The Pneumatic Hybridization Concept for Downsizing and Supercharging Gasoline Engines

Research SuperCharging

Authors The Pneumatic Hybridization Concept for Downsizing and Supercharging Gasoline Engines

Prof. Dr. Lino Guzzella is Director of the Chair for Extensive fundamental research at ETH Zurich has yielded the world’s first fully Thermotronics at the Institute for Dynamic Systems and functional hybrid pneumatic engine. The pneumatic hybridization of gasoline engines Control (IDSC) at ETH Zurich primarily aims at maximal downsizing and increased driveability with minimal (Switzerland). additional cost. When comparing engines with the same maximum power, the presented engine system proves to be up to 35 % more efficient on the NEDC.

or scie al f ntif ov ic r ar pp t A ic l f e o s l a in e S M

Dr. Christopher Onder e T Z h . is Senior Scientist at the T

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Peer Review Institute for Dynamic Systems

R and Control (IDSC) at Received 2009-08-24 . e y v r i Reviewed 2009-09-11 ETH Zurich (Switzerland). e t w s Accepted 2009-09-24 u e d d n b i y d e an xp h ert rc s from resea

Dipl.-Ing. Christian Dönitz is Research Assistant at the Institute for Dynamic Systems and Control (IDSC) at ETH Zurich (Switzerland).

MSc ETH ME Christoph Voser is Research Assistant at the Institute for Dynamic Systems and Control (IDSC) at ETH Zurich (Switzerland).

Dr. Iulian Vasile is Research Assistant at the Institute for Dynamic Systems and Control (IDSC) at ETH Zurich (Switzerland).

38 Research SuperCharging

Authors 1 Introduction ate level in order to retain good driveability. The turbo-lag is reduced The Pneumatic Hybridization 2 Downsizing by using small turbines or turbines with costly variable geometry. In 3 Pneumatic Hybridization order to fully exploit the potential of downsizing and supercharging, Concept for Downsizing and 4 The Concept Developed at ETH Zurich a concept is needed that guarantees excellent driveability even at 5 Hardware and Testbench low engine speeds. Engine concepts using pressure wave super- Supercharging Gasoline Engines 6 Measurements and Controls chargers [4] and dual-stage compression [5] were introduced; here 7 Drive Cycle Results an alternative solution is presented. Prof. Dr. Lino Guzzella 8 Summary is Director of the Chair for Extensive fundamental research at ETH Zurich has yielded the world’s first fully Thermotronics at the Institute 3 Pneumatic Hybridization for Dynamic Systems and functional hybrid pneumatic engine. The pneumatic hybridization of gasoline engines Since the late 1990s, pneumatic hybridization of ICEs has been Control (IDSC) at ETH Zurich primarily aims at maximal downsizing and increased driveability with minimal 1 Introduction (Switzerland). additional cost. When comparing engines with the same maximum power, the discussed [6, 7]. The key idea is to use the ICE also as a pump to One always has to be careful with propulsion systems that are based recuperate the vehicle’s kinetic energy during braking phases, and presented engine system proves to be up to 35 % more efficient on the NEDC. on exotic energy carriers. Compared to conventional fuels, pressu- as an expansion motor for propulsion. This can be realized by con- rized air exhibits an extremely low energy density. This would yield necting an air pressure tank to all cylinders via electronically con- or scie 1 al f ntif low driving ranges for propulsion systems primarily based on pres- trolled charge valves as shown in , left. ov ic r ar pp t A ic l surized air. Therefore it must be emphasized that the concept pre- In addition to the recuperation capability, the idea offers the pos- f e o s l a in e sented here does not rely on pressurized air as the prime source of sibility of a rapid start/stop and permits to shift the engine’s oper-

S M

Dr. Christopher Onder e T Z h . T energy, but on conventional fuel. ating point to high efficiency zones. The latter can be achieved by is Senior Scientist at the

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Peer Review operating half of the cylinders conventionally while the other half of Institute for Dynamic Systems

R and Control (IDSC) at Received 2009-08-24 . the cylinders work in the pump mode (“recharge” mode). Previous e y v r 2 Downsizing i Reviewed 2009-09-11 ETH Zurich (Switzerland). e t w s Accepted 2009-09-24 u concepts assumed two-stroke pump and pneumatic motor modes e d d n b i y d Large, naturally aspirated gasoline engines continue to enjoy great which is possible only if all valves of the cylinders can be variably e an xp h ert rc s from resea popularity among customers who value power and excellent drivea- actuated. bility. Unfortunately, such engines have high fuel consumption par- ticularly at part-load conditions. New propulsion systems are need- 4 The Concept Developed at ETH Zurich ed that satisfy consumer demands and environmental requirements. Electric hybridization is one possible option; however, its associat- At the outset of the project, theoretical investigations were carried Dipl.-Ing. Christian Dönitz is Research Assistant at the ed additional cost is very high. out to determine whether a less complex design for the pneumatic Institute for Dynamic Systems Downsizing internal combustion engines (ICEs) without comple- hybridization could provide the same benefits. In [8] it was shown and Control (IDSC) at mentary electric hybridization also has the potential to reduce fuel that it is sufficient to keep all intake and exhaust valves actuated ETH Zurich (Switzerland). consumption significantly. The peak power of a larger naturally as- by non-variable camshafts while only the charge valve has to be ac- pirated gasoline engine can be recovered using a turbocharger. Low- tuated in a fully variable manner. Consequently, four-stroke opera- er friction and, more importantly, operating the ICE more frequent- tion is retained in all engine modes, ①, right, using a much less ly in high efficiency regions results in lower fuel consumption [1, 2]. complex system with minimal additional cost. The first downsizing and supercharging concepts were developed 2 shows a simplified illustration of the additional engine modes more than ten years ago [3], and it has become a frequently used in double-logarithmic p-V diagrams. The four-stroke pneumatic mo- method. Most of the time, however, it is implemented at a moder- tor mode reveals a peculiarity: more torque can be produced in this MSc ETH ME Christoph Voser is Research Assistant at the Institute for Dynamic Systems and Control (IDSC) at ETH Zurich (Switzerland). Exhaust Charge Intake Valves (EV) Valve (CV) Valves (IV) upstroke downstroke upstroke downstroke 2-stroke pneumatic pneumatic modes motor mode EV/EV CV EV/IV CV 4-stroke pneumatic motor mode CV EV IV 2-stroke pneumatic Dr. Iulian Vasile pump mode CV IV CV IV is Research Assistant at the 4-stroke pneumatic Institute for Dynamic Systems pump mode CV EV IV and Control (IDSC) at ETH Zurich (Switzerland). air tank conventional ﬁred modes combustion EV IV supercharged CV EV EV

BC TC BC TC BC

1 Principle of pneumatic hybridization (left); valve actuation requirements (right), EV = exhaust valves, CV = charge valve, IV = intake valves

38 01I2010 71. Volume 39 Research SuperCharging

2 Additional engine modes – pump mode (left), pneumatic motor mode (center), “supercharged” mode (right)

5 6 p p p log log log 4 3 4, CVC pTank

CVC, 2, 7, 3 2, CVO pTank CVO EVO 3, 5, CVC EVO p EVC, Tank EVC, EVC, 2, IVO, p IVO, IVO, CVO exh 6 5 1, p exh 7 6 p 9 8 p IVC exh 1, in 7 p 4, 1, in 10 IVC p 8 EVO in IVC

log V log V log V VTC VBC VTC VBC VTC VBC

mode by closing the throttle valve. Owing to the lowered intake pres- Another consequence of the described synergy effect is the elim- sure, the work to be done during compression is reduced. Further, ination of the necessity to design the turbocharger for an optimal this enables more air to flow from the tank to the cylinder. dynamic response. By contrast, it is now possible to maximally su- However, it should be emphasized that the main benefit of this con- percharge the engine system by configuring the turbocharger for cept is seen in the so-called supercharged mode. This is a modifica- highest efficiency. Thus, higher mean effective pressures and max- tion of the conventional combustion cycle, ②, right. During compres- imal downsizing are enabled. sion, pressurized air is admitted via the charge valve into the cylinder To minimize emissions, the system must be tuned to ensure a sto- allowing more fuel to be injected for the same engine cycle. ichiometric air-to-fuel ratio. This is another advantage of the concept: The “supercharged” mode enables the fastest torque step response using the established and cost-efficient three-way catalyst technolo- possible. The main advantages of this mode lie in its use in combi- gy results in very low emissions. nation with a turbocharger. The missing air in the system during tran- The main objective of the concept presented is to reduce fuel con- sients is now made available using the air tank. The high fuel energy sumption without compromising driveability. Quasi-static simulations produces a high exhaust enthalpy that accelerates the turbocharger, conducted in [9] revealed the amount of fuel savings that can be ex- making the additional air necessary for only a few seconds. This leads pected from the indiviual concept features. The results are summarized to the core of the concept: taking advantage of the synergy effects of in 4. The base engine for this investigation is a naturally aspirated gaso- downsizing with supercharging and the pneumatic hybridization. An line engine with a displaced volume of 2.0 l and a rated power of 100 illustration of the combined system investigated is shown in 3. kW. The downsized engines investigated reach the same rated power

catalyst

air pressure 0 tank turbocharger air ﬁlter wastegate −5

−10

−15

EHVS MPE750 EHVS −20 air return valve vs. 2.0L base engine (%) 2 −25

−30 downsizing downsizing, start/stop charge air downsizing, start/stop, hybrid cooler −35 Change in CO downsizing, start/stop, hybrid, "recharge"

