4848 Blog 4 Anti-lock Braking System

Anti-lock Braking System

Background:

The ABS was invented  for aircraft use in 1929 by France, the system use a flywheel and valve attached to a hydraulic line that connected to the brake cylinders. In testing, a 30% improvement in braking performance with ABS was noted than braking without ABS, the pilots can just immediately apply full brakes instead of slowing increasing pressure manually in order, and one other benefit is can save tires from burning.

Chrysler was the first to use ABS on cars which was the 1971 Imperial equipped with a three-channel, 1 speed sensor per wheel ABS called "Sure Brake", at later the same year, Nissan used EAL( Electro Anti-lock System) as an option on the Nissan President which was the first electrical ABS used in Japan.

BMW was the first to use ABS on motorcycles which was in 1988 and Honda followed in 1992 with ABS equipped in its ST1100.

An ABS is a vehicle safety system which allows the wheels to continue interacting and rotating with the road surface and preventing the wheels from locking up when the driver applies maximum brake or closer to maximum brake, therefore the driver can still turn the steering wheel and avoid barriers and skidding, it will also improve vehicle control and decrease braking distance on dry and slippery surfaces but on gravel or snow surfaces the braking distance may increases but it can still improve vehicle control.

The photo above shows two cars which the one on the right was equipped with ABS but the one on the left was not. The right one can easily dodge the boxes in the front when maximum braking applied even on the wet surface but the one on the left ended up hitting the boxes because the wheels stopped rotating and the braking distance was longer when maximum braking applied and the driver wasn't able to steer as well.

This also can show you what's the differences between ABS and non ABS  :)

Theory:

This is picture shows what a Anti-lock Braking System looks like and also the components in the system

The components equipped in the system:

• Brake master cylinder
• Brake calipers and discs
• Wheel speed sensors
• Pump & accumulator
• Control module
• Hydraulic control unit

There is one wheel speed sensors per wheel to monitor the wheel rotation, the ABS will not work without the working wheel speed sensors. The wheel speed sensors are either reluctor type or hall effect type and send out either a sine wave or digital square wave to the control unit.

If the vehicle is under normal braking, the fluid pressure goes right through the hydraulic control unit and the ABS does not operates

If the wheel speed sensors detect the wheels start to lock up, the Hydraulic Control Unit(HCU) will operate in the 3 stages below:

1. HOLD PRESSURE a valve will close to stop brake fluid pressure increasing, if the wheels still locking up then the HCU will:
2. RELEASE PRESSURE a valve will open to release brake fluid pressure and store the fluid into an accumulator for later use, the wheels will back to rotating at this stage and they need to be slowed down again so HCU will:
3. RESTORE PRESSURE the pump will pump back brake fluid pressure into brake lines, if the wheel speed sensors detect the wheels start to lock up again, the HCU will repeat from stage 1

If the driver applies maximum brake to the vehicle at corners then the wheels will be in different rotation speed, the inside wheels will travel slower than the outside ones. If one or two wheels start to lock up but the others are still under normal braking, the control unit can easily identify which one or ones need to operate ABS process and operates the 3 stages to the individual braking system.

There are 3 system configurations for ABS system

1. One Channel: only the rear wheels will be controlled by ABS and only be controlled together
2. Three Channel: all 4 wheels will be controlled but the front two can be controlled individually and the rear wheels still get controlled together.
3. Four Channel: all 4 wheels will be controlled individually

From these informations above we can say that the Four Channel system is the best configuration of ABS system because each wheel can be controlled individually so the vehicle will be a lot more safer.

Experiment:

ON CAR:

The vehicle we used to test was a 1998 Mitsubishi Galant.

As the wheel sensors are the most important components in an ABS so it is necessary to know if all the sensors are working good.

First, jack up the car and take down the wheels, the sensor will be visible and easy to reach afterwards.

I found out there were only 2 wires coming out of the sensor so this means the speed sensors used on this car are reluctor type and will be sending out analogue waveform. Some other cars may use hall effect type of speed sensors with 3 wires coming out of them and they will be sending out digital square waveform.

To get the waveform shown below we used a oscilloscope to capture while spinning the right rear wheel:

OFF CAR:

An ABS demonstrator will be used for ABS off car testing:

The most important things to test for off car testing was the relays, there are 3 relays in this particular demonstrator which are:

• Main relay for the whole system
• One relay for pump
• One relay for Hydraulic Control Unit

Using a dual oscilloscope to capture waveforms for each relay can easily show if the system is having any problems.

First find the terminals for the relay according to the circuit diagram and connect the probes to the identified wires

Here is a waveform of the main relay shows the control side and switching side:

The coil will be energized as soon as the system gets turned on, and drops down when ECU grounds it. The switching side of the relay reads just the opposite to the control side which is shown in the waveform above.

The relays for the pump  and control unit will be in the same manner. When the scale opens we should see a delay between the switching side and control side, if a relay is working bad somehow it will affect the ABS operation straight away.

Reflection:

The testing result did not indicate any problems or issues for both on-car or off-car ABS system. 

But one very common way to affect a speed sensor to work is the magnetic part of the sensor do pick up metal dusts and piece, it will be dirty and not able to get and send correct signal to the control unit. 

Every component is important in a ABS system even a single relay, because ABS needs to operate as fast as it can when something happens so every millisecond saved will be worth to do so.

When the ABS light on the dashboard indicates you there is a problem in the ABS system, from the simple fuse to the more complicated control unit, the job is make sure everything works in good working order.

References:

Unitec moodle

Wikipedia

Vijay Naidu

4848 Blog 4 Electronic Transimission

Background:

GM used semi-automatic transmission in automative in 1937, however a real automatic transmission system was firstly used on the Oldsmobile back in 1948 also by GM.

An automatic transmission also known as auto gearbox is a type of motor vehicle transmission that can automatically change gear ratios when the vehicle moves, so the driver does not have to shift the gears manually and a clutch pedal is not needed. There are more types of automatic transmissions like the older type semi-automatic transmission and the more modern and better Continuous Variable Transmissions(CVTs) and Tiptronic Transmissions.

Comparing the automatic transmissions to the manual gearbox, vehicles equipped with automatic transmissions are less complex to drive, it became a lot more popular after the 1990s. In a lot countries, some driver licenses only allows people to drive automatic vehicles but a manual license can allow the driver to drive both manual and automatic vehicles. Since automative cars are easy to drive and very reliable, a lot people do not even know how to drive a manual car.

In the automatic transmission, there is a torque convertor which takes the place of  a clutch in a manual transmission which you can see is the big blue/green thing on the left to the transmission shown in the above picture. But Honda automatic transmissions use gears like a manual gearbox and apply the correct gear using a clutch, this is different to other manufacturers but all the other automatic transmissions use the same principle.



Theory:




Some common modes for an automatic transmission system:

• P(Park)-- the output shaft is lock for stopping the vehicle to go any directions, often used when the engine is off or the car does not need to be driven.
• R(Reverse)-- the reverse gears are engaged and the vehicle will go backwards
• N(Neutral)--all the gears are disengaged and the wheels are free from transmission control, the vehicle will move forward or backward if the car is not parked on a flat surface, PNP(Park Neutral Position) switch will lock the engine away from starting up for most of the vehicle for safety reason.
• D(Drive)--All the gears can be engaged depends on how fast the vehicle goes, often used for driving
• 2 or S(2nd gear or Second)--only the 1st and 2nd gear can be engaged
• 1or L(1st gear or Low)-- only the 1st gear can be engaged.

A automatic transmission is a system which is way more complicated than a manual gearbox system because all the jobs are done by electrical components rather than shifting gear manually.


An automatic transmission system is running by a PCM( Powertrain Control Module) similar to an engine ECU(Electrical Control Unit), all the electrical components is energized and controlled by the PCM


Here is a diagram how a PCM controls the whole system:

All the solenoids are controlled by the control coils, when the PCM energizes each coils the solenoids will generate magnetic field and do its job.Let me explain this using the shift solenoids with a picture shown below:

We will just assume a vehicle is running on a automatic transmission with 2 shift solenoids. If we put on Drive, and drive the car,at the 1st gear the 1st solenoid will be and 2nd solenoid will be off, when the PCM detects the gear needs to be changed to 2nd gear then it will turn off the 1st solenoids so both solenoids are not working and turn on the 2nd solenoid if it needs transmission to go into 3rd gear,at last if the vehicle is faster enough then the PCM will turn on both solenoids for going into 4th gear.


And how do PCM know when to shift gears?
The PCM gets signal from few sensors to decide if it needs the gear changed and they are:

• VSS( Vehicle Speed Sensor) for how fast vehicle is going
• TPS( Throttle Position Sensor) for engine load
• CKS( Crankshaft Position Sensor) for engine RPM
• ECT( Engine Coolant Temperature Sensor) for engine temperature
• BPS( Brake Pedal Switch) for driver intent

When the vehicle is going faster enough or engine is having enough load or engine RPM is higher enough, the PCM detects the signals from the above sensors and shift up the gears. When the vehicle is slowing down or engine load is decreasing or engine RPM is going low, the PCM also detects the signals from the above sensors and shift down the gears.
Another condition is, when the engine is cold, the PCM always shift up gears a little later than when the engine is hot.
Some unique sensors for the automatic transmission system such as ATF( Automatic Transmission Fluid)sensor and PNP(Park Neutral Position) sensor will also affect on PCM deciding when to change gears.


Another very important thing in an automatic transmission system is the fluid, not just to cool down the temperature of the transmission, it is also used in the valve body to change the gears.The fluid will get pumped to the gear that the PCM wants to change.








Experiment:




To find out the problems of a automatic transmission system, simply use the scan tool in the  OBDII plug of the car for diagnosis.
When the PCM detects there's a problem it will write a fault code in the memory and can be picked up by the scan tool in diagnosis.


The vehicle we used to diagnosis was a 1998 Mitsubishi Lancer

And the gear changing status is shown in the picture below:

From the test, I noticed the TCC pulse width modulation solenoid got turned on at 31km/h,the duty cycle of the solenoid was about 40% and increased to 97% after the vehicle reaches 77km/h.


Here is a list of common OBDII fault code which can help fault finding an automatic transmission system:

These are only a part of the codes, there are a lot more


Let's assume if we find a fault code of P0710 from a vehicle which the list above shows us there is a problem in the Transmission Fluid Temperature Sensor Circuit.However it does not mean the sensor needs to be changed, if the sensor is broken, it must have some reason that caused the problem, maybe the resistor in the circuit is shorted? maybe the vehicle is using wrong type of fluid and broke the sensor by over heating? there could be a lot possibilities. Therefore the fault code can only narrow down the problem to the particular circuit but further investigation needs to be done to get the problem fixed.








Reflection:


The results showing at the test indicated that particular transmission was working good.
The solenoids was in good order as the TCC pulse width modulation solenoid should be off at low speed and turns on with speed increases.


A quite common symptom happens to an automatic transmission system is the gear won't change or get stuck in some gears. This is usually caused by broken shift solenoids.
To fix this, we will need to know how the shift solenoids work from the engine manual and using an oscilloscope to test the sensors. It will be the same way as testing other sensors in the engine, get the waveform and compare it to each solenoid.


There is one more important thing to maintain a automatic transmission is the fluid. The fluid is used to cool down the temperature and also change gears, use the proper fluid is very IMPORTANT for all the automatic vehicles and make sure there is enough fluid and no leak from the transmission and the transmission oil cooler.

References:

Unitec moodle

Wikipedia

Vijay Naidu 

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