k of the variation amplitude of the rear and front oxygen concentration or the lag time t of the rear oxygen signal relative to the front oxygen signal is less than a set value, the catalyst is judged to be disassembled, and the disassembly fault of the catalyst is activated. When the catalyst normally works, the change amplitudes of the back oxygen concentration and the front oxygen concentration are similar and only have phase lag, the response of the front oxygen concentration and the back oxygen concentration is changed due to the throttling action after the transition block cheating device is removed, whether the catalyst is removed or not can be determined according to the lag time of a back oxygen signal and the change amplitude values of the front oxygen concentration and the back oxygen concentration, whether the cheating device is added by a user or not is identified, the real-time monitoring function of preventing the catalyst from being removed is realized, and the vehicle emission is prevented from exceeding the standard.

Description

Anti-dismantling diagnosis method for three-way catalytic converter of fuel gas heavy truck

Technical Field

The invention relates to an engine technology, in particular to a disassembly-preventing diagnosis method for a three-way catalytic converter of a fuel gas heavy truck.

Background

The heavy-duty gas vehicle fully implements high-requirement emission standards, and the gas vehicle reduces the emission of various pollutants through the efficient three-way catalyst and meets the low emission requirement. The conversion efficiency of the catalyst is closely related to the content of noble metal in the catalyst, the content of noble metal reaches more than 50 g in order to meet the durability requirement of 70 kilometers for a gas vehicle, and the price of the three-way catalyst is about 3-5 million. With the increasing price of precious metals, part of users remove the three-way catalyst without permission for selling, and various cheating devices are additionally arranged to interfere the diagnosis of an on-board diagnostic system (OBD) on the conversion efficiency of the three-way catalyst, so that the actual emission of vehicles cannot be judged.

The diagnosis method of the heavy gas vehicle-mounted diagnosis system for the conversion efficiency of the three-way catalyst comprises the following steps: and calculating the oxygen storage capacity of the catalyst according to the time difference of oxygen concentration signals of the front oxygen sensor and the rear oxygen sensor of the three-way catalyst, so as to judge the conversion efficiency of the catalyst. A pair of the modified front and back structures of a cheating modified device is shown in figure 1, the left side is a normal working state, and a sensing part is arranged in an exhaust pipe channel to test the oxygen concentration. After cheating modification, a transition block is installed on the back oxygen sensor seat, gas in the transition block is subjected to diffusion exchange with waste gas in an exhaust pipe through a narrow throttling channel at the bottom of the transition block, and the concentration of diffused gas in an induction cavity in the transition block is detected by an induction component. The response of the oxygen concentration after the catalyst is removed and the transition block is installed depends on the inner diameter of the throttling channel of the transition block and the difference between the oxygen concentration inside and outside the throttling channel, under the condition that the difference between the oxygen concentration is large (the oil cut state is switched to the oil filling richer state), the diffusion of the oxygen concentration is only related to the inner diameter of the throttling channel, the calculated value of the oxygen storage after the transition block with the proper throttling inner diameter is installed and is in the same numerical range as the calculated value of the oxygen storage of a fresh catalyst, the existing catalyst efficiency diagnosis strategy cannot identify whether the catalyst is removed, and a new catalyst anti-removal diagnosis strategy needs to be developed.

Disclosure of Invention

The method for diagnosing the disassembly prevention of the three-way catalytic converter for the heavy truck of the gas aims at solving the problem that the existing efficiency diagnosis of the catalytic converter cannot correctly judge the actual emission because a user arbitrarily disassembles the three-way catalytic converter and additionally installs various cheating devices.

The technical scheme of the invention is as follows: a gas heavy truck three-way catalyst anti-dismantling diagnostic method is characterized in that in the process of carrying out lean-rich switching on the fuel-air ratio of an engine, rear and front oxygen concentration signals of a catalyst are collected, and according to the fact that the rear and front oxygen concentration change amplitude value ratio k or the lag time t of the rear oxygen signal relative to the front oxygen signal is smaller than an alarm set value, the catalyst is judged to be dismantled, and the catalyst dismantling fault is activated; wherein the front oxygen concentration change amplitude value phi _ pro is the difference between the front oxygen maximum concentration and the front oxygen minimum concentration during the lean-rich switching period, the rear oxygen concentration change amplitude value phi _ post is the difference between the rear oxygen maximum concentration and the rear oxygen minimum concentration during the lean-rich switching period, and k is phi _ post/phi _ pro; the central points of the front and rear oxygen concentration waveforms during the front and rear oxygen concentration lean shift periods are extracted, and the time difference between the central points is the lag time t of the rear oxygen signal relative to the front oxygen signal.

