Transmissions: Automatic Transmissions

Torque converters	Torque converter principles	A single stage torque converter has three elements: the impeller, the turbine and the stator.
	Converter operation	The stator redirects the fluid coming from the turbine so that it re-enters the impeller travelling in the same direction as impeller rotation. This provides torque multiplication.
	Torque multiplication	Torque multiplication is proportional to the difference in speed between the impeller and the turbine.
	Fluid flow	Rotary flow, vortex flow and spiral flow are terms which describe fluid flow paths in the torque converter. These paths are dependent on operating conditions.
	Heat exchanger	Converter operation produces heat which is usually dissipated by passing the transmission fluid through a heat exchanger in the cooling system.
	Lock-up converters	In a lock-up converter, the impeller and turbine are locked together when operating conditions are suitable to provide a one to one drive from the engine to the transmission input shaft.
	Sprag one way clutches	The stator one way clutch prevents the stator from turning in the opposite direction to engine rotation during torque multiplication. It allows the stator to rotate with the impeller and turbine when coupling point is reached.

Planetary gearing	Planetary gears	A simple planetary gearset has a sun gear, planet pinions mounted on a planet carrier, and a ring gear.
	Simple planetary gearsets	A simple planetary gearset can illustrate how to control individual members to produce a particular drive output, or neutral.
	Compound planetary gearsets	The Ravigneaux and Simpson gearsets are examples of compound planetary gearsets which are used in automatic transmissions.
	Automatic transmission brake bands	Brake bands in automatic transmissions are externally contracting types which are operated by hydraulic servos.
	Multi-disc clutches	In most transmissions, planetary gear members and shafts are coupled together by multiple-disc clutches. They can also hold members to the case instead of using bands.
	Plate clearance	In the released position, the plates must retain a set clearance. This allows them to separate from one another and avoid excessive or premature wear.

Electronic control transmission	Electronic control	In an electronically controlled transmission, the speed of the vehicle and the throttle opening are sensed by the vehicle speed sensor, and the throttle position sensor.
	Fully hydraulically controlled transmission	In an electronically controlled transmission, the ECU can store different driving patterns which can be selected by the driver to suit the existing driving conditions.
	Electronic shift programs	In adaptive transmissions, driving style can be identified by characteristic accelerator pedal movement patterns.
	Environment identification	Identification of environment means identifying unusual ambient conditions in which the vehicle is operating.
	Driving situation identification	Driving situation identification allows special gear selection for unusual driving situations.
	Fast-off identification	The driver's intention to brake can often be detected by the rapid and complete release of the accelerator pedal, and an unnecessary upshift in gear ratio can be prevented.
	Corner identification	The radius of a curve can be identified by comparing the differences in the rotating speed of the inner and outer front wheels when the vehicle is not travelling in a straight line.
	Downhill gradient	Identifying a downhill gradient prevents any further upshifts occurring. In addition a single downshift is made when the brakes are applied.
	Stop & go	In dense traffic, only a small proportion of the vehicle's performance is needed to keep it moving and first gear may not be engaged.
	Manual selection	A chosen gear ratio can be selected manually by using the selector lever in manual mode.

Layout & operation	Borg Warner 35 gearbox	The Borg Warner 35 is a fully hydraulically controlled transmission which has three forward ratios and reverse.
	Selector positions	Automatic control of gear changes may be over-ridden by use of the 2 and 1 selector positions.
	Planetary gearset	The planetary gearset is a Ravigneaux type with primary and secondary sun gears, primary and secondary planet pinions and a ring gear.
	High range powerflow	In D range, the components and control elements in each gear determine the power flow through the gearset. In selector lever position 1, the front clutch and the rear band are applied. The rear clutch and the rear band are applied in order to obtain reverse gear.
	Low range powerflow	The rear clutch and the rear band are applied in order to obtain reverse gear.

