JP2016107764A - Power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve a steering feeling.SOLUTION: In a power steering device, target additional friction torque Tft for improving a steering feeling is obtained (steps 30 to 90), and assist torque is controlled on the basis of target assist torque Tat based on the sum of a basic control amount Tab for reducing a steering load on a driver (step 20) and the target additional friction torque Tft (steps 140, 150). In a range where vehicle speed V is very low and self-aligning torque acting on a steering wheel becomes a negative value, magnitude of target friction torque is determined so as to increase as the magnitude of steering angle increases (steps 100 to 120).SELECTED DRAWING: Figure 2

Description

  The present invention relates to a steering device for a vehicle such as an automobile, and more particularly to a power steering device.

  The power steering device applies an assist torque to the steering unit, thereby reducing the steering burden on the driver, that is, the burden when the driver rotates the steering wheel, and improves the steering feeling. For example, in Patent Document 1 below, the assist torque is based on the sum of the basic control amount for reducing the driver's steering burden and the friction torque control amount (hysteresis control amount) for improving the steering feeling. A power steering device for controlling the power is described.

  When the steered wheel is at a position other than the straight traveling position of the vehicle, the self-aligning torque acts on the steered wheel. The self-aligning torque increases as the steering angle increases when the vehicle speed is in the medium to high speed range, but decreases as the steering angle increases when the vehicle speed is in the low speed range. In the power steering device described in Patent Document 1 below, when the vehicle speed is in the low speed range and the steering angle is large, the assist torque is reduced as the steering angle increases. This is described, for example, in paragraphs [0053] and [0054] of FIG. According to the assist torque control described above, it is possible to prevent the steering reaction force from becoming insufficient due to excessive assist torque during steering by increasing the vehicle speed in a low speed range and a large steering angle range. .

JP 2011-131629 A

[Problems to be Solved by the Invention]
However, when the vehicle speed is very low, such as in a very low speed range, the self-aligning torque becomes a negative value in a very large range of the steering angle, and the magnitude of the steering angle becomes large. As it grows. Since the negative self-aligning torque generates torque that turns the steering wheel in the direction to increase, if the friction torque control amount is reduced as the steering angle increases, the drag force when steering the wheel is increased. It becomes small and the steering reaction force is insufficient. Therefore, according to the power steering device described in Patent Document 1, it is impossible to prevent the steering feeling from being lowered when the vehicle speed is very low and the steering angle is very large. .

  The present invention has been made in view of the above-described problems in a conventional power steering apparatus that controls assist torque including a friction torque control amount. The main object of the present invention is to improve the steering feeling when the steering is increased in a situation where the self-aligning torque is a negative value.

[Means for Solving the Problems and Effects of the Invention]
According to the present invention, the main problem described above is that the self-aligning torque acting on the steered wheels decreases as the steering angle increases, and increases as the steering angle increases. In a power steering device that determines a target friction torque so as to decrease the friction torque, and applies the friction torque to the steering unit based on the target friction torque.
When the vehicle speed is a vehicle speed at which the self-aligning torque becomes a negative value when the magnitude of the steering angle is equal to or greater than a reference value, the magnitude of the steering angle increases within a range equal to or greater than the reference value. This is achieved by a power steering apparatus configured to determine the target friction torque so as to increase in size.

  According to the above configuration, within the range where the self-aligning torque acting on the steered wheel decreases as the steering angle increases, the target friction is reduced so that the magnitude decreases as the steering angle increases. Torque is determined. However, in the vehicle speed range where the self-aligning torque acting on the steered wheel is negative, the target friction torque is determined so as to increase as the steering angle increases, and the drag force of steering is increased. Will be increased. Therefore, for example, in a situation where the vehicle speed is very low and the steering angle is very large, it is possible to prevent the self-aligning torque from acting in the direction of increasing and the steering reaction force during steering from becoming insufficient. As a result, the steering feeling can be improved as compared with the prior art.

