Caterpillar cat e70 b track excavator (prefix 6ak) service repair manual (6ak00001 up)

Service Repair Manual
Models
E70B TRACK EXCAVATOR

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Product: EXCAVATOR
Model: E70B EXCAVATOR 6AK
Configuration: E70B TRACK-TYPE EXCAVATOR 6AK00001-UP (MACHINE) POWERED BY 4D32 ENGINE
General Service Information
E70B EXCAVATOR TRAVEL DRIVE AND MOTOR
Media Number -SENR4584-00 Publication Date -01/08/1989 Date Updated -11/10/2001
General Notes
* This machine has been designed conforming to JIS (Japanese Industrial Standard) requirements in
which all measurements are based on the metric system. And this manual, wherever practical, these
measurements are shown to the nearest fraction in feet, pound, etc., but whenever in doubt, the
metric value shown should be used.
* Numbers indicated in ( ) in this manual are the part numbers given in structural and exploded
diagrams.
* Specifications are subject to change with or without notice owing to improvements, that may be
introduced after publication of this manual.
Conversion table for metric system indications into Foot-pound units (U.S.A.)
Copyright 1993 - 2019 Caterpillar Inc.
All Rights Reserved.
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Product: EXCAVATOR
Specifications
Specifications
1. General
2. Travel motor
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3. Travel gear
Model Notation
Travel motor
Brake valve
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Product: EXCAVATOR
Function And Construction
Structural Diagram
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Operating Principles
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General
Travel drive and motor (73) consists of four components: swash plate type axial plunger motor (81),
counter-balance valve (80), parking brake (78), and reduction gears (79). Travel drive and motor
(73) converts the energy of pressure oil supplied by the pump into rotational force of proper speed,
and transmits this force to sprockets (74) to run the machine. When the machine is going downhill,
the travel drive and motor prevents it from overrunning, or forces the machine to a halt when it
stops. When the machine parks or stops on a slope, the braking torque of the travel motor shaft
prevents the machine from moving.
Travel drive and motor (73) is mounted on lower frame (72) and is capable of supporting the
machine weight and of countering external force acting on the track frame during digging operation.
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Pressure oil from the hydraulic pump enters port (77) and flows through counter-balance valve (80)
to run motor (81) at high speed. Reduction gear (79) reduces the high rotational speed to produce
slow and large torque which it turn rotates hub (1) (case). The motor return oil flows through
counter-balance valve (80) and out of port (76), and returns to the oil tank. The motor rotates
reversely when the pump pressure oil enters port (76) and is drained from port (77).
During motor rotation, case drain oil from sliding sections returns from port (75) to the tank. The
counter-balance valve controls the motor rotation by controlling the oil flow into/from the motor.
Parking brake operates together with the spool of the counter-balance valve. The parking brake is
released when the motor operates and engaged when the motor stops.
The operating principle will be explained for each of the above four components.
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Motor
The pressure oil from the pump enters port (77) in rear flange (27), and flows through the brake
valve section in the rear flange. It then goes to the cylinder bores in cylinder block (3) through
kidney port (82) in timing plate (35).
Depending on the swash plate angle, kidney port (82) in timing plate (35) allows the pressure oil to
go to only four to five cylinder bores (83) that are situated on one side of Y1 - Y2 line between the
top and bottom dead centers of the piston stroke.
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The pressure oil in cylinder bores (83) of cylinder block (30) generates force (84) to pistons by
acting on the ends of pistons (31) (four or five).
Piston force (84) then acts on swash plate (29) through shoe (32). Swash plate (29) is tilted to the
piston, so pistons (31) are moved down on the tilted surface of swash plate (29) by piston force (84).
As pistons move down, cylinder block (30) rotates.
Since cylinder block (30) and shaft (28) are directly connected with splines, shaft (28) rotates
together with cylinder block (30) which in turn generates torque.
