VGT增压器原理简介(上汽菲亚特红岩动力总成有限公司)
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Boost pressure and temperature Ambient temperature and pressure Turbo speed (FPT patent) Exhaust backpressure …
The control system includes a pressure control valve and air compressed piping
9
VGT control The VGT is normally actuated by a pneumatic cylinder (but solutions with electrical actuators are in development In all cases to exploit all VGT advantages an electronic control system is required (incorporated into the engine ECU) VGT actuator position is controlled using inputs from different sensors
Overstressing Increased fuel consumption
At LOW engine speed (less gas flow) the boost pressure is low and as a consequence the fuel quantity (and the engine power / torque) needs limitation (or/and the smoke level increases) The build-up process is slow and it takes time for the engine to reach the required torque (“Turbo Lag”)
More Power to power to compresso compresso r r
More energy from exhaust …
3
…consequences An equilibrium is reached as the injected fuel quantity is controlled BUT At HIGH engine speed (more gas flow) the boost pressure can be higher than necessary (more air than the amount needed to burn all the fuel)
4
Torque [Nm]
Turbo Lag
Increasing engine speed
SMOKE increase
5
Turbo with Wastegate
A by-pass on the exhaust, reducing gas flow through the turbocharger. When the valve is open at high engine speed, it will reduce boost pressure. This is an energly loss, but a SMALLER turbine can be used, with better low speed performances and better transient response Normally the valve is directly opened by an actuator controlled by boost pressure
0.0% 500 1000 1500 rpm 2000 2500
VGT is also improving Engine Brake performances
11
FG The WG WASTEGATE VGT
100.0%
80.0% % max pressure
60.0%
40.0%
turbo has better low speed performances (as the turbine is smaller)
20.0%
The FIXED GEOMETRY turbo has low performances at low speed
VGT (Variable Geometry Turbocharger)
Claudio Operti Date: 28-08-2008
Turbocharging
In most cases the compressed air (which is hot) is cooled before entering the engine (INTERCOOLER)
6
Turbo with Wastegate
Air OUT
Compressor
Turbine
Exhaust gas OUT Wastegate valve actuator
Wastegate valve (flap) Exhaust gas IN
7
Variable geometry tubocharger
Hale Waihona Puke …driving a compressor…
As the exhaust energy used in the process is anyway available, this FURTER INCREASES engine efficiency
…increasing air pressure at engine inlet and introducing more air into the cylinder. More fuel can be injected, INCREASING engine power
This energy can be used to run a turbine… The exhaust gas has still a high energy
2
…it is not so simple…
More air to engine Energy from exhaust …more fuel …more fuel
10
Results
The VGT has very good low speed performances
120.0%
At high speed the VGT has a controlled pressure, adjusted to the required level with no eccess At high speed the WASTEGATE turbo boost pressure is limited by the bypass valve
8
Variable geometry tubocharger
Closed position (low engine speed)
Cummins – Holset CURSOR engines
Open position (high engine speed)
Second solution: axial moving ring, changing the section of passage for gas
Closed position (low engine speed)
Honeywell – Garret Borg Warner - KKK
Open position (high engine speed)
First solution: moving vanes in the fixed part, changing the direction of gas flow on the turbine wheel and the section of passage for gas
The control system includes a pressure control valve and air compressed piping
9
VGT control The VGT is normally actuated by a pneumatic cylinder (but solutions with electrical actuators are in development In all cases to exploit all VGT advantages an electronic control system is required (incorporated into the engine ECU) VGT actuator position is controlled using inputs from different sensors
Overstressing Increased fuel consumption
At LOW engine speed (less gas flow) the boost pressure is low and as a consequence the fuel quantity (and the engine power / torque) needs limitation (or/and the smoke level increases) The build-up process is slow and it takes time for the engine to reach the required torque (“Turbo Lag”)
More Power to power to compresso compresso r r
More energy from exhaust …
3
…consequences An equilibrium is reached as the injected fuel quantity is controlled BUT At HIGH engine speed (more gas flow) the boost pressure can be higher than necessary (more air than the amount needed to burn all the fuel)
4
Torque [Nm]
Turbo Lag
Increasing engine speed
SMOKE increase
5
Turbo with Wastegate
A by-pass on the exhaust, reducing gas flow through the turbocharger. When the valve is open at high engine speed, it will reduce boost pressure. This is an energly loss, but a SMALLER turbine can be used, with better low speed performances and better transient response Normally the valve is directly opened by an actuator controlled by boost pressure
0.0% 500 1000 1500 rpm 2000 2500
VGT is also improving Engine Brake performances
11
FG The WG WASTEGATE VGT
100.0%
80.0% % max pressure
60.0%
40.0%
turbo has better low speed performances (as the turbine is smaller)
20.0%
The FIXED GEOMETRY turbo has low performances at low speed
VGT (Variable Geometry Turbocharger)
Claudio Operti Date: 28-08-2008
Turbocharging
In most cases the compressed air (which is hot) is cooled before entering the engine (INTERCOOLER)
6
Turbo with Wastegate
Air OUT
Compressor
Turbine
Exhaust gas OUT Wastegate valve actuator
Wastegate valve (flap) Exhaust gas IN
7
Variable geometry tubocharger
Hale Waihona Puke …driving a compressor…
As the exhaust energy used in the process is anyway available, this FURTER INCREASES engine efficiency
…increasing air pressure at engine inlet and introducing more air into the cylinder. More fuel can be injected, INCREASING engine power
This energy can be used to run a turbine… The exhaust gas has still a high energy
2
…it is not so simple…
More air to engine Energy from exhaust …more fuel …more fuel
10
Results
The VGT has very good low speed performances
120.0%
At high speed the VGT has a controlled pressure, adjusted to the required level with no eccess At high speed the WASTEGATE turbo boost pressure is limited by the bypass valve
8
Variable geometry tubocharger
Closed position (low engine speed)
Cummins – Holset CURSOR engines
Open position (high engine speed)
Second solution: axial moving ring, changing the section of passage for gas
Closed position (low engine speed)
Honeywell – Garret Borg Warner - KKK
Open position (high engine speed)
First solution: moving vanes in the fixed part, changing the direction of gas flow on the turbine wheel and the section of passage for gas