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Start stop cars and trucks

Start stop technology

What is start stop technology?

Start stop technology is designed to save gas when the engine doesn’t need to be running at a stop. The system shuts off the engine when the car or truck is stationary. The engine starts again as soon as you depress the  clutch relese brake.

How does start stop work?

The vehicle computer detects when the car is stationary or out of gear. Then it stops fuel delivery and spark. The process happens automatically, but drivers can choose whether the system is active or disabled by pushing their car’s stop-start button; a capital A with an arrow circling clockwise.

The system uses a different electric starter motor designed to cylce for over 500,000 start cycles, as opposed to a traditional starter that’s designed to operate for 50,000 cycles.

Start stop starter motor gear ratio

A higher torque motor and a different gear ration is used to reduce starter RPM during cranking. This is important since 90% of starter motor brush wear occurs as the starter motor has stopped cranking and is coasting down to a full stop. By slowing the rotation speed during cranking, the manufacturers also reduce the coast down time.

Start stop starter motor brushes

A start stop starter motor uses a different combination of carbon and copper brushes to increase longevity and reduce commutator wear.

Start stop starter motor bearings

While traditional starter motors relay on oil-impregnated bushings, start stop  starters mostly use needle bearings.

Start stop starters are faster acting

Some starters are equipped with a ‘tandem solenoid’ designed to cope more smoothly with scenarios where the engine is about to stop and then the driver accelerates again. That would occur if the driver has decided to stop, but for whatever reason has a change of mind, such as when the traffic moves off unexpectedly. The tandem solenoids are there to synchronise the starter’s speed with the engine before the second smoothly engages the gear.

Start Stop effects on engine life

Car makers have gone to great lengths to avoid accelerated engine wear in start stop engines.

The biggest issue car makers face is how to maintain start up lubrication during the many start stop operations. In a tranditional engine, the crankshaft and camshafts are separated from their bearings by hydrodynamic lubrication (pressurized oil centering the shaft between the smooth bearings) and boundary lubrication (the oil film that remains when oil pressure is gone).

In a start stop engine, the crankshaft and camshafts would normally fall onto the bottom bearing surface when the engine shuts off. If boundary lubrication isn’t adequate, the shafts will wear out the bearings.

To prevent that, start stop engines use a different bearing material that is self lubrication to resist start up wear. In fact, Federal Mogul has developed a new bearing material called Irox for start stop applications. The bearing has a polymer coating that contains iron oxide (rust) particles which are actually surprisingly slippery. The new coating is so slippery that the coefficient of friction of an Irox bearing is 50% lower than a conventional aluminium bearing, ensuring it will last the life of an engine equipped with stop-start.

Low friction oils help prolong engine life

The newer synthetic oils have boosted additive packages that reduce oxidation and friction and have increase anti-wear properties.

©, 2020 Rick Muscoplat

Posted on by Rick Muscoplat


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