JPS6050976B2 - AD conversion circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an AD conversion circuit for inputting an analog output of a sensor for engine control to a processor.

A method is known in which the engine of an automobile or the like is controlled by a microprocessor. For example, information regarding the operating state of the engine is detected by various sensors and added to the oil conversion circuit, and the output of the AD conversion circuit is input to the microprocessor. , microprocessor 1 - 1 υ゛1 , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , fuel injection, etc.

In this case, the oil conversion circuit is often of an integral type, and has the configuration shown in FIG. 1, for example. In FIG. 1, the ADC is an integral type AD converter, which adds the outputs of a plurality of sensors 5, 5, to CH, 5, respectively.

terminals, A0 to A2 terminals that add address information to select these CH, ~C terminals, V terminal for grounding, CAP terminal that connects the integrating capacitor C, ST terminal that adds the start signal to start integration, EOC terminal that sends the conversion output to the microprocessor μCPU, power supply voltage VDD
It has a VD terminal to which a reference voltage is applied, a VR terminal to which a reference voltage is applied, and the like. Sensors 5, 52 are water temperature and intake air temperature sensors, sensor s, which are composed of thermistors and the like. is the throttle sensor, sensor s. is an intake pressure sensor with a bridge circuit configuration including a pressure detection element, and R, ~R. is resistance. Figure 2 is an explanatory diagram of the operation, and CH1 to CH4 are
Any one of the terminals is selected, as shown in Figure 2a.
When a start signal of '0'' is applied to the ST terminal, the analog output voltage of the selected sensor causes the capacitor C to
When charging is performed and the start signal returns to i''1'', constant current discharging from the capacitor C starts.

Therefore, the voltage of the capacitor C decreases at a constant slope after being charged to the analog output voltage of the sensor, as shown in FIG. 2b. Therefore, the output shown in FIG. 2c is obtained from the EOC terminal. The analog output voltage of the sensor is Vx, ■8
If the reference voltage applied to the terminal is , then the following relationship is obtained.

Note that TO is the discharge time due to the offset voltage, and T is the time required to discharge the reference voltage (■). As can be seen from equation (1), the analog output voltage x of the sensor and the time Tx shown in Figure 2c have ratiometric characteristics, and by measuring the time Tx with the microprocessor μCPU, the sensor Analog output voltage x can be measured. The analog output voltage of sensors S1 to S4 is
Its magnitude will change depending on the reference voltage ■, but as shown in equation (1), the time T associated with the ratio of the analog output voltage x of the sensors S1 to S4 and the reference voltage ■ Since a converted output is obtained, the influence of changes in the reference voltage (1) can be canceled out.

In addition, the output voltages Xl and X2 of the sensors Sl and S2 are determined by the resistance values RXl and RX2 corresponding to the temperature of the sensors Sl and S2.
(1) X1= However, unless a voltage of at least about 5V is applied to the slot sensor S3 and the intake pressure sensor S4, the linearity will deteriorate and accurate output voltage will not be obtained. Therefore, if the voltage applied to sensors S1 to S4 is 5V, the output voltage will be in the range of 0 to 5V, and the reference voltage (■) will be 5V.
V is required, and in order to guarantee the conversion operation of the AD converter M°C, DD-2 (■), that is, ■. Voltage V applied to the terminal. Since O has to be 2V higher than the reference voltage ■, the voltage VDD needs to be at least 7V or more. Note that the voltage ■ is required for the pigeon converter ADC to perform oil conversion operation. o needs to be at least 4.5V or higher. However, when the engine is started, a large current is supplied from the battery to the starter motor, so the battery voltage B drops significantly. For example, as shown in Figure 3, when the ignition key is turned on at certain times, the battery voltage through the switch is normally 8.
■That's all. When the relay operates and current is supplied from the battery to the starter motor, the voltage may drop to, for example, 4.5V, and the engine rotates to, for example, 400 rpm. P. When it reaches about m, a so-called complete explosion occurs. This is a state at the time when the current to the starter motor is cut off and the voltage generated by the generator driven by the engine rises to 8V or more. When starting the engine like this, the battery voltage
If B decreases as described above and does not satisfy the conditions of ■ and ■DD-2, that is, if the current flowing through resistor tl/LR2 decreases and the voltage drop becomes 2V or less, oil conversion operation is guaranteed. If the battery voltage drops so that the voltage applied to the sensors S3 and S4 drops below 5V, the output voltages of the sensors S3 and S4 will not be proportional to the intake pressure or the like.

