CN101709988A - Method for sensing automotive oil level and sensor - Google Patents
Method for sensing automotive oil level and sensor Download PDFInfo
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- CN101709988A CN101709988A CN200910191849A CN200910191849A CN101709988A CN 101709988 A CN101709988 A CN 101709988A CN 200910191849 A CN200910191849 A CN 200910191849A CN 200910191849 A CN200910191849 A CN 200910191849A CN 101709988 A CN101709988 A CN 101709988A
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Abstract
The invention relates to a method for sensing an oil level of an automobile fuel tank, which adopts two parallel plate capacitors as a measurement capacitor and a reference compensation capacitor respectively; the height of the measurement capacitor is close to or equal to that of the fuel tank, and the measurement capacitor is vertically arranged in the fuel tank; and the reference compensation capacitor is horizontally arranged at the bottom of the fuel tank and immersed in oil liquid. The two capacitors are of an open type; when the oil-level height in the fuel tank changes, the height of oil liquid entering the measurement capacitor also changes and a capacitance value of the measurement capacitor changes correspondingly, but a capacitance value of the reference compensation capacitor does not change with the change of a liquid level. The measurement capacitor is compensated by the reference compensation capacitor, so an accurate change value of the measurement capacitor can be obtained; and an exact value of the oil-level height in the fuel tank can be acquired by the linear relation of the change value of the measurement capacitor and the oil liquid height through circuit processing so as to realize oil-level measurement. Due to the adoption of the reference compensation capacitor, the oil-level measurement which is irrelevant to media under different environments is realized; and the used sensor has corrosion resistance, no mechanical moving parts, long service life, simple structure, low process requirements and low cost.
Description
Technical field
The present invention relates to the liquid level sensing technology, be specifically related to sensing technology automotive oil tank fluid height.
Background technology
Automobile oil level sensor can be used for detecting oil mass, engine motor oil oil mass and the brake fuel tank fuel quantity in the fuel oil fuel tank.When engine motor oil is not enough, this situation of the timely sensing of this sensor also sends electric signal immediately to ECU, and ECU then starts warning system, lights emergency warning lamp or the sound that gives a warning, avoid engine under the situation of insufficient lubrication, to work on, thereby prevent that effectively engine from damaging; When fuel quantity is not enough, remind human pilot to refuel, avoid because Low oil Fuel causes the automobile halfway to cast anchor; When the brake fluid quantity not sufficient, ECU starts warning system, lights emergency warning lamp or the sound that gives a warning, and avoids emergency episodes such as automobile generation brake failure.
Oil level position transducer commonly used at present can be divided into according to principle: types such as condenser type fuel level sensor, ultrasound wave fuel level sensor, resistance-type fuel level sensor, optics fuel level sensor and magnetostriction type fuel level sensor.The sensor of these types relative merits separately are as follows:
The condenser type fuel level sensor
This liquid level sensor is simple in structure, and reliability is very high; High temperature resistant and the high pressure of popping one's head in, the on-the-spot face width that adapts to; Power consumption is extremely low, is suitable for the measurement of inflammable and explosive danger medium.With regard to present capacitance level transducer, when carrying out level gauging, must know the relative dielectric constant of measured liquid.In addition, when measuring that liquid is inhomogeneous, relative dielectric constant changes or fluid to be measured when changing, just must demarcate again, thereby limit its usable range greatly.
The ultrasound wave fuel level sensor
According to the ultrasonic pulsative signal that ultrasonic probe sends, in liquid, propagate, be reflected after running into the interface of air and liquid, can obtain ultrasonic propagation time after receiving echoed signal.Utilize its velocity of propagation and travel-time to calculate its propagation distance, obtain liquid level.The easy temperature influence of this sensor, and price is more expensive.
The resistance-type fuel level sensor
The resistance that this method utilizes resistivity height, material that temperature coefficient is big to make applies the variation that voltage detects oil level in conjunction with the fuel level sensor float with at the resistance two ends.Temperature is high more, and resistance is high more.When resistance is immersed in the fluid, temperature descends, and resistance detects changes in resistance also along with decline, can obtain the variation of fuel oil.This sensor is to adhere to the Fe-Ni sheet resistance on metal forming, thereby makes the electrothermal fuel level sensor.
The influence of measuring accuracy liquid body pollution condition is very big, easily produce mistake, and response speed is slow.Corrosion takes place and causes inefficacy in addition, at present used carbon resister easily in gasoline.
The optics fuel level sensor
This method is utilized reflection of light or transmission principle, carries out oil-level measurement according to the difference of reflection or transmitted light intensity or luminous flux.Owing to cost an arm and a leg, be not extensive use of as yet at present.
