Interrelated power delivery controls – including engine control – Transmission control – Engine controlled by transmission
Utility Patent
1999-05-17
2001-01-02
Ta, Khoi Q. (Department: 3681)
Interrelated power delivery controls, including engine control
Transmission control
Engine controlled by transmission
C477S045000, C477S111000
Utility Patent
active
06168546
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to an arrangement and a method for controlling a transmission in a motor vehicle. The transmission is adjustable continuously with respect to its transmission ratio.
BACKGROUND OF THE INVENTION
In motor vehicles having a continuously adjustable transmission (CVT) having a continuous element (for example, a belt-like member or chain), the pressing force of the belt-like member must be so adjusted by suitable measures that the torque which is to be transmitted, can be reliably transmitted. If the pressing force is too low, then a high slippage between the driving element and the conical pulleys occurs which can lead to damage. If the contact pressure is too high, then the efficiency of the transmission is too low which leads to an unnecessarily high consumption of fuel. For this reason, it is advantageous to so select the contact force that the torque, which can maximally be transmitted at this contact force, is somewhat greater than the actual torque which is to be transmitted.
For CVT controls, as they are known, for example, from European patent publication 0,451,887, the transmission input torque is determined from the torque outputted by the engine and the amplification by a possibly present hydrodynamic converter. From this torque, a belt tension is computed from which a contact force results which makes possible a reliable transmission of this torque. The contact force cannot be increased rapidly enough for rapid changes of the torque to be transmitted because of the inertia of the mechanical/hydraulic system. For this reason, a considerable safety reserve is considered as a rule which causes an increased consumption of fuel.
SUMMARY OF THE INVENTION
The object of the present invention is to provide effective measures to counter the occurrence of excessive slippage in order to reliably avoid damage to the transmission.
As mentioned, the invention proceeds from a control of a transmission, which is continuously adjusted as to its transmission ratio, for a motor vehicle. The transmission together with a drive unit is arranged in the drive train of the motor vehicle and the drive unit has an adjustable output torque. According to the invention, determination means are provided for determining a quantity which represents the instantaneous maximum transmittable torque. Furthermore, the output torque of the drive unit is limited to a boundary value by limiting means. This boundary value is determined in dependence upon the above-determined quantity.
In order to reliably protect the transmission against damage by increased slippage, it is therefore provided according to the invention to limit the torque outputted by the motor when the contact force is so low that the danger of excessive slippage exists. The torque of the engine can, in general, be more rapidly limited than the contact force can be increased. For this reason, one arrives at a reliable system without it being necessary to provide, for the contact force, too great a safety reserve which demands a higher consumption of fuel. With the invention, one therefore arrives at an increase of the efficiency of the transmission by the reduction of the contact force compared to existing systems without a safety loss and therefore to a reduction of the consumption of fuel. In this way, one arrives at an increased reliability of torque transmission by the transmission because slippage is reliably avoided which also leads to an increase of driving safety. In addition, the service life of the transmission is increased by the reliable avoidance of slippage.
In an advantageous configuration of the invention, a converter is provided in the drive train which exhibits a determinable torque amplification. In this case, the determination of the boundary value is made in dependence upon the actual converter amplification.
If a clutch is provided in the drive train, which exhibits a determinable torque transmission, then the determination of the boundary value is advantageously made in dependence upon the actual torque transmission.
As already mentioned, the drive belt transmission, in general, has a drive end as well as an output end and effective means (drive belt, for example, belt-like member or chain) for producing a mechanically effective connection between the drive end and the output end. In an advantageous embodiment of the invention, detecting means are provided which detect a contact quantity representing the contact force between the effective means and the drive and/or output ends. For this purpose, the hydraulic contact pressure can be measured directly or can be determined from corresponding control signals. The determination means of the invention are so configured that that quantity is determined from the detected contact force, which represents the instantaneous maximum transmittable torque of the transmission.
Furthermore, it can be provided that the limiting means are so configured that the output torque of the drive unit can be limited as to positive limit values (drive torque limiting) as well as to negative limit values (drag torque limiting). This means that the magnitude of the output torque of the drive unit is compared to the determined limit value and the output torque of the drive unit is reduced (drive torque limiting) or increased (drag torque limiting) in reaction to the limit value being exceeded.
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Bolz Martin-Peter
H{umlaut over (u)}lser Holger
Löffler J{umlaut over (u)}rgen
Luh Joachim
Ottesen Walter
Robert & Bosch GmbH
Ta Khoi Q.
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