Bilsensortillverkare

Wheel Speed Sensor(ABS)

An anti-lock braking system (ABS) is a vehicle safety system that allows the wheels of a car to maintain tractive contact with the road surface while braking, preventing the wheels from locking up (ceasing rotation) and avoiding uncontrolled skidding. It is an automated system that uses the principles of cadence braking. Cadence braking is a skill practiced by skilful or professional drivers in vehicles without or prior to ABS technology. The ABS system does this at a much faster rate and with better control than many drivers could manage. ABS generally offers improved vehicle control and decreases stopping distances on dry and slippery surfaces. However, on loose gravel, ice or snow covered surfaces, ABS can increase braking distance, although still improving vehicle steering control.

Since their introduction, anti-lock braking systems have been improved considerably in a bid to further improve driver safety and comfort. Later technology not only prevents wheel lock up under braking, but can also provide data for the on board navigation system, traction control system, emergency brake assist, hill start assist, electronic stability control and the front-to-rear brake bias. None of the above would be possible without wheel speed sensors.

The ABS, or wheel speed sensor in a relatively simple yet vitally important part of the ABS system as it is used to communicate the rotational speed of the wheel to the ABS control module.

Wheel speed sensors are installed directly above or next to the pulse wheel, these are also known as a tone wheel, but more often than not, called the ABS ring. The ring is attached to a part of the vehicle that is rotating at the same speed as the road wheel, such as the wheel hub, brake disc, CV joint or the drive shaft. 

Types of ABS Sensors
ABS sensors are classified in to two different types, Passive and Active. Passive is without a power supply and Active is with a power supply.

Passive sensors
These comprise of a wire coil wound around a magnetic core and a permanent magnet. The pole pin inside the coil is connected to the magnet and the magnetic field extends to the ABS ring. The rotational movement of the ABS ring and the associated alternation of teeth and gaps effects a change in the magnetic flux through the pulse wheel and the coil. The changing magnetic field induces an alternating voltage in the coil that can be measured. The frequencies and amplitudes of the alternating voltage are related to the wheel speed. The sensor creates a AC signal that changes frequency as the wheel changes speed. The ABS control unit converts the AC signal to a digital signal for interpretation.

Passive sensors are larger and less accurate than active sensors and only start to operate when the wheel reaches a certain speed, therefore they have limited operation at lower speed. They are also unable to operate in reverse, so thus unable to determine the direction of travel.

Active sensors on the other hand are a lot more accurate and are able to detect speeds of less them 0.06 mph, this is vital for modern traction control systems. Some active sensors can even detect the rotation direction of the wheels. Active sensors require an external power source to operate and work in conjunction with a toothed or magnetic ABS ring. Active sensors create a digital signal which is transmitted to the control unit in the form of a current signal using pulse width modulation. 

There are two types of active sensor. The Hall sensor and the Magneto-resistive sensor

Hall sensor – The hall sensor uses the Hall effect, which is a generation of a voltage (the Hall voltage) across an electrical conductor, transverse to an electric current in the conductor and a magnetic field perpendicular to the current. They react to changes in magnetic fields with a voltage difference which is send to the ABS control unit as a square wave signal. They use a semiconductor sensor coupled to an electronic circuit, protecting the sensor from possible voltage spikes, and a permanent magnet.

Hall sensors record the wheel speed via either a toothed or magnetic encoder (ABS ring) often found on the wheel hub, disc or bearing. The sensors are very accurate, but must be installed with precision.

The advantage of using a magnetic ring over a toothed ring is that the sensor can be a lot smaller as there is no permanent magnet required in the sensor. It is instead located in the virtually flat ‘ABS ring.’ That magnetic ring can be located in the wheel bearing, allowing them to be used in confined spaces. The variation in the magnetic field is now created by the sections of polarity within the ring. 

Magneto-resistive sensor – These sensors use a magnetic encoder ring similar in appearance to the encoder ring associated with the hall sensor. However, the encoder ring associated with this sensor has magnetic arc segments which cause a clear change in resistance when passing the sensor. It is this that enables the control unit to determine the wheel’s rotational direction. Magneto-resistive sensors are much more precise, but generally more expensive than Hall sensors and require a less precise installation position, therefore meaning that it can be located further away from the ‘ABS ring’ than the other types of sensors.

Both active sensors are less sensitive to electromagnetic interference, vibration and temperature fluctuations than a passive sensor.

If any of the warning lights above are illuminated, there is brake pedal judder while braking at low speeds or the wheels lock up while braking, then there is probably a fault somewhere within the ABS system.

Possible causes:
• Corroded, cracked or swollen ABS ring
• ABS ring blocked, damaged, missing teeth or windows
• ABS sensor out of position.
• Damaged ABS sensor from impact with road debris.

One of the most common calls that we currently receive into our technical department is for the Peugeot 308 rear. This particular brake disc also contains the bearing and ABS ring. The workshop replaces the disc, only to find that the ABS sensor is now in contact with the ABS ring of the new disc. Apec or the motor factor usually get the blame for an incorrect part, however Apec parts are made to the exact dimensions as the original disc so it is not the disc that is at fault. What actually happens is that over time, corrosion forms and builds up under the mounting point of the ABS sensor. This forces the sensor towards the ABS ring and begins to wear the surface of the ABS ring. If this is noticed before the disc is bolted up, then usually the sensor (if not too worn itself) can be unbolted and the corrosion removed. However, if it is not noticed then is can result in the ABS sensor snapping as the vehicle is driven out of the workshop.

