From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Technical analysis of the electrical circuit for a magnetic injection valve, with related graphs and equations.
| Identifier | ExFiles\Box 158\5\ scan0036 | |
| Date | 22th April 1939 | |
| 532 MAGNETIC INJECTION VALVE an identical quantity of fuel at each successive operation. These characteristics are readily obtained by means of a simple electrical circuit. Electrical Circuit The complete electrical circuit, as used with the Atlas engine, for actuating the spray valve and supplying energy for ignition, is shown in Fig. 3. The condenser in the spray valve circuit is first charged through a mechanically operated breaker and then discharged through the valve circuit coupled through a second breaker point to the fuel distributor. The amount and duration of the current are determined by the charge of the condenser, the size of the condenser, and the inductance and resistance of the valve. For simplicity, the valve circuit may be reduced to its electrical constants and the simple electrical circuit shown in Fig. 4A. The cycle of operations consists of a charging period when the switch S is thrown to position 1, and a period of discharge when the switch is thrown to position 2. During the charging period the condenser C receives a charge from the battery E through the throttling resistance r.{Sir Henry Royce} If E and C are considered fixed, the magnitude of the charge depends upon the value of r and the length of time that switch S is closed in position 1. The voltage across the condenser may be expressed by the relation E_c = E (1 - e^(-t/rc{R. Childs})) (1) and the charge of the condenser by Q = CE_c = CE (1 - e^(-t/rc{R. Childs})) (2) The variation of the charge as a function of the charging time, t, is shown in Fig. 4B. For increasing values of throttling resistance, r, 2r, 4r, 8r and a constant charging time t (constant engine speed) the condenser will have decreasing values of charge (Q = CE) of Q, Q₁, Q₂, and Q₃. During the discharge period, when switch S is in position 2, the charge of the condenser will flow through the inductance and resistance of the valve circuit. If the resistance of the valve is small in comparison with its inductance, the discharge current will be oscillatory. This condition is expressed by the relation i = - (E_e / Lω) e^(-RT/2L) sin ωt (3) where ω = √(1/CL - R²/4L²) Equation (3) represents a damped sine wave with an amplitude proportional to the charge of the condenser. This is graphically represented in Fig. 4C. The time interval during which the valve is open is a function of the opening current i₀, the closing current i_c, the charge of the condenser, and the frequency of oscillation of the electric charge in the circuit. With a full charge in the condenser, the valve is open for the period Δt₁; with a reduced charge Q₁, for a time Δt₂; with a smaller charge Q₂, for a time Δt₃, etc. If the throttling resistance is sufficiently great, the condenser does not acquire a charge sufficiently large to operate the valve. This condition is indicated by curves 8r in Figs. 4B and 4C. Figs. 4B and 4C are purely illustrative and not to scale for the valve tested. The results represented in Fig. 5 have been calculated for the measured inductance and capacity of the circuit for two values of circuit resistance. The oscillatory case was calculated with a circuit resistance of 0.6 ohm, and the critically damped case for a circuit resistance of 1.0 ohm. In both cases the inductance was 3.25 x 10⁻⁴ henries and the capacity 1200 micro-farads. Fig. 4. The equivalent electrical circuit of the magnetically actuated spray valve and its characteristics. A.{Mr Adams} The equivalent electrical circuit. B. The relation between the condenser charge as a function of charging time for various values of throttling resistance r.{Sir Henry Royce} C. The relation between the current through the nozzle as a function of time for various values of throttling resistance r.{Sir Henry Royce} Fig. 5. The current through the nozzle as a function of time for different circuit resistances. Graph Labels: Fig. 5: CURRENT-AMP, TIME-SECOND x 10⁻³ April 22, 1939 Automotive Industries | ||