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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Fuel flow meter for a car. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Automobile. Electronic devices One version of the device that allows you to control the amount and speed of liquid (in particular, fuel) flowing through the line was described in the article by I. Semenov et al. "Electronic liquid flow meter" ("Radio", 1986, No. 1). The repetition and adjustment of this flow meter is associated with certain difficulties, since many of its parts require high machining accuracy. Its electronic unit needs good noise immunity due to the high level of interference in the car's on-board network. Another disadvantage of this device is an increase in measurement error with a decrease in fuel flow rate (in idle mode and low engine load). The device described below is free from the listed disadvantages, has a simpler sensor design and an electronic circuit diagram. It does not have a device for monitoring the rate of fuel consumption; its function is performed by a total consumption counter. The response frequency is proportional to the rate of fuel consumption and is perceived by the driver by ear. This does not distract from driving, which is especially important in urban traffic. The flow meter consists of two components: a sensor with an electrovalve built into the fuel line between the fuel pump and the carburetor, and an electronic unit located in the passenger compartment. The design of the sensor is shown in fig. 1. An elastic diaphragm 8 is clamped between the body 2 and the pallet 4, dividing the internal volume into the upper and lower cavities. The rod 5 moves freely in the guide sleeve 7 made of PTFE. The diaphragm is clamped in the lower part of the rod with two washers 3 and a nut. A permanent magnet 9 is installed at the upper end of the rod. In the upper part of the body, two additional channels are drilled parallel to the channel in which the rod is located. They have two reed switches 10. In the lower position of the magnet, and hence the diaphragm, one reed switch is activated, and in the upper position, the other.
The diaphragm moves to the upper position under the action of fuel pressure coming from the gasoline pump, and spring 6 returns it to the lower position. Three fittings 1 are provided to turn the sensor into the fuel line (one on the pallet and two on the body). The hydraulic circuit of the flow meter is shown in fig. 2. Through channel 3 and the solenoid valve, fuel from the gasoline pump enters channels 1, 2 and fills the upper and lower cavities of the sensor, and through channel 4 enters the carburetor. The valve switches under the action of signals from the electronic unit (not shown in this diagram) controlled by the reed switch of the sensor.
In the initial state, the solenoid valve winding is de-energized, channel 3 communicates with channel 1, and channel 2 is open. The diaphragm is in the down position as shown in the diagram. The gasoline pump creates an excess of fluid pressure in the lower cavity 6. As the engine produces fuel from the upper cavity and the sensor, the diaphragm will slowly rise, compressing the spring. When the upper position is reached, reed switch 1 will work and the solenoid valve will close channel 3 and open channel 2 (channel 1 is permanently open). Under the action of a compressed spring, the diaphragm will quickly move down to its original position and transfer fuel through channels 1, 2 from cavity b to a. Then the cycle of operation of the flowmeter is repeated. The electronic unit (Fig. 3) is connected to the sensor and the solenoid valve with a flexible cable through the XT1 connector. City committees SF1 and SF2 (1 and 2, respectively, according to Fig. 2) are installed in the sensor (they are shown in the diagram in a position where the magnet does not act on any of them); Y1 - winding of the valve solenoid. In the initial position, the transistor VT1 is closed, the contacts K1.2 of the relay K1 are open and the winding Y1 is de-energized. The sensor magnet is next to the SF2 reed switch, so the reed switch does not conduct current.
