14H and 16H Motor Graders Power Train Transmission Control Valve Caterpillar


Transmission Control Valve
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14H and 16H Motor Graders Power Train [RENR4174]
POWER TRAIN
CONTROL GP-TRANSMISSION HYD
14H and 16H Motor Graders Power Train Transmission Lubrication Oil Pressure - Test
14H and 16H Motor Graders Power Train Transmission Control Valve



Illustration 1g00929713

Transmission Hydraulic Controls

(1) Oil filter

(2) No. 1 clutch lubrication passage

(3) No. 2 clutch lubrication passage

(4) Main relief valve

(5) Oil cooler

(6) Housing for transfer gears

(7) Oil pump

(8) Planetary transmission

(9) Differential lock valve

(10) Selector and pressure control valve

(11) Transmission oil reservoir

(12) Main oil reservoir in the intermediate housing

(13) Oil reservoir (differential and bevel gear)

The basic parts of the transmission system are the following components.

  • transmission oil reservoir (11)

  • main oil reservoir (12)

  • oil reservoir for the differential and bevel gear (13)

  • oil pump (7)

  • oil filter (1)

  • main relief valve (4)

  • selector and pressure control valve (10)

  • differential lock valve (9)

The basic hydraulic controls in the system are the main relief valve (4), the selector and pressure control valve (10) and the differential lock valve (9) .

The selector and pressure control valve (10) is located inside the transmission housing. Selector and pressure control valve (10) sends pressure oil to the proper clutches for the speed that has been selected. The transmission has eight forward speeds and eight reverse speeds.

The main relief valve (4) is used to control the pressure in the hydraulic system. The main relief valve (4) is located on the outside housing of the transmission.

The differential lock valve (9) is used to control the lockup clutch in the differential. The differential lock valve (9) is located on the outside housing of the transmission.

Transmission Valves

Table 1 provides a list of valves and the function of the valves that are used by the transmission controls.

Table 1
Transmission Valves    
Valve     Function    
Differential lock valve (9)     Control the operation of the differential lock clutch.    
Manual modulation spool (14)     The manual modulation spool allows operator control of the direction clutch pressures.    
Differential, check and relief spool (15)     The valve spool controls the pressure between the speed clutches and the direction clutches.
The valve spool opens a return passage in order to release the pressure from the left side of the load piston during a shift.
The valve spool keeps oil from going to the direction clutches if the machine is started in any speed except neutral.    
Pilot selector valve (16)     The valve sends signal pressure to the two speed selector valves that are needed for the selection of a specific speed.    
Two-position speed selector valve (17)     The valve sends pressure oil to No. 4 clutch or to the transmission reservoir.    
Two-position speed selector valve (18)     The valve sends pressure oil to No. 5 clutch or to the transmission reservoir.    
Relief Valve (19)     The relief valve keeps the maximum pressure in the system at 2861 ± 35 kPa (415 ± 5 psi).    
Oil cooler bypass valve (22)     The oil cooler bypass valve keeps the pressure in the oil cooler below a maximum of
1230 kPa (179 psi).
Note: The pressure can go to approximately
1380 kPa (200 psi) when the transmission is in Neutral and the oil is cold.    
Lubrication relief valve (23)     The valve keeps the pressure of oil for lubrication at
614 ± 69 kPa (89 ± 10 psi).    
Priority reducing valve (26)     The valve sends signal pressure to the pilot selector valve. After a signal pressure of
682 ± 69 kPa (96 ± 10 psi) is reached, pressure oil is then sent to the system.    
Modulating reducing valve (27) and load piston (29)     The valve controls the pressure increase in the direction clutches and in the speed clutches in order to gradually engage the clutches.    
Two-position speed selector spool (34)     The spool sends pressure oil to No. 6 clutch or to the transmission reservoir.    
Two-position speed selector spool (33)     The spool sends pressure oil to No. 3 clutch or to the transmission reservoir.    
Three-position speed selector spool (32)     The spool controls the pressure oil to No. 7 clutch or No. 8 clutch.    

