JPH07190825A - Apparatus for detecting amount of suction air - Google Patents

Abstract

PURPOSE:To hold a sensor part at a predetermined position at all times and correctly measure an amount of suction air by using a shape memory alloy for a lead wire. CONSTITUTION:When the pressure of a compressed cleaning air hits a heat resistance element, 9, lead wires 14a, 14b buffer a stretching stress. When the compressed air is relatively weak, a stress buffering part is within an area of an elastic deformation. Therefore, the lead wires return to the original state when the air is finished to be blown, and a sensor part alike returns to a predetermined position against the suction air. If the blown compressed air is strong, the stress buffering part is deformed beyond the elastic deformation. However, the stress buffering part is returned to the original shape owing to a shape memory action when an engine is started to flow a current to a platinum wire 16 of the element 9 and the heat generated by the platinum wire is transmitted to the wires 14a, 14b. The stress buffering part is turned to be at right angles to the flow of the air, so that a flow velocity of the suction air is correctly measured.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an intake air amount detecting device using a thermal resistance element for measuring the amount of intake air supplied to an automobile engine.

[0002]

2. Description of the Related Art In principle, a hot-wire intake air amount detecting device measures the flow velocity of intake air supplied to an internal combustion engine,
The flow rate is calculated from the flow rate by a computer.
That is, the thermal resistance element is arranged so that the sensor portion is arranged at a position orthogonal to the flow of intake air. And
When a current is applied to the thermal resistance element to heat it to a temperature higher than the intake air temperature by a predetermined temperature and the thermal resistance element is cooled by the intake air, the thermal resistance element always has a constant temperature difference with respect to the intake air temperature. The current flowing through the thermal resistance element is controlled so that The flow velocity of the intake air is measured based on the current value, and the flow rate is calculated by multiplying the flow velocity by the cross-sectional area. Therefore, the thermal resistance element is always in contact with the intake air. On the other hand, the intake air coming into contact with the thermal resistance element passes through an air cleaner for removing dust, etc., but it is difficult to remove all the fine dust and blow-by gas, so that the thermal resistance element can be removed over time. There was a problem that dirt adhered. If dirt adheres to the thermal resistance element, the thermal resistance element cannot directly contact the intake air, which causes a problem that an error occurs in the measurement of the flow velocity.

Therefore, after traveling a predetermined distance, at the time of vehicle inspection, etc., the heat ray type intake air amount detecting device is detached from the dealer and compressed air is blown against the thermal resistance element with an air gun to adhere to the surface of the thermal resistance element. I was removing dirt. At this time, the lead wire that holds the heat wire resistance element in place may be bent, and if the lead wire bends with respect to the flow of intake air, the problem that the flow velocity of intake air cannot be accurately measured occurs. Was there. Here, it is conceivable to make the lead wire thick, but if the lead wire is made thick, the amount of heat radiation in the lead wire becomes large and the responsiveness of the flow velocity measurement in the thermal resistance element deteriorates, so the lead wire cannot be made thick. Therefore, in order to solve this problem,
In Japanese Unexamined Patent Publication No. 96527, it is proposed to provide a loop-shaped stress buffer portion on the lead wire.

[0004]

However, the conventional intake air amount detecting device provided with the loop-shaped stress buffering portion has the following problems. That is, when the thermal resistance element is heavily soiled, excessive compressed air may be applied to the thermal resistance element, and the stress limit of elastic deformation of the loop-shaped stress buffering portion may be exceeded, and the lead wire may be damaged. In some cases, the shape could not be restored. In that case, there is a problem that the thermal resistance element is inclined with respect to the flow of the intake air, and the flow velocity of the intake air cannot be accurately measured. The present invention provides an intake air amount detection device that can always maintain a predetermined position with respect to the flow of intake air even if compressed air is strongly blown in order to remove dirt adhering to a thermal resistance element. To aim.

[0005]

In order to achieve the above object, an intake air amount detecting device of the present invention is arranged in a flow of intake air to be supplied to an internal combustion engine and has a thermal resistance for measuring the intake air amount. An intake air amount detection device having an element, in which a thermal resistance element holds a sensor portion formed by winding a platinum wire around a ceramic bobbin and both ends of the sensor portion to hold the sensor portion at a predetermined position. It has a lead wire made of a memory alloy. In addition, the intake air amount detecting device of the present invention is characterized in that, in the above-mentioned configuration, the lead wire has a loop-shaped stress buffering portion.

[0006]

The intake air amount detecting device of the present invention having the above-mentioned structure is arranged in the flow of intake air supplied to the internal combustion engine, and the thermal resistance element measures the intake air amount. That is, the sensor portion of the thermal resistance element is always heated to a high temperature state by the current flowing through the thermal resistance element and maintains a constant temperature difference with respect to the intake air temperature even when cooled by the intake air.
At this time, the flow velocity of the intake air is measured based on the current value flowing through the thermal resistance element, and the flow amount is calculated by multiplying the flow velocity by the cross-sectional area. Therefore, in order to accurately measure the flow velocity of the intake air, it is necessary to always keep the sensor portion of the thermal resistance element in a fixed positional relationship with the flow of the intake air.

