14 Combusti on engine 14 Combusti on engine Combusti on engine 14

The engine Understanding it in its enti rety 14 Kurt Kirsten

204 Schaeffl er SYMPOSIUM 2010 Schaeffl er SYMPOSIUM 2010 205 14 Combusti on engine Combusti on engine 14

The sum of all these requirements and challeng- Efficiency chain of modern gasoline engines Introducti on es requires a holistic approach so that added value can be achieved with new technologies Thermodynamic Camsha phasing In the past, the development of automobiles and compared with current volume production prod- improvements unit 35.3 % exhaust gas heat their drive systems was influenced and pushed ucts. The development of added value can affect Valve trains forward by the application of the latest technol- customers, society, legislators or producers. – - Parally-variable ogies in many cases. This meant it was possible Mastering or controlling this complexity is the - Fully-variable 78 % engine for market participants to strengthen their posi- actual challenge of the present time. – losses tion or the position of their product brands 30.0 % heat loss by direct differentiation in a generally growing 100 % energy market. used The current market scenario is infl uenced by: Core issues for 4.2 % pumping losses Mechanical  Product life cycles which are conti nuously being 8.5 % engine fricon – Fricon current drive improvements – Damping shortened 4.1 % accessories + mech. losses –NVH  Increased segmentati on system development 22 % effecve 4.0 % rolling resistance power  High cost pressure 6.9 % air resistance The core issues for passenger drive system de- 7.0 % acc. resistance  Demanding customers expectati ons velopment are the confl icti ng aims of reducing NEDC related fuel consumpti on (CO emissions) on the one  High social expectati ons 2 Reference: Prof. Leohold, U. Kassel hand and limiti ng pollutant emissions on the oth- Figure 2 Gasoline engine effi ciency chain in the NEDC er hand (Figure 1). The situati on is also characterized by: Boundary conditi ons such as costs, brand image,  Increased legal requirements driving pleasure, comfort, noise and reliability reference. The starti ng points for making improve- 14  A growing percepti on about the limitati ons of must also be taken into account. ments are in the area of variability in the Thermodynamic resources drive. These are: Gasoline and diesel engines are positi oned com- improvements  Signifi cant overcapacity of producti on pletely diff erent with regard to the confl icti ng  Camshaft phasing units aims of fuel consumpti on and emissions.  Diff erent regional and market-segment-specifi c  Parti ally-variable valve train systems The signifi cantly greater potenti al for improve- requirements The gasoline engine is positioned very much in ment is due to the reducti on in the thermodynam-  Fully-variable valve train systems the low-emission cat- ic losses. The thermodynamic improvements are egory due to its very targeted at enabling thrott le-free load operati on. Due to the variability in the valve train, the ther- efficient aftertreat- Instead of controlling the intake normally by means Emissions target modynamic process is infl uenced in the area of the ment of exhaust gas- of a thrott le valve, control of trapped fresh air is low-pressure process so that there is a positi ve ef- es. The , transferred to the valves. The required pumping fect on the pumping losses and the combusti on on the other hand, is losses are reduced due to the increase in the intake process is opti mized in the area of the high-pres- positioned very much manifold pressure. The required control of trapped sure process. These interventi ons also have a di- Gasoline in the low consump- fresh air is primarily undertaken by varying the rect infl uence on the formati on of emissions in the

on tion category due to opening ti me of the intake valve or by the design of

internal combusti on engine and are, therefore, its favorable, thermo- the valve lift curve in the form of the cam contour. parts with direct relevance for engine out emis- dynamic efficiency sions. At the same ti me, the charge moti on can be direct- Transmission and advantageous low

consump ly infl uenced by the use of variable valve control l technology end torque character-

ue The mechanical improvements refer to the mini- systems in the combusti on chamber. The forced in- F Hybridizaon istics. The proceed- Diesel CO target mization of friction losses and the reduction of fl ow moti on resulti ng from the moti on of the pis- 2 ings of this article re- parasitic losses of the accessory drives. The or- ton is converted into a swirl or tumble moti on due fer mainly to the Target der of the mechanical losses is around 10 % to to the design of the intake ports. If the valves open gasoline engine. range 12 % of the fuel energy used. I.e. detailed opti- at diff erent ti mes, the in- fl ow can also be Figure 2 shows a loss mization with an improvement of 10 % to 20 % strongly infl uenced. In conjuncti on with the posi- Emissions distributi on analysis re- with regard to mechanical losses generates a to- ti on of the and the general layout of the (HC, NOx, parculates) lati ng to the NEDC us- tal contribution of around 1 % to 2 % in the driv- combusti on chamber, this opens up opportuniti es Figure 1 Fuel consumpti on/emissions ing a gasoline engine as ing cycle. for a wide range of opti mizati on measures.

206 Schaeffl er SYMPOSIUM 2010 Schaeffl er SYMPOSIUM 2010 207 14 Combusti on engine Combusti on engine 14

The percentage of residual exhaust gases which re- A Longer intake and exhaust valve lift events with Phasing Duraon of valve event Li main in the cylinder can be directly infl uenced by greater valve overlap are desirable in the full the design of the valve overlap or the phasing of load range at nominal speed, in order to en- the valve opening. The temperature of the charge sure that the engine can “breath freely” (later mass at the start of the compression can be closure of the intake valve). infl uenced by adding hot residual exhaust gas di- B The intake and exhaust valve opening ti mes rectly to the fresh mixture. This also enables the should be shortened to opti mize the volumet- temperature at the end of the compression stroke ric effi ciency in the low-speed and high-load to be infl uenced indirectly. This variability opens range. The valve overlap must also be reduced up a new alternati ve method of carrying out opti - compared to the overlap at the nominal speed. mizati on for modern autoigniti on combusti on sys- tems. C The pumping losses should be reduced in the Figure 4 Division of variability in the valve train center area of the engine map by early closing The possibiliti es for infl uencing the thermodynam- of the intake valve. ic process can be described as follows: Division of variability in the of dethrott ling on the engine operati ng behavior. It D Exerti ng an additi onal infl uence on the in-cylin- can be seen that the infl uence of dethrott ling by  Low-thrott le operati on under part load (charge der fl ow and maintaining the temperature of valve train means of diff erent measures cycle) the charge compositi on are required in the The following are used to characterize variability in  Intake phase adjustment only  Control of trapped fresh air (load control) low-load range in order to positi vely aff ect the the valve train (Figure 4): combusti on process. Cylinder deacti vati on can  Intake and exhaust phase adjustment  Incylinder charge moti on unlock further potenti al.  Phasing of the valve event  Double phase adjustment & variable valve lift  Percentage of residual exhaust gases in the E For starti ng the engine, separate measures for  Durati on of the valve event combusti on chamber is parti cularly pronounced in the lower area of the ensuring the highest and most eff ecti ve com-  Maximum lift of the valve event data map and can amount to a fuel consumpti on  Temperature at the start of the compression stroke pression rati o are also required for improved saving of up to 12 % at a stati onary operati ng point. starti ng behavior. A limited charge throughput In Figure 5, variability is divided with regard to 14 There are diff erent requirements for opti mizing en- by means of reduced valve lift or closed valves phase and valve lift and according to the character- The potenti al for improving fuel consumpti on in gine characteristi cs (Figure 3) depending on the has proved reliable for enabling easier restart- isti cs of discrete or conti nuous adjustment. The the driving cycle is between 4 % and 6 % compared load and speed: ing with stop-start functi onaliti es. level of variability increases from left to right in the with an engine with a standard valve train, de- diagram accordingly. pending on the variability selected. A Figure 6 shows a stati onary data map with four op- The control concept and the dynamic response erati ng points as an example to show the infl uence behavior are particularly important for the B transient operating behavior of the sys- Valve train tems. Reliable recog- Max. power nition of the current Max. torque • Full li Phase adjustment Valve li operation mode in in- • Maximum volumetric efficiency • Late closure dividual cylinders is • Early closure (short valve event) (long valve event) of particular impor- C • Greater overlap Connuous Discrete Connuous tance for controlling • Hydraulic • Two-step • Electromechanical • • Electric the air, fuel and igni-

