Crankshaft-Camshaft Position Sensors: What Do They Do?

We have all heard about the crankshaft and camshaft in our car and most likely have a good idea what … Continued

We have all heard about the crankshaft and camshaft in our car and most likely have a good idea what they do. As key components of your car’s engine, they are part of the essential powerhouse that rotates and drives forward the pistons and ultimately creates forward motion as you drive. And when these two essential parts of your car’s engine are not quite working, your drive will certainly let you know! With today’s auto technology, your car now has extra components on your crank and cam called position sensors to ensure a smooth ride.  But what exactly do your car’s crankshaft-camshaft position sensors do and how do they help keep your car on the road? We pop the hood and take a look.

Back to Basics

Before we look at the position sensors, we need to look at the crankshaft and camshaft and how they work inside your car’s engine. And that means briefly going back to basics.

The engine in your car or truck is a technological marvel, but one you don’t really think about as you go about your day. And a whole host of technological advances have made your driving life slick and smooth, and a long way from the motor car’s early days. However, today’s super-charged motors and those first motor cars still have one thing in common, and that is the fundamental principle of the internal combustion engine.

The internal combustion (IC) engine is one of the game-changers of the modern age, bringing power to our daily lives. From chainsaws and lawnmowers to cars, generators and jet engines, the IC engine has got the world on the move. The premise behind the IC – or spark ignition – engine is surprisingly simple: fuel is ignited inside a cylinder, where the combustion pushes down on a piston to create energy that drives the engine. And at the heart of this process are two vital components – the crankshaft and camshaft – that convert the motion of the engine’s pistons into power that turns your car’s wheels.

man writing on a clipboard

Camshaft v Crankshaft

Basic science lesson over with, let’s get on with the task at hand, and look at the specific roles of the crank and cam and how position sensors up their game.  In short, the crank and cam are both shafts inside your engine that have two different functions.

The Crankshaft

The crankshaft works as part of the four-stroke cycle of your car’s engine; that is – compression, power, intake and exhaust.  The specific job of the crankshaft is to convert linear or reciprocating energy – created through the back and forth motion of the piston – into rotational energy that will then be transferred to your car’s wheels. The piston is attached to the crankshaft below the engine’s cylinders via a connecting rod and flywheel. As the engine’s combustion drives the piston forward, the motion rotates the crank which then moves the wheels of your car.

Crankshafts are typically made from forged alloy steel as they are continually working under high load and needs to be strong enough to withstand fatigue.

The Camshaft

The camshaft in your car’s engine enables fuel and air to enter the cylinder at the right moment and then opens the exhaust valve to let the subsequent burnt charge escape into the atmosphere. Timing is everything with the camshaft – the inlet valve needs to open when the piston is top center and the exhaust valve needs to vent when the piston is full of the burnt charge. The cam works in conjunction with the crank and needs to rotate at the same time to push against and open up the valves as the pistons move.

Typically situated above the cylinder, the camshaft is made from cast iron or steel and rotates by the timing belt, which is attached to the crank. Camshafts can be oval, heart-shaped, hexagonal or round.

How the Cam and Crank Work Together

The crank and cam have a beautiful relationship and their position sensors help to keep it that way! Put simply, they start and end the engine’s cycle – from the inlet stroke to the exhaust stroke – by keeping everything working harmoniously. The cambelt keeps these two engine powerhouses together and in time. While they move together, the crank and cam have to be ready for the next steps the other one takes, for example, as the crankshaft moves the piston down, the cam opens up the intake valves and when the piston reaches the bottom, the camshaft closes the valve and opens the exhaust. Continually.

The crank/cam team can be likened to a relay race, as the baton is handed over – if one is out of time, the baton is dropped, and the engine cycle is disrupted. And the impact on your engine? Well, for starters, the fuel/air mix will be off kilter, the combustion will falter, unused and burnt mixture won’t be discharged and there will be no power heading towards the flywheel to move your car forward.  Not a situation that you really want for your car -which is where the crankshaft and camshaft position sensors come in.

Car engine

The Importance of Position Sensors

To keep the crank and cam ‘A-team’ in time and in play, position sensors are used to transmit essential information through to your car’s fuel injection computer in the engine or its ignition control module so it can keep track of how well they are both performing. This information includes the exact position of the engine’s pistons as they go up or down in the compression cycle.

Having these position sensors in place and operating at their optimum is essential to making sure your car’s engine is always running at its best.  Let’s look at the detail for each position sensor.

  • What does a crankshaft sensor do?

