The foundation for every automatic transmission built since the beginning is hydraulic pressure. This pressure applies and releases clutches and bands to produce different gear ratios. Hydraulic pressure is created by the pump’s output, driven by the engine. Also, today, electric pumps create pressure, i.e., in vehicles with start/stop systems. The engine-driven pumps can create a tremendous amount of pressure. As a matter of fact, the pressure they can create is so great that if the pressure is not controlled correctly, internal transmission parts can be blown apart. Examples would be broken pump gears, cracked clutch drums, and broken apply pistons.
There are many articles on pressure regulation on the ATRA website (search for “regulator”). In this edition of Fun With Transmissions, we will check out how the 10-speed transmissions by General Motors and Ford regulate main line pressure.
A DIFFERENT-LOOKING TYPE OF REGULATOR
There are several different styles of pressure regulator valves. The Chrysler-style valve has been around for almost as long as Chrysler has been around (Figure 1). The GM 4L60E valve has a spring and a boost valve. On this type of valve, the boost signal works on the boost valve and sleeve to raise and lower line pressure (Figure 2).
Now, we have something a bit different. These 10-speed units have a valve system that regulates pump output based on engine rpm; it does this without the assistance of the computer or any other outside influence. This means the pump output is the same at a low rpm as at a higher rpm.
Let’s take a look at the GM and Ford 10-speed pressure regulator valve and see how this works (Figure 3). We have line pressure coming into the left side of the valve. Line pressure control solenoid signal (LP) oil is coming on the right. There is “decrease” oil and “decrease” exhaust in the middle. Are you following so far?
To explain: the LP signal increases, which moves the valve to the left. This blocks line oil from becoming decrease oil. This will cause high line pressure. LP signal oil decreases and allows the vale to move to the right opening line to decrease lowering line pressure.
Now if we lose the LP signal altogether, the decrease oil will be regulated by the spring on the right side of the valve.
So far, we have not seen critical valve/bore wear issues that many of today’s transmissions are experiencing.
WHAT DOES DECREASE OIL DO (MECHANICALLY SPEAKING)?
Hey, I am glad you asked. When there is little to no decrease oil, the pump slide is pushed to the left by the pump slide spring. In this position, there is maximum intake (suction) and maximum output (volume) (Figure 4). Note: The slide return spring has been removed for illustration purposes only.
When the decrease pressure increases it moves the slide to the right. This action lowers the suction and output at the same time (Figure 5).
Let’s use a garden hose as an example of the slide action. When we open the spigot, the water flows without much pressure. Now, if we pinch the hose off, it is the same as the slide moving to the left. We create resistance, which in turn builds pressure.
Pressure regulators have always been a part of the hydraulic controls in the automatic transmission. The new 10-speed regulators have a different shape from previous designs, and when we understand how they work, it’s easier to have fun with transmissions!
