Characterize rattling noises that may occur when reversing the direction of the steering gear

Abstract

A method for characterizing a steering gear reversal knock noise in a steering system having a rack and pinion and electric power steering assistance via a steering assist motor includes communicating a steering input angle control signal to a rotary actuator to rotate a steering axle with active assistance to a fixed steering angle. A linear actuator applies an axial force at a constant rate along a longitudinal axis of the rack. The axial rack acceleration is measured after the axial force is communicated. A control action is taken when a peak amplitude of the axial acceleration value exceeds a calibrated threshold of the axial acceleration value indicative of the knock noise.A system includes the rotary actuator and the steering system, a linear actuator for providing a calibrated axial application force along the rack axis, an acceleration sensor for measuring an axial acceleration value of the rack, and the above-mentioned controller.

Description

TECHNICAL FIELDThe present disclosure relates to a method and system for characterizing rattle noise that may occur due to steering gear direction reversal in a steering system.BACKGROUNDVehicle rack and pinion steering systems include an elongated flat gear or rack having teeth that mesh with contact teeth of a rotating gear. The gear is attached to an end of a steering axle. When a steering angle is transmitted to the steering axis by the rotation of a steering wheel, the pinion gear translates along the rack by engaging with the rack teeth. Again, the rack translates in a corresponding steering direction. Tie rods disposed at the opposite distal ends of the rack are connected to the front road wheels of a vehicle via a corresponding steering arm. Therefore, a rack and pinion steering system effectively converts the rotational motion of a steering wheel into a linear motion suitable for steering the vehicle, and while also providing an appropriate gear reduction.The steering functionality provided by typical rack and pinion steering gears may be electrically assisted in some constructions. For example, an electric steering motor may communicate variable steering torque overlay or torque assist along the steering axis, while in other constructions, the electric steering motor may provide the torque assist directly to the rack via a drive mechanism. Such rack and pinion steering gears are known, for example, from the publications DE 10 2011 089 950 A1, DE 10 2009 008 053 A1 and Pepper, Harrer (Ed.), Steeringhandbuch, 2nd Edition, Springer Vieweg, 2013.While manual and electrically assisted steering systems typically operate well, transient steering gear noise may manifest itself during a steering direction reversal under certain driving conditions. Such noise, often referred to as steering gear direction reversal knock, may affect steering quality and feel.It is therefore an object of the invention to improve steering quality and steering feel. This object is achieved according to the invention by the features of the independent claims. Advantageous refinements are defined in the appended claims.BRIEF DESCRIPTION OF THE DRAWINGSFIG. 1 is a schematic illustration of an exemplary test system for characterizing steering gear direction reversal knock noise in a steering gear as described herein. FIGS. 2A and 2B are representative time plots of respective positive and negative application axial force rates for a satisfactorily operating steering system, with measured rack axial acceleration plotted on the vertical axis and the steering input angle plotted on the horizontal axis. FIGS. 3A and 3B are representative time plots of respective positive and negative application axial force rates for an unsatisfactory steering system, with measured rack axial acceleration plotted on the vertical axis, and the steering input angle plotted on the horizontal axis. FIG. 4 is a flow chart describing an example method for characterizing steering gear direction reversal knock noise in a steering system using the test system set forth in FIG. 1.DETAILED DESCRIPTIONReferring now to the drawings, wherein like reference numerals refer to like components throughout the several views, an exemplary test system 10 is schematically shown in FIG. 1. the steering test system 10 includes a conventional steering system 20 of the types mentioned above, as well as associated steering control hardware 40 and a controller (C) 50. the controller 50 is programmed to execute logic embodying a method 100 with the control hardware 40. Execution of method 100 results in characterization of steering gear direction reversal knock noise in steering system 20, as detailed below in further detail with reference to FIGS. 2A-4.The steering system 20 of FIG. 1 may be configured as a manual steering system or an electrically assisted rack and pinion steering gear of the types well known in the art. As such, the steering system 20 may include an elongated rack 22 having a longitudinal rack axis 17 and respective first and second ends 33 and 35. The steering system 20 also includes a gearbox 24 and a steering axle 25 with the gearbox 24 disposed proximate the first end 33 of the rack 22.Depending on the embodiment, a drive mechanism 129 and drive