User interface actuator for a pilot-by-wire system

A user interface actuator for a pilot-by-wire system comprises a rotary electric motor having an output shaft suitable to be connected to a rotating user interface, a first absolute angular sensor for detecting in direct drive the number of revolutions of the shaft and a second absolute angular sensor redundant with respect to the first absolute angular sensor.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a user interface actuator for a pilot-by-wire system. The piloting can be achieved by means of the steering of the wheels in a land vehicle, or by means of the rudder or rotation of the propulsion propellers in case of boats.

PRIOR ART

From EP-A1-1409326 it is known to associate an electronically controlled friction brake to a steering wheel for varying a braking torque acting on the steering wheel thus giving the feel of steering to the user. In particular, the braking torque can be controlled electronically and increase until defining an angular stop for the steering wheel.

A zero angular position of the steering wheel, referring to the condition wherein the wheels are straight, is floating and is updated by means of an electronic control.

The document EP-A1-1332946 describes an actuator for a steering wheel comprising a rotary motor connected in series with a steering column by means of a transmission. The steering column rotates as a result of the action of a user on the steering wheel and/or as a result of the action of the actuator, in particular a rotary electric motor, on the steering column.

The actuator comprises a brake of magnetorheological material to define a maximum angular stroke of the steering wheel. In parallel to the brake, angular mechanical stops are provided. The actuator also comprises angular position sensors to measure the deviation of the steering wheel from the zero position, and a control unit of the electric motor programmed to guide the steering wheel to the zero position. The actuator further comprises a spring mechanism to return the steering wheel to zero position. In particular, the angular sensors are redundant and both arranged downstream to the transmission with respect to the electric motor.

The known devices can be improved with regard to the positioning of the angular sensors so that the latter can support more thorough diagnostics of the actuator.

JP-A-2009248660 discloses an actuator according to the preamble of claim1. Such actuator comprises redundant angular sensors and may be improved to detect possible malfunctioning of a transmission angularly coupling the angular sensors.

SUMMARY OF THE INVENTION

The object of the present invention is to solve the drawback specified above.

The purpose of the present invention is achieved by an actuator, wherein the actuator includes:a rotary electric motor having an output shaft suitable to be connected to a rotating user interface;a first angular sensor for detecting in direct drive the number of revolutions of the output shaft; anda second angular sensor, which is redundant with respect to the first angular sensor,wherein the first angular sensor and second angular sensor are absolute angular sensors;by comprising a transmission having a non-unitary gear ratio and connected to the electric motor; in that the first angular sensor and the second angular sensor are connected to each other by the transmission and coupled according to the non-unitary gear ratio, the transmission being suitable to connect the electric motor to the rotating user interface in a rotational manner;in that the transmission comprises an endless flexible member; andan electronic control unit programmed to detect a deviation from the non-unitary gear ratio of first and second absolute angular sensor and generate a signal when the deviation is above a threshold.

DETAILED DESCRIPTION OF THE INVENTION

InFIG.1is illustrated with1, as a whole, a piloting system for a transport means, in particular a steering by-wire system for a ground vehicle. The piloting system1comprises a user interface2, for example a steering wheel, a steering column3connected torsional to the steering wheel2so that the steering wheel2, operated by a user, causes a rotation of the steering column3, an actuator4acting on the steering column3and a electronic control unit5(shown schematically inFIG.1) to control the actuator4and to control the angular position of the steering wheel2.

The pilot-by-wire system1also comprises a steering actuator acting on the steering wheels6and7controlled by a respective electronic control unit (known and not illustrated), which moves the steered wheels7and is connected with the electronic control unit5so as to be operated for performing the movement on the basis of the angular position of the steering wheel2.

FIG.2illustrates a first embodiment of the actuator4. The actuator4ofFIG.2comprises a rotary electric motor8and a transmission9to connect in series the rotary motor8to the steering column3and having a non-unitary gear ratio. Preferably the transmission9is a transmission synchronous with an endless flexible element, i.e. belt or chain.

The actuator4also comprises a first absolute angular sensor10to measure the position of the steering column3at a 360° revolution and a second absolute angular sensor11to measure the position of an output shaft12of the rotary motor8at a 360° revolution. The absolute angular sensors10,11may be dedicated or integrated in plain bearings or rolling bearings and are coupled in data exchange with the electronic control unit5. Preferably, the output shaft12is a through shaft with respect to a stator of the motor8and comprises a first end portion13connected to the sensor11and a second end portion14connected to the transmission9. The end portions13,14are longitudinally opposite. Alternatively, the sensor11may be arranged on the same side of the transmission9and thus allowing, in this way, a reduction of overall dimensions in the direction parallel to that of an axis of the output shaft12.

Preferably, the transmission9is a speed reduction transmission of the shaft12and comprises a pinion15rigidly connected to the end portion14, a toothed pulley16and a belt17for connecting the pinion15and the toothed pulley16.

According to the embodiment ofFIG.2, the actuator4further comprises the pinion3and an anti-contaminant sealed casing18for housing the rotary motor8, the steering column3parallel to the shaft12and the transmission9. In this case, the absolute angular sensor10is also housed in the casing18and is integrated in a support bearing of the steering column3. Furthermore, out from the casing18is an electrical connection output19for data transmission and power wires towards the electronic control unit5, and a portion3aof the steering column3to be connected to the steering wheel2. The portion3acomes out from the casing18which, in order to prevent the entering of contaminants, carries a seal20, in particular a lip seal. The output19is preferably arranged on the cover24or25adjacent to the absolute angular sensor11. In the non-limiting example ofFIG.2the output19is carried by the cover25.

It is possible that the steering column3comes out from the casing18also from the opposite axial end of the portion3a(FIG.2) and, in this case, a further seal21prevents the entering of contaminants into the casing18.

Preferably, the casing18comprises a body18adefining a seat22for the rotary motor8and a seat23for the steering column3. The seats22,23are through seats and the casing18comprises a single cover24adjacent to the transmission9for closing both seats22,23on one side; and respective covers25,26to close the seats22,23at the axial portion opposite to the single cover24. Preferably, the single cover24supports the seal20, the cover26supports the seal21and the cover25carries the output19. At least one of the covers24,25,26further carries an air exchange valve to drain moisture and allow the balance of pressure with the outside environment.

From the moment the absolute angular sensors10,11are angularly coupled by means of a non-unitary gear ratio and defined in the design step, it is possible to program the electronic control unit5to detect the absolute angular position of the steering wheel2in an interval of several revolutions of the steering wheel2. In particular, since the pinion15has ‘m’ teeth and the pulley16has ‘n’ teeth, the range of revolutions of the steering wheel within which it is possible to determine the absolute position is defined by the least common multiple between ‘m’ and ‘n’ divided by ‘m’. For example, if ‘m’=15 and ‘n’=17, the range within which it is possible to calculate the absolute position of the steering column3is 17 revolutions. If ‘m’=20 and ‘n’=40, the range within which it is possible to calculate the absolute position of the steering column3is 2 revolutions. This allows programming of the electronic control unit5so that more than one revolution of the steering wheel2corresponds to the maximum stroke of the steered wheels7. This example is useful for applications requiring particularly accurate steering adjustments.

Furthermore, once the non-unitary gear ratio of the transmission9is known, the electronic control unit5can be programmed to generate a warning signal when a deviation from the transmission ratio between the sensors10,11exceeding a predefined limit value and eventually programmable is detected. For example, the deviation can be in phase and/or in frequency. In this way the user can be alerted for example for the breaking of the belt17or for displacement of the belt17on the pinion15.

The electric motor8is controllable so as to generate a braking torque and, where necessary, blocking the rotation of the steering column3.

FIG.3illustrates an actuator40according to a preferred embodiment of a user interface actuator for a pilot-by-wire system for the description of which, elements functionally identical to those of the actuator4will be indicated with the same reference numbers already used in the previous paragraphs.

The actuator40comprises a rotary motor8having a stator41fixed to the casing18and a hollow rotor42. The steering column3is fixed to the rotor42and is surrounded both by the latter and by the stator41so that the motor8is in direct drive. Preferably, the steering column3is fixed to the rotor42by means of a coupling49such as a key, a tab, a grooved coupling or the like. When the steering column3is in direct drive on the rotor42, the transmission ratio is unitary and excluding the transients in a condition of constant torque.

The actuator40also comprises a brake43controlled by the electronic control unit5acting on the steering column3. The brake43comprises an electromagnetic drive means43′ fixed to the casing18and a friction disc43″ driven by the drive means43′ and connected to the steering column3for transmitting rotation and in a movable way, to axial translation. For example, the disc43″ is connected in a torsional elastic manner to the steering column3by means of a flat spring50interposed between the disc43″ and the steering column3. The flat spring50applies to the disc43″ both an axial load to allow the disc43″ to return to the rest condition when the brake43is not active, and a torsional load. The torsional deformation of the flat spring50allows a rotation of few degrees between the disc43″ and the steering column3. The disc43″ is also driven in an axial direction by means of pins51put in rotation by the steering column3. Preferably, the pins51comprise a rubber cover, or of other elastic or viscoelastic equivalent material, to suppress any contact noise; the pins51are compressed during relative angular rotation between the disc43″ and the steering column3. The relative rotation of the disc43″ with respect to the steering column3when the brake43is closed is detected by the absolute angular sensors10,11and the electronic control unit5is programmed so that the brake43is opened after having been closed when the rotation of the steering column3with respect to the disc43″ is detected. Advantageously, the brake43is surrounded by the rotor42and/or by the stator41so as to reduce the axial dimension of the actuator40(FIG.3).

The steering column3is also monitored by means of the absolute angular sensors10,11. In particular, the sensor10is arranged axially between the rotor42and the portion3aand the sensor11is arranged axially between the brake43and the cover25provided with the connector19.

According to the embodiment ofFIG.3, the casing18comprises a body44defining a coaxial seat45and a seat46. The seat45houses the sensor10which, preferably, is integrated in a rolling bearing mounted for radially and axially supporting the steering column3. The seat45is sealingly closed by a cover47supporting the seal20. The seat46houses the stator41and the rotor42and the steering column3is passing through the seats45,46.

The casing18also comprises a support48fixed to the body44and configured to carry the drive means43′ and the absolute angular sensor11. Preferably, the support48defines respective seats to radially support the drive means43′ and the absolute angular sensor11. The absolute angular sensor11may be integrated in a bearing radially supporting the steering column3from the opposite axial side of the absolute angular sensor10.

The casing18is closed by the cover25fixed to the support48on the axial side opposite to the cover47.

It may be provided that the steering column3of the actuator40is a torsionally rigid body for connecting one to the other the two sensors10,11so that the electronic control unit5will not register phase shifts in use, as illustrated inFIG.3. It is also possible that the absolute angular sensors10,11are mechanically connected by means of an elastic torsional coupling or a coupling defining a circumferential clearance so that the detecting of the sensors10,11is phase-shifted on the basis of the module and/or the direction of the torque applied to the steering column3by the user. Also in the case, the absolute angular sensors10,11are in direct drive on the steering column3since the effect of the elastic coupling or of the coupling with circumferential clearance exert its effect in the transients due to the change of module and/or the reversal of the torque transmitted. In addition, the absolute angular sensors10,11are connected in direct drive even when they are rigidly connected but not directly to the steering column3and/or to the shaft12. For example, inFIG.3, the absolute angular sensor11is mounted directly on the steering column3by means of a bushing53or other equivalent support element. By means of the detecting of the deviation in phase and/or in frequency between the signals of the absolute angular sensor10,11, the electronic control unit5may detect a possible mounting defect of the sensor11and/or a damage or breakage of the bushing53. Similarly, inFIG.2, also the sensors10,11are in direct drive respectively on the steering column3and on the shaft12.

The advantages that the actuator4,40allows to obtain are as follows.

By monitoring in direct drive the absolute angular sensors10,11to the shaft12and to the rotor42it is possible to allow a diagnosis comprising also the electric motor8. In addition, during normal operation, the sensors10,11are redundant in order to allow the operation of the actuator4,40in case one of the sensors is faulty. During normal operation the electronic control unit5can be programmed to apply a driving torque on the steering column3and return the steering wheel2to the zero position. It is also possible to program the electronic control unit5so that the steering wheel2is being driven in an angular position assigned. The assigned angular position can be predefined in the design step or may be calculated by the control electronic unit5in real time, for example, to return the steering wheel2in a position representative of the instantaneous angular position of the wheels7.

When the actuator4comprises the transmission9and the absolute angular sensors10,11are connected to each other by means of the transmission9, it is possible to immediately detect a malfunction of the transmission9, such as rupture or any displacements of the belt17by means of the combination of the signals generated by the sensors10,11with the transmission ratio of the transmission9. In normal operating conditions, in fact, the signal generated by the sensor10and that generated by the sensor11differ by the transmission ratio of the transmission9and any deviation, in particular a macroscopic deviation in phase and/or frequency, is an indicator of malfunction. For example if the belt17were to break, the signal of the sensor10and of the sensor11would be completely uncorrelated, and this can be detected by the electronic control unit5and cause the signaling of an error.

When it is possible to employ an electric motor having a relatively low maximum torque and amplified by transmission9, as in the example ofFIG.2, it is possible that a braking or blocking torque of the steering column3is generated by an electronic control of the electric motor8, for example, the electronic control unit5, on the basis of the state parameters of the vehicle, such as instant speed, steering angle of the wheels7, or others, and/or dynamic parameters of the vehicle such as mass, position of the gravity center or others.

The actuator ofFIG.3, being mounted in direct drive on the steering column3, requires a torque such as to require radial dimensions of the rotor42relatively high and such as to provide a cavity in the rotor42, which can be used for housing the brake43controlled by the electronic control unit5. The brake43may be dry friction, as inFIG.3, fluid friction, as in the case of a magnetorheological brake. Even the brake43can be controlled by the electronic control unit5exclusively, or in combination with the stator41to generate a braking torque variable and/or a blocking torque applied to the steering column3according to the same criteria already described for the actuator4.

Clearly, modifications or variations can be applied to the actuator4,40, according to the present invention, without departing from the protective scope as defined by the appended claims.

For example the steering column3can be a shaft as illustrated in figures or it may comprise a more complex mechanism, possibly comprising a transmission, to connect the portion3ato the steering wheel2.

It is possible that the actuators4,40do not comprise the steering column3but a coupling suitable to receive the steering column, for example a grooved coupling. In this case, the sensor10can be connected to the toothed pulley16or to the rotor42. The sensor11may be mounted on a bushing connected in a rigid manner to the rotation, for example by means of a tab, a key or a grooved coupling, to the column. In this way an actuator having a particularly compact configuration can be obtained.