Power plants – Fluid motor means driven by waste heat or by exhaust energy... – With supercharging means for engine
Reexamination Certificate
1999-04-08
2001-04-03
Denion, Thomas (Department: 3748)
Power plants
Fluid motor means driven by waste heat or by exhaust energy...
With supercharging means for engine
C180S197000
Reexamination Certificate
active
06209323
ABSTRACT:
BACKGROUND OF THE INVENTION
This application claims the priority of German Application No. 198 15 711.8, filed Apr. 8, 1998, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to a method for controlling or automatically controlling the engine brake of a motor vehicle, and more particularly, to a method in which, in the coasting operation during a transmission shifting operation, the resulting braking torque acting upon the engine is reduced.
U.S. Pat. No. 5,088,348, shows an engine braking system for a motor vehicle which consists of a closable valve in the exhaust gas system of the internal-combustion engine and an associated valve in the intake system. In order to generate braking power in the coasting operation and brake the vehicle, the valve in the exhaust gas system can be closed by an electrically operable control element so that an excess pressure is built up in the exhaust gas system which counteracts the piston movement.
In the motor vehicle, an automatic transmission is used which automatically triggers a shifting change as soon as the vehicle speed falls below a defined value and the accelerator pedal is simultaneously not acted upon. During the shifting change, the transmission is uncoupled from the engine so that no external output torque can be transmitted to the engine by the transmission, and the engine is acted upon without any opposing output torque only by the braking power of the engine brake. In order to avoid the rotational engine speed of the internal-combustion engine from falling considerably as the result of the braking power and a back kick taking place onto the transmission, a control signal is generated in a control system. The control signal is supplied to the control element of the valve in the exhaust gas system whereupon the engine brake is rendered inoperative during a shifting change. As a result, a falling of the rotational engine speed is prevented by the engine brake so that both blades of the converter of the automatic transmission rotate approximately at the same rotational speed.
This known system has the disadvantage that, because of the inherently dynamic behavior of the components of the engine brake, a precise adjustment of the time period during which the engine brake is rendered inoperative cannot be sufficiently achieved. A premature or late disconnection or reconnection of the engine brake results either in an unnecessary loss of braking power or in an undesirably large drop of the rotational engine speed.
SUMMARY OF THE INVENTION
An object of the present invention is to be able to influence, at low expenditures, the torques in the engine braking operation of the vehicle which act upon the internal-combustion engine in a manner which is as precise as possible during a transmission shifting operation.
According to the invention, this object has been achieved by, providing that, during the shifting operation, the decisive cross-section in front of the turbine wheel of an exhaust gas turbocharger having a variable turbine geometry is expanded, braking valves at the cylinder outlet of the internal-combustion engine are closed, and, while using an automatic differential rotational speed control, the injected fuel amount is increased to such an extent that the rotational engine speed and the rotational transmission speed are synchronized.
The fuel quantity injected additionally into the combustion chamber generates an additional engine power which at least partially compensates the engine braking power so that a falling of the rotational engine speed during a shifting operation is largely avoided. The engine brake acting upon the internal-combustion engine is prevented at the point in time of the shifting operation, at which the transmission output shaft is uncoupled from the crankshaft. Therefore, no torque of the transmission opposes the braking torque acting upon the crankshaft to significantly reduce the rotational engine speed, which, when the shifting operation is terminated, would result in a high differential rotational speed with resulting problems when coupling the transmission. The additional engine power counteracts the engine braking power so that differential rotational speeds in the transmission line are essentially avoided or at least satisfactorily reduced. Drive torques and braking torques acting upon the internal-combustion engine are thus essentially compensated.
The method of the present invention can also be used in manual transmissions as well as automatic transmissions. In manual transmissions, the rotational speeds of the crankshaft and of the transmission drive shaft, and subsequently the rotational speeds of the two interacting clutch disks of the clutch, are synchronized. In automatic transmissions, the rotational speeds of the two blades of the torque converter are kept at approximately the same level.
The engine injection is expediently underlaid by an automatic differential rotational speed control which determines the additionally injected fuel quantity fully electronically as a function of the rotational speed difference between the engine and the transmission. The automatic differential rotational speed control can be used in the case of manual transmissions as well as in the case of automatic transmissions.
In a preferred further embodiment, the internal-combustion engine has an exhaust gas turbocharger with a variable turbine geometry for changing the turbine cross-section. The turbine geometry can be changed into a ram position in which the flow cross-section of the turbine or of the exhaust gas duct is reduced and a high exhaust gas counterpressure is built up in the line section between the cylinders and the exhaust gas turbocharger. According to the construction of the used exhaust gas turbocharger, the variable turbine geometry consists of rotary blades, of axially displaceable turbine stator guide blades or flap turbines which have several exhaust gas flows which lead to the turbine wheel and which can be shut off by flaps. The exhaust gas flows at a high speed through the ducts between the guide blades of the turbine and acts upon the turbine wheel, whereupon the compressor in the intake system builds up an excess pressure. As a result, the cylinder is acted upon on the input side by an increased charging pressure. An excess pressure exists on the output side between the cylinder outlet and the exhaust gas turbocharger, and counteracts the blowing-off of the air compressed in the cylinder by way of brake valves into the exhaust gas system. During the braking operation, the piston must carry out compression work in the compression stroke against the high excess pressure in the exhaust gas system, whereby a high braking effect is achieved.
During the shifting operation, the decisive cross-section in front of the turbine wheel is expanded by the adjustment of the turbine geometry and/or of a blow-off device with a blow-off valve. Thereby the excess pressure in the pipe section between the cylinder outlet and the turbine, as well as the engine braking power, are reduced. In combination with the additionally injected fuel quantity, by way of the reduction of the exhaust gas counterpressure, on one hand an active reduction of the braking torque affecting the engine is caused, and, on the other hand, by the additional engine power, an additional drive torque is generated.
The method according to the present invention can also be combined with an operation of braking valves at the cylinder outlet which are normally open in the engine braking operation during the compression phase and/or the expansion phase in order to permit a blowing-off of the compressed combustion chamber content into the exhaust gas system. The braking valves are closed during the shifting operation, whereby a blowing-off and connected flow losses are prevented. As the result of the closing of the braking valves, only the drag moment of the currently existing charging degree still acts upon the engine, connected with a clearly reduced braking torque onto the crankshaft.
REFER
Schmidt Erwin
Sumser Siegfried
Daimler-Chrysler AG
Denion Thomas
Evenson, McKeown, Edwards & Lenahan P.L.L.C.
Trieu Thai-Ba
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