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845RE / 870RE, ZF 8HP45 / 8HP70 / 8HP90:
8-Speed Automatic Transmission for Chrysler cars and trucks

Even before Sergio Marchionne took charges, rumors swirled around the idea of Chrysler using ZF eight-speed automatics, also used by makers such as Porsche and BMW, in their SRT8 cars and selected Dodge Ram pickups. Marchionne himself confirmed the selection in 2010, and in 2011, Chrysler revealed that the eight-speed would also be used in the LX cars — backing the Pentastar V6 engine. Charger and 300 got it first, during 2011 (for 2012 model year cars), followed by Ram (2013 model year).

ZF 8-speed automatic transmission for Chrysler

The transmission, when built by ZF itself, is a ZF design with changes to match Chrysler equipment. The 8HP45 is made by ZF version, while Chrysler has their own versions, 845RE and at least one related heavier duty model.

Chrysler’s 845RE designation indicates that the transmission has 8 speeds, “45 x 10” Nm of capacity, rear wheel drive intent, and fully electronic controls. It can be, and will be, used with 4x4 and AWD setups. An 870RE is reportedly coming; Chrysler may simply buy 8HP90s for the few cars that will require more torque capacity (such as anything with the supercharged 6.2 Hemi engine), but they might also choose to make an 890RE or similar offshoot.

Known differences between the 8HP45 and 845RE include, according to oh2o, the 845RE’s clutches (which have extra friction plates for improved performance) and, for some vehicles, a higher capacity oil pan. oh2o wrote that many internal parts do not interchange between the 845RE and 8HP45.

With the Pentastar V6 and HP8, the Chrysler 300 achieved 0-60 in 7.2 seconds, and cruised at 70 mph with the engine at a mere 1,400 rpm. Gas mileage for this combination is expected to be 30 mpg, up from 27, with city mileage rising from 19 to 20 mpg. The torque rating of 331 lb-ft for this version of the transmission is far above the Pentastar’s 260 lb-ft.

Most of the transmissions used by Chrysler will be made at the automaker’s Kokomo, Indiana, Transmission Plant but some will be built by ZF itself at a new transmission plant in Greenville, South Carolina. Chrysler is investing $300 million in the Kokomo plant. The new ZF facility, the first ZF plant to make car transmissions in the USA, will also make the 9-speed automatic transmission for transverse-mounted engine applications that was presented at the North American International Auto Show (NAIAS) — as will Chrysler, again, in Kokomo.

Torson AWD in ZF aautomatic transmission

ZF 8HP45 / Chrysler 845RE Technical information (and the HP70)

The ZF eight-speed automatic is made in several different forms, including an AWD version and a version with a built in DynaStart electric motor, with 20 horsepower (15 kW) of power, making it into a parallel-hybrid transmission. The key advantages of the transmission are not so much the eight speeds (which help to keep the engine in its optimal range, and reduces the number of tradeoffs required in tuning), but the high efficiency — a claimed 98% efficiency in any gear, with an extremely rapid locking torque converter — and high speed, with shifting taking place faster than a person can perceive it.

There are three basic versions of this transmission; the input torque ranges from 300 to 1,000 Nm, and it can be combined with various starting systems, and as a mild or full hybrid. (The 8HP90 Powershift transmission allows input torque up to 900 Nm, or 664 lb-ft. 1,000 Nm is around 737 lb-ft. While the most powerful Chrysler gas engine produces 470 lb-ft, the Cummins B-engine has the capability to go much higher.)

converter

Other key features are a highly efficient, reduced-mass triple-line converter, whose lower inertia helps during shifting and starting; a hydrodynamically cooled clutch, reducing mass movement and optimizing shifting. The system uses a chain-driven axial parallel vane cell pump for efficiency. The torque converter has a twin torsional damper system to allow extremely rapid engagement, so that travelling time with converter slip is substantially reduced.

An offset, chain-driven oil pump helps keep the package compact, while a low-viscosity transmission fluid cuts spin losses.

As Allpar predicted, the transmission uses four planetary gearsets and five gear shift elements (two brakes, three clutches); there are two opened shift elements per gear, minimizing drag losses. Efficiency is higher than the 6HP transmission in first gear, lower in third through fifth, and higher in sixth (identical in second). Only two shift elements are open in each gear, cutting parasitic losses, and extreme transmission shifts, such as eight-to-second kickdown, are possible.

ZF 9-speed automatic

Despite the eight speeds and four planetary gearsets, the 8HP70 transmission to be used in the Chrysler 300 / Lancia Thema (pegged at 700 NM / 516 lb-ft of torque, about right for the SRT8) weighs around 90 kg (198 lb), which is the same as the 6HP26 and less than the 5HP24 or 6HP28 (the first numeral is the number of gears)... while beating both in peak torque. The 8HP70 is larger than the 8HP45, but not much longer.

The very tall first gear allows for early lockup of the torque converter clutch.

Gear12345678R (RWD)R (AWD)Spread
Ratio4.713.142.101.671.291.000.840.672.653.067.03

Chrysler will have 40 different “control maps” to change shift patterns based on operating conditions (covering both rear and all wheel drive systems).

The replacement cost of this transmission, when we checked in December 2012, was $3,935 MSRP — which is what most dealers are likely to charge ordinary customers — or $2,950-$3,550 on-line via a mail-order dealership.

[See the ZF 9-speed automatic]

The Chrysler-ZF partnership

According to Mike Kirk, Chrysler’s director of axle, driveline, and manual transmissions, there were two main reasons for Chrysler’s changes to the ZF automatics.

First, Kokomo was already set up to build transmissions, with its own tooling and robotics, which are far different from those used by ZF. Some changes were made to accommodate the design of the transmission to the equipment and methods used successfully for many years at Kokomo.

In addition, Chrysler needs far more of the transmissions than ZF plans to make. Design choices that make sense for production of 50,000 transmissions a year may not make sense for production of 200,000 per year. To pump out the number of transmissions Chrysler will need, some changes had to be made.

Mr. Kirk said that the partnership with ZF had been mutually productive; while Chrysler owns the intellectual property of any changes they make to the transmissions, they do keep ZF informed. Chrysler can patent any of their changes and methods, including the software and controls, and has some internal motivation to improve the transmissions and their production methods to maintain balance with ZF.

Standards for both manufacturers are high; and both ZF and Chrysler use the same end-of-line test centers, driven by the same software.

A first-hand look at Chrysler’s new 8-speed automatic transmission

Chrysler’s newest technology to improve performance and fuel economy is their segment exclusive 8-speed automatic transmission, hitting the market in for model-year 2012. At first, it will be offered in the Dodge Charger and Chrysler 300 models equipped with the 3.6L Pentastar V6 and recently, we had a chance to log a few miles in the 2012 Dodge Charger Blacktop equipped with the 292hp V6 and the new 8-speed transmission.

The 8-speed automatic transmission comes with the innovative news touch-shifter on the console with manual shift control included by means of Chrysler’s new steering wheel mounted paddle shifters. This paddle shift system made its debut recently in the high performance SRT lineup but when these new 8-speed models begin reaching dealerships around the country, this will mark the first application of the Chrysler paddle shifters on a non-performance model…supposing that you don’t consider the 292 horsepower Dodge Charger a performance model.

paddle shifters

Lots of automakers offer some form of steering wheel mounted shift control ranging from F1-style paddles to buttons mounted in the back of the steering wheel spokes, but with their new paddle shift system, Chrysler has done it right. They have used metal for the shift paddles with a sleek, smooth finish that adds a great look and feel with plenty of accessibility under hard cornering. (The SRT8 has the + and - signs filled in with black paint, while the V6 uses unpainted impressions.)

Some paddle systems leave you hunting for the paddles when you get to crossing over your hands for shifting under hard cornering but that is not the case with the Chrysler paddle system with the ergonomically perfect levers making for quick, smooth shifts. The paddle shift system from Chrysler mated to the 8-speed ZF automatic transmission looks great and performs even better.

slapstick shifterThe other component of the new Chrysler 8-speed automatic transmission is the unique console mounted shifter that uses a “slapstick” motion rather than the traditional shifter movement. The low profile shifter bears a similar shape to the old school slapstick shifter and rather than the normal PRNDL pattern, the 8-speed automatic shifter has just Park, Reverse, Neutral and Drive/Sport mode (in cars without Sport mode and paddle shifters, it has Drive and Low). When you pull it back to move into gear, the shifter does not stay in place – instead returning back to the middle position. As you shift from Reverse into Neutral and then into Drive or Sport, the shifter clicks through the gears but always returns to the center position of the shift console.

The driver information center keeps you updated as to what gear you are in since the shifter does not but should you get confused and try to shift “past” the Park or Sport shift modes, the information center reminds you what gear the transmission is in.

In the long run, the goal of Chrysler’s 8-speed transmission was to be able to combine aggressive gear ratios for the lower gears to bolster torque multiplication and low end acceleration while also offering very fuel economy friendly higher gears to improve the MPGs of this sporty sedan when cruising on the open road. The problem is that the average American consumer seems to frown upon the idea of an 8-speed transmission, believing that they will spend their time complaining about how often the transmission shifts but having spent time soaring around Chrysler’s test track in Chelsea Michigan, I was blown away at the smoothness of the new ZF 8-speed automatic.

8HP 90 powershift

Under normal driving circumstances, such as accelerating away from a stop sign like you would on the open road up to a cruising speed of 55mph, the ZF-designed Chrysler 8-speed is seamless in normal Drive mode and you can barely tell when the transmission is shifting. Once you have gotten to a smooth cruising speed of 55 to 70mph and the transmission has gotten through the gears, the extremely low RPM range allows for minimal amounts of fuel consumption on the open road. However, unlike some traditional transmissions that use non-aggressive gear ratios to bolster fuel economy, the Chrysler 8-speed has plenty of gearing to get the 2012 Charger with the 3.6L V6 from 0-60 in a hurry – as well as allowing the Pentastar to do a pretty impressive smokey burnout.

On the other hand, if you want manual control of the 8-speed Chrysler transmission for some spirited driving fun (or more smokey burnouts), you can pop the slapstick shifter into Sport Shift mode at which point the steering wheel mounted paddle shifters take over. From there on, the driver has full control of the upshifts and the transmission only downshifts when necessary to prevent the engine RPMs from dropping too low. Under most driving conditions, your hands don’t need to leave the 10 and 2 positions so the paddles are in ideal areas for quick shifts during sporty driving situations and when using the manual shift mode while exercising all 292 horsepower, the shifts are much more positive – like you would expect from a modern sports sedan.

planetary gears

Based on my time behind the wheel of the 2012 Dodge Charger Blacktop equipped with the 292hp Pentastar V6 and the new ZF 8-speed automatic transmission, it is clear that this new gearbox does a great job of combining a sporty driving experience with high fuel economy. The sport shift mode allows the driver a more engaging driving experience and when left in Drive mode, the new transmission works through the gears with no notice of the high number of shifts.

Chrysler “broke the rules” once again with the introduction of an 8-speed automatic transmission to the passenger car segment but once consumers see and accept this great system, we can expect other automakers operating in the US offering similar technology. However, with being the first to introduce the 8-speed automatic the Pentastar V6 is made even more efficient in the beautifully redesigned Dodge Charger and Chrysler 300.

 

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