NOTE
If the fluid level is low, the oil pump will draw in air along with the fluid, which will cause bubbles to form inside the hydraulic circuit. This will in turn cause the hydraulic pressure to drop, which will result in late shifting 'and slipping of the clutches and brakes. If there is too much fluid, the gears can churn it up into foam and cause the same conditions that can occur with low fluid levels.
In either case air bubbles can cause overheating and oxidation of the fluid which can interfere with normal valve, clutch, and brake operation. Foaming can also result in fluid escaping from the transmission vent, in which case it may be mistaken for a leak.
-Securely insert the oil level gauge
-The fluid and the oil filters should always be replaced when overhauling the transmission or after the vehicle has been driven under severe conditions.
AUTOMATIC TRANSMISSION FLUID REPLACEMENT
If you have a fluid changer, use his changer to replace the fluid. If you did not have a fluid changer, replace the fluid by the following procedure.
(1) Disconnect the hose shown in the illustration, which connects; the transmission and the oil cooler (inside the radiator). Refer Figure 5
(2) Start the engine and let the fluid drain out
Running conditions: N range with engine idling
Caution
The engine should be stopped within one minute after it is started. If the fluid has all drained out before then, the engine should be stopped at that point.
Discharge volume: Approx. 3.5 L
(3) Remove the drain plug from the bottom of the transmission case to drain the fluid. Refer Figure 6
Discharge volume: Approx. 2.0 L
(4) Install the drain plugs via the gasket, and tighten it to the specified torque.
Tightening torque: 32 Nm
(6) Pour the new fluid in through the oil filler tube.
Adding volume: Approx. 5.5 L
Caution
Stop pouring it the full volume of fluid cannot be poured in.
(7) Repeat the procedure if step (2).
NOTE
Check the old fluid for contamination. If it has been contaminated, repert the steps (6) and (7)
(8) Pour the new fluid in through the oil filler tube.
Adding volume: Approximately 3.5 L
(9) Reconnect the hose, which was disconnected in step (1) above, and firmly replace the oil level gauge.
(10) Start the engine and run it at idle .for 1-2 minute.
(11) Move the selector lever through positions and then move it to the N position.
(12) Check that the fluid level is at the COLD mark on the oil level gauge. If the level is lower than this, pour in more fluid.
(13) Drive the vehicle until the fluid temperature rises to the normal temperature (70-80°C), and then check the fluid level again. The fluid level must be at the HOT mark.
GENERAL INFORMATION (Torque Converter)
The "Fundamentals of Fluid Coupling and Torque Converter" section is to acquaint the students with the basics of fluid couplings and torque converters. This section will explain the basics of fluid couplings first, then the basics of the torque converter will be covered. There are many similarities between the fluid coupling, which was used extensively some years ago; and the torque converter, which is used in today's transmissions. In order to completely understand the operation of the three-element torque converter, a thorough understanding of the basic fluid coupling must be mastered.
A SIMPLE FLUID COUPLING
Fig. 1 represents a simple fluid coupling using two common electric fans as the coupling halves. Fan #1 is plugged in and allowed to run, while fan #2 is unplugged and immobile before fan #1 is turned on. As fan #1 begins to turn after starting, air is pulled in through the back of the fan cage -and blown out through the front. The air currents will hit fan #2 causing that fan to turn also. In this case the air, or air currents may be visualized as a fluid, or a medium of transfer. Each fan can be considered to be each half of the fluid coupling with fan #1 being the impeller or pump, and fan #2 being the turbine. Referring back to the illustration, there is air leakage around the #2 fan cage. This shows that this coupling would be very inefficient due to the leakage of air around the fan.
In order to make this coupling more efficient, a shroud would have to be constructed around both fans in order to contain the air. The design of a simple fluid coupling does have a shroud or cover around both coupling halves to prevent the fluid or oil from leaking out.
FLUID COUPLING CONSTRUCTION
In the early development stages of the automatic transmission, the two members of the fluid coupling looked somewhat like
Fig. 2 The two halves in this case are identical to each other in every respect. Each half strongly resembles a doughnut sliced in half and hollowed-out on the inside. The vanes in each half are placed racially around the hollowed-out section of the coupling. The placement of these vanes is very important to coupling efficiency and operation.
OPERATION OF A FLUID COUPLING
Fig. 2 a cross section of a fluid coupling. The driving member, termed the impeller, is attached to the engine flex plate, while the driven member, termed the turbine, is attached to the transmission input shaft.
The fluid coupling is filled with oil. As the engine runs, the impeller begins to rotate. The oil is set into motion. The impeller vanes start to carry the oil around with them. As these vanes spin round the oil, it is thrown outward by centrifugal force. The oil flow, depicted in Fig. 2, would be circular, due to the shape of the coupling. Before the engine is even started, both members of the coupling are stationary. Upon starting the engine, the impeller starts its rotation; leaving the turbine member stationary for a short period of time. As the oil is being carried around with the rotating impeller, it is thrown by centrifugal force, into the turbine at an angle (Fig. 3). The oil will strike the vanes of the turbine at this angle, thus imparting torque, or turning effort, to the turbine. As engine speed is increased, the force of the oil striking the turbine vanes is also increased. I thus, greater torque is imparted to the input shaft of the transmission via the turbine.
FLUID COUPLINGS IN ACTION
It is easy to see that as the angle of oil flow increased from the horizontal reference the greater the torque or power imparted to the turbine member. In other words, the greater the difference in speed between the two members; more power will result. As both members approach each other in speed, the oil will not pass from one member to the other as it had before. With very little oil passing between the two members, no power, or torque will be transmitted through the coupling. Using this same basic fluid coupling, engine braking may also be obtained. This is accomplished by first having both members turning at the same speed. The engine speed is then lowered so that the turbine member is driving the impeller. The engine will not increase its speed, so the turbine has to slow itself down due to the reversed effect upon the members. It should be noted that the more efficient fluid coupling would be the one that has less slippage between its two members. Refer figure 4
VORTEX, ROTARY, AND TURBULENT FLOW
In the following discussion on the different types of flow, it may be best understood if one single molecule of oil can be visualized flowing through its usual path. Rotary flow may be defined as the complete path a molecule of oil would take in a torque converter, or fluid coupling as the oil in the converter or coupling is rotating between the impeller and turbine. The molecule will follow a general spiral path at, or near the diameter of the fluid coupling or torque converter (Fig. 5. Vortex flow, shown in Fig. 5 is the circular path within the coupling this molecule of oil will follow due to the centrifugal force and curvature of the coupling. The -actual vortex flow is between the impeller and the turbine. Turbulence appears when there is violent random motion or agitation of the oil. When there is a great difference in speed between the members, there is a great amount of vortex flow. With this flow, which happens to occur faster than usual, the oil would be striking the vanes of the turbine with a great amount of force. This would cause the oil to swirl about in all directions, particularly in the center sections of both members (Fig. 5).
THE ADDITION OF THE GUJDE RING
The turbulence conditions led to many problems within the torque converter or fluid coupling. This turbulent if not corrected, or controlled, would hamper all the efficiency of the converter at that point. The fluid couplings and torque converters of that time were redesigned to reduce the turbulence problem. A cavity which looked like a small hollowed-out doughnut, sliced in half was inserted into the coupling and converter halves. Fig. 15 represents what this "split guide ring" will look like inside an actual torque converter, or fluid coupling. With this arrangement, the oil does not have a chance to set up the turbulences depicted in Fig. 6. Each half of this guide ring is set exactly halfway between each outside boundary of the converter or fluid coupling. Each half is set into the vanes of each member.
TORQUE CONVERTER VANE CONSTRUCTION
Contrary to the construction of the fluid coupling vanes, which happen to have a flat-type vane, the torque converter vanes are curved. This. Curvature is shown in Fig. 16. The reason for the curvature is that it will allow the oil to change directions rather gradually as it passes between the impeller and turbine. The heavy arrows show the oil flow. The small arrows indicate the driving force with which the oil strikes the vanes of the turbine. The oil, which js moving around with the impeller,
is thrown with a forward motion, or velocity, into the turbine. As the oil passes into the turbine, it "presses" forward all along the vanes, as shown by the small arrows. This produces push, which causes the turbine to rotate. The main reason for torque converter curved vane construction is to change the direction of the oil in order to get more force hitting the vanes of the turbine. The trailing edge of the vane actually does the re-direction process so that the oil flow can be put to better use driving the turbine member. Fig. 8 shows what would happen if the vanes in Fig. 7 were continuous. The inner ends of the vanes are not shown here. In this illustration, the split guide ring and the outer ends of the vanes have been cut away. If the vanes were shown here, the oil leaving the trailing edges of the turbine would be thrown upward against the forward faces of the, impeller vanes, opposing the driving force. This effect, shown by the smaller arrows would cause wasted power and loss of torque.
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