Power plants – Fluid motor means driven by waste heat or by exhaust energy... – With supercharging means for engine
Patent
1990-01-17
1992-01-28
Koczo, Michael
Power plants
Fluid motor means driven by waste heat or by exhaust energy...
With supercharging means for engine
F02B 3712
Patent
active
050834347
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a control system and more specifically, although not exclusively, to a system for controlling the boost pressure of a turbo-charged internal combustion engine.
In the case of turbo-charged Otto-cycle engines, it is necessary to control the boost pressure in a manner which will ensure that the maximum permitted pressure is not exceeded. This maximum permitted pressure is determined by the dimensions of the cylinder head, crank shafts, connecting rods, etc. The maximum permitted transmission torque may also be a limiting factor in this regard.
The simplest method is to dimension the turbocharger in a manner which makes it impossible for the pressure to exceed a maximum permitted value. The maximum permitted supercharge, and therewith the highest torque, is obtained solely within the highest engine speed range with the throttle open to a maximum. This results in poor engine performance.
A more usual method is to feed back the boost pressure with the aid of a pressure-sensing device which activates a shunt valve, also referred to as a Waste Gate. The function of the shunt valve is to open a passageway which shunts part of the exhaust flow past the turbine, resulting in a reduced supercharge. The advantage with this system in comparison with a system which lacks feedback is that maximum torque can be moved down to more suitable engine speeds, e.g. speeds in the range of 3000-4000 rpm. The torque curve, however, still has a pronounced peak within a narrow range of engine speed range.
The function of the pressure-sensor shunt valve control system can be greatly improved with the aid of an electronic control system. In brief, the electronic system regulates the feedback pressure to the valve actuator, which in turn controls the shunt valve or Waste Gate. The feedback pressure is controlled by an on-off valve which taps-off a variable flow in pulsatile fashion, subsequent to constricting the flow in the feedback circuit from inlet to actuator. There is consequently applied to the actuator a pressure which corresponds to the pressure in the inlet minus the pressure drop across the constriction. By giving the actuator a lower nominal setting, i.e. a pressure setting at which the actuator will begin to open the Waste Gate, and by regulating the flow tapped off, it is possible to control the boost pressure in a manner to obtain a straight torque curve within a greater area than can be possibly achieved with solely mechanical feedback.
This basic technique is used today by several vehicle or car manufacturers and is consequently well known. The problem with present systems is that even though the control system is well tuned during manufacture of the engine, the engine data changes with time as a result of wear, such as to impair the performance of the control system with the passage of time. Rectification requires a certain amount of labor and retuning of the system takes time, all of which is cost intensive.
An object of the invention is to provide a self-teaching control system which is continuously self-adjusting to achieve optimum control.
Another object of the invention is to provide a control system which will produce a straight torque curve within the highest possible range of engine speed. Engine speed is limited by two factors:
a) There is insufficient exhaust-gas flow to drive the turbo in the lower engine-speed range (RPM-range).
b) In the higher engine-speed range, the maximum boost pressure is restricted by the highest dynamic that can be achieved in the flow through the control valve. In turn, this flow is contingent on the construction of the valve and the control unit.
It is desirable to achieve maximum torque at the lowest possible engine speed with the turbocharger provided. Attention must be paid, however, to driveability, as will be made more apparent hereinafter. Furthermore, the torque curve should be straight throughout all speeds up to high engine speeds.
When the engine or vehicle is accelerated, the response of a turbo-charged engine will be poorer than that of
REFERENCES:
patent: 4428199 (1984-01-01), Moore et al.
patent: 4452044 (1984-06-01), Iwamoto et al.
patent: 4702080 (1987-10-01), Ueno et al.
Dahlgren Mats
Jonsson Nils
Koczo Michael
Nira Automotive AB
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