At the Detroit Auto Show, I had the chance to talk with the director of Ram Truck Engineering, Rob Wichman, about the new 2019 Ram 1500. As there was a naked chassis just sitting on display, we got a close-up look at some of the nerdy bits of Ram’s new truck.
The big story for the 2019 Ram 1500 is the mild-hybrid system, which uses a Motor Generator Unit in place of an alternator. That Motor Generator Unit, or MGU, charges the 12-volt system, sends torque to the engine (especially to start the engine in stop-start events), and receives power from the drivetrain for regenerative braking (using that power to charge the 48-volt battery).
The Motor Generator Unit, which FCA calls the “eTorque” machine, is actually rather unique on the 5.7-liter V8 in that it uses air to cool the motor and power electronics (which are all packaged as one piece on the accessory drive). On most motor generator units found in other mild hybrids, liquid coolant from the main cooling loop keeps the motor temperatures down.
An air-cooled MGU is beneficial because it reduces overall system complexity. There are no coolant lines that need to go to the unit, the water pump doesn’t need to be able to handle the additional pressure drop, and the cooling system doesn’t have to be designed to handle the heat loads of the MGU (which, admittedly, are relatively minuscule).
An air-cooled MGU is simple: just bolt this device to the front of the engine, along with some beefy belt tensioners to handle the torque coming from and going to the MGU, hook up some cables, and boom: your MGU is all set. Granted, FCA had to do quite a bit of computational fluid dynamics modeling to ensure that the fan blast temperature (the temperature of the air leaving the back side of the radiator) and the exhaust don’t cause any overheating issues, and packaging was probably a tough chore, but overall, this setup like a clever choice.
The 3.6-liter V6, on the other hand, uses a liquid-cooled MGU plumbed into the high temperature circuit (i.e. the main circuit that keeps the engine cool). The photo above shows the eTorque machine hanging off the front of the engine, inverted so that the MGU’s accessory pulley actually points towards the back of the truck.
Shown in the image above, the small 48-volt battery pack that receives and sends current to the MGU is actually located behind the rear seats. It draws air in from the cabin, and sends it out through rubber exhausters at the back of the cab.
Wichman told me that the MGU is capable of producing up to 130 lb-ft of torque, though he mentions that this isn’t additive torque (i.e. you don’t add it to engine torque to get a total), it’s just torque that’s provided during startups to ensure that when the engine fires back after the driver takes his or her foot off the brake, it’s smooth and seamless. That seems to be the biggest benefit of this mild hybrid system—start stop performance. The motor doesn’t seem to contribute much to actually propel the vehicle forward.
The next thing we talked about was the frame, which is 100 pounds lighter than the outgoing one, in part due to heavy use of high-strength steel. There’s also a bit of aluminum in the frame, especially the transmission crossmember, which you can see here pointed out by the red arrow:
There’s also an aluminum lower control arm:
And the upper is a stamped steel control arm with nylon reinforcement on the underside:
Speaking of the frame, the thing looks wild from the front. It’s got these big octagonal “splayed” rails that—starting near where the front suspension hooks up—actually reach towards the outside of the truck, and attach to the very ends of the front bumper beam.
Here’s a top view in CAD:
The idea, here, is to allow that frame to absorb impacts in a number of different crash conditions, especially the Insurance Institute for Highway Safety’s small overlap crash, which only subjects the outer 25 percent of a vehicle’s front end to an impact with a barrier. The splayed frame rails prevent that small overlap test from bypassing the truck’s crash absorbing structure.
Another key component that allows the Ram to perform better on the small overlap crash test is the frame-welded high strength steel tire blocker, which is found on both sides of the truck, and acts to keep the wheel from intruding into the cab.
The final frame-related things Wichman and I talked about were the Active Tuned Mass Modules, ATMMs, which are essentially little cans bolted to the frame rails on either side of the truck, with solenoid-activated weights inside.
As the HEMI engine’s Multi-Displacement System kicks in, and sends the truck into four-cylinder mode, an underhood sensor picks up unwanted vibrations, and triggers these ATMMs to shake their internal weights in a way that’s 180 degrees out of phase with the engine’s unwanted vibration, thus canceling it out and yielding a smooth experience for occupants. This concept is called destructive interference, and it requires tweaking to the ATMMs depending upon the frame length.
Back when I worked in the powertrain cooling team at Fiat Chrysler, I saw quite a number of studies on the benefits of a “Thermal Axle,” and now, for 2019, it’s an option on certain 4x2 configurations of the Ram.
After the engine has been on for a few minutes, and the cabin heater performance has reached a certain level, coolant is sent through metal tubes, along the frame, down through “jounce hoses,” and into a water jacket in the rear differential cover. That warm coolant heats up the oil in the rear differential, thinning it, and reducing the energy needed for the internal gears to shear the fluid as the axle spins. The result is better fuel economy.
A similar device called a Transmission Oil Heater exists on the ZF eight-speed (see arrow in the image above).
Of all the Ram’s changes, Wichman’s favorite improvement is aerodynamics, which is 9 percent better than the outgoing model in terms of drag coefficient—now reaching 0.357.
That improvement, Wichman told me, came through two primary means. The first has to do with changes made in the rear of the truck, namely the “dovetailed” roof, and changes to the bed, whose sides are 1.5-inches higher, and whose tailgate has a little spoiler on top.
The second major enabler for the lower drag coefficient is the active air dam, which deploys at 35 mph to divert oncoming air down and away from the suspension and other underbody components.
The air dam, which you can see below, retracts at 15 mph, and is clutched, meaning it will break free instead of breaking if a driver hits something.
An interesting tidbit that Wichman mentioned was that the engineering team at Fiat Chrysler actually looked at deployable air dams that reached lower towards the ground, but at a certain point, the dam actually became less effective.
It’s worth mentioning that the only vehicles that get the deployable air dam are those with coil spring suspensions. Air suspension trucks make do without the feature, as they’re able to lower the truck’s ride height 0.6-inches to reduce drag at higher vehicle speeds.
Another major feature that reduces the 2019 Ram 1500's drag coefficient is the active grille shutters, which you can see below:
The main point is to block air (when it’s not needed to cool the engine) from entering the grille and bouncing around in the engine bay—which isn’t particularly aerodynamic—and instead send the air out and around the truck.
Here’s a closer look at the grille shutters from behind the grille:
And here’s the electric actuator (see where the wire leads), which pushes and pulls the plastic “column” up and down, opening and closing the grille shutters:
The active grille shutters, and some of the other feature mentioned are carryover from the previous Ram, but they’re interesting nonetheless. And it will be cool to see how these features work with the new ones to change the truck’s overall demeanor. We’ll report back when we get some time behind the wheel.