5102 Gear train power flow for individual gear ratios

D drive range — first gear (Fig. 5.31) With the position selector lever in D drive range, the one way clutch (OWC) holds the front planet carrier while multiplate clutch (B) and the multiplate brake (G) are applied. Power flows from the engine to the torque converter pump wheel, via the fluid media to the output turbine wheel. It is then directed by way of the input shaft and the applied multiplate clutch (B) to the front planetary large sun gear (SL). With the front planet carrier (CF) held stationary by the locked one way clutch (OWC), power passes from the large sun gear (SL) to the long planet gears (PL) in an anticlockwise direction. The long planet gear (PL) therefore drives the short planet gears (PS) in a clockwise direction thus compelling the front annular ring gear (AF) to move in a clockwise direction. Power thus flows from the front annular ring gear (AF) though the rear intermediate shaft to the rear planetary gear annular ring gear (AR) in a clockwise direction. With the rear sun gear (SR) held stationary by the applied multiplate brake (G), the rear planet gears (PR) are forced to roll around the fixed sun gear in a clockwise direction, this in turn compels the rear planet carrier (CR) and the output shaft also to rotate in a clockwise direction at a much reduced speed. Thus a two stage speed reduction produces an overall underdrive

Clutch A B C D

Brakes E F G

Input from engine

Clutch A B C D

Brakes E F G

Input from engine

Fig. 5.30 Five speed and reverse automatic transmission (transaxie/iongitudinai) layout

Front planetary gear train

Input

Input from engine

Output gear

Rear planetary gear train

Fig. 5.31 Five speed and reverse automatic transmission power flow first gear

Input

Input from engine

Output gear

Rear planetary gear train

Fig. 5.31 Five speed and reverse automatic transmission power flow first gear first gear. If the '2' first gear is selected multiplate brake (F) is applied in addition to the multiplate clutch (B) and multiplate brake (G). As a result instead of the one way clutch (OWC) allowing the vehicle to freewheel on overrun, the multiplate brake (F) locks the front planetary carrier (CF) to the casing. Consequently a positive drive exists between the engine and transmission on both drive and overrun: it thus enables engine braking to be applied to the transmission when the transmission is overrunning the engine.

D drive range — second gear (Fig. 5.32) With the position selector lever in D drive range, multiplate clutch (C) and multiplate brakes (B) and (G) are applied.

Power flows from the engine via the torque converter to the input shaft, it then passes via the multiplate clutch (B) to the first planetary large sun gear (SL). With the multiplate brake (E) applied, the front planetary small sun gear (SS) is held stationary. Consequently the large sun gear (SL) drives the long plant gears (PL) anticlockwise and the short planet gears (PS) clockwise, and at the same time, the short planet gears (PS) are compelled to roll in a clockwise direction around the stationary small sun gear (SS).

The drive then passes from the front planetary annular ring gear (AF) to the rear planetary annular ring gear (AR) via the rear intermediate shaft. With the rear sun gear (SR) held stationary by the applied multiplate brake (G) the clockwise rotation of the rear annular ring gear (AR) compels the rear planet gears (PR) to roll around the held rear sun gear (SR) in a clockwise direction taking with it the rear carrier (CR) and the output shaft at a reduced speed. Thus the overall gear reduction takes place in both front and rear planetary gear trains.

D drive range — third gear (Fig. 5.33) With the position selector lever in D drive range, multiplate clutches (B) and (D), and multiplate brake (E) are applied.

Power flows from the engine via the torque converter to the input shaft, it then passes via the multiplate clutch (B) to the front planetary large sun gear (SL). With the multiplate brake (E) applied, the front planetary small sun gear (SS) is held stationary. This results in the large sun gear (SL) driving the long planet gears (PL) anticlockwise and the short planet gears (PS) clockwise, and simultaneously, the short planet gears (PS) are compelled to roll in a clockwise direction around the stationary small sun gear (SS). Consequently, the annular ring gear (AF) is also forced to rotate in a clockwise direction but at a reduced speed to that of the input large sun gear (SL). The drive is then transferred from the front planetary annular ring gear (AF) to the rear planetary annular ring gear (AR) via the rear intermediate shaft. With the multiplate clutch (D) applied the rear planetary sun gear (SR) and rear annular ring gear (AR) are locked together, thus preventing the rear planet gears from rotating independently on their axes. The drive therefore passes directly from the rear annular ring gear (AR) to the rear carrier (CR) and output shaft via the jammed rear planet gears. Thus it can be seen that the overall gear reduction is obtained in the front planetary gear train, whereas the rear planetary gear train only provides a one-to-one through drive.

