AU4852897A - Pendulo-hydraulic machine levelling device - Google Patents

Description

PENDULO-HYDRAULIC MACHINE LEVELLING DEVICE 1. The purpose of this device is to control the movement of hydraulic rams in such a way as to maintain a machine in the level working attitude.

2. The control is effected by means of gravity acting on a pendulous mass or pendulum linked to hydraulic spool valves which are suitably damped to prevent unwanted oscillations. Other types of valve such as rotary or electric may be used if desired.

3. There are two pairs of three-way valves mounted at right angles to each other.

4. The valves on the machines transverse axis controls the attitude in the rolling plane whilst the valves positioned on the longitudinal axis controls pitch attitude.

A three-way valve consists of a valve body and a sliding spool. The body contains three ports opening into the spool gallery. The centre port is connected to hydraulic rams and the other two are connected to the pressurised fluid supply and to the fluid reservoir. When the spool is in the central position all ports are closed and fluid is locked in the ram. As the spool moves in one direction it exposes the pressurised port and allows oil to flow into the ram. In the opposite direction it exposes the reservoir port and allows oil to drain from the ram.

6. The pendulum is suspended from a universal joint allowing it to swing in any direction. The pairs of control valves are attached to the stem of the pendulum and are mounted at 90 degrees to each other in the horizontal plane.

One pair is mounted along the centre axis of the machine and controls pitch and the other pair controls roll. The valves are attached to a hinge mechanism (e) which in turn is connected to the stem by means of ball joints so that movement in one plane does not affect or be affected by movement in the other plane.

7. When the device and the machine to which it is attached is level all the valves are in the neutral position and the hydraulic fluid is trapped in the attitude control rams thus preventing any movement.

8. As the machine moves onto sloping ground it tilts but the pendulum remains vertical causing the spool valves to activate. The valves controlling attitude in roll admit high pressure fluid to the ram/s controlling the down-hill side of the machine whilst allowing fluid from the ram/s controlling the up-hill side to return to reservoir. The down-hill side rams extend, the up-hill side rams retract, the valves return to neutral and the machine remains level. Various ram and wheel arrangements are possible. In the case of a three wheeled machine with a single castor wheel trailing, the rams on both sides retract when the machine encounters rising ground and extend on the down-slope. When the machine moves onto obliquely sloping ground both valve groups operate in harmony to maintain the machine as a level working platform.

9. In practice it was found that the pendulum needed to be damped to prevent overreaction of the valves. This was achieved by using valves with built in dampers as well as immersing the pendulum in a viscous fluid thus slowing down the action of the pendulum to a point where the dampers can control it over rough terrain or in sudden changes of direction.

Where electro valves are to be used, micro switches are mounted in place of the spool valves. Two groups of micro switches are mounted at right angles to each other. The transverse group controlling roll and the axial group controlling pitch.

For each ram there are four switches, two controlling roll and two controlling pitch. Piston type dampers are fitted in both roll and pitch planes to eliminate unwanted oscillations.

11. There are two solenoid valves of the normally closed type per ram, one connecting the ram to the high pressure supply and the other to the reservoir return.

12. The following describes the operation of the system when fitted to the three wheel machine. When the machine is level or at the desired pre-set angle all switches are at "off', all solenoid valves are closed and the fluid remains trapped in the rams. As the machine encounters a sideways slope it begins to tilt. The pendulum remains vertical activating the transverse micro switches and thus the solenoid valves. The high pressure solenoid valve on the down-slope side ram opens causing that ram to extend and forcing the wheel down. At the same time, the reservoir return solenoid valve on the up-slope side ram opens allowing fluid to return to the reservoir thus causing that ram to retract and the wheel to rise.

The machine remains level. When the machine encounters rising ground, the pendulum activates the axially mounted micro switches controlling the reservoir return solenoid valves. The valves open allowing fluid to escape from both rams, both wheels to rise and the machine to remain level. On the down-slope the axially mounted micro switches for the high pressure solenoids activate, fluid enters both rams, the rams extend forcing the wheels down and levelling the machine. Where ground sloping in both planes is encountered the switches operate the solenoid valves in harmony to maintain the machine level.