2003-01-0410 Turbocharging the Chrysler 2.4L Engine

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Downloaded from SAE International by Old Dominion Univ, Wednesday, October 19, 2016 SAE TECHNICAL PAPER SERIES 2003-01-0410

Turbocharging the Chrysler 2.4L Engine

Garry W. McKissick Jr. and David M. Schmidt DaimlerChrysler Corporation

Reprinted From: New SI Engine and Component Design (SP-1747)

2003 SAE World Congress Detroit, Michigan March 3-6, 2003

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2003-01-0410 Turbocharging the Chrysler 2.4L Engine

Garry W. McKissick Jr. and David M. Schmidt DaimlerChrysler Corporation

ABSTRACT

A turbocharged version of the 2.4L engine has Several internal modifications were required to been developed by the Chrysler Group of DaimlerChrysler satisfy durability and emissions requirements. The Corporation. This new engine is derived from the proven modifications include new valves, pistons, piston rings, 2.4L 4-cylinder, with significant changes to achieve a connecting rods, crankshaft, and bearings. durable, high performance package for the PT Cruiser vehicle. The package includes an integrated turbocharger / A unique, extremely compact exhaust manifold exhaust manifold, oil squirters for piston cooling, and and turbocharger unit was developed to work within the numerous other upgrades to satisfy the demanding minimal under-hood packaging space. The turbocharger performance, emissions, and durability requirements is integrated into the exhaust manifold as one assembly. unique to this powertrain. The purpose of this paper is to This feeds the newly designed aluminum intake manifold describe the mechanical changes to the base engine, the via an air-to-air intercooler mounted in the front fascia. unique turbocharger configuration, and the new parts necessary to accommodate the higher output. 300 300

GENERAL ENGINE DESCRIPTION 250 250

200 200 The 2.4L Turbo engine (Figure 1) shares a common 87.5 mm bore, 101 mm stroke, and 2429 cm3 150 150 BHP (HP) Torque (ft-lbs) displacement with its naturally aspirated (NA) counterpart. 100 100 The rated output, 332 N-m (245 ft-lb) @ 3600 RPM and 50 50 160 kW (215 HP) @ 5000 RPM, (Graph 1) is approximately 51 percent greater in torque and 43 percent 0 0 1500 2500 3500 4500 5500 6500 higher in power than the standard 2.4L engine. RPM Turbo HP NA HP Turbo Torque NA Torque

Graph 1. 2.4L Turbo vs. NA Power & Torque

Variations of the 2.4L Turbo engine are used in three different vehicles: PT Cruiser, SRT-4, and the

Mexican Stratus R/T. Although all versions are derived from the same basic design, there are significant

differences (especially manifolds, oil pump, and accessories) due to packaging constraints in each vehicle

application. This paper specifically describes the PT Turbo engine.

OBJECTIVES

The principal design objectives for the engine were to: Figure 1. 2.4L Turbo Engine · Provide significantly improved output to offer increased performance in the PT Cruiser vehicle. Downloaded from SAE International by Old Dominion Univ, Wednesday, October 19, 2016

· Fit within the limited space of the engine process. It was determined early in the program that the compartment without changes to the vehicle desired strength could be obtained from a cast piston structure. without the added cost and potential noise issues of a forging. A full floating pin design was chosen due to the · Achieve maximum performance using high specific output (89.6 hp/l) and cylinder pressures. premium grade fuels and provide satisfactory The “ski-ramp” pop-up on the crown was carried over from operation with “regular” fuel. the 2.4L NA engine. On both the turbocharged and NA 2.4L engines, the ski-ramp design showed improvements · Maintain maximum commonality with the to the combustion chamber air/fuel mixture through existing 2.4L engine, both in design and computational fluid dynamics (CFD) analysis. These manufacturing. improvements were confirmed through dynamometer testing and translated into improved WOT spark and idle stability. The top land height was set at 4 mm to help NEW AND REDESIGNED ENGINE meet hydrocarbon emission requirements. Due to the small top land and the predicted temperatures and COMPONENTS pressures, hard anodizing was added to the top ring groove to prevent microwelding of the upper compression Many new base engine components were ring. necessary to accommodate turbocharging the 2.4L engine. Several of the changes have subsequently been In another effort to reduce crevice volume, the incorporated into the NA engine to further improve its piston is machined with a double-ovality profile. This durability and maintain maximum component machining allows for tighter clearances between the top commonality. land and bore in the pin axis than otherwise would have TM been possible. The skirts are coated with Mahle Grafal PISTONS – New pistons were designed to meet the to protect against scuff and improve NVH. Final piston-to- following requirements: bore clearance was selected to minimize friction during break-in and hot scuff, while still surpassing the goals for - Strength for peak cylinder pressures that are cold and hot NVH. 50% higher than in the NA engine. - Strength at higher in-cylinder temperatures, Due to the high thermal loading expected on the protecting for stoichiometric wide open piston, block-mounted oil squirters were added to help throttle (WOT) operation per US-06 federal cool the pistons. Targeting the underside of the piston test requirements. crown for the full length of its stroke, tests demonstrated - Minimized crevice volume to help meet future that the squirters reduced piston temperatures enough so emissions requirements. that higher cost piston materials were not required. - Reduced mass so that a common balance Temperatures were measured real-time using thermistors shaft assembly could be used for both the mounted at various locations on the piston. This allowed turbocharged and the NA engines. for greater accuracy than end-of-test hardness measurements and also gave information as to the effects of calibration changes on piston temperatures.

Through testing, a compression ratio of 8.1:1 was chosen as optimum for such things as performance, WOT spark (knock limit), fuel economy and idle quality. In order to obtain this compression ratio with the proposed pop-up crown geometry, the compression height of the piston was set at an aggressive 28.0 mm. Although this did help in driving the mass of the piston down to 335 grams, 18 grams less than the NA piston, it left very little room in which to package the rings.

PISTON RINGS – The 1.2 mm upper compression ring is a barrel shaped, steel ring with a positive twist and a plasma sprayed molybdenum face coating for added wear resistance. The lower compression ring is a 1.5 mm, Figure 2. 2.4L Turbo Piston micro-Napier design made of grey iron. With the full face contact of the micro-Napier edge, no chrome plating is The pistons (Figure 2) are made from a Mahle 124 required in order to meet wear and durability objectives. In eutectic aluminum alloy using a permanent-mold casting addition to cost and environmental benefits, the absence of chrome also yielded the advantages of a faster seat-in Downloaded from SAE International by Old Dominion Univ, Wednesday, October 19, 2016 time for the ring and not requiring outside diameter chamfers that tend to hurt oil consumption. Pressure BEARINGS – The main and connecting rod bearings used balancing of the ring pack, and thus control of the ring in the turbocharged engine are aluminum–tin alloy on motion during piston travel, was obtained through steel backing. They were derived from the bearings used judicious specification of the end gaps. The 2.5 mm oil in the NA versions of this engine, with two major ring assembly is a flexvent (ES-80) three-piece design differences. First, the new connecting rod bearings have featuring a stainless steel expander and chrome-plated holes to feed the oil squirt feature in the connecting rod. steel rails. It was designed to be lower tension and a Second, due to higher transmission thrust loads, the smaller radial thickness than the NA ring, thus upper and lower thrust bearings have contoured faces to maintaining conformability for oil control while reducing provide a higher load-carrying capacity. Standard mains friction for fuel economy. are carried over from the NA 2.4L engine.

CONNECTING RODS – New connecting rods were INTAKE MANIFOLD – The unique underhood packaging of designed to meet the durability requirements of the the intercooler plumbing drove a new design for the intake engine. Previous Chrysler turbocharged engines used a manifold (Figure 3). Sand-cast aluminum (AA319) was two-piece forged steel design that, while more than strong chosen to minimize development and manufacturing lead enough for the application, was heavier than necessary. time versus a plastic manifold as used on the NA engine. After studying possible options such as powdered metal, Aluminum also provided some NVH advantages over the two-piece forgings, and cracked forged steel rods, the plastic manifold. advantages of choosing a crackable C-70 forged steel rod for this application became clear. The all-new design is 78 grams lighter at the big end of the rod than the old Turbo rod, putting the mass of the crank end of the new rod equal to that used on the NA 2.4L engine. This allowed for the use of a common machining set-up of the crankshaft between the NA and Turbo without compromising engine balance or bearing loading. Also, in order to meet engine balance targets, machined weight pads were added to both the small and big ends of the rods. Oil squirt holes are drilled into the rod and fed by the rod journal. These holes, directing oil onto the bore walls, improve cold-start NVH and scuff resistance.

The floating-pin bushing in the small end of the rod was developed so as not to require oil feed holes or the extra machining and bushing orientation that go along with them. To make the joint face of the rod and cap stronger, the M9 fasteners from the NA engine were replaced by ones with an MJ9 threadform. This MJ- Figure 3. 2.4L Turbo Intake Manifold specification, used most frequently in applications susceptible to high-cycle fatigue, reduces the stress concentration at the roots of the threads by providing a The new Turbo manifold is very similar to the 2.4L more generous radius. NA with the main changes being throttle body location, runner length, and plenum volume. The manifold is a two- piece design, with a die-cut gasket sealing the two halves VALVETRAIN – Engine simulations with various camshaft together. The plenum wall is bowed to give nearly equal profiles and timing showed that the new Turbo engine did runner lengths: #1 and #4 are 388mm, and #2 and #3 are not require any change to the NA 2.4L intake and exhaust 382mm. This also serves to create a “low rumble” design, camshafts in order to achieve its performance targets. minimizing half-order frequencies for improved NVH. The intake and exhaust valve materials were upgraded Spark plugs are accessible without removing the upper based on valve temperature measurements taken early in half of the intake manifold for easy service. The manifold the program. The Turbo intake valves are Silchrome-1 and has shown low restriction, low turbulence, good runner to the exhaust valves are Inconel. As with other critical runner distribution (Graph 2), and uniform velocity parameters, valve temperatures were measured again near distribution at runner outlets. the end of the development program for verification purposes with the production calibration. Downloaded from SAE International by Old Dominion Univ, Wednesday, October 19, 2016

THERMOSTAT HOSE 200 TURBO 190

180 FAN ENGINE 170 cyl #1 WATER cyl #2 JACKET HEATER 160 cyl #3 cyl #4 PUMP

Airflow, (CFM @ 25in. H2O) 150 OIL 140 RADIATOR HOSE COOLER 0.2 0.3 0.4 0.5 Valve Lift, (inches)

Graph 2. Turbo Intake Manifold Runner Distribution

Figure 4. Turbo Coolant System Schematic OIL PUMP – A new high capacity oil pump was designed to satisfy the added oil demand due to the piston oil WATER PUMP – A new water pump was designed to squirters and oil feed to the turbocharger bearing. An oil handle the increased cooling demands of the 2.4L Turbo demand study on the turbo engine yielded pressure engine. The previous stamped steel, 6-blade impeller was versus flow data at various temperatures in the operating replaced with a new dual-shroud, injection molded plastic, range. A new oil pump was then designed which would 7-blade impeller (Figure 5). The water pump body was be able to generate the required flow. The die-cast pump modified for the new impeller to tighten clearances and is similar to the carry-over pump in that it is a gerotor improve pump efficiency. The new water pump produces design, driven by the nose of the crankshaft. The gerotor 24% more flow and 48% more pressure rise across the set is based on a proven design from the Chrysler 4.7L oil pump at the 5500 rpm design point than the pump it pump. By changing the thickness of these powdered replaces (Graph 3). No changes to the engine block 3 metal parts, the desired displacement of 15 cm per portion of the pump volute were made. revolution was obtained (up from the old pump’s displacement of 12 cm3 per revolution). Development work made the new pump quieter than the one previously used on the NA engine. This new pump is now used on both Turbo and NA engines for this vehicle.

BALANCE SHAFTS – The balance shaft drive chain, guide, and tensioner have been upgraded to withstand the higher loads of this application. The new chain uses solid bushings with fine surface finish on the links. HNBR material is used on the guide and tensioner faces for excellent high-temperature wear resistance. The actual balance shafts are common between Turbo and NA engines.

LUBRICATION / COOLANT ROUTING – Six tube and hose assemblies were added to the engine and all existing plumbing was modified to accommodate the turbocharging system and the oil cooler (Figure 4). Figure 5. 2.4L Turbo Water Pump Impeller General attention was given to corrosion resistance and thermal resistance relative to material choices. Pressure boundary integrity and packaging were also strong drivers where design choices were made. Downloaded from SAE International by Old Dominion Univ, Wednesday, October 19, 2016

essential areas and coated with a thin elastomer for micro

60 sealing. The outer layers are “step” embossed and

55 coated on both sides for general coolant and oil sealing.

50 Combustion sealing around cylinder bores is achieved

45 primarily through welded-on stopper technology, with a secondary seal created by “full” embosses around each 40 bore in all three layers. All embosses of the Turbo head 35 gasket are of a new geometry to help increase fatigue life 30 and recovery given the increased motion of the joint

Flow (gpm) 25 relative to the 2.4L NA version. The gasket is coated with 20 a higher heat-resistant coating designed to extend sealing 15 life, especially in the inter-bore areas where deck 10 temperatures tend to be higher and sealing is more 5 challenging. 0 0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000 6500 7000 Pump Speed (rpm) Turbo Pump Turbo Radiator Baseline Pump Baseline Radiator EXHAUST MANIFOLD / TURBOCHARGER – The turbocharger chosen for the 2.4L engine is the Mitsubishi Graph 3. Turbo Water Pump vs. 2.4L NA Pump Heavy Industries reverse rotation TD04H-16GK model. This unit employs a 6cm2 turbine inlet cross-section and an integral surge (bypass) valve. The turbine housing and CYLINDER BLOCK – The 2.4L Turbo cylinder block is a outlet passage are integrated with the exhaust manifold. close derivative of the NA iron block. The structure of the The assembly weighs 11.6 kg (25.5 lbs.) (Figure 6). NA block was found to be sufficiently robust so that no changes were required for strength. Additional features were added to the NA block so that both the Turbo and NA can be machined from a common casting. These added features include: oil and water bosses to supply the turbocharger, a water supply boss to the oil cooler and an oil return boss from the turbocharger back to the crankcase. Four cast pads were added to the interior, exhaust side of the crankcase for the installation of piston oil squirters. The squirters are fed from the engine’s main oil gallery located directly above.

Controlling the interbore temperatures at the block head deck is known to be a challenge on high Figure 6. Turbocharger Assembly specific output engines. The most significant enhancement to the Turbo block was the addition of the “ramp” water jacket. There are two cast ramps adjacent to The 6cm2 turbine inlet was selected for minimal cylinder 1 and water diverters located between cylinders boost lag and excellent part-throttle response while being 1-2 and 3-4. This water jacket geometry promotes able to produce 14 PSI maximum boost pressure and increased coolant flow between the bores, adjacent to the sufficient high rpm airflow. The reverse rotation design head deck. Specifically, CFD analysis predicted a six-fold was chosen for its advantageous packaging in the tight increase in the mass flow rate in the three interbore under-hood environment. A key part of this turbocharged passages. These block enhancements added less than powertrain is an air-to-air intercooler (mounted in the front one pound to the casting weight. of the vehicle) allowing increased efficiency at elevated boost pressure operation. CYLINDER HEAD GASKET – Fluid and combustion sealing is accomplished by way of a multi-layer steel The turbine housing and post-turbine outlet are cylinder head gasket. An all-new gasket was needed to integrated into the cast exhaust manifold to satisfy handle the more challenging sealing environment created packaging requirements and reduce the system’s thermal by turbocharging the 2.4L engine. Areas that had to be inertia to benefit emissions. The emissions consideration addressed were: higher combustion pressures, higher is additionally addressed through the strategic positioning head and block deck temperatures and increased head of the waste-gate valve, which completely bypasses the lift. turbine housing to give the shortest possible flow path and enable reduced catalyst light-off time. The new gasket is constructed of three active layers of 0.8mm thick stainless steel embossed in Downloaded from SAE International by Old Dominion Univ, Wednesday, October 19, 2016

The bi-planar exhaust manifold was configured underhood temperatures, and improved operation in cold with paired runners through extensive CFD analysis and climates. flow-bench development. Ni-Resist D5S cast iron was selected for durability at elevated exhaust gas The induction side of the make-up air hose is temperatures. routed to the atmospheric side of the air box. This eliminates the potential of damaging the turbo by Durability of the turbocharger rotating assembly is ingesting moisture or ice formed from blow-by gasses specifically addressed by utilizing a water-and-oil-cooled freezing inside of the clean air duct. A new pocket was bearing housing. Particular attention to the routing of the added to the air cleaner box to accommodate a dedicated coolant return tube prevents excessive bearing make-up air filter. temperature after shut-down.

A two-layer clam-shell type heat shielding system ENGINE CONTROLLER encapsulates the turbocharger exhaust manifold and its integrated turbine scroll to allow heat to vent away from In addition to all the new engine hardware, this is key under-hood components. Finite element analysis the corporation’s first production application of its Next was used to maximize stiffness and improve NVH. Generation Controller (NGC) on a forced-induction engine. Although NGC debuted on a 2002 V-6 engine, the CYLINDER HEAD COVER – A new aluminum cylinder software was still in its early design stages when the 2.4L head cover (Figure 7) was developed to accommodate Turbo engine program began. Learning about a new changes to the PCV system. The PCV system baffling controller and inventing 4-cylinder turbocharger control inside the cover was upgraded to allow for proper algorithms simultaneously provided a significant challenge crankcase ventilating without consuming oil. As with an for the calibration team. NA engine, the system typically draws crankcase vapors using vacuum from the intake manifold. However, when The NGC algorithms are ‘model-based’, the Turbo engine is operating in boost, the induction continuously calculating the appropriate control system pressurizes, and flow through the PCV valve parameters to keep the engine at its desired performance. stops. Blow-by gases must now vent through the make- This is a departure from past control strategies that relied up air baffling. For NA engines the make-up air typically on pre-programmed tables of operating conditions. supplies fresh air to the crankcase and rarely has flow out Combustion air flow is calculated from speed and density of the crankcase. Reversing the flow through the make-up so that an expensive mass airflow sensor is not required. air required significant improvements to the make-up air baffling. Unlike mechanical boost control strategies of the past, the 2003 2.4L Turbo has torque-based boost control. The driver’s throttle input is interpreted as a desired torque. For a given throttle input, the driver will receive the same torque output from the engine, regardless of ambient conditions (temperature, barometric pressure, etc.). NGC can also reduce the torque as required under certain conditions to ensure powertrain durability.

The 2.4L Turbo engine is calibrated to achieve maximum performance using premium fuel. NGC monitors the block-mounted knock sensor and will adjust spark, fuel, and boost if needed to prevent detonation when lower octane fuels are used.

Two new sensors are required for the 2.4L Turbo to measure the temperature and pressure of the air entering the throttle body. First, an Air Charge Temperature (ACT) sensor is located after the intercooler. Second, a Throttle Inlet Pressure (TIP) sensor is needed Figure 7. 2.4L Turbo Valve Cover to predict turbine speed and to measure the pressure drop across the throttle blade. Measurements from the To compliment the improved baffling inside the ACT and TIP are used to calculate the air mass flowing cover, the PCV valve was relocated from the rear of engine through the throttle body and the Linear Idle Air Control to the front. The new PCV valve location is ideal for PCV Valve. Because the turbocharged engine breathes and make-up air hose routings. The shorter hose routing compressed air above barometric pressure, both the TIP minimized hose cost, minimized exposure to high Downloaded from SAE International by Old Dominion Univ, Wednesday, October 19, 2016 and the Manifold Absolute Pressure (MAP) sensors are increased in range to 2.25 bar.

Three NGC-controlled solenoids were added. One allows the TIP sensor to measure barometric pressure during some steady state conditions. The second is used to actuate the bypass valve on the compressor, preventing compressor surge and its associated noise. The third controls wastegate duty cycle, which can be varied continuously from zero to 100 percent.

CONCLUSION

The DaimlerChrysler 2003 2.4L Turbo engine was designed to significantly improve the performance of the Chrysler PT Cruiser. By way of a thorough development process, utilizing advanced analysis and measurement techniques, the goals have been met. The horsepower and torque are increased by approximately 43 percent and 51 percent, respectively, over the standard 2.4L NA engine. The engine can be assembled on the same manufacturing line as the other members of the 2.4L family, and it fits under the hood without requiring any structural changes to the vehicle.

ACKNOWLEDGMENTS

The authors would like to thank all the members of the Engineering and Manufacturing teams that have participated in the design, development and production of this engine. Without their dedication and cooperation, this project would not have been accomplished within the aggressive time schedule.

Special thanks go to the engineers who contributed descriptions of their components for this paper:

Salvatore J. Aluia Michael G. Brigman Gregory P. Faubert Kerry D. Franks James W. Joyce Garth E. LaVere Stan Mashkevich Kevin J. Royce Mark D. Thelen Alexander Zelikov

REFERENCES

1) Alejandro Regueiro. “DaimlerChrysler’s New 1.6L, Multi-Valve 4-Cylinder Engine Series” SAE paper 2001-01-0330