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Adapting through the years

A look at Chrysler's shift adapt strategy
Tuesday, November 3, 2015 - 08:00
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A look at Chrysler's shift adapt strategy

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:

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“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
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