housing 29 may be positioned proximate the second end 35 of the rack 22, as shown, which is typical of a rack and pinion electric power steering (EPS) system. A rotor axis 15 of the steering assist motor 43 is aligned and operable to enable electrical assistance from a steering maneuver or operation by the drive mechanism 129, which may be embodied as a suitable transmission, chains, belts, and / or other speed reduction mechanism. Although omitted from FIG. 1 for illustrative simplicity, the steering assist motor 43 and drive mechanism structure similar to the drive mechanism 129 and drive housing 29 may alternatively be positioned on or along the steering axis 13 to form a column or gear EPS system of the type known in the art. A column EPS embodiment may also include a steering column and an intermediate shaft as is known in the art, wherein the steering assist motor 43 provides the steering assist torque to a separate drive mechanism mounted adjacent to the steering column. A gear EPS system, in contrast, may place the steering assist motor 43 close to the transmission case 24 so that assist torque directly acts on the rotary gear 26. Regardless of the embodiment, a bracket 27 and a base plate 28 may be used to secure the steering system 20 in a test environment.The gear housing 24 located at the first end 33 of the rack 22 contains a rotatable pinion gear 26 Since a steering input in the form of an arranged steering angle is transmitted to the steering axle 25 via the steering axle 13, typically from a steering wheel (not shown), but in the present controlled test environment via a rotary actuator 42, the pinion gear 26 engages within the gear housing 24 with engaging gears (not shown) of the rack 22. The gear drive 26 thus translates along the rack axis 17, as indicated by the double arrow A.This movement, in turn, moves the rack 22 in a corresponding direction to steer the front wheels of a vehicle (not shown) in which the steering system 20 is deployed.It is recognized herein as a basis for the method 100 that steering gear direction reversal knock noise results from tolerances in the various mechanical interfaces of the steering system 20, for example, between the mating surfaces of the pinion gear 26 and the rack 22, and / or the drive mechanism 29 and the rack 22, when a vehicle equipped with the steering system 20 is operating. Such noise may manifest itself upon a steering direction reversal under certain driving conditions. The extent to which these steering gear noise manifests may vary with the steering angle and rate of drawbar forces acting axially along the axis 17 of the rack 22. The present method 100 thus performs affirmative diagnostic and control steps to replicate such conditions in a controlled test environment for the purpose of isolating and correcting the above-mentioned steering gear reversal knock noise problems.For this purpose, the control hardware 40 illustrated in FIG. 1 includes a rotary actuator 42, e.g., an electric motor, that is responsive to steering input angle control signals (arrow θ 42) from the controller 50, as well as a torque transducer 44 and a rotary encoder 46, each of which is aligned on the steering axis 13 of the steering shaft 25 coaxial with the others. The rotary encoder 46 is operable to transmit a measured steering angle (arrow θ 46) to the controller. Also, a measured steering output torque value (arrow T 44) is transmitted to the controller 50 through the rotary encoder 46 for use in overall control of the system 10. Because axle variation may be present in the control hardware 40, an extension shaft 45 may be coupled to the steering axle 25 via a set of flexible couplings 48, as shown. The flexible couplings 48 serve to simplify the connection of the rotary actuator 42 to the steering shaft 25.A linear actuator 49 is disposed at the end 35 of the rack 22 and is connected to a drawbar 75 of the steering system 20. In addition, an acceleration sensor 41 is connected to the rack at the end 33 opposite to the linear actuator 49, as shown. The controller 50 is then placed in wired or wireless communication with the linear actuator 49 and the accelerometer 41 such that the controller 50 is capable of transmitting and receiving rate controlled axial force control signals (arrow F 49) to and from the linear actuator 49.The controller 50 of FIG. 1 is specifically programmed to arrange a calibrated axial force along the rack axis 17 at a constant rate and monitor the rate and magnitude of the applied axial force. The controller 50 is further configured to receive a measured axial acceleration value (arrow A 17) from the accelerometer 41 in response to the applied axial force along the rack axis 17. When the steering system 20 is of the electrically assisted type, an additional controller (not shown), such as an electronic control unit (ECU), for the steering assist motor 43 may be programmed to transmit steering torque assist control signals (arrow T 43) to the steering assist motor 43 to control a torque assist output (arrow TA) of such a motor. That is, an integrated ECU in the steering assist motor 43 determines and controls the amount of torque overlay that the assist motor 43 should generate based on an input torque signal from an internal torque sensor (not shown) disposed along the steering axis 13 and a variety of other signals, such as vehicle speed, ignition state, etc., as is known in the art of EPS systems.The controller 50 may be configured as a host machine, e.g., a digital computer or microcomputer, specially programmed to perform the method steps of the method 100, for example, as shown in FIG. 4. To this end, the controller 50 is configured with sufficient hardware to perform the required steps, i.e., sufficient memory (M), a processor (P), and other hardware such as high-speed clock (high-speed clock), analog-to-digital and / or digital-to-analog circuits, a timer, input / output circuits, and connected devices, signal programming and / or signal buffer circuits. The memory (M) includes sufficiently concrete permanent memories such as magnetic or optical ROM (read-only memory), flash memory, etc., as well as RAM (random access memory), EEPROM (electrically erasable programmable read-only memory), and the like.As described in more detail below, referring to FIGS. 2A-4, as part of the method 100, the controller 50 of FIG. 1 may command the rotary actuator 42 to proceed in discrete steps through a predetermined amount of motion / steering angle, for example ± 360 degrees, for example 45 degree steps, and then lock the steering angles at each increment for a particular discrete steering angle as the test proceeds. The controller 50 also transmits the above-mentioned axial force control signals (arrow F 49) to the linear actuator 49 of FIG. 1 to position the axial forces (arrows F) along the rack axis 17 and measures the axial acceleration (arrow A 17) of the rack 22 via the acceleration sensor 41. such acceleration is ideally zero in a properly functioning / silent steering system 20.Curves 75 of FIGS. 2A and 2B illustrate example acceptable rack axial acceleration behavior upon application of a calibrated axial force via the linear actuator 49 shown in FIG. 1, for example a force application rate of about 15-25 kN / s or about 20 kN / s in various embodiments. FIGS. 2A and 2B illustrate a negative application rate and a positive application rate, respectively, with terms negative and positive with respect to the direction of axial forces (arrow F) along the rack axis 17 from the linear actuator 49, An amplitude (A) of the measured axial acceleration is plotted on the vertical axis and the steering input angle in degrees is plotted on the horizontal axis, with different discrete data points 77 forming the curves 75. The test uses a series of application rates for each steering angle, for example 15-25 kN / s in 2 kN / s steps. The range of application rates may be selected based on actually measured vehicle loads.The controller 50 may use various threshold values, for example, a first threshold value 70 at amplitude A 1, which indicates acceptable steering knock noise performance, and a second threshold value 72 having a higher relative amplitude A 2, which indicates unacceptable knock noise performance. The range between the first and second thresholds 70 and 72 may be as large or small as desired for the given test being performed, for example, about 0.05 to 1G in one possible embodiment. In FIGS. 2A and 2B, all measured axial acceleration values clearly fall below the level of the first threshold 70, and so a steering system 20 having the illustrated performance characteristics would be deemed acceptable as part of each resulting control decision.In contrast to FIGS. 2A and 2B, the curves 175 of FIGS. 3A and 3B depict example unacceptable rack acceleration behavior. The curves 175 have values that are above the second threshold 72. In addition, the acceleration behavior shown for the positive application rate in FIG. 3B is different from that of the negative application rate of FIG. 3A, which is an indication that the direction of force application along the rack axis 17 may also affect any transmission direction reversal knock noise that ultimately manifests itself during the test. Thus, FIGS. 2A-3B show that the method 100 is controlled by the rotary actuator 42 during execution of the method 100 in response to arrangements of the controller 50, by measuring an axial acceleration response of the rack 22 at each of a plurality of different discrete or fixed steering angle setpoints over the predetermined amount of motion of the steering axis 25.Referring to FIG. 4, an embodiment of the method 100 for characterizing steering gear direction reversal knock noise in a steering system, such as the example steering system 20 of FIG. 1, begins with step S 102. In this step, the steering system 20 is connected to the control hardware 40 and set in communication with the controller 50 described above. In addition to connecting the controller 50 to the rotary actuator 42, step S 102 includes connecting the linear actuator 49 to the accelerometer 41 along the rack axis 17. the method 100 proceeds to step S 104 when the test system 10 is substantially constructed as shown in FIG. 1 and the controller 50 is in communication with the rotary actuator 42, the linear actuator 49, and the accelerometer 41. In EPS systems, electronic steering assist is active throughout the test. Moreover, since steering gear direction reversal knock noise typically occurs most clearly during low speed parking maneuvers, the simulated vehicle speed may be