Power plants – Fluid motor means driven by waste heat or by exhaust energy... – With supercharging means for engine
Reexamination Certificate
1999-08-09
2001-05-01
Denion, Thomas (Department: 3748)
Power plants
Fluid motor means driven by waste heat or by exhaust energy...
With supercharging means for engine
C123S564000, C415S157000, C415S150000, C415S151000, C415S167000
Reexamination Certificate
active
06223534
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to an engine-braking arrangement for an internal combustion engine with an exhaust-gas turbocharger including a brake valve in the exhaust pipe upstream of the turbine and a pressure relief line, which is connected to the turbine upstream of the turbine rotor and includes a control valve.
DE 195 40 060 A1 discloses a multi-cylinder internal combustion engine, in the exhaust tract of which is arranged a turbine of an exhaust-gas turbocharger, the said turbine driving, via a shaft, a compressor which generates an increased intake pressure in the intake duct. In order to achieve a high engine-braking action in the coasting mode of a vehicle, in which the engine is installed, a brake valve in the exhaust line is closed during braking, with the result that excess pressure is built up in the exhaust line upstream of the brake valve. The built-up exhaust gas flows at high velocity through a bypass directly into a spiral duct of the turbine and acts on the turbine rotor, whereupon the compressor builds up excess pressure in the intake duct. The cylinder is thereby subjected to an increased charging pressure at the entry side. On the exit side, an excess pressure develops between the cylinder outlet and the brake valve and counteracts the discharge of the air compressed in the cylinder into the exhaust tract via the exhaust valves. During braking, the piston must, in the compression stroke, perform compression work against the high excess pressure in the exhaust tract, with the result that a strong braking action is achieved.
In order to prevent an unacceptably high load caused by an excessive build-up pressure upstream of the rake valve during braking, the engine-braking device of DE 195 40 060 A1 has a discharge arrangement consisting of a relief line with a stop valve. When a pressure limit value is reached, the stop valve is opened, so that backed-up exhaust gas is discharged via the relief line and the back-up pressure is reduced.
To control the high pressure upstream of the brake valve, the exhaust-gas quantity to be discharged via the discharge arrangement must finely adjustable, since even slight pressure drops in the line section upstream of the brake valve lead to a drastic reduction in engine-braking capacity. For this reason, stringent requirements must be met as regards an accurate setting of small cross sections of the stop valve in the relief line. In particular, exhaust-gas pulsations caused by pressure fluctuations in the engine, which generate disturbing forces acting on the stop valve, should not impair the blow-off operation.
It is the object of the present invention to provide an engine-braking device with a reliably operating blow-off arrangement, by means of which overloading of the internal combustion engine during large braking loads is prevented.
SUMMARY OF THE INVENTION
In an engine braking arrangement for an internal combustion engine with an exhaust gas turbocharger including a turbine arranged in the engine exhaust duct and a compressor driven by the turbine and arranged in the engine intake duct, a brake valve disposed in the exhaust duct upstream of the turbine and a pressure relief line extending from the exhaust duct upstream of the turbine rotor to an area downstream of the turbine and including a stop valve, the stop valve is a rotationally adjustable rotary valve operable by an actuating device depending on the intake pressure in the intake duct.
Since the stop valve is a rotary valve, it remains unaffected by the exhaust-gas pulsations in the exhaust tract. The exhaust-gas stream to be blown off can be controlled accurately so that the desired pressure limit value can be maintained with a high degree of accuracy and, at the same time, there are no significant losses of braking capacity due to the discharge of the exhaust gas. Even the smallest discharge cross-sections can be controlled by an appropriate rotational control movement of the rotary valve.
The actuating device acting upon the rotary valve utilizes as setting criterion and/or as control value the intake pressure in the intake duct, which prevails at the cylinders at the engine intake side.
When the intake pressure reaches a predetermined limit value, the stop valve is opened and the exhaust gas is blown off via the relief line, whereupon the exhaustgas back pressure drops, the turbine power is reduced and, consequently, the intake pressure is also lowered to a subcritical value. The blow-off of exhaust gas eliminates the energy of the latter and reliably avoids component overloading. The intake pressure may be utilized either as an actuating signal for the actuating device acting upon the stop valve, the actuating signal being converted into a physical control value adapted to the type of actuating device. The actuating signal may also be supplied directly as a physical control value to a pneumatically operable actuating device, by which the rotary valve can be controlled.
The positions of the brake valve and the stop valve may be set independently of one another, so that, during braking with the brake valve closed, the exhaustgas back-pressure can be manipulated, without the brake-valve position being affected. For this purpose, in a first embodiment, the relief line bridges the brake valve, so that, with the stop valve opened, the exhaust-gas line section upstream of the brake valve communicates with the exhaust-gas line section downstream of the latter. The exhaust-gas back-pressure is lowered and the pistons in the cylinders have to perform less work against the pressure in the exhaust duct.
The brake valve is advantageously bridged by the integration of the relief line into the brake valve, in particular into a shaft of the brake valve which is designed as a rotary valve, with the result that a particularly space-saving design can be implemented. In this case, the axis of rotation of the rotary valve disposed in the shaft is preferably orthogonal to the axis of rotation of the brake valve. The rotational movements of the brake valve and of the rotary slide may be executed independently of one another.
According to a another embodiment, the relief line is an independent line which runs outside the exhaust line and can branch off from the latter both upstream and downstream of the brake valve.
If the relief line branches off upstream of the brake valve, it is connected to the exhaust line again downstream of the brake valve, either upstream or downstream of the turbine. In the first instance, only the brake valve is bridged and pressure equalisation is provided between the line sections on both sides of the brake valve. As a result the high exhaust-gas flow velocities of the exhaust-gas stream guided through the by-pass are reduced and the turbine power is lowered correspondingly. In the second instance, the exhaust-gas is discharged directly outwards through the relief line, by-passing the turbine, and exhaust-gas energy is lost.
If the relief line branches off downstream of the brake valve, particularly directly from the spiral inlet duct of the turbine casing, the pressure acting on the turbine, and correspondingly the turbine power, is lowered.
The rotary valve advantageously has a hollow-cylindrical rotary body with radial flow orifices which, depending on the position of the rotary body, communicate with the exhaust line for the discharge of exhaust gas. The flow orifices may be designed as flow grooves, which extend over a portion of the circumference, in particular over an angle of 90° to 180°. Depending on the rotary position of the rotary valve a section of greater or lesser length of the flow grooves comes into contact with the exhaust line providing for continuously adjustable intermediate positions between the closing position and the maximum opening position being obtainable. The exhaust gas can be discharged into the relief line via an axial flow orifice in the rotary body.
The actuating device of the rotary valve is preferably designed as a pneumatic pressure bellows, to which the intake pressure of the intake duct can
Erdmann Wolfgang
Funke Carsten
Lenz Jurgen
Löffler Paul
Schmidt Erwin
Bach Klaus J.
Daimler-Chrysler AG
Denion Thomas
Trieu Thai-Ba
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