Transmission: Automotive Engineering Fundamental: Dodge operation system

SYSTEM OPERATION OF ZF 8HP.

The main powertrain improvement was the eight speed automatic, based on our look at the Dodge Charger V6 with its five-speed and then with the eight-speed. It is the first eight-speed automatic to be used in a pickup truck. Just as the new transmission cut around two seconds off the Charger’s 0-60 times while adding several miles per gallon to its highway mileage, it helps the new Ram V6 to beat the 2012 model by three seconds, 0-60, while increasing gas mileage 20%.

The eight-speed does not just add gears; it dramatically increases the range from first to top gear, shifts much faster than the older automatics, and is reportedly lighter than the 65RFE transmission.

The eight-speed makes a stop-start system possible, and one is available on “select Ram 1500 models:” it automatically shuts the engine off when the truck comes to a complete stop, conserving fuel. The engine restarts instantly when the gas pedal is used. The feature can be shut off if desired, but has little impact on acceleration and a large impact on city-cycle driving.

The V6 will come only with the 8HP45 “Torqueflite 8” is the sole automatic. The Hemi will start the year with the 2012 six-speed automatic and later will transition to a higher-torque version of the eight-speed, the 8HP70, which has identical gear ratios; it will become available during the first three months of calendar year 2013.

Unlike the shifter for cars, which some critics have disliked, trucks with the eight-speed get a dash-mounted dial shifter, a style used on Class 6-8 heavy duty trucks. The class-exclusive shifter allows quick blind-shift transitions from Reverse to Drive when towing or navigating out of mud or snow; it is completely electronic, with no shift linkage, cutting maintenance and eliminating a common source of problems in older, well-worked trucks. Low gear is obtained by using the gear-change buttons on the steering wheel.

Both the 8HP45 and 8HP70 transmissions are fully electronic, and can change their shift maps to meet current conditions; Ram has over 40 shift maps for specific conditions to optimize shift quality and shift points. The software uses engine torque gradients, kick down, longitudinal and lateral acceleration, hill detection, friction detection, downshift detection, cruise control, stability control interaction, and temperature to determine shift points and methods.

	1	2	3	4	5	6	7	8	Reverse	Range	Peak Torque
65RFE	3.00	1.67	1.50	1.00	0.75	0.67			3.00	2.33	410 lb-ft (540 Nm)
8HP	4.71	3.14	2.10	1.67	1.29	1.00	0.84	0.67	3.30	4.04	332 / 516 lb-ft (450/700 Nm)

The 8HP has a much higher range than the 65RFE, which means you can get a good economy gear for efficient highway runs without sacrificing a low first gear for power and speed. Rather than comparing any particular gear ratio to Ford, Chevy, or Toyota, we suggest that you look at the range and the overall top gear ratio with one of the four axle ratios

Gear changes are nearly imperceptible due to the even spacing of gear ratios and the speed of shifting. The transmissions have four gear sets and five shift elements (multi-disc clutches and brakes); only two shift elements are open at any time (on both six and eight speeds). By minimizing the number of open shift elements, drag losses can be reduced.

Our modular construction system

For the 8-speed automatic transmission, ZF set out to design and develop an entirely new gear set concept. The result is a revolution in transmission design: a transmission concept with 4 gearsets which requires only 5 shift elements – of which only two are open in any given gear.

The 8HP also requires no more than 3 multi-disk clutches and 2 brakes, which allows it to achieve a greater degree of efficiency than other concepts. As a result of the fact that only 2 shift elements are open per gear, drag losses in the transmission are sustainably reduced. This effect is supported by the use of a new parallel-axis vane-type oil pump. The flexible modular construction system of the 8HP is full of innovations and is well-suited to serve as the basis for a wide range of future development possibilities. The following technologies can be implemented without altering the transmission installation space:

• Hydrodynamically cooled clutch

• Integrated starting clutch

• Crankshaft starter generator