Method of controlling a gear-shifting process

Details Method of controlling a gear-shifting process Method of controlling a gear-shifting process

2000-10-06

2002-10-22

Marmor, Charles A. (Department: 3681)

Interrelated power delivery controls, including engine control

Transmission control

Control by sensed ambient condition, pattern indicia,...

C477S107000, C477S906000

Reexamination Certificate

active

06468182

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a method of controlling a gear-shifting process in a power-shift transmission of a vehicle, wherein the power-shift transmission is coupled to an engine and uses a frictional slip clutch as a power-shift clutch.
To change gears in known manually shifted transmissions, e.g., for passenger cars, it is necessary to interrupt the flow of tractive force from the combustion engine to the drive train of the vehicle, e.g., by disengaging a start-up element such as a friction clutch, where the disengagement can he performed either by the driver of the vehicle or by an actuator. The time gap in vehicle traction is noticeable for the user of the vehicle at every gear change. The interruption in traction occurs also in automated transmissions in which the gear-shifting process is performed by means of an actuator. While there are known transmissions that can be shifted while traction is maintained (also known as power-shift transmission s), the state-of-the-art units are primarily automatic transmissions of a planetary-gear design. Although they are practically proven, they are complex and therefore expensive.
To make the gear-shifting process in vehicles more comfortable, the known state of the art also offers a power-shift transmission in the form of a so-called interruption-free gear-shift transmission. This interruption-free transmission, like conventional transmissions, includes a start-up element such as a friction clutch, but in addition, a frictional slip clutch on either the input or output shaft of the transmission is arranged in a such a manner that an engine torque acting on the transmission-input shaft in the engaged condition of the start-up clutch is transmitted through the frictional slip clutch to the transmission-output shaft, whereby it becomes possible to transmit torque also while a gear-change of the transmission is in process. In other words, the flow of traction from the engine to the drive train of the vehicle is maintained during the gear change.
It has been found that the increase in vehicle comfort achievable with an interruption-free transmission of this kind depends to a great extent on the characteristics of the additional frictional slip clutch, which will be referred to as power-shift clutch. Especially when shifting gears under full traction, the heat load on the power-shift clutch is very high, because to a large extent, a transmission of this kind has to be able to transmit the entire engine torque to the drive train of the transmission, if an interruption in traction is to be avoided. Otherwise, a time-gap in the tractive force could be noticed by the driver of the vehicle during a phase of full acceleration when the full amount of driving torque is delivered by the engine.
The heat load on the power-shift clutch becomes greater if the power-shift clutch is arranged to be effective with a higher gear of the power-shift transmission. For example, if the power-shift transmission has five forward gears, the heat load on the power-shift clutch is greater if the power-shift clutch is arranged to be effective with the fifth gear of the transmission than if it were arranged to act on the fourth gear. However, it is desirable in a transmission of this kind that the power-shift clutch be effective in fifth gear because otherwise a shift from fourth into fifth gear could no longer be performed under traction and would therefore be accompanied by an interruption of the tractive force. However, in order to achieve a high degree of durability of a power-shift clutch that is configured as a frictional slip clutch, it is necessary to avoid a thermal overload of the power-shift clutch.
OBJECT OF THE INVENTION
The present invention therefore aims to provide a method of controlling a gear-changing process of a power-shift transmission, whereby the heat load on the power-shift clutch is reduced in order to make the power-shift transmission more durable.
SUMMARY OF THE INVENTION
The invention is based on the observation that the gear-shifting process in a power-shift transmission is influenced to a high degree by the clutch torque that is transmitted through the power-shift clutch. The clutch torque affects all of the following: a) the amount of output torque delivered to the drive train of the vehicle during the gear-shifting process, b) the amount of time needed for synchronization and thus the time required for the gear-shifting process, c) the amount of heat generated in the power-shift clutch due to the slipping engagement, and d) the amount of power transmitted through the power-shift clutch. Although it is possible, in principle, to influence the output torque during the entire gear-shifting process by way of the clutch torque flowing through the power-shift clutch, a process of controlling the output torque by way of the clutch torque leads to a large accumulation of energy in the power-shift clutch in the form of heat that is generated by the frictional slip of the power-shift clutch. Albeit that in a power-shift clutch designed as a frictional slip clutch with two or more friction linings or as a laminar-disc clutch with a plurality of friction linings, the heat can be carried away by convection, radiation, or heat conduction into the pressure plate and the disc or discs of the clutch, the power-shift clutch is nevertheless subjected to a high heat load if power-shift processes are performed in rapid succession so that no effective temperature reduction of the power-shift clutch can take place between the individual power-shifts.
The present invention solves the foregoing problem by providing an advantageous method of controlling the gear-changing process, whereby the amount of energy introduced into the power-shift clutch can be lessened. The method also has a favorable effect on the fuel consumption of a vehicle equipped with a power-shift transmission, but has no negative consequences on the desired shifting comfort in the interruption-free power-shift processes.
Under the method according to the invention, a gear-changing process in a power-shift transmission coupled to an engine and equipped with a frictional slip clutch works in a manner where the engine torque as well as the clutch torque are being varied in such a way that the amount of heat introduced into the frictional slip clutch is lowered and, consequently, the temperature increase of the frictional slip clutch is reduced. In other words, in the gear-changing process that is performed as a power-shift process, the inventive method provides that the engine torque as well as the clutch torque are being varied and that the variation is performed in a manner where the amount of energy introduced into the power-shift clutch and converted into heat is reduced in comparison to a gear-changing process where only the clutch torque of the power-shift clutch is being varied and the torque produced by the engine remains, at least to a large extent, constant during the gear-changing process.
In a first phase of the gear-shifting process according to the inventive method, the torque entering the drive train of the vehicle is reduced by lowering the engine torque while the gear clutch of the current gear level is still engaged. Thus, at the beginning of a power-shift process, the torque level is lowered at first by an intervention of the engine control system rather than by using the power-shift clutch. The power-shift clutch is therefore in the disengaged condition and not transmitting any torque at the beginning of the shift process. Because the power-shift clutch uses a slipping engagement to transmit torque between the input shaft and the output shaft of the power-shift transmission, a transmission of torque through the power-shift clutch will cause the latter to heat up. However, at the beginning of the power-shift process according to the inventive method, the output torque is lowered by controlling the engine torque, so that there is no load on the power-shift clutch, and thus no energy is introduced in the power-shift clutch, during the corresp

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