As fuel is consumed from cavity a of the sensor, the magnet slowly moves from reed switch SF2 to reed switch SF1. At some point, the SF2 reed switch will switch, but this will not cause any changes in the block. At the end of the stroke, the magnet will switch the reed switch SF1 and the base current of the transistor VT2 will flow through it and the resistor R1. The transistor will open, relay K1 will operate and contacts K1.2 will turn on the valve solenoid, and contacts K1.1 will close the power supply circuit of the pulse counter E1. As a result, the diaphragm, together with the magnet, will begin to move down rapidly. At some point, the reed switch SF1, after switching back, will break the base current circuit of the transistor, but it will remain open, since the base current now flows through the closed contacts K1.1, the diode VD2 and the reed switch SF2. Therefore, the rod with the diaphragm and the magnet will continue to move. At the end of the return stroke, the magnet will switch the reed switch SF2, the transistor will close, the electromagnet Y1 of the valve and the counter E1 will turn off. The system will return to its original state, and a new cycle of its work will begin. Thus, the counter E1 fixes the number of sensor operation cycles. Each cycle corresponds to a certain amount of fuel consumed, which is equal to the volume of space limited by the diaphragm in the upper and lower positions. The total fuel consumption is determined by multiplying the meter readings by the amount of fuel consumed in one cycle. This volume is set when calibrating the sensor. For the convenience of counting the fuel consumed, the volume per cycle was chosen to be 0,01 liters. If desired, this volume can be slightly reduced or increased. To do this, you need to change the distance between the reed switches in height. With the specified sensor dimensions, the optimum aperture travel is approximately 10 mm. The duration of the sensor cycle depends on the engine operating mode and ranges from 6 to 30 s. When calibrating the sensor, it is necessary to disconnect the pipeline from the car's gas tank and insert it into a measuring vessel with fuel, and then start the engine and develop a certain amount of fuel. By dividing this number by the number of cycles on the counter, the value of a unit volume of fuel per cycle is obtained. The flow meter provides the ability to turn it off with the toggle switch SA1. In this case, the sensor diaphragm is constantly in the lower position and fuel through channels 2 and 3 through cavity a will directly flow into the carburetor. To implement the possibility of switching off the device in the solenoid valve, it is necessary to remove the rubber cuff that blocks channel 3, but this will worsen the error of the flow meter. The electronic unit is mounted on a printed circuit board made of fiberglass 1,5 mm thick. The board drawing is shown in fig. 4. The parts installed on the board are circled in the diagram with a dash-dotted line. The board is mounted in a metal box and fixed in the car under the instrument panel.
The device uses the RES9 relay, passport PC4.529.029.11; solenoid valve - P-RE 3 / 2,5-1112. Counter SI-206 or SB-1M. Any permanent magnet can be used with end poles and a length of 18 ... 20 mm, it is only necessary that it move freely in its channel without touching the walls. For example, a magnet from the RPS32 remote switch is suitable, you just need to grind it to the desired size. The sensor body and tray are machined from any non-magnetic, petrol-resistant material. The wall thickness between the channels of the reed switches and the magnet should not be more than 1 mm, the diameter of the hole for the magnet should be 5,1 + 0,1 mm, and the depth should be 45 mm. The stem is made of brass or steel 45, diameter - 5 mm, length of the threaded part - 8 mm, total length - 48 mm. The thread on the sensor fittings is M8, the hole diameter is 5 mm, and on the solenoid valve fittings it is conical K 1/8 "GOST 6111-52. The spring is wound from steel wire with a diameter of 0,8 mm GOST 9389-75. The spring diameter is 15 mm, pitch - 5 mm, length - 70 mm, full compression force - 300 ... 500 g. If the rod is made of steel, then the magnet is held on it due to magnetic forces. If the rod is made of non-magnetic metal, then the magnet must be glued or strengthened in any other way. To ensure that the sensor does not interfere with the pressure of the air compressed above the magnet, a bypass channel with a cross section of about 2 mm2 should be provided in the sleeve. The diaphragm is made of 0,2 mm thick polyethylene film. Before installation in the sensor, it must be molded. To do this, you can use the sensor tray assembly with the fitting. It is necessary to make a technological clamping ring from sheet duralumin 5 mm thick. The shape of this ring exactly matches the pallet assembly flange. To form the diaphragm, the rod assembly with its blank is inserted from the inside into the opening of the fitting of the pallet and the blank is clamped with a technological ring. Then the assembly is evenly heated from the side of the diaphragm, holding it above the burner flame at a distance of 60 ... 70 cm and, slightly raising the rod, the diaphragm is formed. In order for the diaphragm not to lose elasticity during operation, it is necessary that it is constantly in the fuel. Therefore, when the car is parked for a long time, it is necessary to pinch the hose from the sensor to the carburetor in order to prevent the evaporation of gasoline from the system. The sensor and the solenoid valve are mounted on a bracket in the engine compartment near the carburetor and fuel pump and connected to the electronic unit with a cable. The performance of the flow meter can be checked without installing it on the car using a pump with a pressure gauge connected instead of the fuel pump. The pressure at which the sensor is triggered must be 0,1...0,15 kg/cm2. Tests of the flow meter on Moskvich and Zhiguli vehicles showed that the accuracy of measuring fuel consumption does not depend on the engine operating mode and is determined by the error in setting a unit volume during calibration, which can easily be increased to 1,5 ... 2%. Author: V. Gumenyuk, Kharkov; Publication: N. Bolshakov, rf.atnn.ru
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