Automatic Transaxle System

AUTOMATIC TRANSAXLE SYSTEM

DESCRIPTION
The automatic transmission is a combination of 3-element 2-phase 1 -stage torque converter and double shaft electronically-controlled unit which provides 4 speeds forward and 1 reverse. To improve the efficiency of power transmission, the line pressure control was changed applying Variable Force Solenoid (VFS) valve on this model. However, adopting VFS on this model, the line pressure is variably changed according to TPS and the vehicle speed, this will enable more improved efficiency of power transmission and fuel consumption.

CHARACTERISTICS
Some of the characteristics include:
^ Different power transfer
^ Different component layout
^ New shift logic (HIVEC) to improve shift feeling
^ Position of Valve Body > Variable shift pattern
^ Communication protocol and method
^ Step gate type shift lever.











MECHANICAL SYSTEM

OPERATION COMPONENTS AND FUNCTION

OPERATION COMPONENTS AND FUNCTION:

OPERATING ELEMENTS

OPERATING ELEMENTS:

TORQUE CONVERTER AND SHAFT
The torque converter consists of a impeller (pump), turbine and stator assembly in a single unit. The pump is connected to the engine crankshaft and turns as the engine turns. This drawing force is transmitted to the turbine through the oil which is recycled by the stator. The transmission has two parallel shafts ; the input shaft and the output shaft. Both shafts are in line with the engine crankshaft. The input shaft includes the overdrive clutch, reverse clutch, underdrive clutch, one way clutch, 2ND brake, low & reverse brake, overdrive planetary carrier, output planetary carrier and transfer drive gear. The output shaft includes the transfer driven gear.

CLUTCHES
The gear changing mechanism utilizes three mufti-disc clutches. The retainers of these clutches are fabricated from high-precision sheet metal for lightness and ease of production. Also, more responsive gearshifts at high engine speeds are achieved by a pressure-balanced piston mechanism that cancels out centrifugal hydraulic pressure. This mechanism replaces the conventional ball check valve.

UNDERDRIVE CLUTCH
The underdrive clutch operates in 1st, 2nd, and 3rd gears and transmits driving force from the input shaft to the underdrive sun gear (A).

The components comprising the under clutch are as illustrated.

Hydraulic pressure acts in the piston pressure chamber (B) (between the piston (c) and retainer) and thus pushes the piston (C). In turn, the piston depresses the clutch discs and thereby transmits driving force from the retainer (D) to the hub (E) side.





At high speed, fluid remaining in the piston pressure chamber is subjected to centrifugal force and attempts to push the piston.
However, fluid in the balance fluid chamber (A) (the space between the piston and return spring retainer (B) ) is also subjected to centrifugal tome. Thus, the hydraulic pressure on one side of the piston cancels out the hydraulic pressure on the other side, and the piston does not move.





REVERSE CLUTCH AND OVERDRIVE CLUTCH
The reverse clutch� operates when the reverse gear is selected and transmits driving force from the input shaft to the reverse sun gear. The overdrive clutch (D) operates in 3rd and 4th gears and transmits driving force from the input shaft to the overdrive planetary carrier and low-reverse annulus gear.





BRAKES
The gear changing mechanism utilizes two multi-disc brakes.

LOW & REVERSE BRAKE AND SECOND BRAKE
The low & reverse brake (A) operates in 1st and reverse gears, when the vehicle is parked, and during manual operation. It locks the low & reverse annulus gear and overdrive planetary carrier to the case. The second (C) brake (B) operates in 2nd and 4th gears and locks the reverse sun gear (D) to the case. The components comprising the low & reverse brake and second brake are as illustrated. As shown, the discs and plates of the two brakes are arranged on either side of the rear cushion plate (E), which is itself secured to the case (F) by a snap ring.





OWC
To improve the shift feeling from 1st to 2nd gear, OWC was adopted on the low & reverse brake annulus gear. Instead of hydraulic fixing by Low & reverse brake at the 1st gear, this mechanical fixing device was used. This structure is not a new concept, because this OWC already has been installed on the previous models.

