JP5541006B2 - Liquid volume and liquid state sensor - Google Patents

Description

  The present invention relates to a liquid amount and a liquid state sensor for detecting a liquid amount in a tank and performing a liquid state determination. The liquid amount and the liquid state sensor can accurately detect the liquid state and detect the liquid amount and the liquid state by a single member. The present invention relates to a liquid state sensor.

  As an exhaust gas purification system for removing nitrogen oxides (NOx) contained in vehicle exhaust gas, there is a combination of urea water and a reduction catalyst device. By storing urea water in a vehicle-mounted tank and injecting it into the exhaust pipe as necessary, NOx can be removed by causing ammonia to act on NOx in the reduction catalyst device.

  However, urea water has a property of freezing at a low temperature, for example, -15 ° C. In cold regions in winter, urea water in the tank may freeze due to low outside air temperature. When the urea water in the tank freezes, it becomes difficult to inject the urea water into the exhaust pipe. However, if an antifreeze agent is mixed in urea water to prevent freezing, the performance of the reduction catalyst device deteriorates. In order to prevent urea water from being unreasonably increased, there is also a regulation that detects the concentration of urea water and prohibits the engine from starting when the concentration is inappropriate. I will be involved. Therefore, urea water without impurities is used. Since it is inevitable that the urea water in the tank is frozen, a means for determining whether or not the urea water injection is a precondition for the urea water injection is required.

  On the other hand, if the urea water in the tank is not consumed, NOx removal cannot be performed, so it is necessary to detect the amount of urea water in the tank.

  Patent Documents 1, 3, and 4 include an inner cylinder and an outer cylinder that are suspended in a tank so that a part of the urea is immersed in urea water, and the amount of urea water is detected from the capacitance between the inner and outer cylinders. The freezing is determined from the temperature and concentration. When the urea water temperature is equal to or lower than the melting point and the urea water concentration is a concentration indicating a solid state, it is determined to be frozen.

  Patent Documents 2 and 5 include an inner cylinder and an outer cylinder that are suspended in a tank so that a part of the urea is immersed in urea water. The amount of urea water is detected from the capacitance between the inner cylinder and the outer cylinder, and is detected by a temperature sensor. Freezing is determined from the urea water temperature. If the temperature of the urea water is lower than the threshold value, it is determined that it is frozen.

JP 2008-248710 A JP 2009-002718 A JP 2008-248714 A JP 2008-248709 A JP 2007-114181 A

  Freezing determination based on urea water temperature and urea water concentration as in Patent Documents 1 to 5 needs to detect all of the urea water temperature and urea water concentration with high accuracy, but there is also an unfrozen part that is partially frozen. In such a state, the temperature differs depending on the location, and it is difficult to accurately detect the urea water temperature and the urea water concentration just before the melting point. For this reason, the determination is not accurate.

  Moreover, in patent documents 1-5, the capacitance sensor provided for the urea water amount detection is used for the detection of the urea water amount, and the temperature sensor and the heater are used for the detection of the urea water temperature and the urea water concentration for freezing determination. Use in combination. However, freezing determination is necessary only in a limited season or region such as a cold region in winter, and in other seasons or regions, the freezing determination member is wasted.

  Accordingly, an object of the present invention is to provide a liquid amount and liquid state sensor that solves the above-described problems, enables accurate determination of the liquid state, and can detect the liquid amount and the liquid state with a single member.

  To achieve the above object, the present invention provides a pressure sensor installed in a tank and capable of detecting the static pressure and dynamic pressure of the liquid in the tank, and the liquid in the tank from the static pressure detected by the pressure sensor. A liquid amount detection unit that detects the amount, and a state determination unit that determines the liquid state in the tank from the dynamic pressure detected by the pressure sensor.

  The state determination unit may determine that at least a part of the liquid in the tank is frozen when the dynamic pressure detected by the pressure sensor during vibration of the vehicle is less than a threshold value.

  The pressure sensor may be installed on the inner surface of the tank.

  The present invention exhibits the following excellent effects.

  (1) The liquid state can be accurately determined.

  (2) The liquid amount and the liquid state can be detected by a single member.

It is a block diagram of the liquid quantity and liquid state sensor which shows one Embodiment of this invention. It is a time characteristic figure of the output of a pressure sensor. It is a flowchart which shows the urea water management procedure using the liquid quantity and liquid state sensor of this invention.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

  As shown in FIG. 1, a liquid amount and liquid state sensor 1 according to the present invention is installed in a tank 2, a pressure sensor 3 capable of detecting the static pressure and dynamic pressure of the liquid W in the tank 2, and a pressure A liquid amount detection unit 4 that detects the amount of liquid in the tank 2 from the static pressure detected by the sensor 3, and a state determination unit 5 that determines the liquid state in the tank 2 from the dynamic pressure detected by the pressure sensor 3.

  Here, the liquid amount and liquid state sensor 1 of FIG. 1 is applied to a tank (tank) 2 for storing urea water of an exhaust gas purification system mounted on a vehicle. That is, in the exhaust gas purification system, the liquid W stored in the tank 2 is urea water, and a pump 6 for pumping the urea water is installed in the tank 2, and between the engine 7 and the reduction catalyst device 8. The exhaust pipe 9 is connected to a discharge pipe 10 that guides the urea water pumped up by the pump 6 to the upstream side of the reduction catalyst device 8 and injects it.

  The pressure sensor 3 may be of any type as long as the static pressure and dynamic pressure of the liquid W can be detected, and a commercially available water pressure sensor can be used. The output of the pressure sensor 3 is, for example, a voltage, and the output voltage is passed through a filter (not shown) so that a low frequency component (DC component) can be separated as a static pressure and a high frequency component (AC component) can be separated as a dynamic pressure.

  The pressure sensor 3 is preferably installed at or near the bottom of the tank 2 so that pressure can be detected even when the amount of liquid is near empty (minimum remaining amount). Further, the pressure sensor 3 is preferably installed on the inner surface of the tank 2 because the liquid W freezes from the vicinity of the wall surface of the tank 2, that is, from the portion in contact with the inner surface. In addition, since a pressure wave due to a liquid-specific wave, which will be described later, becomes noticeable in the horizontal direction, the pressure sensor 3 is preferably installed on the side surface in the tank 2 so that the sensitive direction is directed in the horizontal direction. Therefore, the pressure sensor 3 is installed on the side surface near the bottom in the tank 2 here.

  The liquid amount detection unit 4 and the state determination unit 5 are provided as software in a so-called electronic control unit (ECU) 11.

  The operation principle of the liquid amount and liquid state sensor 1 will be described.

  As shown in FIG. 2, the voltage output from the pressure sensor 3 is detected by mixing static pressure and dynamic pressure. The filter separates low frequency components as static pressure and separates high frequency components as dynamic pressure. The static pressure is proportional to the depth from the liquid surface because it is the water head pressure, that is, the pressure generated by the depth of the liquid. Therefore, the liquid amount detection unit 4 can detect the liquid amount from the static pressure using a coefficient set in advance in consideration of the specific gravity of the liquid.

  On the other hand, the state determination unit 5 determines from the dynamic pressure the state of the liquid in the tank, specifically, whether or not the liquid is frozen.

  When the liquid W in the tank 2 is not frozen, the vibration of the vehicle body due to engine vibration or road running propagates to the tank 2 and the tank 2 vibrates, so that the liquid W is shaken in the tank 2 and is peculiar to the liquid. A wave is generated. For this reason, in the pressure sensor 3, the pressure wave which has the specific frequency resulting from the wave peculiar to a liquid is detected as dynamic pressure. That is, the dynamic pressure is generated by the wave of the liquid W when the liquid W in the tank is not frozen, and acts on the pressure sensor 3.

  When the liquid W in the tank 2 begins to freeze, a frozen portion is generated near the wall surface in contact with the outside air, and such a frozen portion grows into the tank 2. Since the pressure sensor 3 is installed on the side surface of the tank 2, as shown by a broken line in FIG. 1, the pressure sensor 3 is covered with the frozen portion when a part of the liquid W is frozen. At this time, even if the tank 2 vibrates and a wave peculiar to the liquid is generated in the unfrozen portion in the tank 2, the pressure wave does not reach the pressure sensor 3 covered with the frozen portion. Therefore, the dynamic pressure is not detected by the pressure sensor 3.

