Double Hooke's Type CV Joint
Double Hooke's Type CV Joint
One method of obtaining very near constant velocity characteristics is to position two Hooke's joints back to back so that their yoke arms remain in line with one another (Fig. 26.12). 
Fig. 26.12. Double Hooke's type constant velocity joint.
After assembly, both pairs of outer yoke arms must be at right angles to the arms of the central double yoke member. This double joint combination can be considered in two stages. The first stage hinges the drive yoke and driven central double yoke together, and the second stage links the central double yoke (now drive member) to the driven final output yoke. Consequently, the second stage drive half of the central double yoke is placed a quarter of a revolution out of phase with the first stage drive yoke (Fig. 26.13).
After assembly, both pairs of outer yoke arms must be at right angles to the arms of the central double yoke member. This double joint combination can be considered in two stages. The first stage hinges the drive yoke and driven central double yoke together, and the second stage links the central double yoke (now drive member) to the driven final output yoke. Consequently, the second stage drive half of the central double yoke is placed a quarter of a revolution out of phase with the first stage drive yoke (Fig. 26.13).
Fig. 26.13. Double Hooke's type joint shown in two positions 90 degrees out of phase.
Therefore, if the input and output shafts are inclined to each other and the first stage driven central double yoke is speeding up, then the second stage driven output yoke slows down. On the other hand when the first stage driven member reduces its speed the second stage driven member increases its speed. The speed lost or gained by one half of the joint equals that gained or lost by the second half of the joint respectively. As a result no cyclic speed fluctuation occurs between input and output shafts during rotation.
This double joint incorporates a centring device (Fig. 26.12) normally of the ball and socket spring loaded type. This device maintains equal angularity of both the input and output shafts relative to the central double yoke member. Although this is a difficult task to execute due to the high end loads experienced by the sliding splined joint of the drive shaft, but the accuracy of centralizing the double yokes is not critical at the normal relatively low drive shaft speeds.
This double Hooke's joint is specifically suitable for heavy duty vehicles with rigid front wheel drive live axle requiring large lock to lock wheel swivel. This type of joint is relatively large in size compared to its torque transmitting capacity. This forms a major limitation with this joint.
Therefore, if the input and output shafts are inclined to each other and the first stage driven central double yoke is speeding up, then the second stage driven output yoke slows down. On the other hand when the first stage driven member reduces its speed the second stage driven member increases its speed. The speed lost or gained by one half of the joint equals that gained or lost by the second half of the joint respectively. As a result no cyclic speed fluctuation occurs between input and output shafts during rotation.
This double joint incorporates a centring device (Fig. 26.12) normally of the ball and socket spring loaded type. This device maintains equal angularity of both the input and output shafts relative to the central double yoke member. Although this is a difficult task to execute due to the high end loads experienced by the sliding splined joint of the drive shaft, but the accuracy of centralizing the double yokes is not critical at the normal relatively low drive shaft speeds.
This double Hooke's joint is specifically suitable for heavy duty vehicles with rigid front wheel drive live axle requiring large lock to lock wheel swivel. This type of joint is relatively large in size compared to its torque transmitting capacity. This forms a major limitation with this joint.
Velocity Ratio.
Double hooke's joint (Fig. 26.14) connects driving shaft A and driven shaft B which are parallel but lie in different axis through an intermediate shaft C. The yokes of shaft A and B lie in the same plane and the two yokes of shaft C also lie in another plane. The correct positioning of the yokes specially those on the intermediate shaft is essential to keep the angles same for both joints and thus to obtain constant velocity ratio.
Fig. 26.14. Simplified diagram of a double Hooke's joint.
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