ACCUMULATORS

ACCUMULATORS:

OBJECTIVE
^ Energy (hydraulic pressure) storage
^ Impact and pulsation damping when solenoid valves operating
^ Operation as spring element
^ Smooth shifting by preventing sudden operation of clutches and brakes

TRANSFER DRIVE GEAR
With the transfer drive gear, increased tooth height and a higher contact ratio have reduced gear noise. Also, the bearing that supports the drive gear is a preloaded type that eliminates rattle, and the rigidity of the gear mounting has been increased by bolting the bearing directly onto the case.





OUTPUT SHAFT/TRANSFER DRIVEN GEAR
As shown in the illustration, the transfer driven gear is press-fitted onto the output shaft, and the output shaft is secured by a locking nut and supported by bearings. The locking nut has a left-handed thread, and a hexagonal hole in the other end of the shaft enables the shaft to be held in position for locking nut removal.





MANUAL CONTROL SYSTEM

MANUAL CONTROL LEVER
The manual control lever is fitted to the top of the valve body and is linked to the parking roller rod and manual control valve pin. A detent mechanism is provided to improve the gear shift feeling during manual selection.

PARKING MECHANISM
When the manual control lever is moved to the parking position, the parking roller rod moves along the parking roller support and pushes up the parking sprag. As a result, the parking sprag meshes with the transfer driven gear (parking gear), thereby locking the output shaft. To minimize the operating force required, a roller is fitted to the end of the rod.





POWER TRAIN

P POSITION
Hydraulic pressure is applied to the LR brake and the RED brake, so power is not transmitted from the input shaft to the UD clutch or OD clutch, and the output shaft is locked by the park brake pawl interlocking the park gear.

N POSITION
Hydraulic pressure is applied to the LR brake (A) and the RED brake, so power is not transmitted from the input shaft to the UD clutch or OD clutch.





1ST GEAR POWER FLOW
Hydraulic pressure is applied to the UD clutch (B) the LR brake (A) and the one way clutch (OWC), then the UD clutch transmits driving force from the input shaft to the UD sun gear, and the LR brake locks the LR annulus gear to the case. The LID sun gear of the planetary gear drives the output pinion gear, and the LR brake locks the annulus gear, and the output pinion drives the output carriers, and the output carrier drives the transfer drive gear, and the transfer drive gear drives the transfer driven gear of the output shaft, and power is transmitted to the differential gear through the differential drive gear.





2ND GEAR POWER FLOW
Hydraulic pressure is applied to the UD clutch (A) the 2nd brake (B) and the one way clutch (OWC), then the UD clutch transmits driving force from the input shaft to the UD sun gear, and the 2nd brake locks the reverse sun gear to the case. The UD sun gear of the planetary gear drives the output pinion gear and the LR annulus gear, and the LR annulus gear drives the OD planetary carriers, and OD planetary carriers drives OD pinion gear, and the OD pinion gear drives the output carriers, and the output carrier drives the transfer drive gear, and the transfer drive gear drives the transfer driven gear of the output shaft, and power is transmitted to the differential gear through the differential drive gear.





3RD GEAR POWER FLOW
Hydraulic pressure is applied to the UD clutch (A) and the OD clutch (B), then the UD clutch transmits driving force from the input shaft to the UD sun gear, and the OD clutch transmits driving force from the input shaft to the overdrive planetary carrier and low & reverse annulus gear. The UD sun gear of the planetary gear drives the output pinion gear and the LR annulus gear, and the LR annulus gear drives the OD pinion gear through the OD planetary carrier, and the OD pinion gear drives the reverse sun gear and the output carrier. The OD clutch drives the OD carrier, and the OD carrier drives the OD pinion gear, a:, ' and the OD pinion gear drives the reverse sun gear and the output carrier, and the output carrier drives the transfer drive gear, and the transfer drive gear drives the transfer driver, gear of the output shaft, and power is transmitted to the differential gear through the differential drive gear.





