JPH09273959A - Level detection circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To upgrade the indication accuracy with higher resolutions. SOLUTION: The voltage of a power source P DET for detection is homopolar with the voltage of a reference power source P REF while the absolute value of the voltage of the power source P DET for detection is set larger than the absolute value of the voltage of the reference power source P REF. This allows reduction in the variation of the resistance value of a sender resistor 6 with respect to the change in the input voltage of an A/D converter 11A to accomplish accurate detection of the level thereby achieving a higher indication accuracy. In addition, a voltage dividing resistor R1 is held within an input voltage of the A/D converter 11A whose range of the output voltage is prescribed by the voltage of the reference power source while the resistance value is set to reduce a difference between the range of the output voltage and the range of the input voltage. Thus, the range of the output voltage can be larger within the range of the input voltage of the A/D converter 11A to allow the further deriving of the capacity of the A/D converter 11A thereby achieving a detection of levels with higher resolutions.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a level detection circuit for detecting the liquid level of a liquid, and more particularly to a level detection circuit used as a fuel gauge for measuring the amount of fuel remaining in a fuel tank of a vehicle.

[0002]

2. Description of the Related Art A vehicle is provided with a fuel gauge for measuring the remaining amount of gasoline, engine oil, or the like. The fuel gauge is
For example, there are a sliding resistance type, an induction type, a hall element type and the like.

A sliding resistance type fuel gauge will be described below. A sliding resistance type fuel gauge is installed in the fuel tank,
A float floated on the surface of the liquid, a float arm that supports this float so that it can swing, and a sender resistance as a sliding resistance whose resistance value changes according to the swing angle of the float arm. It has a potentiometer, a controller having an A / D input terminal T connected to the other end of the sender resistor, and a fuel meter for displaying the remaining amount of fuel.

FIG. 4 shows a detailed block diagram of the controller. The controller 50 has one end connected to the other end of the sender resistor 51, and the pull-up resistor (voltage dividing resistor) R11 connected to the power source P (+5 [V]) and the sender resistor 51 and the pull-up resistor R11 are common. The low pass filter 52 has one end connected to the connection point, and the CPU 53 has the reference voltage input terminal AVREF connected to the power source P and the AD input terminal AD connected to the low pass filter 52.

In this case, an AD input terminal AD of the CPU 53 is connected to an A / D converter 53A for analog / digital converting the output signal of the low pass filter 52. The low-pass filter 52 has one end connected to a common connection point of the sender resistor 51 and the pull-up resistor R11, and the other end connected to the resistor R12 connected to the A / D input terminal AD.
And a capacitor C1 having one end connected to an intermediate connection point between the resistor R12 and the A / D input terminal AD and the other end connected to the low potential side power source PLO.

Next, the general operation of the fuel gauge will be described. The float of the fuel gauge follows the displacement of the liquid level and changes the swing angle of the float arm. As a result, the resistance value of the sender resistor 51 changes in accordance with the swing angle of the float arm. Therefore, this change in resistance value is detected and output as a corresponding voltage change to, for example, a controller for driving the meter. As a result, the controller 50 performs a display or the like according to the detected remaining liquid amount.

Next, the operation of the controller will be described. The resistance value of the sender resistor 51 changes following a float (not shown). As a result, the difference voltage between the voltage of the power supply P and the voltage of the low-potential-side power supply PLO is determined according to the resistance ratio of the resistance value of the sender resistor 51 and the resistance value of the pull-up resistor R11 connected to the sender resistor 51. Then, the divided voltage is output from the common connection point to the low-pass filter 52.

The low-pass filter 52 removes the high frequency noise component of the input signal and outputs it to the A / D input terminal AD of the CPU 53. As a result, the A / D converter 53A of the CPU 53 performs analog / digital conversion of the divided voltage and outputs it as remaining amount data, and the CPU 53 controls various processes such as meter display based on the remaining amount data.

FIG. 5 is an explanatory diagram showing the relationship between the resistance value of the sender resistor 51 and the voltage input to the A / D input terminal AD. In this case, the resistance value of the sender resistance when the fuel tank is empty (corresponding to the "Empty" display state) is 50 [Ω], and the fuel tank is full (corresponding to the "Full" display state).
At this time, the resistance value of the sender resistor is set to 450 [Ω].

