47 Three stage hydrokinetic torque converter

A disadvantage with the popular three element torque converter is that its stall torque ratio is only in the region of 2:1, which is insufficient for some applications, but this torque multiplication can be doubled by increasing the number of turbine and stator members within the converter, so that there are more stages of conversion (Fig. 4.16).

Consider the three stage torque converter. As shown in Fig. 4.17, it is comprised of one impeller, three interlinked output turbines and two fixed stator members.

Tracing the conversion vortex circuit starting from the input rotating member (Fig. 4.18), fluid is pumped from the impeller P by centrifugal force to the two velocity components Vt and Vr, making up the resultant velocity Vp which enters between the first turbine blades T1 and so imparts some of its hydrokinetic energy to the output. Fluid then passes with a velocity VT1 to the first fixed stator, S1, where it is guided and redirected with a resultant velocity Vs1, made up from the radial and tangential velocities Vr and Vt to the second set of turbine blades T2, so that momentum is given to this member. Fluid is now transferred from the exit of the second turbine T2 to the entrance of the second stator S2. Here the reaction of the curved blades deflects the fluid towards the third turbine blades T3 which also absorb the fluid's thrust. Finally the fluid completes its circulation cycle by again entering the impeller passages.

The limitation of a multistage converter is that there are an increased number of entry and exit junctions between various members which raise

(b) Inner and outer race members freewheeling

Fig. 4.15(a and b) Overrun freewheel sprag type clutch

(b) Inner and outer race members freewheeling

Fig. 4.15(a and b) Overrun freewheel sprag type clutch

Constant input torque no

Constant input torque no

Input

Fig. 4.16 Characteristic performance curves of a three stage converter

Input

Fig. 4.16 Characteristic performance curves of a three stage converter the fluid flow resistance around the torus passages. Subsequently, efficiency drops off fairly rapidly with higher speed ratios compared to the three element converter (Fig. 4.16).

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