Camshaft Position Sensor(CMP)

A camshaft position sensor is found in every modern automobile. This sensor is an essential component of any car since it ensures that the engine is operating correctly. When looking under the hood of your car, you can have problems finding the sensor. Typically, each car manufacturer will have its unique location for putting the sensor near the engine. It can be found behind the cylinder head, in the vehicle’s lifter valley, or adjacent to the engine block.

A camshaft position sensor’s job is to figure out where the camshaft is with the crankshaft. The powertrain control module (PCM) receives this information and uses it to operate the fuel injectors and/or ignition system.
 

Tire Pressure Sensor(TPMS)

The purpose of the tire pressure monitoring system (TPMS) in your vehicle is to warn you that at least one or more tires are significantly under-inflated, possibly creating unsafe driving conditions. The TPMS low tire pressure indicator is a yellow symbol that illuminates on the dashboard instrument panel in the shape of a tire cross-section (that resembles a horseshoe) with an exclamation point.

That indicator light in your vehicle has a history. It’s a history rooted in years of uncertainty about proper tire pressure and many serious car accidents that might have been avoided had drivers known their air pressure was low. Even now, it’s estimated that a substantial number of vehicles hit the road each day with underinflated tires. However, proper tire maintenance with the aid of a TPMS can and does help prevent many serious accidents.

Before this indicator light became commonplace, knowing whether your air pressure had reached unsafe levels meant getting out, crouching down, and using a tire gauge. With few exceptions, this was the only pressure-checking tool ordinary consumers had at their disposal.

Then, in response to a surge in accidents due to underinflated tires, the US government passed the Transportation Recall Enhancement, Accountability, and Documentation (TREAD) Act. One of the outcomes of this legislation is that most vehicles sold in the United States since 2007 include a tire pressure monitoring system of some kind.

Not every TPMS works the same way. The illumination of the low tire pressure indicator represents the final step in the process of either an indirect TPMS or a direct TPMS.

INDIRECT TPMS: WHAT IS INDIRECT TPMS & HOW DOES IT WORK?

An indirect TPMS typically relies on wheel speed sensors that the anti-lock brake system uses. These sensors measure the rate of revolution each wheel is making and can be used by on-board computer systems to compare with each other and to other vehicle operation data such as speed.

Based on the rate of revolution of each wheel, the computer can interpret the relative size of the tires on your vehicle. When a wheel starts spinning faster than expected, the computer calculates that the tire is underinflated and alert the driver accordingly.

So, an indirect tire pressure monitoring system doesn’t actually measure tire pressure. It’s not electronically processing the same kind of measurement you might see with a tire gauge. Instead, an indirect tire pressure monitor simply measures how fast your tires are rotating and sends signals to the computer that will actuate the indicator light when something in the rotation seems amiss.

ADVANTAGES OF INDIRECT TPMS

-- Relatively inexpensive compared to a direct TPMS

-- Requires less programming/maintenance over the years than a direct TPMS

-- Less overall installation maintenance than its direct counterpart

DISADVANTAGES OF INDIRECT TPMS

-- May become inaccurate if you purchase a bigger or smaller tire

-- May be unreliable when tires are unevenly worn

-- Must be reset after properly inflating every tire

-- Must be reset after routine tire rotation

DIRECT TPMS: WHAT IS DIRECT TPMS & HOW DOES IT WORK?

Direct TPMS uses pressure monitoring sensors within each tire that monitor specific pressure levels – not just wheel revolution data from the anti-lock brake system.

Sensors in a direct TPMS may even provide tire temperature readings. The direct tire pressure monitoring system sends all of this data to a centralized control module where it’s analyzed, interpreted, and, if tire pressure is lower than it should be, transmitted directly to your dashboard where the indicator light illuminates. A direct tire pressure monitor usually sends all of this data wirelessly. Each sensor has a unique serial number. This is how the system not only distinguishes between itself and systems on other vehicles, but also among pressure readings for each individual tire.

Many manufacturers use proprietary technology for these highly specialized systems, so replacing a TPMS in a way that’s consistent and compatible with your vehicle will require an experienced, knowledgeable technician.

ADVANTAGES OF DIRECT TPMS

-- Deliver actual tire pressure readings from inside the tire

-- Not prone to inaccuracies because of tire rotations or tire replacements

-- Simple resynchronization after tire rotation or tire replacements

-- Batteries inside the sensors usually last for about a decade.

-- May be included in a vehicle’s spare tire

DISADVANTAGES OF DIRECT TPMS

-- More expensive overall than an indirect TPMS

-- Though simple, resynchronization may require costly tools.

-- Battery rarely serviceable; if the battery is drained, the whole sensor must be changed.

-- Proprietary systems make installation, service, and replacement confusing for consumers and auto shops.

-- Sensors are susceptible to damage during mounting/demounting

TIRE PRESSURE AND SAFETY

Although the methods may be different, both systems serve the same purpose and activate the same indicator light. Even though a TPMS can deliver accurate alerts when properly maintained, it’s not a replacement for manual air pressure checks, consider it just another item in your car maintenance toolbox.

CONTINUE YOUR JOURNEY

There’s never a good time for a flat. That’s why Bridgestone DriveGuard tires are masterfully engineered to keep you moving for up to 50 miles at speeds up to 50 MPH without disruption.

 
Crankshaft Position Sensor(CKP)

A crank sensor (CKP) is an electronic device used in an internal combustion engine, both petrol and diesel, to monitor the position or rotational speed of the crankshaft. This information is used by engine management systems to control the fuel injection or the ignition system timing and other engine parameters.