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Functionality and potentials of the novel electro-hydraulical valve train “FlexWork”
Patrik Soltic
Abteilung Fahrzeugantriebssysteme Empa, Dübendorf, Schweiz [email protected]
Norbert Zsiga, Empa Andyn Omanovic, Empa
Wolfgang Schneider, Ingenieurbüro Thun
Zürich, 24.06.2019
Introduction Main goals for powertrains:
Reduce CO2 Emissions Efficiency increase Defossilized fuels
Produce «virtually zero» pollutants
Key element for IC engines: flexibility! …in boosting …in load control …in EGR control …in displacement …in compression ratio
2
Fully variable valve control
Content
Introduction
Presentation of the «FlexWork» system
Experimental results (steady state)
Simulation results (driving cycles)
Conclusions
3
FlexWork – Intake Side
4
FlexWork – Exhaust Side Difference to Intake Side
Has to safely open against high(er) cylinder pressure levels Higher opening force needed Robust maximum lift control needed
(even in the case of a misfire)
Solution: maximum lift control via twistable edge
5
FlexWork – Experimental Setup Invention, design and setup
of a running system without an industrial partner
In-house control system for engine & valvetrain
Basis Volkswagen 1.4TSI (EA111) engine (4 cylinder, 1.4 l displacement) 6
FlexWork – Experimental Setup
7
Intake Side Exhaust Side
FlexWork – Design Specifications
200 bar maximum hydraulic supply pressure level
Hydraulic fluid: Wather-Glycol (BASF Glysantin G64), 50:50 Stiffer than oil Oil-free cylinder head Lower additivation of oil possible
No sophisticated valve position sensors needed (only low-cost magnetic position sensor used for diagnostics, not for closed-loop position control)
8
Content
Introduction
Presentation of the «FlexWork» system
Experimental results (steady state)
Simulation results (driving cycles)
Conclusions
9
Experimental Results – Example of Options
10
3000 rpm, bmep 4.5bar, Miller intake valve timing Variation of exhaust valve activation
-60 -40 -20 0 20
Auslass öffnet [°KW n. UT]
28
28.5
29
29.5
30
max = 29.54 %
exh. valve open [°CA]
-50 0 50
Ventilüberschneidung [°KW]
28
28.5
29
29.5
30
max = 29.66 %
valve opverlap [°CA]
2 3 4
Auslassventilhub [mm]
28
28.5
29
29.5
30
effe
ktiv
er W
irkun
gsgr
ad [%
]
max = 29.51 %
Lift exh. valve [mm]
Brak
e th
erm
al e
ffici
ency
(%) Effect: compromise
backpressure vs. Valve actuation energy Effect: Internal EGR
Experimental Results – Example of Options
2000U/min, bmep = 2bar : Throttled operation: η = 20.9% FW: η = 24.0% FW, 2 cylinders deactivated : η = 26.4%
11
10 -1
Volumen [l]
10 0
10 1
Zylin
derd
ruck
[bar
]
Messdaten, 2000U/min, 2bar p me
DK
FW
Measured data @ 2 bar bmep
V [l]
cylin
der p
ress
ure
[bar
]
-20% fuel consumption
Experimental Results – Valve Lift Profiles versus actuation energy demand
12
FlexWork actuation energy @ 2000 rpm Valve lift profiles @ different BMEP levels
crank angle [°CA]
valv
e lif
t [m
m]
Mea
n ef
fect
ive
fric
tion
pres
sure
[bar
]
BMEP [bar]
Camshaft FlexWork total FlexWork hydraulic FlexWork electric
Experimental Results – System Dynamics Increase of Valve Lift
Increase hydraulic pressure level
Comarably slow (due to size of hydraulic accumulator of 75cm3)
Too slow for transient use in vehicles
13
-1.5 -1 -0.5 0 0.5 1 1.5 2 2.5 3
Zeit [s]
45
50
55
60
65
70
75
Dru
ck [b
ar]
0.6
1.3
1.9
2.6
3.2
3.8
4.4
max
. Hub
[mm
]
Hydraulik Einlass, 1500 U/min (Messung)
Experimental Results – Optimal Load Line
14
2000rpm
2.53
33.5
3.54
44.5
4.55
5
5.5
5.5
6
6
6.5
6.5
7
7
7.5
7.5
8
8
8.5
8.5
9
80 100 120 140 160 180 200
IVC [°CA a. GTDC]
70
75
80
85
90
95
Hyd
raul
ic P
ress
ure
Inta
ke [b
ar]
pmi [bar]
Optimal Load Line
Main control parameters: IVC and valve lift
Optimal load line gives the efficiency-optimal combination of IVC and valve lift (=pressure)
Experimental Results – Load Increase
15
IVC can be controlled from one cycle to the next; valve lift is controlled much slower
Strategy: adjust ICV immediately, adjust for increasing valve lift slowly
2000rpm
2.53
33.5
3.54
44.5
4.55
5
5.5
5.5
6
6
6.5
6.5
7
7
7.5
7.5
8
8
8.5
8.5
9
80 100 120 140 160 180 200
IVC [°CA a. GTDC]
70
75
80
85
90
95
Hyd
raul
ic P
ress
ure
Inta
ke [b
ar]
pmi [bar]
Optimal Load Line
Step Response
Experimental Results – Load Decrease
16
2000rpm
2.53
33.5
3.54
44.5
4.55
5
5.5
5.5
6
6
6.5
6.5
7
7
7.5
7.5
8
8
8.5
8.5
9
80 100 120 140 160 180 200
IVC [°CA a. GTDC]
70
75
80
85
90
95
Hyd
raul
ic P
ress
ure
Inta
ke [b
ar]
pmi [bar]
Optimal Load Line
Step Response
Experimental Results – Time Domain
17
Measured response to load step demand IMEP 4.5 bar -> 8.5 bar
0 2 4 6
Time [s]
75
80
85
90
95
Hyd
r. P
ress
ure
Inta
ke [b
ar]
Step Response
Desired
Measured
0.6 0.8 1 1.2 1.4
Time [s]
4
6
8
10
pm
i [bar
]
Step Response (Detail Plot)
Desired
Cyl.1
Cyl.2
Cyl.3
Cyl.4
0 2 4 6
Time [s]
100
150
200
IVC
[°C
A a
. GTD
C]
Step Response
Desired
Measured
Content
Introduction
Presentation of the «FlexWork» system
Experimental results (steady state)
Simulation results (driving cycles)
Conclusions
18
Simulation: Main Questions
What is the benfit from a fully variable valve train in a classical vehicle configuration? → Simulation: Compact car, 1370kg, 1.4 l engine
Is there any advantage from a fully variable valve train in a hybrid electric vehicle or is part load efficiency completely irrelevant? → Simulation: Compact hybrid car, 1470kg, 1.4 l engine, 25 kW electric, 1.5 kWh battery
All simulations using optimal strategies, cold start model included 19
Simulationsergebnisse – Hybridisierung (2)
20
Increase of part load efficiency is always beneficial
Lower electrification (e.g. 48V systems): more relative benefit
Higher power/mass ratio: more relative benefit
CO
2 E
mis
sion
s [%
]
Throttled Operation
FlexWork
FlexWork with Cylinder Deactivation
Conclusions The FlexWork VVT was designed to be as simple / robust /cost effective as possible It proved to work as intended on a 4 cylinder engine, we have actually more than 3
million valve actuation without any problems Part-load efficiency can be enhanced considerably, due to low energy demand of the
VVT and due to the reduction of pumping losses The achievable transient reponse of the engine is (too) fast Other operation modes easily adaptable (e.g. cylinder deactivation, 4+2i-stroke
operation) VVT gives also advantages in hybrid powertrains
Co-finanded by Swiss Federal Office of Energy (Project «FlexWork»)
Technology partner Mubea (Valve springs) Elgo Electronic (Valve position sensors) Hydac and Bieri (Hydraulic components)) BASF (Fluid)
21
Contact: [email protected]