Transmission Control (Lever) in the NEUTRAL Position with the Engine Off




Illustration 2g00930088

Hydraulic controls with the engine off and the transmission control lever in the NEUTRAL position

(14) Manual modulation spool

(16) Pilot selector valve

(17) Speed selector spool (No. 4 clutch)

(18) Speed selector spool (No. 5 clutch)

(19) Relief valve

(22) Oil cooler bypass valve

(23) Lubrication relief valve

(24) Passage to differential lock clutch

(25) Direction selector spool

(29) Load piston

(32) Speed selector spool ( No. 7 and No. 8 clutches)

(33) Speed selector spool (No. 3 clutch)

(34) Speed selector spool (No. 6 clutch)

When the engine is off, the pump will not be turned and there is no oil in the system. The following two-position selector spools are held against stops by spring force: spool (17), spool (18), spool (33) and spool (34). Load piston (29) is also held by spring force. The three-position selector spool (32) is held in the center position by spring force.

The transmission control valve has three spools that are manually operated. The following spools are manually operated spools: pilot selector valve (16), direction selector spool (25) and manual modulation spool (14). All the other spools are operated by pilot pressure oil. Pilot selector valve (16) sends pilot oil to the speed selector spools. The speed selector spools send oil to the speed clutches. Direction selector spool (25) sends oil to the direction clutches. Manual modulation spool (14) controls the oil pressure to the direction clutches.

The main relief valve contains the following valves: relief valve (19), oil cooler bypass valve (22) and lubrication relief valve (23). Relief valve (19) protects the system from excessive pressure. The oil cooler bypass valve (22) protects the oil cooler from excessive pressure. The lubrication relief valve (23) protects the lube circuit from excessive pressures.

Transmission Control (Lever) in the NEUTRAL Position and the Engine On




Illustration 3g00930089

Hydraulic controls with the engine on and the transmission control lever in the NEUTRAL position

(4) Main relief valve

(5) Oil cooler

(15) Differential, check and relief spool

(16) Pilot selector valve

(19) Relief valve

(22) Oil cooler bypass valve

(26) Priority reducing valve

(27) Modulating reducing valve

(32) Speed selector spool ( No. 7 and No. 8 clutches)

(33) Speed selector spool (No. 3 clutch)

(35) Passage to No. 8 clutch

(37) Passage to No. 3 clutch

(38) Passage for signal pressure

(42) Passage for signal pressure

When the engine is running and the transmission control lever is in the NEUTRAL position, oil from the pump goes to the main relief valve (4). Oil then flows around relief valve (19) to the selector and pressure control valve. Relief valve (19) allows some oil to go to cooler (5). Oil from the cooler flows behind oil cooler bypass valve (22) and into a cavity for lubrication.

At the selector and pressure control valve, the flow of oil divides into two separate circuits. The flow divides into the signal pressure circuit and the system pressure circuit.

Signal Pressure Circuit

At engine start-up, spring force holds priority reducing valve (26). Priority reducing valve (26) allows the signal pressure passage to the pilot selector valve (16) to receive oil first. When the pressure of the oil that is acting on valve (26) becomes greater than the force of the spring that is acting on valve (26), the valve moves to the right. When valve (26) moves to the right, the valve opens the system pressure passage. When the pressure has reached 682 ± 69 kPa (99 ± 10 psi) and the valve has moved to the right, no oil will flow to the pilot selector valve.

Pilot selector valve (16) has nine positions. When the transmission direction and speed control lever is in the NEUTRAL position, pilot selector valve (16) sends signal pressure to passage (38) and to passage (42) .

The signal pressure circuit controls the movement of the speed selector spools. The signal pressure in passage (38) and in passage (42) moves spool (32) to the left. The signal pressure in passage (38) and in passage (42) also moves speed selector spool (33) to the right.

System Pressure Circuit

As the pressure reaches 682 ± 69 kPa (99 ± 10 psi) in the signal pressure circuit, priority reducing valve (26) opens the passage to modulating reducing valve (27). The system pressure moves modulating reducing valve (27) to the left until speed clutch pressure is at 682 ± 69 kPa (99 ± 10 psi). Pilot pressure holds spool (32) and spool (33). Oil will flow into passage (35) and into passage (37) .

Speed selector spool (32) is held in position by signal pressure in passage (38). A passage is opened by speed selector spool (32). The open passage allows oil on the left end of spool (15) to go to the reservoir. Spool (15) can not move to the right. Since spool (15) is not able to move right, the direction clutches receive no oil.

If the engine is started in any speed except neutral, system pressure is sent from spool (32) through the orifices in spool (15) to the spring side of spool (15). The valve is held against the stop. The direction clutches will get no oil flow. When the transmission control lever is moved to NEUTRAL position, the oil in the spring side of the valve is free to go to the transmission reservoir. The oil pressure on the left side of the valve works against the spring force and spool (15) moves to the NEUTRAL position. In the NEUTRAL position, the direction clutches have no oil and the direction clutches will not engage.

Transmission Control (Lever) in the FIRST GEAR FORWARD Position and the Engine On




Illustration 4g00930091

Hydraulic controls with the engine on and the transmission control lever in the FIRST GEAR FORWARD position

(15) Differential, check and relief spool

(16) Pilot selector valve

(25) Direction selector spool

(27) Modulating reducing valve

(28) Passage to No. 7 clutch piston

(29) Load piston

(30) Passage to No. 1 clutch (forward)

(32) Speed selector spool (No. 7 and No. 8 clutches)

(33) Speed selector spool (No. 3 clutch)

(34) Speed selector spool (No. 6 clutch)

(35) Passage to No. 8 clutch

(36) Passage to No. 6 clutch

(37) Passage to No. 3 clutch

(38) Passage for signal pressure

(39) Passage for signal pressure

(40) Passage for signal pressure

(42) Passage for signal pressure

When the transmission control (lever) is shifted into the FIRST GEAR FORWARD position, pilot selector valve (16) allows signal oil in passage (38) and in passage (42) to flow into the reservoir. The pilot selector valve (16) allows signal oil into passage (39) and into passage (40) .

When the signal pressure in passage (42) goes to the reservoir, the spring force on speed selector spool (33) moves the spool to the left. The oil in the passage for No. 3 clutch (37) flows to the reservoir. The signal pressure in passage (39) moves speed selector spool (32) to the right. Oil in the passage for the speed selector spool for No. 8 clutch (35) flows to the reservoir. The No. 3 clutch and the No. 8 clutch will not be engaged.

Speed selector spool (32) and speed selector spool (34) are moved by signal pressure in passage (39) and in passage (40). The passages to No. 7 clutch (28) and to No. 6 clutch (36) are open to system pressure.

Oil shifts spool (15) to the right. Spool (15) allows oil to flow to the direction clutches. Direction selector spool (25) will allow flow into passage (30) for the No. 1 clutch.

When the transmission control lever is moved from the NEUTRAL position to the FIRST GEAR FORWARD position, No. 6 and No. 7 clutches start to fill with oil. As the clutches fill the system pressure has an increase in pressure. The increase in pressure in the slug chamber moves modulating reducing valve (27) to the left. The pressure increase to the clutches stops. As the pressure against load piston (29) raises, the load piston moves to the right. The spring force between the modulating reducing valve and the load piston increases. The increase in spring force moves the modulating reducing valve to the right and the clutch pressure increases. The cycle repeats until the system pressure is at the maximum. The cycle of gradual increase in pressure is called modulation. The modulating reducing valve modulates all of the speed clutches and all of the direction clutches.

Spool (15) creates a pressure differential of 415 kPa (60 psi) between pump pressure and reduced pressure oil. The oil pressure at the direction clutches is always lower than the oil pressure at the speed clutches. The pressure differential allows the speed clutches to engage prior to the direction clutches. The direction clutches engage last in order to handle the load.

Transmission Control (Lever) in SEVENTH GEAR REVERSE and the Engine On




Illustration 5g00930092

Hydraulic controls with the engine on and the transmission control lever in the SEVENTH GEAR REVERSE position

(15) Differential, check and relief spool

(16) Pilot selector valve

(18) Speed selector spool (No. 5 clutch)

(20) Passage to No. 4 clutch

(21) Passage to No. 5 clutch

(27) Modulating reducing valve

(29) Load piston

(35) Passage to No. 8 clutch

(39) Passage for signal pressure

(40) Passage for signal pressure

(41) Passage for signal pressure

(43) Passage for signal pressure

When the transmission control lever is moved from SIXTH GEAR REVERSE position to SEVENTH GEAR REVERSE position, pilot selector valve (16) permits oil in passage (43) to flow to the reservoir. The pilot selector valve sends signal pressure to passage (41) .

