Overview
Closeup |
Solenoid injectors used for engines are mechanisms that spray fuel through
the valve which opens when the plunger is moved by magnetic force from
an electromagnet. Injectors in engines need to respond quickly to applied
voltage to improve fuel consumption by maintaining the fuel flow. In solenoid
injectors, one factor causing the response delay is eddy currents produced
by the current flow. This note presents the use of magnetic field analysis
to obtain the response characteristics of a solenoid injector. |
Current Density Distribution
Closeup |
Figure 1 shows the current density distribution when the current starts
flowing (1 millisecond), when the plunger starts moving (2.3 milliseconds)
and when the plunger moves one stroke (4.2 milliseconds). The moving direction
of the plunger is the opening direction of the valve. When the current
flows in the coil, eddy currents are produced in the core, yoke and plunger.
When the current starts flowing, magnetic flux flows significantly, thereby,
eddy currents concentrate on the surface of each part. Since direct current
is used, eddy currents flow inside the parts over time. These eddy currents
delay the response. |
Response Characteristics
| Figure 2 shows the response characteristics of the plunger. Figure 3 shows
the attractive force characteristics. The result without eddy currents
is used for comparison. The opening direction of valve is the positive
direction. When the plunger moves 0.1 mm, the valve is open. There is response
delay between when current starts flowing and when plunger starts moving.
When the attractive force exceeds 5N, plunger starts moving. Without eddy
currents, the response is delayed about 0.9 milliseconds due to fuel pressure,
spring weight and plunger weight. With eddy currents, the response is delayed
about 1.0 millisecond. It is seen that eddy currents reduce attractive
force, causing the response delay. |
Closeup |
Closeup |
|
