In-depth analysis of automatic gearbox - take you easy to understand automatic gearbox

10/05/2021

In-depth analysis of automatic gearbox - in oil pump - pressure regulating valve - molar - radiator lubrication loop flow

In the automatic wave box repair industry, controlling the renovation rate is always one of the most concerned factors, because it is directly related to the profit of the enterprise, the brand of the company and the development prospect of the business. However, this is the most difficult problem to solve. If the repair is limited to the surface without finding out the root cause of the internal fault of the transmission, the repair rate is very difficult to control, especially when the transmission enters the normal maintenance period and the internal fault begins to appear.

自动变速箱的深入剖析-带你轻松了解自动变速箱(图1)

To achieve correct failure analysis and successful gearbox refurbishment, it is particularly critical to understand an important oil circuit in the gearbox: oil pump-main pressure regulator-torque converter-radiator lubrication circuit. It can be seen from Figure 1 that the oil pump/pressure regulating valve and the variable lubricating oil circuit are actually in a series relationship and are connected in sequence. Changes in any part of this will directly affect other parts. Here we are going to explore in depth how these systems are interconnected, and how to use a flow meter (SonnaFlow®) to help monitor their operation, and it is also easier to understand how Sonnax’s valve body parts are repaired in the gearbox. The hydraulic circuit makes it work normally.
The pressure regulating valve (hereinafter referred to as "PR valve") is the core component of this oil circuit. The hydraulic pump can generate very large oil pressure, and the PR valve can limit or adjust the oil pressure within the range of 50-250 psi (pounds per square inch, US pressure unit) usually in the gearbox. The variation range of the modulated main oil circuit pressure is determined by the spring and oil circuit pressure at both ends of the PR valve. Under normal circumstances, the PR spring and the booster valve push the PR valve to move in one direction, and the balance pressure at the other end of the valve prevents or pushes the PR valve in a direction, so that the PR valve is in a balanced adjustment position. At startup, when the oil pressure at the balance end of the PR valve reaches a certain value, the PR valve will overcome the pressure of the spring (and the booster valve) and move toward its balance adjustment position. Once the oil pump generates enough oil pressure to push the PR valve into its balance adjustment position, the PR valve will direct the excess oil pump capacity into the drain hole or back to the suction end of the oil pump.
The modulated main oil pressure is the oil pressure acting on the balance end of the PR valve that can make the PR valve overcome the resistance and push it into the balance adjustment position. The actual situation is always the case, whether the PR valve is a simple structure connected with a spring and a booster valve, or a more complex structure that interacts with multiple reaction and balance areas at both ends of the valve. Here we call the PR valve in its equilibrium adjustment position under sufficient pressure as the PR valve under the equilibrium position, and the PR valve cannot be in its equilibrium adjustment position due to insufficient oil pressure as the non-equilibrium position. PR valve.
In many gearboxes, the PR valve also has a function that people are not familiar with. The main oil pressure regulating valve can also control the oil flow into the torque converter: this will directly affect the torque converter's release/charge oil pressure, cooling, lubrication, and in some cases the TCC lock-up oil pressure. In the realization of various functions, the PR valve is divided into primary and secondary. It firstly meets the function of controlling the pressure of the oil circuit, and secondly realizes the control of the pressure of the torque converter/lubricating oil circuit. Although some gearboxes have exceptions in this regard, the torque converter inlet oil in most gearboxes is not directly supplied by the PR valve, or supplied by the oil circuit controlled by the PR valve.

自动变速箱的深入剖析-带你轻松了解自动变速箱(图2)

Figure 2 shows a simple structure of the PR valve in its 2 positions: balanced position (the torque converter oil inlet is open) and unbalanced position (the torque converter oil inlet is blocked). Regardless of the structure of the PR valve, this concept of balanced and unbalanced positions is applicable to all types of main pressure regulating valves that control the oil intake of the torque converter. It is important to remember that when the PR valve is in the equilibrium position (when the torque converter oil circuit is open), the forces on both ends of the PR valve must be approximately equal. If the PR valve is in an unbalanced position for a long time, the torque converter/lubricating oil circuit will be blocked. Once the critical state is reached, this unbalanced position of the PR valve will severely damage the gearbox and stop working.