When the signal pressure in passage (43) goes to the reservoir, the spring force on speed selector spool (18) moves the spool to the left. Oil in the passage for No. 5 clutch (21) flows to the reservoir. When the passage to No. 4 clutch (20) is opened, system pressure decreases and the oil fills the passage for the No. 4 clutch. As the No. 4 clutch fills, a decrease of pressure in passage (39) causes a decrease in pressure on the left end of spool (15). The spool moves to the left.

When spool (15) moves to the left, oil in the No. 2 direction clutch flows to the reservoir. The oil in passage (40) will go to the reservoir through spool (15). A decrease in pressure in passage (40) causes load piston (29) to move to the left. The modulating reducing valve will move to the right. A decrease in pressure in passage (40) causes a decrease in the pressure in the passage for the No. 8 clutch (35) and the No. 8 clutch is not engaged.

As the passage to the No. 4 clutch (20) is filled, there is an increase in pressure in passage (39). Spool (15) moves to the right. This closes passage (40) to the reservoir. The system pressure will increase.

The modulating reducing valve (27) modulates the pressure oil until the pressure in No. 4 clutch and in No. 8 clutch is approximately 2861 kPa (415 psi). The pressure in the No. 2 clutch is approximately 2400 kPa (348 psi).

Pilot Selector Valve




Illustration 6g00930093

Pilot selector spool in the FIRST GEAR FORWARD position

(38) Passage for signal pressure

(39) Passage for signal pressure

(40) Passage for signal pressure

(41) Passage for signal pressure

(42) Passage for signal pressure

(43) Passage for signal pressure

(44) Chamber that is connected to the transmission reservoir

(45) Chamber that is connected to signal pressure from the priority reducing valve

The pilot selector valve controls the movement of the speed selector spools. The speed selector spools are controlled by signal oil. Signal oil is directed to the speed selector spool or signal oil is drained to the reservoir.

The pilot selector valve has two chambers in the center. Chamber (44) is connected to a passage from the priority reducing valve for signal pressure.

Table 2
Position     Passage with Signal Pressure    
N     (38) and (42)    
1     (39) and (40)    
2     (39) and (43)    
3     (39) and (41)    
4     (39) and (42)    
5     (38) and (40)    
6     (38) and (43)    
7     (38) and (41)    
8     (38) and (42)    

Six passages connect the speed selector spools to one of two chambers. The chambers are in the pilot selector spool. When the selector spool is in FIRST GEAR FORWARD position through FOURTH GEAR FORWARD position, two of the passages have signal pressure that is supplied by chamber (45). The other four passages are connected to the transmission reservoir through chamber (44). When the selector spool is in FIFTH GEAR FORWARD position through EIGHTH GEAR FORWARD position, one of the passages has signal pressure that is supplied by chamber (45). The other five passages are connected to chamber (44) .

Manual Modulation Valve

The manual modulation valve allows the operator to control the oil pressure to the direction clutches. A cable connects the transmission modulator control (pedal) to the manual modulation valve.




Illustration 7g00945513

Hydraulic controls in the FIRST GEAR FORWARD with the manual modulation valve open.

(14) Manual modulation spool

(27) Modulating reducing valve

(29) Load piston

(46) Passage

(47) Chamber

(48) Orifice

(49) Piston

(50) Slug

(51) Passage from the load piston

When the transmission modulator control (pedal) is depressed, spool (14) moves to the left. Passage (51) from the load piston is connected to passage (46). Oil from the load piston (29) flows to the reservoir. The location of the orifice for passage (51) at load piston (29) prevents the pressure from going lower than 620 kPa (90 psi). The clutches are now operating at a lower pressure.

When passage (51) is connected to passage (46), chamber (47) is connected to passage (46). Oil in the chamber flows to the reservoir. Oil that is acting on slug (50) moves piston (49) to the left. A restriction to oil flow around piston (49) is created. The restriction causes a pressure decrease in the direction clutches. The direction clutches slip and the machine moves at a reduced rate.

When the transmission modulator control (pedal) is released, spool (14) moves to the right. The oil pressures will increase. The modulating reducing valve (27) modulates the oil pressure and the clutches will engage smoothly.

If the transmission modulator control (pedal) is not depressed spool (14) is stationary. Oil from load piston (29) flows through passage (51) and the flow is stopped by spool (14). Reduced pressure oil flows around piston (49) and to the direction clutches. Reduced pressure oil also flows through orifice (48) and into chamber (47).

Information System: