Anti-Lock Braking System (ABS)

It is a safety system in automobiles. It prevents the wheels from locking while braking. The purpose of this is to allow the driver to maintain steering control under heavy braking and, in some situations, to shorten braking distances (by allowing the driver to hit the brake fully without skidding or loss of control).

How Do Wheels Lock?

During braking, wheels lock if the brake force applied is more than the friction between the road and tyre. This often happens in a panic braking situation, especially on a slippery road. When the front wheels lock, the vehicle slides in direction of motion. When the rear wheels locks, the vehicle swings around. It is impossible to steer around an obstacle with wheels locked. Locked wheels can thus result in accident. Skidding also reduce tyre life.

What Does ABS Do?

The system detects when the wheel are about to lock and momentarily release the pressure on locking wheel. The brakes are reapplied as soon as the wheels have recovered.
A toothed wheel (pole wheel) is fitted to the rotating wheel hub. A magnetic sensor mounted on each wheel in close in close proximity to the teeth, generates electrical pulses when the pole wheel rotates. The rate at which the pulses are generated (frequency) is a measure of wheel speed. This signal is read by electronic control unit (ECU). When a wheel is lock, the ECU sends an electrical signal to the modulator valve solenoid, which release pressure from the brake chamber. When the wheel recovers sufficiently, the brake pressure is reapplied again by the switch off signal to the modulator valve.
The modulator valve has an addition ‘hold’ state which maintains pressure. In break in the chamber, thus optimizing the braking process. The cycling of modulator valve (5 to 6 times per second) is continued till the vehicle comes to a controlled stop.
With ABS, the vehicle remains completely stable even when the driver continues to press the brake pedal during braking, thus avoiding accidents.

Components:

The anti-lock braking system consists of following components.

Wheel Speed Sensor

    The wheel speed sensor consists of a permanent magnet and coil assembly. It generates electrical pulses when the pole wheel rotates. The rate at which the pulses are generated is a measure of wheel speed. The voltage induced increases with the speed of rotation of the wheel and reduces with increasing gap between the pole wheel and the sensor.

Pole Wheel
    Pole Wheel is a toothed wheel made of ferrous material. It normally has teeth on the face. In some cases where it is not possible to install the sensor parallel to the axle, the pole wheels are designed with teeth on periphery. The pole wheel fitted on standard 9-20, 10-20 tires has normally 100 evenly spaced teeth. 80 evenly spaced teeth pole wheels are used for the vehicles having the tyre diameter less than 9mm.

Sensor Extension Cable
    The sensor extension cable is a two core cable which connects the wheel speed sensor to the Electronic Control Unit. The inner core sheathing is of EPDM rubber and the outer sheathing is polyurethane which provide abrasion resistance to the cable. The cable has a module plug with two pins is connected to the control assembly. The cable has two cores-brown and black in colour.

Electronic Control Unit
    The ECU is the core component of the ABS system. Wheel speed sensor signal are the input to the Electronic Control Unit. The ECU computers wheel speeds, wheel deceleration and acceleration. If any wheel tends to lock, the ECU actuates the corresponding Modulator valve to prevent wheel lock. The ECU is normally mounted in driver's cabin.

    The ECU consists of 7 major circuits,
> Input circuit
> Master circuit
> Slave circuit
> Driver circuit
> Feedback circuit
> Power supply circuit
> Fail safe circuit

The functions of ECU,
> It receives wheel speed signal from the sensor. The wheel speed signals are processed and appropriate output signals are sent to the modular valves in the event of a wheel lock.
> It continuously monitors the status and operation of ABS components and wiring.
> It alerts the driver in the event of occurrence of any electrical fault in the ABS system by actuating a warning lamp.
> It disconnects the exhaust brakes during ABS operations.
> It enables the service technician to read the faults in the system either through a diagnostic controller or a blink code lamp.

Modulator Valve Cable
    The Modulator valve cable has thee cores. There are two solenoid interface lines and a common ground line. The inner core sheathing is of EPDM type and the outer sheathing is polyurethane which provide abrasion resistance to the cable.
    The cable has a three pin moulded socket is connected to the modulator valve solenoid at one and an interlock connector with locking feature at the other end. The cores are brown, blue and green.

Modulator Valve
    ABS Modulator valve regulate the air pressure to the brake chamber during ABS action. During normal braking it allows air to flow directly from inlet to delivery. Modulator valve cannot automatically apply the brakes, or increase the brake application pressure above the level applied by the driver through the dual brake valve.

    There is an inlet port, Delivery port and Exhaust passage.
> The inlet port is connected to the delivery of quick release valve or relay valve.
> The delivery port is connected to the brake chamber.
> The exhaust passage vents air from the brake chambers.

    The modulator valve has two solenoids. By energizing the solenoids, the modular valve can be switched to any of the following modes.
> Pressure
> Pressure hold
> Pressure release

Quick Release Valve
    Quick release valve are fitted in air braking system to release the air from the brake chamber quickly after release of brake pedal. This prevents delay in brake release due to long piping runs or multiples of brake chamber being exhausted through the brake valve.