D drive range — fourth gear (Fig. 5.34) With the positive selector lever in D drive range, multiplate clutches (B), (C) and (D) are applied. Power flows from the engine via the torque converter to the input shaft, it then passes via the multiplate clutch (B) to the front planetary large sun gear (SL) and via the multiplate clutch (C) to the front planetary planet-gear carrier (CF). Consequently both the large sun gear and the planet carrier rotate at the same speed thereby preventing any relative planetary gear motion, that is, the gears are jammed. Hence the output drive speed via the annular ring gear (AF) and the rear intermediate shaft is the same as that of the input shaft speed. Power is then transferred to the rear planetary gear train by way of the front annular ring gear (AF) and rear intermediate shaft to the rear planetary annular ring gear (AR) and rear intermediate shaft to the rear planetary annular ring gear (AR). However, with the multiplate clutch (D) applied, the rear annular ring gear (AR) becomes locked to the rear sun gear (SR); the drive therefore flows directly from the rear annular ring gear to the rear planet carrier (CR) and output shaft via the jammed planet gears. Thus there is no gear reduction in both front and rear planetary gear trains, hence the input and output rotary speeds are similar.

D drive range — fifth gear (Fig. 5.35) With the position selector lever in D drive range, multiplate clutches (C) and (D) and multiplate brake (E) are applied. Power flows from the engine via the torque converter to the input shaft, it then passes via the multiplate clutch (C) to the front planetary planet planetary planetary

gear train

Fig. 5.32 Second gear gear train

Fig. 5.32 Second gear

planetary

train

Fig. 5.34 Fourth gear train

Fig. 5.34 Fourth gear

Front planetary

Front planetary

Fig. 5.35 Fifth gear

OutPut J Rear planetary gear gear train

Input from engine

Fig. 5.35 Fifth gear

Output shaft

OutPut J Rear planetary gear gear train carrier (CF). With the multiplate brake (E) applied the front planetary short sun gear (SS) remains stationary. As a result the planet gear carrier (CF) and both long and short planet gear pins are driven around in a clockwise direction; it thus compels the short planet gears (PS) to roll clockwise around the fixed small sun gear (SS). It also causes the annulus ring gear (AF) to revolve around its axis; however, this will be at a speed greater than the input planet carrier (CF). Note that the long planet gears (PL) and large sun gear (SL) revolve but are both inactive. The drive then passes from the front planetary annular ring gear (AF) to the rear planetary annular ring gear (AR) via the rear intermediate shaft. With the multiplate clutch (D) applied both rear annular ring gear (AR and rear sun gear (SR) are locked together. Hence the rear planet gears sandwiched between both the sun and the annular gears also jam; the drive therefore is passed directly though the jammed rear planetary gear train cluster to the output shaft without a change in speed. An overall speed step-up is thus obtained, that is, an overdrive fifth gear is achieved, the step-up taking place only in the first stage planetary gear train, the second planetary gear train providing only a through one-to-one drive.

R reverse gear (Fig. 5.36) With the position selector in reverse R position, the multiplate brakes (F) and (G) and the multiplate clutch (A) are applied. Power flows from the engine to the torque converter to the input shaft, it then passes via the multiplate clutch (A) to the front planetary small sun gear (SS). With the multiplate clutch (F) applied, the front planet gear carrier (CF) is held stationary, and the drive passes from the clockwise rotating small sun gear (SS) to the short planet gears (PS) making the latter rotate anticlockwise. As a result the internal toothed front annular ring gear (AF) will also be compelled to rotate anticlockwise. The drive then passes from the front planetary annular ring gear (AF) to the rear planetary annular ring gear (AR) via the rear intermediate shaft. With the rear sun gear (SR) held stationary by the applied multiplate brake (G) the anticlockwise rotation of the rear annular ring gear (AR) compels the rear planet gear (PR) to roll around the held rear sun gear (SR) in an anticlockwise direction taking with it the rear carrier (CR) and the output shaft at a reduced speed.

