966K Wheel Loader and 972K Wheel Loader Power train Caterpillar

Transmission Hydraulic Control Operation

Usage:

966K PBG

Starting the Engine with the Transmission in the NEUTRAL position

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Illustration 1	g03254478
Transmission hydraulic control in the NEUTRAL position and with the engine running. (1) Transmission hydraulic control relief valve (2) Torque converter (3) Torque converter outlet relief valve (if equipped) (4) Transmission oil filter (5) Modulating valve for the Number 1 clutch (6) Modulating valve for the Number 4 clutch (7) Modulating valve for the Number 2 clutch (8) Modulating valve for the Number 5 clutch (9) Modulating valve for the Number 3 clutch (10) Modulating valve for the Number 6 clutch (11) Transmission oil pump (12) Torque converter inlet relief valve (13) Suction screen and magnet (14) Oil sump (15) Transmission lubrication (16) Oil cooler (A) Pump pressure tap at the transmission hydraulic control relief valve (B) P3 Torque converter inlet pressure tap (C) Torque converter outlet pressure tap (D) Pump pressure tap at the oil filter (G) Number 1 clutch pressure tap (H) Number 4 clutch pressure tap (J) Number 2 clutch pressure tap (K) Number 5 clutch pressure tap (L) Number 3 clutch pressure tap (M) Number 6 clutch pressure tap (N) Transmission lubrication pressure tap (AA) Pressure oil (BB) P3 Torque Converter inlet pressure (CC) Torque converter outlet pressure (DD) Lubrication pressure (EE) Return oil

When the engine is started, the transmission oil pump (11) pulls oil from oil sump (14) . The oil flows through the suction screen and magnet (13) . Transmission oil pump (11) sends pressurized oil through transmission oil filter (4) . Pressurized transmission oil flows from the transmission oil filter to the oil inlet in the torque converter housing. The pressurized oil flows through internal passages in the torque converter housing in order to supply transmission hydraulic control relief valve (1) with oil. The pressurized oil also flows through internal passages in the transmission housing. The pressurized oil flows out of the internal passages in the transmission housing into modulating valves (5-10) . Number 3 clutch solenoid (9) is energized because the transmission is in neutral. None of the remaining modulating valves (5) , (6) , (7) , (8) and (10) provide oil to the transmission clutches. The pressurized oil leakage drains to oil sump (14) .

The transmission hydraulic control relief valve (1) sends P3 converter inlet oil to torque converter (2) . Torque converter outlet oil flows to oil cooler (16) . After the oil cools, the oil flows to the transmission for transmission lubrication (15) . After the transmission is lubricated and cooled, the oil drains to the oil sump (14) .

Torque converter inlet relief valve (12) limits P3 torque converter inlet oil pressure to a maximum of 900 ± 70 kPa (130 ± 10 psi). Torque converter inlet relief valve (12) is located in the torque converter housing. Transmission hydraulic control relief valve (1) must be removed in order to attain access to torque converter inlet relief valve (12) .

Shifting the Transmission to the FIRST SPEED FORWARD position

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Illustration 2	g03255057
Transmission hydraulic control in the FIRST SPEED FORWARD position and with the engine running. (1) Transmission hydraulic control relief valve (2) Torque converter (3) Torque converter outlet relief valve (if equipped) (4) Transmission oil filter (5) Modulating valve for the Number 1 clutch (6) Modulating valve for the Number 4 clutch (7) Modulating valve for the Number 2 clutch (8) Modulating valve for the Number 5 clutch (9) Modulating valve for the Number 3 clutch (10) Modulating valve for the Number 6 clutch (11) Transmission oil pump (12) Torque converter inlet relief valve (13) Suction screen and magnet (14) Oil sump (15) Transmission lubrication (16) Oil cooler (A) Pump pressure tap at the transmission hydraulic control relief valve (B) P3 Torque converter inlet pressure tap (C) Torque converter outlet pressure tap (D) Pump pressure tap at the oil filter (G) Number 1 clutch pressure tap (H) Number 4 clutch pressure tap (J) Number 2 clutch pressure tap (K) Number 5 clutch pressure tap (L) Number 3 clutch pressure tap (M) Number 6 clutch pressure tap (N) Transmission lubrication pressure tap (AA) Pressure oil (BB) P3 Torque Converter inlet pressure (CC) Torque converter outlet pressure (DD) Lubrication pressure (EE) Return oil

The power train electronic control module (ECM) modulates the electrical current that is sent to the selected modulating valves. Modulating the current to the modulating valve controls the transmission clutch pressure.

