Continued from: MaxxForce® Engine Plant Tour – Huntsville, AL
MaxxForce pistons are machined cold to accommodate the distortions of expansion after they get hot. The wrist pin for example is not straight line bored but slightly arched so that the mass acting on the wrist pin is equally distributed between the journal in the piston and the wrist pin. I found it fascinating to know that even a short massive piece of steel like a wrist pin actually bends while in operation due to the extreme pressures imparted by the combustion process in the cylinder.
Jason pointed out the immediate difference between a conventional connecting rod and one used in the MaxxForce 11 and 13 engines. In a similar manner to the main bearing caps, which are fractured, the connecting rods are also fractured. MaxxForce calls this “Sure Lock Technology.” Each cap is unique to its connecting rod and cannot be mismatched. Once torqued, the rod assumes a singularity not found in conventionally machined connecting rods, where faces are machined. MaxxForce 11 and 13 rods caps are also offset as well and sit at approximately a 45° angle. The advantage of this feature is that the maximum amount of pressure that is applied to the rod is translated to a continuous portion of the rod cap rather than being imparted on a seam or machined surface.
As the engine continues down the assembly line additional components are added to the block.One of the design features that were pointed out is the gear set on the face of the engine. These gears translate power from the crankshaft to other devices and lie in recesses inside the block. When the engine is operating, this feature attenuates the sound of the gear sets and contributes significantly toward reducing NVH (noise, vibration & harshness) levels. In reviewing the construction features of the outside of the engine block, one immediately observes the rounded profiles adjacent to the cylinder locations. The designed arc disperses sound over a wider area, thereby reducing the amount of sound from the engine.
As we approached the end of the first production line, the engine is pushed over to the second line via rollers in the floor, which will eventually return it to the front of the building where we started. At this point the engines have exceeded the thousand pound mark, since the bottom end of the engine is nearly complete. Continuing, the engine is fitted with bell housing, flywheel and engine mounts, as various covers and accessories are also fitted. As the engine continues, it approaches the station where the oil pan is installed. Care has been taken to engineer an effective, long lasting, reliable seal for the oil pan, which will be trouble free for years. A wide single piece neoprene material gasket fits over the edges of the oil pan. The pan is then positioned on the line sits and waits for another engine to come along. One can immediately see that there are no holes in the oil pan and gasket which could be used to bolt the pan directly to the block.
As the engine arrives one can see that the oil pickup tube is in place. The pan is positioned on the engine. Fasteners are threaded into holes immediately adjacent to the pan and secured in place using special bolts and blocks that span the lip of the pan. As the bolts are torqued against the underlying spacer block, a finger applies pressure to the flange on the pan as the gasket is compressed exactly to the designed specification. On completion, the pan applies equal pressure across the entire gasket without any distortion of the pan itself. The material used for the pan on the MaxxForce 11 and 13 is steel. Steel is more resilient and resists penetration from foreign object better than a cast oil pan. This is important consideration for commercial use in off road situations.
Shortly after the oil pan is installed, the engine is rotated 180°. The top of the block displays its coffee can size openings as the block is prepared to be mated with its overhead cam, 4 valve, cylinder head, turbos, associated intake, exhaust manifolds, and other components. The cylinder head and gasket are positioned on top of the block and a number of bolts are inserted and started by hand. The engine continues into a caged in area where the robots again resume their task of inspecting, torquing and recording the values to the asset tag in the engine carrier.
Along the line, the engine takes on its high pressure common rail fuel system. This technology is one of the signature components of the MaxxForce engine that are part of the in cylinder emission reduction strategy. The system provides pressures of 32,000 psi for precise fuel delivery, injection timing and fuel combustion. This results in better fuel efficiency, quieter operation and reduced emissions. It was explained that there are 5 injection sequences so that combustion and fuel consumption are optimized. There are 2 pre-charge fuel deliveries, one approximately top dead center and 2 additional injections post top dead center. The spacing out of the fuel delivery allows the fuel to burn more completely and somewhat cooler.
In these last few stages electrical connectors and sensors are fitted and covers are installed to begin sealing the top of the valve train on the cylinder head. During this phase of the production, Jake Brake components are fitted onto the valve train. The MaxxForce engines have a 3 stage Jake Brake as there are 3 separate valve assemblies installed in the head. Each of the Jake Brakes is operated by its own cam lobe driven by the overhead camshaft and can be called in when the driver needs additional braking power. There’s no mistaking what these component are because they are clearly identified as a “Jake Brake” on the castings.
The next stations involve installing emission control devices, which are part of the Navistar Advanced Exhaust Gas Recirculation (AEGR) strategy. The EGR Valve Electric Stepper Motor with Power Open and Close, along with Floating Core EGR Cooler, comprise the bulk of the AEGR technology. The EGR valve is controlled by advanced electronics and is on board diagnostic (OBD) capable and ready. The valve is water cooled and is protected to a temperature of 302° degrees. The EGR valve is operated by a brushless DC motor, reducing maintenance requirements and providing a positive open or closed state without the use of springs. The Floating Core EGR Cooler is encased in an aluminum housing to reduce corrosion. The core of the EGR actually floats within its enclosure as the temperatures rise and fall. Tensional stress and thermal cycling are eliminated by the Navistar design of the cooler.
Moving along, the MaxxForce engine receives its Twin Sequential Turbochargers. The dual staged turbo helps the engine deliver power off the line and power up the grade. A smaller primary turbo initially responds quickly for instant power off the line at low engine speeds. A larger turbo takes over at mid engine speeds and provides the charge needed to power up steep grades. Jason explained that peak torque is achieved between 1,000 RPM to 1,400 RPM and affords the driver the ability to up shift at lower engine speeds with less need to downshift the vehicle. The turbo design that is used has fewer moving parts than VGT and sliding nozzle turbos, which makes it more economical to replace if the need arises.
During the completion phases of the engine’s assembly, all the electrical harnesses are now in place, external hoses and clamps have been installed and tightened, inspection covers are now secured, and the engine is ready for cold testing. Each engine is cold tested in order to prove out that the assembly of the engine was flawless. Throughout the assembly of the engine many sensors, cameras and other electronic and robotic processes have verified and documented every phase of the manufacturing process. In cold start, the engine is hooked up to sensors and hoses and is operated by an electric motor in a secure enclosure. Once the green light is seen on the computer monitoring the status of the engine, it begins spinning over by the press of a button from the console operator. The RPM that are indicated are in the 500 RPM range and observed for a short period of time. While this is happening, oil is being transported to all the critical locations where it needs to perform. After a specific amount of time has passed, the engine is spun up to about 1,500 RPM and it is allowed to operate at that speed for a predetermined amount of time.
The engine being rotated 180°, the cylinder head and gasket have been fitted. A worker has inserted the head bolts loosely in the holes. Robotics examine the top of the engine for faults prior to torquing the head bolts.
It’s amazing to hear this engine spinning over without undergoing any combustion in the cylinders. After a period of run time, the engine slowly unwinds and becomes silent. Technicians open the enclosure and quickly disconnect the engine and roll it out to where it can be moved to ship out. On the test instrument’s monitor, Jason pointed out the performance curves and data of the different components of the engine, which were numerous. Shown on the display were a number of green status check lights arranged in a vertical row, which signified that the engine passed those individual tests. In reviewing the data, the operator can immediately see the performance variables of the engine and if there are any anomalies in that performance envelope. A device like a stethoscope listens and records all mechanical operating components and that data is displayed as a flat line. When that data is zoomed up, one can see small oscillations along the path of the line. No transient spikes from the engine components that are metered in this test verify that the engine is within design specifications. The data that is recorded in this test becomes a permanent record for that engine and is combined with the data in the asset tag.
Once the engines complete the cold run test, a 50% audit is accomplished from randomly selected engines to verify performance. The engines are placed in a queue where they will be run under their own power on a dynamometer and monitored on computer equipment. The engine is placed in a stand and completely hooked up. As the engine is started and comes to life, test instrumentation begins to record the performance of the engine. What is observed during the run is every possible dynamic that the engine can produce. The run monitors much the same performance parameters as the cold run, but what is introduced into the mix is thermal expansion and operational stresses. After observing and recording the performance of the engine, it is subsequently shut down and allowed to cool. Once the engine is disconnected it’s rolled back out into the ship out as another engine is brought in to repeat the process.
MaxxForce 15 Twin-Turbo engine side view. Filling the viewfinder on my camera was not difficult at all. The 15.2L engine will deliver 450-550HP and 1,550-1850 lbs/ft of torque. EGR cooler is seen horizontally on top of engine.
In all of the text above I had not included commentary about the new MaxxForce15 engine. At the beginning of the tour I was told that I would be one of the first guests in the plant to see a 15 coming down the production line. (Awesome) This behemoth of an engine is so much visibly larger than the 11 and the 13 that I have been describing, however, there are a number of unique differences that I would like to talk about. First off, the iron (engine block) comes from Caterpillar and during manufacture all the components are fitted in much the same manner. The 15’s engine block is grey iron design, which has been proven in over 1.2 million on-road units that use the caterpillar C-15. The unique connecting rod and piston assembly on the 15 are massive and feature 4 bolt rod caps. These caps are traditionally machined and feature large bearing surfaces for extended heavy load use and durability. The oil pan on the MaxxForce15 is cast and is described as being isolated to reduce engine noise. A number of special fasteners with blocks are used to secure the pan so that it does not distort the fit of the pan around the bottom of the crankcase. Unlike the 11 and 13 the bolts go though the edge of the pan into the engine block.
L to R: Engines are hooked up in the cold run box and spun up via an electric motor. The engine is initially observed at low RPM for a specific amount of time. The engine is then spun up to over 1500 RPM and its performance is observed and recorded. Important in this test are acoustics where a data line is recorded that monitors every sound the engine makes.
The MaxxForce 15 is a twin turbo, 4 valve, in-cylinder emission compliant engine that uses a high pressure common rail fuel system and the same AEGR components as the MaxxForce 11 and 13 previously described. The MaxxForce 15 can be used in any application where the Caterpillar C15 was used in the RV industry. As I recall, the last C15 that I saw was in the rear of a Newell motorhome at the Tampa Supershow.
50% of the engines that come off of the production line are tested on a dynamometer under their own power. Any fault here will be trapped and identified and resolved before this or any other engines ship.
MaxxForce® Engine Plant Tour – Part 3