COVER You STORY will find the figures

mentioned in this article in the German issue of MTZ 3/2005 beginning on page 164.

Der neue Ford Duratec 1,6-l-Ti-VCT-Motor

The New Ford Duratec 1.6 l Ti-VCT Engine A new variable cam timing variant of the 1.6 l Duratec gasoline engine known from Fiesta and Focus has further enhanced efficiency compared to the base engine. This Ti-VCT engine (Twin Independent Variable Cam Timing) offers less consumption as well as improved torque characteristics and peak power. This report leads through the design of the new engine. Furthermore the thermodynamical development of this concept is introduced.

1 Introduction

By Harald Kaufeld, Ulrich Kölsch, Manfred Rechs, Helmut Ruhland and Klaus Moritz Springer

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With the 1.6 l Duratec Ti-VCT (Twin Independent Variable Cam Timing) Ford introduces a new engine of the successful Duratec engine family. This engine will first be introduced to the new Ford Focus and Ford Focus C-Max. Key features of this engine are two independent variable cam shifting units on intake and exhaust camshaft. The main focus during the development of this engine was the improvement of fuel economy in the new Ford Focus. Fully variable cam phasing units enable a de-throttled engine operation in part load. Within the complete engine speed range an extremely competitive torque characteristic could be achieved combined with a 15% improvement in peak power. This sort of improvement in the low speed range can be seen as a downsizing concept comparing the engine to 1.8 l displacement. During the development of the engine the aim was always to maximize the reusability of available components and the integration into existing production

lines. By that the 1.6 l Duratec Ti-VCT engine does not only meet the customer requirements in terms of performance, fuel economy and emissions. The careful redesign of the engine also met stringent targets for part cost and investments. Summarizing this concept is an interesting alternative to other SI engine concepts as i.e. direct injection. 2 Development Targets

The development targets for the new 1.6 l Duratec Ti-VCT are based on customer requirements and on Ford's pretension to be competitive in the C-car segment. For this vehicle segment the customer is expecting reliable and fuel-efficient vehicles with a quality level comparable to CD class level. These requirements can be met using robust technologies, which enable on one hand a significant improvement in efficiency and on the other hand deliver a superior performance. A good basis for this development can be seen in the 1.6 l Duratec engine. This engine that is already in-

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stalled in the Ford Fiesta and in the Ford Focus provides best in class quality and reliability since years. Ford internally this powertrain is preferred as this offers the opportunity for installation into different vehicles within the Ford brands. 3 Engine Design

As the intention was to built this engine on the existing transfer lines the targeting for maximum reusability of existing components was a major requirement during the development of the new 1.6 l Duratec TiVCT. Besides from the financial benefits of this strategy the well-known quality of existing parts supported this manufacturing requirement. Hence the available architecture was only modified if the new concept could either not be realized within the constraints of the given hardware or if significant improvements could be achieved. 3.1 Engine Bottom End

Cylinder block, main- and conrod bearings as well as accessories like i.e. oil and water pump have been carried over from the base engine [1]. The thermostat was exchanged to an electrically controlled type to support a faster engine warm up. Furthermore a water oil heat exchanger was attached to the oil filter to shorten the warm up phase of the oil on one hand and to improve the cooling of the oil under extreme operating conditions on the other hand. The increased torque output of the engine requires a robust piston design. The piston pin area of the piston and the piston pin itself where reinforced and the piston crown thickness was increased. To maintain a sufficient clearance between the valves and the piston surface for all possible cam timings 3.5 mm deep valve pockets where designed into the rough part casting. Similar to the baseline engine the piston skirt is still coated for friction and NVH reasons, Figure 1. The crankshaft has been redesigned from a 8 counterweight type to a 4 counterweight design. By that the crankshaft weight could be reduced by 2.3 kg. With the help of CAE methods the torsional stiffness could be improved while the bending stiffness remained constant. Moreover all the NVH behaviour of the engine could be improved compared to the base engine. 3.2 Cylinder Head

To utilize the maximum potential of the selected concept the cylinder head has been redesigned in several important details. An interesting challenge for the engineers arose from the requirement to manufacture the new designed cylinder head with

