What’s New in Transmission Technology?
Today's transmissions are governed electronically through engine control. For instance, if your car's performance system senses that a heavy load has been placed on the transmission for any reason (i.e., passing a car, additional payload, pulling a trailer, or driving up a hill) a signal is sent to the transmission to downshift into a lower gear. Transmission operation is governed through speed sensors and solenoids and controlled through electronic valve bodies, solenoid packs and lockup torque converters. These systems can blur the distinction between engine driveability problems and those caused by a malfunctioning transmission. There’s also more communication and interaction between the ABS/traction control system and powertrain control module (PCM), which further blurs the cause of a Check Engine or Malfunction Indicator Lamp being on.
How Transmission Components Interact
When a gear is selected, oil (or transmission fluid) is routed under pressure (created by its internal pump) through the valve body. The valve body (or brain of the transmission) is electronically and hydraulically controlled. Oil is then forced through the torque converter at high pressure, creating a fluid coupling between the engine and transmission. This fluid coupling is similar to what happens when the clutch is applied on a standard transmission. Just as the clutch connects the engine to the transmission, so does the torque converter through a fluid coupling. This fluid coupling is achieved by forcing the transmission fluid through a series of restrictive passages called fins (very similar in design to turbine engines on a jet).
Bringing It All Together to Create Motion
Now that there is a fluid linkup, how do we accelerate forward and shift gears? The gears are applied by a series of mechanisms called servos and bands; engine electronics and hydraulic pressure control the application of these. For example, when the gas is depressed, the ECM (engine control module) sees the need to shift, so an electronic signal is sent to the transmission to downshift into passing gear. Electrical switches called solenoids are then tripped, valves within the valve body divert the flow of oil to the bands or servos, which in turn apply or disengage gears. Just like magic—the transmission shifts. For all this to happen in perfect harmony, there must be smooth oil flow, strong calibrated oil pressure and properly functioning engine controls.
Common Transmission Problems
Take away any of these conditions and problems start to appear in the form of transmission malfunction. For instance, if the electronic engine controls malfunction, incorrect signals are sent to the transmission causing it to shift erratically. Or, if the flow of oil is inhibited due to a clogged filter or other malfunction, the transmission can "drop out" of gear into neutral due to low internal oil pressure. Dirt flowing through the system can cause valves in the valve body to stick, which will cause the transmission to get stuck in a particular gear and resist shifting. The loss of strong, calibrated oil flow due to a worn internal pump or a stuck pressure regulator valve can cause all of the above. And of course extreme high temperatures, such as are found in heavy towing conditions, can cause a wide variety of problems such as metal-to-metal fusing, stress breakage and sludging.
Tips to maximize transmission life: