JPH04256837A - Control device for liquid mixing-ratio sensor - Google Patents

Abstract

PURPOSE:To obtain a control device form liquid mixing-ratio sensor whose operation is stable and detecting accuracy is excellent. CONSTITUTION:An edge 21 of optical glass 20 is submerged into liquid to be measured. The emitted light of a light emitting diode 31 which emits the light on the edge 21 is directly received with a monitoring photodiode 33. The feedback control is performed for the light emitting diode 31 based on the received light of the monitoring photodiode 33. For this purpose, a LED-current controlling circuit 70 wherein a high amplifier circuit is formed of an operation amplifier 71 is provided. A capacitor 74 is connected in parallel with a feedback resistor 73 for feeding the output of the operation amplifier to the input.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device for an optical liquid mixture ratio sensor for measuring the mixture ratio of liquids in a mixed fuel or the like in which two types of fuel are mixed.

0002

[Prior Art] For example, in order to measure the mixing ratio of a liquid such as a mixed fuel mixture of gasoline and alcohol, the end face of an optical prism provided in a container is exposed from the container and immersed in the mixed liquid. The mixing ratio of the mixed liquid is detected by using the fact that when the end face is irradiated with light from inside the container, the reflectance of the irradiated light at the interface differs depending on the refractive index of the mixed liquid. A liquid mixture ratio sensor is being considered. To this end, a light emitting element and a light receiving element are placed in a container in a predetermined relationship with respect to an optical prism, and the light emitting element reflects the light emitted from the end face of the light emitting element, and the control device receives the received light amount. The mixture ratio is calculated based on.

0003

[Problems to be Solved by the Invention] However, when determining the mixture ratio using the above configuration, it is necessary to maintain the irradiation light emitted from the light emitting element at a constant brightness. For example, a photodiode is placed inside the container as a monitoring light receiving element for monitoring the irradiated light (luminance) of the light emitting element in addition to the light receiving element for determining the luminance, and the light emitting element is controlled by feedback control based on the light reception signal of the photodiode. It is possible to do so. However, since the output current of the photodiode is small and the output signal cannot be directly used as a control signal for feedback control, the current value must be amplified using a high amplification circuit. However, when a signal amplified by a high amplifier circuit is used for feedback control, there is a possibility of oscillation due to the high gain of the high amplifier circuit, and there is a problem that stable operation cannot be expected.

SUMMARY OF THE INVENTION An object of the present invention is to provide a control device for a liquid mixture ratio sensor that has stable operation and excellent accuracy.

[0005]

[Means for Solving the Problems] The present invention provides an optical prism in a container whose end face is immersed in a liquid to be measured which is a mixture of two types of translucent liquids, and emits irradiation light toward the end face. A liquid mixture ratio sensor that includes a light-emitting element and a light-receiving element that receives at least the irradiated light reflected by the end face, each disposed in the container, and calculates the mixture ratio of the liquid to be measured based on the amount of light received by the light-receiving element. In the control device, a monitoring light-receiving element for directly receiving the irradiated light from the light-emitting element is disposed in the container, and the light-emitting element is feedback-controlled based on the light reception signal of the monitoring light-receiving element. The control circuit includes a high amplification circuit for amplifying the light reception signal of the monitoring light receiving element using an operational amplifier, and a capacitor connected in parallel with a feedback resistor for feeding back the output of the operational amplifier to the input. The technical means is that it is connected to the

[0006]

According to the present invention, a monitoring light receiving element is disposed within the container, and the light receiving signal of this light receiving element is amplified by a high amplification circuit constituted by an operational amplifier and used for feedback control of the light emitting element. Therefore, the brightness of the light emitting element can be maintained at a predetermined state. On the other hand, in an operational amplifier, a capacitor is connected in parallel to a feedback resistor to feed back the output to the input, so the entire control circuit for feedback control forms a low-pass filter. Even when feedback control is performed by the control circuit based on the amplified signal, oscillation does not occur in the control circuit including the operational amplifier.

