Technical Training
- Author: Mike Cargil
- Subject Matter: 8F24, 8F35, 8F57
- Issue: Ford 8-speed transmission
Mike Cargil examines the Ford 8F series 8-speed transmission line.
Transmissions are complex and co-dependent mechanisms. Their architecture may reflect early design or the collaboration between competing OE manufacturers, but there always seem to be differences. Charging into this complexity is Ford Motor Company, with the concept of creating a new front-wheel drive design and doing it in partnership with General Motors Propulsion. This is not the first time for these two companies, but it may be their most complicated partnership yet.
The point of the 8-speed transmissions for front-wheel drive vehicles (in the case of GM, a 9-speed) is the ultimate pursuit of fuel efficiency. Vehicles are no longer being built with only one market in mind, but with global markets and modular design that allows for broad usage in multiple applications.
In creating the 8-speed designs, Ford decided to do something never done before. They decided to launch three new transmission platforms in new vehicles in the same calendar year. Horse racing has the trifecta, hockey has the hat trick and whatever you want to call it in transmissions, the accomplishment is a significant engineering, manufacturing and marketing accomplishment.
The three series are all listed under the 8F naming convention, and range from small to medium to large. Each platform is mated to an appropriately sized engine and vehicle for model years beginning in 2019. The small is the 8F24, the medium is the 8F35 and the large is the 8F57.
The 8F24 is designed for engines with torque loads to 240 Nm. This is a unique design by Ford and was not developed in cooperation with GM (figures 1 and 2).
The 8F35 is the brainchild of the collaboration with GM on their GF9 platform. There are changes that are made by specific application. This unit is designed for use in vehicles up to 350 Nm of engine torque (figures 3 through 5).
The 8F57 is the next generation of the joint development of the 6F50 and 6T70 platforms between Ford and GM. Ford has uniquely changed this unit to create an 8 speed transmission. This unit is designed for applications to 575 Nm of engine torque (figures 6 through 8).
The application details are in the chart below.
The initial launch for the 8F transmission series is for eight powertrain combinations in 12 vehicle applications. Year one has limited applications, but more are coming.
In the initial design phase, Ford and GM parted ways as to how many gears they would have in their platform. GM opted to use nine gears in the GF9 front wheel drive platform to allow for smoother gear ratio transitions. When Ford tested the design for the 8-speed, they ended up with a large ratio step between the 2-3 and 3-4. This is a result of reusing the 6F50 series planetary designs. Although this was a 0.45 ratio change, it didn’t affect the fuel economy or durability of the unit in testing. Functionally, 2nd gear is often skipped and sees use mainly in manual mode.
In the end, Ford only allowed this large ratio change in the 8F35 and 8F57. In the smaller 8F24, they did a clean sheet design and optimized the step into a smaller move (figures 9 and 10).
The planetary design for 8F24 is different than the 8F35 and 8F57. The 8F24 has 4 independent planetary gear sets. The 8F35 and 57 use planetaries 1 and 2 (Overdrive and Reaction) in combination to achieve gear ratios, and is why you see the large step in ratio change in the larger units.
The 8F24 gear set map is shown in Figure 11, the 8F35 gear set map in Figure 12 and the 8F57 gear set map in Figure 13.
The valve bodies for the 8F series are based in the design for the 10R joint venture transmission series. The 10-speed hydraulic system is called the Casting Integrated Direct Acting Solenoids (CIDAS) layout. The direct copy of the design allowed Ford to use the same TRIECS control software from the 10R platform, thereby speeding up the development and launch of the new units.
The 8F24, 8F35 and 8F57 valve bodies are seen in Figure 14.
Another design feature of the 10R platform that found its way into the 8F series units is the selectable one-way clutch. The design reduces drag by eliminating the large reverse reaction clutch. Due to the size differences in the units, each 8F series uses a unique selectable OWC. There are even two different ways of activation: 8F24 and 8F57 are electric, while 8F35 is hydraulic.
The 8F24 selectable OWC is shown in Figure 15, the 8F35 selectable OWC in Figure 16 and the 8F57 selectable OWC shown in Figure 17.
The largest part of the fuel efficiency gain is found in the use of remote pumps and in their specific design per torque platform. The 8F24 utilizes a variable vane design. The 8F35 features a binary vane pump and is the same as is found in the GM mid-range GF9 platform. The 8F57 uses a variable vane-pivoting pump, which is common with the large GF9 platform and proven in the 6F50 platform.
The 8F24 pump is shown in Figure 18, 8F35 pump in Figure 19 and the 8F57 pump in Figure 20.
The vehicles with the new 8F platforms all have start stop devices. They have overlap between the 8F24 and 8F35. The smaller series use an external accumulator type, and is the same as GM uses in the GF9 platform. The 8F57 has an internal electric pump very similar to the start stop pump in the 10R transmission. The accumulator type costs less, but the electric type has more flexibility in how it is used.
The 8F24/8F35 start stop device is shown in Figure 21 and the 8F57 device is shown in Figure 22.
In the end, Ford had design decisions to make when working with GM on this joint venture unit. By going with eight speeds instead of nine, Ford eliminated the C4 clutch. It reduced weight, loss of efficiency and overall cost. By doing so, Ford had to make shift ratio and timing decisions that made a useable 4th gear unavailable. It also meant that the 2-3 step is quite small, and the transmission will often run as a 7-speed unit instead of an 8-speed platform.
Ford also chose to use the 10R platform’s torque converter design. This is called the integrated torque converter (ITC). This particular torque converter has three fluid channels instead of two, has integrated functional components and applies the torque converter clutch toward the hub impeller assembly instead of toward the cover. This is more challenging to control, but it saves space and weight.
Ford also chose to redesign the main controls, which includes the valve bodies and oil pump assemblies. This redesign allowed for the use of the common 10R software platform, reduced the amount of valves required to achieve hydraulic control, and streamlined the process into a common design amongst all 8F series units.
The expedited delivery of all three platforms has created a surprising opportunity for Ford. They intend to allow these units to carry them through the next few years as they heavily invest in more electrified vehicles. As a global manufacturer, they are serving mature and emerging markets the world over. Outside of North America, the electric powertrain is required due to rapidly evolving local regulations. Ford, GM and other OE manufacturers are heavily investing in electric. The 8F is the latest series that will help Ford get there.