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Counter-balance valve
Starting and traveling
Pressure oil comes into port (77) in rear flange (27), opens valve (52), and flows into kidney port (82
-1) in motor timing plate (35). From the kidney port, this oil flows into cylinder bores (83) in
cylinder block (30) to run the motor.
At the same time this pressure oil flows through passage (88) into spool chamber (89) from small
hole (87) of spool (48), thereby pushing spool (48) that is held in its neutral position by spring (54)
to the left. As spool (48) is pushed leftward, it introduces passage (85), recesses of spool, against
rear flange (27). Through passage (85) created between kidney port (82-2) in timing plate (35) and
port (76) in rear flange (27), return oil flows back into the tank. As spool (48) moves from its neutral
position, passage (86) to the parking brake opens, and pressure oil flows into the cylinder chamber
of the parking brake. This releases the parking brake force and allows the motor to run.
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When pressure oil flows to port (76) in rear flange (27) and is drained from port (77), the directions
of each component reverse, thereby causing the motor to run in reverse direction.
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Stopping
Suppose the machine is traveling, with pressure oil supplied to port (77) in rear flange (27). As soon
as this supply is shut off, spool (48) tends to move back to its neutral position due to the force of
spring (54), because the hydraulic pressure that pushes spool (48) is lost. In this case, the oil in spool
chamber (89) tries to flow into port (77) through passage (88), pushing spool (48). However,
because the oil flow is restricted at passage (88), back pressure occurs which in turn slows down the
movement of spool (48).
The motor keeps running by inertia even when the pressure oil is stopped. The motor return oil
therefore tries to flow back to port (76) from kidney port (82-2) in timing plate (35) through passage
(85), a clearance between the recess of spool (48) and rear flange (27). When spool (48) returns fully
to the neutral position, it blocks the motor return line completely, thereby forcing the motor to a halt.
To smoothly stop the motor running by inertia, the counter-balance valve slows down the movement
of spool (48) using the back pressure generated by restricting the motor return line through the
recess shape of spool (48).
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When the brake is applied to stop the motor, the motor keeps rotating by inertia if pressure oil is
stopped, and act as a pump. However, oil is no longer supplied because the suction line is blocked
by spool (48), thereby inducing possible cavitation. Valve (52), which takes action at a slight
negative pressure under this condition, then causes the oil to flow into kidney port (82-1) in timing
plate (35) from port (76) so as to prevent cavitation.
When pressure oil is supplied to port (76) in rear flange (27) during operation, each of the above
components moves reversely, forcing the motor to a halt.
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Overspeeding
As the machine goes down a steep slope, its speed increases, and the motor will run faster than oil
can be supplied. This faster motor rotation is called "overspeed". When this happens, port (77) goes
negative to pull the oil, moving spool (48) to the right. As a result, return passage (85) is restricted,
which in turn causes back pressure. This back pressure causes a resistance to the motor which tries
to overspeed by inertia so that the motor will run in accordance with the flow rate of oil supplied
from the pump.
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Parking brake
Starting and travelling (Parking brake released;)
When the pressure oil moves spool (48) of the counter-balance valve to the left from the neutral
position, passage (86) to the parking brake opens. And the pressure oil pushes valve (45) until it
closely contacts with the bottom face of valve seat (44). This blocks passage (90) to the drain port.
Thus, the pressure oil enters piston chamber (91) through passage (92).
As the pressure rises beyond the set value, it overcomes the force of spring (39) that pushes piston
(38), and forces spring (38) to move. The movement of piston (38) eliminates the force of spring
(38) which is acting on separator plates (42) and friction plates (41) and allows friction plates (41) in
cylinder block (30) of the travel motor to freely rotate, thereby releasing the brake force acting on
cylinder block (30) of the travel motor.
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Stopping (Parking brake applied;)
When the supply of pressure oil is shut off, spool of the counter-balance valve returns to the neutral
position. Passage (86) which is connected to the parking brake closes and there is no pressure.
