JPH0522850B2 - - Google Patents

Description

Detailed Description of the Invention [Technical Field of the Invention] The present invention, for example, when electronically controlling an internal combustion engine, measures the amount of intake air corresponding to the operating state of the engine, and controls the electronic control of the engine. The present invention relates to a thermal air flow rate measuring device that is configured to supply a measurement detection signal to a control unit.

[Technical Background of the Invention] For example, when an engine, which is an internal combustion engine installed in a car, is controlled by an electronic control means, the operating state of the engine is constantly monitored,
It is necessary to ensure that control actions corresponding to the operating conditions are executed. For this reason, a detection and measurement device is set up in connection with the engine to constantly monitor the operating condition of the engine, and the monitoring means include engine rotational speed detection means, engine temperature detection means, exhaust gas Gas detection means etc. are present, and furthermore, as a means directly related to the operating state of the engine, there is provided a measuring and detecting means for intake air flow rate.

Various types of intake air flow rate measuring means are known, and for example, thermal air flow rate measuring means is known. In other words, this measuring means sets a temperature sensing element that is heated and controlled in the intake pipe, and measures the state of the heat dissipation effect of the temperature sensing element, which changes depending on the air flow flowing inside the intake pipe, and the temperature change state of the temperature sensing element. The detection signal is used to express the measured air flow rate.

The form of such an output signal is considered to be, for example, a pulse signal with a time width corresponding to the measured air flow rate, and is used, for example, to perform electronic control of the fuel injection amount in an engine control unit. In this case, the time width of the pulse-like signal corresponding to the measured air flow rate is a digital signal that calculates the opening time of the fuel injection valve corresponding to the injection amount by digitally counting the time width. It will be possible to use it as a.

The output circuit of such a measuring device is usually configured to supply the pulsed signal to the base circuit of a transistor, and use the transistor to amplify and output the pulsed signal. ing. In other words, the above transistor is turned on/off.
An output signal corresponding to the OFF state is taken out and supplied to the engine control unit, but in such a circuit, the output impedance of the transistor in the ON state and the OFF state are greatly different. become. Therefore, when a signal from such an output circuit is supplied to the above control unit, the time constants of the rise and fall of the signal after passing through the filter circuit for noise removal in this control unit are It becomes difficult to make them equal. Also,
In particular, when the transistor in the output circuit is in the off state, the signal transmission line becomes high impedance on the detection device side, making it easy to malfunction due to ignition noise, radio noise, etc. to the engine.

[Object of the Invention] This invention has been made in view of the above points, and when the measurement signal is a pulse-like signal with a set time width, it is possible to , a thermal air flow rate measuring device that performs accurate signal detection operations and is not influenced by external noise, etc., so that, for example, fuel injection amount setting control for the engine can be effectively executed. This is what we are trying to provide.

[Summary of the Invention] That is, in the thermal air flow measuring device according to the present invention, a temperature sensing element having temperature characteristics is set in the air flow path, and this temperature sensing element is periodically generated. The heating is controlled by the heating current that rises in response to the energization start signal.
The width of this heating current is set and controlled in response to the temperature rise of the temperature sensing element to a specific temperature state. Then, a pulse-like signal corresponding to the time width of this heating current is outputted as an output signal, and the output circuit for this signal consists of a pair of circuits that are controlled on and off reciprocally by the above-mentioned pulse-like signal. The transistor is connected in series to a power supply, and the output signal is taken out from the series connection point.

