Overall Description
The control (auxiliary) system pump is an axial piston, swashplate design, variable displacement pump with a pressure compensator control. The pressure compensator control gives maximum output flow to the system until the system reaches the pre-adjusted pressure setting of the control. The pressure compensator control then regulates the pump output flow to equal the flow requirements of the system while maintaining the pre-adjusted output pressure. When the system no longer requires flow, the pressure compensator control will cause the pump to destroke so that there is no output flow while maintaining the pre-adjusted pressure.
PR-750B CONTROL (AUXILIARY) HYDRAULIC SYSTEM
The pressurized hydraulic oil from the pump flows through a pressure filter and then to various control valves. The control valves direct the hydraulic pressure to the appropriate ports of the hydraulic cylinders, elevation sensors or motors.
Steering Control
The steering assembly consists of two hydraulic cylinders, a hydraulic control valve and two interconnected control levers. The control levers, one at each end of the control panel, set the position of a spool in the control valve located under the console. The position of the valve spool determines whether control system hydraulic pressure is blocked at the valve or routed to one or the other end of each of the steering cylinders. When either control lever is moved to "L" (left), control pressure is applied to the head end of the right cylinder, extending the cylinder rod, and to the rod end of the left cylinder, retracting the cylinder rod. The combined action of the two cylinders turn the front leg assembly and the attached track to the left. Moving either control lever to "R" (right) applies control pressure to the rod end of the right cylinder and to the head end of the left cylinder. The front track can be turned 60 degrees each side of center.
Elevation Control
System Description
The elevation of the mainframe and the attached cutter can be controlled manually or automatically. When using manual control, the operator manually positions a control valve to adjust the elevation of each of the three legs.
PR-750B ELEVATION CONTROL SYSTEM
When automatic control is used, the elevation of the front leg is controlled by an elevation sensor mounted on the left side of the machine. The elevation of the rear legs is controlled by an elevation sensor or by the cross slope sensor, or either rear leg can be manually adjusted to a set elevation above the cut grade (locked to grade) at which the leg will remain. See page 2-34 for more information on the possible modes of elevation control.
Elevation Sensors
Each elevation sensor consists of a patented hydraulic valve, a wand and a counterweight arm. The counterweight position is adjustable to ensure that the wand will ride firmly against the wand guide. Any change of machine elevation in relation to the wand guide will cause the wand and counterweight arm to rotate the shaft in the hydraulic valve. The rotation of the valve shaft opens a valve port which allows the pressurized hydraulic oil to flow to the end of the hydraulic cylinder that will bring the machine back into proper relation with the wand guide. As the machine moves back to its proper position, the wand and counterweight arm rotate in the opposite direction, closing the valve port and stopping the movement of the hydraulic cylinder.
When the sensor is in the null position (there is no hydraulic flow at the C1 and C2 ports) the counterweight arm should be 90° to the valve body centerline and the wand should be in line with the counterweight arm.
Cross Slope Sensor
The cross slope sensor (pendulum assembly) is a pendulum-type hydraulic sensor that senses any change in machine cross slope from that entered in the system. If the cross slope sensor detects a change in the machine cross slope, the sensor directs hydraulic oil to the appropriate end of the selected rear elevation cylinder to bring the machine back to the correct cross slope.
The damping adjustment on the cross slope sensor can be set to meeet individual needs, but "3" is generally satisfactory. The hydraulic oil temperature should be in the normal operating range before attempting to set the damping adjustment. Cold hydraulic oil will naturally slow the response of the sensor.
| NOTICE |
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THE PENDULUM ASSEMBLY IS A PRECISION INSTRUMENT THAT IS ACCURATELY CALIBRATED AT THE FACTORY. DO NOT ADJUST OR CHANGE THE POSITION OF THE POINTER, THE ADJUSTMENT GUIDE BLOCK, THE ADJUSTMENT SHAFT BEARINGS OR THE BELT THAT EXTENDS FROM THE ADJUSTMENT SHAFT TO THE SLOPE INDIAVSOR. IF NECESSARY, ADJUST THE BELT TENSION BY MOVING THE INDIAVSOR SUPPORT BRACKET. DO NOT MOVE THE ADJUSTMENT SHAFT BEARINGS. |
Elevation Reference Assemblies
- 1. Grade sensing wheel assembly - a rod (pivot post) is rigidly held to a mounting arm by a bracket. The pivot post supports a mounting arm that holds the sensor mounting assembly. A wheel mounting post mounts to the pivot post by means of two links that allow the mounting post to move up and down as the wheel at the bottom of the mounting post rides on the ground. A U-shaped reference rides up and down with the wheel mounting post and moves the sensor wand. The assembly mounts on the end of the cutter and can be swung around to ride outboard of the cutter or to ride in front of the cutter. Since the wheel rides on the uncut grade, irregularities in the uncut grade will be reproduced in the cut grade. If the wheel rolls into a chuck hole, the cutter will attempt to drop a corresponding amount.
- 2. Averaging ski - the optional averaging ski mounts on the side of the machine. The front of the ski rides on small wheels near the front track and is free to pivot up and down around the pin which attaches to the rear leg yoke. The reference for the elevation sensor is a rod that extends out from the ski. The wheels of the ski ride on uncut grade, but the length of the ski provides an "averaging" of grade irregularities which makes the cut grade smoother than the original grade.
Automatic Elevation Control Modes
The PR-750B has four possible modes of automatic elevation control.
Mode 1 Automatic elevation selector at "On". Right sensor selector at "On". Left sensor selector at "On". Cross slope selector at "Off".
The front and right rear elevation cylinders are controlled by elevation sensors which can be mounted to operate from single wheel elevation reference assemblies or from optional averaging skis. The left rear elevation cylinder is locked to grade.
The depth of cut will be held constant at either edge of the cut grade where a single wheel elevation reference assembly is used. An averaging ski used on either side will provide a depth of cut at that edge of the cut grade that averages the original grade irregularities.
Mode 2 Automatic elevation selector at "On". Right sensor selector at "Off". Left sensor selector at "On". Cross slope selector at "Right".
This mode is the same as mode 1 except the right rear elevation cylinder is controlled by the cross slope sensor. The right side elevation sensor is not used.
If operating from the single wheel elevation reference assembly, the depth of cut at the left edge of the cut grade and the cross slope of the cut grade will be held constant. An averaging ski will provide a depth of cut at the left edge of the cut grade that averages the original grade irregularities.
Mode 3 Automatic elevation selector at "On". Right sensor selector at "On". Left sensor selector at "On". Cross slope selector at "Left".
The front elevation cylinder is controlled by the left side elevation sensor which can be mounted to operate from a single wheel elevation reference assembly or from an optional averaging ski. The left rear elevation cylinder is controlled by the optional cross slope sensor. The right side elevation sensor controls the right rear elevation cylinder.
If operating from single wheel elevation reference assemblies, the depth of cut at the edges of the cut grade and the cross slope of the cut grade will be held constant. Averaging skis will provide a depth of cut at the edges of the cut grade that averages the original grade irregularities.
Mode 4 Automatic elevation selector at "On". Right sensor selector at "Off". Left sensor selector at "On". Cross slope selector at "Left".
The front elevation cylinder is controlled by the left side elevation sensor which can be mounted to operate from a single wheel elevation reference assembly or from an optional averaging ski. The left rear elevation cylinder is controlled by the cross slope sensor. The right rear elevation cylinder is locked to grade.
If operating from the single wheel elevation reference assembly, the depth of cut at the left edge of the cut grade and the cross slope of the cut grade will be held constant. An averaging ski will provide a depth of cut at the left edge of the cut grade that averages the original grade irregularities.