JPH04110968U - alcohol concentration sensor - Google Patents

Abstract

(57) [Summary] [Purpose] To improve the detection accuracy even in the low concentration range in a sensor that detects alcohol concentration by detecting changes in capacitance between the outer electrode and the inner electrode through which fuel passes. Plan. [Structure] The cylindrical housing 21 is composed of a cylindrical portion 31 and a cylindrical portion 23 made of an insulating material (for example, resin name: PPS), and a hollow center electrode is provided inside the cylindrical portion 2 and extends along its central axis.
24 has been inserted. The cylindrical portion 31 includes a large diameter portion 32 and a small diameter portion 33, and an outer electrode 35 is provided on the inner peripheral surface of the large diameter portion 32 facing the tip 6a of the center electrode 6. [Effect] When electricity is applied between the terminals 29 and 36, a change in capacitance between the center electrode 6 and the outer electrode 35 is detected only in the vicinity of the tip 6a of the center electrode 6.
Even when the detection range of capacitance change is limited and the relative dielectric constant of the fuel is low and the alcohol concentration is low, a stable output voltage is output and detection accuracy is improved. The tip portion 6a has a symmetrical shape with no intervening material between the center electrode 6 and the outer electrode 35, and no opening 31a formed in the middle of the cylindrical portion 31, so that detection accuracy is further improved. .

Description

[Detailed explanation of the idea]

0001

[Industrial application field]

The present invention relates to an alcohol concentration sensor, and particularly to a capacitive type sensor.

0002

[Conventional technology]

In recent years, methanol and ethanol have been added to gasoline as alternative fuels for automobile internal combustion engines. An alcohol-mixed fuel containing alcohols such as alcohols has been proposed. When using such alcohol mixed fuel, the stoichiometric air-fuel ratio depends on the alcohol concentration. Since the alcohol concentration changes, the alcohol concentration of the supplied alcohol-mixed fuel is detected and It is necessary to control the fuel supply amount and ignition timing based on the alcohol concentration of For example, see Japanese Unexamined Patent Publication No. 56-958540).

0003 Therefore, the fuel supply passage of the internal combustion engine is equipped with a An alcohol sensor configured with a capacitive alcohol concentration sensor that outputs voltage. Alcohol concentration detection devices are known, and capacitance type alcohol concentration sensors have been proposed. ing. This capacitive alcohol concentration sensor has conventionally been configured as shown in Figure 2. Ru.

0004 That is, the cylindrical housing 1 that constitutes a part of the fuel supply passage of the engine is connected to the outer electrode. For example, a cylindrical portion 2 made of a steel pipe or the like, and an opening 2a formed in the middle of the cylindrical portion 2. and a cylindrical portion 3 connected in a direction orthogonal to the central axis of the cylindrical portion 2. A fuel inlet portion 4 to which a fuel pipe (not shown) is connected is opened at one end of the cylindrical portion 2; A fuel outlet portion 5 to which a fuel pipe (not shown) is connected to the opposite end of the cylindrical portion 3 is opened. A solid center electrode 6 is inserted into the cylindrical portion 2 and extends along its central axis. The tip of the center electrode 6 is located a predetermined distance downstream from the fuel inlet 4. However, the rear end portion is connected to an insulator 7 fitted to the inner peripheral surface of the rear end portion of the cylindrical portion 2 and a conductive member. A bush 9 and an O-ring are fitted to the inner circumferential surface of the rear end of the cylindrical portion 2 via a pipe 8. It is supported through the groove 10. Note that the insulator 7 is made of synthetic resin (for example, the trade name Teflon). It consists of In addition, the protruding end of the center electrode 6 from the bush 9 is fitted with a washer 11. and a fastener 13 consisting of a nut 12.