about 0 km / h, which corresponds to a maximum level of steering assist. Thus, the electric power steering assist is the test over active.At step S 104, the controller 50 transmits the steering input angle control signal (arrow θ 42) to the rotary actuator 42 of FIG. 1, thereby causing the rotary actuator 42 to rotate the steering axis 25 to a first steering angle target value, for example, -360 degrees, and then freeze or hold this first steering angle target value. As is known in the art, once an electric motor is not energized, its rotor may be locked, for example via a lock-up clutch or other suitable mechanical or electrical means to ensure that the commanded steering angle is held fixed. The method 100 proceeds to step S 106 when the steering axle 25 has been rotated to the first steering angle setpoint.Step S 106 includes placing a calibrated axial application force via transmission of the axial force control signals (arrow F 49) to the linear actuator 49 of FIG. 1 at a constant application rate. The value of the constant rate of axial application force should be high enough to cause a measurable response to the end 33 of the rack 22, for example, about 15-25 kN / s or about 20 kN / s in non-limiting exemplary embodiments. Step S 106 also includes measuring the axial acceleration of the rack 22 via the accelerometer 41 and transmitting the measured axial acceleration to the controller 50 as the measured axial acceleration value (arrow A 17). The method 100 then proceeds to step S 108.Next, in step S 108, the controller 50 of FIG. 1 receives whether all desired steering angle command values have been tested. For example, if a full range of angular motion of ±30° is divided into equal 45-degree increments, the controller 50 determines whether all positive and negative application rate directions have been tested for each of the steering angle target values, i.e., the value [-360°, -315°, -270°,..., +27°, +315°, +3 360°] set in the 360° example has been tested for a total of at least seventeen different steering angles in this example. If yes, the method 100 proceeds to step S 110. Step S 104 is otherwise repeated for the next steering angle target value.Step S 110 of the method 100 may include determining whether the test results from steps S 102-S 106 correspond to a pass / acceptable or fail / unacceptable steering system 20. The performance criteria used for step S110 may vary with design. For example, considering the exemplary unacceptable response of FIGS. 3A and 3B, controller 50 may determine whether any acceleration measurements exceed second threshold 72. Alternatively, the controller 50 may determine how many measurements exceed the second threshold 72 and how much the second threshold 72 is exceeded in determining whether or not a given test sample should be considered acceptable. The method 100 proceeds to step S 112 if the sample is unacceptable and to step S 114 if the sample is acceptable.Step S 112 may include executing a control action with respect to the manual steering system 20 of FIG. 1 if the previous steps result in a decision that the steering system 20 has unacceptable performance. For example, the controller 50 of FIG. 1 may record a first diagnostic code as an output signal indicated by the arrow 14 of FIG. 1 when the measured acceleration (A 17 arrow) exceeds the calibrated threshold acceleration indicated above with respect to step S 108, i.e., the peak acceleration indicates an unacceptable steering gear direction reversal noise for the particular steering system 20 being tested. Additional control steps may include applying the first diagnostic code to validate a given design of the manual steering gear 20, for example, by rejecting a given design during a validation process or creating a design specification.Step S 114 is reached when the measured amplitude of the received measured acceleration exceeds the calibrated threshold acceleration, or in other words, when no perceptible state is detected in steps S 102-S 106 via tests over the entire range of motion of the steering axle 25. Step S 114 may include detecting, via the controller 50, a second diagnostic code, that is, via the output signal (arrow 14 of FIG. 1 ) when the rate of the received measured steering output torque does not exceed the aforementioned calibrated threshold rate with respect to step S 108. Since step S 114 reveals a fully functional manual steering gear 20, additional control steps may include applying the second diagnostic code to validate a given design of the manual steering gear 20, for example, by assuming a given design during a validation process or creating a design specification.As used herein with reference to the disclosed values or ranges, the term "about" indicates that the disclosed numerical value allows some imprecision, for example reasonably close to or almost as high as, for example, plus ±10% of the stated values or ranges. If the imprecision provided by the term "about" is not otherwise understood by those of ordinary skill in the art with this ordinary meaning, then "about" as used herein indicates at least variations that result from ordinary measurement methods and the use of such parameters. Moreover, the disclosure of ranges includes the disclosure of all values of further divided ranges within the entire range.