Relay Valve
    Relay valve provides a means of admitting and releasing air to and from brake chamber quickly, in accordance with the signal pressure from the delivery of the dual brake valve.
    Air from the reservoir passes through the valve into the brake chamber. The pressure applied to the brake is equal to the signal pressure from the dual brake valve. When the brake pedal is released the signal pressure is released. The pressure in the brake chamber is released directly through the exhaust port of the relay valve.

Warning Lamp
     Vehicle are fitted with an ABS warning lamp. It is a LED indicator lamp amber in colour and lights up when the system has detected any electrical fault. ABS warning lamp is located on the instrument panel in form of a driver.

Blink Code Lamp
    This lamp is green in colour and is used to indicate the stored faults in the system to the service technician on operating a blink code switch. The nature of fault in the system can be diagnosed by the number of flashes.

Off Highway Switch
    This is an optional switch in front of the driver which can be switched ON when the vehicle is operating off highway. In this mode, ABS control will; allow higher wheel slip to achieve shorter stopping distance than with normal ABS control.

Blink Code Switch
    A momentary switch that grounds the ABS Indicator Lamp output is used to place the ECU into the diagnostic blink code mode and is typically located on the vehicle's dash panel.

Read more about Blink Code in Antilock Braking system(ABS)

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Why doesn’t my navigation system understand me?

A story where big is good, but small is even better.

Yoshiki Chubachi

My wife and I are about to go shopping in a nearby town. So I get into my car, turn the key, and set the destination from POIs on the navigation system. The route calculation starts and gives me today’s route. But somehow, I feel a sense of doubt every time this route comes up on the system...

Route calculation in navigation uses Dijkstra's algorithm, invented by Edsger Dijkstra in 1956 to determine the shortest path in a graph. To save calculation time, navigation systems use two directional searches: one as the starting point and the other as the destination point. The data scheme that navigation systems use to represent maps consists of nodes, links, and attributes. Typically, a node represents a street intersection; a link represents the stretch of road, or connection, between two nodes; and attributes consist of properties such as street name, street addresses, and speed limit (see diagram).

Features of a map database. From Wikipedia.

As you may guess, it can take a long time to calculate the shortest path from all of the routes available. The problem is, automakers typically impose stringent requirements on timing. For example, I know of an automaker that expected the route from Hokkaido (in northern Japan) to Kyushu (in southern Japan) to be calculated in just a few seconds.

To address this issue, a system can use a variety of approaches. For instance, it can store map data hierarchically, where the highest class consists of major highways. To choose a route between two points, the system follows the hierarchical order, from high to low. Another approach is to use precalculated data, prepared by the navigation supplier. These examples offer only a glimpse of the complexity and magnitude of the problems faced by navigation system vendors.

An encouraging trend
Big data is the hot topic in the navigation world. One source of this data is mobile phones, which provide floating car data (current speed, current location, travel direction, etc.) that can be used by digital instrument clusters and other telematics components. A system that could benefit from such data is VICS (Vehicle Information and Communication System), a traffic-information standard used in Japan and supported by Japanese navigation systems. Currently, VICS broadcasts information updates only every 5 minutes because of the bandwidth limitations of the FM sub-band that it uses. As a result, a navigation system will sometimes indicate that no traffic jam exists, even though digital traffic signs indicate that a jam does indeed exist and that service is limited to the main road. This delay, and the inconvenience it causes, could be addressed with floating car data.


An example of a VICS-enabled system in which traffic congestion, alternate routes, and other information is overlaid on the navigation map. Source: VICS

During the great earthquake disaster in East Japan, Google and automotive OEMs (Honda, Nissan, Toyota) collaborated by using floating car data to provide road availability — a clear demonstration of how can big data can enhance car navigation. Leveraging big data to improve route calculation is an encouraging trend.

Small data: making it personal
Still, a lot can be accomplished with small data; specifically, personalization. I may prefer one route on the weekend, but another route on a rainy day, and yet another route on my wife's birthday. To some extent, a self-learning system could realize this personalization by gauging how frequently I've used a route in the past. But I don’t think that's enough. As of now, I feel that my navigation system doesn't understand me as well as Amazon, which at least seems to know which book I’d like to read! Navigation systems need to learn more about who I am, how well I can drive, and what I like.

Personalization resides on the far side of big data but offers more convenience to the driver. The more a navigation system can learn more about a driver (as in “Oh, this guy has limited driving skills and doesn’t like narrow roads”), the better. It is best to store this data on a server; that way, the driver could benefit even if he or she switches to a different car or navigation system. This can be done using the latest web technologies and machine learning. Currently, navigation systems employ a rule-based algorithm, but it would be interesting to investigate probability-based approaches, such as Bayesian networks.

I’m looking forward to the day when my navigation system can provide a route that suits my personal tastes, skills, and habits. Navigation suppliers may be experiencing threats from the mobile world, including Google and Apple, but I think that returning to the original point of navigation — customer satisfaction — can be achieved by experienced navigation developers.

Yoshiki Chubachi is the automotive business development manager for QNX Software Systems in Japan

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