阅读说明：本技术 一种尿素箱解冻和加热状态的控制方法 (Control method for unfreezing and heating states of urea box ) 是由 杨海飞 陈志超 张金鹤 胡博文 倪银堤 牛彦雷 李�昊 代东波 于 2020-06-24 设计创作，主要内容包括：本发明公开了一种SCR尿素箱解冻和加热状态的控制方法,包括以下步骤：1)判断尿素箱是否需要解冻,若是,当满足解冻的条件后,进行解冻,直至退出解冻状态；2)若尿素箱温度传感器发生故障,则解冻退出条件变更为时间计时方式；3)判断尿素箱是否需要加热,若是,则进行加热,直至退出解冻状态；4)若尿素箱温度传感器发生故障,则使用环境温度作为尿素箱加热状态进入和退出的输入；5)若尿素箱在加热状态时,则报出故障,提示客户进行维修。本发明能排除外部干扰因素,快速、可靠完成SCR系统的解冻加热,从而在尿素箱温度满足国标中关于尿素解冻的技术要求。(The invention discloses a control method for defrosting and heating states of an SCR urea box, which comprises the following steps: 1) judging whether the urea box needs to be unfrozen, if so, unfreezing the urea box after the unfreezing condition is met until the urea box exits from the unfreezing state; 2) if the temperature sensor of the urea box breaks down, the unfreezing exit condition is changed into a time timing mode; 3) judging whether the urea box needs to be heated, if so, heating until the urea box exits from a unfreezing state; 4) if the temperature sensor of the urea box breaks down, the ambient temperature is used as the input of entering and exiting of the heating state of the urea box; 5) and if the urea box is in a heating state, a fault is reported, and a customer is prompted to maintain. The invention can eliminate external interference factors and quickly and reliably finish the unfreezing and heating of the SCR system, thereby meeting the technical requirements on the unfreezing of the urea in the national standard at the temperature of the urea box.)

1. A control method for the unfreezing and heating states of an SCR urea box is characterized in that the urea box is unfreezed and heated by controlling whether cooling water of a diesel engine circulates or not through a water cut-off electromagnetic valve, and the control method is applied to a selective catalytic reduction SCR system consisting of an electronic control unit of the diesel engine, the urea box, a temperature sensor of the urea box, a urea quality sensor and the water cut-off electromagnetic valve and is carried out according to the following steps:

step 1, judging whether the urea box needs to be unfrozen or not according to the current temperature of the urea box, if so, outputting an unfreezing request of the urea box to the diesel engine electronic control unit, and then executing step 2, otherwise, directly executing step 4;

step 2, the electronic control unit of the diesel engine judges whether the unfreezing enabling condition of the urea box is met or not according to the current temperature of cooling water and the current state of a water-cut solenoid valve, if yes, step 3 is executed, and if not, the step 1 is returned to execute;

step 3, outputting a fixed unfreezing duty ratio to the water cut-off solenoid valve, judging whether the unfreezing state of the urea box can be quitted or not according to the state of the temperature sensor of the urea box, if the unfreezing of the urea box is finished, executing the step 4, and if not, returning to the step 2 for execution;

step 4, judging whether the urea box needs to be heated or not according to the current temperature of the urea box, if so, outputting a urea box heating request to the diesel engine electronic control unit, and executing step 5, otherwise, exiting the unfreezing and heating state of the urea box;

step 5, outputting a fixed heating duty ratio to the water-cut electromagnetic valve and heating the urea box;

and 6, in the heating process of the urea box, if the temperature of the urea box is higher than a heating closing threshold value, the urea box is quitted from the heating state, and if the SCR system has a heating fault, the temperature of the urea box is reduced to a unfreezing opening threshold value, a fault maintenance signal is reported.

2. The control method according to claim 1, wherein in step 4, if the urea tank temperature sensor is faulty, the temperature signal sent by the urea quality sensor is used as a basis for determining whether heating is required and whether the heating state can be exited.

3. The control method according to claim 1, wherein the thawing enabled condition is that the diesel engine cooling water temperature is higher than a set threshold value and the water cut solenoid valve is not failed.

4. The control method according to claim 1, wherein whether the thawing of the urea tank is completed is based on:

1) if the urea box temperature sensor has no fault, when the temperature of the urea box is higher than a thawing closing threshold of the urea box, judging that the urea box is thawed, wherein the set thawing closing threshold is higher than 2-3 ℃ of a thawing opening threshold of the urea box;

2) and if the urea box temperature sensor has a fault, when the thawing time of the urea box is greater than a time threshold, determining that the thawing of the urea box is finished, wherein the set time threshold is based on the cooling water temperature when the engine is electrified.

