book in series
A more efficient solution to make the cylinder block rotate is
the cardan joint (rotary shaft with joints at both ends - Figure
4.63) because it provides more traction than small pistons
alone as it helps the spindle/preload spring. The preload
system is now placed inside the cylinder block and the cardan
joint end (Figure 4.64).
Figure 4.61
All the versions of these pumps need a quite robust
dimensioning of the axial bearings of the transmission shaft
because the cylinder block revolves without a mechanical
support: the strain of the whole component affects roller
bearings. The hydraulic performances of these pumps are
similar to swash plate pumps with rotary cylinder block, but
bent axis piston pumps are more robust; in addition, they are
more expensive and obviously they cannot be mounted in
tandem.
Figure 4.63
The plate in the versions with connecting rods is rigidly
connected to the transmission shaft; the hemispheric seats
for the connecting rods are on the face opposite to the
shaft. These seats are made up of a small cylinder with ball
ends; the plate ball has a larger diameter than the ball fit
into the internal seat of the piston. The cylinder block can
rotate thanks to the torsion movement on the pistons. The
hydraulic principle is the same as swash plate pumps with
rotary cylinder block, piston reciprocation results in the inlet/
outlet phases and a bush with slotschannels the fluid in the
inlet/outlet.
A single-ball joint is in its seat at the centre of the plate and
it presses on the preload spring that makes the cylinder
block adhere between the plate and the distribution bush.
In some types, the spring twisted around the small piston of
the central joint presses between the upper part of the rotary
block and a ring before the ball, while in others the preload
spring is inside the cylinder block opposite to the small piston
(Figure 4.62).
Figure 4.64
The plate and the upper part of the cylinder block in the
versions with bevel gears become respectively the leading
and driven gearwheels (Figure 4.65).
Figure 4.65
Figur.e 4.62
66 | JuNe-july 2018 | Global MDA Journal
Their pistons are simpler as they have neither cylinders nor
ball joints. Drain clearances directly connected to the inlet
are manufactured inside the aluminium pump casing.