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Ford Duratec 1.6 l Ti-VCT Engine

the existing manufacturing lines of the baseline engine. The intake ports of the baseline engine where symmetrical tumble ports. Within the combustion system development these ports have been modified to asymmetrical ports with a tumble port on one side and a neutral filling port on the other side. This configuration provides an improved volumetric efficiency. Additionally with this port design the tumble motion is overlaid by a swirl motion. Valve angles and valve diameters where kept unchanged. Additionally the combustion chamber was redesigned to a more compact geometry for improving the knock behaviour of the engine. The spark plug has been lifted upwards by 1.5 mm to enable a closer positioning of the water jacket to the combustion chamber, Figure 2. With the help of CFD simulations the flow paths inside the water jacket have been improved so that the heat transfer was optimized especially in the area of the exhaust valves. This is supported by a modified distribution of the coolant flow between cylinder block and head. The latter was realized by a detailed optimization of the cylinder head gasket holes. Here a bigger portion of water was directed to the cylinder head. A further advantage of the redesign of the water jacked was seen in improved degas paths for locally boiling coolant. Figure 3 shows the modified oil circuit. In order to incorporate the cam phasing units into the oil circuit the diameter of the oil feed line from the oil pump into the cylinder head has been enlarged. This requirement was key to realize sufficient VCT shifting velocities. A restrictor has been built into each cam gallery in front of the second cam bearing avoiding excessive oil leakage in the cam bearings and hence providing enough oil pressure to the main bearings. Finally a filter element has been integrated into the oil feed line to prevent the cam phasing units from malfunction due to particle-polluted oil, Figure 4. Designing the new cylinder head for the 1.6 l Duratec Ti-VCT engine special emphasis has been put on the integration of the variable cam phasing units (VCT) into the oil circuit. For this purpose the frond end of the cylinder head has been changed as well as the front-end cam bearings and the camshafts. A new part, the VCT bridge, Figure 5, has been designed integrating several functions such as the bearing caps and oil supply to the VCT units. Furthermore the oil control solenoid valves are plugged into this VCT bridge. The VCT units are flowed /drained via radial grooves integrated into the VCT bridge. These grooves are connected to four axial drillings in each

camshaft that are directly mounted to the VCT units. The vane type VCT units have a shifting range of 52°CA on the intake and 47°CA on the exhaust side. When the engine is off, during the engine start and at idle the cam phasing units are blocked mechanically by a locking pin in a defined base position. This locking pin prevents the uncontrolled phasing of the VCT units while starting the engine. For a controlled cam phasing during engine operation the locking pin is automatically released when pressurising the VCT units with engine oil. During engine shut down the VCT unit on the intake side is depressurised and then moved into the base position by drag torque of the camshaft. A torsion spring is integrated into the exhaust cam-phasing unit that moving the exhaust camshaft in the base position as soon as the VCT unit is depressurised. The torsion spring is strong enough to work against the drag moment even if the engine is running. The valvetrain of the engine remained unchanged. Only the Cam event length and the valve lift have been adapted to the thermodynamic engine concept. According to this the event length on the intake side increased from 232 deg CA to 240 deg CA and as a consequence of this the Valve lift could be increased from 7.3 mm to 8.9 mm. For the exhaust camshaft the same cam lobes as for the intake side have been chosen (base engine: 224 deg CA / 6.93 mm). The plastic (Nylon) intake manifold has got an all-new design with a central plenum, Figure 6. It consists of three friction-welded shells with a total volume of 3.3 l. The runner diameter is 36 mm and the length of 350 mm for all runners is relatively short. Figure 7 shows the 4-2CC-1 exhaust manifold. After the junction of cylinders 1&4 and 2&3 close coupled catalytic converters are integrated into the manifold. The ceramic catalysts have a volume of 0.75 l each and are coated with a Tri-metal coating basing on Palladium. Special emphasis has been put on the runner lengths in order to provide the best tuning in the low engine speed area. 4 Thermodynamics

Key points to improve the effective efficiency of an SI engine are improving the combustion cycle, optimizing the mechanical efficiency and minimizing pumping work during the gas exchange phase. The 1.6 l Duratec engine is already designed to a compression ratio of 11.0. A further increase of the compression ratio to

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3.2 Cylinder Head

Figure 4: Oil supply to VCT units

Figure 5: VCT Bridge

Figure 7: 4-2CC-1 Exhaust manifold

improve the thermal efficiency of the engine does not make sense as the knock limitation at full load and high part load operation limits the benefit of this measure. Another potential to improve the efficiency of the engine would be an increase of the cycle averaged polytrophic exponent by means of lean operation. Independent from running the engine stratified lean or homogeneous lean this would require the installation of a cost intensive exhaust gas after treatment to handle the NOx emissions. With respect to mechanical friction of the base engine and the attached accessories the Duratec engine is already best in class and represents the lower boundary of the FEV benchmarking spread. Therefore it can not expected that a significant improvement could be achieved. A promising potential to improve the engine's efficiency can be seen in the reduction of charge exchange losses. Table 1 shows a comparison of different concepts to improve fuel consumption. Based on comprehensive investigations on the different concepts Ford has decided to select a twin independent cam timing configuration for the upgrade of the 1.6 l Duratec engine as this promises to offer the greatest value for the customer. In addition to the variable cam timing an intelligent thermal management system has been applied controlling the cooling of the engine for best fuel economy. The cam phasing units enable high levels of internal EGR. Compared to external EGR this offers advantages in terms of introduction, distribution and control characteristics – especially during transient operation. By means of the internal EGR the engine is less throttled leading to a reduction in pumping work. Additionally the process temperatures are reduced leading to improved raw emissions of the engine. As already mentioned the exhaust after treatment relies on proven 3-way catalyst technology. A further big advantage of cam phasing is evident at full load operation. In combination with optimized valve lift profiles and intake- and exhaust manifold the full load torque could be improved significantly. Incorporation of twin VCT's leads to a high degree of optimization parameters which leads to the necessity of CAE methods for achieving best results for both, part load and full load optimization. 4.1 Part Load Concept

Starting from 20 deg ATDC intake valve opening the intake VCT unit enables a shift towards earlier cam timing by 52 deg CA. In a similar manner the exhaust cam timing

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can be shifted by 47 deg CA from 1 deg BTDC towards later timing. These large shifting ranges enable a valve overlap reaching from –21 deg CA to 78 deg CA. The negative overlap position represents the starting condition of the engine enabling a robust engine start down to ambient temperatures of –40 deg °C. Since the cam phasing units are moved to that high negative overlap condition even for idle the associated low internal EGR content leads to extremely stable idle quality as well. During part load the cam timings are optimized for each operating point. Figure 8 shows the measured specific fuel consumption for 2000rpm / 2 bar as a function of intake and exhaust cam timing. A line of 45 deg inclination represents a constant valve overlap. Additionally the engine stability limit based on standard deviation imep is plotted. Figure 9 shows the EGR content predicted by CAE for the same cam timing map as in the previous figure. As expected the EGR content correlates in large areas of the map to the fuel economy. In the operation point shown in these charts the EGR content for minimum bsfc is close to 35%. It is obvious that a prerequisite for the very low fuel consumption is basically a result of the excellent EGR tolerance of the engine. Therefore this portion was the key focus of the combustion system development. With the help of asymmetrical intake ports a swirl motion overlie the tumble flow of the engine. Hence the combustion could be accelerated throughout their complete duration. By that arrangement calculated EGR rates up to 40 % can be tolerated by the engine without the necessity of a device for port deactivation. The shifting range of the VCT unit has been reduced to the required range defined by the combustion system. A further increase in shifting range was not possible due to mechanical and thermodynamical limitations. The shifting range of the exhaust cam phaser towards the retard direction is limited by the valve to piston clearance and additionally by an excessive increase in internal EGR. This would result in instable combustion and due to the deceleration of the heat release rate the inner thermal efficiency would decrease. Another strategy for improving fuel economy is a late intake valve closure. Using that strategy charge is pushed back into the intake system leading to an additional unthrotteling of the engine. While the pumping work is reduced the inner efficiency decreases for very late intake valve closing due to the effective compression ratio decreasing in parallel with the timing of intake valve closure. Towards higher loads the decrease in compression ratio can be

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utilized to improve knock behaviour, which usually would increase due to the high internal EGR rates. Finally a strategy with late exhaust valve closure and late intake valve phasing was selected in this operating point. Besides from the excellent fuel consumption this strategy offers superior combustion stability. For the application a smooth cam timing map should be generated to support an acceptable transient behaviour. The Figure 10 yields that starting from the lock positions of the VCT units the exhaust cam phaser is retarded leading to a late position of the valve overlap. This leads to storing the EGR within the cylinder [2]. With increasing speed and load the intake camshaft is advanced. At WOT the intake cam is then advanced again with increasing engine speed to utilize the gas dynamics for optimizing volumetric efficiency. Figure 11 shows the percentage of the improvement in fuel consumption relative to the non-VCT engine. The following table shows measurement results of fuel consumption for a few selected operating points indicating the excellent capabilities of the selected concept. Relative to the non-VCT engine the twin VCT technology of the 1.6 l Duratec Ti-VCT improves fuel economy within the NEDC cycle by 4.5 %. 4.2 Full Load Concept

The shifting strategy of the cam phasing units was already subject of the last chapter. Although the engine is equipped with relatively long cam events of 240 deg CA the Ti-VCT technology offers the opportunity to create an extremely attractive torque curve. Typically a sufficient low-end torque requires an early intake valve closing which would result in a high valve overlap if the VCT functionality in combination with long event intake cams was utilized. The associated high EGR rate would result in a high internal EGR with negative influence on low-end torque. To resolve this conflict a tuned 4-2CC-1exhaust system with two closed coupled catalysts has been installed. This exhaust system enables a split of the exhaust streams of cylinders 1 and 4 from cylinders 2 and 3 resulting in the positive pressure differential between intake and exhaust ports in the low speed range, Figure 12. By means of this feature the potential disadvantage of a high valve overlap at low speed could be utilized to enable a superior cylinder filling as the combustion gases of the previous combustion cycle are scavenged of the combustion chamber in the

subsequent cycle. To avoid direct fuel loss into the exhaust system the injection timing needs to be calibrated very carefully. On one hand a blow though of fuel into the exhaust system would increase fuel consumption in that area of the map. On the other hand it can't be avoided that air is blown through the combustion chamber. If fuel would be poured into the exhaust system the catalysts could be damaged. Besides from the improvement in volumetric efficiency the scavenging of the residuals supports the high-pressure cycle by an improvement in knock resistance. Figure 13 shows that the combustion phasing is very close to the optimum value although volumetric efficiency could be improved to values of above 100 %. This could be achieved by utilizing the scavenging process in the low speed range. The improvement of the water jacket mentioned already earlier in this document improves knock resistance as shown in Figure 14. It can be observed that introducing this water jacket to the baseline engine improves combustion phasing up to 3.5 deg closer to the optimum value of 8 deg CA ATDC. The introduced concept exhibits a very flat torque curve on an extremely high level, Figure 15. Already at 2000 rpm the engine exhibits a bmep of 12 bar. 90 % of the 156 Nm peak torque can be offered within an engine speed range between 1500 rpm and 5800 rpm. In combination with VCT the runner lengths of the intake manifold could be reduced by 150 mm. This short runner length enables an increase in peak power to 115 PS at 6000 rpm. 5 Active Thermal Management

Passenger cars are used mainly in short distance driving [3]. Throughout short distance driving the optimal engine operation temperature are rarely reached. Hence another focus during the development of the 1.6 l Duratec Ti-VCT has been put on the warm-up phase of the engine. Due to the influence of oil temperature on engine friction losses it was aimed to raise the oil temperature as fast as possible to a high level. This was achieved by adapting an active thermal management consisting of a map controlled thermostat and an oil water heat exchanger. Figure 16 shows the warm-up behaviour of coolant and oil during the NEDC cycle for a vehicle with and without thermal management. At the beginning of the warm-up phase coolant temperatures for both derivatives increase rapidly, while the oil temperatures raises relatively slow.

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Ford Duratec 1.6 l Ti-VCT Engine

With the help of an oil water heat exchanger this temperature difference can be used to accelerate oil warm-up. In the NEDC cycle this leads to the result that the engine with thermal management reaches 60 °C oil temperature 100 seconds prior to engine with out thermal management. This is equivalent to the distance of approximately 0.7 km of the NEDC cycle. The effect of the map-controlled thermostat can be seen approximately 600 seconds after the cold start. At this point in time the coolant temperature with thermal management exceeds the one with out thermal management. Although the temperature difference between coolant and oil decreases, the oil temperature with thermal management still rises faster. Both, the oil water heat exchanger and the map-controlled thermostat cause this positive effect. Fuel consumption measurements during cold NEDC confirmed a 1.5 % fuel saving with active thermal management. The start to open temperature of the thermostat, which acts as an inlet controller, was increased from 82°C to 98°C. Part load engine friction is reduced due to the increased coolant temperature and thereby increased oil temperature. Wall heat losses are minimized as well. Additionally it the engine is thermally dethrottled. Depending on the customer usage profile the fuel consumption benefit due to these effects can add up to 2 % in daily use. If required (e.g. in case of a full load acceleration) the active thermal management reduces the coolant temperature by applying current to the heating element of the map-controlled thermostat. 6 Lubrication System

In addition to the 1.6 l Duratec base derivative the 1.6 l Duratec Ti-VCT lubrication circuit is equipped with the oil water heat exchanger and two camshaft phasing units mentioned above. Operating with high oil temperatures at low engine speeds it was observed that the VCT shifting speeds were borderline. This can be accounted to the low oil pressure induced by the thin oil due to high temperatures. In parallel to the measurements a CAE model of the lubrication circuit has been built up in order to calculate shifting speeds based on computed oil pressure and flow distribution. Figure 17 shows the good correlation between measured and calculated shifting velocities, as an example for the critical oil temperature of 130 °C. The big difference in shifting speeds between intake-early- and –late shifting direction can be explained by shifting once with and once against the

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camshaft drag torque. On the exhaust side the differences are smaller due to above mentioned torsion spring. In order to increase shifting speeds in the low engine speed range a capacity increase of the oil pump was discussed initially. Although package was not the limiting factor this concept was rejected due to the expected fuel consumption impact. In the 1.6 l Duratec base engine an orifice controls the oil supply to the cylinder head. By that an excessive oil flow to the cylinder head is prevented during hot idle to ensure a sufficient oil supply to the crankshaftand con-rod bearings. For the 1.6 l Duratec Ti-VCT the oil supply of the camshaft phasing units was downstream of this orifice. Two single orifices have been introduced into the cylinder head main oil galleries within the second camshaft bearing in lieu of the orifice inside the head gasket. A variation of the orifice diameters done by a CAE simulation showed only a small increase in shifting speeds for diameters below 2 mm. With this diameter configuration balanced oil supply for the crank shaft- and con-rod bearings compared to the 1.6 l Duratec base derivative was achieved. Hence a further diameter reduction was rejected in favour of not increasing the risk of contamination unnecessarily. Figure 18 shows the improvement of shifting speeds achieved by the relocation of the orifice for an oil temperature of 130 °C. This temperature is equivalent to the maximal possible oil temperature that can be reached under extreme driving conditions. Noticeable higher oil temperatures would be seen without the oil water heat exchanger. The chart shows an improvement in VCT shifting velocity throughout the whole engine speed range. While this improvement in the high-speed range does not offer a significant advantage it is key for an acceptable transient operation in the low speed range.

could be reduced by 6 % in NEDC. This fuel economy benefit is based in the consequent utilization of Ti-VCT technology combined with the active thermal management. Additionally this concept offers improved torque characteristics combined with a peak power of 115 PS. Already at 2000 rpm the engine offers a mean effective pressure of 12 bar. The peak torque of 156 Nm is reached at 4150 rpm. By utilizing the Ti-VCT technology the speed range where 90 % of the peak torque is achieved could be expanded to a range of 1500 rpm to 5800 rpm. The mentioned improvements of the engine could be realized by using standard technologies without major redesigns of the base engine architecture. That makes this new engine concept a promising basis for a new generation of SI engines at Ford.

References [1]

[2] [3]

Wölfle, M.; Tielkes, U.; Grünert, T.; Hohage, C.D.; Warren, G.: The Upgraded 16-Valve Zetec-E Engines. In: ATZ/MTZ Special Edition “The new Ford Focus”, November 1999 Pischinger, M. et. al.: Darstellung der Potentiale des elektromagnetischen Ventiltriebs im Fahrzeugbetrieb. Aachener Kolloquium 1999 Himmelsbach, J.; Dilgen, P.; Limbach, S.: Zum Kraftstoffeinsparpotenzial bei Minimierung der Wärmeverluste des Motors an die Umgebung. Wärmemanagement des Kraftfahrzeugs, HdT 1999

7 Summary

With the 1.6 l Duratec Ti-VCT engine Ford introduces a new engine for the new Ford Focus and for the Ford Focus C-Max. This engine is based on the 1.6 l Duratec engine already known from the current Ford Fiesta and Ford Focus. Key design features of this engine are continuous variable cam phasing units on intake and exhaust cam and an active thermal management. With a fuel consumption of 6.4 l/100 km during NEDC in the new Ford Focus this engine proves to be an interesting alternative to other SI engine concepts. Compared to the baseline engine the fuel consumption

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