发布时间 : 星期六 文章01M自动变速器电液控制系统原理设计 - 图文更新完毕开始阅读
天津工程师范学院2009届本科生毕业设计
temperature，a portion of the fluid is sent through one of two steel tubes to a special chamber that is submerged in anti-freeze in the radiator．Fluid passing through this chamber is cooled and then returned to the transmission through the other steel tube．A typical transmission has an average of ten quarts of fluid between the transmission，torque converter，and cooler tank．In fact，most of the components of a transmission are constantly submerged in fluid including the clutch packs and bands．The friction surfaces on these parts are designed to operate properly only when they are submerged in oil． 2．7 Oil Pump
The transmission oil pump (not to be confused with the element inside the torque converter)is responsible for producing all the oil pressure that is required in the transmission．The oil pump is mounted to the front of the transmission case and is directly connected to a flange on the torque converter housing．Since the torque converter housing is directly connected to the engine crankshaft，the pump will produce pressure whenever the engine is running as long as there is a sufficient amount of transmission fluid available．The oil enters the pump through a filter that is located at the bottom of the transmission oil pan and travels up a pickup tube directly to the oil pump．The oil is then sent，under pressure to the pressure regulator，the valve body and the rest of the components，as required． 2．8 Valve Body
The valve body is the brain of the automatic transmission．It contains a maze of channels and passages that direct hydraulic fluid to the numerous valves which then activate the appropriate clutch pack or band servo to smoothly shift to the appropriate gear for each driving situation．Each of the many valves in the valve body has a specific purpose and is named for that function．For example the 2-3 shift valve activates the 2nd gear to 3rd gear up-shift or the 3-2 shift timing valve which determines when a downshift should occur．The most important valve，and one that you have direct control over is the manual valve．The manual valve is directly connected to the gear shift handle and covers (or uncovers) various passages depending on what position the gear shift is placed in．When you place the gear shift in Drive，for instance，the manual valve directs fluid to the clutch pack(s) that activates 1st gear．It also sets up to monitor vehicle speed and throttle position so that it can determine the optimal time and the force for the 1-2 shift．On computer controlled transmissions，you will also have electrical solenoids that are mounted
- 43 -
天津工程师范学院2009届本科生毕业设计
in the valve body to direct fluid to the appropriate clutch packs or bands under computer control to more precisely control shift points． 2．9 Computer Controls
The computer uses sensors on the engine and transmission to detect such things as throttle position，vehicle speed，engine speed，engine load，stop light switch position etc， to control exact shift points as well as how soft or firm the shift should be．Some computerized transmissions even learn your driving style and constantly adapt to it so that every shift is timed precisely when you would need it．
Because of computer controls，sports models are coming out with the ability to take manual control of the transmission as though it were a stick shift，allowing the driver to select gears manually．This is accomplished on some cars by passing the shift lever through a special gate，then tapping it in one direction or the other in order to up-shift or down-shift at will．The computer monitors this activity to make sure that the driver does not select a gear that could over speed the engine and damage it．
Another advantage of these “smart” transmissions is that they have a self diagnostic mode which can detect a problem early and warn you with an indicator light on the dash．A technician can then plug test equipment in and retrieve a list of trouble codes that will help pinpoint where the problem is．
2．10 Governor，Vacuum Modulator and Throttle Cable
These three components are important in the non-computerized transmissions．They provide the inputs that tell the transmission when to shift．The Governor is connected to the output shaft and regulates hydraulic pressure based on vehicle speed．It accomplishes this using centrifugal force to spin a pair of hinged weights against pull-back springs．As the weights pull further out against the springs，more oil pressure is allowed past the governor to act on the shift valves that are in the valve body which then signal the appropriate shifts．
Of course，vehicle speed is not the only thing that controls when a transmission should shift，the load that the engine is under is also important．The more load you place on the engine，the longer the transmission will hold a gear before shifting to the next One．
There are two types of devices that serve the purpose of monitoring the engine load：the Throttle Cable and the Vacuum Modulator．A transmission will use one or the other but generally not both of these devices．Each works in a different way to monitor engine load．
- 44 -