Interrelated power delivery controls – including engine control – Electric engine – Brake actuation opens switch to engine
Reexamination Certificate
2000-05-12
2002-03-26
Marmor, Charles A. (Department: 3681)
Interrelated power delivery controls, including engine control
Electric engine
Brake actuation opens switch to engine
C477S029000, C188S069000
Reexamination Certificate
active
06361469
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a parking lock for a vehicle having an electrical device, and to a method for operating such a parking lock. The present invention also relates to an electrical drive for a vehicle.
2. Description of the Related Art
Motor vehicles such as passenger vehicles have a parking brake for preventing the vehicle from rolling away inadvertently when the vehicle is parked. A problem with known parking brakes in terms of safety is that in some cases the parking brake cannot completely prevent the vehicle from rolling away inadvertently, particularly when said vehicle is located on a grade.
For this reason, it is desirable to use a parking lock in addition to the parking brake. The parking lock is intended to make it impossible for the vehicle to roll away inadvertently at any time and in any place. In particular, the parking lock is designed to prevent the vehicle from rolling away when the vehicle is parked on a grade.
When the vehicle includes a conventional internal combustion engines with a manual transmission, the additional parking lock may be provided by also selecting a low gear, for example the reverse gear or the like, in addition to operating the actual parking brake. In this solution, the compression forces and friction forces in the internal combustion engine produce a braking effect which supplements the braking force of the parking brake.
However, when the vehicles includes an internal combustion engine and an automatic transmission, the selection of a low gear for producing the braking effect to supplement the parking brake cannot be produced because of the torque converter that is present in the automatic transmission. Therefore, automatic transmissions use separate parking locks instead of a selected gear. The parking lock may, for example, comprise a mechanical interlock in the transmission output shaft on the transmission housing. A ratchet wheel may be provided for this purpose, which is provided with teeth and is arranged on the transmission output shaft such that it rotates with that shaft. Furthermore, a toothed catch is arranged on the transmission housing so that it latches in the spaces between the teeth of the ratchet wheel. When the parking lock is operated and when the vehicle speed is appropriately low, the toothed catch latches suddenly in the ratchet wheel, thereby suddenly stopping the rotary movement of the transmission output shaft. The loads which occur as the catch latches in can generally be damped by the elasticity that exists in the drive train, for example by means of appropriate joints, jointed shafts, suspension, tire damping or the like.
No separate parking lock has yet been provided for vehicles with an electrical drive. Nevertheless, for the same reasons mentioned above, the additional parking lock is also desirable for these vehicles. In fact, electrical drives are subject to different problems relating to the possible use of parking locks, in particular when, as described above, the aim is to use parking locks with a ratchet wheel and a toothed catch.
The electrical drive of a vehicle normally has an electrical machine comprising a rotor, a stator and power electronics for controlling the electrical machine. The torque produced by the rotation of the rotor is in this case used as the basis of the drive for the vehicle. If a parking lock comprising the toothed catch and ratchet wheel as described above were to be used, the rotor rotation would have to be braked via the ratchet wheel and the toothed catch. When the toothed catch suddenly latches in the ratchet wheel, the rotor is suddenly brought to rest. Due to the high torques and the rotor inertia, very high forces are produced by the sudden stop in rotation which are not damped as easily as in the configuration having an internal combustion engine and automatic transmission.
Accordingly, conventional commercially available parking locks can not be used since they would not be adequate for withstanding the occurring loads and would be damaged very quickly. To overcome this problem, parking locks of considerably greater size would have to be used or damping elements would have to be integrated into the parking locks. However, both of these solutions necessitate a large installation volume and would have a very high intrinsic weight, which is a major disadvantage, particularly in automobile construction. Furthermore, parking locks of such a design are considerably more expensive. Furthermore, the development of appropriately modified parking locks for the electrical drive of a vehicle would involve a major time penalty and design effort.
Since the high torque peaks and reductions to be compensated for occur only during the latching-in process, and thus only very briefly, the use of parking locks designed for these maximum loads would not be acceptable financially, for the reasons stated above.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a parking lock and an electrical drive for a vehicle, in which the described disadvantages are avoided. More specifically, it is an object of the present invention to provide a parking lock for use with an electric drive that is physically simple and cost-effective.
According to an embodiment of the invention, the object is achieved by a parking lock for a vehicle having an electrical drive train, wherein the electrical drive train includes an electrical machine with a rotor, a stator having a number of stator windings, and power electronics for controlling the electrical machine, the parking lock having a mechanical component which is mechanically operatively connectable to the electrical drive train when the parking lock is operated to stop rotary movement of the electric drive train.
According to the present invention, this parking lock is distinguished in that it has both a mechanical component and an electrical component. The mechanical component may be mechanically operatively connected to the electrical drive train when the parking lock is operated to stop the rotary movement of the electric drive train. Examples of this will be described in more detail further on in the description. The electrical component is designed for producing a short-circuit in the stator windings, at least temporarily, when it is intended to operate the parking lock. The present invention also provides for the electrical component to be activated in a specific time interval before operation of the mechanical component when the parking lock is operated.
The parking lock according to the invention also allows vehicles having an electrical drive to be provided with a simple and cost-effective with a braking system which protects the vehicle from rolling away inadvertently—preferably in addition to a conventional parking brake.
The fundamental idea of the parking lock according to the invention is that the characteristic properties of the electrical machine are incorporated in the parking lock. To this end, the parking lock has an electrical component in addition to the mechanical component. The electrical component is designed so that it can, at least temporarily, switch the stator windings of the stator to be active so that the individual windings of the electrical machine are connected to one another, as a result of which a short-circuit is produced in the stator windings. The short-circuit produces a high braking torque in the electrical machine. This braking torque brakes the rotary movement of the electrical drive train.
The mechanical component of the parking lock is not activated until a specific time interval has elapsed, which allows the rotary movement of the electrical drive train finally to be brought to rest in this case. Since, owing to the short-circuit, the rotary movement of the electrical drive train has already been braked by the previous braking process, high torque peaks on the mechanical component of the parking lock are avoided. This allows even relatively small parking locks to be used.
If, for example, parking locks having a ratchet wheel
Oppitz Horst
Röder Manfred
Cohen & Pontani, Lieberman & Pavane
Mannesmann Sachs AG
Marmor Charles A.
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