With the market launch of the three-cylinder turbo engine CE12 with direct injection in 2020, PXC completes its engine portfolio of the new core engine family. It meets all project goals in terms of performance, torque, low-speed torque, fuel consumption, emissions and NVH behavior. The engines, which in the meantime consist of two assemblies, are already manufactured with a high proportion of series tools, have successfully completed various engine test runs and vehicle tests in more than 10,000 hours, and have achieved a high level of maturity.


New gasoline engines for the Chinese market

The strategy of Power Xinchen Engine (PXC) is to modernize the entire engine portfolio and to enable the new gasoline engines for future requirements of the Chinese market with regard to further tightening of emissions legislation as well as improved fuel consumption and comfort. These engines must be very flexible for integration into different vehicle concepts from different vehicle manufacturers. The new core engine (CE) family consists of three- and four-cylinder engines.

After the in-line four-cylinder CE16, which started in October 2017, and the CE18, which started as a 1.8-l variant in early 2019, the next step now follows with the completely newly developed in-line three-cylinder CE12 - a 1.2-l- TGDI (Turbocharged Gasoline Direct Injection) engine that will be launched in the first half of 2020. It completes the current PXC engine portfolio in the growing segment with a displacement of 1.0 to 1.5 l. The concept contains many new design features to meet the future emission level CN6b and other, but also the constantly increasing customer requirements. The CE12 engine can be used as a drive for conventional cars, SUVs or light vehicles, but is also available in various hybrid concepts (48 V belt starter generator (RSG), hybrid, PHEV-P1 and -P2,

This article describes the technology and objectives of the CE engine family, in particular the CE12, the basic design features, the NVH concept and the thermodynamic design. In addition, the route to various hybrid applications and further improvements in fuel consumption is shown.


Core engine platform

The PXC core engine platform currently consists of four-cylinder engines with 1.6 and 1.8 l displacement with 84 mm bore spacing. This platform is derived from the well-known four-cylinder engine family, which was developed in a cooperation between BMW and PSA [1] and has been successfully used in various vehicles from these OEMs for many years.

In order to increase the displacement, a 1.8 l variant was derived on the basis of this engine development, in which - with largely identical technology - the bore and stroke were increased. The next step is to further develop the CE engine family in the direction of smaller displacement and lower power, Figure 1 .



Due to the reduced overall length, the CE12 concept with three-cylinder offers a good basis, on the one hand for smaller vehicles, and on the other hand for hybrid applications, since the additional integration of an electric motor in the drive train is thus made significantly easier. As a consequence, the distance between the holes of the three-cylinder engine was reduced to 82 mm, Figure 2 . The CE12 is a completely new development from PXC, even if some components of the existing CE motors are used.



Main techniques

PXC supplies engines of various types to various vehicle manufacturers and has placed great emphasis on developing a modern, flexible, compact and robust concept. In addition to the goals for performance, fuel consumption, emissions, weight and costs, the NVH (Noise, Vibration Harshness) behavior was also important. Although the final NVH result is strongly influenced by the specific vehicle design [2], the goal was the engine best possible execution, Figure 3 .




Crankcase

The crankcase is made of ductile iron (GJL 250) as an open-deck construction with a long water jacket, long oil pan shirt and conventional, individual bearing brackets made of GJS 450. There are two cooling holes between the cylinder bores to reduce the high temperature load due to the high maximum specific output of 87.6 kW / l and the BMEP level of almost 25 bar. When designing the structure, the strength and general stiffness were of particular importance, since this central component is an important part of the entire engine-transmission system. The result of this consistent optimization in the direction of preferred sound radiation shows the benchmark position of the CE12 in calculated sound levels of the combustion excitations in a scatter band of three-cylinder engines of this displacement class.

Although a maximum combustion pressure of over 120 bar is possible, the structure offers good deformation behavior of the cylinder bores for the best shape filling capacity of the piston rings, Figure 4 . This is the prerequisite for developing piston rings with low preload, low friction and low sensitivity to oil thinning during cold starts and low blow-by rates [3].



Crank drive with balance shaft

The main part for low fuel consumption in the crank mechanism is provided by the small diameters of only 42 mm for main bearings and connecting rod bearings. High-strength forged steel is used to achieve the required structural strength and rigidity. Different combinations of material qualities and surface treatments were analyzed and tested in order to achieve the best compromise between durability, cost, reliability and stability in the manufacturing process. Finally, a high-strength 42CrMo4 forged steel with strength rolling was chosen in all bearings.

On the control side of the crankshaft, two pulleys drive the belts running in oil for the valve train or the oil pump. In addition to the small bearing diameters on the crankshaft, the design of the operation for low-viscosity oil of quality 0W20 also makes an important contribution to the low friction power level of the engine. This combination was made possible by careful and balanced bearing selection using 3D elasto-hydrodynamic (EHD) calculation. High-quality bearing shells with three layers were selected for both the main and connecting rod bearings in the standard design.

On the flywheel side, the driving gear for the balancer shaft and the encoder wheel are pressed from stamped sheet steel. The drive gear is bolted to the balancer shaft and carries one of the balancing weights for the compensation of the first order mass moments. To optimize acoustics, the gear wheel of the balance shaft is decoupled by an elastic intermediate element. The leveling compound at the other end of the shaft is forged directly onto the shaft.

The balance shaft is supported on the drive side via a ball bearing and on the side of the second counterweight via a needle bearing, Figure 5 . The balancing concept is ideal for completely compensating for 1st order mass moments in a three-cylinder engine, whereby 50% of the oscillating forces are balanced by the counterweights of the crankshafts. The remaining 50% are eliminated by the counter-rotating counterweights of the balancer shaft, which completely eliminates the free mass moments of the 1st order [4].



In addition, the balance shaft drives the water pump at the free end. This makes it very easy to design a beltless engine as part of a hybridization (P2 / P3 concept) without design changes if both the air conditioning compressor and the power steering pump are electrically driven.


Cylinder head

The cast aluminum cylinder head, Figure 6 , is equipped with four-valve technology, a central spark plug position and the injectors are arranged on the side below the suction system. This enables good cooling of the combustion chamber roof, which is difficult with small cylinder bores and limits the achievable maximum engine output. The two-part water jacket enables an integrated, water-cooled exhaust manifold.


This can drastically reduce the need for enrichment at high loads. The maximum exhaust gas temperature at the turbocharger inlet can be maintained without disadvantages [5]. This represents an important contribution to reducing full load consumption and is at the same time an integral part of a future RDE concept.

The intake side of the cylinder head is shaped in such a way that it represents part of the intake system volume, which on the one hand helps to optimize it for the response behavior of the engine, and on the other hand makes the intake system inexpensive as a single shell.

Parts of the camshaft bearing are integrated in the upper part of the cylinder head. It houses both camshaft sensors and the high pressure fuel pump that is driven by the exhaust camshaft. At the rear end of the head is the flange for the thermostat module, which collects water from the crankcase, the oil cooler and the cylinder head and contains a map-controlled thermostat. The housing also connects the coolant pump inlet, cooler, heating cooler and expansion tank. Depending on the requirements of the vehicle manufacturer, a vacuum pump mechanically driven by the intake shaft can be integrated at the end of the cylinder head.

The cylinder head cover is designed as a plastic injection molded part, with integrated crankcase ventilation and an oil separation module. The lines for low loads (suction mode) and higher loads (charger mode) are separated in the hood. The oil separation is optimized for the entire map area and guarantees maximum oil consumption below 1 g / h.
The design of the gas exchange with inlet and outlet channels, combustion chamber and piston crown design was optimized with the help of 3-D flow calculations in order to achieve the best possible compromise between air flow and charge movement.



Valve train

The four valves of a cylinder unit are driven by roller rocker arms. These are based on HVAs, Figure 6 . The cast iron camshafts on the exhaust shaft drive the high-pressure fuel pump via a triple cam. In addition to the roller cam followers, both camshaft bearings are also provided with roller bearings in order to achieve the desired low level of friction. Both camshafts are driven by camshaft adjusters, which each contain central control valves.

A belt running in oil drives the valve train. The belt drive has a guide roller on the tension side and a mechanical tensioner on the empty side. Both camshaft adjusters are equipped with tri-oval belt wheels, the design of which is designed in such a way that the dynamic forces generated by a drive of the high-pressure pump and the valves avoid belt flutter and tensioner movements and achieve an overall optimum with regard to the precision of the timing. The second short belt drives the two-stage adjustable oil pump directly from the crankshaft.

The ignition system consists of centrally arranged spark plugs with platinum-coated electrodes. Cylinder-specific ignition coils supply the spark plugs with the required energy.

The fuel injection system works with a maximum injection pressure of 350 bar. After intensive injection simulations in advance, a six-hole injector with a special jet design was finally selected, which represents the optimum for good performance data, emissions, fuel consumption, oil dilution and combustion stability of the engine.

The CE12 is equipped with a turbocharger with an electrical wastegate actuator. The design achieves low-end torque values ​​of 200 Nm at 1400 / min and 235 Nm at 1550 / min and a full load value of 105 kW at 5250 / min. The maximum turbine speed is 210,000 rpm, which guarantees a good height reserve, Figure 7 . The turbocharger consists of standard materials that are durable up to a maximum exhaust gas temperature of 950 ° C.



The CE12 standard configuration provides a catalytic converter close to the engine, which is screwed directly to the turbocharger. The exact design is variable and is adapted to the requirements of the target vehicle. The alternative considered integration of a particle filter in a common housing with the catalyst is provided and can be used if necessary. Together, this represents a compact solution that can be installed in a slightly modified configuration in a wide variety of vehicle concepts if required. However, due to the good raw emission values ​​of the CE12, solutions without a particle filter are also developed.


Power

The CE12 is able to meet all target values ​​for full load. The maximum combustion pressure can be kept below 100 bar in the entire map. The full load enrichment is used successively from around 3000 / min, Figure 7 .


Fuel consumption

For the CE12, the target values ​​for fuel consumption were defined for a combination of different map points. All of these goals have already been confirmed in the development engines. With these values, the CE12 will set a new benchmark in its class on the Chinese market, which the scatter band shows as an example for the operating point at 2000 rpm and 2 bar medium pressure. The map of the different measured specific consumption values ​​also shows that very good consumption values ​​can also be achieved in real driving, Figure 8 .




NVH

In the previous chapters, the constructive design of the engine in the direction of good NVH behavior was described and it was shown how the dynamic structure simulation ensures successful implementation in the early phase.

Figure 9 shows the airborne sound radiation on the engine test bench without load with external drive. The high potential of the CE12 is clearly visible in the FEV scatter band. The engine lands in the lower third of the scatter band during the first tests.



Emissions

With the completion of the engine application on the test bench, the CE12 achieves a low level of raw emissions and thus offers a good basis for further emission applications in vehicle development.

Various vehicles are already operated with a vehicle application that, depending on the vehicle weight and size, already fulfills the emission target values ​​with or without a particle filter on roller test benches.


Endurance testing

In addition to the performance, emissions and acoustics development, the CE12 goes through an intensive mechanical program that includes both component tests and a variety of endurance programs that cover different customer profiles. The hedging runs with the third engine assembly were successfully completed in the first half of 2019, and in the second half of the year this hedging will be completed with components from series tools.


Summary and Outlook

The CE12 will set a new benchmark in the 1.0 to 1.5 l engine segment in terms of power, torque, low-end torque, fuel consumption and NVH. Taking into account the future conceptual range of drive trains, the engine will be able to operate various configurations at short notice, such as mild hybrid (48 V RSG), full hybrid (MPI engine) and PHEV (P2 / P3), Figure 10 .




Alternative engineering scenarios were also considered in the design and can be offered at short notice if required. The majority of these modifications are coupled with a reduction in costs, but usually also have an impact on installation space, engine weight, fuel consumption and performance. Some of them make the CE12 more interesting for hybrid applications because they compensate for part of the additional costs and the additional weight of the hybrid concepts and because the combustion engine and electric motor complement each other.

Already during the first development phase of the engine, PXC considered the integration of an RSG system for mild hybrid applications, which are increasingly used in the market. The development of such a CE12 version for series production is possible with a slight delay after the first start of production.

Techniques that guarantee engine operation over the entire map in the stoichiometric range are increasingly coming into focus when RDE limit values ​​have to be met [6]. If the legislation in China also requires compliance with the RDE limit values, the CE12 is prepared. PXC considered all the necessary technology improvements for the CE family or provided them as an additional option in the concept.


References

[1] Kiesgen, G .; Curtius, B .; Steinparzer, F .; Klueting, M .; Kessler, F .; Schopp, J .; Lechner, B .; Dunkel, J .: The new 1.6 l Turbocharged Mini Cooper S Engine with Direct Injection and Fully Variable Valvetrain. 31st Vienna International Motor Symposium, Vienna, 2010

[2] Nussmann, C .; Van Keymeulen, J .; Eisele, G .; Steffens, C; Seo, JY; Kim, SG: Powertrain Mount Designer - Fast interactive tool for conceptual mount lay out. Aachen Acoustics Colloquium, Aachen, 2015

[3] Schwaderlapp, M .; Dohmen, J .; Jannsen, P .; Schürmann, G .: Friction reduction - the contribution of engine mechanics to fuel consumption reduction of powertrains. 22nd Aachen Colloquium Vehicle and Engine Technology, Aachen, 2013

[4] Köhler, E .; Flierl, R .: Internal Combustion Engines - Engine Mechanics: Calculation and Design of the Reciprocating Engine. ATZ / MTZ technical book, 5th revised and expanded edition, chapter 5.2.1.2.3. - Compensation of the free moments of mass, p. 400ff. Heidelberg: Vieweg and Teubner, 2009

[5] Friedefeldt, R .; Zenner, T .; Ernst, R .; Fraser, A .: Three-cylinder gasoline engine with direct injection and turbocharging. In: MTZ 73 (2012), No. 5, pp. 354ff.

[6] Goergen, M .; Balazs, A .; Boehmer, M .; Nijs, M .; Lehn, H .; Scharf, J .; Thewes, M .; Mueller, A .; Alt, N .; Classen, J .; Sterlepper, S .: All Lambda 1 Gasoline Powertrains. 5th International Motor Congress, Baden-Baden, 2018