[0005] One end of the terminal 14 is clamped and fixed at the joint between the pipe 8 and the bush 9. This terminal 14 is connected to the cylindrical part 2 constituting the outer electrode via the pipe 8. Ru. Also, one end of the terminal 15 is clamped and fixed at the joint between the fastener 13 and the bush 9. This terminal 15 is connected to the center electrode 6. By applying electricity between the terminals 14 and 15, the inside of the cylindrical housing 1 is The control device outputs an output voltage according to the alcohol concentration in the fuel passing through the It has become. Here, gasoline has a dielectric constant of about 2, and alcohol The relative dielectric constant of alcohol is approximately 32, and as the alcohol concentration increases, the fuel As the dielectric constant of increases, the output voltage increases as shown by the solid line in Figure 3. Therefore, the alcohol concentration can be detected.

[0006]

[Problem that the idea aims to solve]

However, in such conventional alcohol concentration sensors, for example, Although the dielectric constant is small (ε=2), it also exists in the insulator 7. This ratio is Because the effect of dielectric constant is added to the output voltage, it is said that alcohol concentration may be detected incorrectly. There is a problem. Specifically, when the alcohol concentration is low, the relative attraction of fuel is lower than when the alcohol concentration is high. Since the electric constant is small, the influence of the dielectric constant of the insulator 7 becomes large. As shown by the broken line in Figure 3, the output voltage varies greatly between products (approximately ±8%). ), there is a risk of deteriorating detection accuracy.

[0007] In addition, due to the asymmetrical shape of the outer electrode due to the opening of the fuel outlet portion 5, This also worsens the detection accuracy. Therefore, this invention was devised in view of the conventional situation as described above, and it The aim is to provide an alcohol concentration sensor that can improve detection accuracy even when Ru.

[0008]

[Means to solve the problem]

Therefore, the present invention detects changes in capacitance between electrodes through which fuel passes. An alcohol concentration sensor that outputs a voltage corresponding to alcohol concentration by , one end of the L-shaped fuel supply passage is closed, the other end is open, and the fuel supply passage is branched from the closed end. A cylindrical insulating member constituting the section, and a closed end along the central axis inside the insulating member. located between a center electrode extending from the side and a branch point and an open end of the fuel supply passage; an outer electrode provided inside the insulating member facing the tip of the center electrode; It consists of:

[0009]

[Effect]

In such a configuration, a part of the fuel supply passage with one end closed and the other end open is Fuel passes between the cylindrical insulating member and the center electrode. Here, the insulation An outer electrode is provided inside the member only at a position opposite to the tip of the center electrode. Therefore, the range for detecting changes in capacitance between the center electrode and the outer electrode is the center electrode. Limited to the tip of the pole. At the tip of the center electrode, there is a Detection accuracy is improved due to the symmetrical shape with no branching fuel supply passage openings. do.

0010

【Example】

Regarding the capacitive alcohol concentration sensor as an embodiment of the present invention, This will be explained with reference to FIG. In the following explanation, the same elements as those in the conventional example are given the same symbols as in FIG. to simplify the explanation.

[0011] That is, the cylindrical housing 21, which constitutes a part of the fuel supply passage of the engine, has an insulating member ( For example, a cylindrical portion 31 made of resin (PPS) and an opening formed in the middle of the cylindrical portion 31. In a direction perpendicular to the central axis of the cylindrical portion 31 with respect to the opening 31a, that is, form an L shape together with the cylindrical portion 31. and a cylindrical portion 23 formed to have the same shape. As shown at one end of the cylindrical portion 31, The fuel inlet section 4 to which the fuel pipe is connected is opened, and the end of the cylinder section 23 on the opposite side to the connection side is opened. Similarly, a fuel outlet portion 5 to which a fuel pipe (not shown) is connected is opened. Inside the cylindrical part 31 A solid center electrode 6 extending along its central axis is inserted, and the center electrode 6 is The tip 6b is located a predetermined distance downstream from the fuel inlet portion 4, and the rear end is located at the rear end of the cylindrical portion 31. An insulator made of an insulating member (for example, resin name PPS) fitted to the inner circumferential surface of the It is supported through the tab 27. In addition, the protruding end of the center electrode 6 from the insulator 27 is It is fixed by a fastener 13 composed of a washer 11 and a nut 12.

0012 Further, the cylindrical portion 31 is composed of a large diameter portion 32 and a narrow diameter portion 33, and the tip of the center electrode 6 is An end portion 35a on the side of the fuel inlet portion 4 is located in the inner peripheral surface of the large diameter portion 32 facing the end portion 6a. The end portion 35b on the insulator 27 side substantially coincides with the tip 6b of the cardiac electrode 6, and the end portion 35b on the insulator 27 side An outer electrode 35 is provided that extends to the vicinity of the opening 31a. One end of the terminal 29 is attached to the joint between the insulator 27 and the washer 11. is clamped and fixed, and this terminal 29 is connected to the center electrode 6. Also the outer electrode 35 One end of a terminal 36 inserted into the large diameter portion 32 is connected to the terminal 36 .

[0013] Then, the fuel passes through the cylindrical portion 31 and the cylindrical portion 23, and electricity is applied between the terminals 29 and 36. According to the alcohol concentration in the fuel passing through the cylindrical housing 21, The output voltage is output to the control device. Here, one end 35a of the outer electrode 35 substantially coincides with the tip 6b of the center electrode 6, and Since the other end 35b is located near the opening 31a, it is attached to the inner circumferential surface of the large diameter portion 32 of the cylindrical portion 31. In this case, the outer electrode 35 is provided only at a position opposite to the tip 6a of the center electrode 6. becomes. When current is applied between the terminals 29 and 36, the tip 6 of the center electrode 6 A change in capacitance between the center electrode 6 and the outer electrode 35 is detected only in the vicinity of a. It will be. In other words, the detection range of capacitance change is between the opposing electrodes (center electrode 6 and Since it is within the range where the outer electrode 35) exists, it is the range shown by S in Figure 1, and the relative dielectric The insulator 27 with electric constant ε of 4 to 5 is not affected at all, and therefore the fuel A stable output voltage is output even at low alcohol concentrations where the dielectric constant is small. It will be done. Furthermore, at the tip 6a of the center electrode 6, the center electrode 6 and the outer electrode 35 are connected to each other. Symmetrical shape with no intervening material and no opening 31a formed in the middle of the cylindrical portion 31 Since the detection accuracy is also improved, the detection accuracy is improved.

[0014]

[Effect of the idea]

As explained above, one end is closed and the other end is opened, and the L is branched from the closed end side. A cylindrical insulating member that constitutes a part of the fuel supply passage, and a cylindrical insulating member that A center electrode extending from the closed end side along the central axis, and a branch point and an opening of the fuel supply passage. installed inside the insulating member opposite to the tip of the center electrode and located between the distal end and the tip of the center electrode. Since the alcohol concentration sensor was constructed by including an outer electrode that can be The range for detecting changes in capacitance between the center electrode and the outer electrode is limited to the tip of the center electrode. Therefore, when detecting the change in capacitance, it is not affected by the closed end side. This improves detection accuracy, especially in low concentration ranges. In addition, the Detection accuracy is further improved as there is no need for any interference and detection is performed between symmetrically shaped electrodes. Ru.

[Brief explanation of drawings]

[Fig. 1] Partial cross-sectional front view of an alcohol concentration sensor showing an embodiment of the present invention.

[Figure 2] Partial cross-sectional front view of a conventional alcohol concentration sensor

[Figure 3] Diagram for explaining conventional issues

[Explanation of symbols]

4 Fuel inlet 6 Center electrode 21 Cylindrical housing 23 Cylinder part 27 Insulator 31 Cylinder part 32 Large diameter part 33 Narrow diameter part 35 Outer electrode

Claims (1)

[Scope of utility model registration request] Claim 1: An alcohol concentration sensor that outputs a voltage corresponding to alcohol concentration by detecting a change in capacitance between electrodes through which fuel passes, wherein one end is closed and the other end is open, and the closed end side a cylindrical insulating member constituting a part of an L-shaped fuel supply passage branched from the insulating member; a center electrode extending from the closed end side along the central axis inside the insulating member; and a branch point of the fuel supply passage. and an outer electrode provided inside the insulating member and facing the tip of the center electrode and located between the center electrode and the open end.