When the resistance value of the sender resistor 53 is RSD 'and the resistance value of the pull-up resistor R11 is RPU', A /
The power supply voltage of the voltage VAD 'input to the D input terminal is 5
Since it is [V], VAD '= 5.RSD' / (RSD '+ RPU').

As a result, the resistance values RSD 'and A of the sender resistance are
The relationship of the voltage VAD 'input to the / D input terminal is as shown in FIG.

[0012]

If the A / D converter 53A connected to the A / D input terminal AD of the CPU 53 is an 8-bit A / D converter, the input voltage is In the entire range of 0 [V] to 5 [V], the maximum 256 levels can be represented.

However, in the above conventional fuel gauge, FIG. 5 shows the voltage change from the empty state (corresponding to the "Empty" display state) to the full state (corresponding to the "Full" display state) of the fuel tank. As about 1.7 [V] to 4.1
It is about 2.4 [V], which is a problem that only 128 steps of resolution can be realized.

Further, the closer to the full state, the larger the resistance value change amount of the sender resistance with respect to the input voltage change of the A / D converter (see the stepped arrow in FIG. 5), and the movement of the pointer of the fuel gauge is as shown in FIG. As shown in FIG. 6, there is a problem that the pointing accuracy becomes poorer as the tank becomes closer to the full state.

Therefore, an object of the present invention is to provide a level detection circuit capable of improving pointing accuracy with high resolution.

[0016]

In order to solve the above-mentioned problems, the invention according to claim 1 is a sender resistance whose resistance value changes according to a liquid level detected via a float floated on the liquid surface, One end is connected to the sender resistor, the other end is connected to a power source for detection, a voltage dividing resistor, an intermediate connection point between the sender resistor and the voltage dividing resistor is connected to an input terminal, the sender resistor and the voltage dividing resistor. A level detection circuit for detecting the liquid level, which comprises an A / D converter which performs analog / digital conversion by comparing the output voltage at the intermediate connection point of the resistor with the voltage of the reference power source and outputs as the detected liquid level data. In, the detection power supply and the reference power supply is provided as a separate power supply, the voltage of the detection power supply has the same polarity as the voltage of the reference power supply, and the absolute value of the voltage of the detection power supply is , The reference power source Configured as set larger than the absolute value of the voltage.

According to the invention of claim 1, the voltage of the detection power supply has the same polarity as the voltage of the reference power supply, and the absolute value of the voltage of the detection power supply is greater than the absolute value of the voltage of the reference power supply. Since it is set to be large, the resistance value change amount of the sender resistance with respect to the input voltage change of the A / D converter can be reduced.

According to a second aspect of the invention, in the first aspect of the invention, the voltage dividing resistor has a range of input voltage of the A / D converter in which a range of the output voltage is defined by a voltage of the reference power source. The resistance value is set so as to be within the range and the difference between the range of the output voltage and the range of the input voltage is small.

According to the invention of claim 2, in addition to the operation of the invention of claim 1, the voltage dividing resistor has an input voltage of the A / D converter whose output voltage range is defined by the voltage of the reference power source. Since the resistance value is set so that the difference between the output voltage range and the input voltage range is small, the output voltage range is set to the input voltage of the A / D converter. It will be wide within the range.

[0020]

Preferred embodiments of the present invention will now be described with reference to the drawings. FIG. 1 shows a schematic block diagram of a fuel gauge using a sender resistance that is a sliding resistance. The fuel meter 1 is arranged in a fuel tank 2 and floats on the liquid surface of the fuel 3, a float arm 5 that supports the float 4 so that the float 4 can swing, and a low-potential-side power source PLO at one end.
(= 0 [V]) and the sender (Se) as a sliding resistance whose resistance value changes according to the swing angle of the float arm 5
nder) Potentiometer 7 having a resistor 6, a controller 8 having an A / D input terminal TAD connected to the other end of the sender resistor 6, and a fuel meter 9 for displaying the remaining amount of fuel.
And is provided.

