TRANSMISSION OF 797B TRUCK.
Transmission
Power from the transmission flows through the differential and is divided
equally to the final drives in the rear wheels. The transmission is electronically controlled and hydraulically operated. The transmission and Chassis ECMs receive inputs from various sensors and switches. The ECMs analyze the inputs and the Transmission ECM energizes the solenoids that control the flow of oil to the transmission clutches.
The transmission is a power shift planetary design which contains seven hydraulically engaged clutches. The transmission provides seven FORWARD speeds and one REVERSE speed. The transmission control filter (1) is mounted on the front transmission case. The transmission lubrication valve (2) is mounted on the rear
transmission case.
Transmission input shaft.
Shown are the two modules of the 797B transmission. Power flows from the torque converter through the input shaft (1) into the transmission front module (2). Clutches 1, 2, and 3 are in the front module.
The transmission rear module (3) sits on top of the front module.
Clutches 4, 5, 6, and 7 are in the rear module. Power flows from the front module through the rear module and the output shaft (4) to the differential.
Transmission front module.
Shown is the 797B transmission front module. Clutch No. 1 (1) is a rotating clutch. Clutch No. 2 (2) and clutch No. 3 (3) are located above clutch No. 1. Supply oil from the electronically controlled clutch valves flows through port (4) to clutch No. 1, port (5) to clutch No. 2 and port (6) to clutch No. 3.
Lubrication oil flows from the lube valve located on the rear transmission
case , through an orifice and the port (7) to the transmission front module. The lubrication oil is used to cool and lubricate all of the gears, bearings, and clutches in the transmission front module.
The intermediate speed sensor (8) is located on the front module. The intermediate speed sensor is used for transmission development purposes only. This information is not used by VIMS for clutch slippage calculations. The intermediate speed sensor can be accessed through a cover plate on the transmission case.
Transmission rear Module.
Shown is the 797B transmission rear module. Lubrication oil flows from the lubrication valve located on the rear transmission case, through the port (1) to the REVERSE drive train bearings and clutches No. 4 and 5 and their bearings. Lube oil flows through the port (2) to clutches No. 6 and No. 7.
Supply oil from the electronically controlled clutch valves flows through manifold (3) to the four clutches in the rear module. Clutch No. 4 (4) is a rotating clutch. Clutch No. 5 (5), clutch No. 6 (6), and clutch No. 7 (7) are located above clutch No. 4.
797B transmission.
Shown is the 797B transmission. Oil flows from the transmission control pump , through the port (1) to the transmission control filter (2). Oil flows through the control filter to the transmission control valves. When the control valve solenoids are energized by the
Transmission ECM, oil flows to the transmission clutches. Oil also flows from the top of the transmission control filter to the torque converter lockup valve. Transmission control oil is used to engage the lockup clutch and provide DIRECT DRIVE.
After the clutches are engaged, most of the transmission control oil flows out a port on the right front side of the transmission case to the torque converter inlet relief valve. Transmission control oil joins with the torque converter charging oil and is used by the torque converter to provide a fluid coupling.
Oil flows from the transmission lube pump , through the port (3) to the transmission lube manifold and differential valve (4). Oil flows through the lube valve to the rear transmission module and through the port (5) to the front transmission module. The lubrication oil is used to cool and lubricate all of the gears, bearings, and clutches in the
transmission modules. Transmission control and lubrication oil that falls to the bottom of the transmission case is scavenged from the case through two magnetic screens located in the housing (6). The scavenged oil returns to the torque converter housing through a diffuser .
Transmission control pressure unfiltered.
Located on top of the transmission control filter are two pressure taps.
The left pressure tap (1) can be used to measure the unfiltered transmission control pressure. The right pressure tap (2) can be used to measure the filtered transmission control pressure. Together, these two taps can be used to calculate the oil filter restriction.
Transmission control pressure should be measured with the oil temperature at 80°C (175°F). In NEUTRAL with 30 weight TDTO oil at 80°C (175°F) the transmission control pressure should be:
* LOW IDLE--2340 ± 275 kPa (340 ± 40 psi)
* HIGH IDLE--2585 ± 170 (375 ± 25 psi)
Transmission oil samples can be taken at the Scheduled Oil Sampling (S•O•S) tap (3) located in the top center of the filter housing. An oil filter bypass valve (4) is located on the transmission control filter.
The bypass valve will open to provide flow to the transmission control system if the filter is restricted. An oil filter bypass switch (5) is also located on the filter housing. The
bypass switch provides an input signal to the Transmission ECM. The Transmission ECM sends the signal to the VIMS, which informs the operator if the filter is restricted.
Transmission lube pressure for the front transmission module can be measured at the tap (6). Transmission lube pressure should be measured with the oil temperature at 80°C (175°F). In NEUTRAL with 30 weight TDTO oil at 80°C (175°F) the front transmission module lube pressure should be:
* LOW IDLE: 55 to 96 kPa (8 to 14 psi)
* HIGH IDLE: 380 to 550 kPa (55 to 80 psi).
Transmission lube valve.
Oil flows from the transmission lube pump into the bottom of the transmission lube valve. Some of the lube oil flows to the front transmission module through the hose (1) and the remaining lube oil enters the rear transmission module. A transmission lube supply pressure sensor (2) and a transmission oil temperature sensor (3) are located in the lube valve manifold. The sensors provide input signals to the
Transmission ECM.
The Transmission ECM sends the signals to the VIMS, which informs the operator of the transmission lube supply pressure and the transmission oil temperature.
A transmission lube relief valve is installed in the lube valve manifold.
The setting of the relief valve is 618 ± 35 kPa (90 ± 5 psi). Lube supply pressure is measured at the tap (4). Clutch 6 and 7 lube pressure can be measured at the tap (5) located on the bottom rear of the lube valve.
Normally, the pressures measured will be less than the relief valve setting.
The pressures measured will be equal to the back-pressure caused by the transmission components being lubricated. Lube pressures should be measured in NEUTRAL with the oil temperature at 80°C (175°F).
Lube supply pressure (at tap 4) should be:
* LOW IDLE--between 105 ± 35 kPa (15 ± 5 psi)
* HIGH IDLE--between 480 ± 100 kPa (70 ± 15 psi)
Clutch 6 and 7 lube pressure (at tap 5) should be:
* LOW IDLE--62 ± 14 kPa (9 ± 2 psi)
* HIGH IDLE--345 ± 70 kPa (50 ± 10 psi).
Lube manifold
Shown is a sectional view of the transmission lube manifold and the mounting plate. The transmission lube relief valve is installed in the lube valve manifold. The manifold is fastened to the mounting plate.
Oil flows from the transmission lube pump into the bottom of the transmission lube valve. The lube relief valve controls the maximum
pressure in the lube circuit. An orifice controls the amount of lube flow to clutches 4 and 5 and gear trains 4, 5, and 6.
Transmission control pack.
Shown is the transmission control pack. Transmission control oil flows from the transmission control pump (see Visual No. 1), through the transmission control filter and the inlet tube (1), to the transmission main relief valve. The transmission main relief valve can be adjusted with a screw located behind the cover (2).
Transmission control pressure should be measured with the oil temperature at 80°C (175°F). In NEUTRAL with 30 weight TDTO oil at 80°C (175°F) the transmission control pressure should be:
* LOW IDLE--2340 ± 275 kPa (340 ± 40 psi)
* HIGH IDLE--2585 ± 170 (375 ± 25 psi)
The control oil is used to shift the transmission and fill the clutches.
Some of the control oil drops to the bottom of the housing to be scavenged, but most of the oil flows to the torque converter through the outlet tube (3) to provide charging oil for the torque converter. Oil flows through the tubes (4) to the clutches in the rear transmission module. From left to right, the tubes supply oil to clutches 7, 4, 5, and 6.
The Transmission ECM energizes seven clutch supply valve solenoids (5) and a latching solenoid (6) to control the clutch engagement of the 797B transmission.
The clutch supply valves provide oil to the following clutches:
Top row, left to right--clutches 7, 4, 5, and 6
Bottom row, left to right--clutches 1, 3, and 2
There are two sizes of clutch supply valves. Clutches 1 and 2 do not require as much flow to fill with oil, therefore they use the smaller valves.
The clutch supply valves all operate the same. There is a latching valve located below each clutch supply valve.
The latching valve consists of a shuttle spool, an orifice, and a spring type accumulator. The latching valves are used to keep the transmission in the current gear if there is a loss of electrical power to the Transmission ECM or a clutch valve solenoid. The lockup solenoid will also be de-energized if the transmission latches in a gear.
The latching solenoid is normally energized and controls the pilot drain of the clutch supply valves. The latching system will be discussed in more detail on the following pages.
797B transmission control valve.
Shown is the 797B transmission control valve removed from the transmission case. The components that make up the transmission control valve are:
1. Transmission main relief valve
2. Seven transmission clutch supply valves
3. Latching solenoid (normally energized)
4. Six latching valves (Reverse clutch No. 7 does not have a latching valve)
Transmission main relief valve.
Oil pressure moves the slug in the left end of the spool to the left and the spool moves to the right against the spring force. The slug
reduces the effective area on which the oil pressure can push. Because of the reduced effective area, a smaller, more sensitive spring can be used. Relief pressure will be equal to the force of the spring on the right end of the spool. The spring force can be adjusted with the adjustment screw.
Clutch engagement.
The latching solenoid valve is energized by the Transmission ECM allowing supply pressure to flow to the left side of the shuttle spool in the latching valve. The supply pressure in combination with a bias spring prevents the shuttle spool from blocking the pilot drain from the clutch supply valve. When a clutch supply valve solenoid is energized, supply oil flows to the clutch and through an orifice to the accumulator.
The accumulator becomes fully stroked at 1550 kPa (225 psi) clutch pressure.
Clutch pressure also builds up on the right side of the shuttle spool, but it will not move the spool because it is unable to overcome the supply pressure and bias spring combination.
Clutch latching
If the Transmission ECM detects clutch supply solenoid or latching valve solenoid faults (short to ground, short to battery, or open circuit), the latching solenoid is de-energized. When the latching solenoid is deenergized, the transmission is immediately latched (held) in the current gear. When electrical power is lost to both the latching solenoid and the clutch supply valves, the control port pressure to the clutch pistons decays.
An accumulator and an orifice are provided for each clutch to slow the clutch accumulator decay so that the shuttle spool in the latching valve shifts to the latch position before an engaged clutch is released. If current to the clutch supply valves or the latching solenoid valve is lost due to an electrical system failure, the pump pressure in the shuttle spool spring cavity is vented to tank through the latching solenoid.
Accumulator pressure moves the shuttle spool against the bias spring and blocks the pilot drain from the clutch supply valve. Pump supply pressure then flows past the latching valve shuttle spool and enters the pilot chamber of the clutch supply valve. The clutch supply valve spool moves all the way to the right causing clutch pressure to be the same as pump pressure.
Transmission main relief pressure tap
Shown is the top of the 797B transmission case. Transmission main relief pressure can be measured at the pressure tap (1). Latching pressure can be measured at the latching pressure tap (2). The latching pressure sensor (3) provides an input signal to the Transmission ECM. The
Transmission ECM uses the latching pressure sensor input to determine if the transmission is in the latched or unlatched mode. The pressure for clutch No. 7 can be measured at the pressure tap (4). To the right of the clutch No. 7 tap are the pressure taps for clutches No. 4, 5, and 6.
The pressure for clutch No. 1 can be measured at the pressure tap (5). To the right of the clutch No. 1 tap are the pressure taps for clutches No. 3 and 2.
797B transmission specifications.
Shown are the specifications for the 797B transmission. Seven clutches provide one REVERSE speed and seven FORWARD speeds. REVERSE is CONVERTER DRIVE only. FIRST GEAR is CONVERTER DRIVE below 4 mph and DIRECT DRIVE above 4 mph. The transmission clutch pressures must be calibrated using a laptop computer with the Electronic
Technician (ET) software installed. The calibration procedure is performed to compensate for variations in the transmission control components and connected transmission components (pumps, seal leakage, etc).
The transmission can be damaged within 20 seconds if the engine is run and no clutches are engaged in the transmission. When no clutches are engaged, the planetary can rotate up to 10,000 rpm. This can occur at start-up if there are any of the following active faults:
* invalid shift command - latch solenoid fault
* latch sensor fault - low latching pressure
NOTE: Be sure to stop the engine immediately if there is ever a No
Clutch Neutral warning.
Calibration is required in a variety of situations:
* Before dealer delivery to the customer
* After replacing or servicing any of the transmission clutch valves
* After replacing or servicing the Transmission ECM
* After flashing in new transmission software
* After replacing or servicing any of the transmission clutches, seals,pumps, etc. that would change the flow rate delivered to the controls
The Transmission ECM must detect the following conditions before starting the calibration procedure:
1. Parking brakes are ENGAGED
2. Service brakes and retarder are RELEASED
3. Gear selector is in NEUTRAL
4. Transmission oil temperature is above 80°C (176°F) to start calibration
5. Transmission oil temperature is between 70°C (158°F) to 10°C (230°F) during
calibration
6. Transmission Output Speed (TOS) is 0 rpm
7. No clutch solenoid electrical faults such as open circuit, short to ground, or short
to battery
8. No transmission speed sensor faults
9. No transmission/TC temperature sensor faults
10. Engine speed is 1300 ± 50 rpm
If any of these conditions are not met during the calibration, the procedure is aborted immediately, all clutches are disengaged, and the calibration values for the clutch being calibrated are lost.