Torque Switchable • Pivot element • Mechanical tion paths. Therefore, • Finger follower • Valvetronic “dynamic” valve train Opmizaon of pumping • Shi ing cam lobe losses • Roller tappet • Electrohydraulic systems also unlock • UniAir greater potential for D • Three-step • Finger follower fuel consumption sav- E Opmizaon of pumping Combuson opmizaon • Shi ing cam lobe ings in the driving cy- losses (Charge moon) cle. Combuson opmizaon

Engine speed Figure 3 Diagram showing requirements for engine characteristi cs Figure 5 Level of variability in the valve train

208 Schaeffl er SYMPOSIUM 2010 Schaeffl er SYMPOSIUM 2010 209 14 Combusti on engine Combusti on engine 14

Engine map  Stop-start functi onaliti es change the load profi le 6 Design examples and for ti ming drives. 105 100 the infl uence of variable  Fast and cycle by cycle variabiliti es make use of 5 95 the full potenti al in the transient operati ng 105 90 valve trains on the engine mode, increase the comfort of stop-start 100 BSFC in % 85 operati ng behavior 4 95 functi onaliti es and improve the starti ng points 90 105 Figure 7 shows an overview of current, variable for hybridizati on.

BSFC in % 85 100 valve train systems and their market launches.  3 95 A good ti ming drive is more than the sum of 105 105 90 The following are used to evaluate the diff erent good individual components, but a comprehensive 100 100 BSFC in % 85 systems: overall design. 95 2 95 90 Mean pressure in bar 90  Fuel consumpti on in

BSFC in % 85 BSFC in % 85 the driving cycle Camsha phasing Camsha phasing Camsha phasing Camsha phasing Electrohydraulic 1  unit unit + electro- unit + shi ing cam unit + electro- system Control concept hydraulic tappet lobe + electronic mechanical sha (intake only)  Dynamic response actuator 0 0 1000 2000 3000 4000 behavior Engine speed in 1/min  Timing characteristi c Throled, no valve train variability Variable intake cam ming An evaluati on of the in- Variable intake and exhaust cam ming fl uence of valve train Throleless, combined camsha ming and variable valve train variability on the com- busti on process is con- Figure 6 Improvement in fuel consumpti on by means of dethrott ling Pumping losses ducted on the basis of 14 the following fi ve criteria: Camsha Camsha phasing Camsha phasing Camsha phasing Electrohydraulic  Pumping losses phasing unit unit + electro- unit + shi ing cam unit + electro- system Trapped fresh air Percentage of residual hydraulic tappet lobe + electronic mechanical sha (intake only)  Percentage of residual exhaust gases actuator exhaust gases  Temperature at the start of the compress- ion stroke Temperature at the start of the  Charge moti on Charge moon compression stroke  Trapped fresh air Figure 8 Evaluati on of diff erent variable valve train systems Fuel savings*: approx. 4 % approx. 7 % approx. 8 % approx. 8 % approx. 8 % - 15 % Figure 8 shows evaluated design examples using a Control: per per cylinder bank per cylinder per cylinder bank valve by valve cylinder by cylinder spider diagram. The “fi lling capacity” of the spider Mechanical diagram also increases with an increasing level of Dynamic slow slow medium slow fast variability. response: improvements Characterisc: connuous two-step two-step connuous connuous In summary, the following can be noted in view of (poss. three-step) the thermodynamic improvements: As already noted in Figure 2, the mechanical improvements refer to the friction and parasitic In volume 1997 1989, 1999, ... 2006 2001 2009  Variability in the valve train is not only relevant producon losses of the accessories. Overall, the following (Ford, BMW, (Porsche, Honda, (Audi, …) (BMW, PSA) (FIAT) for reducing pumping losses, but also assures since: optimization criteria must be taken into ac- VW, Audi, GM, …) potenti al for reducing fuel consumpti on and Fiat, Opel, count: Porsche, Ferrari, emissions during combusti on (especially with direct-injecti on gasoline and diesel engines). SAIC, Chrysler,  Fricti on Volvo, …)  Downsizing and downspeeding increase the  Damping * NEDC related, relave to standard valve train requirements for the basic layout of the drive Figure 7 Comparison of diff erent, variable valve train systems train.  NVH behavior