  Accordingly, when the vehicle body is vibrated, such as when the engine 7 is started, if the dynamic pressure above the threshold is detected by the pressure sensor 3, it may be determined that the liquid W is not frozen, and the movement below the threshold is determined. If only the pressure is detected, it may be determined that the liquid W is frozen.

  The urea water management using the liquid amount and liquid state sensor 1 of the present invention is performed as shown in FIG.

  When the engine 7 is started in step S1, the freezing of urea water is immediately determined based on the dynamic pressure from the pressure sensor 3 in step S2 before the engine vibration due to the start is not finished.

  If it is determined that the urea water is frozen, the thawing device is operated in step S3. As a thawing device, for example, a device that draws a cooling water circulation pipe of the engine 7 into the tank 2 and defrosts urea water using waste heat is known.

  If it is determined that the urea water is not frozen, the thawing device is stopped in step S4, and the urea water injection is performed in step S5 to start the NOx removal in the reduction catalyst device.

  Although not shown in FIG. 3, the amount of urea water is detected based on the static pressure from the pressure sensor 3. If the amount of urea water is a value that needs to warn of a shortage of remaining amount, or a value that does not allow urea water injection, a warning is given or urea water injection is prohibited.

  As described above, urea water management is performed.

  It should be noted that at the time of determination of freezing in step S3 and after, the engine 7 is already in operation and vibration due to engine start cannot be used. However, if the vehicle is traveling, the vehicle vibration due to the road surface is used as the source of dynamic pressure. Good. Further, since diesel vehicles have larger engine vibration during operation than gasoline vehicles, engine vibration during operation can also be used as a source of dynamic pressure.

  The freezing determination may be performed only when the engine is started. If the urea water is frozen at the time of starting the engine, the engine 7 is then warmed up so that the engine cooling water and the urea water in the tank 2 exchange heat and the thawing proceeds, and the preset thawing time elapses. This is because the entire urea water is surely thawed and urea water injection can be started.

  According to the liquid amount and liquid state sensor 1 of the present invention, the liquid amount and the liquid state can be detected using the pressure sensor 3 capable of detecting static pressure and dynamic pressure. For this reason, since the pressure sensor 3 operates as a liquid amount sensor even in a tropical / subtropical region where freezing does not occur throughout the year or a warm region where freezing occurs only in a short period in winter, the pressure sensor 3 is not wasted. On the other hand, in a warm region or a cold region where freezing occurs in winter, the pressure sensor 3 can be operated exclusively as a liquid amount sensor in summer and can also be operated as a liquid state sensor in winter. In extremely cold regions where freezing occurs throughout the year, the liquid amount sensor and the liquid state sensor can always be operated.

  According to the liquid amount and liquid state sensor 1 of the present invention, since the dynamic pressure that is remarkably different between the frozen state and the non-frozen state is used, the determination of the liquid state is more accurate than in the prior art using the temperature just before the melting point. .

  According to the liquid amount and liquid state sensor 1 of the present invention, since the pressure sensor 3 is installed on the inner surface of the tank 2 where freezing starts, it is possible to determine freezing at first when a part is frozen.

  According to the liquid amount and liquid state sensor 1 of the present invention, the liquid state is determined by detecting the dynamic pressure. Therefore, when applied to the urea water management of the vehicle, the vibration due to the engine start is used to determine the freezing. It can be suitably used. Since the vibration of the vehicle is large when the engine is started and the vibration is particularly large when the engine is started at a low temperature, the dynamic pressure can be easily detected by the pressure sensor 3.

DESCRIPTION OF SYMBOLS 1 Liquid quantity and liquid state sensor 2 Tank 3 Pressure sensor 4 Liquid quantity detection part 5 State determination part

Claims (3)

A pressure sensor installed in the tank and capable of detecting the static pressure and dynamic pressure of the liquid in the tank;
A liquid amount detection unit that detects the amount of liquid in the tank from the static pressure detected by the pressure sensor; and a state determination unit that determines a liquid state in the tank from the dynamic pressure detected by the pressure sensor. A liquid amount and liquid state sensor.   The state determining unit determines that at least a part of the liquid in the tank is frozen when a dynamic pressure detected by the pressure sensor during vibration of the vehicle is less than a threshold value. The liquid amount and liquid state sensor according to 1.   The liquid amount and liquid state sensor according to claim 1, wherein the pressure sensor is installed on an inner surface of the tank.

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