[Embodiment of the Invention] An embodiment of the invention will be described below with reference to the drawings. Figure 1 shows the circuit configuration.
For example, a case will be explained in which the intake air flow rate of an engine is measured. That is, the temperature sensing element 11 is installed and set inside the intake pipe of the engine so as to be exposed to the intake air flow. The temperature sensing element 11 is constructed of a resistance wire, such as a platinum wire, having temperature resistance characteristics, and an auxiliary temperature sensing element 12 is further attached and set inside the intake pipe. That is, the temperature sensing element 11 is heated and controlled by supplying a heating current to a state where the temperature rises, and its resistance value is set to a state corresponding to the temperature.
In this case, the temperature sensing element 11 is in a state where heat radiation is controlled by the air flow flowing through the intake pipe, and the temperature increase state corresponds to the air flow rate flowing through the intake pipe. In addition, the auxiliary temperature sensing element 12
The resistance value is set in accordance with the temperature of the air flowing through the intake pipe, and a reference temperature state is set for the temperature of the temperature sensing element 11 which is subjected to heating control. The temperature sensing element 11 and the auxiliary temperature sensing element 12 constitute a bridge circuit together with fixed resistors 13 and 14, and the connection between the temperature sensing element 11 and the resistor 13 serves as an output terminal of this bridge circuit. The point a and the connection point b between the auxiliary temperature sensing element 12 and the resistor 14 are connected to the comparator 15 . That is, the output signal from the comparator 15 is set to rise when the temperature of the temperature sensing element 11 rises within a specified temperature range relative to the air temperature due to the heating current.
The output signal from 5 is sent to flip-flop circuit 16.
reset control.

This flip-flop circuit 16 is set-controlled by a current supply start signal, and this current supply start signal is constituted by, for example, a rotation synchronization signal generated in synchronization with the rotational state of the engine (not shown). That is, flip-flop circuit 1
6 is set-controlled in response to a specific rotational angle of the engine, and reset-controlled when the temperature sensing element 11 is heated to a specific temperature state. Now generates an output signal. In this flip-flop circuit 16, priority is given to the set signal. The output signal of the flip-flop circuit 16 is used to turn on and off a transistor 18 via a buffer amplifier 17, and this transistor 18 turns on and off the power to the bridge circuit including the temperature sensing element 11. I come to do it. The temperature sensing element 11 is heated and controlled by a heating current corresponding to the pulsed signal, and the temperature increase state of the temperature sensing element 11 due to this heating current is determined by the air flow rate in the intake pipe. , the rate of temperature rise to the specific temperature state, that is, the time width until the output signal is generated from the comparator 15, corresponds to the air flow rate. Therefore, the time interval from the setting to the reset of the flip-flop circuit 16 corresponds to the air flow rate in the intake pipe.
The output signal from the flip-flop circuit 16 is directly used as a measurement output signal, and this signal is taken out via the output circuit 19 and coupled to an engine control unit (not shown) as an intake air amount measurement signal. Become so.

Here, the transistor 1 that controls the heating current
For the base of 8, the voltage of the heating current and
Differential amplifier 2 supplied with the voltage of reference power supply 20
1, so that the voltage state of the heating current is set as a reference.

Here, the output signal from this measuring device is used in the engine control unit to control the fuel injection amount, and this fuel injection amount control is executed by controlling the opening time of the injection valve. . That is, it is executed under the same pulse time width control state as the air flow rate measurement signal mentioned above.
There is a need for the pulsed output signals from the measuring device to be transmitted to and processed in a sufficiently accurate manner to the control unit.

For example, if the engine is composed of 6 cylinders and is rotating at 6000 rpm, the rotation synchronization signal that constitutes the energization start signal is 3.3 ms.
It will be generated at an interval period of . If the minimum pulse width of the measurement output is 300 μs, and the metering error of the injection valve is ±4%, the pulse width error needs to be ±12 μs. Considering other error factors such as temperature and variations in individual measuring devices, it is necessary to measure the pulse width with high accuracy, with the pulse width error being approximately ±3%.
That is, highly accurate pulse signal transmission processing is required in the process of transmitting pulse signals from the measuring device to the control unit.

FIG. 2 shows a specific circuit configuration of the output circuit 19 that satisfies the above-mentioned requirements. supply That is, this transistor 3
Reference numeral 2 indicates that the flip-flop circuit 16 is in the set state and is turned on when the input signal to this circuit 19 is "1". The output signal obtained from the collector circuit of this transistor 32 is of NPN type and PNP type. to the base electrodes of second and third transistors 33 and 34, respectively. That is, corresponding to the on/off state of the first transistor 32, the second and third transistors 33 and 34 are controlled to be on/off reciprocally.