自动变速箱的深入剖析-带你轻松了解自动变速箱(图3)

Figure 3 shows an example of how the PR valve controls the torque converter/lube circuit. The figure shows the changes in main oil pressure and cooler flow during a gear shift. One phenomenon we can all see is a momentary drop in pressure during gear shifting. If you observe the main oil pressure and the flow through the cooler at the same time, you will find that when the main oil pressure drops, the flow through the cooler will also change accordingly. This is because the decrease of the main oil pressure will eventually act on the balance oil circuit end of the PR valve, and the force on the other end of the valve will overcome the reduced balance oil pressure and push the PR valve to its unbalanced position. This will limit the supply oil path of the torque converter and the amount of oil that is redirected back to the suction side of the oil pump (see Figure 2). The PR valve is always in this state before the main oil pressure is restored. When the main oil pressure returns to a sufficient level, it will push the PR valve back to its original balance adjustment position. If all parts of the gearbox are in good running condition, the change process of this PR valve is completed in an instant, which is how the entire system should operate. If the PR valve stays in its unbalanced position, problems start to appear.
The PR valve first meets the main oil pressure, which means that if the PR valve is in a critical state close to the unbalanced position, the torque converter and lubricating oil circuit will be blocked. In fact, it will block the oil circuit and eventually lead to serious consequences such as overheating, TCC lock slippage, or lubrication failure.
Problems on either end of the PR valve will cause the PR valve to be placed in an unbalanced position. There may be too much spring force or pressure of the booster valve at one end of the PR valve, causing the oil pump to bear excessive load (see the example in Figure 4: 1a, 1b, 1c, 1d). At the other end of the PR valve, the balance pressure may be insufficient due to oil leakage or weak oil pump (see the example in Figure 4: 2a, 2b, 2c, 2d). Let's imagine a truck on a long slope: the RPM is low, but the main oil pressure required is high. If the oil pump output cannot maintain the required main oil pressure, the PR valve will be moved to its unbalanced position to adjust the oil pressure. Remember that the PR valve adjusts the oil pressure first, so it can be imagined that the main oil pressure (and clutch engagement capability) may be close to its normal value under such a situation, but the oil flow or lubricating oil flow through the radiator may drop to The reason is that the PR valve stays in its unbalanced position. Imagine that the oil flow in the radiator dropped to zero at this critical moment. How terrible it is!

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Figure 4
1 Example of excessive spring force on PR valve or excessive pressure of booster valve
a. RWD Chrysler/E4OD, etc., the PR spring is too tight or adjusted too much.
b. 4L80-E, etc., the cross leakage caused by the abrasion of the booster valve makes the reverse gear oil pressure too high.
c. The gearbox is in fail-safe, and the EPC boost has reached its maximum value.
d. 4L80-E, the idle speed is too low, and the EPC current is too large.
2 Examples of low balance pressure
a. 400/200C, PR valve hole is worn.
b. CD4E, PR valve holes are worn.
c. 4L80-E, PR end plug leaks oil.
d. Any gearbox with worn or weak oil pump, or gearbox with serious internal oil leakage.

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You may have seen these results: the planetary wheel burns again, or the mysterious black ring around the torque converter appears, or the vehicle needs to wait a long time at idle before starting. Usually the most tested time for an oil pump is at high temperature, idle speed (when the speed RPM is very low), or in reverse gear. At these times, the required pressure is higher and the load of the oil pump is at the highest point. In order to keep the locking piston in the torque converter away from the front cover (ie, the unlocked state), it is necessary to have sufficient oil flow from the torque converter release/charge oil path to the torque converter. If the oil pump cannot maintain sufficient main oil pressure, the PR valve will be pushed to its unbalanced position and stay there, which means that there is little or no oil flow inside the torque converter, causing the TCC of the torque converter to lock The stop piston drags the front cover, causing idle speed fluctuations, engine stalling, or TCC friction material being polished on the surface. Once the friction material is polished or overheated, the friction plate will reduce or lose the TCC locking function.
Whether it is 60 psi at idling speed or 160 psi under load, a certain main oil pressure value is far less important than the ability of the oil pump to maintain that oil pressure and keep the PR valve in its equilibrium position. This conclusion is valid regardless of whether it is a vane-type oil pump or a gear-type oil pump, but the vane-type oil pump has a variable displacement, so their pump capacity can be increased to maintain the oil pressure, while the gear-type and crescent-type oil pumps have some Troublesome, because they only have a fixed displacement, and therefore have a lower output at low speeds and idling speeds.
The ability of the oil pump to maintain the required oil pressure and maintain the equilibrium position of the PR valve also has multiple variables. You may have a good oil pump, but there is oil leakage in other oil circuits inside the gearbox, which will consume the capacity of the oil pump and reduce the ability of the oil pump to generate pressure. On the other hand, if there is no internal oil leakage but the oil pump is worn or inefficient, the same problem of maintaining oil pressure will also occur. Just like your air compressor, its ability to maintain pressure is related to how many air tools you run at the same time. If you use too many air tools at the same time, your compressor will not have enough air flow (capacity). Maintain the air pressure, so the air pressure will drop below the normal range.
For fuel efficiency reasons, a typical transmission oil pump does not have much excess pump capacity. The size of the oil pump capacity is only used to maintain the oil pressure, and the size of the oil pressure is only used to keep the PR valve in its equilibrium position. Various oil leaks inside the gearbox waste oil pump capacity. All these internal oil leaks that accumulate over time will eventually consume considerable pump capacity and reduce the ability of the oil pump to maintain the main oil pressure and maintain the equilibrium position of the PR valve. Some attempts to compensate for this wear use re-adjusted springs and drills to enlarge the orifice. These methods are temporary remedies and cannot fundamentally solve the problem of wear and tear, or solve the problem of continuous internal leakage. If you have read the SONNAX TS Catalog (SONNAX TS Catalog), you will find that most of the parts are used to solve internal leakage problems. All valve sleeves and end plugs with O-rings, valve hole repair methods, enlarged plunger valves, precision-machined cups, etc. are all for synergy to minimize internal oil leakage. This not only eliminates the symptoms related to the parts, but also preserves the oil pump capacity.

