De velo pment In jecTIon SySTemS
The New DeNso CommoN Rail Diesel soleNoiD iNjeCToR The new G4S injector from Denso with a three-way valve function improves hydraulic efficiency, thus cutting fuel consumption by around 1 %. A 75 % reduction in moving masses results in significantly improved hydraulics. Due to its minimised leakage, the injector has considerably lower fuel cooling requirements and is significantly more robust in dealing with variations in diesel fuel qualities.
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AuThorS
SHuIcHI matSumoto is Director Diesel Injection engineering Division at Denso corporation in Kariya (japan).
KenjI Date is manager at the Diesel Injection engineering Division, Denso corporation in Kariya (japan).
tooru taGucHI is Project Assistant manager at the Diesel Injection engineering Division, Denso corporation in Kariya (japan).
Dr. olaF erIK Herrmann is Team Leader Advanced Diesel engine management System at Denso International europe in Wegberg (Germany).
IntroDuctIon
Worldwide increasing numbers of diesel engines will be sold with a growth espe cially in the emerging markets. On the other hand in the developed countries extremely strict emission regulations and CO2 regulation need to be fulfilled. There fore the diesel injection equipment is required to realise higher fuel metering accuracies and to provide increased injection pressures to meet the stricter emission and fuel consumption regula tions while realising the higher specific engine performance. The engine makers and OEM further require improved robustness against diversified market fuels, pressure main tenance characteristics in the idle stop system (ISS) and easy installation of the fuel injection equipment (FIE). One key component to meet these demands is the injector. Technically it is possible with a today inproduction 3rd genera tion piezo injector G3P (generation 3 piezo) to fulfil the coming require ments [1]. However the solenoid tech nology guarantees for high robustness, long lifetimes and cost optimisation. Thus Denso has developed a new gener ation solenoid injector G4S (generation 4 solenoid) meeting the same perfor mance as the G3P injector. The focus was on the following development targets, ❶:
FeatureS
eliminate clearance
leakage
G4S Injector HyDraulIc FunctIon anD perFormance
The current inproduction G3S injector has mounted the solenoid valve on the top of the injector. Thanks to the more than 70 % reduced switching leakage, the G4S solenoid could be minimised in size and moved centrally to the injector close to the nozzle needle. As shown in
FIe beneFIt
Start-stop capability, fuel robustness,
leakage minimise switching
Thanks to its high actuation forces, the G3Pinjector realises a direct three way valve, which can minimise switch ing leakage significantly. It is a disadvan tage of conventional today inproduction solenoid injectors, that high switching leakages plus clearance leakages cause waste of energy and fuel deterioration due to high local temperatures in the fuel return lines [2]. A breakthrough was required to the control valve structure [1] to accomplish zero clearance leakage using a solenoid actuator. In the new 4th generation solenoid injector G4S this could be achieved by a new threeway valve function. Compared to current solenoid injector (G3S, generation 3 sole noid) the overall hydraulic performance was improved [2]. Compared to G3P, thanks to simple solenoid technology, long lifetime requirements of commer cial applications are enabled with up to 2500 bar and later 3000 bar injection pressure [3].
efficiency Further improved fuel robustness and fuel efficiency
G3S
G3p
G4S
no
yes
yes
no
yes
yes
no
yes
yes
no
yes
yes
no
yes
yes
2000 bar
2000 bar
easy installation, pressure sensor Small size control valve
option (i-ArT, intelligent accuracy refinement technology)
Individual nozzle open/ close speed
Injection rate tuning option
Locate actuator and
reduced moving mass to improve
control chamber direct
hydraulic performance, injection
close to needle Increase injection pressure
accuracy and stability reduced emissions, reduced fuel consumption, high power
2500 to 3000 bar*
* next step for heavy duty application
❶ Development targets for the new G4S injector compared with other Denso diesel injectors 02I2013
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De velo pment In jecTIon SySTemS
❷ there is no additional command piston needed any more and the needle is actu ated directly by the pressure in the con trol chamber. There is no part in the injector which is sliding and has sealing function at the same time. Thanks to the direct positioning of the control chamber above the needle, the moving mass can be reduced drastically by 75 %. Part of the control chamber shown in ② is the so called control plate, which is normally closing the inlet orifice as seen on top left side. The outlet orifice is in cluded in the control plate and can be tuned to determine the opening speed of the needle. When the control valve opens, the pressure in the control chamber will be dropped. During injection the control plate keeps the inlet orifice closed, so no flow into the control chamber occurs. When the control valve is closed, as shown in ② on bottom right side, thanks to a highpressure circular groove the force balance on the control plate will change. The intermediate chamber pressure will become same as in the control chamber and the pressure in the highpressure circular groove is higher. This creates a change in force balance on the control plate and the control plate is moving and opening the inlet orifice. Then, the pres sure in the control chamber can rise again very quickly thanks to an independent inlet orifice. The closing speed can be influenced by tuning of the inlet orifice – typically fast closing is preferred. The positive impact on the injector hydraulic performance is shown in ❸. Thanks to the ballistic needle the so
Control valve Intermediate chamber Inlet-orifice High-pressure circular groove Outlet orifice
Control plate Control chamber Nozzle needle Start of injection
70 60 50
called gain curve of the injector is very linear, same or better as known from the G3P [1, 2]. Up to 2500 bar the curves can be kept linear and for each pressures well separated, which is needed for accurate injection control and for efficient com pensation functions. Also to keep the gain curves smooth especially in the small quantity area is beneficial for stable pilot injection quantities in production and during lifetime. As indicated in ③ the conventional solenoid injector requires some connect
ing element, which creates friction and increases the moving mass. For G4S the repeatability from injection to injection has been improved. The so called shot toshot performance is also shown in ③. With even 2500 bar injection pressure the shottoshot deviation is improved by up to 50 % compared to the conventional injector with 2000 bar injection pressure. To inject on every cylinder at every com bustion cycle same injection quantities is beneficial. In the pilot quantity area minimised shottoshot deviations enable
Conventional G3S
Actuator
New G4S
30 20 10 Command piston
10 8 6 4 2 0
Shot to shot quantity deviation [mm3/stroke]
40
0
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End of injection
❷ G4S solenoid injector structure and function
Rail pressure [bar] 2500 2000 1600 1200 800 400
80 Injection quantity [mm3/stroke]
Before injection
G3S (2000 bar)
G4S (2500 bar)
Injected fuel quantity [mm3/stroke]
Nozzle needle 0
0.20
0.40 0.60 0.80 Energising time [ms]
1.00
❸ Injection quantity of G4S as function of electrical energising (left) and injection quantity deviation from injection-to-injection (right)
H
L
Control chamber Command piston Nozzle needle
20 0.5 kW mech. power
0
G3S
H
G4S
Rated power 40 20 0
G3S
Clearance leakage
L Low-pressure side
Switching leakage
beneFIt oF tHree-Way-FunctIon valve
The elimination of clearance leakage and reduction of switching leakage was a major development target. Hydraulic simulations, engine bench and vehicle investigations have shown, that, thanks to leakage reduction, about 1 % fuel con sumption reduction is possible for pas senger car application and for heavy duty application in the whole map area [4]. Leakage from the highpressure side results in more fuel to be delivered by the highpressure pump and thus fuel consumption increase of the engine. Fur thermore leakage reduction is essential for efficient injection pressure increase, which offers emissions and fuel con sumption potential [3, 4]. ❹ shows the actual quantity of the leakage of a conventional solenoid injec tor compared to G4S. On current solenoid injector G3S clearance leakage occurs at the command piston and nozzle needle. Volume 74
2 kW mech. power
G4S
H High-pressure side
directly a reduction of the minimum possible injection quantity. In combina tion with conventional learning func tions or optional with iART stable pilot injections can be realised for example to ensure stable emissions and perfor mance for passenger car applications during lifetime.
02I2013
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It is known that clearance leakage in creases progressive with the utilised injection pressure [2]. Also at lower en gine speeds clearance leakage becomes bigger due to more time between the injections. The second contribution is the switching leakage, which for conven tional injectors occurs not only from control chamber, but also from high pressure side as long as the armature of the solenoid valve is opened. That means
❹ Injector fuel leakage for G3S and G4S injector for a four-cylinder engine at 2000 bar injection pressure
for each injection it occurs and the longer the injection duration is, the more switching leakage occurs. The worst case thus is full load operation as shown in ④. At low end torque a bit more than 40 mm3 per stroke leakage fuel need to be additionally delivered by the high pressure pump – this is a saving poten tial of more than 500 W pump driving power (at a fourcylinderengine and 2000 bar injection pressure). At high
Injection quantity: 80 mm3/stroke 80
G3S (2000 bar)
60 Leakage [mm3/stroke]
L
G4S Three-way function without command piston
Leakage [mm3/stroke]
G3S Two-way valve with command piston
Leakage [mm3/stroke]
Low end torque
40
G4S (2500 bar)
20
❺ Stability of leakage during durability test
0
0
200
400
600
800
1000
1200
Durability test time [h]
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De velo pment In jecTIon SySTemS
Fuel exchange
Time
Maximum TAN [mg KOH/g]
Total acid number
Minimum TAN 0.05
Fuel drift happens
0.4
Maximum TAN
No fuel drift
G4S 0.3
Leakage temperature [°C]
G3S 0.2
120
0
0 G3S
G4S
engine speeds the clearance leakage per stroke is reduced due to less time between injections. However the total by the high pressure pump to be delivered leakage flow increases. Thus at rated power the leakage creates almost 2000 W of pump driving power as total saving potential. With G4S the clearance leakage is avoided completely. This allows espe cially at low end torque a drastic leakage reduction and thus CO2 potential. This feature is also supporting the ISS (idle start stop) function in an optimum way. After engine stop, the pressure can be maintained in the rail easily for several minutes. For the next startup the rail pressure is available directly from the rail. Additionally the switching leakage can be reduced by more than 70 % thanks to the threeway valve function. The re maining leakage correlates to the mini mum required energy to operate the servo injector (at low end torque less than 100 W). This increase of efficiency is also key for further hydraulic efficient increase of injection pressure beyond 2500 bar up to 3000 bar [4]. ❺ shows the leakage characteristics after durability test. The clearance leak age is proportional to the cube of the clearance, and the clearance, which is usually approximately 1 μm, is very sen sitive to wear. On the other hand, orifice flow is proportional to the orifice area, which explains, why switching leakage is less sensitive in the durability test. The new structure without sliding portion and with threeway valve function
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❻ Accelerated bio fuel robustness test on pump bench (schematic)
60 600
800
1200
1600
Endurance test time [h]
thanks to its principle is free from effects of temporal wear even after the durabil ity test, so the leakage quantity hardly changes at all. Very stable and small leakage quantities were verified, as shown in ⑤ [2]. Worldwide experience with different fuels [5] has leaded to counter measures, like DLC coatings applied to the valve sliding portion of the inproduction injector. By this, formation and adhesion of biopolymer deposits was improved. An accelerated test cycle to evaluate the injection system in terms of robustness against deposits is shown in ❻. Here the worst case bio fuel mixture of 20 % soya bean based bio diesel is tested. The so called TAN (Total Acid Number) increases due to oxidisation of fuel during fuel storage accelerated by high temperatures in the injection system – for example in jector leakage. The test shows how long the conventional inproduction solenoid system survives till fuel drift as function of maximum selected TAN occurs. The achieved robustness is sufficient for today’s market fuel situation [5]. The new solenoid injector is significant more robust against this extreme test and showed no fuel drift within 1600 hours even if the maximum TAN number is increased. Thus there is a bigger poten tial to keep the robustness of the system even if fuels will change in the future. The explanation why the new devel oped solenoid injector G4S is more robust to biopolymer deposits is on the one hand the number of moving parts
and the actually internal sliding area are reduced drastically. On the other hand the internal temperature of the injector can be reduced. concluSIon
Denso’s new solenoid injector G4S real ises a threewayfunction valve. By this the hydraulic efficiency can be increased allowing about 1 % fuel savings. Also the hydraulic performance of the injector was improved – the shottoshot devia tion was reduced by 50 %. The fuel leak age temperature can be reduced, which improves the fuel robustness of the injec tor and reduces the need for fuel cooling. Denso will launch the G4S injector at the beginning of 2013 with up to 2500 bar injection pressure and later will increase the injection pressure up to 3000 bar. reFerenceS [1] Kondo, S.; Toyoshima, y.; Takayama, T.; yamaguchi, m.: 200 mPa Piezo common rail System. journal of Society of Automotive engineers of japan, no 20095709, 10/2009 [2] matsumoto, S.; Date K.; yamada, K.: concepts and evolution of Injector for common rail System, SAe 2012-01-1753, 2012 [3] Shinohara, y.; Takeuchi, K.; herrmann, o.; Laumen, h. j.: 3000 bar common rail System, In: mTZ 72 (2011), no. 1, pp. 4-8 [4] herrmann, o.; nakagawa, m.; Kenhard, m.; Schwab, h.; miyaki, m.; Shinohara, y.; Takeuchi, K.; uchiyama, K.: ultra high Pressure and enhanced multiple Injection – Potentials for the Diesel engine and challenge for the Fuel Injection System. Fuel Injection Systems for Ic engines, Imeche, 2012 [5] omori, T.; Tanaka, A.; yamada, K.; Bunne, S.: Biodiesel deposit formation mechanism and improvement of FIe. SAe 2011-01-1935, 2011