210 Schaeffl er SYMPOSIUM 2010 Schaeffl er SYMPOSIUM 2010 211 14 Combusti on engine Combusti on engine 14

Along with the chal- and, therefore, represents a complete system Timing drive Drive / power transfer lenge of transmitti ng Bank model complete with chain: simulation. The challenge to come up with an • Camsha • Accessories (FEAD) EVT comparison (5000 1/min) the drive power, there • Balancer sha optimized system solution is to find the right are further require- • Injecon pumps trade-off between reduced friction and ensure ments for the basic de- the necessary level of damping. This requires the sign of the components Valve development of calibrated and validated simula- in the ti ming and ac- acceleraon tion models which model the overall relation- cessory drive: Valve ship. acceleraon  Preloads should be kept as low as Camsha possible (low bearing ming angle Summary loads, low fricti on) Camsha ming angle Figure 12 shows an overview of the potenti al for  Noise generati on in making individual improvements to current inter- the ti ming drive nal combusti on engines. It can be seen that in the should be minimized case of diesel engines there is only minimal poten- Figure 9 Accessory and ti ming drives of internal combusti on engines ti al for improvement by means of thermodynamic  Dynamic peak loads measures. Improvements of 10 % to 12 % can sti ll should be avoided Figure 10 shows the components which the Schaef- be achieved for gasoline engines. Figure 9 shows design examples. fl er Group supplies as typical engine components In addition, an overall potential of 3 % to 5 % can and modules. It can be seen that most parts are The potenti al improvement can be derived from be unlocked by initiating mechanical measures components which are subjected to a sliding or ro- Figure 2. The percentage losses due to mechanical in the engine. The potential due to stop-start tary moti on. fricti on in the engine and the drive power for ac- Figure 11 Complete system simulati on functionalities, downsizing and thermo man- cessories in the NEDC are approximately 12 % to The minimizati on of losses is parti cularly impor- agement round out the overall potential for im- 14 13 % of the primary energy. tant. In additi on, these components are elements of vibratory systems, which can only be opti mized provement. to a limited extent as individual components and With the modular range of components and engi- must, therefore, be opti mized in a total system ap- neering services on off er, Schaeffl er Engine Sys- proach. tems is well equipped to make a contributi on to- Figure 11 shows this relati onship using the exam- wards unlocking potenti al for improving fuel ple of a chain-driven camshaft of a four-cylinder consumpti on. Finger follower engine. It is assumed in the complete dynamics + pivot element simulati on that excitati on is initi ated in the crank- Diesel < 3 % Gasoline < 7 % 1 – 2 % shaft plane, and considerati on is given both to the Combuson system Demand-controlled behavior of the opmizaon accessories Tappet UniAir Variable camsha phasing system  chain 4 – 6 % 2 – 3 % Throling losses Fricon reducon  chain blades Gasoline  hydraulic tensioner 3 – 5 % 1 – 2 % and also the valve actuati on components on the Stop-start Funcon Thermal management camshaft side Thermodynamic 5 – 8 %  fi nger follower improvement Downsizing Accessory drive Mechanical improvement  valve spring Further improvements  valve Figure 12 Overview of the potenti al for improvements

Balancer sha module Timing drive

Figure 10 Typical components for engine applicati ons

212 Schaeffl er SYMPOSIUM 2010 Schaeffl er SYMPOSIUM 2010 213