(57) s7 An axial piston pump comprises a drive shaft (2), a cylinder block (4) rotatable
with the drive shaft (2), a plurality of pistons (6a-6i) provided within the cylinder
block (4), a swashplate (12) situated at one axial end of the cylinder block (4) for
causing reciprocation of the pistons (6a-6i) when the said cylinder block (4) is rotated,
and a valve plate (26) situated at a second axial end of the cylinder block (4) ;
wherein either one of the cylinder block (4) or valve plate (26) is urged against
the other to form a hydrostatic seal between the cylinder block (4) and a face (52)
of the said valve plate (26). The pump may be characterised by one or both of the
following features :-A spiral groove bearing (50) is provided between the valve plate
(26) and the cylinder block (4).
The valve plate (26) is urged against the cylinder block (4) by means of a second
piston (60) which has an arcuate load face.
Additionally, an axial piston pump comprises a drive shaft (2), a cylinder block (4)
rotatable with the drive shaft (2), a plurality of pistons (6a-6i) provided within
the cylinder block (4), a swashplate (12) situated at one axial end of the cylinder
block (4) for causing reciprocation of the pistons (6a-6i) when the cylinder block
(4) is rotated ; the said swashplate (12) being provided with a curved back, the curved
back being seated within a curved recess in a swashplate cradle (14), a hydrostatic
bearing (70, 72) being formed between the said curved back of the swashplate (12)
and the curved recess of the swashplate cradle (14), and the said swashplate (12)
being capable of swivelling within the said recess ; wherein high pressure oil is
supplied to the said hydrostatic bearing (70,72) via a passage provided in at least
one of the said pistons and via a hole (80) provided in the body of the said swashplate
(12).
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