What is a solenoid?

Your vehicle’s starter motor has the important job of starting the engine. But something also has to start the starter. And that something is the solenoid. In most automotive applications today, the solenoid is attached to the starter, with the two of them getting removed as a unit when necessary.

How a solenoid works

When running properly, and as long as it has a supply of fuel, the internal combustion engine continues to run by itself in an ongoing process from the inertia of the engine’s moving parts. But starting the engine is a separate process to get that inertia moving in the first place. This is the job of the starting system, whose main components include the:

  • Battery
  • Starter motor
  • Solenoid
  • Starter switch

Starting an engine: The first action

The process involves not one, but two separate electric currents – a stronger one and a weaker one. When activated, usually by turning a key in the ignition switch, the weaker current passes through the switch and to the solenoid. At that point, the current forces two large contacts to come together in the solenoid, which allows the stronger electric current to pass through the solenoid’s contacts. These contacts carry a current that requires heavy wiring cables directly from the battery. This current is heavy enough that it would be unwise to send it through a hand-operated switching mechanism. Hence, the need for the weaker current through the ignition switch.

The stronger current passes to the starter motor where it initiates two separate actions. The starter motor is designed so that the electric current activates a lever, forcing a small gear outward on a spring shaft. When extended, this gear, called a pinion, comes in contact with a toothed gear on the outer rim of a large flywheel on the end of the engine’s drive shaft. This large gear is called the starter ring gear.

Starting an engine: The second action

The second action in a direct current electric motor is the rotation of its central shaft, caused by the larger current passing through the motor. A motor transforms electric energy into the mechanical energy of the central shaft’s rotation. It does this because the electric current interacts with the magnetic field in the starter motor and results in the rotor on the shaft beginning to turn. By the time this turning action reaches the motor’s designed top speed, the pinion at the end of this shaft has already engaged the ring gear on the flywheel. The engine then starts running on its own and the starter’s safety features automatically disengage the pinion from the ring gear. The spring brings the pinion safely back to its resting position and the job of the starting mechanism is done.

When starting, if you hold the ignition key in the “start” position a little too long, you will encounter a problem. Here, too, is a spring that brings the switch back to the “on” position from “start” as soon as you release the key. If you fail to do so, you will hear the evidence of your mistake pretty quickly. The good news is that your mistake is not as bad as it sounds. The safety mechanism in the starter has already released the pinion from the ring gear. The bad news is if you do this often or for any extended period, you may drastically shorten the life of the starter motor.


2018 Ford EcoSport


The big news in SUVs these days is actually pretty small. After years of wondering when Ford would join the subcompact SUV fray in the U.S. with its EcoSport global subcompact utility vehicle, we now have our answer courtesy the 2016 Los Angeles Auto Show: early 2018. That’s when this newly refreshed cute SUV arrives on our shores.
img1259592277-1479175449089And it really is cute. It’s got the Ford family front end, but it’s on a scale not normally seen from the automaker. Standing next to the EcoSport, you realize just how tiny it is on the outside, with its low beltline and big windows helping to create some interesting proportions. You can see why it’s been one of Ford’s best sellers globally, especially in developing countries with tight urban environments. It’s not going to be difficult to park this thing anywhere in a big city.


It’s fitting that the model on display is painted a kind of Tardis blue — just like Dr. Who’s mode of transportation, it certainly feels bigger on the inside than it looks on the outside. The front seats have plenty of room, with ample legroom and headroom, and excellent outward visibility. Width is a little on the narrow side, but this is a subcompact SUV made primarily for foreign markets where lane widths aren’t as ample as they are here. The backseat is comfortable as well, but the Titanium trim’s moonroof eats into headroom a tad. Legroom is tight in back unless front seat occupants sacrifice a little of theirs to allow the backseaters some comfort.
img2030690101-1479175540536Material quality in the EcoSport is typically Ford, with soft-touch materials, slick switchgear and bright LEDs to give a surprisingly upscale appearance to the Titanium; we’ll see how well the base S trim stacks up when it’s launched, however. The 8-inch touchscreen has Ford’s excellent Sync 3 system, which continues to impress with its ease of use and clarity of information. It’s a nice interior for sure, certainly a step up from a Chevrolet Trax or Honda HR-V and even nicer in some ways than the Buick Encore.


The cargo area is versatile as well, with a decent amount of space behind the rear seats for a few parcels. Drop the rear seats and you can fit some larger items in the cargo area enough for most people’s daily use but stuffing a 60-inch flatscreen TV in there might stretch the EcoSport’s utility. The side-opening swing gate isn’t really much of a benefit, especially if you’re in a congested urban environment, where people will park inches from your rear bumper. A more conventional hatchback tailgate might have been a better idea.

Overall, the new EcoSport should find some willing buyers when it hits showrooms more than a year from now. The turbocharged 1.0-liter engine is a fantastic little motor in the Fiesta and Focus, and if the so-equipped EcoSport is as much fun to drive as those models, it should be a winner for Ford in the U.S.