1. Field of the Invention
The invention relates to an electric steering and drive system for a vehicle having a wheel-based steering system with a pair of drive shafts, a differential gear mechanism connected to the drive shafts, a traction drive including at least one traction motor connected to at least one of the drive shafts, and an electric steering drive which is drive-connected to the differential gear mechanism.
2. Description of the Related Art
Vehicles having a wheel-based steering system travel around bends by one drive side being driven at a different speed to the other. The wheel-based steering system is used mainly in tracked vehicles. In order to travel around bends, the drive device drives the traction track on the outside of the bend at a higher speed than the traction track on the inside of the bend and therefore, in addition to the task of driving, also assumes the steering function of the vehicle. In order to rotate a vehicle of this type on the spot, the traction tracks of the two vehicle sides can be driven in opposite directions.
As the steering system also fails in vehicles of this type in the event of the failure of or problems with the drive system, special measures have to be taken in order to bring the vehicle at least to a standstill safely. In military vehicles, the requirements are even higher. Vehicles of this type are also intended to be drivable and steerable in the event of partial damage to their drive system, in order to move themselves, for example, out of a danger zone under their own power, but optionally admittedly with reduced drive power.
U.S. Pat. No. 4,998,591 describes an electromechanical drive system for fully tracked vehicles. A generator which is driven by an internal combustion engine is provided for the generation of the electric power. According to one embodiment, this drive system comprises an electric traction motor, which drives both vehicle sides in the same direction via a central shaft, and an electric steering motor which drives a zero shaft, the rotational speed of which has a positive effect on one side and a negative effect on the other side. Steering differentials on the left and the right add the rotational speeds of the two motors and forward the sum to the track wheels. This electromechanical steering system can transfer a multiple of the nominal power of the steering motor as what is known as “regenerative power” from the drive side on the inside of the bend to the drive side on the outside of the bend. As a result of this electromechanical power transfer, the reactive power flows via the mechanical gear mechanism arrangement and not via the electric motors, with the result that the latter can be configured in accordance with the primary performance of the vehicle.
A further embodiment of this document provides an electric traction motor which drives the carrier of a differential bevel gear mechanism. An electric steering motor is provided on both output shafts of the differential bevel gear mechanism, which output shafts are connected to the track wheels of the vehicle. In this arrangement, the electric steering motors can be used to assist the traction drive. For this reason, the three electric motors can be designed to be smaller. In this arrangement, however, drive power cannot be transmitted from one drive side to the other drive side mechanically.
In a similar arrangement is known from US 2004/0116228, a differential gear mechanism which comprises two planetary gear mechanisms is provided between the two drive sides. The two planetary gear mechanisms are arranged next to one another and their planetary carriers are coupled fixedly in terms of rotation to one another. An electric steering motor can drive the two sun gears in opposite rotational directions and the planetary gear mechanisms output their drive via their internal gears. The internal gears are connected to a first end of motor shafts of electric traction motors. The track drive wheels or wheels are arranged at the other ends of the motor shafts. If the single current supply circuit fails, a vehicle having a drive axle of this type can no longer be steered.
EP 1 060 941 B1 has disclosed a device for the actuation and operation of an electric vehicle drive. The vehicle has current generation devices and devices for detecting the operating signals of the driver for driving, braking and steering. The operating signals are forwarded via devices for the electronic processing of signals to power units which actuate electric traction motors.
One drive motor is provided for each drive side, which drive motor is assigned in each case one power unit. Each drive motor and power unit is divided in each case into at least two part motors or part units. The part units of the power units and the part motors of the two drive sides are connected to one another in such a way that every power unit can actuate in each case at least one part motor of every drive motor present.