Isuzu KB P190. Manual - part 1063

CONSTRUCTION AND FUNCTION  7A1-13 

 

2-4 Brake and Low & Reverse Brake (Multi-Plate Brake) 

• The multi-plate brake is composed of drive plates and driven plates.  By applying the oil pressure onto 

the end surface of the plates, the clutch is engaged.    The oil pressure is adjusted with the control valve 
according to the signal from the TCM. 

• All brakes use dish plates to prevent uncontrolled operation of the clutches when engaged, causing a 

shock. 

• The solenoid in the control valve is driven based on the shift signal from TCM, it moves the shift valve, 

thereby engaging the drive plate and driven plate through the piston of each clutch. 

• As a result, rotation of each element of the planetary gear unit is fixed. 
• When the oil pressure is removed, the piston returns to the original position via the force of the return 

spring. 

 

 

 

 

Figure 19. Construction of 2-4 Brake 

 

Figure 20. Construction of Low & Reverse Brake

 

Low One-way Clutch 

• The low one-way clutch employs the sprag, which locks the counterclockwise rotation of the front 

planetary carrier and the rear internal gear. 

• The one-way clutch outer race is fitted with the low clutch drum, and the inner race is fitted with the 

transmission case. 

• The outer race rotates freely clockwise, but, when it attempts to rotate counterclockwise, the sprag locks 

the outer race. 

• When the vehicle is traveling in 1st gear in the D, 3 or 2 position, the low one-way clutch locks the rear 

internal gear via the low clutch. It is left free in the 2nd, 3rd or 4th gear. 

 

 

Figure 21. Construction of Low One-way Clutch 

7A1-14  CONSTRUCTION AND FUNCTION 

CONTROL VALVE 

• Employing the direct electronic control (Direct Electronic Shift Control: DESC) for the clutch pressure has 

simplified the oil pressure circuit, reduced the number of functional components and made the control 
valve compact. 

• The control valve body is divided into the upper body and the lower body.    All solenoids, the oil pressure 

switch and the ATF thermo sensor are installed to the lower body. 

• Three-way valve type solenoids providing high responsibility are employed.    Some of the solenoids are 

switched between ON and OFF, and others repeat ON and OFF at 50Hz (duty cycle system).  
Functionally, some supply output pressure when power is not supplied, and others drain the output 
pressure. 

• When the solenoid is driven based on the signal from the TCM, the oil pressure is changed. 

 

 

Figure 22. Construction of Valve Body 

CONSTRUCTION AND FUNCTION  7A1-15 

 

Line Pressure Solenoid 

• The line pressure solenoid is turned ON or OFF according to the signal from the TCM.    It switches the 

line pressure between high and low pressure. 

• While no power is supplied, the solenoid supplies high pressure. 

 
Shift Solenoid   

• The shift solenoid is of the duty cycle type, which is turned ON or OFF at 50Hz.    The ratio of the ON and 

OFF time can be freely controlled in the position of 0 - 100%. 

• While no power is supplied, the solenoid supplies output pressure. 
• The low clutch solenoid adjusts the low clutch pressure, the high clutch solenoid adjusts the high clutch 

pressure, the 2-4 brake solenoid adjusts the 2-4 brake pressure, and the low & reverse brake solenoid 
adjusts the low & reverse brake pressure respectively. 

 
Lock-up Solenoid 

• The lock-up solenoid is of the duty cycle type which is turned ON or OFF at 50Hz.    The ratio of the ON 

and OFF time can be freely controlled in the position of 0 - 100%. 

• While no power is supplied, the solenoid drains the output pressure. 

 

 

 

 

Figure 23. Shift Solenoid 

 

Figure 24. Lock-up Solenoid 

 

 

 

Figure 25. Location of Solenoid 

 

 

 

7A1-16  CONSTRUCTION AND FUNCTION 

Control Valve Fail-safe Function 

• To prevent interlocking due to engagement of more than three clutches and brakes at the same time, the 

2-4 brake fail-safe valve A and B, and the low & reverse brake fail-safe valve A and B are provided. 

• When oil pressure is generated in the high clutch and the low clutch, the 2-4 brake solenoid is turned ON 

to drain the oil pressure applied to the 2-4 brake. 

• When oil pressure is generated in the high clutch or 2-4 brake, the low & reverse brake solenoid is turned 

ON to drain the oil pressure applied to the low & reverse brake. 

 
 
 
Oil Pressure Switch 

• The oil pressure switch detects the condition of the oil pressure supply to the clutch and brake, and then 

sends the detection result to the TCM. 

• The oil pressure switch is turned ON when the oil pressure reaches the switch working pressure, and 

turned OFF when the pressure decreases below the specified value. 

• The high clutch oil pressure switch detects the high clutch oil pressure, the 2-4 brake oil pressure switch 

detects the 2-4 brake oil pressure, and the low & reverse brake oil pressure switch detects he low & 
reverse brake oil pressure respectively. 

 

 

 

 

Figure 27. Oil Pressure Switch 

 

Figure 28. Location of Oil Pressure Switch