4848 Blog 4

Controller Area Network;

Unfortunately I did not get a chance to do much work on CAN systems in practical, So I thought id do abit of a theoretical post on CAN BUS systems. I believe that these systems are very important to learn about as they are in most modern day vehicles and no doubt we may have to fix some of these systems one day.

What is a CAN system?

Controlled area network;
A CAN system is a communication system between a number of different nodes through-out the vehicle. The CAN main node  communicates to these nodes in the vehicle by using bi-nary codes. Each of these Bi-nary codes are specifically programmed to trigger actuation of components.

Basically this system allows multiple amounts of micro-controllers to be inter-connected through-out the vehicle, meaning that the system only uses the two signal lines (can hi/low) to allow these micro-controllers to actuate components through-out the vehicle.

Whats the advantages of having a CAN system;

each and every component is connected using the same lines it cuts alot of length of wire out of the circuitry, which means less weight, less room for error as there is just the Can High and Can Low wires (these are the communication lines). Less manufacturing costs, because of the reduced amounts of wiring (this is very attractive to vehicle manufactors as it reduces there manufactoring prices)


Can hi speed and low speed:

Can low speed refers to components that are controlled with a can system but are not the top priority, for example; Lighting, Adjustable seating, Radios, Window wipers, door locking etc. High speed would be the components that involve safety sort of stuff like; Traction control, Electronic stability program, Anti-lock braking system etc.


 The reason that these components are in the high speed part of can is that these components need to be contacted as fast as possible if an emergency situation occurs. The components that are in the low side of can arent necessary to keep the driver and passengers safe. 

Also Can high speed and Can low speed are not to be confused with CAN HI and CAN LOW, as can high and can low are the actual signals that the nodes communicate with.






I got to get a tiny amout of CAN work done on the range rover, we got to use a scan tool in it to show us live data that is involved with the CAN system. We also found another menu which allowed us to actuate components controlled by the can system, this was very cool as the range rover has so many different components connected to the CAN network that there was so much different things to communicate with and actuate. It was amazing to see how the CAN system could be controlled with the touch of a button, this just shows the complexity and amount of time that has gone into engineering these systems perfectly.



ABS + Electronic trans booklet.

ABS (anti-lock braking system) was developed in the early 1950s-60s by a French physicist. The first application was to a passenger plane. ABS was developed to allow drivers to keep steer-ability and control through-out situations where the braking system would lock.
ABS works by having various electronically controlled solenoids which control the flow of hydraulic pressure. There is another HUGE part ABS needs to work properly, The wheel speed sensor. This sensor is usually an inductive type sensor, as the velocity of the wheel is increased, so is the frequency through the sensor, The ABS ecu takes reading from all four wheel sensors and compares them to each other, as soon as a vehicles braking system locks up, the ABS ecu knows that the wheels are locked, so the ecu will control the solenoids mentioned earlier to suit the amount of hydraulic pressure needed to each wheel cylinder to allow the vehicle to not lock and the driver to maintain steerability.



The first task 


First of all we had to do a quick little session of naming parts, shown in the picture below;

This was a pretty simple task, so moved on to the next one,

These diagram below are for the next task;

        

In the ABS wheel sensor what is the reason for the braded wire?;
The reason that the sensor has a braded wire is because its very important that the ECU reads correct signals, Basically having two wires wrapping around each other eliminates the problem of having signal interuption.


Identify and list all the fuses that are used by the ABS circuit;
Here is a list of the wires found;


*50AMP (ABS) fuse
*10AMP (Gauge) fuse
*20AMP (Done) fuse
*15AMP (Stop) fuse
*15AMP (ECU) fuse

Identify all of the earths for the ABS unit using the diagram above. State their colours and pin numbers;
The earths we found in the diagram were; Pins 10(b), 7(b) & 1(A). Each of these earths wire colours were Black and white. This is pretty common colour for earth wires in the automotive industry.


Our next task set was using the wiring diagram to identify which solenoids actuate which wheel cylinder, We also had to include what the pin numbers were and what colour the wires are. Below are my results;


Front right wheel;Pins; 2(b) & 6(b)
Wire colours; Red and white.


Front left wheel;
Pins; 1(A) & 3(B)
Wire colours; Blue and red


Rear left wheel;Pins; 12(B) & 1(B)
Wire colours; Brown and white

Rear right wheel;
Pins; 14(A) & 4(B)
Wire colours; Green and black


That task was quite fun, it gave us a little bit of knowledge towards reading wiring diagrams.


Now, the next task was to identify which solenoids would be opend/closed in different situations, using the diagram below;

In the four cases above state when the ABS motor will be working?;


I believe that the motor will be working when the car is in scenario 4. This because the hydraulic pressure to the brakes will need to be increased, for brake pressure to increase the ABS pump needs to force fluid through-out the brake lines to allow the hydraulic pressure to become higher.




Now our next task was to draw how we think a digital signal would look if it was switching 5 volts every 2 seconds, this will be displayed in the graph below;

As you can see, each box diagonally represents two seconds, each box vertically represents 2 volts.

We also needed to show what we though an analogue signal would look like if it had a frequency of 0.5Hz and a max voltage of +3 volt, this is shown in the graph below;

Each of the squares in the graph that run diagonally represent 0.25Hz and each of the squares vertically represent 1 volt. The reason the signal looks like it does is because analogue signals are usually produced by inductive type sensors, and as we all know an inductive type sensor will show this sort of signal because of the interuption of the magnetic field.

Okay, now we get to move onto some of the good stuff. These next tasks are to do with the testing we did on the ABS demonstrator machines.

Below is the wiring diagram needed for the ABS demonstrator;

The first task we were set for the demonstrators was to find the pin outs on the ABS ecu for each wheel speed sensor, using the diagram above;
Left front; ECU pin # 4 & 5Left rear; ECU pin # 4 & 5
Right front; ECU pin # 11 & 21
Right rear; ECU pin # 24 & 26


Next we had to figure out what type of sensor this was;


This sensor is an inductive pick up type. I could tell this by looking at the wiring diagram, as you can see each sensor has a signal in and one out, this shows that a voltage is sent to the sensor but as each tooth on the rotor wheel passes the pickup, a voltage is sent back to the ecu as a frequency analogue signal, aswell as the diagram indicates that the wires are shielded.


Our next task is to record the wave signal we recieve from each wheel speed sensor, using an osilloscope.

Each of the pictures below are of the different speed sensor signals;

Left rear

Left front

Right rear

Right front

As you can see all of these signals above look alot alike, there is some small differences though. A couple of the signals have a higher output rather than the others, we came to the conclusion that so many students have done experiments on them so that different sensors maybe be worn out compared to the other sensor, causing the difference in patterns. The reason that we will be getting bigger readings and more frequent readings is that because the sensors both have different gaps between the rotor wheel and the inductive pickup. The closer the rotor wheel can get to the inductive pickup, means that the output voltage will be higher. The further away the rotor is from the pick up the lesser the voltage output will be. And also with the frequency situation we believe that one of the wheels motors is faster than the other, this is what causes the difference in frequency between some of the patterns.

Osilloscopes are much more useful at reading these types of sensors because a multimeter cannot keep up with the speed at which these sensors operate at, where as an osilloscope can display a waveform, as shown above. By observing a waveform we can see faults alot easier which makes it more simple to diagnose faults which in turn saves us time whilst fault finding.

That task was quite a hard one, we had to have a really good think as to why the signals may vary as much as they did

Now we moved on to abit more wiring diagram excercises, but this task involved indentifying which relay powers which component etc;

Unfortunately this was the last task I was able to do on the ABS demonstrators, but we moved on to some of the on car ABS stuff.


The first task we had to do with on car testing was to show one of the tutors that we could correctly raise a vehicle using a jack, safely supporting the vehicle with axle stands

Below is a few pictures of components we had to find on the vehicle;

*This is a vehicle speed sensor, this measures the velocity of the wheel and sends the signal back to the ECU

*This is the ABS control unit, basically this controls where the hydraulic pressure goes in the braking system

*The black motor at the bottom of this picture is the ABS pump motor, this allows the ABS system to pressurize and distribute hydraulic fluid where ever it needs to in the braking system.

*The picture below is the ABS modulator, this is the brains of the ABS system. This is the part that receives signals and actuates the pump motor and the control unit when needed

*As you can see this is a foot park brake, the part pointed out by an arrow on the right hand side is the park brake switch, as the park brake is engauged so is this switch, it lets the ecu know the park brake is on and it displays a warning light on the speedo

*This is the master cylinder and the resivoir. The master cylinder forces hydraulic pressure through the brake lines at the drivers intent, this is fully operated by the driver. The resivoir is where all the hydraulic/brake fluid is stored for use in the braking system

*The brake booster sits behind the master cylinder, really this is the part which is controlled by the driver, this is actuated by the brake pedal, which allows hydraulic pressure to be distriuted through the master cylinder to the brakes.

ABS wheel sensors

The next tasks we were set was to determine whether the sensors we were testing on the vehicle were analogue or digital.

We used the mazda familia in the down stairs room.

We inspected the wheel speed sensors and found that they were analogue sensors, because they had inductive pick up sensors, which obviously means there will be a magnetic field which is interupted, giving an analogue signal.

Now we had to test the gaps between the toothed rotor and the inductive pick up sensor for each wheel;
Our specifications state that the sensors gap must be between 0.4mm & 1.00mm

*Front right;

0.5mm

*Front left;0.5mm

*Rear right;

0.4mm

*Rear left;0.6mm