Interrelated power delivery controls – including engine control – Transmission control – Continuously variable friction transmission
Reexamination Certificate
1999-12-16
2002-03-19
Estremsky, Sherry (Department: 3681)
Interrelated power delivery controls, including engine control
Transmission control
Continuously variable friction transmission
C477S045000, C477S046000, C477S050000
Reexamination Certificate
active
06358181
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a motor vehicle, in particular a motor vehicle with a continuously variable transmission, as well as a method of operating the motor vehicle.
Motor vehicles, including those with a continuously variable transmission, belong to the known state of the art.
From DE 195 46 293 A1, a continuously variable transmission is known that has two pairs of conical disks, each pair comprising a fixed conical disk and, arranged to face the latter, a movable conical disk. A torque is transmitted from one pair of conical disks to the other by means of a chain. Corresponding to the position of the movable conical disks in their respective pairs, different transmission ratios can be set in a continuous range without steps. To hold the position of the chain at a given transmission ratio, or to change the transmission ratio, there is an arrangement of two valve devices connected to the transmission through hydraulic conduits. A first valve device, the ratio-control valve, has seven connector terminals, three of which lead to an oil sump. Connected to a further terminal is a pressure-supply conduit. The pressure that exists in the latter conduit is also communicated to a connector terminal of the second valve device, which has five terminals. The first valve device is controlled by applying to one of the faces of a piston guided inside a cylinder an amount of pressure that is adjustable by means of a proportional valve. Each of two further connector terminals of the ratio-control valve leads to a respective pressure chamber, where one of the two pressure chambers is arranged at the first disk pair and the other is arranged at the second disk pair. From the two further connector terminals, a return conduit branches off towards the second valve device. A connector terminal that is arranged at the axially directed end surface of the second valve device communicates with a pressure supply conduit. Further connected to the second valve device is a conduit that divides into branches outside of the valve device, one branch leading to the first disk pair and one branch leading to the second disk pair for maintaining a previously set level of the transmission ratio.
Each of the two valve devices comprises one pre-tensioning spring. The spring of the second valve device, in particular, has the function of increasing the pressure that is returned from the first valve device by an amount corresponding to the spring force, so that the pressure in the pressure supply conduit is always increased by an amount corresponding to the spring force. This assures that the pressure in the pressure supply conduit is always sufficient for changing the positions of the disk pairs.
The motor vehicle of the foregoing description, which has a continuously variable transmission that is controllable through a hydraulic system, has been practically proven. The pressure return, particularly with the addition of the spring, as well as the comparator device that constantly compares the comparative pressures supplied to the disk pairs, ensure that the pressure in the supply conduit, i.e., on the side of the pressure source, can always be relied on to be sufficient for controlling the transmission.
Nevertheless, there is a desire for improvements, particularly with respect to the space required by the hydraulic valve devices. Also, a more cost-effective design configuration based on a smaller number of individual components would be desirable.
OBJECT OF THE INVENTION
Therefore, the present invention has the object of providing a motor vehicle with a continuously variable transmission as well as a method of operating the motor vehicle whereby the amount of space required for the controls of a continuously variable transmission is reduced, the manufacturing cost of the motor vehicle is lowered, and assembly times are shortened, while at the same time a high level of operating safety and an uncomplicated design configuration are achieved.
SUMMARY OF THE INVENTION
In accordance with the invention, the foregoing objective is met by providing a motor vehicle with at least one continuously variable transmission and at least one hydraulic device for controlling a transmission ratio change and for holding a set transmission ratio at a fixed level. The term “holding a set transmission ratio at a fixed level” means in particular that an unintentional change of the transmission ratio, which may be inherent in the design or associated with a static or dynamic behavior of the transmission, is prevented. In accordance with the invention, the hydraulic device in particular comprises a valve device with at least one connector terminal for a hydraulic conduit by which the transmission ratio can be changed within a continuous range, i.e., without steps. In particular, this means that a transmission ratio change is effected by an overpressure, an underpressure, or a pressure-free condition in a hydraulic line connected to a terminal of the valve device. As a particular feature of the invention, a valve is provided for switching from the state of holding to the state of changing the transmission ratio. The terminals at the transmission-oriented side of the valve can be or are connected to conduits for supplying the respective amounts of pressure required for changing or maintaining the transmission ratio.
In comparison to the arrangement proposed in DE 195 46 293 A1, the inventive concept of providing a single valve device offers the advantage of a space-saving configuration of the hydraulic controls of a transmission. In addition, the invention saves several components such as, e.g., valve cylinders, valve pistons, or connecting conduits between valves. Furthermore, the invention increases the operational safety of a control device for a motor vehicle transmission and thus of the motor vehicle itself.
The objective of the invention is met further by equipping a motor vehicle with at least one continuously variable transmission comprising at least two pairs of conical disks for receiving an endless flexible torque-transmitting device. At least one of the conical disk pairs includes two elements that are movable in relation to each other in the axial direction, particularly the two conical disks themselves. For example, one conical disk may have a fixed attachment or other fixed relation to a shaft or similar element while the second conical disk may, e.g., have a movable seat on the shaft. By changing the axial distance of the two conical disks, a location where the mutually facing surfaces of two conical disks have a given distance from each other will be caused to move radially in or out to a corresponding extent. The given distance is occupied in particular by an endless flexible torque-transmitting device of a defined width. As a result, the radial distance of the endless flexible torque-transmitting device from the central axis of the conical disk pair is selectable, preferably at each of the conical disk pairs.
At least one, preferably two, and with particular preference all of the conical disk pairs are provided with means for applying hydraulic pressure to at least one side. This application of hydraulic pressure can, e.g., ensure that a currently existing transmission ratio is being held at a fixed level, unless at the particular instant the control device is directing a change of the transmission ratio. The control can, e.g., function in such a way that essentially one and the same pressure is applied to both conical disk pairs. However, the same function of maintaining the transmission ratio can also be realized by applying different amounts of pressure to the conical disk pairs, if the holding pressure at the respective conical disk pair depends on an operating parameter such as, e.g., the transmission ratio.
In accordance with a first preferred embodiment of the invention, a pressure differential between the conical disk pairs can be generated by arranging a throttle valve in a connecting conduit between pressure chambers of which at least one is located at a first conical disk pair and at
Friedmann Oswald
Panther Urban
Darby & Darby
Estremsky Sherry
LuK Getriebe-Systeme GmbH
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