Automotive Basics Part2

Anti-lock braking system (ABS)
Anti-lock braking system is an automotive safety system that allows the wheels on a motor vehicle to maintain tractive contact with the road surface according to driver inputs while braking preventing the wheels from locking up (ceasing rotation) and avoiding uncontrolled skidding. It is an automated system that uses the principles of threshold braking and cadence braking which were practiced by skillful drivers with previous generation braking systems. It does this at a much faster rate and with better control than a driver could manage.
The theory behind anti-lock brakes is simple. A skidding wheel(where the tire contact patch is sliding relative to the road) has less traction than a non-skidding wheel. If you have been stuck on ice, you know that if your wheels are spinning you have no traction. This is because the contact patch is sliding relative to the ice. By keeping the wheels from skidding while you slow down, anti-lock brakes benefit you in two ways: You’ll stop faster, and you’ll be able to steer while you stop.
There are four main components to an ABS system:
  • Speed sensors
  • Pump
  • Valves
  • Controller
Speed Sensors
The anti-lock braking system needs some way of knowing when a wheel is about to lock up. The speed sensors, which are located at each wheel, or in some cases in the differential, provide this information.
There is a valve in the brake line of each brake controlled by the ABS. On some systems, the valve has three positions:
  • In position one, the valve is open; pressure from the master cylinder is passed right through to the brake.
  • In position two, the valve blocks the line, isolating that brake from the master cylinder. This prevents the pressure from rising further should the driver push the brake pedal harder.
  • In position three, the valve releases some of the pressure from the brake.
Since the valve is able to release pressure from the brakes, there has to be some way to put that pressure back. That is what the pump does; when a valve reduces the pressure in a line, the pump is there to get the pressure back up.
The controller is a computer in the car. It watches the speed sensors and controls the valves.
ABS at Work
There are many different variations and control algorithms for ABS systems. We will discuss how one of the simpler systems works.
The controller monitors the speed sensors at all times. It is looking for decelerations in the wheel that are out of the ordinary. Right before a wheel locks up, it will experience a rapid deceleration. If left unchecked, the wheel would stop much more quickly than any car could. It might take a car five seconds to stop from 60 mph (96.6 kph) under ideal conditions, but a wheel that locks up could stop spinning in less than a second.
The ABS controller knows that such a rapid deceleration is impossible, so it reduces the pressure to that brake until it sees an acceleration, then it increases the pressure until it sees the deceleration again. It can do this very quickly, before the tire can actually significantly change speed. The result is that the tire slows down at the same rate as the car, with the brakes keeping the tires very near the point at which they will start to lock up. This gives the system maximum braking power.
When the ABS system is in operation you will feel a pulsing in the brake pedal; this comes from the rapid opening and closing of the valves. Some ABS systems can cycle up to 15 times per second.

Car Engine working:
Referred Documents:

What is Calibration?
Calibration is a process of optimizing or tuning a control algorithm to get the desired response from the system.  A calibration tool is a combination of a hardware interface and a software application that enables the engineer to access the calibration variables in an ECU and change them.  Typical control algorithm components that need calibration are look-up tables, gains, and constants.
A powertrain control algorithm may have hundreds of calibrate-able parameters.  The more parameters that are used, the more difficult the task of finding an optimal calibration.  The calibration tool helps the engineer arrive at an acceptable calibration parameter set.  All of the calibrate-able parameters are grouped into a special section of ECU memory called the calibration memory.  Calibration tools give the user access to this memory to allow.

A basic calibration system consists of an ECU interface, a link to the host PC, and a PC application.   A more capable system will add a vehicle network link as well as analog data acquisition modules.  The ECU interface is typically a CAN interface when a CAN-based calibration method is used, or a Read-Only-Memory (ROM) emulator when a direct memory access method is used.  The link back to the host PC can be CAN, USB, Ethernet, or other method.  The PC application is typically a MS-Windows® application.  Figure 1 shows a typical calibration system.
What is CCP?
The CCP (CAN Calibration Protocol) is, just as the name indicates, a protocol for calibration of and data acquisition from electronic control units (ECU). The protocol is defined by ASAM (Association for Standarisation of Automation- and Measuring Systems), earlier known as ASAP (Arbeitskreis zur Standardisierung von Applikationssystemen). This is an international organization consisting of a number of significant vehicle manufacturers i.e. Audi, BMW, VW etc. Until now different technical solutions have been used for developing, calibration, production and service of ECU hardware and software. The aim with CCP is to create a common tool for all stages of ECU developing and which is compatible with different kinds of hardware and software.
The ASAM group defines a lot of standards. The CCP and XCP standards are found in subsection AE (Automotive Electronics) and are grouped into something called AE MCD 1. The current version of the CCP specification is 2.1, released in February, 1999.
The CAN Calibration Protocol is basically used as a monitor program. Similar to many earlier serial RS232-type monitors and bootstrap loaders that provide basic read and write memory capabilities, CCP provides the same functionality using a standard protocol rather than a company-specific proprietary protocol. However, when a high-speed CAN bus is used, CCP, unlike some previous 9600 baud UART-based monitors, provides the ability to access data at such a fast rate that it is possible to run an application at the same time.
Developers now have a significant advantage over the earlier monitoring methods.
In the dialog used by CCP and most monitor programs it is the tool or PC that is the Master that sends commands into the ECU. The ECU does not send information without the Master (Tool) initiating commands. A CCP-compliant tool can read data from the ECU and can write data into the ECU with the appropriate CCP messages.
With CCP, the software developer can read:
With CCP, the software developer can write to:
However, this is only CAN Calibration Protocol’s minimum capability. CCP includes several additional monitor commands, and provides several new features including automatic data acquisition processing based on events or periodic updating, flash programming and data security. Since there is no requirement to use all its features, CCP is a scalable protocol.
 CCP users have access to online measurement data and can calibrate modules, so software development can occur not only in a lab environment but also during an in-vehicle test.

What are the functions of CCP?
CCP is a application layer for CAN 2.0B (11- or 29-bits CAN id). The Protocol is a top layer (layer 7) according to the OSI model, which means that the protocol does not describe how bits and bytes are created but uses the CAN 2.0B protocol physical, data link and network layer.
CCP supports the following functions:
  • Reads and writes to ECU memory.
  • Synchronous cyclic data acquisition from a ECU.
  • Simultaneous calibration and data acquisition.
  • Handles multiple nods on the CAN bus.
  • Flash programming.
  • Plug and play.
  • Protection of resources (data acquisition and calibration).
CCP in detail
CCP is built on a master/slave application where CCP-master starts communication by sending commands to a slave node. There can be several slave nodes connected on a CAN bus. CCP uses generic commands for data acquisition and simple memory handling for calibration. These two resources are independent and can therefore be used simultaneously.
CCP has been designed to handle the restrictions and demands of both small 8-bits microcontrollers and ECUs with high performance. No extra hardware has to be connected to the ECU. The CCP driver is fully implemented in the software. A simple implementation of CCP only needs a small part of the available RAM, ROM and CPU time for execution. A simple implementation only need two CAN message identifiers, which can be set as low priority that does not disturb the ordinary traffic. If CCP is to be used from an ordinary PC, the same simple and low cost CAN interface which is used in microcontrollers can be used.

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