The sustain pressure calibration requires pressure gauges to measure the actual pressure in the clutch. The Data View diagnostic tool should be used if possible. Ideally, all eight pressure gauges should be installed before the calibration procedure begins. The eighth gauge is for the torque converter lockup clutch pressure. The pressure taps are located on the torque converter and the transmission control cover (see Visuals No. 9 and 24).
The transmission and lockup clutch pressures are calibrated using a laptop computer with the ET software installed. Select the CALIBRATION option from the pull-down menu and follow the instructions provided. ET will provide the technician a means of increasing or decreasing the individual clutch pressures while viewing the pressure on the gauge.
Other calibrations:
Fill calibration--Fill calibration is performed to optimize shift quality.
Two parameters are adjusted during fill calibration: pulse time and hold
level. The hold level is calibrated first, followed by the pulse time. The
fill calibration for each clutch is completed before the next clutch begins.
During fill calibration, the system software needs to detect the End Of Fill
(EOF) for the clutch. End of fill is detected using a drop in converter output speed, as well as a drop in the relative clutch (slip) speed. To effectively detect a drop in converter output speed, a load must be applied to the transmission. This is accomplished by engaging one or more of the clutches not being calibrated.
Hold level calibration determines the pressure at which the clutch piston touches up to the clutch pack. One at a time, each clutch command is pulsed and held at the minimum allowable hold level pressure for a specific duration of time. After approximately a 3.0 second pause, the next clutch is pulsed, held, and released. This is repeated until all the
clutches have been cycled. Hold level pressure is incremented and the cycle repeats. A clutch's hold level pressure is calibrated when an end of fill is detected during the specified hold time (the corresponding hold level pressure is the calibrated value).
Once a clutch is calibrated, it is taken out of the cycle and a 3.0 second delay is inserted. The delay allows for complete drainage of the clutches still cycling. This process continues until hold level pressure reaches its maximum allowable value,
or all of the clutches have been calibrated. If the hold level pressure for any single clutch exceeds its maximum value or the clutch fills quicker than the allowed envelope when the hold level pressure is set at its minimum value, a warning is displayed.
Fill time is calibrated by adjusting one parameter; the pulse time. The ramp levels for each clutch are set to their default values. Each clutch command is pulsed, ramped, and held at the calibrated hold level pressure until the end of fill is detected or 1.0 second, whichever comes first while holding the appropriate clutch. The actual fill time is compared to the target fill time. The pulse time is increased/decreased to shorten/lengthen the fill time based on the difference between actual and target fill time.
After a 3.0 second pause,the clutch is filled again with the new pulse time.
This procedure is repeated many times. At the end of the last cycle, the calibrated pulse time values are set. If pulse time is smaller than or larger than allowed, a warning is displayed. The procedure is repeated for all clutches.
797B power train hydraulic schematic
Shown is the 797B power train hydraulic schematic. Supply oil is pulled from the torque converter housing through a magnetic screen and three ports in a suction log at the bottom of the torque converter.
Oil flows from the torque converter charging pump through the torque converter charging filter to the torque converter inlet relief valve. Transmission control oil joins with the torque converter charging oil at the inlet relief valve. The charging oil flows through the torque converter, the outlet relief valve, the torque converter outlet screen, and the power train oil coolers. The oil flows through the coolers and returns to the torque
converter housing.
Oil flows from the transmission lube pump to the transmission lube manifold. Oil flows through the lube valve to the rear transmission module and to the front transmission module. The lubrication oil is used to cool and lubricate all of the gears, bearings, and clutches in the transmission modules.
Oil flows from the transmission control pump to the transmission control filter. Oil flows through the control filter to the transmission control valves. When the control valve solenoids are energized by the Transmission ECM, oil flows to the transmission clutches.
Oil also flows from the top of the transmission control filter to the torque converter lockup valve. Transmission control oil is used to engage the lockup clutch and provide DIRECT DRIVE.
Transmission control and lubrication oil that falls to the bottom of the transmission case is scavenged from the case through two magnetic screens by the transmission scavenge pump. The scavenged oil returns to the torque converter housing through a diffuser .
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TRANSMISSION OF 797B TRUCK
Reviewed by heri
on
9:56 PM
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Reviewed by heri
on
9:56 PM
Rating:
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