Technical Field

The invention belongs to the field of control over an SCR (selective catalytic reduction) system for post-treatment of a diesel engine, and particularly relates to a control method for unfreezing and heating states of a urea box.

Background

With the implementation of the national six emission legislation on heavy vehicles, there is a clear demand for the low temperature performance of SCR systems, i.e. the manufacturing company should ensure that the urea solution is available within 70 minutes of the start of the vehicle operation at ambient temperature of-17 ℃. When the environmental temperature is lower than the freezing point temperature of urea to minus 11 ℃, particularly after the vehicle is subjected to cold soaking for more than 8 hours, a large amount of urea in the urea box is easy to freeze, and the normal operation of the urea injection function of the SCR system is influenced. Therefore, need to carry out the heating of unfreezing to the SCR system, including urea case, urea pump, urea feed liquor pipe, return liquid pipe, manometer pipe, heat up to the SCR system is all accomplished the heating of unfreezing, just can carry out the urea and spray.

When the SCR system is used for defrosting and heating, the urea solution stored in the urea tank is the most, so that the defrosting and heating are the most difficult, and the defrosting and heating are generally finished at last. If the urea box can not finish unfreezing and heating within the specified time after unfreezing, the diesel engine can discharge unqualified tail gas for a long time, and the requirements of regulations can not be met.

Disclosure of Invention

The invention aims to overcome the defects in the prior art, and provides a control method for the unfreezing and heating states of a urea box, so that external interference factors can be eliminated, the unfreezing and heating of an SCR system can be completed quickly and reliably, and the technical requirements of national standards on the unfreezing and heating of urea can be met.

The invention adopts the following technical scheme for solving the technical problems:

the invention relates to a control method for defrosting and heating states of an SCR (selective catalytic reduction) urea box, wherein the urea box is used for defrosting and heating by controlling whether cooling water of a diesel engine circulates or not through a water-cut electromagnetic valve, and is characterized in that the control method is applied to a selective catalytic reduction SCR system consisting of an electronic control unit of the diesel engine, the urea box, a temperature sensor of the urea box, a urea quality sensor and the water-cut electromagnetic valve, and is carried out according to the following steps:

step 1, judging whether the urea box needs to be unfrozen or not according to the current temperature of the urea box, if so, outputting an unfreezing request of the urea box to the diesel engine electronic control unit, and then executing step 2, otherwise, directly executing step 4;

step 2, the electronic control unit of the diesel engine judges whether the unfreezing enabling condition of the urea box is met or not according to the current temperature of cooling water and the current state of a water-cut solenoid valve, if yes, step 3 is executed, and if not, the step 1 is returned to execute;

step 3, outputting a fixed unfreezing duty ratio to the water cut-off solenoid valve, judging whether the unfreezing state of the urea box can be quitted or not according to the state of the temperature sensor of the urea box, if the unfreezing of the urea box is finished, executing the step 4, and if not, returning to the step 2 for execution;

step 4, judging whether the urea box needs to be heated or not according to the current temperature of the urea box, if so, outputting a urea box heating request to the diesel engine electronic control unit, and executing step 5, otherwise, exiting the unfreezing and heating state of the urea box;

step 5, outputting a fixed heating duty ratio to the water-cut electromagnetic valve and heating the urea box;

and 6, in the heating process of the urea box, if the temperature of the urea box is higher than a heating closing threshold value, the urea box is quitted from the heating state, and if the SCR system has a heating fault, the temperature of the urea box is reduced to a unfreezing opening threshold value, a fault maintenance signal is reported.

In step 4, if the urea tank temperature sensor fails, the temperature signal sent by the urea quality sensor is used as a basis for judging whether heating is required or not and whether the heating state can be exited or not.

The unfreezing enabling condition is that the temperature of the cooling water of the diesel engine is higher than a set threshold value, and the water cut-off electromagnetic valve has no fault.

The basis of whether the unfreezing of the urea box is finished is as follows:

1) if the urea box temperature sensor has no fault, when the temperature of the urea box is higher than a thawing closing threshold of the urea box, judging that the urea box is thawed, wherein the set thawing closing threshold is higher than 2-3 ℃ of a thawing opening threshold of the urea box;

2) and if the urea box temperature sensor has a fault, when the thawing time of the urea box is greater than a time threshold, determining that the thawing of the urea box is finished, wherein the set time threshold is based on the cooling water temperature when the engine is electrified.

