ELECTRONIC SPARK GENERATOR AND SENSOR FOR THE TL PNEUMATIC INDICATOR

E. N. Silov, A. S. Tsekhanov

(Presented by the scientific seminar of the Radio Engineering Faculty)

The inclusion of a two-contact sensor (1) in the TL indicator (the thermal laboratory of the N. E. Bauman Moscow Higher Technical School) directly in the circuit of the primary winding of the induction coil of the spark generator causes, as is known, burning of the sensor contacts, disruption of sparking, and a large scatter of points on the indicator diagram; this is also facilitated by unequal gaps in the contacts of the sensor breaker because of the difficulty of adjusting them.

To eliminate the indicated shortcomings and to increase the sensitivity of the TL indicator, at the Tomsk Polytechnic Institute a single-contact sensor and an electronic spark generator, described below, were manufactured.

The sensor (Fig. 1), a diaphragm-type single-contact sensor, consists of a body (1), an upper limiter (2) with a central fixed contact (4). The cover (5) is screwed onto the body and, through the limiter (2), presses the diaphragm against the lower limiter, made integral with the body. The cavity under the diaphragm is connected by six holes of 2.5 mm diameter with a channel 8 mm in diameter, which connects the sensor with the combustion chamber of the engine.

Fig. 1. Single-contact sensor: 1 — sensor body; 2 — upper limiter; 3 — insulator; 4 — fixed contact; 5 — sensor cover; 6 — contact; 7 — nipple; 8 — nut; 9 — gasket; 10 — diaphragm.

The sensor contacts are formed by the fixed contact (4) and the diaphragm (10), which open and close under the action of the pressure of gases from the engine cylinder on the diaphragm, 0.1 mm thick, stamped from heat-resistant steel. Its diameter is equal to 36 mm. With the indicated diaphragm dimensions, the highest sensitivity of the sensor to pressure changes is ensured, not exceeding 14 mm of mercury. The insulator (3) is made of textolite. All the remaining parts are made of steel. The surfaces of the body and of the upper limiter on the diaphragm side are spherical, with a spherical depth at the center of 0.03 mm.

Installing the fixed contact in the upper limiter of the membrane simplifies adjustment of the gap between the latter and the contact. Adjustment of the gap consists in the following: a control ruler is placed on the limiter, with the fixed contact installed in it (the sensor being disassembled), from the membrane side. With a 0.03 mm feeler gauge, the gap between the plane of the ruler and the fixed contact is set by turning the latter. The fixed contact is screwed into the insulator (3) by means of a thread. The screw-in part of the sensor has an \(18 \times 1.5\) thread. To avoid overheating of the membrane and its limiters, the sensor is cooled with water.

Fig. 2. Circuit of the electronic converter.

The electrical circuit of the electronic spark generator is shown in Fig. 2. In developing the circuit of the electronic converter, certain converters of electrical signals used in pulse technology (2, 3) were used; the authors sought to create a simple and reliably operating device.

The electronic spark generator includes a power-supply unit \((L_1, L_2, L_3)\), a thyratron relay \((L_4, L_5)\), and a unit that converts the sensor signals into triggering pulses with steep leading edges \((L_6)\). To ensure constancy of the thyratron ignition potential, the bias voltage on the thyratron grids is taken from a gas-discharge voltage regulator \((L_3)\). The discharge-current pulse through the primary winding of induction coil B is selected so as to provide, in the secondary winding, a voltage sufficient to produce in the spark gap a spark 5–7 mm long. It is evident from the circuit that the spark in the gap will occur only at the moments when the sensor contacts close and open. A protective electromagnetic maximum-current relay is included in the anode-supply circuit of the thyratrons.

The construction of the spark generator is made on a metal chassis with a vertical panel attached to it. The transformer, induction coil, lamps, and circuit wiring are located on the chassis. The controls are brought out to the vertical panel.

Use of the described spark-generator circuit made it possible to reduce the current at the sensor contacts and to eliminate burning of the contacts and disturbances in its operation. The sensor controls the electron tube \((L_6)\), and the current of the primary winding of induction coil B does not pass through its contacts. Prolonged operation of the sensor and electronic spark generator on a carburetor engine in the study of the indicated process showed their complete reliability in operation. The sensor was disassembled after 100 hours of operation only for the purpose of removing carbon deposits from the channel connecting its lower cavity with the engine cylinder. No electroerosion of the membrane or of the contacts was found during operation of the sensor.

References

1. Soloukhin E. N., Electropneumatic Indicator TL-3 of the Brake Laboratory of MVTU named after N. E. Bauman. Sb. “Diesel Locomotive Engineering,” Mashgiz, 1957.

2. Petrov A. V., Generation and Conversion of Electrical Pulses. Gosenergoizdat, 1954.

3. Recording Pressure Diagrams of Internal-Combustion Engines, “Gas and Oil Power,” December, 1951.