Drivtrains Flashcards
(119 cards)
1
Q
What is the function of the shift valve in solenoid shift valves?
A
Provides controlled pressure oil to engage or release the element
Each clutch and A-Brake has one shift valve.
2
Q
Where are the solenoid shift valves located?
A
On the transmission rear cover and manifold
Valves are positioned for optimal oil flow control.
3
Q
What is the orientation of the input and output valves in solenoid shift valves?
A
Input valves are horizontal and output valves are vertical
This orientation aids in effective fluid management.
4
Q
How are shift valves controlled in solenoid shift valves?
A
By the Powershift Control Unit (PCU) through a Pulse Width Modulated (PWM) signal
The PCU regulates the operation of the valves.
5
Q
What does the pulse width in PWM control?
A
Regulates the average current flow by turning the power ON & OFF rapidly during each cycle
This modulation allows for precise control of valve operation.
6
Q
What is the duty cycle in the context of PWM?
A
The ratio of ON time to total cycle time
It determines how long the valve is engaged during a cycle.
7
Q
What type of shift valves were used in the early 8000 series (up to 19,999)?
A
Digital shift valves
This technology was replaced in later models for improved performance.
8
Q
What type of shift valves are used in the later 8000 series (after 20,000), 8010, 20, 30, and 8R?
A
Analog shift valves
All 8000 track machines also utilize this type.
9
Q
What controls the digital shift valve?
A
The digital valve is controlled by a PWM signal from the PCU
10
Q
What is the frequency of the signal from the PCU for early 8000 series tractors?
A
The signal from the PCU is at a constant rate of 50 Hz.
11
Q
How is the duty cycle varied during the shift?
A
The duty cycle is varied depending on several factors as determined by the PCU.
12
Q
What happens with every pulse of the PWM signal?
A
The pilot plunger in the electromagnet covers the orifice for a specified time period and then returns to its ‘home’ position due to spring force.
13
Q
What is the state of the pilot plunger and main spool valve when the valve is OFF?
A
Both the pilot plunger and main spool valve are disengaged or in their home position.
14
Q
What happens to pilot oil when the valve is OFF?
A
Pilot oil (System 1) flows freely from the pilot section of the valve, through the orifice in the nozzle back to sump, putting very little pressure on the spool valve.
15
Q
What does the spring at the bottom of the main valve do?
A
The spring forces the spool valve upwards and opens a passage from the clutch port to sump.
16
Q
What is the status of the passage for engagement oil to the clutch?
A
The passage for engagement oil to the clutch is blocked.
17
Q
What happens when the spool valve returns to its home position?
A
It cuts off engagement oil to the element.
18
Q
What occurs when the solenoid is de-energized?
A
The plunger retracts and allows engagement oil to be routed to sump.
19
Q
What controls the Digital Shift Valve - Engaged?
A
It is controlled by the PCU with a variable duty cycle.
20
Q
How is the spool valve moved?
A
The spool valve is moved by pressure built up in the pilot section.
21
Q
What happens when the solenoid is energized?
A
The plunger extends to cut off the pilot oil’s path to the sump.
22
Q
What occurs when the signal from the PCU engages the digital shift valve?
A
The plunger is pushed toward the pilot section of the valve.
23
Q
What happens to the pilot oil flow when the valve is engaged?
A
The pilot oil flow through the valve starts to be restricted.
24
Q
What is the effect of restricting the flow to the sump?
A
It increases the pressure on the main spool valve.
25
What is the relationship between pilot oil flow restriction and valve spool movement?
The more the pilot oil flow is restricted, the more pressure will be applied to the valve spool, causing it to shift further.
26
What happens when the spool valve moves?
Engagement oil is routed to the clutch from the inlet section of the valve.
27
What are the inlet hole sizes for digital and analog shift valves?
The input valves have 1/8" inlet holes and the output valves have 1/4" inlet holes.
28
What does the plunger do with each cycle of the signal?
The plunger moves back and forth to its home position.
29
How is the control of oil flow determined?
It is determined by the amount of time the valve is in the ON position and the restriction of pilot oil flow to the sump.
30
What controls the Digital Shift Valve when engaged?
The Digital Shift Valve is controlled by the PCU with a variable duty cycle.
31
What is the current required for the Digital Shift Valve?
It requires a small current of only about 1 Amp.
32
How is the spool valve moved?
The spool valve is moved by pressure built up in the pilot section.
33
What does the pressure in the pilot section allow?
It allows oil to flow to the elements for engagement.
34
What happens when the solenoid is energized?
The solenoid extends the plunger to cut off the pilot oil's path to the sump.
35
What change was made to the shift valves?
The change to analog shift valves increased the amount of control the PCU has on the movement of the spool valve.
36
What type of signal do analog shift valves use?
Analog shift valves still use a PWM signal but at a much higher frequency (500-2000 Hz) to control the shift valve.
37
How can analog valves be distinguished from digital shift valves?
Analog valves can be easily distinguished from the digital shift valves by the larger electromagnet.
38
What mechanism returns the digital valve to its home position?