FIG. 2 shows a detailed block diagram of the controller 8. The controller 8 has one end connected to the other end of the sender resistor 6 and the other end connected to the detection high potential side power source (+8
[V]) A pull-up resistor (voltage dividing resistor) R1 connected to PDET, a low-pass filter 10 having one end connected to a common connection point of the sender resistor 6 and the pull-up resistor R1,
The reference voltage input terminal AVREF is connected to the reference power source PREF, and the AD input terminal AD is connected to the low-pass filter 10 and the CPU 11 is provided.

In this case, the AD input terminal AD of the CPU 11 is connected to the A / D converter 11A for analog / digital converting the output signal of the low pass filter 10. The low-pass filter 10 has one end connected to a common connection point of the sender resistor 6 and the pull-up resistor R1 and the other end connected to the resistor R2 connected to the A / D input terminal AD.
And a capacitor C having one end connected to an intermediate connection point between the resistor R2 and the A / D input terminal AD and the other end connected to the low-potential-side power supply PLO.

In this case, the high potential power supply P for detection
The DET voltage is set to +8 [V] because the battery voltage in an automobile is 10 to 10 even in normal use.
This is because it fluctuates within a range of about 16 [V], so that stable operation is possible even when the predicted lowest voltage of the battery voltage = 10 [V]. From the viewpoint of measurement accuracy and the like, it is preferable to set the voltage of the detection high potential side power source PDET to a voltage on the higher voltage side if stable operation is possible. At this time, the voltage of the reference power source is set to VREF, the resistance value of the sender resistor 6 in the fuel gauge 1 when the output voltage corresponds to the reference voltage VREF is set to RSD, and the voltage of the detection high potential side power source PDET is set to VDT. In this case, the resistance value RPU of the pull-up resistor is RPU = VDT.RSD / VREF-RSD = (VDT / VREF-1) .RSD.

Next, the general operation will be described. The position of the float 4 changes and the float arm 5 swings as the position of the liquid surface changes as the fuel 3 increases and decreases. Following the swing of the float arm 5, that is, the position of the sliding piece 6A of the sender resistor 6 changes according to the swing angle of the float arm, and the resistance value of the sender resistor 6 changes.

As a result, the voltage of the detection high-potential side power supply PDET and the low-potential side power supply correspond to the resistance ratio of the resistance value of the sender resistor 6 and the resistance value of the pull-up resistor R1 connected in series with the sender resistor 6. The voltage difference from the voltage of PLO (= 8 [V]) is divided, and the divided voltage is the low-pass filter 1 from the common connection point.
Output to 0.

The low-pass filter 10 removes the high frequency noise component of the input signal and outputs it to the A / D input terminal AD of the CPU 11. As a result, A / of the controller 11
The D converter 11A performs analog / digital conversion of the divided voltage and outputs it as remaining amount data, and the CPU 11 displays the remaining amount of fuel 3 on the fuel meter 9 based on the obtained remaining amount data.

FIG. 3 is an explanatory diagram showing the relationship between the resistance value of the sender resistor 6 and the voltage input to the A / D input terminal. In this case, the resistance value of the sender resistor 6 when the fuel tank 2 is empty (corresponding to the "Empty" display state) is 50 [Ω], and the fuel tank 2 is full (corresponding to the "Full" display state). At this time, the resistance value of the sender resistor 6 is set to 450 [Ω].

When the resistance value of the sender resistor 6 is RSD and the resistance value of the pull-up resistor R1 is RPU, the voltage VAD input to the A / D input terminal is the detection power supply voltage of 8
Since it is [V], VAD = 8 · RSD / (RSD + RPU). In FIG. 3, the resistance value RPU of the pull-up resistor R1 is set to 300 [Ω].

As a result, the resistance values RSD of the sender resistance and A /
The relationship of the voltage VAD input to the D input terminal is represented by the curve shown by the solid line in FIG. More specifically, the voltage change from the empty state (corresponding to the "Empty" display state) to the full state (corresponding to the "Full" display state) of the fuel tank 2 is about 1.2.
It is about 3.5 [V] from [V] to 4.7 [V], and the CPU
If the A / D converter 11A connected to the 11 A / D input terminal AD is an 8-bit A / D converter, then 18
It is possible to realize resolution of about 0 steps, and display can be performed with higher resolution than in the past.

Further, even when the full state is approached, the resistance value change amount of the sender resistor 6 with respect to the input voltage change of the A / D converter 11A becomes smaller as compared with the conventional example (see the alternate long and short dash line in FIG. 3). Therefore, the movement of the pointer of the fuel gauge 9 becomes smooth, and even if the fuel gauge 9 approaches the full state, the reduction of the indication accuracy is suppressed.

As described above, according to this embodiment, the detection power supply is provided separately from the reference power supply of the A / D converter, and the detection power supply voltage is set higher than the reference voltage of the A / D converter. Therefore, the change in the resistance value of the sender resistance with respect to the change in the input voltage of the A / D converter becomes smoother and approaches a linear line (when the change in the resistance value of the sender resistance is proportional to the change in the input voltage of the A / D converter). Therefore, the detection accuracy can be improved, and the display change corresponding to the detection data on the full tank side can be smoothed.

In the above embodiments, the detection high potential side power source PDET and the reference power source PREF are positive side power sources, but the detection power source voltage has the same polarity as the reference power source voltage,
Moreover, the same effect can be obtained by setting the absolute value of the voltage of the detection power source to be larger than the absolute value of the voltage of the reference power source.

In the above embodiment, only the fuel gauge has been described, but the present invention can be applied to other level detecting devices as long as it can detect the liquid level of the liquid.

[0034]

According to the invention described in claim 1, the voltage of the detection power supply has the same polarity as the voltage of the reference power supply, and the absolute value of the voltage of the detection power supply is the absolute value of the voltage of the reference power supply. Since it is set to be larger than the value, it is possible to reduce the amount of change in the resistance value of the sender resistance with respect to the change in the input voltage of the A / D converter, it is possible to perform level detection with high accuracy, and improve the pointing accuracy. be able to.

According to the invention of claim 2, in addition to the operation of the invention of claim 1, the voltage dividing resistor has an input voltage of the A / D converter whose output voltage range is defined by the voltage of the reference power source. Since the resistance value is set so that the difference between the output voltage range and the input voltage range is small, the output voltage range is set to the input voltage of the A / D converter. Since it will be wide within the range of A / D
The ability of the converter can be further extracted, and level detection can be performed with high resolution.

[Brief description of drawings]

FIG. 1 is a schematic configuration block diagram of a fuel gauge using a sender resistance.

FIG. 2 is a detailed configuration block diagram of a controller.

FIG. 3 is an explanatory diagram of a relationship between a sender resistance value and an A / D input terminal input voltage.

FIG. 4 is a detailed configuration block diagram of a conventional controller.

FIG. 5 is an explanatory diagram of a relationship between a conventional sender resistance resistance value and an A / D input terminal input voltage.

FIG. 6 is an explanatory diagram of a conventional problem.

[Explanation of symbols]

 1 Fuel meter 2 Fuel tank 3 Fuel 4 Float 5 Float arm 6 Sender resistance 7 Potentiometer 8 Controller 9 Fuel meter 10 Low pass filter 11 CPU 11A A / D converter PDET High voltage side power supply for detection PREF Reference power supply R1 Pull-up resistance R2 resistance

Claims (2)

[Claims] 1. A sender resistor whose resistance value changes according to the liquid level detected via a float floated on the liquid surface, one end of which is connected to the sender resistor, and the other end of which is connected to a power source for detection. A voltage dividing resistor and an intermediate connection point between the sender resistor and the voltage dividing resistor are connected to an input terminal, and an analog voltage is obtained by comparing the output voltage at the intermediate connection point between the sender resistor and the voltage dividing resistor with the voltage of the reference power source. / A / D converter for digitally converting and outputting as detected liquid level data, and in the level detection circuit for detecting the liquid level, the detection power supply and the reference power supply are provided as separate power supplies, The voltage of the detection power supply has the same polarity as the voltage of the reference power supply, and the absolute value of the voltage of the detection power supply,
A level detection circuit, which is set to be larger than an absolute value of a voltage of the reference power supply. 2. The level detection circuit according to claim 1, wherein the voltage dividing resistor is within the input voltage range of the A / D converter in which the output voltage is regulated by the voltage of the reference power source, and A level detection circuit, wherein a resistance value is set so that a difference between the output voltage range and the input voltage range is reduced.