Adapting through the years

Nov. 3, 2015
From 1989 to 2015, from a four-speed to a nine-speed transmission, it is interesting to see how through the years Chrysler adapted their shift adaptations. 

From 1989 to 2015, from a four-speed to a nine-speed transmission, it is interesting to see how through the years Chrysler adapted their shift adaptations. Their first clutch-to-clutch shifting transmission was the 41TE (A604) four-speed front wheel drive automatic transmission. Still to this day it is an amazing transmission from an engineering standpoint. A total of four solenoids provide shift sequence and shift feel for each and every shift along with partial and full converter clutch apply. There were no one-way clutch holding devices (spring and rollers, sprags, etc.) to assist in any shift transition. It was the first of its kind on many levels. To this very day, I still do not know of any other manufacturer that monitored each and every solenoid’s circuit integrity by turning off the solenoid to watch for an approximate 42-volt inductive spike. If the spike is too high or too low, it sets a diagnostic service code for the failed electrical solenoid circuit; fascinating to say the least, especially back in 1989. Another first and the subject of this article is their “shift adapt” strategy they referred to as “Clutch Volume Tracking.” They described this process as follows:

“To execute the shift logic, the controller must maintain a continuous record of each clutch element apply status. This is done by tracking the instantaneous fluid volumes in each clutch circuit. Instantaneous fluid volumes are tracked using predetermined flow rates and learned ‘clutch fill volumes.’ This is particularly useful for closely spaced shifts or change-mind shifts.

Learned clutch fill volumes represent the volume of fluid that is required to stroke a clutch piston to the point where zero clutch pack clearance is obtained, without stroking the accumulator or picking up any torque load on the clutch. This learned fill volume is updated for each clutch element as it wears and clutch pack clearance increases.”

What this all boils down to is that the controller/computer can monitor gear ratio and the rate of gear ratio change through the input and output speed sensors. It compares a ratio change to the pulse width modulation of the solenoid, which controls the flow rate of the solenoid. In reverse, they are supplied with 175 to 235 psi of pressure. In drive, first and second gears, they receive 110 to 145 psi; while in third and fourth they receive 75 to 95 psi. With each of the solenoids being supplied with consistent pre-determined fixed pressure levels, the computer can calculate fill time and clutch pressure as it is proportional to solenoid pulsed width modulation (PWM).

With this capability, it can control the rate in which each clutch assembly is applied and released. As one clutch is being applied while another is being released, the controller watches the ratio change through the speed sensors. It can determine if this “clutch overlap” is too tight or too lose and then make solenoid PWM adjustments to smooth the shift out.

Each of these clutch assemblies are assigned an acceptable “clutch volume” numerical range, which a scan tool can retrieve for diagnostic purposes. The Low/Reverse Brake assembly has a numerical value of 35 to 85, the 2-4 Brake is 20 to 77, the Underdrive Clutch is 24 to 70 and the Overdrive Clutch is 75 to 150 (Figure 1). Clutch volumes must fall between these values to be considered functional. Should any one of these clutch assemblies’ values exceed the range given to them, it typically indicates the application of that particular clutch has become difficult to control.

These numerical values are representations of what it takes to complete a good, clean, consistent clutch overlap shift. Various reasons cause these values to exceed themselves on both the low end as well as on the high end. Some examples on the high end would be leaking clutch circuits or excessive clutch clearances resulting in slip shift storing gear ratio error codes. A couple of examples on the low end would be clutch clearances being too low or cross leaks that supply unintentional residual pressure into a given circuit. When it becomes charged with pressure during the initial stage of a shift, the clutch applies sooner than expected.

Moving forward in time now to Oct. 7, 1998, Daimler-Benz announces the purchase of Chrysler Corporation, a relationship that lasted 9 years. At the time of purchase, they had already developed their 5G-Tronic known as the 722.6 transmission. Five years later, this transmission showed itself in Dodge Sprinter and Chrysler Crossfire vehicles and they called it the NAG1 transmission. By 2005 and later several Dodge, Chrysler and Jeep vehicles were fitted with this transmission. The NAG1 is a fully electronic five-speed transmission, which also incorporates shift adapt strategies. The way adaptations are represented with 722.6 Mercedes equipped vehicles is in Newton Meters (Nm) as seen in Figure 2.

Figure 1 Figure 2

Similar to CVI values having a numerical range to indicate consistent controllable quality shifts, an Nm range is assigned to each shift tailored by specific engine sizes. Take for example a vehicle with an M11.973 engine; the adaption torque requirement for a 1 to 2 shift is 15 to 36Nm. An M11.974 would to 15 to 28Nm.

The idea here is that Newton Meters in laymen’s terms indicates the strength of the shift. As mentioned previously, the quality of the shift is monitored through the input and output speed sensors. The output speed with the 722.6 transmission is calculated by the ABS module and sent to the TCM over the network. The output rpm is divided into the input rpm to see what gear ratio the transmission is in. When the transmission shifts from a 3.59 first gear ratio into a 2.19 second gear ratio, the computer can observe the speed in which the values change from one ratio to the next. If the overlap of the off-coming and oncoming clutch is too lengthy, a slight tie-up will occur and the shift will feel harsh. The computer can see this by the rate in which the input speed rpm drops. It will appear as if the shift is trying to stop the input shaft from spinning. The decline is too rapid and the computer will re-adjust to control the shift on its next drive cycle. 

Going to the other extreme, if the off-coming clutch comes off sooner than the oncoming clutch, the computer will see the input speed sensor rise higher in rpm, indicating a slip or flare in the shift. The computer will re-adjust to control the shift on its next drive cycle. 

The question is, how does it control the strength of the shift overlap (Nm) based on ISS and OSS calculations?

Besides seeing an Nm parameter through a scan tool, two other very significant parameters are provided. One is called “Fill Pressure,” while the other is called “Fill Time” (Figures 3 and 4). Fill pressure for each shift is represented by numerical values in millibars, while Fill Time is in cycles. Without getting overly complicated, the computer adjusts these two parameters via solenoids in the transmissions to acquire the desired Nm shift. The specification value for maximum first to second fill pressure is 1600 mbars (23 psi).  This represents the pressure a solenoid will produce in the valve body based on how it is controlled by the computer electronically.

Figure 3 Figure 4

The maximum specification value given per shift is 15 cycles. The computer can change the way it controls solenoids in the valve body once every 20 milliseconds. Each cycle represents a 20-millisecond change in the control of a solenoid. Three cycles would indicate that it took three “20-second millisecond cycles” to alter pressure enough to accomplish the correct application of a clutch. 

In 2007, Daimler-Benz bailed on Chrysler to stop the financial bleeding they were experiencing for reasons not related to this article. The point is Chrysler continued using the NAG1 transmission for many years after their departure. But in an interesting twist in the use of transmissions, Chrysler decided to utilize a rear wheel drive eight-speed transmission as early as 2013, and a nine-speed front wheel drive transmission in 2014 from ZF Industries. The rear wheel drive ZF8HP45/70/90 – 845RE is being used in The Ram 1500 Pickup, the Charger, 300C, Durango, Grand Cherokee and Challenger vehicles. The front wheel drive ZF9HP48 – 948TE is being used in Cherokee KL vehicles like the Trailblazer.

When transmissions begin to have six speeds or more, you see an increase use of skip shift strategies. Depending on the driving conditions of the vehicle, the computer is programmed to skip gears, preventing shift busyness. This takes clutch adaptations to a whole new level. The computer now needs to control a wider variety of scheduled shift overlap scenarios. Quite impressive when you consider the programming involved with eight- and nine-speed transmissions using skip shift technology.

The way in which Chrysler chose to control and present clutch adaptations is going to sound very familiar to you now. They use millibars and milliseconds to control fill time and fill pressure. Dodge Service bulletin 21-012-14 REV B is an 11-page informative 845RE document that explains the adaption methods used with these transmissions. The 21-013-13 is a very similar document for the 948TE. Here is an excerpt from the 845RE document:

The 845RE, 8HP45, 8HP70, or 8HP90 eight-Speed Automatic Transmission uses a sophisticated shift algorithm that includes learned information so that the shift quality remains excellent even as the transmission wears. This learned information is recorded in memory cells referred to “Adaptation Memory Cells.” Each applied clutch records the amount of time it takes to fill the clutch (Fast Filling Counter/Filling Time) and the amount of pressure (Filling Counter/Filling Pressure). The adaptation memory cells are set to zero (0) on every new transmission (new in vehicle and/or replaced for service) and when the transmission control module is replaced for service. In addition, the adaptation memory cells are set to zero (0) when the transmission control module adaptation memory cells are cleared using the wiTECH diagnostic scan tool. Until the adaptation has been learned/relearned, the transmission shift quality may not meet the customer’s expectations.

NOTE: Any time the transmission has been overhauled (unless the Valve Body/TCU assembly (mechatronic) was replaced), the adaptation memory cells must be cleared using the wiTECH diagnostic scan tool.

The adaptation memory cells appear on the wiTECH for every clutch. Each clutch will include:

Fast Filling Counter = the number of filling time events that has taken place. Filling Time = +/- number of ms (milli seconds) from zero (standard set value). Filling Counter = the number of filling pressure events that has taken place. Filling Pressure = +/- mb (millibar)/PSI (Pounds Per Square Inch) from zero (standard set value). If the adaptation memory cell “counter” is zero (0), than the adaptation memory cell has not been updated. The filling counter ideally should be at least 12 (6 on 8HP70/90) and Fast Filling counter at least 4 (2 on 8HP70/90) to improve shift quality and with each subsequent count, shift quality will improve even more.

From 1989 to 2015, from a four-speed to a nine-speed transmission, it is interesting to see how through the years Chrysler adapted their shift adaptations.

Sponsored Recommendations

Best Body Shop and the 360-Degree-Concept

Spanesi ‘360-Degree-Concept’ Enables Kansas Body Shop to Complete High-Quality Repairs

ADAS Applications: What They Are & What They Do

Learn how ADAS utilizes sensors such as radar, sonar, lidar and cameras to perceive the world around the vehicle, and either provide critical information to the driver or take...

Banking on Bigger Profits with a Heavy-Duty Truck Paint Booth

The addition of a heavy-duty paint booth for oversized trucks & vehicles can open the door to new or expanded service opportunities.

Boosting Your Shop's Bottom Line with an Extended Height Paint Booths

Discover how the investment in an extended-height paint booth is a game-changer for most collision shops with this Free Guide.