On the digital valve, the coil return spring brought the valve back to its 'home' position after each signal.
39
What type of springs does the analog valve use?
The analog valve has flat springs welded to the valve plunger instead of using a return spring.
40
How do flat springs differ from coil springs in the analog valve?
The flat springs have a different spring rate and length of travel than the coil spring.
41
What happens when the valve is in the OFF position?
When the valve is in the OFF position, the plunger allows the pilot oil (System 1) to go to sump through the orifice in the nozzle unrestricted.
42
How much pressure is placed on the spool valve to move it?
Very little pressure is placed on the spool valve to move it - same operation as a digital valve.
43
What happens when the spool valve returns to its home position?
It cuts off engagement oil to the element.
44
What occurs when the solenoid is de-energized?
The plunger retracts and allows engagement oil to be routed to sump.
45
What is the effect of the flat spring design and electromagnetic field on the plunger?
The plunger does not return to its 'home' position like the digital shift valve did with the OFF signal.
46
How does the plunger position affect the pilot orifice?
The plunger position in relation to the pilot orifice is variable, determining the amount of restriction.
47
What happens as the plunger is pushed closer to the pilot oil nozzle?
Restriction and pressure increase, causing the spool valve to shift.
48
What advantage does this mechanism provide?
It gives much better control of the position of the spool valve and the amount of oil flow to engage the clutches.
49
What change has occurred to obtain variable movement of the plunger?
The PWM signal from the PCU has changed.
50
How is the strength of the electromagnet determined?
The strength is determined by the amount of current flowing through it.
51
What can the PCU control regarding the PWM signal?
The PCU can control the frequency of the signal as well as the duty cycle.
52
What does the PCU do with the signal?
The PCU will adjust the signal and produce the programmed current flow as required.
53
What controls the Analog Shift Valve when engaged?
The PCU controls the Analog Shift Valve with variable frequency and duty cycle.
54
How is the spool valve moved? In an analog shift valve - engaged
The spool valve is moved by pressure built up in the pilot section.
55
What does the pressure in the pilot section allow?
It allows oil to flow to the elements for engagement.
56
What happens when the flat solenoid is energized?
The plunger extends to cut off the pilot oil's path to the sump.
57
What is Wake-up Pulse?
The shift valve gets a 'full-on' command to fill the clutch to 90% full.
## Footnote
This is from the calibrated values stored in the PCU.
58
What is Valve Setting?
The valve is off for a short time to reset itself.
59
What is Final Fill?
The remaining 10% of the clutch is filled, along with another 10% of the calibrated value applied.
## Footnote
The clutch is now capable of transferring power.
60
What is Modulation?
The clutch is full, transferring some power but slipping at a controlled rate.
## Footnote
The upward angle of the chart is controlled by the PCU based on the load that is being applied and sensed by the PCU.
61
What happens during the clutch exchange?
The clutch exchange takes place between the oncoming clutch and the off-going clutch for the gear being selected.
## Footnote
Timing for this exchange is controlled by the PCU.
62
What is Complete Engagement?
The clutch is fully engaged and the shift solenoid is at 100% duty cycle.
63
What changes have been made to the transmission hydraulic system?
Several changes have been made to provide more consistent shifting and improved operation.
64
What has been the leading factor in the design changes?
Consistent and improved shift quality has been the leading factor in these design changes.
65
What feature did early 8000 series below serial number 20,000 have?
They had blow-off ball valves inserted into the clutch drum, behind the piston.
66
What is the purpose of the blow-off ball valves in the transmission?
They protect the transmission from over-speeding and prevent the clutch from engaging due to centrifugal force of the oil.
67
What happens when the drum is over speeding?
The balls roll off their seat, allowing a variable amount of oil to leave the drum and air to enter.
68
What change occurred at serial number 20,000 regarding the ball valves?
The balls were replaced by dowel pins that sealed up the passage.
69
How were clutches prevented from engaging after serial number 20,000?
By using stronger return springs, which made it simpler and easier to control.
70
What changes were required for the increased force needed to engage the clutches?
Higher system pressure and a change in shift valve commands were required.
71
What significant change occurred with the production of the 8010 series?
The entire passage was eliminated from the clutch drums.
72
What were added to the 8000 series transmission rear cover at serial number 20,000?
External shift accumulators (black hoses) for B, C, and D clutches only.
73
What is the purpose of shift accumulators?
They help to stabilize the electrohydraulic shift valves and to improve shift consistency.
74
What replaced the external accumulators in the 8010 series for B and C clutches?
Internal shift accumulators located in the rear manifold.
75
What remains on the rear cover for the D clutch?
The external accumulator.
76
What are input shift accumulators?
Internal shift accumulators located in the rear cover added to clutches C1, C2, C3, and C4 with 8010 series changes.
77
What is the purpose of input shift accumulators?
They help to stabilize the shift valve and provide more consistent shifts.
78
Where are shift valves located?
Shift valves are located below the centrelines of the input shaft and countershaft.
79
What is the purpose of a High Sump?
