Control system for a motor vehicle transmission comprising a...

Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – Transmission control

Reexamination Certificate

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C701S067000, C477S159000

Reexamination Certificate

active

06785598

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to a control system for a transmission comprising a torque converter or a hydrodynamic clutch in a motor vehicle for control or regulation of a starting operation of the motor vehicle.
BACKGROUND OF THE INVENTION
Engines with exhaust gas turbo-charge are often used in modem motor vehicles having diesel prime movers. From ecological viewpoints an almost smoke-free operation of the diesel engine is sought in the whole range of operation. For the purpose can be injected only as much fuel as can be burnt without soot with the air mass delivered via the exhaust gas turbo-charger. When the engine is idling, the air mass delivered is accordingly small. The starting behavior of a motor vehicle thus motorized can be felt by the driver as unsatisfactory, especially in case of a quick and high power demand. The rise in rotational speed of the exhaust gas turbine and the increase associated therewith of the air mass charge directly limit the amount of fuel in the starting operation that can be injected for increasing the power in preventing a “sooting”. Only with the rising rotational speed of the engine does the air mass charge increase and therewith the injection amount of fuel and consequently the engine torque. The torque increase at the beginning of the starting operation is accordingly low followed by a sharply progressive build up of the torque.
A similar problem results when using an otto engine turbo-charged with exhaust gas. The ecological critical value are here the exhaust gas composition in the idling operation and when greasing the fuel-air mixture during the starting operation. The air mass supplied to the engine by the turbo charge depends directly on the rotational speed of the exhaust gas turbine. The rotational speed acceleration of the exhaust gas turbine always occurs with a certain time offset relative to the power demand (accelerator pedal movement) of the driver more or less according to the size of the exhaust gas turbine. The driver feels this as an undesirably slow build up of the output torque of the vehicle usually designated as “turbo-lag”.
In relation to converter automatic transmissions, the starting weakness of a motor vehicle turbo-charged with exhaust gas can be positively affected via the characteristic of the torque converter (trilok converter). In the converter is usually provided a lock-up clutch by which the hydraulic power transmission can be mechanically bridged for reducing slip losses in the operation of the vehicle at high velocities. The hydrodynamic torque transmission produces a jerk-free starting operation with corresponding increased comfort. But it is disadvantageous for the starting dynamics that the engine rotational speed must accelerate in direction of the absorption torque of the torque converter. To this are also added as losses training torques of the drive train that necessarily exist. Since the absorption torque of a converter with strong torque reinforcement (“weak” converter characteristic) is smaller than the one in a converter with low torque reinforcement (“strong” converter characteristic), the weakness described can be compensated, of course, at the cost of a “rubber-band like” guiding behavior of the engine rotational speed due to the weak characteristic. The converter absorption torque generally increases sharply, especially in the cold, whereby the starting weakness is further worsened.
If a hydrodynamic clutch is used instead of a trilok converter, a similar problem arises. Due to the lack of stator opposite to the torque converter, the torque of the engine cannot be reinforced whereby another disadvantage results in the uninterrupted build up of the output torque of the motor vehicle. A hydrodynamic clutch also is often combined with a lock-up clutch in order to eliminate slip losses at high velocities of the vehicle.
U.S. Pat. No. 4,775,938 has disclosed a method for the control of a starting operation of a vehicle having a converter automatic transmission in which, during the starting operation of the vehicle the differential rotational speed of a starting clutch rear-mounted on the torque converter is regulated taking into account an accelerator pedal position of the engine as load standard in the calculation of the clutch pressure.
From U.S. Pat. No. 5,272,630 has become known a method of the control of a starting operation of a vehicle having a converter automatic transmission from a stationary uncoupling function, that is, of a starting operation with previously opened starting clutch. The converter slip is adjusted to a nominal differential rotational speed via the starting clutch to be re-engaged. A load standard of the driver acts as interference variable in the proposed control circuit.
Neither of the two methods results in any satisfactory performance in relation to the above described problem of the starting weakness of a driving train with diesel engine loaded with exhaust gas, since the acceleration behavior of the rotational speed and the actual power development of the prime mover remain without being taken into account (disregarded) in the clutch regulation and the closing operation of the starting dutch therefore acts as interference variable upon the rotational speed acceleration of the prime mover.
The invention is based on the problem of providing a control system which is improved the starting behavior of a transmission having a torque converter or a hydrodynamic clutch, the same as a torque-conducting and regulatable clutch or brake mounted in the transmission.
This problem is solved with a control system having the features stated in the main claim.
SUMMARY OF THE INVENTION
According to the invention, it is, therefore, proposed that the starting operation of the motor vehicle be regulated, as function of a driver's wish, via a torque-conducting slip clutch or brake mounted in the transmission taking into account parameters of the torque converter or of the hydrodynamic clutch.
Via the slip in the torque-conducting clutch or brake, the rotational speed acceleration of the driving engine can be advantageously and purposefully controlled or adjusted. A turbo-lag described above, for example, is in this manner effectively prevented in the starting power of a vehicle with internal combustion engine loaded with exhaust gas.
The hydraulic absorption torque of the torque converter or of the hydraulic clutch to be applied by the engine becomes reduced to the extent to which the torque-conducting clutch or brake is opened, that is, brought to slip.
In the extreme case, the torque-conducting clutch or brake is briefly opened completely or almost completely up to the contact point, the piston, clutch or brake is in contact but transmission of torque has not occurred, that upon a power demand by the driver (accelerator pedal actuation) the engine can rotate at high speed almost free. Therefore, in the extreme case the engine acceleration is prevented in power flow direction until the open clutch or brake with the corresponding friction loss portions of the transmission, only by the rotatory inertia and the friction losses of the engine, the same as by the rotatory inertia of the rotary parts of the transmission, the loss portion of the converter absorption torque is completely eliminated.
Prior to and at the beginning of the starting operation the pressure in the torque-conducting clutch or brake is advantageously reduced to a value scarcely above the filling pressure of the clutch or brake, the piston of the clutch or brake thus remains at the contact point of the friction elements and a weak torque is transmitted. In this manner, the closing operation of the clutch or brake can be regulated shock-free and comfortably without dead times for the driver determined by the filling technology.
It has been found in tests that a small time offset between the power demand of the driver and the loose rolling of the vehicle, that is, the increase of the output rotational speed of the transmission, is not felt as negative, especially on account of the acoustic percep

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