The position sensor on your crankshaft is one of the most important sensors in your car and the data it collects is key to the health of the engine. The sensor is typically mounted on the main crank pully, the fly wheel or the crank itself and so the teeth on the reluctor ring of the crankshaft passes close to the tip of the sensor. The ring has one of its teeth missing so it provides the engine’s computer a reference point for the crankshaft position. The crankshaft position sensor then measures the rotation speed and precise position of the engine’s pistons and crankshaft. This works as the gas and air in the ignition chambers combust and the piston force causes the crank to turn. As the turning crankshaft is what powers the engine and moves the car, the sensor keeps a close ‘eye’ on the rate at which it rotates.

This information is then used by the engine management systems to control the injection of fuel and the ignition system timings. As injection and ignition is timed from the crankshaft position sensor signal, errors or a failing signal will mean the engine will not start or will cut out if already running.

In short, the function of the crankshaft position sensor is to:

Provide an exact positioning of the cylinder pistons

Help the ignition system to produce a spark

Ensure the fuel system injects at the right time

  • What does a camshaft sensor do?

Alongside the crankshaft sensor, the position sensor on the camshaft is an essential for the modern car and is used in all sequentially fuel injected engines to ensure optimum performance. The position sensor on your car’s camshaft continually assesses the frequency at which the camshaft is turning. As you will remember from earlier in this blog, the camshaft’s function is to ensure the engine’s valves open and close at the right time to enable ignition and to exhaust burnt charge. To be able to do this, the camshaft rod has strategically placed ‘cams’ that protrude from its shaft. When the rod turns, these cams press against individual valves to open them. As the cam passes the valve, it then closes so the rate of the rotation is paramount to the engine’s performance. This is where the camshaft’s position sensor comes in.

The camshaft position sensor records the rotation of the shaft and tells the car’s computer the rate at which the engine’s valves are opening and closing. This way it can also tell the engine which cylinder is at the top, so it knows which to fire next.

In short, the function of the camshaft position sensor is to:

  • Monitors the rotational rate of the camshaft
  • Tells the engine which valves are open and closed
  • Determines the timing of ignition

It’s All a Matter of Timing

So, what exactly does your car’s engine do with all the information it is sent from the position sensors on the crank and cam? The collective data enables the engine computer to see just how effectively and efficiently the engine is performing. As the cam dictates the opening and closing of the cylinder’s valves for combustion, then the rate of the crankshaft rotation indicates the speed at which the pistons are actually firing. This ultimately means that, for your car engine to be at the top of its operating game, the rates of the crank and cam must be in total synch.  If these rates start to fluctuate or differ, then this is where performance problems can start.

Symptoms of Underperforming Sensors

The position sensors on your cam and crankshaft are little techno powerhouses that keep you and your car’s engine on the move, but they are not indestructible and can succumb to wear and tear. It’s important to be aware of the signs that your engine’s position sensors are starting to under-perform or are perhaps getting beyond their best.  Here are the main signs to keep an eye out for:

  • The engine light

One of the very first symptoms that perhaps your crank or camshaft position sensor is on the wane is when you see the engine light on your dashboard console. Never ignore this light as it is a real signal that all is not right – get it checked out as soon as you can. Ignoring the red light – which is tempting to do – can lead to serious problems with your engine, which can, in turn, be as costly and disruptive as it sounds.

  • ‘Hit and miss’ driving

Your driving experience will certainly tell you when there are problems starting with your engine’s position sensors. As the sensors begin to fail, you will start to see a host of technical issues, including the engine idling, frequent stalling, a distinct reduction in engine power, problems with accelerating and a car that is drinking fuel like there is no tomorrow. If you have turned a blind eye to that light on the dashboard and are now starting to experience any of the above symptoms, get you and your car to the garage and a good mechanic, pronto.

  • Power down

A failing position sensor on either your crankshaft or camshaft will send disrupted signals to your engine’s computer, leading to some or all of the issues we have listed above. When the sensor totally shuts down, then this is a whole new ball game as the engine will have absolutely no idea whether the crank or cam are working at all.  And, if the computer isn’t being told the injectors need fuel, then it simply won’t send any. With no fuel at the start of the four-cycle, then the rest of the process will not follow. No fuel, no power, no movement – simple as. And this means your engine will shut down, wherever you are and could put you at risk of being stranded and facing a hefty recovery and repair bill.

So, there you have it, the lowdown on your car’s cam and crank position sensors. Next time you put your keys in the ignition and fire up your car, give them a little nod. They are keeping a watch on how your engine is working so you can go about your business, hopefully without a cam or crankshaft care in the world!

Source:

  1. 5 ways modern car engines differ from older cars – How Stuff Works