When the transmission direction and speed control lever (if equipped) is moved to the FIRST SPEED FORWARD position, both Number 2 clutch solenoid (7) and Number 6 clutch solenoid (10) are energized. When the transmission direction control switch (if equipped) and the transmission upshift switch are shifted to the FIRST SPEED FORWARD position, both Number 2 clutch solenoid (7) and Number 6 clutch solenoid (10) are energized.

Number 2 clutch solenoid (7) is electronically modulated when the Number 2 clutch is filled. Number 6 clutch solenoid (10) is electronically modulated when the Number 6 clutch is filled. When the electrical current is modulated to the full current, the Number 6 clutch and the Number 2 clutch are at full oil pressure.

Modulating valves (5) , (6) , (8) , and (9) are not energized. The leakage oil drains to oil sump (14) .

Transmission in the FOURTH SPEED REVERSE position

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Illustration 3	g03255078

When the transmission direction and speed control lever (if equipped) is moved to the FOURTH SPEED REVERSE position, both Number 1 clutch solenoid (5) and Number 3 clutch solenoid (9) are energized. When the transmission direction control switch (if equipped) and the transmission upshift switch is shifted to the FOURTH SPEED REVERSE position, both Number 1 clutch solenoid (5) and Number 3 clutch solenoid (9) are energized.

Number 1 clutch solenoid (5) is electronically modulated when the Number 1 clutch is filled. Number 3 clutch solenoid (9) is electronically modulated when the Number 3 clutch is filled. When the electrical current is modulated to the full current, the Number 3 clutch and the Number 1 clutch are at full oil pressure.

Modulating valves (6) , (7) , (8) , and (10) are not energized. The leakage oil drains to oil sump (14) .

Single Clutch Speed Shifting

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Illustration 4	g02825938
Conventional speed shift logic

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Illustration 5	g02825956
Single clutch speed shift logic (A) Clutch pressure (B) Time (1) On-coming speed clutch (2) Off-going speed clutch (3) Directional clutch

Three clutches are involved during a conventional speed shift: The on-coming speed clutch (1) , the off-going speed clutch (2) and and the directional clutch (3) . Illustration 4 shows the ECM signals to the three modulation solenoid valves.

When conventional speed shift is initiated, the ECM sends full current to the on-coming speed clutch solenoid for a set time. After the set time, the ECM reduces the current and goes through a ramp and hold times. When the ramp and hold times are completed, the ECM begins to increase the current (modulation). The ECM modulation rate is controlled by a closed loop control system. After modulation the ECM increases current to the "full on level". Following a predetermined period, the ECM decreases current to the "hold on level".

The ECM maintains the "hold on level" current to the off-going speed clutch solenoid for a set amount of time during the speed shift. The ECM then gradually decreases the current (ramp down) to zero.

The ECM also maintains the "full on level" current to the directional clutch solenoid for a set amount of time during the speed shift. The ECM then decreases the current to the "hold Level" until the oncoming speed clutch completes the modulation cycle. When the oncoming speed clutch solenoid modulation cycle is completed, the ECM begins to modulate (gradually increase) the current to the directional clutch. The modulation rate is controlled by a closed loop system in the ECM. After modulation, the ECM increases the current to the "full on level". The speed shift is complete. The ECM maintains the current at the "full on level" to the directional clutch solenoid.

Two clutches are involved during a conventional speed shift: The on-coming speed clutch (1) and the off-going speed clutch (2) . Illustration 5 shows the ECM signals to the two modulation solenoid valves.

When a single clutch speed shift is initiated, the ECM sends full current to the on-coming speed clutch solenoid for a set time. After the set time, the ECM reduces the current and goes through the ramp and hold times. When the ramp and holds times are completed, the ECM begins to increase the current (modulation). The ECM modulation rate is controlled by a closed loop control system. After modulation, the ECM increases current to the "full on level". Following a predetermined period, the ECM decreases current to the "hold on level".

The ECM maintains the "hold on level" current to the off-going speed clutch solenoid for a set amount for time during the single clutch speed shift. The ECM then gradually decreases the current (ramp down) to zero.

The ECM maintains the current at the "full on level" to the solenoid for directional clutch (3) during a single clutch speed shift.

The benefits from a single clutch speed shift include: