Swash Plate Oscillations
due to Piston Forces
Liselott Ericson
Introduction
Problem
Noise is a well known challenge in hydraulic systems. Hydrostatic
machines are one of the largest noise contributors in a hydraulic system.
The noise from the machine originates from flow pulsations at the
discharge and suction ports, as well as pulsations in piston forces and
bending moments.
Project
There are large piston forces acting on the swash plate. These forces
will affect the swash plate movement and start an oscillation on the
swash plate. The question is how much will this oscillation affect the
noise and efficiency in the pump. To be able to measure the difference,
measurements can be performed both with fixed swash plate (red screw
on the picture below) and free swash plate.
This study investigates the oscillations of swash plates caused by piston
forces acting on the swash plate. Earlier investigations of variable axial
piston pumps assume a fixed swash plate angle, i.e. the swash plate is
fixed at different displacement angles. Under normal operating
conditions, the swash plate is controlled by a hydraulic actuator which
affects the swash plate. The presented models are able to separate
different losses caused by the swash plate oscillations and the
controller. The results show oscillations on the swash plate which affect
both efficiency and flow pulsation and hence the noise level.
Closed-loop model for variable pump
The model includes a simple controller for the pump’s setting angle
and also a simplified external system consisting of a load valve and a
volume.
Results
Pump model
The pump model includes the important forces created due to pressure
built up in the pump and acting on the swash-plate. The swash-plate
interacts with the control actuator and pistons.
Piston velocity [m/s]
The oscillation of the swash plate is significant. The amplitude of the
oscillations is dependent on the mass-spring system’s resonance
frequency. When designing a pump controller the oscillating forces on
the swash plate should be considered. A change of valve plate design
will also change the interaction between the forces in the pump and
hence the actuator force.
Cylinder
barrel
Outlet
flow
Swashplate/
axis
Inlet
flow
1
0.5
0
-0.5
-1
0
50 100 150 200 250 300 350
Rotation angle [degrees]
Fixed swash plate
Oscillating swash plate
Future
Further investigation is needed. The topic regarding control
mechanism in pumps and motors is important research topic. It will
affect the noise created in the pump/motor, the efficiency of the
hydraulic systems and the control performance of the pump/motor.
Linköping University, Fluid and Mechatronic Systems, www.iei.liu.se/flumes, [email protected], 2015-03-10