When compressed air for removing dirt is strongly blown to the sensor section, the lead wire made of a shape memory alloy having a loop-shaped stress buffer section is deformed by the stress buffer section to generate air pressure. receive. When the compressed air to be blown is relatively weak, it is within the elastic deformation area of the stress buffer, so the lead wire returns to its original state when the blowing of air is complete, so the sensor also has a predetermined amount of air relative to the intake air. Can return to position. When the compressed air blown is strong, the stress buffer section is deformed beyond elastic deformation. However, when the thermal resistance element is returned to the flow of the intake air and heated, the lead wire made of the shape memory alloy returns to its original shape, so that the sensor unit can also return to a predetermined position.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 2 shows a state in which the intake air amount detection device 1 is fixed to the engine. The intake air amount detecting device 1 is fixed to a shaft 4 in a passage of a throttle body 2 so that a throttle valve 3 can rotate. The shaft 4 is attached to the throttle body 2. A detection flow path 5 having an L-shaped passage is provided upstream of the throttle valve 3. An inlet 6 is opened at one end of the detection flow path 5 in the flow direction of the intake air and the other end is closed, and an outlet 7 for discharging the introduced air is formed at the left and right side surfaces of the closed other end. A hot-wire type flow meter 8 is attached near the inlet 6. The flowmeter 8 includes a thermal resistance element 9 and a temperature compensation element 10.
Are each stretched by a pair of conducting wires. The thermal resistance element 9 and the temperature compensation element 10 are connected to a detection circuit 11 attached to the outside of the throttle body 2.

Next, the thermal resistance element 9, which is an important part of the present invention, will be described in detail with reference to FIGS. Since the temperature compensating element 10 measures the intake air temperature by its resistance value, the measurement accuracy is not affected even if it is deformed to some extent, and therefore its explanation is omitted. A heat resistance element 9 and a temperature compensating element 1 are provided in the element mounting portion 12 of the hot wire type flow meter 8 in a direction perpendicular to the intake air flow.
0 is extended. Thermal resistance element 9 and temperature compensation element 10
Since it has the same structure as,
The structure of is shown in FIG. One end of a pair of lead wires 14a and 14b forming a lead portion is fixed by welding to the inside of the tips of the support members 13a and 13b standing upright in parallel with the element mounting portion 12. The other end of the pair of lead wires 14a and 14b is fixedly provided with a ceramic bobbin 15 which constitutes a sensor section.
Platinum wires 16 are wound at regular intervals between the lead wires 14a and 14b with a ceramic bobbin 15 interposed therebetween. Platinum wire 1
An electric current is passed through 6 through the supporting members 13a and 13b to detect the amount of intake air. The lead wires 14c and 14d are made of a shape memory alloy and form loops 14c and 14d to form stress buffering portions. As the shape memory alloy material, a conductive material such as titanium / nickel alloy or copper alloy is used.

Next, the operation of the present invention will be described based on embodiments. When the vehicle is operated for a long period of time and fine dust, blow-by gas, or other dirt adheres to the inside of the intake air passage A and the intake air amount detecting device 1, the air cleaner is removed and the air gun is used to clean the compressed air. This is done when you bring your car to a dealer. And
When the pressure of the compressed air hits the thermal resistance element 9, the lead wire 14
a and 14b buffer the extension stress as shown by the chain double-dashed line in FIG. 1, for example. When the compressed air to be blown is relatively weak, it is within the elastic deformation area of the stress buffer, so the lead wire returns to its original state when the blowing of air is completed. Return to the position. When the compressed air blown is strong, the stress buffer section deforms beyond elastic deformation. When the engine is started, current flows through the platinum wire 16 of the thermal resistance element 9 to generate heat.

Then, the heat is applied to the lead wires 14a and 14b.
The original shape, that is, the shape shown in FIG.
Return to the state of the solid line, and it becomes a right angle to the air flow, and the flow velocity of the intake air is correctly measured. FIG. 4 shows another embodiment of the thermal resistance element. The lead wires 14A and 14B are made of a shape memory alloy as described above to form the wavy portions 14C and 14D. The operation is similar to that described above.

[0012]

As described above, according to the present invention, since the lead portion of the thermal resistance element is formed of the shape memory alloy, the lead portion buffers the stress due to the influence of compressed air, etc.
The shape memory effect restores the original shape and makes a right angle with respect to the intake air amount, so that the intake air amount can be accurately measured.

[0013]

[Brief description of drawings]

FIG. 1 is a front view showing the structure of a thermal resistance element of an intake air amount detection device according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view showing a state in which the intake air amount detection device according to the present invention is used.

FIG. 3 is a side view showing a configuration of a hot-wire flow meter according to the present invention.

FIG. 4 is a front view of another embodiment of the thermal resistance element according to the present invention.

[Explanation of symbols]

 1 Intake air amount detection device 9 Thermal resistance element 11 Detection device 14a, 14b, 14A, 14B Lead wire 14c, 14d Loop 14C, 14D Wavy portion 16 Platinum wire

Claims (2)

[Claims] 1. An intake air amount detecting device having a thermal resistance element arranged in a flow of intake air supplied to an internal combustion engine, for measuring the intake air amount, wherein the thermal resistance element is platinum on a ceramic bobbin. It has a sensor part formed by winding a wire, and a lead wire made of a shape memory alloy that is connected to both ends of the sensor part and is connected to both ends of the sensor part to hold the sensor part at a predetermined position. Intake air amount detector. 2. The intake air amount detection device according to claim 1, wherein the lead wire has a loop-shaped stress buffering portion.