Design of an electronic purification device for automobile exhaust

Won: Second Prize in the Second Shenzhen-Hong Kong Technology Innovation Competition & Hangsheng Cup Automotive Electronics Application Solution Competition

Tao Xianfang 2010-12-1

1. Acceptance Speech

Compared with the goods on the counter in the store, he looks very ugly; but compared with the transistor invented by Shockley, he is not inferior. He is not a product yet, he only represents the birth of a new technology; perhaps in the future, he will enter the museum of history like the transistor invented by Shockley. His birth is not to show people his beauty and beauty, but to benefit mankind. The "Automobile Exhaust Electronic Treatment Device" technology of this invention will free people from the suffering of automobile exhaust pollution. 2. A problem that mankind urgently needs to solve As of March 2010, the number of motor vehicles in China was about 192 million, of which more than 70 million were cars, and it continued to maintain a rapid growth momentum. It is estimated that by the end of 2010, it will exceed 75 million, with an average annual increase of 17%. While the number of cars is growing strongly, China's annual gasoline consumption has reached 55 million tons. After gasoline is burned in the car engine, most of the substances are converted into toxic gases and discharged into the air, making air pollution more and more serious.

Automobile exhaust pollutants mainly include: carbon monoxide, hydrocarbons, nitrogen oxides, sulfur dioxide, smoke particles (certain heavy metal compounds, lead compounds, black smoke and oil mist), odor (formaldehyde, etc.). At present, automobile exhaust has become the "culprit" of urban air pollution. In some cities, automobile exhaust pollution has accounted for 80% of air pollution sources. Due to automobile exhaust pollution, many cities have become unbearable. People can no longer see the blue sky. The turbid air makes the visibility less than 200 meters in broad daylight. Not only does it increase traffic accidents, but it also makes people depressed, have difficulty breathing, and proliferate various diseases, seriously affecting people's health.

For the sake of human health, solving the problem of automobile exhaust pollution, that is, the problem of automobile exhaust purification and treatment, has become an urgent problem that humans need to solve.

My purpose in participating in the Hangsheng Cup Automotive Electronics Application Solutions Competition is to showcase my technical concept to all those who are concerned about the issue of automobile exhaust pollution - a technical solution that can achieve automobile exhaust purification, or an automobile exhaust purification device.

3. An electronic automobile exhaust purification device

At present, there are many forms of automobile exhaust purification devices, such as: the commonly used three-way catalyst purifier, the multi-catalyst purifier, and the ozone purifier, the ozone plus water vapor purifier, and the ozone plus catalyst purifier.

However, these existing technologies have their own shortcomings. Although the three-way catalyst purifier and the multi-catalyst purifier play a certain role in the absorption of hydrocarbons, carbon monoxide and nitrogen oxides, they have little effect on the absorption of other smoke particles. In addition, the service life of the catalyst is generally short and needs to be replaced frequently, which is costly. In addition, the catalyst generally contains rare heavy metals, and active heavy metals are toxic to the human body. Therefore, the recovery of toxic substances after the catalyst is used is also a troublesome matter. The ozone plus water purifier has a complex structure and is bulky. It also needs to change the water frequently, which is costly and inconvenient to use. There is no obvious improvement in the technical performance of the ozone plus catalyst purifier and the three-way catalyst purifier, but the cost has increased a lot, and there are also many shortcomings.

In view of the shortcomings of the current automobile exhaust purification devices, the automobile exhaust electronic purification device of the present invention not only avoids many technical deficiencies of the above-mentioned automobile exhaust purification devices, but also further enhances the automobile exhaust purification processing capacity.

The automobile exhaust purification device of the present invention (patent application number: 201010261026.3) is an automobile exhaust electronic purification device that uses high-voltage static electricity to ionize and charge the smoke particles in automobile exhaust (waste gas), and then attracts and collects the charged smoke particles through a strong electric field. Since the electric field force can penetrate the atomic structure of a substance, the strong electric field can ionize or polarize the molecules, thereby destroying the molecular structure of the substance, so that the molecular structure or mixture of harmful gas substances in automobile exhaust is broken and converted into non-toxic substances.

By using this automobile exhaust electronic purification device, harmful gases and smoke particles in automobile exhaust can be very effectively attracted and collected, and carbon monoxide in the exhaust gas can be converted into carbon dioxide, and then the carbon dioxide can be decomposed into oxygen and carbon substances, so that the harmful smoke particles in the automobile exhaust are firmly adsorbed and solidified on the smoke collecting plate in the automobile exhaust electronic purification device. Then, after the harmful smoke waste collected on the smoke collecting plate is accumulated to a certain thickness, it is ignited between the electrodes under the action of the strong electric field force, so that the harmful smoke waste that has been solidified on the smoke collecting plate falls off and is discharged, thereby reducing exhaust gas pollution, purifying the environment, and benefiting human health.

The working principle of the dust collecting plate is very similar to that of electrocoagulation or electroplating, except that the dielectric between the two electrodes in the electrocoagulation or electroplating tank is the electrolyte, while the dielectric between the dust collecting plates is the charged exhaust gas particles. Under the action of a strong electric field, the charged exhaust gas particles will also conduct electricity like the electrolyte, but the conductivity and potential gradient of the two are quite different. When current flows through the electrolyte, the positively charged electrolyte will run to the negative plate, and the negatively charged electrolyte will run to the positive plate. Therefore, electrocoagulation or electroplating is a process of ion deposition, which uses electrodes to pass current to make metal adhere to the surface of an object.

According to this principle, in the smoke collecting plate, the charged smoke material is under the action of the strong electric field, and the exhaust smoke particles will be easily deposited and attached to the surface of the charged smoke collecting plate. Therefore, compared with other automobile exhaust purifiers, this automobile exhaust electronic purification device is not only simple in structure but also very effective in automobile exhaust purification.

The electronic purification device for automobile exhaust gas of the present invention mainly consists of three parts: a bar grid structure or a grid structure with a positive high voltage anode plate, a group of mutually insulated smoke collecting plates with positive and negative high voltages, and a high voltage power supply. The bar grid structure or the grid structure with a positive high voltage anode plate is installed in front of the smoke collecting plate and fixed in a shell with the smoke collecting plate by insulating materials. The anode plate and the cathode plate in the smoke collecting plate are also isolated by insulating materials and fixed in the same shell. The high voltage power supply has two groups of high voltage power outputs, one group is used for the bar grid structure or the grid structure anode plate, and the other group is used for the smoke collecting plate. The negative poles of the two groups of high voltage power outputs are connected together and connected to the cathode plate in the smoke collecting plate. The bar grid structure or the grid structure with a positive high voltage anode plate is called a first high voltage anode plate, a group of positive poles of the high voltage power supply connected to it is called a first high voltage anode, the anode plate in the smoke collecting plate is called a second high voltage anode plate, and another group of positive poles of the high voltage power supply connected to it is called a second high voltage anode.

Figures 1, 2, and 3 are respectively a structural diagram, an electrical connection diagram, and an electrical schematic diagram of a high-voltage switching power supply for an electronic purification device for automobile exhaust. In Figures 1, 2, and 3, "1" is the first high-voltage anode plate, which is connected to the first high-voltage anode (HV1) in the DC switching high-voltage power supply in Figure 3 and is insulated from other components. "200" is a smoke collection plate assembly, which is composed of multiple cathode plates and multiple anode plates. "21" is the cathode plate in the smoke collection plate assembly, which is connected to the cathode in the DC switching high-voltage power supply in Figure 3. "22" is the anode plate in the smoke collection plate assembly, also called the second high-voltage anode plate, which is connected to the second high-voltage anode (HV2) in the DC switching high-voltage power supply in Figure 3.

When exhaust gas is discharged from the exhaust pipe of a car, since the exhaust gas is basically uncharged, that is, at a "0" potential, the uncharged exhaust gas, driven by the pressure difference, must first pass through the middle of the grid of the first high-voltage anode plate. The first high-voltage anode plate is a positively charged plate, and there is a very strong electric field around it. When an object approaches it, a corona discharge will be generated. At this time, the object will emit electrons to the anode plate, making the object positively charged. Especially in a high-temperature environment, the work function of the object to emit electrons is much smaller than that under normal temperature conditions, which greatly enhances the ability of the object to emit electrons to the first high-voltage anode plate. Some objects that are not easy to emit electrons will also produce polarized charging under the action of strong electric field forces, that is, the charge in the object must also be redistributed, so that the end of the object close to the first high-voltage anode plate is negatively charged and the other end is positively charged.

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Oxygen can be easily polarized or ionized in a strong electric field. After emitting electrons, oxygen will be positively charged (becoming O+2). Positively charged oxygen can easily recombine with polarized charged oxygen to produce ozone (O3), and ozone can easily combine with carbon monoxide (CO) to produce carbon dioxide (CO2), turning it into a non-toxic gas.

