Anand Patel
Application Report
Dt :-
Microcontroller
used in Automobile (Automatic Transmission)
Automatic
transmission has been around many years.
The earliest automobiles offered only manual transmissions. Similar in
principle to today's stick-shift vehicles, these cars, such as the Ford Model
T, sported two forward gears and one reverse, coupled to the engine via a
series of pedals. But as cars grew larger and traffic got worse, engineers
began searching for a way to have the car "automatically" shift from
one gear to another.
Designers spent decades perfecting the modern automatic transmission.
Although groundwork had been laid in the early 1900s by German manufacturers of
marine engines, the first appearance of an automatic transmission in a car did
not occur until 1938, when GM invented "
No more missed shift gates. No engine lugging or racing. No torn-stocking,
high-heel clutch-pedaling dramas. None of that. Just
press the gas and go.
Now let’s talk about Mechanical side of the automatic trnasmission.
The key to the modern automatic transmission is the torque converter. It takes the place of a clutch in a manual transmission. Inside the torque converter are several components that help multiply the power. These are the impeller (or pump), the turbine, and the stator (or guide wheel).
These are different-sized gears,
just like the ones on the back of your mountain bike. They're called planetary
because they're circular and revolve around a central gear known as a sun gear.
Gear shifting in an automatic transmission is very similar to the action taken while riding your mountain bike -- except that a series of valves, sensors, and other components take the place of your brain, deciding when to upshift and downshift to a larger or smaller gear.
Where is Electronics used ?
Well, all of the above processes are controlled by microcontroller or ECU (engine control unit ).
The Electronic Control Unit (ECU) controls the fuel
injection system, ignition timing, and the idle speed control system. The ECU
also interrupts the operation of the air conditioning and EGR systems, and
controls power to the fuel pump (through the control relay). The ECU consists
of an 8-bit microprocessor, random access memory (RAM), read only memory (ROM),
and an input/output interface.
Based on information from the input sensors (engine coolant temperature, barometric pressure, air flow, etc.), the ECU determines optimum settings for the output actuators (injection, idle speed, ignition timing, etc.).
ECU can’t function by itself. Now a days average car contains about 70 microcontroller providing data to ECU over CAN ( controlled area network ).
Some of the key components integrated in this cheap is A/D (analog to digital converter), Communication chips, Signal conditioners.
CAN
It is a two-wire, half duplex, high-speed network system and
is well suited for high speed applications using short messages. Its
robustness, reliability and the large following from the semiconductor industry
are some of the benefits with
Some of the Sensors that feeds data to ECU
·
Camshaft (or
Crankshaft) Position Sensor (CPS)
The camshaft position sensor tells the computer where the piston is. When
the piston is in the proper position, the computer will fire the plug for that
cylinder.
ECU Gets the data from all different kind of sensors and
manipulates them in fraction of time. It
is very time sensitive information. Now a
day more and more sensors are being used loading up ECU. Automakers have come over this problem by
dividing all the processes in several modules such as door controller, vent controller,
lighting etc. All this modules talk to
ECU via
Let’s see how
automatic transmission system is designed and how microcontrollers and sensors
play roll.
Let's talk
about that last feature -- inhibiting the upshift
when going into a turn on a winding road. Let's say you're driving on an
uphill, winding mountain road. When you are driving on the
straight sections of the road, the transmission shifts into second gear to give
you enough acceleration and hill-climbing power. When you come to a
curve you slow down, taking your foot off the gas pedal and possibly applying
the brake. Most transmissions will upshift to third
gear, or even overdrive, when you take your foot off the gas. Then when you
accelerate out of the curve, they will downshift again. But if you were driving
a manual transmission car, you would probably leave the car in the same gear
the whole time. Some automatic transmissions with advanced control systems can
detect this situation after you have gone around a couple of the curves, and
"learn" not to upshift again. Speed sensor plays very big roll in making
decision of shifting gears.
What if Chip fails?
One might think what happen if one of the chips goes bad while driver is driving the car. In the case of a sensor malfunction, the computer may go into a "fail safe" or "limp in" mode. For example, the Crank Angle Sensor dies and no longer sends a signal to the computer. The computer sees the signal is missing and notes the malfunction code and turns on the check engine light. Now lacking that CAS, signal it goes to the base values stored in the computer and uses that value to control the ignition timing. It's not perfect, but it doesn't leave you stranded on the side of the road. Quite often the computer limits engine RPM to about 2500 RPM to prevent any possible engine damage and further alert the driver to a problem.
Check out these websites for information on particular chip that is used in automobile industry.
http://support.intel.com/design/auto/engback.htm