Automatic Transmission/Transaxle: Description and Operation
Description
The Automatic Transmission is a combination of a 3-element torque converter and dual-shaft automatic transmission which provides 4 speeds forward and 1 speed reverse. The entire unit is positioned in line with the engine.
TORQUE CONVERTER, GEARS, AND CLUTCHES
The torque converter consists of a pump, turbine and stator, assembled in a single unit.
They are connected to the engine crankshaft so they turn together as a unit as the engine turns. Around the outside of the torque converter is a ring gear which meshes with the starter pinion when the engine is being started. The entire torque converter assembly serves as a flywheel while transmitting power to the transmission mainshaft.
The transmission has two parallel shafts, the mainshaft and countershaft. The mainshaft is in line with the engine crankshaft.
The mainshaft includes the clutches for 1st, and 2nd/4th, and gears for 3rd, 2nd, 4th, Reverse and 1st (3rd gear is integral with the mainshaft, while reverse gear is integral with 4th gear).
The countershaft includes 3rd clutch and gears for 3rd, and 4th, Reverse and 1st.
4th and reverse gears can be locked to the countershaft at its center, providing 4th gear or Reverse, depending on which way the selector is moved.
The gears on the mainshaft are in constant mesh with those on the countershaft. When certain combinations of gears in the transmission are engaged by the clutches, power is transmitted from the mainshaft to the countershaft to provide D3, D4, 2,and R
HYDRAULIC CONTROL
The valve assembly includes the main valve body, secondary valve body, servo valve body, modulator valve body, regulator valve body and lock-up shift valve body, through the respective separator plates.
They are bolted to the torque converter case as an assembly.
The main valve body contains the manual valve, 1-2 shift valve, 2-3 shift valve, 3-4 shift valve, pressure relief valve, 2nd orifice control valve, and oil pump gears.
The secondary valve body includes the CPC valve, REV control valve, lock-up cut valve, kickdown valve, accumulator control valve and shift timing valve.
The servo valve body contains the accumulator pistons, 3rd orifice control valve, throttle A and B valves, and the modulator valve. The regulator valve body contains the lock-up timing valve A, pressure regulator valve and lock-up control valve. Fluid from the regulator passes through the manual valve to the various control valves.
The lock-up shift valve body contains the lock-up timing valve B and lock-up shift valve. The 1st, 3rd and 4th clutches receive oil from their respective feed pipes.
LOCK-UP MECHANISM
In D4 pressurized fluid is drained from the back of the torque converter through an oil passage, causing the lock-up piston to be held against the torque converter cover. As this takes place, the mainshaft rotates at the same speed as the engine crankshaft.
The lock-up shift valve body controls the range of lock-up according to vehicle speed and throttle pressure. The lock-up timing valve controls the flow of oil to the lock-up shift valve in 2nd, 3rd and 4th gears (in D4 range).
The lock-up cut valve is housed in the secondary valve body and prevents lock-up from taking place when the throttle is not opened sufficiently.
GEAR SELECTION
The selector lever has six positions: [P] PARK, [R] REVERSE, [N] NEUTRAL, [D4] 1st through 4th gear ranges, [D3] 1st through 3rd gear ranges, and [2] 2nd gear
Starting is possible only in [P] and [N] through use of a slide-type, neutral-safety switch.
POSITION INDICATOR
A position indicator in the instrument panel shows what gear has been selected without having to look down at the console.
Clutches
[1st Clutch]
The 1St clutch is on the right end of the mainshaft. In the [D3] or [D4] range, constant hydraulic pressure is applied to the mainshaft through the 1st clutch to the mainshaft 1st gear.
The clutch plate is mounted on the clutch drum, while the clutch disc is fitted to the mainshaft 1st gear.
The 1st gears are attached to the mainshaft and countershaft through needle bearings, one for each gear.
When select lever is placed in the [D3] or [D4] range, hydraulic pressure is applied from the right side cover through the mainshaft, and thus to the clutch drum; as the pressure rises, the clutch piston presses the clutch plate and clutch disc, thus causing the clutch to engage.
Power is transmitted from the mainshaft 1St gear, through the countershaft 1St gear, to the one-way clutch, parking gear, and finally to the countershaft. The one-way clutch locks in the forward direction when in 1st gear. In the D3 or D4 range, all others beside 1st gear are not engaged, thus transmitting no power.
[2nd Clutch]
The 2nd clutch is left of center on the mainshaft, and is the same construction as the 1st clutch; The 2nd clutch is joined back-to-back to the 4th clutch. The mainshaft 2nd gear uses a needle bearing. The countershaft 2nd gear is splined on the countershaft.
In 2nd gear of [2], [D3] or [D4], hydraulic pressure is applied to the clutch drum from the mainshaft, thus transmitting power from the mainshaft 2nd gear to the countershaft 2nd gear.