Consequently, spring (46) moves valve (45) away from the surface of valve seat (44). The pressure
oil in piston chamber (91) goes through passages (92) and (90) to port (75). The drain is then led to
the tank. There is no longer pressure in piston chamber (91) and spring (39) forces piston (38)
against the inner surface of the spindle. When piston (38) is pushed, free separator plates (42) and
friction plates (41) are also pushed to spindle (2). The friction force caused by this pushing force
stops the rotation of cylinder block, thereby causing the brake torque to act on the motor shaft.
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Reduction gear
When shaft (28) of the motor makes one turn, input gear (6) that is splined to shaft (28) also makes
one turn. Three spur gears (7) whose involute teeth are engaged with input gear (7) rotate in reverse
direction to one another. Each spur gear (7) rotates at a speed, inversely proportional to the gear
ratio. The rotational speed and direction of crankshaft (9) are the same as those of spur gear (7),
since they are directly connected with splines.
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When crankshaft (9) rotates, eccentric portions (93) and (94) also rotate and provide eccentric
movement to gear A (4) and gear B (5).
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Each gear A or B has 35 teeth. As gear A (4) and gear B (5) start eccentric movement, their trochoid
teeth rotate in rolling contact with 36 pins (12) which are located on the inside surface of hub (1).
When crankshaft (9) makes one turn, gear A (4) and gear B (5) perform one cycle of eccentric
movement, respectively. During this one cycle, pin (12) shifts by one pitch, a difference between 36
pins and 35 teeth, in the same direction as crankshaft (9) rotates. This pin rotation is transmitted to
hub (1). Hub (1) advances by 1 pin. The ratio is 1/36. The overall reduction ratio is 1/57.6. This ratio
is obtained by multiplying the reduction ratio 15/24 between input gear (6) and spur gear (7) by the
reduction ratio 1/36 due to eccentric movement.
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Product: EXCAVATOR
Disassembly
Preparation
Make the following preparations prior to disassembly.
1. Workbench
* Prepare the travel motor workbench.* The workbench must be sturdy and large enough to
disassemble or reassemble the travel motor and to hold its disassembled parts during work.
2. Supplies
Prepare the supplies and special tools shown in the previous section.
General Precautions
1. Before starting the disassembling work, check the specified inspection items to see the nature of
trouble. And follow the disassembly procedures.
2. Use care in handling precision parts during work to avoid damage caused by striking other parts
or from being dropped.
3. Never strike or prize parts forcibly when they are held fast to prevent damage, burring, oil
leakage or deteriorated performance. Use care and patient.
4. Protect parts from corrosion and dust when disassembly is interrupted for some time. Parts rust
easily due to moisture or dust when left disassembled.
Disassembly Procedure
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Washing travel motor
1. Fit a blind plug into each port in rear flange (27).
2. Install and tighten two eye bolts 180° apart in the tapped holes in spindle (2).
3. Hitch a lifting sling to the eye bolts through shackles. Lift and bring the travel motor over to the
washing sink.
4. Wash the travel motor with a brush and kerosene.
NOTE: Some dirt will be found in the running clearance (where the floating seal is installed)
between hub (1) and spindle (2). Wash the dirt off thoroughly.
Draining gear oil
1. Loosen three plugs (25) with a torque wrench and hexagon socket.
NOTE: If the motor is lifted with the plugs (25) removed, the gear oil will come out. Loosen these
plugs until each plug comes out with its one or two threads remaining in the cover.
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2. Run two eye bolts into spindle (2) 180° apart.
3. Hitch a lifting sling to the eye bolts through shackles and lift the travel motor with the crane.
4. Place a clean vessel under the travel motor and drain the gear oil into the vessel by removing
three plugs (25) from cover (8).
Setting travel motor
1. Set the travel motor on the travel motor fixture.
NOTE: Place the travel motor carefully with the bolt holes of hub (1) and the fixture aligned.
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2. Bolt the travel motor unit to the bench using two hexagon bolts.
Removing cover (8)
1. Turn the travel motor upside down.
2. Using an oil paint marker, scribe match marks across the joint seam between hub (1) and cover
(8).
3. Look into the seam to locate the gap of ring (13). Make a punch mark on hub (1) at a point
about 20 mm (0.787 in.) from the end of ring (13) in circular direction and 6.5 mm (0.256 in.)
from its top end face.
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4. Using an electric drill, make a 2 mm (0.079 in.) diameter hole at the punch mark, from the
outside of hub (1) toward ring (13).
NOTE: Be sure to center the drill on the punch mark, and keep drilling until ring (13) is pushed
up from cover (8) by the drill.
NOTICE
After drilling, wipe off chippings completely. This is necessary to
protect parts which are disassembled subsequently.
5. Insert the ring pick, a special tool, into the drilled hole. Push ring (13) with this tool until the
end of ring (13) comes out of cover (8). Hold the raised ring end by hand and remove ring (13)
from the groove of hub (1).
6. Run PT eye bolts into threaded holes on top of cover (8) and tighten.
7. Hitch a lifting sling to the PT eye bolts through shackles and lift cover (8) off hub (1) with a
crane.
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NOTE: O-ring (22) may prevent cover (8) from sliding out. If cover (8) will not move, lift the
cover while tapping on it with a plastic hammer.
8. Remove O-ring (22) from cover (8).
NOTICE
Do not use any sharp tools such as a screwdriver to remove O-ring
(22). The use of such a sharp tool may cause burrs, galls, etc., in the
groove. Oil leaks will be the result if the O-ring is installed in the
damaged groove.
Removing input gear (6)
1. Remove snap ring (20) from shaft (28).
2. Remove input gear (6) from shaft (28).
Removing rear flange (27)
1. Turn the travel motor upside down.
2. Loosen two plugs (49).
NOTE: This step is necessary only when the rear flange is to be disassembled, and a preliminary
work to make it easier to remove plugs (49). So, do not try to remove plugs (49) but loosen them
to the extent where they can be removed by hand.
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3. Loosen two plugs (51).
NOTE: This step is also necessary only when the rear flange is to be disassembled and a
preliminary work to make it easier to remove plugs (51).
4. Remove hexagon socket bolts (67).
5. Remove rear flange (27) from spindle (2), and put the removed rear flange on the bench with its
mating face with spindle (2) on top.
NOTICE
Hold rear flange (27) with both hands, and gently lift it straight up. Do
not cock it while lifting it. Any attempt to shake it loose by tapping or
otherwise is not permitted. Remember, timing plate (35), a very critical
part, may come out with the rear flange.
6. Remove parallel pins (64) from spindle (2).
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7. Remove O-ring (23) from spindle (2).
NOTICE
Do not use any sharp tools such as screwdriver to remove O-ring (23).
The use of such a sharp tool may cause burrs, galls, etc., in the groove.
Oil leaks will be the result if the O-ring is installed in the damaged
groove.
8. Remove springs (39) from spindle (2).
Removing parts from rear flange
1. Remove timing plate (35) from rear flange (27).
NOTE: It might be found that the timing plate is stuck to the mating surface of rear flange (27).
To separate the plate from the flange, insert a flat lever into the cast-out groove of the rear flange
and prise the plate slowly.
NOTICE
Never try to pry the plate off with a sharp cornered or pointed tools
such as a screwdriver, or the precision-finished mating faces will be
damaged, resulting in oil leakage.
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2. Pull parallel pins (65) out of rear flange (27).
3. Remove ball bearings (56) from rear flange (27).
Disassembling brake valve in rear flange
1. Put rear flange (27) on the workbench with its mating face with spindle (2) on bottom.
NOTICE
The bench top surface must be clean, flat and free of scar to avoid any
damages to the precision-finished surface of the rear flange.
2. Remove two plugs (49) from rear flange (27) by hand.
3. Remove O-ring (62) from each plug (49).
4. Remove two spring retainers (50) and two springs (54) from rear flange (27).
5. Remove spools (48) from rear flange (27).
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Caterpillar cat e70 b track excavator (prefix 6ak) service repair manual (6ak00001 up)

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