−40 gasoline 1 1.2 1.4 1.6 1.8 2 engine size (liter) throttle

3 Schematic of the downsizing boost concept 4 Fuel saving potential study (NEDC)

40 5 Modified gasoline engine MPE750 with electro-hydraulic valve system

using turbochargers. The most significant share of fuel consumption remains near ambient temperatures. This cold-tank strategy reduces reduction results from strongly downsizing the engine. The start/stop the likelihood of knock when utilizing the “supercharged” mode. and recuperation functionalities as well as the optional “recharge” The testbench architecture, 6, was designed to accommodate mode only play minor roles for reducing fuel consumption. crank angle and time based sensors and actuators. This requirement calls for a flexibly programmable controller (FPGA). The IDSC has a long history of developing suitable research tools [12]. Hence, the 5 Hardware and Testbench very powerful tool ICX-3 was used to quickly advance the planned All experiments were conducted by modifying a conventional gaso- research activities. line engine (MPE750 produced by Weber Automotive). The MPE750 is a turbocharged two-cylinder engine with a displaced volume of 6 Measurements and Controls 0.75 l (compression ratio 9.0), port fuel injection and a rated power of 61 kW. The pneumatic hybridization was realized by replacing The “supercharged” mode with inducted pressurized air proves to one of the two exhaust valves per cylinder by a charge valve. A se- be advantageous for the combustion process, 7, left. The generat- ries production engine would of course require a cylinder head re- ed turbulence results in a fast and stable combustion. design to ensure an optimal compromise between exhaust back pressure at high engine speeds, volumetric efficiency and boost ca- pacity. Adding direct injection devices to the engine would further °CA-based

3 actuator signals increase the requirements for the cylinder head design. power ampliﬁcation units The charge valves are actuated by the electro-hydraulic valve sys- 5 tem (EHVS, ), a research tool by Robert Bosch GmbH. The EHVS ICX3 (FPGA enables almost any variation of the opening angle, the closing an- controller) hydraulic crank & gle, the opening speed and the lift from one cycle to the next [10]. aggregate cam

Collisions of the charge valves with the piston are ruled out by lim- EHVS EHVS signal update iting the maximum valve lift to 5 mm. This fully variable valve ac- dynamic tuation system allows all additional engine modes illustrated in ②. brake dSPACE sensor realtime PC In order to fully exploit the downsizing potential of the engine, the two-cylinder signals cluth turbine of the GT12 turbocharger was replaced by the turbine of the damper SI PFI HP engine ﬂywheel update GT14 turbocharger. A 30-l steel air tank was used. It is mainly operated in the range of time-based actuator signals 2nd dSPACE 4 to 16 bar. The calculations presented in [11] have shown that the realtime PC for volume of the air tank could also be decreased to about 10 to 15 l safety system incl. knock detection on Freescale MPC 555 brake control without having to compromise on the fuel saving potential of the engine concept. The air tank is not insulated, so that the air in the tank 6 Testbench architecture

01I2010 71. Volume 41 Research SuperCharging

90 100 60 90 p 80 cyl1 55 p 80 cyl2 70 p 70 50 intake 60 60 45 50 50 T (Nm)

(bar) 40 40 (bar) T

cyl Supercharged cyl p p 40 30 T desired 35 20 T 10x conventional 30 conventional 30 conventional - mean 10 10x supercharge 20 −0.5 0 0.5 1 1.5 2 2.5 3 3.5 4 25 supercharge - mean 1.2 10

(−) 1

20 λ 0 0.8 4.5 5 5.5 6 6.5 BDC TDC BDC TDC BDC TDC BDC TDC BDC −0.5 0 0.5 1 1.5 2 2.5 3 3.5 4 V (m3) −5 cyl x 10 time (s)

7 “Supercharged” mode measurements – combustion properties (left), torque step (center), overcoming the turbo lag (right)