When charged gas or charged exhaust gas particles pass through the smoke collecting plate, due to the strong electric field between the anode plate and the cathode plate of the smoke collecting plate, the positively charged gas or positively charged exhaust gas particles are easily attracted to the cathode plate, and the negatively charged gas or negatively charged exhaust gas particles will also be easily attracted to the anode plate, so that the anode plate and the cathode plate of the smoke collecting plate are coated with a layer of a sticky substance generated by automobile exhaust emissions.

When the collected viscous material accumulates to a certain thickness on the smoke collection plate, spark discharge will occur between the anode plate and the cathode plate, and the strong instantaneous current will cause the objects collected on the anode plate and the cathode plate to ignite, expand and fall off, and emit a popping discharge sound. Because there is a distributed capacitance of several thousand P between the anode plate and the cathode plate, a fully charged capacitor will generate a large current when discharging, and the current will cause the discharge gas to explode and emit a popping sound.

4. Working principle of high-voltage power supply for electronic purification device of automobile exhaust gas

Figure 3 is the working principle diagram of DC switching high-voltage power supply, and its input voltage is 12V (can also be 24V), because automobiles are generally powered by 12V storage batteries. The DC switching high-voltage power supply is a push-pull switching power supply, because among low-voltage switching power supplies, the push-pull switching power supply has the highest working efficiency.

In addition, the push-pull switching power supply in Figure 3 is different from the general push-pull switching power supply in that the alternating time of the two push-pull tubes here is not equal to zero, but is delayed (or staggered) for a certain time (the duty cycle of the two push-pull tubes when working is only about 48%). The purpose is to prevent the latter tube from turning on when the former tube is not completely turned off at the moment of the two push-pull tubes working alternately, so that the on and off time of the two tubes overlap, increase the loss of the switch tube, and reduce the working efficiency of the DC high-voltage switching power supply.

IR2155 is selected as the driving circuit in Figure 3. IR2155 is commonly used as a half-bridge switch driving circuit in energy-saving lamps. The circuit structure of half-bridge driving and push-pull driving is quite different, so in Figure 3, the original circuit of IR2155 used for half-bridge switch driving has been greatly modified, with pin 6 directly connected to the ground (originally connected to the half-bridge output) and pin 8 directly connected to the power supply (originally connected to the bootstrap capacitor).

In addition, the normal working voltage of IR2155 is 15.6V, but the input voltage in Figure 3 is only 12V. Obviously, this voltage cannot make IR2155 work normally. In order to increase the working voltage of IR2155, rectifier diodes D2 and D4 are used in Figure 3 to rectify the back electromotive force generated by the primary coil of the switching transformer T1, and then superimposed with the 12V power supply (to 24V) and then powered to U1 (IR2155) through resistor R1 to ensure that the working voltage of IR2155 is 15.6V.

Under normal working conditions, the output power of the DC switching high-voltage power supply in Figure 3 is not large (less than 20W), but when the smoke collecting plate is ignited, its output power is very large, reaching more than 100W. Since the operating voltage of the two push-pull tubes Q5 and Q6 is relatively low, the operating current is relatively large. Therefore, Q5 and Q6 must use field-effect tubes with relatively large drain currents, or IBGT tubes with relatively large collector currents.

The output power of IR2155 is very small, so it cannot be used to directly drive push-pull tubes Q5 and Q6. Especially when Q5 and Q6 work at low voltage and high current, the output signal of IR2155 must be amplified. In Figure 3, two groups of push-pull follower amplifier circuits (Q1, Q2 and Q3, Q4) are used to amplify the two groups of output signals of IR2155 respectively, so as to ensure that sufficient driving current is provided to the two push-pull tubes Q5 and Q6 at the moment of opening and closing, so as to reduce the switching loss generated when Q5 and Q6 are turned on and off. C5, R5 and C6, R6 are differential circuits, which have a certain effect on accelerating the turn-on and turn-off time of Q5 and Q6.

C1 is an energy storage filter capacitor, but its main function is to demagnetize the magnetic core of the switching transformer. At the moment when the power switch is disconnected, the charge stored in C1 can maintain the switching power supply to continue working for a period of time, so that the working voltage of the primary coil of the switching transformer slowly decreases and finally reaches zero. This process ensures that the magnetization curve of the switching transformer core can return to the origin of the coordinates every time the power is turned off, that is, the core is completely demagnetized, to prevent magnetic saturation due to the magnetization of the transformer core when the switching power supply works again. If there is no effect of C1, when the power switch is disconnected, the magnetization curve of the switching transformer core will stop at a non-zero point, and the transformer will easily saturate when the power is turned on next time, causing the two push-pull tubes to burn out due to overcurrent.

D21, D22, D23, D24 and C21, C22, C23, C24 form a voltage doubler rectifier circuit. The output voltage of HV1 is generally higher than 10,000 volts, while the output voltage of HV2 is higher than 5,000 volts.