[3rd Clutch]
The 3rd clutch is on the left end of the countershaft.
The clutch hub is joined to the countershaft 3rd gear, on the countershaft, supported by a single needle bearing. In 3rd gear of [D3] or [4], hydraulic pressure is applied to the 3rd clutch on the countershaft, thus causing the clutch to engage, and transmitting power.
[4th Clutch]
The 4th clutch is identical to the 2nd clutch, to which it is joined on the mainshaft. The clutch hub is joined to the mainshaft 4th gear and reverse gear, supported by two needle bearings.
In 4th gear of [D4], hydraulic pressure is generated within the mainshaft, applying pressure to the 4th clutch on the mainshaft.
[One-way Clutch)
A one-way sprag clutch disengages 1st gear when in the 2nd, 3rd and 4th gear ranges. The clutch is splined to the countershaft between 1st gear and the parking gear, with sprag elements and the retainer which Supports the central section of the sprags. When countershaft 1st gear rotates counterclockwise and parking gear clockwise, the sprags incline to the left, the gears together.
When shifting from 1st to 2nd in the [D3] or [D4] range, the higher ratio of 2nd gear causes the countershaft to rotate clockwise at a speed greater than that of 1st gear. The parking gear then rotates counterclockwise, and the sprags move away from their locking position. In D3 or D4 the higher ratio of 3rd gear prevents the sprags from locking, keeps 1st gear disengaged.
[Lock-up Clutch]
Operation (clutch on)
With the lockup clutch on, the oil in the chamber between the converter cover and lockup piston is discharged, and the converter oil exerts pressure through the piston against the converter cover. As a result, the converter turbine is locked on the converter cover firmly. The effect is to bypass the converter, thereby placing the car in direct drive.
Operation (clutch off)
With the lock-up clutch off, the oil flows in the reverse of CLUTCH ON. As a result, the lock-up piston is moved away from the converter cover; that is, the torque converter lock-up is released.
Power Flow
Hydraulic Flow
In the hydraulic control unit, the regulator valve, manual valve and oil pump connected to the torque converter are unified and contained inside the valve body. The valve bodies include the main valve body, the regulator valve body, the secondary valve body, the servo body, and the lock-up valve body.
The oil pump is driven by splines on the left end of the torque converter which is attached to the engine. Oil flows through the regulator valve, to maintain specified pressure through the main valve body to the manual valve, governor valve, and servo body, directing pressure to each of the clutches.
In the hydraulic control unit, the regulator valve, manual valve and oil pump connected to the torque converter are unified and contained inside the valve body. The valve bodies include the main valve body, the regulator valve body, the secondary valve body, the servo body, and the lock-up valve body.
The oil pump is driven by splines on the left end of the torque converter which is attached to the engine. Oil flows through the regulator valve, to maintain specified pressure through the main valve body to the manual valve, governor valve, and servo body, directing pressure to each of the clutches.
Hydraulic Control
[Regulator Valve]
The regulator valve maintains a constant hydraulic pressure sent from the oil pump to the hydraulic control system, while also furnishing oil to the lubricating system and torque converter.
Oil flows through B and B'. The oil which enters through B flows through the valve orifice to A pushing the regulator valve to the right. According to the level of hydraulic pressure through B, the position of the valve changes, and the amount of the oil through B' from D thus changes. This operation is continued, thus maintaining the line pressure.
(Stator Reaction Hydraulic Pressure Control)
Hydraulic pressure increase according to torque is performed by the regulator valve using stator torque reaction. The stator shaft is splined in the stator and its arm end contacts the regulator spring cap. When the car is accelerating or climbing Torque Converter Range), stator torque reaction acts on the stator shaft and the stator arm pushes the regulator spring cap in proportion to the reaction from the torque converter. The spring compresses and the valve moves to increase the regulated control pressure or line pressure. Line pressure is maximum when the stator reaction is maximum.
Throttle Valve A]
Throttle Valve A converts changes in the throttle opening to changes in transmission hydraulic pressure, to determine transmission shift timing. The end of the valve contacts the throttle cam which is connected by a cable to the throttle body. The cable pulls the cam, which, in turn moves the valve. The valve-to-cam engagement is adjustable to allow setting of specified shift speeds.
[Throttle Valve B Modulator Valve]
Throttle valve B is similar to valve A, except that it controls the accumulator pressures, to make smooth changes from one gear to another. An assist function is used to lessen the throttle load~ The modulator valve maintains line pressure from the regulator, after which the pressure to throttle valve A, thus maintaining accurate shift characteristics.
[Second Orifice Control Valve]
or smooth shifting between second to third, the open pressure on the second gear side is relieved through a fixed orifice. The valve also moves to equalize pressure differences between second and third gears.