Manual Transmission/Transaxle: Description and Operation
1 thru 5 - Pairs of Gear Wheels
R - Reverse Gear Wheel Set
A - Hollow Shaft
B - Pinion Shaft
C - Transfer Box
D - Transfer Box Multiple Plate Set
E - Rear Axle Differential
F - Pinion Differential
G - Transverse Lock Multiple Plate Set
H - Transverse Lock Operation
G64 Manual Transmission with Integrated Transfer Box and Rear Axle Differential
The fully synchronized, five speed manual transmission employs proven components from the G50 transmission series as well as additional components, which make up the transfer box and therefore permit permanent four wheel drive.
The design of the five speed transmission with synchronized reverse gear is precisely the same as that of the G50/00 transmission. The entire shift mechanism, excluding the interior shift rod, as well as the synchronization of all gears are also identical.
Output is a special feature of the G64 manual transmission. Gear wheels are not driven off of pinion shaft (B), but instead hollow shaft (A), which is connected with transfer box (C). The transfer box has the task of driving the front axle differential and rear axle differential (E). Rear axle differential (E) is integrated in the transmission case and designed as a ball type differential. A multiple-plate limited slip differential, which makes up a slip-controlled transverse lock together with the pinion differential for production of a stabilizing effect while driving in curves or cornering, is installed in addition to the differential side gears in differential case (F).
Normally torque will be distributed from the left rear wheel to the right rear wheel at a ratio of 1 to 1 via the differential side gears.
However, if slip of one of the rear wheels is recognized by the ABS sensors, the multiple-plate lock is capable of building up a locking torque of more than 1,000 Nm in fractions of a second with help of external hydraulics.
Lock control for the transfer box (distribution of drive torque to the front axle and rear axle) as well as the transverse lock for the guarantee of rear wheel drive to both wheels is known as the PORSCHE DYNAMIC FOUR WHEEL DRIVE CONTROL.
Power Flow in First Gear
Drive from the engine is accomplished via a single-plate dry clutch to input shaft (1). The fixed wheel for 1st gear (2) makes up an assembly together with the input shaft.
If the operating sleeve for 1st and 2nd gears (3) is meshed with the loose wheel for 1st gear (4), the hollow shaft (5) is driven at a speed equal to the engine speed divided by the 1st gear ratio.
Example:
Engine speed -- 4000 rpm
1st gear ratio -- 3.500
Hollow shaft speed -- 4000 : 3.500 = 1143 rpm
Transfer box (6) is driven off of the hollow shaft at this speed.
Power Flow in Transfer Box
Hollow shaft (9) as an input shaft of the manual transmission is connected with bearing carrier (7) in a non-rotating manner. The bearing carrier in turn is connected with clutch sleeve (4). The clutch sleeve has internal splines, which guide the outer plates of interaxle clutch (2) as well as planet gear carrier (3) of the transfer box.
The front axle differential is connected via the central shaft and output shaft (1) with sun gear (10) of the transfer box.
Drive of the rear axle differential is accomplished via ring gear (5) to the drive carrier (6) and pinion shaft (8). If hollow shaft (9) of the transmission is now driven and therefore also planet gear carrier (3), the drive torque is distributed via planet gears (P) to ring gear (5) and sun gear (10).
Torque distribution is according to the pitch circle radii of the sun gear and ring gear, namely:
31% to the front axle (sun gear radius)
69 % to the rear axle (ring gear radius)
This ratio can be changed infinitely from 0 to 100% or 100 to 0% in fractions of a second by operating the interaxle clutch in case of front or rear axle wheel slip.