Modification of main oil circuit-lubricating oil circuit
The main oil circuit-lubricating oil circuit, whether to open or not to open, that is indeed a problem. The modification of the main oil circuit to the lubricating oil circuit directly adds an oil passage between the main oil pressure and the torque converter oil inlet circuit, which somewhat bypasses the PR valve. Therefore, even if the PR valve is in an unbalanced position, the oil will always pass through this The oil passage directly enters the oil inlet circuit of the torque converter. So why don’t the original manufacturers incorporate this modification from the main oil circuit to the lubricating oil circuit into the gearbox? In fact, many gearbox manufacturers do! In 4L60-E, the small platform on the plunger of the PR valve plays this role. Other gearboxes achieve this through a built-in throttle or a small notch in the gasket. Can you drill a passage from the main oil circuit to the lubricating oil circuit by yourself? Yes, but the result is almost always that the opening is too large, so that too much oil enters the torque converter, causing excessive pressure inside the torque converter, backflow of torque converter oil, and many customer complaints. The PR valve of SONNAX shown in Figure 5 has a built-in passage from the main oil circuit to the lubricating oil circuit, and is also equipped with a check valve to prevent backflow, which prevents the torque converter oil from flowing back to the oil bottom after the vehicle is turned off. shell.
Torque converter pump wheel journal/oil pump cups deserve special attention. Excessive torque converter cup clearance will cause abnormal noise, wear and oil pump efficiency. In addition to supporting its weight at one end of the torque converter and helping to position the internal gear of the oil pump in the center, this journal/oil pump cup can also help prevent the torque converter oil from leaking through the return hole of the front oil seal. This kind of leakage is a common problem with AXODE, AX4N and Chrysler gearboxes. Figure 6 shows a cross-sectional view of a typical torque converter connected to an oil pump. The figure shows the leakage path of the torque converter oil from the inside of the torque converter through the oil pump cup. Excessive torque converter oil leakage from this journal/oil pump cup will cause oil leakage from the front oil seal, creating a direct path for torque converter oil pressure leakage. This will reduce the oil pressure in the torque converter/lubricating oil circuit and, in some cases, the oil pressure for the TCC lock.

自动变速箱的深入剖析-带你轻松了解自动变速箱(图4)

This is also why some gearbox manufacturers have begun to place the oil seal between the internal gear of the oil pump and the shaft journal of the torque converter (such as 4R44E), or place the oil seal between the guide wheel tube of the torque converter and the inner side of the journal (such as 48RE). ). These characteristics keep the oil pump oil in the oil pump and the torque converter oil in the torque converter. Let’s take an example to see how an excessively large torque converter cup gap can cause us trouble: If a 2" diameter torque converter journal has a 0.003" additional gap from the journal to the cup, then This 0.003" clearance area is equivalent to a 0.100" opening, so that the torque converter oil can leak from here. A 0.100" hole is a considerable leak for the torque converter.
When dealing with any gearbox, please keep in mind the interconnections between the various gearbox components discussed here, and why you need to check the oil flow through the cooler, how it reveals not only the cooler and cooling pipe information, but also Including information about the entire series of PR valves and oil pumps, as well as when parts and gaps should be inspected, and what the comprehensive symptoms will look like when internal leakage occurs.

Use Sonnen flowmeter to detect ATF flow
SonnaFlow® is a simple method that anyone can use to detect the flow rate of the cooler under actual driving conditions. The traditional method of measuring the flow of the cooler is to remove the oil return pipe and see if the oil can fill a 1 quart barrel within 20 seconds. This old method cannot tell you the actual situation of any car in normal driving. Think about the last time the car could not start because of lubrication failure? The Sonnen flowmeter tool includes a flow probe that can be temporarily installed on the cooler tubing conveniently and quickly, and the real-time flow value (GMP, gallons/minute) can be read from the digital display hung in the cab. This is particularly useful for monitoring the flow in the cooler when the TCC is locked and engaged, and can be used to determine that the flow of ATF oil has not dropped to the critical value allowed under load or idling conditions. Such convenient operation makes Sonnen flowmeter not only a very effective tool for checking the flow rate of the cooler/lubricating oil circuit, but also the oil pump-main pressure regulator-torque converter-cooler and lubricating oil circuit of the gearbox. An effective tool for the healthy operation of the entire circulatory system.

自动变速箱的深入剖析-带你轻松了解自动变速箱(图5)