Compared with the prior art, the invention has the beneficial effects that:

1. the method can monitor the SCR system in real time, judge which state the urea box is in and switch the state, and accordingly unfreeze and heat the urea box timely and accurately;

2. the invention adopts two control methods of unfreezing and heating, and uses different duty ratios, thereby avoiding frequent and high-strength use of the water-cut electromagnetic valve and protecting the water-cut electromagnetic valve;

3. the invention can play a substitution function when the temperature sensor of the urea box breaks down, and uses the temperature signals of the cooling water temperature and the urea quality sensor as the basis for the urea box to enter and exit the unfreezing and heating states, thereby improving the robustness and reliability of the unfreezing and heating control system of the urea box;

4. the invention can feed back to a terminal client through the electronic control unit of the diesel engine when the thawing and heating have problems, thereby reminding a driver to maintain in time.

Drawings

FIG. 1 is a flow chart of the defrosting heating control of the urea tank according to the invention.

Detailed Description

In the embodiment, the urea box adopts cooling water for unfreezing and heating, and the unfreezing and heating are carried out by controlling whether the cooling water of the diesel engine circulates or not through the water-cut electromagnetic valve; a control method for unfreezing and heating states of an SCR urea box is characterized in that calculation is carried out based on the temperature of the urea box and used as input of the unfreezing and heating states of the urea box, the duty ratio of a water cut-off electromagnetic valve of the urea box is output, and the control method is applied to a selective catalytic reduction SCR system composed of a diesel engine electronic control unit, the urea box, a urea box temperature sensor, a urea quality sensor and a water cut-off electromagnetic valve, wherein the urea box temperature sensor and the urea quality sensor are integrated in the urea box, the water cut-off electromagnetic valve is installed outside the urea box, a temperature module is also arranged in the urea quality sensor and used for correcting the concentration of urea, and values measured by all the sensors are output to the diesel engine electronic control unit, and as shown in figure 1, the control method is:

step 1, in a low-temperature environment, after a vehicle key is powered on, when a diesel engine electronic control unit detects that the current temperature of a urea box is lower than a thawing opening threshold, the set thawing opening threshold is higher than the urea freezing point temperature by 2-3 ℃, and accordingly the diesel engine electronic control unit judges that the urea box needs to be thawed;

step 2, because the urea box needs to be defrosted by cooling water, if the temperature of the cooling water is low, the due unfreezing effect cannot be achieved, the unfreezing is started only when the temperature of the cooling water is required to be increased to a certain set value, such as 55 ℃;

step 3, because thawing needs larger heat, in order to finish thawing as soon as possible, the electronic control unit of the diesel engine needs to output a larger thawing duty ratio, for example, a duty ratio of 95% is set, namely a water-cut electromagnetic valve is opened for 0.95s within 1s, the urea tank is thawed, when the temperature of the urea tank is higher than a thawing closing threshold value, the thawing state is exited, if the temperature sensor of the urea tank fails, a fixed thawing time needs to be set according to the temperature of cooling water during power-on, and when the timer exceeds the time, the thawing state is exited;

step 4, judging whether the urea box needs to be heated or not according to the current temperature of the urea box, and sending a heating request of the urea box when the temperature of the urea box is lower than a heating starting temperature;

step 5, because the energy required by heating is low, in order to reduce the load of the electromagnetic valve, the electronic control unit of the diesel engine outputs a low heating duty ratio to the water-cut electromagnetic valve, for example, the duty ratio of 5% is set to heat the urea box, when the temperature of the urea box is higher than the heating closing temperature, the heating state is exited, and if the temperature sensor of the urea box has a fault, the temperature signal value sent by the urea quality sensor is used as the judgment basis for entering and exiting the heating state;

step 6, when the urea box enters a heating state, the temperature of the urea box is gradually reduced due to the fact that a cooling water pipeline is in a problem or the urea heating capacity is insufficient, when the temperature is as low as a unfreezing opening threshold value of the urea box, a corresponding fault is reported to prompt a customer to overhaul, and under the condition, the SCR system must be guaranteed to be closed before being frozen again and the reverse pumping action is completed;

and 7, considering that some vehicles can always run in areas with higher environmental temperature, in order to prevent the water-break electromagnetic valve from being suddenly blocked and losing efficacy when entering a cold area, the electromagnetic valve needs to be tested for action after the engine is started every time, and if the electromagnetic valve has no effective feedback signal, a fault is reported to prompt a client to maintain as early as possible.

In conclusion, the control method is a quick and reliable unfreezing and heating method for the urea box, and on one hand, the method needs to meet the requirements of regulations and on the other hand, the method aims to unfreeze the urea more thoroughly. For example, in an extremely cold environment, after the defrosting and heating state of the SCR system is finished, urea injection is resumed after urea injection is stopped for one hour, and if the urea injection function can still normally operate, the SCR defrosting and heating control method is reliable and effective.