4TH GEAR POWER FLOW
Hydraulic pressure is applied to the OD clutch (A) and the 2nd brake (B), then the OD clutch transmits driving force from the input shaft to the OD planetary carrier and LR annulus gear, and the 2nd brake locks the reverse sun gear to the case. The OD clutch drives the OD carrier, and the OD carrier drives the OD pinion gear and the LR annulus gear, and the CID pinion gear drives the output carrier, and the output carrier drives the transfer drive gear, and the transfer drive gear drives the transfer driven gear of the output shaft, and power is transmitted to the differential gear through the differential drive gear.





REVERSE GEAR POWER FLOW
Hydraulic pressure is applied to the reverse clutch (A) and the LR brake (B), then the reverse clutch transmits driving force from +he input shaft to the reverse sun gear, and the LR brake locks the LR annulus gear and OD planetary carrier to the case. The reverse clutch drives the reverse sun gear, and the reverse sun gear drives the output carrier through the OD pinion gear, and the output carrier drives the transfer drive gear, and the transfer drive. gear drives the transfer driven gear of the output shaft, and power is transmitted to the differential gear through the differential drive gear.





HYDRAULIC CONTROL SYSTEM

DESCRIPTION

DESCRIPTION:

Better and smoother shift quality. In order to prevent ATF leakage from the valve body or each elements, the exhaust ports have been grouped into only one with an addition of a check ball. If a failure occurs in its electric control, the switch valve and fail safe valve is able to move to enable 3rd speed drive or reverse. The hydraulic system consists of oil pump, regulator valve, solenoid valves, pressure control valve and valve body
In order to control the optimal line pressure and improve the efficiency of power transmission according to maximize the efficiency of the oil pump, VFS (Variable Force Solenoid) valve has been added in the valve body hydraulic circuit.





VFS (VARIABLE FORCE SOLENOID)

VRS Function
The spool rod in VFS is not duty cycled like one of PWM, it minutely vibrates at the range between the control port and exhaust port to control the hydraulic pressure. That is, it uses the equilibrium effect between the spring force and the magnetic force, the spring force is mechanical characteristics decided at the stage of design and the magnetic force is controlled by TCM. This electrical magnetic force is proportional to the current. So TCM will control the current. In case of VFS valve, the electrical time constant is considered to decide the frequency for the current not to be fluctuated even though turns on or off the input signal. The electrical 'time constant' is much more fast than one of mechanical so the frequency of VFS is extremely higher than the conventional PWM type.





Characteristics of Bosch VFS:
Supply pressure: 700 - 1600 kPa
Control pressure: typically 600 - 0 kPa
Current range: typically 0 - 1,000 mA
Dither frequency: Up to 600 Hz
Dimension: 32 mm protrusion reach 42 mm





The reducing pressure will be supplied to the 'Supply' port of the VFS valve on the above illustration to control the line pressure.

REDUCING PRESSURE
FUNCTION





As same as one of Alpha or Beta automatic transaxle system, this reducing valve length can be adjusted by rotating the screw on the picture. As you rotate the screw toward clockwise by 90°, the reducing pressure will increase about 1.0 bar. However, the reducing pressure is used just as a 'supply pressure' for the solenoid valves (except Low & Reverse, Reduction and Damper Clutch control solenoids), so this may not be handled to rotate in the field service shop. VFS is operated based on the 'supply pressure' and it outputs the 'control pressure' to control the regulator valve indirectly. While developing the VFS system, the line pressure was used as a 'supply pressure' for VFS and other solenoid valves but it has been changed into additional 'reducing pressure' because the line pressure is variably changed by VFS so the control pressure becomes unstable and some hydraulic pressure oscillation occurred. That is why the reducing pressure has been added in the hydraulic circuit of VFS system for both 4th and 5th speed A/T.








The reducing pressure is about 6.5 bar and this value does not be changed regardless of the driving or engine load condition. Be sure that the conventional line pressure is used for the 'supply pressure' of Low & Reverse, Reduction solenoid because the variable line pressure is not available at reverse range.