Further, before the catalyst is judged to be dismantled, firstly, the diagnosis condition detection of the dismantling prevention of the catalyst is carried out: namely, the catalyst is activated to prevent the disassembly diagnosis module when the engine meets the operation condition, and the operation condition of the engine is as follows: the method comprises the steps of starting the engine, running time, water temperature, vehicle speed, environment temperature, front and rear exhaust temperatures of the catalytic converter, bed temperature of the catalytic converter, closed-loop correction coefficient, self-adaptive correction coefficient and steady-state condition, and activating the catalytic converter anti-disassembly diagnosis module when the running condition of the engine is in a set range.

Further, the closed-loop correction coefficient and the adaptive correction coefficient which reflect the state of the air-fuel ratio control system of the engine in the engine running condition are both less than +/-10%.

Further, the steady state conditions among the engine operating conditions are: and when the engine speed fluctuation is more than 30rpm or the intake pressure fluctuation is more than 5kpa, the catalyst disassembly prevention diagnosis is stopped.

Further, the actual value of k is determined according to the ratio of the rear oxygen concentration change amplitude value phi _ post to the front oxygen concentration change amplitude value phi _ pro, and the alarm set value of k is determined according to the oxygen storage characteristic of the selected catalyst.

Further, the actual value of t is determined according to the difference between the rear oxygen concentration phase and the front oxygen concentration phase, and the alarm set value of t is determined according to the oxygen storage characteristic of the selected catalyst.

The invention has the beneficial effects that: the anti-disassembly diagnosis method for the three-way catalyst of the fuel gas heavy truck identifies whether a cheating device is additionally arranged on a user, realizes the anti-disassembly real-time monitoring function of the catalyst, and prevents the vehicle emission from exceeding the standard.

Drawings

FIG. 1 is a schematic diagram comparing the pre-retrofit and post-retrofit configurations of a cheating retrofit device;

FIG. 2 is a flow chart of the disassembly prevention diagnosis method for the three-way catalyst of the fuel gas heavy truck of the invention;

FIG. 3 is a graph showing the response characteristics of the oxygen concentration before and after the normal operation of the catalytic converter and the oxygen sensor according to the present invention;

FIG. 4 is a graph showing the response characteristics of the oxygen concentration of the catalyst and the oxygen sensor of the present invention before and after the cheating means is installed.

Detailed Description

The invention is described in detail below with reference to the figures and specific embodiments. The present embodiment is implemented on the premise of the technical solution of the present invention, and a detailed implementation manner and a specific operation process are given, but the scope of the present invention is not limited to the following embodiments.

The method for preventing the disassembly of the three-way catalyst with the heavy truck is added in an on-board diagnostic system (OBD), the tiny change of the front oxygen-fuel ratio is controlled, the change amplitude of the back oxygen concentration and the change amplitude of the front oxygen concentration are similar and only have phase lag when the catalyst works normally, the response change is caused after the cheating device of the transition block is disassembled and the change amplitude of the back oxygen concentration is far smaller than that of the front oxygen concentration, whether the catalyst is disassembled or not can be determined according to the lag time of a back oxygen signal and the change amplitude values of the front and back oxygen concentrations after the cheating device is assembled, the problem that whether the catalyst is disassembled or not cannot be judged by the existing catalyst diagnostic strategy under the condition of adding the cheating device is solved, the real-time monitoring function of preventing the disassembly of the catalyst is realized, and the over standard of vehicle emission is prevented.