However, the “supercharged” mode is only needed for a very valve is always closed once the cylinder pressure exceeds the short time in this concept: until the turbocharger approaches its tank pressure. steady state speed. The main contribution of the “supercharged” The purely pneumatic modes were realized for wide operating mode is therefore most directly described as overcoming the tur- ranges. As expected, the use of the recuperated energy for pneu- bo lag. The “supercharged” mode allows instantaneous torque matic driving does not contribute much to the overall fuel savings. steps to be realized, ⑦, center. Here a torque step from 10 to 90 % This can also be concluded from looking at the measured effec- load was performed and the cylinder pressure sensor signals are tive regenerative efficiencies, shown in 8, left. evaluated. Using this kind of torque step, the turbo lag can be The pneumatic start could also be realized, ⑧, right. The in- eliminated, ⑦, right. The red curve represents the dynamic re- curred pressure drop amounts to about 300 mbar per start (for an sponse of the system without the “supercharged” mode. This com- air tank volume of 30 l). The pneumatic start is more than twice parison shows clearly that the pneumatic hybridization inherently as fast as a conventional engine start and thus justifies the start/ enables a strong downsizing without the loss of driveability. stop operation. The realization of this kind of torque step poses difficult chal- lenges to the control algorithms and the physical models that 7 Drive Cycle Results they are based on. The air mass inducted during the intake stroke as well as the fuel mass actually entering the combustion cham- The verification of the fuel consumption reduction of the concept ber has to be estimated very accurately to avoid misfire or in- presented was conducted by means of a vehicle emulation using creased emissions. Prior to injecting pressurized air into the cyl- the test bench’s fully programmable dynamometer. The dynamom- inder, air-to-fuel ratios of down to l = 0.4 are obtained. Hence, eter serves in this procedure as a virtual vehicle in a drive cycle. precise control of the EHVS has to ensure that exactly the miss- All relevant control algorithms for the engine and the brake sys- ing air mass to reach l = 1 is injected into the cylinder. Addi- tems were programmed in a Matlab/Simulink environment. This tionally, supervisory algorithms must guarantee that the charge implementation has three principal modules. First, there are the

measured max. effective recuperation efﬁciency (%) pneumatic engine start, speed measurement from 0.04s 4000 2500 9

3500 0 2000 8.8 2 3000 4 1500 8.6 2500 6 1000 8.4 2000 8 engine speed (rpm) engine speed (rpm) conventional tank pressure (bar) 10 combustion 500 8.2 1500 12 14

1000 0 8 3 4 5 6 7 8 9 10 11 12 0 0.1 0.2 0.3 0.4 0.5 tank pressure (bar) time (s)

8 Pneumatic modes measurements – measured regenerative efficiencies (left), measurement of a pneumatic engine start (right)

42 engine mode (x), driver mode (-) v control schematic stopping gear switch driving t vehicle launch umode dynamic standstill vehicle programming combustion model ptank pneumatic pump pneumatic motor stop / elim. ωref eω controller ue MPE750 M wallﬁlm e 12 400

(driver) hybrid ) - 10 300

200 feed-forward 8

6 100 ωe fuel consumed (g) tank pressure (bar ∫ 1/θe 4 0 - feed-forward desired velocity 100 real velocity

T e 50 ref T controller Ib dynamic Tb (emulation) brake -

vehicle velocity (km/h) 0 0 200 400 600 800 1000 1200 time (s)

9 Control schematic for vehicle emulation (left), fuel consumption, tank pressure and virtual speed measurements of a VW Polo with modified MPE750, including engine and driver modes (right)

control algorithms for the conventional operation and the addition- Since the pump mode is based on a four-stroke cycle, the torque al modes, the mode change phases, and the optimal pneumatic that can be recuperated is limited. Hence, 500 kJ of the available start. Next there is a controller designed to emulate the torque de- braking energy cannot be recuperated when considering a VW Polo mands of a typical driver. Finally, a controller for the brake is need- emulated in the New European Drive Cycle (NEDC). However, one ed that emulates the vehicle according to the control structure il- still has the option of using an electric generator to provide this en- lustrated in 9, left. ergy to electric auxiliaries.

NEDC EUDC ECE

9 8 7 6 5 4 3 2 fuel consumption (l/100km) -35.4% -31.9% -24.6% -29.8% 1 0 VW Polo `05 VW Polo `09 Nissan Micra Nissan Micra engine 1.39 l Hybrid 0.75l 1.39 l Hybrid 0.75l 1.24 l Hybrid 0.75l 1.39 l Hybrid 0.75l rated power 59 kW 61 kW 63 kW 61 kW 59 kW 61 kW 65 kW 61 kW

ECE 8.30 4.20 8.00 4.23 7.40 4.25 7.90 4.25 ❿ Measured EUDC 5.20 3.99 4.70 3.88 5.10 4.57 5.40 4.52 l / 100km consumption NEDC 6.30 4.07 5.90 4.02 5.90 4.45 6.30 4.42 reductions for various emulated vehicles

01I2010 71. Volume 43 Research SuperCharging

The results for the modified engine in a virtual VW Polo are shown in ⑨, right. The algorithms specify and implement the optimal engine mode for every point of time, thereby guaranteeing charge sus- tenance for the air tank over the whole drive cycle. The virtual driver can follow the demanded velocity trajectory without problems within the given boundaries. To establish a fair comparison, commercially available vehicles with engines of similar rated power were chosen as the basis of comparison. The measured amounts of fuel consumed are illustrated in ❿. The fuel savings of the concept presented are in the range of 25 to 35 %, depending on the vehicle and engine power investigated. It was assumed that no additional torque was required for the operation of electric auxiliaries since electric recuperation provides a sufficient amount of energy throughout the drive cycle.

8 Summary

The downsizing and supercharging concept for gasoline engines based on pneumatic hybridization developed at ETH Zurich was realized using a modified two-cylinder engine (displaced volume of 0.75 l, rated power of 61 kW). The anticipated driveability and fuel economy benefits were observed. In particular, the ability of this concept to eliminate the effect of turbo lag on the driveability of downsized and supercharged engines was confirmed. This engine concept proved to be capable of providing the fastest torque step that is possible using an engine’s air path. Fuel consumption reductions of up to 35 % proved to be realistic. The results shown could also be achieved using an electric hybridization. However, the additional drive train costs for a pneumatic hybridization are a small fraction of those associated with an electric hybridization.

References [1] Guzzella, L.; Onder, C.: Introduction to Modeling and Control of Internal Combustion Engine Systems. Berlin: Springer, 2004 [2] Guzzella, L.; Sciarretta, A.: Vehicle Propulsion Systems. Berlin: Springer, 2nd Edition, 2007 [3] Pfiffner, R.; Weber, F.; Amstutz, A.; Guzzella, L.: Modeling and Model-based Control of Supercharged SI-Engines for Cars with Minimal Fuel Consumption. In: Proceedings 16th American Control Conference (1997), Vol. 1, pp. 304-308 [4] Guzzella, L.; Martin, R: Das Save-Motorkonzept. In: MTZ 59 (1998), Nr. 10, S. 644-650 [5] Krebs, R.; Szengel, R.; Middendorf, H.; Fleiß, M.; Laumann, A.; Voeltz, S.: Neuer Ottomotor mit Direkteinspritzung und Doppelaufladung von Volkswa- gen. Teil 1. In: MTZ 66 (2005), Nr. 11, S. 844-856 [6] Schechter, M.: New Cycles for Automobile Engines. SAE Technical Paper 1999-01-0623, USA, 1999 [7] Higelin, P.; Charlet, A.; Chamaillard, Y.: Thermodynamic Simulation of a Hybrid Pneumatic Combustion Engine Concept. In: Int. J. of Applied Thermo- dynamics, Vol. 5 (2002), No. 1, pp 1-11 [8] Dönitz, C.; Vasile, I.; Onder, C.; Guzzella, L.: Modelling and Optimizing Two and Four-Stroke Hybrid Pneumatic Engines. In: Proc. IMechE, Part D: J. Auto- mobile Engineering, Vol. 223 (2009), No. 2, pp 255-280 [9] Dönitz, C.; Vasile, I.; Onder, C.; Guzzella, L.: Dynamic Programming for THANKS Hybrid Pneumatic Vehicles. In: Proceedings 28th American Control Confer- ence (2009), USA, pp 3956-3963 [10] Mischker, K.; Denger, D.: Anforderungen an einen vollvariablen Ventil- The research work on the pneumatic hybrid engine project at IDSC of trieb und Realisierung durch die elektrohydraulische Ventilsteuerung EHVS. In: 24. Internationales Wiener Motorensymposium, Österreich, 2003 ETH Zurich is supported by the Swiss Federal Office of Energy (BfE [11] Dönitz, C.; Vasile, I.; Onder, C.; Guzzella, L.: Realizing a Concept for High Bundesamt für Energie der Schweiz) and the companies Robert Efficiency and Excellent Driveability: The Downsized and Supercharged Hybrid Bosch GmbH and swissauto Wenko AG. The authors like to thank Pneumatic Engine. SAE Technical Paper 2009-01-1326, USA, 2009 these partners for their help cordially. [12] Guzzella, L.; Geering, H. P.; Hirzel, H.: Anwendungsspezifische Chips für die Regelung von Ottomotoren. Technische Rundschau, 1987, Nr. 1/2, S. 46-49