In other words, accurate oil conversion cannot be performed due to a drop in the battery voltage (8) when starting the engine.The present invention is designed to detect information such as water temperature and intake air temperature that are required when starting the engine because of the drop in battery voltage. The purpose of this is to ensure oil conversion operation.

Examples will be described in detail below. FIG. 4 shows an embodiment of the present invention, where the same reference numerals as in FIG. 1 indicate the same parts, and D
1 to D3 are diodes for providing a difference of 2V or more between the voltages DD and ■ applied to the VD and VR terminals respectively by the forward voltage d, VCS is a constant voltage circuit,
C1 is a capacitor, ZD is a Zener diode, R9, R
IO is a resistor, and RG is a constant voltage control circuit such as a series control type.

The resistor RlO is for allowing current to flow so that the diodes D1 to D3 can be maintained in the on state, and the
2 and the current flowing to the VR terminal side is the diode D1 to D3.
It can be omitted if it always flows to the extent that it is in the on state. Further, the resistor R9 is used to keep the voltage (DO) applied to the VD terminal constant due to the current flowing through the Zener diode. The engine fuel injection time width is controlled to a fixed time width determined only by the detected information of water temperature and intake air temperature when the engine starts, and after the engine starts, the time width is controlled using the detected information of the throttle and intake pressure. The water temperature sensor S1 and the intake temperature sensor S2 are
Reference voltage ■ to be applied to the R terminal is applied through resistors 11/LR3 and R4, and CH is applied through resistors R5 and R6, respectively.
l, connected to the CH2 terminal.

Further, the throttle sensor S3 and the intake pressure sensor S4 have a voltage of, for example, 5V±10% of the output of the constant voltage control circuit RG.
. is added to CH3 and CH4 through resistors R7 and R8.
connected to the terminal. Also, the voltage ■Cc is CH3, CH4
It is added to the CFI5 terminal to use as a reference voltage for the input voltage to the terminal. If the voltage drop due to the resistor R9 of the constant voltage circuit VCS is VR9, the voltage applied to the o terminal is .

o becomes ゛, and assuming that the forward voltage of the diodes D1 to D3 is 6, then the reference voltage 2 applied to the R terminal becomes . This forward voltage ■d is almost constant even if the current flowing through the diodes D1 to D3 changes, so ■6=2
When (■) is set, the conditions of (■) VDD-2 can always be satisfied. Also, water temperature sensor S1 and intake temperature sensor S2
Output voltage from ■Xl, ■X2 and AD from EOC terminal
As shown in equations (1) to (3), the conversion output signal is unaffected by changes in the reference voltage (1), and even if the battery voltage (B) decreases, the detection output voltage for water temperature and intake temperature will not change. A
D conversion becomes possible. For example, when the battery voltage ■B becomes 5V, the Zener diode ZD of the constant voltage circuit ■CS
is in the off state and cannot perform constant voltage operation.
If the voltage drop due to the resistor R9 is, for example, 0.5V because the current flowing through the AD converter ADC and the sensors Sl and S2 is about 2rT1A, then VDD=4.
5V, and if ■d=2V, Vr=2.5V, and the output voltages of sensors Sl, S2, ■Xl, ■X2 become O.
~2.5V.

■C. Since D=4.5V, the pigeon converter ADC is operable, and ■ku■. o-2, so sensors Sl, S
AD conversion of the second output voltage is performed. That is, even if the battery voltage B drops to 5V, the output voltages of the water temperature sensor S1 and the intake air temperature sensor S2 can be converted to oil, so that control at the time of starting the engine can be performed. Also, when starting the engine, the throttle sensor S3 and intake pressure sensor S4
The output voltage of the constant voltage control circuit RG does not require AD conversion.

