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Understanding Car Computers, Sensors and Actuators

Updated on August 1, 2014
Audi R8
Audi R8

The modern car today has a computer, which helps in running the engine. This hub is intended for the person who is interested to know how computers are currently used in a car, and how it all works.

ok lets do it...

Think of a decision maker of any kind, whether a director of a company or a doctor treating a patient.

In order for the director of a company to direct others, he or she needs information to work with. And that information comes from the people working under the director (subordinates).

In the case of a doctor the information comes from the patient in order to diagnose the patient correctly. I'll stick with the director of the company example in this hub.

Sample Company Structure
Sample Company Structure | Source

The main job of a director is to gather all the information from his or her subordinates and make decisions. The more accurate the information the better decisions are made by the director.

For example, a product has been created and is now ready for launch in the market so the director will get the information from the production team and will instruct the sales team to start selling the product. Here timing is important, if the production team have made a product yet not informed the director no one will be selling the product and the optimum performance of the company will go down.

Similar to the director/production team/sales team, in a car we have a Computer, Sensors and Actuators.

Edited Pic
Edited Pic

Now think of the car as a company.

The computer is the director, the sensors are where the information comes from (production team) and the actuators are the instruction followers (sales team).

So the computer makes all the decisions based on all the information it gets from the sensors. The computer then analyzes the information from the sensors and tells the actuators what to. The more accurate the information from the sensors the better decisions will be made by the computer.

Car Computer
Car Computer | Source
MAP Sensor
MAP Sensor | Source
Typical Fuel Injector - Actuator
Typical Fuel Injector - Actuator | Source

But how does it all work inside a car?

The simple answer is voltage.

Every sensor produces a certain amount of voltage (between 0 and 5V) depending on the conditions surrounding the sensor. Each sensor is directly connected to the computer with a wire.

I'll give you a real life example now,

You start your car and are ready to go. You press the accelerator pedal to move forward.

Here a sensor called Throttle position sensor moves with the pedal (attached with a cable to engine). You can also think of the Throttle position sensor as a regulator (light switch) to dim lights or set the fan speed in your house, the more current you allow, the brighter the light or faster the fan.

This throttle position sensor tells the computer of the car that the driver is pressing the accelerator pedal, the computer can also verify this information with a sensor called the MAP sensor (manifold absolute pressure). The MAP sensor monitors the air pressure inside the engine.

So, the engine is started, the throttle position sensor is signalling that the driver is pressing the accelerator pedal and there is more than normal air pressure inside the engine (intake) area, therefore computer decides we need to accelerate, and knows in order to accelerate we will need more fuel.

The computer then instructs the fuel injectors (actuators) to open for a longer duration because we are accelerating. This is achieved by sending current to the actuator for a longer period.

Thus the car has the right amount of fuel to accelerate and you notice the car moving smoothly.

When the sensors get dirty their accuracy of information is decreased and therefore the computer starts giving out the wrong commands and the overall performance of the car goes down. Some examples may include increased fuel consumption, or slower acceleration.

Typical Check Engine Light
Typical Check Engine Light | Source

The computer knows the range of voltages allowed for specific sensors and if the voltage readings are out of range you get the check engine light on your dashboard. You will also get the check engine light if a wire going from the computer to the sensor is broken or if the sensor is faulty.

To get rid of the check engine light you will need to visit a dealership or a local mechanic who has a scanner for your specific vehicle. There are many scanners out there for specific cars. The price range of scanners are between $50 - $4,000. The scanners basically give a code and a description of the problem which help locate the problems in the vehicles much faster. To find an extended description you can use the internet and search for OBD-II codes.
(OBD = On-Board Diagnostics)

Once the problem is fixed the check engine light will automatically go off.

With the advancement of technology several sensors and actuators as well as multiple computers have been introduced in the functioning of a vehicle. This hub gave an example of one decision that a car makes, but cars today can make up to and over 2000 decisions every second while driving.

Next we are going to look at the types of controllers found in a vehicle.


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