The magnetostriction type fuel level sensor
Magnetostrictive liquid level sensor is to utilize the magnetostrictive effect of material to experience the variation of liquid surface float, thereby reaches the purpose of non-cpntact measurement oil level.This fuel level sensor measuring accuracy height, environmental suitability is strong, security good, easy for installation, also can be applicable to level gauging fields such as oil, chemical industry, because of costing an arm and a leg, in the aircraft oil-level measurement, use mostly at present.
Summary of the invention
The present invention is directed to the fuel tank fluid height sensor relative merits separately of common in the market different principle, propose a kind of level height position sensing method and sensor of inner no mechanical moving component based on the parallel flat capacitance principle.
The inventive method has adopted parallel flat electric capacity, and referring to Fig. 1, its principle is as follows:
Two is that its appearance value of two parallel plates electric capacity C of S is at a distance of D, useful area:
Wherein: ε-specific inductive capacity
The k-dielectric constant
From formula (1) as can be seen, if the distance D of two-plate is a constant, when dielectric constant ε fixed (be between two-plate electrolyte constant), capacitance was directly proportional with useful area S.
Thereby with the corresponding change that becomes parallel flat electric capacity useful area S of the height of oil level, when S changed, the appearance value by measuring electric capacity and the relation of level height just can obtain level height so.
Based on this, the oil level position sensing method that the present invention proposes is as follows:
Adopt a parallel flat electric capacity as measuring electric capacity, this measurement electric capacity is the fixing capacity plate antenna of a structure; The length of measurement electric capacity is approaching or equal the fuel tank height, and vertically is installed in the fuel tank.This electric capacity is non-tight formula structure, communicates with fluid space in the fuel tank, and fluid can enter between the pole plate, and oil level changes, and the fluid height between the pole plate of electric capacity changes simultaneously, and the appearance value and the fluid height of electric capacity are linear;
The parallel flat electric capacity that capacitance remains unchanged when adopting another operate as normal is as the reference building-out capacitor, its capacitance equates or relation in direct ratio with the maximum capacitor value that above-mentioned measurement electric capacity can reach, should also be non-closed structure with reference to building-out capacitor, level is installed in the fuel tank bottom, be immersed in the fluid, by measuring this variation, obtain the change amount of environment (for example the fluid of temperature or heterogeneity etc.) to capacitance with reference to building-out capacitor appearance value;
To measure electric capacity capacitance that records and the environment that obtains by the reference building-out capacitor to the change amount of capacitance processing of circuit through the rear end, compensation temperature and different fluid become to grade other environmental factor to measuring the influence of capacitance, obtain the accurate capacitance variations value of measuring, by measuring the linear relationship of capacitance variations value and fluid height, through processing of circuit, can obtain the fluid height value, realize the automobile oil level measurement.
From the method for foregoing description of the present invention as can be known, it has adopted the fixing parallel flat electric capacity of open structure, when oil level changes, also corresponding the changing of level height in the parallel flat electric capacity, as shown in Figure 2, the D apart of two-plate, plate width W, pole plate height L, fluid height L
1, the fluid DIELECTRIC CONSTANT
2, dielectric constant of air ε
1, then this parallel flat electric capacity can be regarded the parallel connection of two parallel flat electric capacity as, and one is formed by fluid, and another is formed by air, and then total capacitance is:
According to formula (2) as can be seen, the appearance value C of electric capacity:
C＝A[B+(ε
2-ε
1)L
1] (3)
Wherein,
B＝ε
1L (5)
DIELECTRIC CONSTANT when structure certain (being that polar plate spacing D, width W, height L are constant), air
1DIELECTRIC CONSTANT for constant, fluid
2During for constant, A, B are constant in the formula 4,5, i.e. the height L of capacitance and fluid
1Linear.Shown in the solid line among Fig. 3.Also promptly, adopt the capacity plate antenna of the fixed sturcture of the capacitance structure preparation shown in Fig. 2, its appearance value and fluid height are linear, thereby just can measure the height of fluid by the appearance value of measuring electric capacity.
Because electric capacity is subject to Temperature Influence, and its relative dielectric constant of heterogeneity fluid can be different, and the economize on electricity constant of identical fluid also can change under the condition of different temperatures.Thereby can change according to the linear relationship that formula (2)～(5) draw, shown in the dotted line among Fig. 3.Simple this measurement electric capacity that relies on obviously can't obtain liquid level signal accurately.Given this, in order to make measurement electric capacity be subjected to the influence of other factorses such as temperature and environment to reduce to minimum, the inventor considers that the electric capacity that adopts identical material and technology is as the reference building-out capacitor, when work, be fully immersed in the fluid with reference to building-out capacitor, its capacitance with measure electric capacity maximum capacitor value when being full of whole pole plate (be fluid) and equate or proportion relation, be in the same environment with reference to building-out capacitor and measurement electric capacity, by measuring this variation with reference to building-out capacitor appearance value, obtain the change amount of environment, promptly obtain the C under this environment temperature and ambient condition among Fig. 3 capacitor's capacity
Oil, and the specific inductive capacity of air is constant, i.e. C
EmptyKnown, can calculate the straight slope under this condition; With measuring electric capacity capacitance that records and the environment that is obtained by the reference building-out capacitor change amount of capacitance being handled through back-end circuit, is the measurement capacitance of this moment by straight slope promptly, then can obtain the exact value of fluid liquid level.As the formula (6).
In the formula (6), the scale-up factor when n is work between reference capacitance value and the measurement capacitance maximum.Represent when n=1: the reference capacitance value equates with the measurement capacitance maximum during work.
Based on the above method, the applicant has proposed to realize a kind of specific implementation structure of sensor on sensing automotive oil level of this method, and it is measured electric capacity, one by one and forms with reference to building-out capacitor and treatment circuit.
The parallel flat electric capacity that described measurement electric capacity is a non-closed structure is non-tight between its pole plate, can communicate with the fluid space in the fuel tank, it vertically is installed in the fuel tank, fluid can enter between the pole plate, and when oil level changed, appearance value was corresponding changes for it.
Described also is the parallel flat electric capacity of a non-closed structure with reference to building-out capacitor, and its capacitance equates with the maximum capacitor value of above-mentioned measurement electric capacity or proportional during operate as normal, and this is installed on the fuel tank bottom with reference to the building-out capacitor level, is immersed in the fluid;
Described measurement electric capacity and with reference to building-out capacitor respectively by output line connection processing circuit, to measure electric capacity and with reference to the exact value of building-out capacitor by treatment circuit, the treatment circuit rear end connects counting circuit, utilize the linear relationship of measuring capacitance variations value and fluid height, calculate and obtain the fluid height value.
As seen, advantage of the present invention is fairly obvious:
At first, its adopts capacity plate antenna principle to realize the sensing of oil level, high resolving power, high-acruracy survey under having realized on a large scale;
The second, it is that a kind of inner non mechanical movable is measured, and has realized the characteristics of survey sensor sensing unit on-mechanical contact, helps prolonging the serviceable life of sensor;
The 3rd, its adopts with reference to building-out capacitor and carries out temperature and other environmental factor to the compensation of capacitance influence, has eliminated the influence of factors such as environment, has improved the degree of accuracy of measuring, and has realized the oil-level measurement with media independent;
The 4th, it is simple in structure, and technological requirement is not high, low price.
Description of drawings
Fig. 1 is a parallel flat tunable capacitor principle schematic;
Fig. 2 is a kind of implementation of fuel level sensor;
Fig. 3 is the linear relationship chart of fuel level sensor;
Fig. 4 is the mounting structure synoptic diagram of this sensor;
Fig. 5 is the circuit diagram of capacitance measurement.
Embodiment
Further specify content of the present invention below in conjunction with accompanying drawing:
Referring to Fig. 4, automobile oil level sensor is measured electric capacity 1, one by one and is formed with reference to building-out capacitor 2 and treatment circuit.Measuring electric capacity 1 is a parallel flat electric capacity, is non-tight between its pole plate, be connected with fluid space in the fuel tank 3, its length near or equal fuel tank 3 height, vertically be installed in fuel tank 3 medial surfaces, fluid 4 can enter between the two-plate.The constant parallel flat electric capacity of capacitance when being an operate as normal with reference to building-out capacitor 2, its capacitance equates or proportion relation with the maximum capacitor value of above-mentioned measurement electric capacity 1, this is installed in the same fuel tank 3 with reference to building-out capacitor 2 and measurement electric capacity 1, be installed in fuel tank 3 bottommosts with reference to building-out capacitor 2 levels, be immersed in the fluid 4, with reference to also being non-tight between the pole plate of building-out capacitor 2.Measure electric capacity 1 and pass through output line connection processing circuit respectively, measuring-signal is handled, thereby treatment circuit outputs to the concrete height that counting circuit obtains fluid with reference to building-out capacitor 2.
The treatment circuit that this sensor adopts can adopt existing techniques in realizing to the processing of measuring-signal, below enumerates a kind of treatment circuit structure, sees Fig. 5.CAV424 among Fig. 5 is a special chip of measuring electric capacity, C
X1Be measured capacitance, C
X2Be fixed capacity.The CAV424 principle of work is such, and one by capacitor C
OSCThe reference oscillator of determining frequency is being controlled the integrator of the constant symmetric construction identical with the cycle of two phase places.The amplitude of these two integrators passes through capacitor C
X1And C
X2Determine.Relatively the voltage amplitude difference of two integrators just can draw capacitor C
X1And C
X2Relative capacitance variations difference, this differential signal converts d. c. voltage signal and through the output of the adjustable differential signal output stage of output promptly 5. and the V 6. to by a secondary low-pass filter
DIFF, promptly obtain accurate capacitance.
Two-way V
DIFFThe measurement electric capacity of representative and be connected respectively to the input end of A/D capture card with reference to the appearance value of building-out capacitor, as shown in Figure 5, the output terminal of A/D connects computing machine.Computer control A/D sticks into row and gathers, and can calculate actual liquid level according to the measurement capacitance that collects with reference to the building-out capacitor value and with the relation of liquid level.Wherein, A/D card and computing machine can be made up of the multi-channel A that can reach similar functions/D conversion chip and single-chip microcomputer.
Because electric capacity involved in the present invention has two, one is to measure electric capacity, and another is with reference to building-out capacitor, thereby can utilize 2 CAV424 to carry out the measurement of these two electric capacity respectively, after obtaining accurate capacitance, can obtain accurate level value according to formula (6) again.
Wherein: C
SurveyFor measuring capacitor's capacity, C
GinsengBe reference capacitance appearance value,
L, W, D are divided into measurement capacitor plate length, width and polar plate spacing, L
1Be the fluid height, k is for measuring the dielectric constant of capacitor dielectric, ε
1Be the specific inductive capacity of air, the scale-up factor when n is work between reference capacitance value and the measurement capacitance maximum.
Claims (3)
1. automotive oil tank oil level method for sensing is characterized in that:
Adopt a parallel flat electric capacity as measuring electric capacity; The length of described measurement electric capacity is approaching or equal the fuel tank height, and vertically is installed in the fuel tank; Be the non-tight structure between the pole plate of described measurement electric capacity, communicate with fluid space in the fuel tank that oil level changes in the fuel tank, the fluid height in the electric capacity changes simultaneously, and the appearance value and the fluid height of described measurement electric capacity are linear;
Adopt another parallel flat electric capacity as the reference building-out capacitor, its capacitance equates with the maximum capacitor value that described measurement electric capacity can reach or is directly proportional; Be installed in the fuel tank bottom with described with reference to the building-out capacitor level, be immersed in the fluid, change, obtain the change amount of the fluid of heterogeneity under the varying environment temperature conditions capacitance by measuring described appearance value with reference to building-out capacitor;
The capacitance that described measurement electric capacity is recorded and the environment temperature of being obtained by the reference building-out capacitor and fluid are to the change amount of the capacitance processing circuit processes through the rear end, compensation temperature and different these environmental factors of fluid composition are to measuring the influence of capacitance, obtain the accurate capacitance variations value of measuring, utilize the linear relationship of measuring capacitance variations value and fluid height, counting circuit through the rear end is handled, can obtain the fluid height value, realize the automobile oil level measurement.
2. automobile oil level sensor is characterized in that: it is measured electric capacity, one by one and forms with reference to building-out capacitor and treatment circuit;
Described measurement electric capacity is a parallel flat electric capacity, the length of described measurement electric capacity near or equal the fuel tank height, and vertically be installed in the fuel tank, it between the pole plate of described measurement electric capacity the non-tight structure, communicate with the fluid space in the fuel tank, when fuel level in tank changed, the level height that enters between the pole plate of measuring electric capacity changed thereupon, measured corresponding the changing of capacitance of electric capacity;
Described is a parallel flat electric capacity with reference to building-out capacitor, the non-tight structure, and its capacitance equates with the maximum capacitor value of described measurement electric capacity or proportional during operate as normal, describedly is installed on the fuel tank bottom with reference to the building-out capacitor level, is immersed in the fluid;
Described measurement electric capacity and with reference to building-out capacitor respectively by output line connection processing circuit, to measure electric capacity and with reference to the exact value of building-out capacitor by treatment circuit, the treatment circuit rear end connects counting circuit, utilize the linear relationship of measuring capacitance variations value and fluid height, calculate and obtain the fluid height value.
3. automobile oil level sensor according to claim 2 is characterized in that:
Described treatment circuit adopts two chip capacitor special test chip CAV424 to carry out the test of capacitance; The initial capacitance value of two parallel flat electric capacity is replaced with a close fixed condenser of appearance value respectively, be connected to the fixed capacity C of CAV424
X1End is at the C of two CAV424
X2End connects described measurement electric capacity respectively and with reference to building-out capacitor, and the output of two chip capacitor special test chip CAV424 is promptly represented described measurement electric capacity and with reference to the exact value of building-out capacitor;
Described treatment circuit rear end connects counting circuit, carries out the calculating of fluid height; Counting circuit is made up of A/D capture card and computing machine, or is made up of A/D conversion chip and single-chip microcomputer; The output of two CAV424 is connected respectively to A/D capture card or A/D conversion chip in the treatment circuit, the measurement capacitance that computing machine or single-chip microcomputer promptly collect according to A/D and calculate actual liquid level with reference to the building-out capacitor value and with the relation of liquid level.
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