. This means that even if the value fluctuates, it will not affect engine start control. The engine is in a complete explosion state and the battery voltage V8 is 5.
V, the zener voltage of the zener diode rises to 7
．． Assuming 5V, a voltage of 7.5V DO is applied to the VD terminal by the constant voltage circuit CS, and the reference voltage ■ is 5.5V.
It becomes V. Further, the constant voltage control circuit RG outputs a voltage ■Cc of 5V±10%, and the voltage ■Cc is applied to the throttle sensor S3 and the intake pressure sensor S4. . can be applied, and an output voltage with a desired dynamic range can be applied to the CI (3, C1I1 terminal). Also, since the voltage Vcc is applied to the CH5 terminal and AD converted, in the microprocessor μCPU,
Connect CH3 and CH4 terminals to A. The throttle and intake pressures can be detected by determining the ratio between the AD-converted output signal selected based on the terminal address information and the AD-converted output signal selected from the CH5 terminal. Note that the output voltages of the water temperature sensor S1 and the intake temperature sensor S2 are also converted to oil. It is also possible to use Zener diodes instead of the diodes D1 to D3.
At least 2 ■ power supply terminals ■ as constant voltage elements.

It is only necessary that a potential difference of 2 V between the reference voltage terminal (2) and the reference voltage terminal (2) can be obtained even when the battery voltage (2)8 fluctuates. As described above, the present invention provides a power supply terminal (2) of an integral type oil converter ADC which selects input terminals CH1 to CH5 according to address information to the AO-A2 terminal and converts an analog voltage. To the engine A reference voltage ■1 is applied from the reference voltage terminal VR via resistors R3 and R4 to the sensors Sl and S2 that detect information such as water temperature and intake temperature required at the time of starting, and the throttle and Sensors S3 and S4 that detect information such as intake pressure are supplied with a voltage VO obtained by stabilizing the battery voltage (1)8 by a constant voltage control circuit RG.
Even when the engine is started, the power supply voltage V is maintained by the constant voltage element. Since a predetermined potential difference between O and the reference voltage V is obtained, even if the battery voltage (2) 8 decreases, the AD conversion output of the detection information required at the time of starting the engine can be obtained. Further, after the engine is started, the dynamic range of each sensor can be widened and the oil conversion operation can be performed, so that the reliability of pigeon conversion for engine control can be improved.

[Brief explanation of drawings]

Fig. 1 shows a conventional oil conversion circuit, Fig. 2 shows an explanatory diagram of AD conversion operation, Fig. 3 shows an explanatory diagram of battery voltage at engine start, and Fig. 4 shows a pigeon conversion circuit according to an embodiment of the present invention. It is something. ADC is an integral type AD converter, VD is a power supply terminal, ■1 is a reference voltage terminal, CHl~CH5 are input terminals, A~A2 is an address information input terminal, ST is a start signal input terminal, E
OC is an AD conversion signal output terminal, C is an integrating capacitor,
μCPU is a microprocessor, VCS is a constant voltage circuit,
RG is a constant voltage control circuit, S1-S4 are sensors, R1-R
IO is a resistor, D1 to D3 are diodes, and 1 is a Zener diode.

Claims (1)

[Claims] 1 AD the analog output voltage of the sensor for engine control
In the AD conversion circuit for converting and inputting the data to the processor, the power supply terminal of the integral type AD converter which AD converts the analog voltage to the input terminal selected by the address information from the processor and outputs the AD converter. A battery voltage is applied through a constant voltage circuit, a constant voltage element is connected between the power supply terminal and a reference voltage terminal, and the water temperature is detected through a resistor to the reference voltage terminal to detect the information required when starting the engine. , the battery voltage is stabilized by a constant voltage control circuit and is applied to the throttle, intake pressure, etc. sensors that detect necessary information after the engine starts, by connecting sensors for intake air temperature, etc. AD conversion circuit.