As shown in fig. 2, the diagnosis method for preventing the disassembly of the three-way catalyst for the heavy truck of the gas comprises the following steps:

step one, detecting and judging whether the conditions for carrying out the anti-disassembly diagnosis of the catalyst meet the following conditions: the engine activates the catalyst anti-disassembly diagnostic module when meeting the operating conditions, and the engine operating conditions are as follows: the method comprises the steps of starting an engine, and then carrying out operation time, water temperature, vehicle speed, environment temperature, front and rear exhaust temperatures of a catalyst, bed temperature of the catalyst, closed-loop correction coefficient, self-adaptive correction coefficient, steady-state condition and the like, when the engine is in a set range under the operation condition, activating a catalyst anti-disassembly diagnosis module, and carrying out catalyst anti-disassembly diagnosis under the set working condition of the engine so as to improve the diagnosis precision and eliminate misguidance of diagnosis under other faults or special conditions.

Judging whether the fuel-air ratio control correction coefficient meets the following conditions: the closed-loop correction coefficient and the self-adaptive correction coefficient are less than +/-10%, and the correction coefficients comprehensively reflect the state of the engine air-fuel ratio control system.

Judging whether the steady state condition of the engine is met: the diagnosis is stopped when the fluctuation of the engine speed is more than 30rpm or the fluctuation of the air inlet pressure is more than 5kpa, and the signal stabilization time of the front and rear oxygen sensors is influenced by the fluctuation of the engine working condition.

And step two, as shown in fig. 3 and 4, when the catalyst and the oxygen sensor work normally and the cheating device is installed, and the front and rear oxygen concentration response characteristic diagrams are obtained, the target concentration curve of the selected catalyst in the ideal state of designing the fuel-air ratio is shown as a dot-and-dash line in the diagrams, wherein phi _ ref is a reference fuel-air ratio, phi _ lean is a target lean offset, phi _ rich is a target enrichment offset, the front and rear oxygen concentration response conditions of the actual catalyst in the normal work are shown as a dotted line and a solid line in fig. 3, phi _ pro is a front oxygen concentration change amplitude value, phi _ post is a rear oxygen concentration change amplitude value, and t is a rear oxygen signal lag time. The front oxygen target fuel-air ratio is switched between lean and rich, and the front oxygen concentration and the rear oxygen concentration slightly change from lean to rich; selecting a median target fuel-air ratio phi _ ref as a reference fuel-air ratio according to the characteristics of the catalyst, carrying out lean offset on the basis of the median target fuel-air ratio phi _ ref, wherein the target offset is phi _ lean, carrying out oxygen storage on the catalyst, carrying out enrichment offset on the target fuel-air ratio when the oxygen storage of the catalyst is in a certain degree (the concentration of the post oxygen is reduced to a set value phi _ post _ lean), wherein the target offset is phi _ rich, releasing oxygen from the catalyst, and stopping enrichment when the oxygen release of the catalyst is in a certain degree (the concentration of the post oxygen is increased to a set value phi _ post _ rich). The catalyst in the oxygen storage stage stores a certain oxygen storage value to ensure that the oxygen storage state before oxygen release of the catalyst is consistent, and the catalyst in the oxygen release stage releases a certain oxygen storage value to ensure that the oxygen storage state after oxygen release of the catalyst is consistent.

Calculating the fluctuation amplitude of front and rear oxygen signals and the lag time of rear oxygen relative to front oxygen during the front oxygen target fuel-air ratio lean-rich switching period; and calculating the front oxygen concentration change amplitude value phi _ pro, the rear oxygen concentration change amplitude value phi _ post, the rear and front oxygen concentration change amplitude value ratio k as phi _ post/phi _ pro and the lag time t of the rear oxygen signal in the lean-rich switching period through the front and rear oxygen signals. The front oxygen concentration change amplitude value phi _ pro is the difference between the front oxygen maximum concentration and the front oxygen minimum concentration during the lean-rich switching period, the rear oxygen concentration change amplitude value phi _ post is the difference between the rear oxygen maximum concentration and the rear oxygen minimum concentration during the lean-rich switching period, and the rear-front oxygen concentration change amplitude value ratio k is the rear oxygen concentration change amplitude value phi _ post/front oxygen concentration change amplitude value phi _ pro. The central points of the front and rear oxygen concentration waveforms during the front and rear oxygen concentration lean shift periods are calculated, respectively, and the time difference between the central points is the lag time t of the rear oxygen signal relative to the front oxygen signal.

