4848 Blog 4 Controller Area Network system

Background:


Controller Area Network is known as CAN bus system.

Bosch started developing CAN bus back in 1983 and the first vehicle equipped with CAN bus system was the BMW 850 coupe in 1986, the first CAN chip was produced by Intel and Philips in 1987.

The CAN bus system reduces the vehicle wiring loom by 2km and reduces at least 50kg overall weight using only half of the connectors. But a CAN bus system increases the vehicles complexity and makes aftermarket installations very difficult to perform or even impossible to do so.

The CAN bus system is designed to allow devices to communicate with each other in the vehicle without everything depends on the ECU. At first the CAN bus system only equipped on the luxury cars with lots of electrical features.

The CAN bus system also uses OBDII vehicle diagnostics system which is the same to engine ECU diagnosis and transmission diagnosis.

We can compare the electrical system between CAN bus equipped and not equipped in vehicles in the above pictures which we can easily find out the CAN bus system made the electrical system a lot simpler.




Theory:


In a CAN bus equipped vehicle, all the individual modules are able to "talk' to each other with only one or two data wires connected and each module is called an Node.

A gateway module is used to transfer different speed and different signal between the Nodes.

Let's make an example, say if a vehicle does not have a CAN bus system, it would need one coolant temperature sensor for ignition, one coolant temperature sensor for fuel injection, one coolant temperature sensor for transmission if it is automatic and one coolant temperature sensor for climate control if it has this feature, but if this car has got CAN bus system installed, it would only need one coolant temperature sensor to run all of those function and the gateway module will transfer the signal to each Node which controls the system.

However the CAN bus system is only connected with each module, the particular sensor will not be connected to the CAN system, they will still go to the module who controls them.

The CAN bus system also have the low and high speed differences, some devices such as ABS, Injectors, Ignition coils and Air bags are using high speed CAN system, the signal transferred and sent to them need to be as soon as possible but some devices such as door locks, window switches, windscreen wipers and indicators do not need to be responsed that fast so they are using low speed CAN system.

Experiment:

This is a photo of the CAN bus system on board we were testing in the classroom:

This is a typical CAN bus system

The indicators, brake lights and reverse light are been controlled by the stick switch on the top right conner.

As we can see there were only 2 wires connected between the two nodes and all the other wires are connected to the nodes behind the board.

We used the same way as testing the coils for ABS which was using a dual pattern oscilloscope to capture 2 waveforms at the same time.

Both pattern is the same but only showed reversed to each other having a tiny delay.

Reflection:

The CAN bus system is probably the latest technology on vehicles and provides some very good advantages like:

• Save wires
• Save money
• Save connections
• All the modules can share information to each other
• More features

However the CAN bus system makes the vehicle electrical system more complex and how a CAN bus system operates is very complicated and there are a lot more to learn at this stage.

References:

http://canbuskit.com

wikipedia

Unitec Moodle

Vijay Naidu