Machine element or mechanism – Gearing – Interchangeably locked
Reexamination Certificate
1999-12-27
2001-04-03
Wright, Dirk (Department: 3681)
Machine element or mechanism
Gearing
Interchangeably locked
Reexamination Certificate
active
06209406
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a toothed gear transmission having two partial transmissions disposed parallel to each other in the power flow as well as a process for shifting such toothed gear transmissions.
BACKGROUND
The manual transmissions with a friction clutch which are usually used in motor vehicles are simple and sturdy, but they have the disadvantage that an interruption in tractive power occurs during gear changes. Conventional automatic transmissions with torque converters avoid an interruption of tractive power during gear changes, but due to the torque converter they are less efficient than manual transmissions. Moreover, they are heavier and more cost-intensive.
In toothed gear transmissions having two frictionally engaged load shifting clutches and two partial transmissions disposed parallel to each other in the power flow, it is possible to change gears under load, which is done with an overlap control of the load shifting clutches. This makes it possible to achieve an inexpensive automatic transmission having good efficiency. Generally speaking, the even gear speeds are allocated to one partial transmission and the odd gear speeds are allocated to the other partial transmission, so that shifting can be done sequentially under load, although individual gear speeds cannot be skipped without further action, so-called double upshifting or double downshifting.
A generic toothed gear transmission is known from U.S. Pat. No. 4,658,663. In the toothed gear transmission, an input shaft is connected to an output shaft through a first and a second partial transmission, which are disposed parallel to each other in the power flow and which both have a frictionally engaged load shifting clutch. The load shifting clutches can be used to connect concentrically arranged intermediate shafts of the partial transmissions with the input shaft. The intermediate shafts can be effectively connected with the output shaft through transmission constants, through a joint countershaft disposed parallel to the input shaft, and through toothed gear pairs. The toothed gear pairs for the forward gear speeds I, III, and IV, as well as the toothed gear pair for the reverse gear speed, belong to the first partial transmission. The fourth gear speed is designed as a direct gear speed and can be selected by engaging a shifting component between the output shaft and the intermediate shaft of the first partial transmission.
The second partial transmission comprises the toothed gear pairs of forward gear speeds II and V, as well as an additional toothed gear pair, whose gear ratio is equal to that of the third gear speed, whose toothed gear pair belongs to the first partial transmission. In the first partial transmission, a toothed gear clutch for the third gear speed and the direct clutch for the fourth gear speed are combined into a change clutch having a joint synchronizer sleeve, which can be coupled with an idler gear of the toothed gear pair for the third gear speed or with the output shaft.
The load shifting clutches of the partial transmissions are alternately allocated to the gear speeds. The first load shifting clutch of the first partial transmission is always used to start from the first gear speed, which causes greater wear to occur on it than on the second load shifting clutch.
SUMMARY OF THE INVENTION
The aim of the invention is to further develop a generic toothed gear transmission and in particular to achieve longer maintenance intervals, less wear, and greater security. It is fulfilled in accordance with the invention by the features of the independent claims. Additional embodiments are contained in the subclaims.
The invention is based on a toothed gear transmission in which an input shaft is connected to an output shaft by a first and a second partial transmission, which are disposed parallel to each other in the power flow. The partial transmissions each have a frictionally engaged load shifting clutch and an intermediate shaft, and each of the intermediate shafts can be effectively connected to the input shaft through the load shifting clutch. In addition, the toothed gear transmission has at least one first transmission constant.
It is proposed that for starting, the first load shifting clutch can be brought in effective connection with the output shaft through a transmission constant, and the second load shifting clutch can be brought in effective connection with the output shaft through a transmission constant having the gearing of the lowest gear speed. Both load shifting clutches can be used for the process of starting from the lowest or first gear speed. The stress resulting from the starting process can be distributed to both load shifting clutches. An excess temperature can be avoided in spite of inexpensive dimensioning, wear can be reduced, and maintenance intervals can be extended. Moreover, if one load shifting clutch fails, the second load shifting clutch can be used to start from the first gear speed, increasing mobility security. It is also possible to construct the load shifting clutches differently for different starting processes.
The solution in accordance with the invention can be used in a toothed gear transmission in which the intermediate shafts can be connected to an output shaft through at least one countershaft and through at least one toothed gear pair. In addition, the solution in accordance with the invention can also be used in a toothed gear transmission in which the intermediate shafts having at least one transmission constant are directly connected to at least one output shaft. Toothed gear transmissions with a countershaft are generally used in motor vehicles having rear-wheel drive, and toothed gear transmissions without countershafts are generally used in motor vehicles having front-wheel drive.
It is particularly advantageous for it to be possible to connect the first and the second load shifting clutches simultaneously to the output shaft with the gear ratio of the lowest gear speed. This allows the load shifting clutches to be dimensioned so they are particularly inexpensive and light.
The solution in accordance with the invention can be achieved by various embodiments appearing appropriate to those skilled in the art, for example with two equal transmission constants, where one transmission constant is allocated to the first intermediate shaft and one transmission constant is allocated to the second intermediate shaft, and where output to an output shaft can take place through the transmission constants, through at least one countershaft, and through a common toothed gear pair or through two equal toothed gear pairs, or where output can take place through two equal transmission constants directly onto at least one output shaft. Moreover, with different transmission constants it is possible to create two first gear speeds using different toothed gear pairs.
However, it is particularly advantageous for it to be possible to place at least the transmission constant allocated to the lowest gear speed in effective connection with the first and the second load shifting clutches. Both load shifting clutches can be connected to the output shaft through the same transmission constants and through the same toothed gear pair. Additional toothed gear pairs, weight, and construction space, as well as assembly effort and costs, can be saved, and greater efficiency can be achieved due to low weight and a low rotating mass. Moreover, the load shifting capabilities can be increased and, with a small number of toothed pairs, in addition to sequential shifting at least the most important double upshifts and double downshifts under load are made possible. Double upshifts and double downshifts are particularly necessary before and after a passing maneuver.
For various reasons, it may be useful to start from the second or an even higher gear speed instead of from first gear, for instance when slowly starting with a high-power internal combustion engine, when starting on slippery ground, on slopes, and/or when starting with little or no loaded
Sperber Ralf
Tscheplak Ernst
Worner Gunter
Daimler-Chrysler AG
Kenyon & Kenyon
Wright Dirk
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