Servos & clutches	Rear servo	The rear servo in a Borg Warner 35 transmission is a pressure apply/spring release type.
	Front servo	The front servo in a Borg warner 35 transmission is a pressure apply/pressure release type with unequal piston areas.
	One way clutch	In the Borg Warner 35 transmission a one way clutch is located between the center support and the planet carrier.
	Multi-plate front clutch	In the Borg Warner 35 transmission the front clutch is a multi-plate type which is engaged in all forward gears.
	Clutch pack	There are two sets of plates in a clutch pack; driving plates and driven plates.
	Rear clutch	The rear clutch is engaged in third gear together with the front clutch, and in reverse gear together with the rear band.

Hydraulic system & controls	Hydraulic system components	The hydraulic system comprises a crescent type gear pump, a centrifugally operated hydraulic governor and a control valve body assembly.
	Spool valves	The valve body contains spool valves which can be positioned manually or by hydraulic pressure or by springs.
	Regulating or flow control valves	Spool valves can be regulating valves or flow control valves. Regulating valves regulate fluid pressure in the system.
	Control valves	Control valves are simple 'gate' type valves which either open or close off a circuit with no alteration in pressure.
	Orifices	Orifices can be used in hydraulic circuits to restrict fluid flow for timing purposes or to prevent valve fluctuations.

Valve types & functions	Basic valve action	The basic action of the valves in the hydraulic system can be summarized in a simple line diagram.
	Regulator & control valves	The transmission has a number of regulating and control valves which can be readily identified in a hydraulic circuit diagram.
	Shift & governor valves	The shift valves are control valves supplied with line pressure which is varied by the governor valve depending on road speed. Low speed equals low pressure, high speed equals high pressure.

Pressure regulation	The primary regulating valve	The primary regulating valve regulates the value of line pressure in the transmission.
	Line pressure variation	Throttle valve pressure is derived from line pressure and is applied to the spring end of the primary regulating valve to increase line pressure relative to accelerator depression.
	Modulator valve pressure	Modulator valve pressure is directed to the lower end of the primary regulating valve, opposite to the regulating spring.
	The governor	The governor is in two sections comprising the governor valve and its spring, and a bob-weight retained by a 'C' clip.
	Governor pressure	Upward movement of the 1-2 shift valve allows fluid at line pressure to flow to the apply side of the front band servo.
	Kickdown pressure	Kickdown pressure is supplied to the spring end of the 1-2 shift valve to force a 2-1 downshift under 'kickdown' conditions.

Flow control	Gear position 1	When gear lever position 1 is selected, the manual valve directs fluid at line pressure to the front clutch and to the rear band servo.
	1-2 shift valve	The 1-2 shift valve has a lower valve section and an upper section plug and spring.
	2-3 shift valve assembly	The 2-3 shift valve assembly consists of the shift valve, its spring and a throttle pressure regulating plug.
	The servo orifice control valve	The servo orifice control valve is a shuttle valve which can be positioned at rest by a spring or can be moved by governor pressure.
	3-2 kickdown	Governor pressure determines whether or not a 3-2 kickdown downshift can be made.

Continuously variable transmission (C.V.T.)	Continuously variable transmission	An electronically controlled magnetic clutch transmits the drive from the engine to the transmission.
	Drive or reverse	A belt and pulley system continuously varies the ratios and transmits the drive to the final drive gears.
	The steel belt	The steel belt has a large number of hardened steel vee blocks which are held together by two endless steel bands.
	Secondary pulley shaft	Placing the selector lever in 'D' provides a normal driving mode, from starting off to maximum speed. Selecting 'D' provides engine braking on overrun.

Automatic transmissions procedures	Checking automatic transmission fluid	A correct fluid level is critical to effective and efficient operation. If the level is too high, it will cause the fluid to churn and aerate, causing air bubbles that can trap heat and make the fluid run hotter. This can lead to early failure of bearings or gears. The objective of this procedure is to show you how to check and adjust transmission and transaxle fluid for automatic transmissions.
	Changing transmission fluid & filter	The objective of this procedure is to show you how to change automatic transmission/transaxle fluid. You will need to refer to the owner's manual for the specified intervals for lubricant servicing. Selecting and using the correct type and grade of lubricant is critical. The wrong selection can lead to premature failure of the internal components.

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