Step four, judging whether the catalyst is dismantled; and determining whether the catalyst is removed or not according to the amplitude ratio k of the change of the rear and front oxygen concentrations or the lag time t of the rear oxygen signal, namely activating the catalyst removal fault when the amplitude ratio of the change of the rear and front oxygen concentrations is less than a set value (stronger throttling action) or the lag time of the rear oxygen signal is less than the set value (weaker throttling action).

The fuel-air ratio target deviation value phi _ lean/phi _ rich and the target deviation time T in the diagnosis module are related to the characteristics of the catalyst, the ratio of the change amplitude values of the rear oxygen concentration and the front oxygen concentration can be reduced by reducing the target deviation value and the deviation time, and the diagnosis precision of the detachment prevention of the catalyst is improved; when the target offset value and the offset time are too small, the fuel-air ratio cannot complete the lean-rich switching, and the diagnosis cannot be carried out; if the target offset value and the offset time are too large, the change amplitude of the back and front oxygen concentration is close, and the anti-dismantling diagnosis cannot be carried out.

The target offset time T is used to control the oxygen storage and release times, depending on the post-oxygen signal, to stop the lean offset during the oxygen storage period when the post-oxygen concentration is below a set value and to stop the enrichment offset during the release period when the post-oxygen concentration is above the set value.

The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.

Claims

1. A disassembly-preventing diagnosis method for a three-way catalytic converter of a fuel gas heavy truck is characterized in that in the process of carrying out lean-rich switching on a fuel-air ratio of an engine, rear and front oxygen concentration signals of the catalytic converter are collected, and according to the fact that the value k of the amplitude of the change of the rear and front oxygen concentration or the lag time t of the rear oxygen signal relative to the front oxygen signal is smaller than an alarm set value, the catalytic converter is judged to be disassembled, and the catalytic converter is activated to disassemble faults; wherein the front oxygen concentration change amplitude value phi _ pro is the difference between the front oxygen maximum concentration and the front oxygen minimum concentration during the lean-rich switching period, the rear oxygen concentration change amplitude value phi _ post is the difference between the rear oxygen maximum concentration and the rear oxygen minimum concentration during the lean-rich switching period, and k is phi _ post/phi _ pro; the central points of the front and rear oxygen concentration waveforms during the front and rear oxygen concentration lean shift periods are extracted, and the time difference between the central points is the lag time t of the rear oxygen signal relative to the front oxygen signal.

2. The gas heavy truck three-way catalyst disassembly prevention diagnosis method as claimed in claim 1, wherein before the catalyst is judged to be disassembled, the catalyst disassembly prevention diagnosis condition detection is performed: namely, the catalyst is activated to prevent the disassembly diagnosis module under the condition that the engine meets the operation condition, and the engine operation condition is as follows: the method comprises the steps of running time after the engine is started, water temperature, vehicle speed, environment temperature, front and rear exhaust temperatures of a catalyst, bed temperature of the catalyst, closed-loop correction coefficient, self-adaptive correction coefficient and steady-state condition, and activating a catalyst anti-disassembly diagnosis module when the running condition of the engine is in a set range.

3. The gas heavy truck three-way catalyst disassembly prevention diagnostic method as claimed in claim 2, wherein the closed-loop correction coefficient and the adaptive correction coefficient both reflecting the state of the engine air-fuel ratio control system in the engine operating condition are both < ± 10%.

4. The gas heavy truck three-way catalyst disassembly prevention diagnostic method according to claim 2, wherein the steady state conditions in the engine operating conditions are: and when the engine speed fluctuation is more than 30rpm or the intake pressure fluctuation is more than 5kpa, the catalyst disassembly prevention diagnosis is stopped.

5. The gas heavy truck three-way catalyst disassembly prevention diagnosis method as claimed in any one of claims 1 to 4, wherein the actual value of k is determined according to the ratio of a rear oxygen concentration change amplitude value phi _ post to a front oxygen concentration change amplitude value phi _ pro, and the alarm set value of k is determined according to the oxygen storage characteristics of the selected catalyst.

6. The gas heavy truck three-way catalyst disassembly prevention diagnosis method as claimed in any one of claims 1 to 4, wherein the actual value of t is determined according to the difference between the rear oxygen concentration phase and the front oxygen concentration phase, and the alarm set value of t is determined according to the oxygen storage characteristic of the selected catalyst.