Machine element or mechanism – Gearing – Interchangeably locked
Reexamination Certificate
2002-04-22
2004-01-13
Pang, Roger (Department: 3681)
Machine element or mechanism
Gearing
Interchangeably locked
Reexamination Certificate
active
06675668
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a double clutch transmission and a method for controlling an automated double clutch transmission.
Double clutch transmissions have long been known and are used by preference in motor vehicles. In general, a double clutch transmission has a first transmission input shaft, connected to a first clutch and speed change gears for a first group of gear speeds, a second transmission input shaft connected to a second clutch and speed change gears for a second group of gear speeds, and a shared transmission output shaft. Usually, the first group of gears comprises the odd-numbered forward gears and the reverse gear, while the second group of gears comprises the even-numbered forward gears. In a double clutch transmission of this nature, a shifting operation, which is to say a change from an active gear to the next higher or next lower destination gear, consists of an initial engagement of the destination gear, which can, for example, be accomplished via a suitable gear change sleeve and a synchromesh mechanism associated with the destination gear, and a subsequent overlapping disengagement of the clutch associated with the transmission input shaft for the active gear and engagement of the clutch associated with transmission input shaft for the destination gear, wherein an interruption of tractive power can largely be avoided. Aside from the shifting operations, the transmission of power is accomplished by means of the first and second transmission input shafts in alternation.
Variations and further refinements of the double clutch transmission have been developed to fit specific application requirements and to implement additional functions.
Thus, for example, DE 3,546,454 A1 discloses a double clutch transmission in which the two transmission input shafts can be connected through an additional clutch. In this way, both clutches can be engaged, particularly for a startup process, which makes it possible to increase the available clutch capacity and reduce the thermal load on the clutches. No other use may be made of the additional clutch, for example for a parking lock.
The class-defining patent DE 4,316,784 A1 describes a double clutch transmission that is designed for an electrically driven vehicle and has only two gears.
The speed change gears for the two gear speeds are each rigidly connected to one of the transmission input shafts and the shared transmission output shaft. A gear change is thus accomplished solely by means of the two associated clutches. To implement a parking lock and a so-called hill holder, both clutches are designed so as to be capable of simultaneous engagement. However, a parking lock of this design cannot be used with the double clutch transmissions that are customary in motor vehicles and that have actively engaging clutches and multiple gears for each transmission input shaft.
Also known in the state of the art is a double clutch transmission (EP 0,691,486 A1) that has two transmission input shafts, wherein a multiplicity of gears are associated with one of the transmission input shafts. In a certain shifting state of this double clutch transmission, only the engine prevents the vehicle wheels from turning, which cannot be called a “real parking lock.”
Additionally known from the state of the art is a transmission with a transmission input shaft (DE 198 00 880 A1) that has a shifter, wherein two gears are engaged simultaneously to produce a parking lock. However, releasing the parking lock when there is a relatively large load on the simultaneously engaged gears presents a problem in this transmission.
The object of the invention is to further develop this class of double clutch transmission for use in a motor vehicle equipped with an internal combustion engine, providing a simple and cost-effective parking lock and to specify a suitable method for controlling an automated double clutch transmission in accordance with the invention.
SUMMARY OF THE INVENTION
The double clutch transmission intended particularly for use in a motor vehicle is equipped with a first transmission input shaft that has a starting gear and is connected to a first clutch, and with a second transmission input shaft that has a driving gear and is connected to a second clutch, and with a shared transmission output shaft. A plurality of gear speeds are associated with at least one of the two transmission input shafts.
In order to implement a parking lock function, in accordance with the invention two of the gears associated with one of the two transmission input shafts are designed to be capable of being engaged simultaneously.
A quite high number of gears makes it possible to adapt the double clutch transmission to the specific characteristics of an internal combustion engine serving as a drive motor whose usable operating range lies within a limited speed range. By means of a simultaneous engagement of two gears associated with one of the transmission input shafts, which is to say an engagement of associated clutches, the transmission output shaft connected to the drive wheels of the motor vehicle is locked by corresponding speed change gears of the engaged gears and the transmission input shaft connected with them, which makes it possible to reliably prevent the motor vehicle from rolling. Thus, without significant additional effort an effective parking lock is implement that is preferably applied by using actively engaged clutches that are disengaged in the quiescent state. This makes it possible to dispense with a separate parking lock, which frequently is designed in the form of a dog clutch lock located on the transmission output shaft.
In the double clutch transmission, the first transmission input shaft can have all starting gears, and the two simultaneously shiftable gears can be associated with the second transmission input shaft. Such an arrangement makes it significantly easier, or may even be necessary to make it possible, to release the parking lock when the gears that are engaged simultaneously as the parking lock are under great load. For instance, if the motor vehicle is parked on a downhill grade using the parking lock, a coasting torque resulting from the downhill component of the vehicle weight is applied to the transmission output shaft through the drive wheels and other components of the drive train. As a result of the different gear ratios of the gears engaged in the parking lock function, and an input-side connection via the shared transmission input shaft, the speed change gears of the lower gear speed are loaded in the coasting direction and the speed change gears of the higher gear speed are loaded in the direction of powered operation. In this way, the torques acting at the associated clutches can be so large that the gears can be disengaged only with unacceptably large actuating forces or cannot be disengaged at all. Thus, it is advantageous for a startup process if a torque opposite to the direction of the load can first be applied to the transmission output shaft via a gear of the other transmission input shaft, which the present invention makes possible. During this process, the gear in question is first engaged and the associated first clutch is engaged. As a result, an increasing torque acts through the transmission output shaft and relieves the load on at least one of the clutches of the two engaged gears acting as the parking lock so that it can be released with a relatively small actuating force. This then also relieves the load on the other clutch so that it too can be disengaged largely without force, with the result that the parking lock is then fully released. In the example described of the motor vehicle parked on a downgrade, the reverse gear is the appropriate gear for compensation of the load. In the case of a motor vehicle parked on an upgrade, the direction of load is reversed, so in this case a forward gear, for example the first gear, is suitable for compensation of the weight-related load. Because they each have a fairly high available torque while simultaneously having a low startin
Baker & Botts LLP
Pang Roger
Volkswagen AG
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