阅读说明：本技术 电动动力转向系统 (Electric power steering system ) 是由 R·威尔森-琼斯 于 2020-10-21 设计创作，主要内容包括：本发明公开了一种电动动力转向系统包括：转向杆,所述转向杆的相反的端部均机械地连接至相应车轮支架；通过齿轮机构连接至转向杆的电动马达,使得马达的旋转引起转向杆沿其主轴线平移从而使车轮支架移位；以及包括至少一个长形特征的线性位置传感器,所述长形特征沿着转向杆的长度沿对角线方向延伸,使得长形特征相对于转向杆的轴线倾斜；以及感测装置,所述感测装置面向转向杆、并且在任何给定时间只观察到长形特征的某一片段,所述片段在特征整个宽度上且仅沿着特征的一部分长度延伸,所述感测装置产生信号,所述信号根据感测装置所观察到的、由特征和转向杆的相邻部分形成的图案而变化,信号将转向杆的轴向位置编码。(The invention discloses an electric power steering system comprising: a steering rod, opposite ends of the steering rod each mechanically connected to a respective wheel carrier; an electric motor connected to the steering rod by a gear mechanism, such that rotation of the motor causes the steering rod to translate along its main axis to displace the wheel carrier; and a linear position sensor comprising at least one elongate feature extending diagonally along the length of the steering rod such that the elongate feature is inclined relative to the axis of the steering rod; and a sensing device facing the steering rod and observing only a certain segment of the elongate feature at any given time, the segment extending across the width of the feature and along only a portion of the length of the feature, the sensing device generating a signal that varies according to the pattern formed by the feature and the adjacent portion of the steering rod observed by the sensing device, the signal encoding the axial position of the steering rod.)

1. An electric power steering system comprising: a steering rod, opposite ends of the steering rod each being mechanically connected to a respective wheel carrier; an electric motor connected to the steering rod through a gear mechanism such that rotation of the motor causes the steering rod to translate along its primary axis, thereby displacing the wheel carrier; and a linear position sensor comprising at least one elongate feature extending diagonally along the length of the steering rod such that the elongate feature is inclined relative to the axis of the steering rod; and a sensing device facing the steering rod and observing only a certain segment of the elongate feature at any given time, the segment extending across the full width of the feature and along only a portion of the length of the feature, the sensing device generating a signal that varies according to a pattern formed by the feature and adjacent portions of the steering rod observed by the sensing device, the signal encoding the axial position of the steering rod.

2. An electric power steering system according to claim 1, wherein the elongate features comprise raised ridges, or recessed channels or slots.

3. An electric power steering system according to claim 1 or 2 wherein the elongate feature lies in a plane parallel to and offset from a plane containing the axis of the steering rod.

4. An electric power steering system according to any preceding claim wherein the sensor comprises an array of sensor elements extending orthogonally to the diagonal elongate feature or orthogonally to the axis of the steering rod, each sensor element generating a signal dependent on the relative alignment of the elongate feature and the sensor element.

5. An electric power steering system according to any preceding claim wherein at least one additional reference elongate feature is provided, the reference elongate feature extending axially along the shaft the same length as the diagonal elongate feature.

6. An electric power steering system according to claim 5 wherein the orientation of the reference feature and the further elongate feature is selected such that the spacing between the features, measured orthogonally to the long axis of the steering rod, varies along the length of the features.

7. An electric power steering system according to claim 5 or 6, wherein the sensor determines the position of the part of the reference feature facing the sensor and the position of the part of the other feature facing the sensor, and both positions are processed together to determine the axial position of the steering rod in dependence on the spacing between the two segments of the two features.

Technical Field

The present invention relates to an electric power steering system, and more particularly, to a steer-by-wire power steering system.

Background

In one conventional arrangement for a non-assisted steering system for an automobile, a steering wheel is connected to a steering shaft. The steering shaft is in turn connected to a steering mechanism. There are generally two solutions for connecting the motor to the "rack", i.e. converting between rotary motion and linear motion: (a) the motor drives the worm gear box, thereby driving the pinion; (b) a motor drives the recirculating ball nut and lead screw via a belt drive.

For example, the steering mechanism may include a rod having a rack (referred to as a steering rack or steering rod). A pinion gear, which rotates with the steering shaft, engages the rack such that rotation of the steering wheel causes the pinion gear to rotate, which in turn causes the steering rack to translate. Each end of the rack is connected to a wheel carrier of a wheel of the vehicle via a tie rod, the wheel steering angle varying with translation of the rack.

In most automobiles, no-assist steering systems are not common because the driver requires a significant effort to turn the steering wheel. In an electric power-assisted steering system, a motor is provided which acts on a steering shaft or a steering rack via a worm gear and a worm wheel. The torque applied to the steering wheel by the driver is detected and the motor is commanded to generate an appropriate assistance torque from the motor. The assistance torque is applied to the components of the steering system in a manner that increases the torque applied by the driver. The effect is to make the steering wheel easier to turn.

In recent developments, electric power steering systems are being developed in which there is no direct mechanical link from the steering wheel to the steering rack. In practice, the steering shaft is removed. The electric motor is retained together with means for measuring the torque applied to the steering wheel by the driver. In this arrangement, rather than increasing the torque applied by the driver, the motor assist torque is the only force applied to cause rack translation and wheel rotation. The motor may turn the pinion gear, thereby duplicating the action of the steering shaft. In the alternative, the rack may be replaced by a lead screw, wherein the motor acts directly on the recirculating ball nut through a transmission driven by the motor.

For safety reasons, it is important for the system to be able to monitor or calculate the position of the rack, i.e. the position of the rack within its available range of translational motion. In conventional systems, the position can be inferred by measuring the angular position of the steering wheel or the steering shaft, whether unassisted or in the presence of a mechanical connection from the steering wheel to the rack. For an electric power steering system without a mechanical connection, this is not possible because the angle of the steering wheel does not clearly indicate the position of the rack. This position can be inferred by counting the number of motor revolutions from a nominal starting position that will be aligned with the center of travel of the rack.

Applicants have appreciated that in the event of a loss of system power, such a count may be corrupted or may be lost. A start-up routine for re-knowing the position may be implemented, but this will affect the performance of the steering immediately after start-up until the position of the rack has been re-known.

Disclosure of Invention

It is an object of the present invention to provide a simple power steering system arrangement which enables the position of the steering rack to be determined quickly after system start-up.

According to a first aspect, the present invention provides an electric power steering system comprising: a steering rod, both opposite ends of which are mechanically connected to respective wheel carriers; an electric motor connected to the steering rod through a gear mechanism such that rotation of the motor causes the steering rod to translate along its primary axis, thereby displacing the wheel carrier; and a linear position sensor comprising at least one elongate feature extending diagonally along the length of the steering rod such that the elongate feature is inclined relative to the axis of the steering rod; and a sensing device facing the steering rod and observing only a certain segment of the elongate feature at any given time, the segment extending across the full width of the feature and along only a portion of the length of the feature, the sensing device generating a signal that varies according to a pattern formed by the feature and adjacent portions of the steering rod observed by the sensing device, the signal encoding the axial position of the steering rod.

Because the elongate feature is diagonal, when the steering rod is translated in one direction, the elongate feature will move across the sensitive area of the sensing device from side to side, and when the steering rod is translated in the opposite direction, the elongate feature will move across the sensitive area in the opposite direction. Thus, as the position of the segments of the encoder element will move from side to side, the pattern observed by the sensing element will change. The benefit of this arrangement is that, unlike prior art arrangements in which a count value is stored, the output of the sensor will be an absolute value that is not lost on power down.

The elongate features may be raised ridges or recessed channels.

The encoder element may comprise a strip of material having physical characteristics different from those of the portion of the steering rod.

The elongate features may be recessed, or raised, or flush with respect to other flat portions of the steering rod. In the case of a flush, the elongate features may appear as stripes.

The elongate feature may lie in a plane parallel to and offset from a plane containing the axis of the steering rod. In the case where the steering column is a cylinder, the elongate edge of the plane which is effectively formed by cutting away a portion of the cylinder may lie on a radius of the cylinder.

The width of the flat portion may be greater than the width of the elongate feature to form a plateau on each side of the elongate feature.

The sensing device may be located a small distance above the flat surface and parallel to the surface.

Most preferably, the elongate feature comprises an elongate channel or slot formed in the steering rod, the elongate channel or slot comprising a material different from the material of the steering rod adjacent the sides of the channel.

The material in the channels may be air, with the slots forming open channels. Although a U-shaped cross-section is preferred, the slot may have any cross-section within a certain cross-sectional range.

The material may be a solid material having different properties than the surrounding material of the steering rod. The top surface of the solid material may be flush with the material surrounding the steering rod.