Claims

A system comprising: a rotary actuator (42) configured to respond to a steering input angle control signal; a steering system (20) having a steering axis (25), a rack (22) having a longitudinal axis (17), a pinion gear (26) disposed at an end of the steering axis (25) in meshing engagement with the rack (22), and a steering assist motor (43) operable to assist a steering maneuver; a linear actuator (49) operable to provide a calibrated axial force along the longitudinal axis (17) of the rack (22) at a constant application rate of about 15-25 kN / s; an acceleration sensor (41) operable to measure an axial acceleration of the rack (22) along the longitudinal axis (17) in response to application of the calibrated axial force; A controller (50) programmed to characterize a rattling noise when reversing the direction of the steering gear in the steering system (20), and wherein execution of the instructions of the controller (50) causes the controller (50) to: transmit the steering input angle control signal to the rotary actuator (42) while the steering assist motor (43) assists the steering maneuver to thereby adjust the steering axis (25) at a calibrated fixed steering angle; transmit an axial force signal to the linear actuator (49) to thereby transmit a calibrated axial force along the longitudinal axis (17) of the rack (22) at a constant application rate; after transmitting the calibrated axial force, measure an axial acceleration value of the rack (22) via the acceleration sensor (41); To execute a control action related to the steering system (20) when a peak amplitude of the measured axial acceleration value exceeds a calibrated axial acceleration value threshold indicative of an unacceptable level of the rattling noise upon reversal of the direction of the steering gear, wherein the calibrated axial acceleration value threshold indicative of the rattling noise upon reversal of the direction of the steering gear is at least about 0.2G.The system of claim 1, wherein the rack (22) has a first end (35) and a second end (33), and wherein the linear actuator (49) is disposed at the first end (35) and the accelerometer (41) is disposed at the second end (33).The system of claim 1 or 2, wherein the controller (50) is programmed to command the rotary actuator (42) to rotate the steering axis (25) stepwise into each of a plurality of different fixed steering angles over a calibrated range of motion of the steering axis (25).The system of claim 3, wherein the calibrated range of motion is ±3 360° and the plurality of different fixed steering angle ranges comprise seventeen fixed steering angles.The system of at least one of the preceding claims, wherein the control action comprises detecting a diagnostic code in a memory (M) of the controller (50).A method of characterizing a rattling noise in reversing the direction of a steering gear in a steering system (20) having a rack (22) and a pinion gear (26) disposed at an end of a steering axle (25) in meshing engagement with the rack (22), and a steering assist motor (43) operable to electrically assist a steering maneuver, the method comprising: transmitting a steering input angle control signal from a controller (50) to a rotary actuator (42) while the steering assist motor (43) electrically assists the steering maneuver to thereby rotate the steering axle stepwise into a plurality of different fixed steering angles over a -360 degree to + 360 degree range of motion of the steering axle (25); transmitting an axial force signal from the controller (50) to a linear actuator (49) to thereby communicate a calibrated axial force along a longitudinal axis (17) of the rack (22) at a constant application rate, for each of the various fixed steering angles; measuring an axial acceleration value of the rack (22) via an acceleration sensor (41) in response to communication of the calibrated axial force; Execution of a control action with respect to the steering system (20) by the controller (50) when a peak amplitude of the measured axial acceleration value exceeds a calibrated threshold acceleration value indicative of an unacceptable level of the rattling noise upon reversal of the direction of the steering gear, wherein the calibrated axial force is applied at a rate of about 15-25 kN / s, and wherein the calibrated threshold axial acceleration value indicative of the rattling noise upon reversal of the direction of the steering gear is at least about 0.2 G.The method of claim 6, wherein the plurality of different fixed steering angles comprise at least seventeen different steering angles.

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