High Sump allows more oil to stay behind the input clutch pistons to improve shift consistency.
80
When was the High Sump design added to the wheel tractor?
A high sump was added to the wheel tractor at serial number 20,000 and to all 8000T tractors as part of the transmission rear cover casting.
81
Why was the High Sump design implemented?
This was done to prevent too much oil from draining out of the input clutch passages, as a result of gravity.
82
How did oil drainage occur in previous models?
On previous models, oil from a disengaged input clutch drained through holes in the end of the shift valve and fell to sump.
83
Why is the location of the shift valves significant?
The location of the shift valves is below the input shaft so that gravity was forcing the oil out of the clutch.
84
What factors affect the amount of oil lost to sump?
The amount of oil that was lost to sump was dependent on the temperature of the oil as well as the time since the last engagement.
85
What is a key feature of the new high sump design?
The ends of all the input shift valves protrude into the high sump reservoir.
86
How does oil flow into the high sump reservoir?
Oil flowing from the disengaged clutch fills the reservoir through the shift valves.
87
What must happen to the oil from the full reservoir due to its location?
The oil must go above the shift valves to fall to the bottom of the transmission case.
88
What is the benefit of the high sump design regarding the clutch piston?
It leaves more oil behind the clutch piston and improves shift consistency.
89
What assumption can the PCU make before a shift begins?
The PCU can assume the oil passage is full before the shift begins.
90
What is installed in the output shaft passages of 8000 series tractors after serial number 20,000?
A one way check valve is installed in each output shaft passage that connects to BC, CC, and DC.
91
What happens when the clutch is disengaged?
Low pressure lube oil from the driveshaft coupler enters the check valves and fills the passages.
92
How does oil flow when the clutch is disengaged?
Oil flows through the passage, behind the clutch piston, and also through the shift valve.
93
What is the pressure of the oil when the clutch is disengaged?
The pressure is very low and does not put enough pressure on the clutch piston to engage it.
94
Where does the oil flow from the shift valve?
The oil flows to the sump.
95
What does the constant supply of oil help improve?
It helps to improve shift consistency.
96
How does the drilled passage behave with a check valve compared to a plug?
The drilled passage does not drain to the sump as it did when a plug was inserted instead of the check valve.
97
What can the PCU assume before beginning the shift?
The PCU can assume that the passage is full before beginning the shift.
98
What happens when the clutch engages?
When the clutch engages, the shift valve is turned on and system 2 pressure is directed to the clutch through the rear cover manifold, sealing rings, and output shaft passages.
99
How does system 2 pressure interact with the check valve?
System 2 pressure is greater than the lube oil pressure, which keeps the check valve closed and allows full system 2 pressure to engage the clutch.
100
What role does the pin in the check valve play?
The pin in the check valve acts as an orifice that controls oil flow, depending on oil viscosity.
101
What issue can arise with cold oil in output clutches?
The output clutch blow off balls cannot drain the oil out fast enough with cold oil, which might cause output clutches to self-engage.
102
How does the pin's orifice function with cold oil?
Since the pin acts as an orifice, very little oil can get to the clutch, eliminating the possibility of auto engagement of the clutches with cold oil.
103
What is the effect of warm oil conditions on the orifice?
Under warm oil conditions, the orifice has very little effect on the oil flow.
104
What series of tractors have mistake proof shift valves?
All 8010 series tractors have mistake proof shift valves.
105
What was changed on the input and output shift valves?
Land diameters were changed on each of the input and output shift valves to ensure that the valves could not be interchanged.
106
What should be noted about the o-rings for the shift valves?
The o-rings for the different sized lands are different from valve to valve.
107
What should you do when servicing the valve and replacing o-rings?
Be sure to order the correct o-ring when servicing the valve and replacing the o-rings.
108
What type of valves are used in the 8010 series tractors?
Valves are still the analog type as used in the later 8000 series tractors.
109
How many different analog valves are available?
Four different analog valves are now available.
## Footnote
Use caution.
110
What is the total number of test port locations for the 15 speed?
There are a total of eleven test port locations.
111
How many test port locations are there for the input clutches?
There are five test port locations for the input clutches C1 - C4 and CR.
112
How many test port locations are there for the output clutches?
There are four test port locations for the output clutches BC - DC and AB.
113
What type of pressure does the test port for park brake measure?
The test port measures park brake pressure.
114
What type of pressure does the test port for MFWD measure?
The test port measures MFWD pressure.
115
What is a DR in the context of the rear cover test port locations?
A DR is installed for system testing at all shift valve locations.
116
Where is the Diagnostic Receptacle (DR) located for testing lube pressure?
The DR is located on the upper left side of the oil cooler when seated in the cab.
117
What is the purpose of the DR located on the upper left side of the oil cooler?
It is used to test lube pressure and to help determine pressure differential across the oil cooler.
118
Where is the second location for a DR to test pressure differential across the oil cooler?
A test port is located on the bottom side of the cooler inlet area on the lower right of the transmission rear cover.
119
What does the technical manual contain regarding the DR?
The technical manual contains a complete description to perform all required test procedures.
