Electricity: motive power systems – With particular motor-driven load device – Plural – diverse or diversely controlled load device
Patent
1995-06-01
1998-05-05
Sircus, Brian
Electricity: motive power systems
With particular motor-driven load device
Plural, diverse or diversely controlled load device
318564, 318588, G05B 903
Patent
active
057479500
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a steering system for vehicles or ships with a steering handwheel and a steering element with no mechanical linkage line therebetween, with a steering handwheel sensor device, a steering element sensor device and a control arrangement which, in dependence on the output signals of the sensor devices, operates an electromechanical transducer, on the output side of which the steering element is arranged.
In this connection, steering element is a collective term for direction-defining units on a vehicle or a ship. These are, for example, the steered wheels of the vehicle or the rudder of a ship.
In a known steering system of that kind (U.S. Pat. No. 4,771, 846), the wheels of a vehicle are steered by means of a hydraulic piston-cylinder unit. The hydraulic piston-cylinder unit is supplied by way of a proportional valve with pressurized hydraulic fluid by a pump. The proportional valve is operated by an electrical control unit by means of electromagnets and together with the magnets forms the electromechanical transducer. For this purpose, the electrical control arrangement receives signals from a steering angle sensor, which detects the lock of the wheels, and from a steering handwheel sensor, which detects the position of the steering handwheel shaft. The proportional valve is controlled so that the value predetermined by the steering handwheel sensor can be set at the steered wheels and reported back by the steering angle sensor. A steering system of that kind has the disadvantage that in the event of failure of the electrical control arrangement or the proportional valve, the entire steering system fails. The vehicle can then no longer be steered.
A further steering system is known from DE 35 36 563 C2. Movement of the steering handwheel causes an electric motor, which drives a pump, to be set in operation by way of switching electronics. The pump in its turn is connected to one of the two work chambers of a work cylinder. The direction of rotation of the pump determines the direction in which the work cylinder is extended. The steering also fails in this system if the switching electronics, the electric motor or the pump are defective.
DE 40 11 947 describes a further steering system which steers two steerable wheels independently of one another. Here, each wheel is controlled by means of an electric servomotor which drives a gearwheel that acts on a rack. The servomotor is supplied by an electronic control unit which operates with input data from the sensors. If the electronic control unit fails, the vehicle can no longer be steered.
The invention is therefore based on the problem of providing a steering system which has a greater degree of reliability.
This problem is solved in a steering system of the kind mentioned in the introduction in that the control arrangement has at least two independent control units, and a fault-monitoring device is provided which precludes a defective control unit from influencing the steering element.
The terms control unit and fault-monitoring device are to be understood in this context in functional terms. The fault-monitoring device may also be formed by a control unit. Conversely, a control unit can be used as fault-monitoring device. The system is therefore constructed with a redundancy factor. Even when a control unit fails, the vehicle or the ship can continue to be steered provided that at least one control unit is still intact. A largely fault-tolerant system is consequently achieved, which operates with the same reliability as steering systems which are equipped with a mechanical emergency steering function. Unlike these systems, in which a higher operating force is necessary in the event of a fault, operation of the present system can be continued with the same degree of convenience, even in the event of a fault. The vehicle can continue to be driven. Repairs can be carried out at a later date at a more convenient time.
In a preferred embodiment, at least one sensor device has several independently operating sensors, especially a number of
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Baag.o slashed. Jepsen Aksel
Friedrichsen Welm
Danfoss A/S
Sircus Brian
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