[0007]

Effects of the Invention In the present invention, since the output and input of the operational amplifier for amplifying the signal of the monitoring light-receiving element are connected by a capacitor, the control circuit amplifies the light-emitting element based on the light-receiving signal of the monitoring light-receiving element. Even with feedback control, oscillation does not occur. Therefore, feedback control of the light emitting element is stabilized, and the brightness of the light emitting element can be maintained constant. As a result, the operation of the control device becomes stable and the accuracy of the measured mixture ratio improves.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be explained based on an embodiment of a fuel mixture ratio sensor 100 for detecting the fuel mixture ratio of a mixed fuel mixture of gasoline and alcohol. In the fuel mixture ratio sensor 100 shown in FIG. 2, 10 is a sensor unit, and 1 is a stainless steel fuel path through which the mixed fuel whose mixture ratio is detected by the sensor unit 10 passes.

The fuel path 1 is arranged in a fuel supply path for supplying fuel to the internal combustion engine from a fuel tank (not shown), and forms a fuel reservoir 2 that serves as a cylindrical measurement chamber for detecting the fuel mixture ratio. Fuel connection pipes 101 and 102 communicating with a fuel reservoir 2 are connected to the fuel path 1 so as to face each other. In the fuel path 1, the upper part of the fuel reservoir 2 is connected to the sensor unit 10.
The sensor unit 10 is fitted facing the fuel reservoir 2 with the O-ring 5 ensuring airtightness.

The sensor unit 10 has a two-stage cylindrical stainless steel main metal fitting 11 and a cylindrical optical glass 20 that are heat-treated for fusion in a nitrogen atmosphere furnace using a predetermined jig. They are joined and fixed by the annular glass 17 to ensure the airtightness of the joint between the metal shell 11 and the optical glass 20, and also include a light emitting diode 31 as a light emitting element and a detection photo as a light receiving element for detecting the mixture ratio. A monitoring photodiode 33 as a monitoring light receiving element for maintaining constant brightness of the diode 32 and the light emitting diode 31 is fixed to ceramic element substrates 34 and 35, respectively, and a resin substrate holder 40 is installed.
, 50 to support the optical glass 20 within the metal shell 11 at a predetermined position.

Note that the light emitting diode 31 is mounted on the element substrate 34 in the form of a chip, and each photodiode 32
, 33 are surface-mounted on an element substrate 35, and each element is connected to a control device 60 (not shown) by a plurality of lead wires 36, 37 via conductor patterns provided on each substrate 34, 35, respectively. ing. In addition, each lead wire 36
, 37 formed in the substrate holder 50 are sealed with a silicone adhesive 18, and the inside of the substrate holder 50 is filled with an epoxy resin 19 to ensure airtightness. .

As shown in FIG. 3, in order to keep the brightness of the light emitting diode 31 constant, the control device 60 uses a light reception signal from the monitoring photodiode 33 that directly receives the irradiation light from the light emitting diode 31. LED current control circuit 7 that performs feedback control of the light emitting diode 31
0 and the end surface 2 of the optical glass 20 that forms an interface with the fuel reservoir 2 among the irradiated light emitted from the light emitting diode 31.
A detection photodiode 32 receives the light reflected by the light emitting diode 31 along with the light reflected by the light emitting diode 31.
The refractive index detection circuit 61 detects the refractive index based on the received light signal, and includes a constant voltage circuit (not shown).

The refractive index detection circuit 61 includes a current-voltage conversion circuit 62 that amplifies the output current of the detection photodiode 32 and converts it into a voltage signal, and a current-voltage conversion circuit 62 that converts the output of the current-voltage conversion circuit 62 into a pulse having a frequency corresponding to the voltage. V/F to convert to signal
The pulse width of the detection signal of the conversion circuit 63 and the temperature sensor 64 arranged to detect the temperature of the mixed fuel passing through the fuel reservoir 2 is modulated using the output signal of the V/F conversion circuit 63 as a carrier wave. It consists of a PWM circuit 65. In this embodiment, the output of the PWM circuit 65 as the output of the control device 60 includes information on the frequency as the refractive index signal and the pulse width as the temperature signal, and the microcomputer 80 mounted on the vehicle Through the calculation process, the detected refractive index is corrected based on the temperature, and the mixture ratio of the mixed fuel is calculated.