Thus the direction of drive is reversed in the first planetary gear train, and there is an under-drive gear reduction in both planetary gear trains.

5.10.3 Gear change-hydraulic control (Fig. 5.30) The shifting from one gear ratio to another is achieved by a sprag type one way clutch (when shifting from first to second gear and vice versa), four rotating multiplate clutches 'A, B, C and D' and three held multiplate brakes 'E, F and G'. The multiplate clutches and brakes are engaged by electro-hydraulic control, hydraulic pressure being supplied by the engine driven fluid pump. To apply a clutch or brake, pressurized fluid from the hydraulic control unit is directed to an annular shaped piston chamber causing the piston to clamp together the drive and driven friction disc members of the multiplate clutch. Power therefore is able to be transferred from the input to the output clutch members while these members rotate at different speeds. Shifting from one ratio to another takes place by applying and releasing various multiplate clutches/brakes. During an up or down gear shift such as 2-3, 3-4, 4-5 or 5-4, 4-3, 3-2 one clutch engages while another clutch disengages. To achieve an uninterrupted power flow, the disengaging clutch remains partially engaged but at a much reduced clamping pressure, whereas the engaging clutch clamping pressure rise takes place in a phased pattern.

5.10.4 Upshift clutch overlap control characteristics (Fig. 5.37 (a-c)) The characteristics of a gear ratio upshift is shown in Fig. 5.37(a), it can be seen with the vehicle accelerating, and without a gear change the engine speed steadily rises; however, during a gear ratio upshift transition phase, there is a small rise in engine speed above that of the speed curve when there is no gear ratio change taking place. This slight speed upsurge is caused by a small amount of slip overlap between applying and releasing the clutches. Immediately after the load transference phase there is a speed decrease and then a steady speed rise, this being caused by the full transmitted driving load now pulling down the engine speed, followed by an engine power recovery which again allows the engine speed to rise.

When a gear upshift is about to commence the engaging clutch pressure Fig. 5.37(b) rises sharply from residual to main system pressure for a short period of time, it then drops rapidly to just under half the main system pressure and remains at this value up to the load transfer phase. Over the load transfer phase the engaging clutch pressure rises fairly quickly; however, after this phase the pressure rise is at a much lower rate. Finally a small pressure

Fig. 5.36 Reverse gear

Time (seconds)

Disengaging clutch torque

Post regulating phase

Load (torque) transfer phase

Fig. 5.37(a-c) Upshift clutch overlap control characteristics

Engaging clutch pressure rise

Disengaging clutch pressure decrease

Time (seconds)

Resultant output torque i_

Disengaging clutch torque

Post regulating phase

Load (torque) transfer phase

Fig. 5.37(a-c) Upshift clutch overlap control characteristics

Time jump brings it back to the main system pressure. Between the rise and fall of the engaging clutch pressure, the disengaging clutch pressure falls to something like two thirds of the main systems pressure, it then remains constant for a period of time. Near the end of the load transfer phase the pressure collapses to a very low residual pressure where it remains during the time the clutch is disengaged. Fig. 5.37(b) therefore shows a pressure overlap between the disengaging clutch pressure decrease and the engaging clutch pressure increase over the load transfer period. The consequence of too much pressure overlap would be to cause heavy binding of the clutch and brake multiclutch plate members and high internal stresses in the transmission power line, whereas insufficient pressure overlap causes the engine speed to rise when driving though the load transfer period. Fig. 5.37(c) shows how the torque load transmitted by the engaging and disengaging clutches changes during a gear ratio upshift. It shows a very small torque dip and recovery for the disengaging clutch after the initial disengaging clutch pressure drop, then during the load transfer phase the disengaging clutch output torque declines steeply while the engaging clutch output torque increases rapidly. The resultant transmitted output torque over the load transfer phase also shows a dip but recovers and rises very slightly above the previous maximum torque, this being due to the transmission now being able to deliver the full engine torque.

Finally the transmitted engine torque drops a small amount at the point where the engine speed has declined to its minimum, it then remains constant as the engine speed again commences to rise.

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