Rotation angle sensor, in particular for an electrical steering system of an industrial truck

Rotation angle sensor, in particular for an electrical steering system of an industrial truck, in which two magnetic field sensitive sensor elements are arranged on orthogonal axes and a permanent magnet is attached to a shaft extending through the axis intersection point and the output signals X, Y of the sensor elements are given to an evaluation unit, which determines from the two output signals X, Y the rotation angle value by means of a function saved in the evaluation unit, characterized in that for a plurality of predetermined values of one of the output signals X or Y associated ideal values calculated from the geometrical relationship of the sensors of the other output signal Y, X are saved in the evaluation unit, the measured values of the other output signal Y, X are compared with the ideal values and a warning or stop signal is created if the difference between the measured and ideal value reaches a predetermined amount.

CROSS-REFERENCE TO RELATED APPLICATIONS

Not applicable.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

Not applicable.

BACKGROUND OF THE INVENTION

It is known to provide industrial trucks and other vehicles with an electrical steering system. The rotation of a steering transmitter is measured with the help of a rotation angle sensor and the rotation angle signal is given to an actuator, which depending on the measured rotation angle creates a steering angle for a wheel to be steered. For these types of electrical steering systems as well as for other applications, the security in the angle capture is of importance. A failure of the electrical steering system or a wrong angle display can have uncomfortable consequences if not detected in a timely manner.

It is known to determine a rotation angle with the help of an electrical potentiometer. It is also known to determine an angle of rotation in that two magnetic field sensitive orthogonally arranged sensor elements, e.g. hall sensors, work together with one permanent magnet, which is e.g. arranged on the shaft of the steering transmitter. The sensor elements create sinusoidal output signals depending on the rotary motion of the magnet [X=A·cos(Θ)+B und Y=A·sin(Θ)+B]. With the help of a formula saved in an evaluation unit, e.g. Θ=α tan 2(Y−B, X−B), a rotation angle is calculated in a processor and processed further. The rotation angle can be determined relatively exactly with this type of rotation angle sensor. It is disadvantageous that errors, which are caused by the failure of a sensor element, e.g. due to a wire break or the appearance of impermissible drift phenomena, such as static external magnetic fields, are not detected right away under some circumstances.

The object of the invention is to create a rotation angle sensor, in particular for electrical steering systems for industrial trucks, which is monitored for failures.

BRIEF SUMMARY OF THE INVENTION

The invention determines the associated ideal output signals of the second sensor for output signals of a sensor, i.e. from the geometric relationships of the sensors with each other. The ideal values are saved and are set opposite each of the measured values. If they match, there is no measurement error. If this is not the case, there may be a measurement error, which requires taking appropriate action in terms of the operation of the vehicle.

In one possible embodiment of the invention, redundant rotation angles are determined from the sensor signals X, Y in accordance with the below formulas:

In these formulas, A is the amplitude and B is the offset for the output signals Y and X. An offset B is established in order to always receive positive values. The redundant rotation angles are related to each other. If the absolute value of the difference of the redundant rotation angles exceeds a predetermined value, a corresponding signal is created, e.g. a warning or stop signal for the vehicle. Then the identified deviation indicates that at least one sensor element is not working reliably or is subject to an impermissible drift.

In the alternative embodiment in accordance with an embodiment of the invention, the formula
|(X−B)2+(Y−B)2−A2|
is used to determine result ε, wherein X and Y, as already specified, represent the output signals, i.e. the voltage at the output of the sensor elements, A the amplitude of the output signals and B the aforementioned offset. If result ε exceeds a predetermined value, a warning or stop signal is in turn created.

The invention provides security in the case of the failure or malfunction of one or both sensor elements so that assistance is obtained in a timely manner or the vehicle can be stopped, if necessary. The invention is advantageous in that simple mathematical principles can be used, i.e. with the help of an already existing processor, to obtain redundant results, which enable a review of the angle values identified by another function. Additional instrumental effort for this safety review during the rotation angle determination is not required.

In accordance with one embodiment of the invention, it is advantageous to determine the redundant angle values in predetermined time intervals (sample rate T), in order to e.g. determine a drift of the output signals. If the rotation angle values between two sampling intervals exceed a predetermined change value, an alarm or stop signal e.g. can in turn be created.

In another embodiment of the invention, a voltage monitoring unit is connected to the output of each of the sensor elements, which determines whether the output signals X, Y lie outside a predetermined voltage band. The output of the sensor element is set to the zero potential, if an output signal lies outside the voltage band.

The invention is explained in greater detail below using a drawing.

DETAILED DESCRIPTION OF THE INVENTION

A first sensor element1and a second sensor element2are supplied with power by a terminal strip10via a line12, a controller14and a line16. These are e.g. hall elements, the axes of which lie orthogonal to each other, wherein through the intersection point of the axes extends the rotation axis of a shaft18, on which a permanent magnet20is arranged (can be identified on the N and S poles). When rotating the permanent magnet20around the rotation axis, sinusoidal voltages are created at the outputs22or24of the sensor elements1,2. The respective rotation angle is determined from the voltage values Y, X e.g. according to the formula arc tan 2(Y−B, X−B). The evaluation occurs in a processor, which is not shown in greater detail. Moreover, the output signals of the sensor elements1,2are further evaluated mathematically, in order to check the accuracy of the rotation angle measurement. This has already been explained above.

Voltage monitoring units26,28are connected with the voltage supply lines leading to the sensor elements1,2. They place the output22or24of the sensor elements1,2on the zero potential, if it is determined that an output voltage does not lie within a predetermined band. It can thus be determined whether e.g. a wire break or another error is present. Moreover, the aversion of the supply voltage outside a triangle of 4.6 to 5.4 volts leads to an impermissible migration of the output signal of the sensor elements1,2.