U2 is a voltage comparator (TL431), which has a reference comparison voltage (about 2.5V) set inside. The other input comparison voltage is obtained by the voltage divider of R24 and R9, and R9 is a sampling resistor. During normal operation, since the sampled output voltage of R9 is relatively high, that is, the input voltage of U2 is relatively high, U2 is in the on state, that is, the output voltage of U2 is 2.5V. The function of U2 is mainly to control the on or off of another voltage comparator Q7. During normal operation, since the voltage (2.5V) applied to the voltage zener diode DZ3 is lower than the breakdown voltage, Q7 is in the off state.

The output voltage of U2 or the input voltage of Q7 is input by diode D5, and the input signal of D5 is obtained through sampling resistor R10. Since one end of R10 is connected to the cathode plate of the smoke collecting plate, the current flowing through the cathode plate will also flow through R10, thereby generating a voltage drop on R10. This voltage is the sampling voltage of sampling resistor R10, or the sampling output voltage. In normal operation, the sampling voltage of R10 is very small. In addition, when U2 is turned on, the sampling voltage of R10 is bypassed by U2 after passing through D5 (embedded on 2.5V). Therefore, the sampling voltage of R10 cannot turn on the voltage stabilizing diode DZ3. At this time, Q7 is cut off.

When sparks appear between the smoke collecting plates, the output current suddenly increases. First, the HV2 high-voltage output voltage will decrease, because the voltage drop generated by R23 will increase, thereby reducing the HV2 high-voltage output voltage. Therefore, the sampling voltage output by the sampling resistor R9 will also decrease. After the sampling voltage output by R9 is delayed by the integration of C7, U2 will be turned from on to off, and its output voltage is greater than 2.5V. At this time, the sampling voltage of R10 passes through D5, and then integrates through the integration circuit C8, R7, and C9, so that the phase of the sampling signal is delayed. The delayed sampling signal passes through the voltage-stabilizing diode DZ3 and is finally added to the input end of Q7, turning Q7 on.

After Q7 is turned on, the output signal of the sawtooth oscillator of U1 is bypassed through R8, U1 stops working, no driving signal is output, and the two push-pull tubes Q5 and Q6 also stop working, resulting in no high voltage output of the switching power supply. After C8 and C9 in the integration circuit are completely discharged, Q7 will return to the previous cut-off state, and then the DC switching power supply will start to work normally again. Therefore, the sparking between the smoke collection plates is intermittent, and the DC switching power supply will be turned off once each time the spark is ignited to protect the safety of the DC switching power supply.

In addition, the threshold of the ignition protection can also be changed. The threshold of the ignition protection can be changed by changing the size of the sampling resistors R9 and R10. For some small ignitions, as long as the power loss does not exceed the maximum output power of the DC high-voltage switching power supply, the DC high-voltage switching power supply does not need protection, which can improve the working efficiency of the automobile exhaust electronic purification device. Therefore, the threshold of the ignition protection and the length of the continuous ignition time can be determined according to the use effect.

The length of the ignition time is mainly determined by the time constants of C7 and C8, R7, C9 and C10 in the integration circuit. The larger the time constant, the longer the ignition time and the longer the interval time. In principle, U2 and Q7 are both sampling amplifier circuits, U2 is for power supply output voltage sampling, and Q7 is for power supply output current sampling, but the phases of the input signals of the two sampling amplifier circuits must be delayed, which is equivalent to two delay times in series in terms of delay effect. However, when the integration circuit is discharged, it is not in series in terms of time. In this way, the charging and discharging time of the integration circuit can be adjusted separately to make the ignition duration as long as possible and the recovery time as short as possible to improve work efficiency.

DZ1 is the limiting diode of the output voltage of the sampling resistor R9. When the sampled output voltage exceeds a certain voltage value, the limiting diode DZ1 is turned on to prevent U2 from being damaged due to excessive input voltage. DZ2 is also a limiting diode. When the sampled output voltage of R10 exceeds the voltage value of the voltage regulator diode, DZ2 is turned on to prevent U2 from being damaged due to excessive working voltage.

The circuit in Figure 3 can also be powered by a 24V DC power supply, but the circuit needs some changes: replace diode D1 with a resistor, remove resistor R1 and diodes D2 and D4, short-circuit diode D3, and increase the number of turns of the primary coil of the switching transformer.

The estimated cost of the automobile exhaust electronic purification device of the present invention is between 100 yuan and 200 yuan. I believe that this automobile exhaust electronic purification device will have a very broad market in the future.