Automatic transmission shift valve
The shift valve in an automatic transmission (AT) is responsible for shifting gears by changing the hydraulic pressure in the system.
Design and principle of operation
The speed change valve consists of a body, a plunger and a spring. The plunger moves inside the housing, opening and closing holes that control the flow of fluid.
The principle of operation is that transmission fluid under pressure from the torque converter flows to the valve. A spring holds the plunger in the closed position, blocking the flow of liquid. However, when the automatic transmission control system receives a signal to change gear, the electronic control unit (ECU) sends a signal to the shift valve solenoid.
The solenoid creates a magnetic field that overcomes the force of the spring and opens the plunger, allowing transmission fluid under pressure to flow to the corresponding clutch pack, which controls the engagement of a new gear.
Types of Speed Shift Valve
There are two main types of shift valves:
* Linear valve: The plunger moves linearly inside the body.
* Rotary valve: The plunger rotates inside the body to open and close the holes.
Shift Valve Malfunctions
Shift valve faults can lead to shifting problems such as:
* Difficulty shifting gears
* Gear slippage
* Shocks when shifting gears
* No shifting to certain gears
Diagnostics and troubleshooting
Diagnosis and troubleshooting of the gear shift valve is usually carried out as follows:
* Scan trouble codes: The transmission ECU can store trouble codes that indicate problems with the shift valve.
*Checking Hydraulic Pressure: The hydraulic pressure in the system can be checked using a pressure gauge to identify possible leaks or insufficient pressure.
* Checking Solenoids: The shift valve solenoids can be checked using an oscilloscope or multimeter.
*Valve Replacement: If the gear shift valve is faulty, it must be replaced.
Maintenance
Regular automatic transmission maintenance, including changing the transmission fluid and filter, can help prevent shift valve problems.