Anand Patel

Application Report

Dt :- June, 28, 2004

 

 

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 "Hydra-matic Drive." The first production automobile to offer this transmission was an Oldsmobile, which rolled off the line in 1940. By 1948, most major American automakers offered passenger cars with optional fully automatic transmissions as an option.

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.

 

  • Torque converter

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).

 

  • Planetary Gearsets

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.

 

  • Clutches, Bands, and Servo Pistons

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 CAN.  CAN can theoretically link up to 2032 devices (assuming one node with one identifier) on a single network. However, due to the practical limitation of the hardware (transceivers), it can only link up to110 nodes (with 82C250, Philips) on a single network. It offers high-speed communication rate up to 1 Mbits/sec thus allows real-time control. In addition, the error confinement and the error detection feature make it more reliable in noise critical environment.

 

 

Some of the Sensors that feeds data to ECU

 

  • Vehicle Speed Sensor (VSS)
    The vehicle speed sensor is installed in the transaxle. It contains a pulse generator that provides a vehicle speed signal to the speedometer. The speedometer then sends a signal to the ECM.
  • Mass Air Flow Sensor (MAF)
    The mass airflow sensor tells the computer how much air is coming into the engine. The more air that enters, the more fuel is needed to get an ideal air/fuel ratio.
  • Intake Air Temperature Sensor (IAT)
    The intake air temperature sensor tells the computer the temperature of the incoming air. Since cold air is denser than warm air, it needs more fuel to achieve the ideal air/fuel ratio. To do this, the computer will open the injectors for a longer period of time.

·        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.

  • Coolant Temperature Sensor (CTS)
    The engine coolant temperature sensor tells the computer what the operating temperature of the engine is.
  • Knock Sensor
    The knock sensor is attached to the cylinder block. It senses engine knocking using a piezoelectric element.

 

  • Throttle Position Sensor (TPS)
    The throttle position sensor tells the computer where the gas pedal is. The computer determines the load being applied to the engine and adjusts injector and ignition timing as required.

 

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 CAN. 

 

Let’s see how automatic transmission system is designed and how microcontrollers and sensors play roll.

 

  • Downshift automatically when going downhill to control speed and reduce wear on the brakes
  • Upshift when braking on a slippery surface to reduce the braking torque applied by the engine
  • Inhibit the upshift when going into a turn on a winding road

 

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

 

http://e-www.motorola.com/webapp/sps/site/prod_summary.jsp?code=MPC533&nodeId=03t3ZGpnLnPCbf8648&tid=tmfp

 

 

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Anand Patel

Application Report

Dt :- June, 28, 2004

 

 

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 "Hydra-matic Drive." The first production automobile to offer this transmission was an Oldsmobile, which rolled off the line in 1940. By 1948, most major American automakers offered passenger cars with optional fully automatic transmissions as an option.

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.

 

  • Torque converter

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).

 

  • Planetary Gearsets

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.

 

  • Clutches, Bands, and Servo Pistons

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 CAN.  CAN can theoretically link up to 2032 devices (assuming one node with one identifier) on a single network. However, due to the practical limitation of the hardware (transceivers), it can only link up to110 nodes (with 82C250, Philips) on a single network. It offers high-speed communication rate up to 1 Mbits/sec thus allows real-time control. In addition, the error confinement and the error detection feature make it more reliable in noise critical environment.

 

 

Some of the Sensors that feeds data to ECU

 

  • Vehicle Speed Sensor (VSS)
    The vehicle speed sensor is installed in the transaxle. It contains a pulse generator that provides a vehicle speed signal to the speedometer. The speedometer then sends a signal to the ECM.
  • Mass Air Flow Sensor (MAF)
    The mass airflow sensor tells the computer how much air is coming into the engine. The more air that enters, the more fuel is needed to get an ideal air/fuel ratio.
  • Intake Air Temperature Sensor (IAT)
    The intake air temperature sensor tells the computer the temperature of the incoming air. Since cold air is denser than warm air, it needs more fuel to achieve the ideal air/fuel ratio. To do this, the computer will open the injectors for a longer period of time.

·        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.

  • Coolant Temperature Sensor (CTS)
    The engine coolant temperature sensor tells the computer what the operating temperature of the engine is.
  • Knock Sensor
    The knock sensor is attached to the cylinder block. It senses engine knocking using a piezoelectric element.

 

  • Throttle Position Sensor (TPS)
    The throttle position sensor tells the computer where the gas pedal is. The computer determines the load being applied to the engine and adjusts injector and ignition timing as required.

 

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 CAN. 

 

Let’s see how automatic transmission system is designed and how microcontrollers and sensors play roll.

 

  • Downshift automatically when going downhill to control speed and reduce wear on the brakes
  • Upshift when braking on a slippery surface to reduce the braking torque applied by the engine
  • Inhibit the upshift when going into a turn on a winding road

 

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

 

http://e-www.motorola.com/webapp/sps/site/prod_summary.jsp?code=MPC533&nodeId=03t3ZGpnLnPCbf8648&tid=tmfp