In a simple arrangement, the position of the steering rod within its translational range can be detected from a change in the pattern, wherein the segment of the elongate feature moves from side to side as viewed by the sensor element.

The sensing device may comprise an array of sensor elements. Each sensor element of the sensor array may generate a single signal that varies according to the alignment of the segment of the elongate feature with the sensor array. For example, the signal may vary from zero when the elongate feature segment deviates from the elongate feature and is not observed by the element to a maximum when the segment of the elongate feature is fully aligned with the sensor element. Of course, the signal may be inverted, with a maximum occurring when the elongate feature is not facing the sensor element.

In a preferred arrangement, the sensor may comprise an array of sensor elements extending orthogonally to the diagonal elongate feature or orthogonally to the axis of the steering rod, each sensor element generating a signal dependent on the relative alignment of the elongate feature and the sensor element.

The signals output from all the sensor elements may be fed to a signal processor which generates a position signal indicative of the position of the steering rod from these signals. As the steering rod moves, the encoder element will move across the array causing a change in the signal from each sensor and this change can be detected by the signal processor.

As an alternative to an array, the sensor may comprise an elongate sensing element having a continuous output corresponding to the position of the feature in a direction perpendicular to the movement of the steering rod.

The sensor element array may have a length and may be oriented relative to the steering rod such that when the steering rod is at one end of its range of translation, the portion of the segment of the elongate feature facing the sensor array is at or near a first end of the sensor array, and when the steering rod is at the opposite end of its range of translation, the portion of the encoder element facing the sensor is at or near a second end of the sensor array.

Thus, the appropriate length of the sensor array will depend on the length of the slot, the range of translational motion allowed, and how diagonal the encoder elements are.

The width of the elongate feature (e.g. slot) may be less than one third of the length of the sensor array and preferably less than one fifth of the length of the linear sensor. The width of the slot may for example be equal to the width of an individual sensor element in the array.

In the context of the present description, the width of a sensor element may be considered as the width of the sensitive area of the sensor element, which may be wider or narrower than the physical width of the sensor element. The sensor will observe anything that is within the width of the sensor.

The sensing device may not comprise an array of elements. The sensing means may for example comprise one or more magnetic sensor devices, such as hall effect sensors, and at least one magnet. The hall effect sensors may be positioned spaced apart and adjacent to segments of the elongate feature such that as the steering rod is moved, the segments face more or less one sensor and the opposite portion faces the other sensor. The magnet may be coupled to the steering rod and supported by the metal bracket so that a magnetic circuit is formed by the steering rod, the bracket, and the hall effect sensor.

The sensor device may alternatively comprise an inductive sensor. For example, the primary coil may be positioned at a location to one side of an elongated feature, and two secondary coils may be positioned near the feature in much the same manner as a hall effect sensor, forming a closed circuit around the core of the support coil and steering rod.

The steering rod may be metal, such as steel.

The skilled person will appreciate that the elongate feature may have a range of different forms, and the selection of the elongate feature may depend on the type of sensing device provided to detect the pattern formed by the segments of the channel and the adjacent portion of the steering rod.

The sensing device should not move as the steering rod translates and therefore may be mounted on a fixed part of the steering system (e.g., a housing surrounding the steering rod).

Suitable sensor element arrays may include magnetic sensor element arrays. The sensor element array may comprise three or more sensor elements.

The material of the rack on either side of the elongate feature (e.g. slot) may be magnetic. In this case, the elongate feature may comprise a slot formed in the steering rod.

Alternatively, the linear position sensor element may be an inductive sensor element.

By applying a scaling factor to the output signal, this signal can be converted into a position signal of the steering rod. This may depend on the ratio of the length of the slot to the offset between the two ends of the slot measured in a direction orthogonal to the long axis of the slot. This signal will indicate the linear displacement of the shaft as it is translated by the motor.

At least one additional reference elongated feature may be provided in the steering rod. The reference elongate feature may extend axially along the shaft the same length as the diagonal elongate feature.

Where the diagonal elongate feature is a slot, the additional reference elongate feature may also be a slot.

The orientation of the diagonal and reference slots may be selected such that the spacing between the slots, measured orthogonal to the long axis of the steering rod, varies along the length of the slots.

As an alternative to the reference slot being in line with the axis of the steering rod, the reference slot may also extend diagonally, as long as the reference slot is oriented differently from the other slot so that the relative spacing varies along the length of the slot.

In the case where reference slots are provided, the sensor element of the sensor may determine the position of the portion of the reference slot facing the array of sensor elements and the position of the portion of the diagonal slot facing the array of sensor elements and process the two positions together to determine the axial position of the steering rod in dependence on the spacing between the two portions of the slots.

The use of reference slots may enable the system to be unaffected by any rolling of the steering rod about its axis, as this does not change the relative position of the two parts of the slots facing the sensor. These parts can be translated along the sensor from the desired position, but the spacing does not change, and can be detected as a basis for position measurement.

The or each slot may be linear such that as the steering rod moves, the position of the portion of the slot facing the linear position sensor will vary linearly with the change in steering rod position. In other arrangements, the slot may not be linear when the steering rod is translated by the motor, thereby producing non-linear movement relative to the position sensor.

The or each slot may be formed in a flattened portion of the steering rod. This may be offset along the rack from the toothed profile forming part of the gear mechanism connecting the motor to the steering rack. A pinion or swivel nut may be engaged with the steering rod and connected to the rotor of the motor.

The or each slot may be machined into the surface of the steering rod.

The steering system may further comprise a steering shaft supporting a steering hand wheel or other user operable actuator.

The system may include a torque sensor that measures torque at the hand wheel and a signal processing unit or microprocessor that receives the torque signal and generates an assist torque demand signal indicative of assist torque to be generated by the motor.

The slot may be an open slot or may be filled with a non-magnetic or non-magnetically susceptible material.

Drawings

Various embodiments of the present invention will now be described, by way of example only, with reference to and as illustrated in the accompanying drawings, in which:

FIG. 1 is a diagrammatic view of an embodiment of a steering system according to the present disclosure;

FIG. 2 is a detailed view of the steering rod and motor of the steering system;

FIG. 3 is a perspective view of the sensor array relative to the steering rod, showing how a segment of the elongate feature is within the field of view of the sensor array;

FIG. 4 is a plan view of the steering rod showing the diagonal orientation of the elongate features;

FIG. 5 is a cross-section through the steering column and sensor array taken through the center of the segment viewed by the sensor array;

FIG. 6 is a perspective view of an alternative wherein the diagonal elongate feature is located alongside two other elongate features parallel to the axis of the steering rod;

fig. 7(a) is a plan view of a steering rod showing the diagonal orientation of the elongate feature and two further elongate features, and fig. 7(b) shows a further alternative having only two elongate features;

FIG. 8 is a cross-section through the steering column and sensor array taken through the center of the segment viewed by the sensor array;

FIG. 9 shows the pattern observed in the field of view of the sensor array for the arrangement of FIG. 1 when the steering is fully locked on the left, and the output signals from each sensor element encoding that pattern; and

fig. 10 shows the pattern observed in the field of view of the sensor array for the arrangement of fig. 1 when the steering is fully locked on the right, and the output signal from each sensor element.

FIG. 11 is a schematic diagram of an arrangement for detecting the linear position of the steering rod using a magnetic sensor;

FIG. 12 shows a similar arrangement using inductive sensors; and

fig. 13 shows another alternative arrangement using an inductive sensor.

Detailed Description

As shown in fig. 1, an electric power steering system 1 of the steer-by-wire type comprises a hand wheel 2 which can be turned by the driver in a conventional manner. The hand wheel is supported by a stub shaft 3. The position sensor 4 measures the angular position θ 1 of the stub shaft 3, and the torque sensor combined with the position sensor measures the torque T applied to the hand wheel 2 by the driver. Unlike conventional steering systems in which the rotation of the hand wheel 2 is limited by the wheels of the vehicle, a mechanism for providing a simulated resistance to rotation of the hand wheel may be provided. The mechanism may also be used to provide simulated feedback to the driver to simulate the steering feel of a conventional steering system. This mechanism is not shown in the drawings, but embodiments of such mechanisms are known to those skilled in the art.

The system further comprises an elongate steering rod 5, the two opposite ends 6, 7 of which are each mechanically connected to a respective wheel carrier 8, 9. Each wheel carrier supports the wheels and tires of the vehicle in a completely conventional manner and is arranged such that translation of the steering rod 5 causes the steering angle of the wheels to change. The electric motor 10 is connected to the steering rod 5 by means of a gear mechanism 11, so that rotation of the motor causes the steering rod to translate along its main axis, thereby displacing the wheel carrier. The gear mechanism may include a worm gear that engages a worm gear mechanism on the steering rod. Alternatively, the motor may drive the steering rod through a screw drive mechanism, wherein a worm gear mechanism on the steering rod engages a set of ball bearings or a nut that is rotated by the motor.

The motor 10 is driven by an assist torque demand signal output from a signal processor 12, and the signal processor 12 generates the torque demand signal in response to the outputs of the torque sensor and the position sensor 4. In general, the higher the torque output from the torque sensor, the higher the assist torque required by the motor.

The system also includes a linear position sensor 13 that determines the axial position of the steering rod as it translates between one locked position and another of the locked positions of the steering system. The sensor 13 comprises an elongate feature in the form of an elongate slot 14 with an open face which extends diagonally along the length of the steering column. The length of the slot 14 is slightly greater than the range of translation possible when the steering rod moves the steering from full lock to lock in use.

An elongate array of sensor elements 15 extends across the slot 14 in a direction orthogonal to the slot 14 formed in the shaft or orthogonal to the axis of the steering rod. The length of the sensor array 15 is greater than the width of the slot and is positioned so that the slot always faces a portion of the sensor regardless of the axial position of the steering rod. In this way, the sensor will view a certain segment of the slot at any given time, with the depth of the segment measured along the length of the slot being determined by the field of view of the sensor array 15.

The slot and sensor array can best be seen in figures 3 to 5 of the drawings.

When the steering is fully locked in one direction, the segment of the slot viewed by the sensor array will be towards one end of the sensor, and when the steering is fully locked in the other direction, the segment will be towards the other end of the sensor. This is shown in fig. 9 and 10, respectively. In this example, the array comprises eight sensor elements, each sensor element producing a zero value signal when facing a portion of the steering rod and a positive value when facing a segment of the slot 14. The pattern may be read from left to right or right to left along the array of sensor elements and encoded as a unique sequence of values for the sensor elements of the array.

Each signal output from the sensor array is fed to a signal processor 16 which combines a plurality of signals to produce an output signal indicative of the position of the steering rod and hence the angle of the wheel.

It is possible to generate a single output that encodes the position of the steering rod because the linear position sensor provides an output that indicates where the portion of the slot facing the sensor is located across the width of the sensor. Thus, the output depends on the pattern formed by the slots and the material of the sides of the slots as viewed by the sensor array 14. The diagonal orientation of the slots forces this pattern to change as the steering rod moves from one lock to another.

From knowledge of the orientation and width of the slot, and hence the expected pattern seen by the sensor array at different positions of the steering rod, the position of the steering rod can be encoded by the output signal from the linear position sensor.

Figures 6 to 8 of the accompanying drawings show an alternative arrangement in which there are two slots, one being diagonal and the other being in line with the axis of the steering rod. In this case, the pattern observed by the sensor array will be more complex and comprise two regions corresponding to respective segments of the two slots and material between the slots. As the steering rod moves, the two slots and the land between them will move along the sensor array. The signal processor can determine the position of the steering rod along its range of travel from the pattern by determining the spacing between the two slots as viewed by the sensor. The actual relative positions of the slots and plateaus in the observed pattern can be ignored. This is advantageous compared to the example with a slot, since it is not affected by any lateral misalignment of the steering rod.

Fig. 11 shows a circuit based sensing device using two magnetic sensors. A pair of linear hall effect devices measure the position of each edge of the slot forming the elongated feature. The magnet is positioned off to one side of the slot and the magnetic circuit is completed by the steel in the steering rod and a metal bracket that couples the magnet to the sensor. The coupling is strong where there is no notch and weak where there is a notch, thereby generating a different magnetic flux at the hall sensor. The linear position will be determined differentially by the relative magnitude of the signals from each device, e.g., (signal 1-signal 2)/(signal 1+ signal 2).

Fig. 12 shows a sensing device based on the use of an inductive sensor. The inductive sensor may be a variable differential transformer. As the notch in the shaft is penetrated, the coupling between the primary coil and one secondary coil increases and the coupling between the primary coil and the opposite secondary coil decreases. The secondary coil may be wired in anti-phase series such that a phase difference from the primary coil indicates the position. This is i's modification to the LDVT of a moving core rather than a moving notch.

In an alternative arrangement shown in fig. 13, a pair of inductive proximity sensors may be used to form the sensing means. The slot will reduce the inductance of the coil. The circuit will measure the relative inductance of the two coils and the difference is used to determine the position of the slot.