Here, the second and third transistors 3
3 and 34 are set to be connected in series with the power supply V _{c and} drive voltages are set symmetrically, and the interconnection point portion of these transistors 33 and 34 is connected to the output terminal 35. It is something that becomes. Here, the capacitor 36 constitutes a filter circuit for removing noise components superimposed on the output signal, and 37 and 38 are diodes for overvoltage protection.

The measured output signal obtained from such an output circuit 19 is supplied to an engine control unit 40, and in this unit 40, the measured signal is passed through a filter circuit consisting of a resistor 41 and a capacitor 42. is supplied to a comparator 43 and shaped into a pulse width signal related to the set and reset states of the flip-flop circuit 16, so that signal processing for engine control is performed.

That is, in this output circuit 19, when the input signal supplied to the input terminal 31 is "1", the first transistor 32 is set to the on state, the second transistor 33 is set to the off state, and the third transistor 34 is set to the on state. are set to the on state.
Then, when the above input signal becomes "0",
The first to third transistors 32 to 34 are each inverted from the above state. Therefore, regardless of whether the input signal is in the "1" or "0" state, one of the second and third transistors 33 and 34 is set to the on state. Therefore, for this signal transmission line,
Ignition signal of igniter, ON/OFF of solenoid mechanism
It becomes possible to suppress noise signals of electrostatic induction and electromagnetic induction that are superimposed during the operation of off signals, transceivers, radios, and various other relays to a sufficiently small state. Furthermore, in any of the above states, the output impedance can be set to be low and equal, so that the rising and falling edges of the signal after passing through the filter circuit made up of the resistor 41 and capacitor 42 in the control unit 40 are The conditions can be made uniform, and measurement errors associated with the transmission of the pulsed signal can be minimized.

FIG. 3 shows another embodiment of the output circuit 19, in which the signal supplied to the input terminal 31 is inverted by the first inverter 51, and this signal is sent to the second and third inverters 52. and 53 in parallel. The output signals from the second and third inverters 52 and 53 are supplied as control signals to the second and third transistors 33 and 34, which are connected to the resistors 54 and 55, respectively. Allow specific base bias to be set via .

Here, each of the inverters 51 to 53 may be constructed by a circuit similar to that of the first transistor 32 shown in FIG.

That is, by configuring the output circuit 19 in this way, the high level of the pulsed signal can be set higher and the low level can be set lower.
By increasing the noise margin, the influence on the noise signal can be more effectively prevented.

[Effects of the Invention] As described above, according to the present invention, when an air flow measurement signal set in a pulse wave shape passes through a filter circuit for removing noise, for example, the rising and falling edges of the waveform are The time constants are made equal in each state, and the transmission control of the measurement signal is executed with sufficiently high precision. Moreover, during this pulse transmission, it is possible to make the engine installed in a car sufficiently strong against noise signals generated from the engine system or car electrical components, etc., and reduce the intake air flow rate to the car engine. This allows it to be used particularly effectively as a measuring device.

[Brief explanation of the drawing]

FIG. 1 is a circuit configuration diagram for explaining a thermal air flow rate measuring device according to an embodiment of the present invention, FIG. 2 is a circuit diagram showing an example of the output circuit shown in the above embodiment, and FIG. FIG. 3 is a configuration diagram of an output circuit illustrating another embodiment of the present invention. 11... Temperature sensing element, 12... Auxiliary temperature sensing element, 1
5...Comparator, 16...Flip-flop circuit, 18...Transistor (heating current control),
19... Output circuit, 32... First transistor, 33, 34... Second and third transistor.

Claims (1)

[Claims] 1. A temperature sensing element that is set in relation to an airflow path and has temperature characteristics that are heated and controlled by a heating current;
means for supplying a heating current to the temperature sensing element in response to a periodic energization start signal corresponding to a flow rate measurement operation; It is equipped with means for setting a current time width, and an output circuit that outputs a pulse-like signal corresponding to the set heating current time width as a measurement output signal, and this output circuit is configured to set a time width corresponding to the heating current width. It is equipped with a pair of transistors that are controlled to be turned on and off reciprocally in response to a pulse-like signal with a width of A thermal air flow rate measuring device characterized by: