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Found 2 results

  1. Thom Cannell Contributor, GM-Trucks.com November 26th, 2018 Out of the gate you have to be asking the same question as we, “A four-cylinder engine in a truck? My Silverado?" Forget that the engine is rated at 21-combined EPA fuel economy rating, similar to base V-6 engines from Ford’s (3.3.L) and Ram (3.6 with a light hybrid system). Forget that the all-new 2.7-liter engine makes more power and torque than the LV3 4.3-liter V-6 and has accumulated over one million test miles in development. Just forget it…But…Like you, we stumbled over the entire concept. For answers to what some in the industry see as a profound mistake, we turned to those directly involved in its inception since a pen was put to paper, more likely a stylus set to a digital tablet at GMs Global Propulsion Systems in Pontiac, Michigan. Read Thom's 2019 Silverado 2.7L First Drive Impressions Here Kevin Luchansky is the assistant chief engineer for the new 2.7L turbo and formerly was the group manager over all valve train and cam drives. Our interview began with his statement, “This valve train is, we believe, industry leading and industry first.” He is, of course, referring to the Tripower system of cylinder deactivation that lets this engine run on just two cylinders. We’ll get to that. A very happy and proud Kevin Luchansky, a critical member of the 2.7-liter engine team. Since pen was put to paper, development has taken approximately five years, three years since metal, and it was specifically developed as an all-new truck engine from inception. Our first question was what you’d ask, “Kevin, why a four-cylinder in a light-duty truck?” That’s a good question,” Kevin responded, “and it’s all about efficiency. A few years ago we started to look at how to make the most efficient, most fun-to-drive package we can offer our customers, … and to provide what we think the customer would want. This four-cylinder (engine) provides us with excellent torque response. On this engine torque is near instant, less than two seconds at 1,500 rpm is very, very good. In order to accomplish this, we looked at several things. The fact that you've got big cylinder displacement allows us to design the dual-volute turbo that we have, keep the (exhaust) pulses separated and allow the turbo to spool very quickly. Also, we were able to package the turbo on the four-cylinder in an ideal location. It's mounted sort of midway up on the engine and directly in the center. If you know much about engines and exhaust systems, effectively we had equal length from every cylinder to the turbo.” We asked about the competition, which is a hard fact. “This engine is the base engine on the LT, the new RST and competes with Ford’s 3.3L and Ram’s 3.6L. This engine provides a lot of torque down low, much more than the competition. We're excited for our marketing-drive events where folks can compare those applications, because this (powertrain) is significantly more powerful down low and is fun to drive because of massive torque down low.” Note that there remains confusion about this motor versus Ford’s 2.7-liter. Though of similar displacement, GM’s engine was designed as a base engine for light duty trucks. Ford’s is a premium high-performance motor. Apples and oranges. The new engine had to meet objectives in fuel economy, power, weight saving. After all, an engine program costs tens of millions of dollars. The new motor is 80 pounds lighter than the 4.3-liter V-6 engine it replaces. That motor will remain available as the base engine in Work Trucks. “We feel we are offering customers great choices with all the powertrain combinations we have. We provide six different powertrain options starting with the 4.3L V-6 and an AFM version (8 cylinders/4 cylinders) version of the 5.3L for the work truck options. Then we step up to the LT, with the 2.7-liter and 8-speed, and you can upgrade to the 5.3 with Dynamic Fuel Management where engine runs on eight cylinders down to two, whatever it needs for optimum displacement and paired with the 8-speed transmission. Then the 6.2-liter paired with the 10-speed in the upper versions like Trail Boss, and 3.0-liter diesel in some models.” One of the prime directives for the new engine was durability. “I'd like to talk about some of the hardware in the 2.7-liter, from a durability perspective. This engine is not a car engine we've taken and put a turbo on to make a lot of power. This engine was specifically designed for this application, for these cylinder pressures, a lot like a diesel engine. If you think about diesel engines, there are four-cylinder heavy-duty diesel engines available. This engine was designed similarly. If you look at the details, the hardware is similar to what you'd find in a light-duty diesel. Like the piston, which has a cast iron ring carrier that holds the top ring; that's much different than a standard naturally aspirated engine. That cast iron ring carrier can handle the high pressures that a downsized turbocharged engine produces, and makes the piston very durable.” Pistons use a cast-in iron top ring carrier for durability against high in-cylinder pressures. It’s noticeable as less reflective in the chromed display cutaway. Kevin says the program spent good money on seemingly small things, like PVD coated rings. Physical Vapor Deposition coatings are very hard coatings that reduce wear. Piston crowns in the 2.7-liter are 100-percent machined for long-term durability. “The point I want to make is that, in terms of rotating and reciprocating parts is, there was no expense spared in making this a very durable engine. For instance, this is the strongest connecting rod we've ever designed for a gas engine, a tri-metal design. It has a forged steel crankshaft, and rod and main bearings are select-fit, as seen in many light-duty diesel engines. This is for excellent wear resistance and debris resistance. There was no holding back on picking the best parts the industry has to offer.” By now you’ve likely looked at some of the power and torque charts. Torque holds at nearly 90-percent almost to the red line, with matching horsepower. “It holds on pretty good,” Kevin responded. “It makes 310 horsepower at peak, but doesn't really roll off dramatically. That makes it fun to drive, very linear.” Though its published "time-to-torque" of two seconds seems long until you count “One and Two”, it’s not much different from other engines. “Let me explain. Time to torque is an industry standard test for turbos, where you hold the engine at 1,500 rpm on a dyno and don't allow it to go up in speed. You go from zero throttle to maximum and start the count. Then you count how quickly the engine achieves 90-percent of torque. It's (a test of) how fast the turbo responds, as 1,500 rpm is where the engine spends a lot of time in its operation. The best way to think of it is, with a manual transmission and you stepped into the pedal, how fast to you get torque. Two seconds is pretty quick.” Of course this introduces questions about the dual-volute turbocharger, which is a technology sometimes seen in diesels, and with a different design than other twin-scroll turbos. “Response is all the dual-volute turbo, one Borg Warner has just released and is an industry first application. Dual-volutes are, effectively, two chambers or two separated exhaust "screws or scrolls". What you see is the integrated exhaust manifold, which does a few things for us. One is provide heat, taking heat away from the turbo when it begins to get hot. That helps us with efficiency at high loads, like towing. You can see that we've paired the center cylinders together, so cylinders two and three are paired, then cylinders one and four are paired together. What that does is make equal firing order (firing order is 1-3-4-2) so you get, basically, even pulses and they are completely separated all the way to the turbine wheel, and we've separated them as far as possible, 180° apart from one-another. That's what the industry first really is. There are dual-scroll turbos that exist in high volume, but they come together at the same point at the turbine wheel, which means you can have exhaust gas bleed over from the cylinder that's firing to the cylinder that's not firing. Keeping them separated as far as we have done provides a very strong pulse hitting the turbine blades. That's how we get the fast spooling; it's pretty neat!” Borg Warner’s dual-volute turbo uses fixed geometry instead of a variable (VGT) design. The ducts, one inside the other, wrap around concentrically with the inner channel wrapping half way around before its gasses hit the turbine wheel, the outer volute wraps an extra 180° before its stream of gas strikes the turbine. “For example, if you put your two fingers together, that's what a typical twin-scroll would resemble, each dumps into the turbo and you can have cross talk,” Kevin explained. “That reduces efficiency as cross talk reduces gas pressure to the turbo. Also, this turbo is very aerodynamically efficient at low rpm.” “What I can't stress enough is that we have focused this engine on low-speed torque delivery. You should be impressed with how much torque is available, and that gets back to efficiency and drivability. If you have lag, you'll press on the gas pedal more. If we provide instant torque the driver doesn't go as deeply into the throttle, which produces better real-world fuel economy. Our new engines are focused on low-speed torque delivery. The big four-cylinder engine arrangement allows for good gas flow separation and equal lengths to the turbo - it's harder to do that with other engine architectures. By this time we were itching to talk about the novel valve train, which GM has called Tripower (when we first heard that name we thought, Pontiac’s three two-barrel carbs?) So, Kevin, what is the new Tripower? It's simple in concept; a single pin shifts the cam's lobes to produce differing lift profiles. What we've done is, couple cylinders one and two and cylinders three and four, so the first are on one slider in this four-valve overhead cam engine. There are three lobes, the high-lift lobe, a low-lift and a no-lift lobe (Note that cylinder one is the cylinder that never de-activates so it has only low-lift lobes). Between the lobes is the shifting groove geometry. We have two pins in the actuator, one moves in one direction, the other in opposition. The way the pins work, one pin drops in and shoves over one lift, the other pin drops in and moves to the next. So, in two cam rotations we can go from high-lift to AFM cylinder de-activation. The first rotation would go from high-lift to low-lift, the next rotation would go from low-lift to AFM. It's extremely fast. We can be in AFM for fuel efficiency, and if the driver steps into the throttle we can get to high-lift within two rotations and at the same time the turbocharger is spooling. Within a few seconds the engine goes from fuel miser to making peak torque. It's really neat and seamless to the driver. The changes are imperceptible. It's simple, and robust.” Kevin points to one of two of the electronically activated fingers that move cam lobes into position for, either high-lift, low-lift, and no-lift, the later for Dynamic Fuel Management. GM is maintaining its own control over the system, the camshaft is machined in-house, “from billets of the best steel money can buy. A neat process and very robust parts and they're like jewelry when you see them on someone's desk.” Moving along, we asked about thermal management. It seems most manufacturers are using electric pumps for power management and variability. “For the 2.7, it all starts with an electric water pump. We're able to control it from basically zero pump speed to maximum. The pump is completely decoupled from the engine, which allows us to flow what the engine and other components require, including cabin heating. Turbo placement is important; the pump is down low relative to the turbo, which we'll get to. The dual-volute turbo is cooled by oil, and by water. The water is either moved by thermocycling, or pumped. Lot of people have had experience with older turbos, and our engine has both oil and water-cooling. What is neat about the four-cylinder engine and turbo placement is, you can see there is a feed line (water) that goes in to the turbo and out of the turbo and they head upward. That provides natural thermal cycling. If that's not enough, we can turn the pump on to keep the turbo cool. 80's turbos didn't have coolant, only oil, and there was lots of oil coking issues. We've designed this engine for a truck, and the devil is in the details. We paid attention to issues like cooling to drive durability.” If you’re into deep tech, or run a parts department, the pump is a brushless DC pump, and completely controlled by the ECU. Kevin says the system, the block and the head, are completely separate in their coolant systems, so, a split cooling system. “When the engine starts, there's a lot of heat in the integrated exhaust manifold. We have a pipe directly off it and we use it for exhaust heat recovery. From an efficiency standpoint, we heat the oil in the transmission and engine to get them rapidly up to operating temperature to reduce friction. What that means for the driver, it makes the engine and transmission hotter, quicker, for friction reduction, cabin heat and emissions control. Though not part of our discussion, the oil cooler is water cooled. The other thing the pump allows us to do is over-cooling unrelated to the engine speed. For instance if you're running at a light load and suddenly tip-in with the throttle and ask for a lot of torque, we can quickly force coolant at a faster speed than if the pump was attached to the crankshaft. We can overcool the cylinder head, forcing coolant into the hottest part of the head, and in turbocharged engines that reduces knock, an efficiency enabler. Remember, this is an 87-Octane engine running at 10:1 compression ratio, high for a turbocharged engine.” Injection pressure is 3,000 psi as the industry moves to higher and higher pressures. It uses mechanical (solenoid) injectors that can deliver multiple injections. There’s also a fully variable oil pump, which means it is always right-volume for the given engine condition. It's controlled by the ECU to deliver the correct oil volume under any condition. And, we confirmed that the block is high-pressure die-cast aluminum with cast-in iron liners and made in-house. The cylinder head is aluminum from a semi-permanent mold, and also made in-house. “It's all machined in-house and the engine is built in Spring Hill, Tennessee. There’s a lot of USA content in this engine.” Some of the engine's technologies focused on City fuel economy, as well as high-load conditions. “The combustion system is designed for either condition and allows us to run 87-Octane fuel. Stop-Start works well for city fuel economy, as does as Active Fuel Management and Active Thermal Management. Hidden are the friction reduction steps we've taken like the electric pumps, select-fit tri-metal bearings and a low-friction roller chain, driving the camshafts. That’s for durability, and it's relatively immune from stretching.” The engine uses driven chains to operate cams. No cogged belts for durability and long life. One other comment on durability; we run the same durability schedules as any small-block truck engine because it is a truck. Don't think we skimped on durability testing; it's as durable as the legendary small block. What we did not know prior to our interview, Kevin was the architect on the engine, putting the first lines on paper five years ago. "This was one of my ideas, and they said why don't you go and execute it." Kevin, we’re honored to know you.
  2. Thom Cannell Contributor, GM-Trucks.com March 7th, 2019 Heavy Duty trucks mirror the contest for market domination in light duty trucks. This year both GM and Ford announced significant upgrades to the engines powering their all new 2500 and 3500 HD trucks as each company upgraded their diesel engine, and delivered new gas engines. At GM, the launch event centered on Chevrolet, who brought in truck writers from every segment—popular to fleet management—to Flint, Michigan’s Flint Truck Plant. Flint is the original home of General Motors trucks and the spiritual and historical home of the UAW. So, Flint Truck Plant is receiving an all-new facility constructed and designed for just HD trucks, with the former truck assembly areas destined for warehousing and future projects. New L8T 6.6-Liter Gas Engine We first spoke to Mike Kociba, a GM engineer and part of the Small Block team to learn about the new 6.6-liter V-8 engine we'd been anticipating. Mike told us the new motor “is a marriage of the six-liter it replaces and an upgrade in technology levels to Gen 5 architecture.” A careful look will disclose similarities in key areas where GM has maximized their experience with the six-liter’s durability and improvements in performance levels derived from Gen 5 architecture. “Specifically, new here is the gray cast-iron block which is unique for this application, hyper-eutectic purpose-built pistons for this application and heavy-duty requirements, forged powdered-metal connecting rods, and a forged steel crankshaft,” Mike continued. The most significant change is the addition of Direct Injection. It’s all new, an industry first for the heavy-duty market and new to GM trucks. “When we added DI, we took the roughly 400 KPa fuel pressure from the low-pressure pump and dialed it up to roughly about 15 mPa for engine operation under key conditions,” Mike continued. “That allows us to increase compression ratio, now 10.8:1 using regular fuel. Without DI you're not going to hit those numbers without losing a lot of spark efficiency. With those additions, and the six millimeter longer stroke, that gets us up to 6.6-liters.” “That suite of changes allows us to hit class-leading gasoline engine torque, at 464 foot-pounds at a lower engine speed than the outgoing six-liter was optimized for. I'm proud of its 401 horsepower, which is SAE Certified, no games, legitimate. This (engine) is purpose-built to crank out those numbers day, after day, after day with no compromise in durability. Customers can have confidence they're going to pull, tow whatever trailer you need.” There are other new features like an all-new water pump and a massive cooling fan to meet the demands of the HD customer base. New is how the water pump drives the fan through a one-inch shaft using purpose-built bearings to handle loads. Another first for HD is a variable-output oil pump. “No mater what the severe operating condition is for the customer, the pump is capable of dialing in more, or less oil pressure regardless the requirement. The engine features an aluminum oil pan, nylon 6-6 air intake, and stainless steel exhaust manifolds unique for the Heavy Duty market. That’s because HD market has specific requirements for (fuel) enrichment and these stainless manifolds will meet those requirements. “We have variable dual-equal valve actuation, like on light duty, where intake and exhaust are phased together and controlled through the actuator on the front cover. It's chain driven for accessories.” GM designed this engine specifically for upcoming standards for particulates and NOx emissions standards. “With this architecture we're not just making power and torque, but improved emissions and improved efficiency.” Mike continued. We noted the massive valves, which Mike said are common with Gen 5 architecture for valve layout and their pushrod technology. “That's how we get this compact shape. When you compare the size of the two engines, they're similar, which is due to the common 4.4-inch bore spacing.” A unique feature of the new engine is inter-bore cooling. Coolant flows between the Siamesed bores, notably in the upper bores where there’s a tendency to generate higher temperatures. “For two-valve technology of course you've got the spark plug, and the fuel injector, splayed outside. To avoid heat, we have the coil mounted directly on the rocker cover and the boot mounted next to the manifold with industry-standard individual coils for each cylinder.” This is great stuff, we though, but engine development isn’t cheap. So, why a new 6.6-liter when the 6-liter was doing well? “We needed to improve to Gen 5 level of technology to be sure (the engine) is capable of delivering on durability requirements. Customers love the convenience of gas, but if you look at the market—for instance trailers with more gadgets and slide-outs—everything is getting heavier. Customers want to be sure they can tow with confidence, no compromises, whether it's fuel economy, power, torque, emissions, efficiency, they don't want to pull up to their neighbor and have to make excuses. That's what we targeted. No compromises. With the significant technology we put into this engine, it makes segment-leading torque without compromising efficiency or emissions. Peak torque is at 4,000 rpm, 400 rpm lower than the 6.0-liter. Three things enable the new 6.6-liter's better power output. Direct injection (DI) allows us a higher compression ratio; longer stroke is good for increased torque (but not as good for horsepower as piston speeds are high) and for heavy-duty application where you need torque everywhere it’s why we focused on a longer stroke to get to 6.6-liter displacement. Those changes enabled us to broaden the torque curve, which is up 20% everywhere, for greater work potential.” We thanked Mike and asked if we’d missed anything. “Small engines with turbochargers allow them peak torque off idle, but for heavy duty we don't want that complexity. For the Heavy Duty segment we (General Motors) have durability requirements—Global Engine Durability—that are unique and very long and stringent requirements. We know customers need 401 horsepower and 464 lb.-ft. of torque today, tomorrow, and every day for years to come with no compromise in durability. We know our customers and, if they can't use their truck today, they might not get paid. That's why we focus on durability.” Brand New HD 6-Speed Transmission With that in mind, we next spoke to the systems chief engineer for six-speed FWD and RWD transmissions Rich Mardeusz. More power and more torque tend to break an older transmission. So, we wanted to know what changes had been made to the new transmission to carry the additional torque. “We started with the 6L90 that's in the current HD vehicles and full-sized vans (and ZL-1 Camaro and CTS-V), received the horsepower and torque curves from the engine engineering teams and then performed an analysis of all mechanical components from front to back,” Rich said. General Motors uses specific simulation tools for different parts. “For instance, we have a "gear damage analysis tool" for analyzing the gear set and how much damage it may receive over the life of the vehicle,” Rich told us. The result was a need to improve the torque converter and the clutch pack, which needed to be more robust to accommodate the greater power output of the upgraded 6.6-liter V-8 engine. From a clutch pack standpoint, changes were simple, according to the engineer, as there was enough room in the case to add a clutch and one backing plate to each of the clutch packs to handle additional power. When it came to the torque converter, things changed. “We looked at the components from a heavy-duty diesel torque converter and a high-output gas torque converter and then took the torque-carrying components from the diesel and married them to the spring and damping components from the gasoline torque converter. That’s what was needed to accommodate the approximate 22 percent across-the-board torque increase.” So, the new torque converter can A) handle the added torque of the new engine and B) damp out the firing frequencies from the gasoline engine, which are significantly different from a diesel engine. All of the shafting and gears were able to handle the torque. Interestingly, there is no dipstick. GM has the confidence to eliminate it, and only change fluid at suggest intervals of approximately 100,000 miles, more often for those who mostly tow, or drive over mountains with full loads. Another surprise, the transmission uses GM-spec Dexron VI fluid, GMs standard since 2005, as they found no reason to change. 2019 L5P Duramax 6.6-Liter Once we’d completed our gas powertrain interviews, we turned to the diesel side of Heavy Duty. We spoke to Max Sala, whose Italian accent tipped us to an affiliation with GM’s diesel engine center of excellence in Turin, Italy. Max said that their objective for the new Silverado HD was to increase towing capacity and ensure functionality with the new Allison/GM transmission. Remember, the Duramax 6.6L Turbo-Diesel V-8 engine makes 445 hp. and 910 lb-ft of torque. “We added a bigger fan now 28-inches, a bigger oil cooler that is upgraded from 14 plates to 19 plates, and we fine-tuned the cylinder head gasket” Next up were improvements to the engine-brake capacity, taking into consideration towing capacity. “It’s better by 14-percent and we introduced smart activation of the engine brake,” Max continued, “There's still a button for manual activation, but for safety there's automatic activation at certain RPMs.” Under the new control system, the powertrain will recognize any need for the engine brake and activate automatically. For instance in driving down hill and forgetting to shift, the higher RPM means automatic activation. “With that, we have better after-run strategy. Every time you tow uphill, temps rise and you have a message to cool the engine when stopping. If, by chance you forget and close the door, the system cooling system activates automatically for up to 15 minutes to cool the engine for reliability.” That isn’t the end of changes, as the engine has been completely recalibrated to match the new 10-speed Allison transmission. “Emissions have been improved and fine-tuned to maintain the best efficiency the transmission can offer to our customers.” With these changes, most importantly, Chevrolet says they are now capable of delivering full torque at any time, in any gear, and that they have done everything to the engine, transmission, driveline, drive shaft and frame to improve strength and durability. “What's important is how safe (the new HD trucks) will be and how comfortable it will be for our customers to drive these huge trailers up, and down hills.” Max concluded. Allison transmissions have gained a peerless reputation for strength and durability. Adding a 10-speed transmission branded with the Allison name is a great choice. David Ames, now GM assistant chief engineer on the Allison transmission and liaison with Allison, is a former Allison engineer. A natural fit. The 10-speed is a collaborative effort with joint development of the analysis, engineering, as well as testing. So, testing was performed at Allison and at GM, each with their own set of rules and test regimes. “We go back and forth”, David told us. “Today we have a ratio-span of five and this transmission has a span of 7.2, so the new 10-speed provides both more overdrive and a lower first gear.” We asked about the projects’ starting point. “We (at GM) come out with a "here's what we're looking for" and we begin an internal development contract. It was a pretty clean sheet of paper. So, the controls on the bottom are from a smaller 10-speed, some pieces and parts, but not the entire controls package. For the most part, it's all new to handle the increased power and much larger torque. We collaborated with Allison on this transmission (GM does have a 10-speed transmission of its own) which made it necessary to meet their (Allison) design requirements, their analysis requirements, their engineering requirements, as well as our own. It's a very compact transmission. If you had a 6-speed for comparison, this more dense, more compact and solid to get ten speeds into a package that would still fit nicely into the vehicle and not take up too much space,” David continued. This transmission’s torque converter has a lock-up clutch and is unique in that it will lock up in first gear, even under max loads. So, if you're pulling 33,500 pounds, you can do a first gear launch and lock up right away, which helps get rid of heat. We asked David why this is important. “Normally in first gear you're under high torque and generating a lot of heat, which puts a lot of demand on the cooling system. Locking up gets rid of that heat and the 7.2 ratio gives you a lower first gear. For instance, the six-speed uses a 3.1 first gear and the new transmission has a much lower 4.5 first gear. It's got four planetary gear sets, six clutches and the main place you'll notice the ten speeds, not only in launches and driving with heavier loads—it's very smooth—is going down a grade. Often you're trying to downshift to save brakes and having ten gears you can usually hold the right speed and not feel like you're running over the car in front of you, tapping the brakes or going too slow.” “Also, we built in the first OEM PTO option. Note that the chain drive to the PTO is engine-speed driven rather than turbine-speed driven, which is important to many commercial customers, and it’s quieter drive than gear driven systems.” We asked David for an overview of the combined Duramax-Allison package. “For those who need it, it’s a nice package, one we're very proud of because of the outstanding durability. I think we're going to do a better job of putting power to the road than anybody out there. Whatever torque the engine is putting out, it's getting to the road in an accurate way. I think this transmission will be far more durable than people need it to be. Four-five years from now people will understand how durable it is.”
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