C O V E R S T O R Y FUEL 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
An increasing numbers of diesel engines will be sold worldwide, with growth especially in the emerging markets. On the other hand, extremely strict emission regulations and CO2 regulation need to be fulfilled in the developed countries. Therefore, the diesel injection equipment is required to realise higher fuel metering accuracies and to provide increased injection pressures to meet stricter emission and fuel consumption regulations, while realising higher specific engine performance. Engine makers and OEMs further require improved robustness against diversified market fuels, pressure maintenance 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 an in-production 3rd generation piezo injector G3P (generation 3 piezo) to fulfil the oncoming requirements [1]. However, the solenoid technology guarantees for high robustness, long lifetimes and cost optimisation. Thus, Denso has developed a new generation solenoid injector G4S (generation 4 solenoid) meeting the same performance as the G3P injector. The focus was on the development targets as mentioned in, ➊.
Thanks to its high actuation forces, the G3P injector realises a direct three-way valve, which can minimise switching leakage significantly. It is a disadvantage of conventional current in-production solenoid injectors, where 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 three-way valve function. Compared to current solenoid injector (G3S, generation 3 solenoid) the overall hydraulic performance was improved [2]. Compared to G3P, thanks to simple solenoid technology, long lifetime requirements of commercial applications are enabled with up to 2,500 bar and later 3,000 bar injection pressure [3].
G4S INJECTOR HYDRAULIC FUNCTION AND PERFORMANCE
The current in-production 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
FEATURES
FIE BENEFIT
G3S
G3P
G4S
Eliminate clearance leakage
Start-stop capability, fuel robustness, efficiency
No
Yes
Yes
Minimise switching leakage
Further improved fuel robustness and No fuel efficiency
Yes
Yes
Small size control valve
Easy installation, pressure sensor option (i-ART, intelligent accuracy refinement technology)
No
Yes
Yes
Individual nozzle open/ close speed
Injection rate tuning option
No
Yes
Yes
Locate actuator and control chamber direct close to needle
Reduced moving mass to improve hydraulic performance, injection accuracy and stability
No
Yes
Yes
Increase injection pressure
Reduced emissions, reduced fuel consumption, high power
2000 bar
2000 bar
2500 to 3000 bar*
* Next step for heavy duty application
❶ Development targets for the new G4S injector compared with other Denso diesel injectors autotechreview
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C O V E R S T O R Y FUEL IN JECTION SYSTEMS
Before injection
the needle, the moving mass can be reduced drastically by 75 %. Intermediate Part of the control chamber chamber shown in ② is Inlet-orifice the so called control plate, which is normally High-pressure circular groove closing the inlet orifice as seen on top left side. The outlet orifice is Outlet orifice included in the control plate and can be tuned Control plate to determine the opening speed of the needle. When the control valve Control chamber opens, the pressure in Nozzle needle the control chamber Start of injection End of injection 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, ❷ G4S solenoid injector structure and function as shown in ②, on bottom right side, thanks to a high-pressure circular groove the force balance on the control and moved centrally to the injector close plate will change. to the nozzle needle. As shown in ➋ there The intermediate chamber pressure is no additional command piston needed will become same as in the control chamany more and the needle is actuated ber and the pressure in the high-pressure directly by the pressure in the control circular groove is higher. This creates a chamber. There is no part in the injector, change in force balance on the control which is sliding and has sealing function plate and the control plate is moving and at the same time. Thanks to the direct opening the inlet orifice. Then, the prespositioning of the control chamber above Control valve
70 60 50
Actuator
New G4S
40 30 20 10 Command piston
0 10 8 6 4 2 0
Shot to shot quantity deviation [mm3/stroke]
Injection quantity [mm3/stroke]
Conventional G3S
Rail pressure [bar] 2500 2000 1600 1200 800 400
80
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 ➌. Thanks to the ballistic needle, the so called gain curve of the injector is very linear, same or better as known from the G3P [1, 2]. Up to 2,500 bar the curves can be kept linear and for each pressures well separated, which is needed for accurate injection control and for efficient compensation 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 connecting 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 2,500 bar injection pressure the shot-to-shot deviation is improved by up to 50 % compared to the conventional injector with 2,000 bar injection pressure. To inject on every cylinder at every combustion cycle, same injection quantities is beneficial. In the pilot quantity area minimised shot-to-shot deviations enable directly a reduction of the minimum possible injection quantity. In combination
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)
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G3S Two-way valve with command piston
L
G4S Three-way function without command piston
H
L
Leakage [mm3/stroke]
Low end torque 40
20
0
H
0.5 kW mech. power G3S
G4S
Rated power Leakage [mm3/stroke]
Control chamber Command piston Nozzle needle
40
20
0
G3S
2 kW mech. power G4S
H High-pressure side
Clearance leakage
L Low-pressure side
Switching leakage
❹ Injector fuel leakage for G3S and G4S injector for a four-cylinder engine at 2000 bar injection pressure
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 consumption reduction is possible for passenger car application and for heavy duty application in the whole map area [4]. Leakage from the high-pressure side results in more fuel to be delivered by the high-pressure pump and thus fuel consumption increase of the engine. Furthermore leakage reduction is essential for efficient injection pressure increase, which offers emissions and fuel consumption potential [3, 4]. ➍ shows the actual quantity of the leakage of a conventional solenoid injector compared to G4S. On current solenoid injector G3S, clearance leakage occurs at the command piston and nozzle needle. It is known that clearance leakage increases autotechreview
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injection pressure). At high engine progressive with the utilised injection speeds, the clearance leakage per stroke is pressure [2]. Also at lower engine speeds, reduced due to less time between injecclearance leakage becomes bigger due to tions. However, the total leakage flow more time between the injections. The delivered by the high-pressure pump second contribution is the switching leakincreases. Thus, at rated power the leakage, which for conventional injectors age creates almost 2,000 W of pump drivoccurs not only from control chamber, but ing power as total saving potential. also from high-pressure side as long as With G4S the clearance leakage is the armature of the solenoid valve is avoided completely. This allows especially opened. That means for each injection it occurs; and the longer the injecInjection quantity: 80 mm3/stroke tion duration is, 80 the more switching leakage occurs. The worst case, G3S (2000 bar) thus, is full load 60 operation as shown in ④. At low end torque, a bit more than 40 40 mm3 per stroke leakage fuel need to be additionally delivered by the G4S (2500 bar) 20 high-pressure pump – this is a saving potential of more than 500 W 0 pump driving 0 200 400 600 800 1000 1200 power (at a fourDurability test time [h] cylinder-engine ❺ Stability of leakage during durability test and 2,000 bar
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Leakage [mm3/stroke]
with conventional learning functions or optional with i-ART, stable pilot injections can be realised, for example, to ensure stable emissions and performance for passenger car applications during lifetime.
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C O V E R S T O R Y FUEL 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 60 0
0 G3S
G4S
600
800
1200
1600
Endurance test time [h]
❻ Accelerated bio fuel robustness test on pump bench (schematic)
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 start-up the rail pressure is available directly from the rail. Additionally, the switching leakage can be reduced by more than 70 % thanks to the three-way valve function. The remaining leakage correlates to the minimum 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 2,500 bar up to 3,000 bar [4]. ➎ shows the leakage characteristics after durability test. The clearance leakage is proportional to the cube of the clearance, and the clearance, which is usually approximately 1 μm, is very sensitive 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 three-way valve function, thanks to its principle, is free from effects of temporal wear even after the durability 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 led to counter measures, like DLC coatings applied to the valve sliding portion of the in-production injector. By
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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 ➏. Here, the worst case bio-fuel mixture of 20 % soya beanbased 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 injector leakage. The test shows how long the conventional in-production 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 significantly more robust against this extreme test and showed no fuel drift within 1,600 hr, even if the maximum TAN number is increased. Thus, there is a bigger potential to keep the robustness of the system even if fuels will change in the future. The explanation why the newly developed 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.
the hydraulic efficiency can be increased allowing about 1 % fuel savings. Also the hydraulic performance of the injector was improved – the shot-to-shot deviation was reduced by 50 %. The fuel leakage temperature can be reduced, which improves the fuel robustness of the injector and reduces the need for fuel cooling. Denso has launched the G4S injector at the beginning of 2013 with up to 2,500 bar injection pressure and later will increase the injection pressure up to 3,000 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
CONCLUSION
Denso’s new solenoid injector G4S realises a three-way-function valve. By this
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