On the other hand, the LED current control circuit 70 includes an operational amplifier 71 for amplifying the output current of the monitoring photodiode 33, as shown in FIG.
and an operational amplifier 72 for feedback controlling the brightness of the light emitting diode 31 based on the output of the monitoring photodiode 33 amplified by the operational amplifier 71.

The operational amplifier 71 forms a current detection circuit using inversion amplification in which the input is in the opposite phase to the output due to the feedback resistor 73, and here, in particular, a high amplification circuit with a very large gain is formed. Therefore, in order to prevent the entire LED current control circuit 70 from oscillating during feedback control by the operational amplifier 72, an oscillation prevention capacitor 74 is connected in parallel with the feedback resistor 73. As a result, the LED current control circuit 70 forms a low-pass filter whose high frequency gain is limited, so that oscillation does not occur.

In the liquid mixture ratio sensor control device 60 of this embodiment having the above configuration, the light emitted from the light emitting diode 31 is directly received by the monitoring photodiode 33, and the LED current control circuit 70 causes the light to be emitted. The brightness of the diode 31 is kept constant. At this time, due to feedback control by the operational amplifier 72, a closed loop is formed in the LED current control circuit 70 via the light emitting diode 31 and the monitoring photodiode 33. Since high frequencies are cut by the capacitor 74, the LED current control circuit 70 does not oscillate.

When the temperature is constant, the refractive index of the mixed fuel passing through the fuel reservoir 2 is uniquely determined depending on the mixing ratio of the mixed fuel, and the light emitting diode 31 is determined depending on the refractive index.
Since the critical angle of the reflection angle of the irradiated light is determined, the above LE
When the brightness of the light emitting diode 31 is held constant by the D current control circuit 70, the amount of irradiation light reflected at the interface between the optical glass 20 and the mixed fuel is determined according to the mixture ratio of the mixed fuel. The detection photodiode 32 receives a light amount corresponding to the amount of light. Therefore, the refractive index detection accuracy is improved and the refractive index can be stably detected. In addition, in this embodiment, since a temperature sensor is provided to detect the temperature of the mixed fuel passing through the fuel reservoir 2, the detected refractive index is corrected according to the temperature, so that the mixed fuel can be mixed. The ratio can be determined with high precision. In this embodiment, the monitoring photodiode 33 for monitoring the light irradiated by the light emitting diode 31 is arranged on the opposite side of the light emitting diode 31 with the optical glass 20 in between. The position may be any position as long as it does not receive the reflected light, for example, it may be near the light emitting diode 31.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an LED current control circuit in a control device for a fuel mixture ratio sensor according to an embodiment of the present invention.

FIG. 2 is a sectional view of a fuel mixture ratio sensor showing an embodiment of the present invention.

FIG. 3 is a block diagram showing the functional configuration of a control device for a fuel mixture ratio sensor according to an embodiment of the present invention.

[Explanation of symbols]

10 Sensor unit (liquid mixture ratio sensor) 11
Metal shell (container) 20 Optical glass (optical prism) 21 End face 31 Light emitting diode (light emitting element) 32 Detection photodiode (light receiving element) 33
Monitoring photodiode (monitoring light receiving element) 60 Control device (liquid mixture ratio sensor control device) 70 LED
Current control circuit (control circuit) 73 Feedback resistor 74 Capacitor

Claims (1)

[Claims] 1. An optical prism whose end face is immersed in a liquid to be measured that is a mixture of two types of translucent liquid is provided in a container, and a light emitting element that emits irradiated light toward the end face and a light emitting element that emits light toward the end face and which is reflected by at least the end face. A control device for a liquid mixture ratio sensor that calculates a mixture ratio of the liquid to be measured based on the amount of light received by the light receiving elements, wherein a light receiving element that receives the irradiated light is arranged in the container, and a mixing ratio of the liquid to be measured is calculated based on the amount of light received by the light receiving element. a monitoring light-receiving element for directly receiving the irradiation light of the light-emitting element, and a control circuit for feedback-controlling the light-emitting element based on a light reception signal of the monitoring light-receiving element, the control circuit a high amplification circuit for amplifying the light reception signal of the monitoring light receiving element using an operational amplifier;
A control device for a liquid mixture ratio sensor, characterized in that a capacitor is connected in parallel to a feedback resistor for feeding back the output of the operational amplifier to the input.