  When the steering angle is greater than or equal to the reference value, the self-aligning torque becomes negative, and the negative self-aligning torque is larger when the vehicle speed is very low. The size increases. Therefore, it is preferable that the magnitude of the target friction torque is determined so as to increase as the vehicle speed decreases in a range where the self-aligning torque is a negative value.

It is explanatory drawing which shows the outline of 1st embodiment of the power steering apparatus by this invention. It is a flowchart which shows the assist torque control routine in 1st embodiment. FIG. 3 is a flowchart showing a routine for calculating a target steering angle θt executed in step 70 of FIG. 2. FIG. It is a flowchart which shows the assist torque control routine in 2nd embodiment of the power steering apparatus by this invention. 7 is a map for calculating a target basic assist torque Tab based on the steering torque T and the vehicle speed V. 6 is a map for calculating a target friction torque Tft based on the absolute value of the steering angle θ and the vehicle speed V. 6 is a map for calculating a gain Kt based on the absolute values of the vehicle speed V and the steering angle θ when the vehicle speed V is larger than a reference value Vc2. 6 is a map for calculating a gain Kt based on the absolute value of the vehicle speed V and the steering angle θ when the vehicle speed V is equal to or less than a reference value Vc2. FIG. 6 is a map for calculating a target friction torque Tft based on the absolute values of the vehicle speed V and the steering angle θ when the vehicle speed V is equal to or less than a reference value Vc2 in the second embodiment. It is a graph which shows the relationship between the absolute value of vehicle speed V and steering angle (theta), and the self-aligning torque Tsat. It is a graph which shows the relationship between the absolute value of steering angle (theta) and the return torque Tre in the case of the past (two-dot chain line) and the case of the first embodiment (solid line).

Several preferred embodiments will now be described in detail with reference to the accompanying drawings.
[First embodiment]

  FIG. 1 is an explanatory diagram showing an outline of a first embodiment of a power steering apparatus 10 according to the present invention. The power steering device 10 of this embodiment is configured as a column assist type electric power steering device. The power steering device according to the present invention may be another type of power steering device as long as the assist torque can be controlled, such as a rack coaxial type electric power steering device.

  In FIG. 1, a power steering device 10 is applied to a steering unit 12. The steering unit 12 includes a steering wheel 14 that is operated by a driver, an upper steering shaft 16 that rotates together with the steering wheel 14, an intermediate shaft 18, and a steering mechanism 20. The intermediate shaft 18 is connected to the lower end of the upper steering shaft 16 via the universal joint 22 at the upper end and is connected to the pinion shaft 26 of the steering mechanism 20 via the universal joint 24 at the lower end.

  The steering mechanism 20 includes a rack and pinion device 28 and tie rods 30L and 30R. The rack and pinion device 28 converts the rotation of the pinion shaft 26 into a linear motion of the rack bar 32 in the lateral direction of the vehicle, The reverse conversion is performed. The tie rods 30L and 30R are pivotally attached to the tip of the rack bar 32 at the inner ends, and the outer ends of the tie rods 30L and 30R are knuckle arms 36L provided on carriers (not shown) of the left and right front wheels 34L and 34R. And 36R.

  Therefore, the rotational displacement and rotational torque of the steering wheel 14 are converted into the swing displacement and swing torque around the kingpin shaft (not shown) of the front wheels 34L and 34R by the steering unit 12 and the steering mechanism 20, and the front wheel 34L. And 34R. The swing displacement and swing torque around the kingpin shaft received by the left and right front wheels 34L and 34R from the road surface 38 are transmitted to the steering wheel 14 by the steering unit 12 and the steering mechanism 20 as rotational displacement and rotational torque, respectively. .

  The power steering device 10 includes a power steering unit 46 including an electric motor 42 and a conversion device 44. Although not shown in FIG. 1, the conversion device 44 includes a worm gear fixed to the rotating shaft of the electric motor 42 and a worm wheel fixed to the upper steering shaft 16. The rotational torque of the electric motor 42 is converted into the rotational torque of the upper steering shaft 16 by the conversion device 44 and transmitted to the upper steering shaft 16 as assist torque. Therefore, the power steering unit 46 applies assist torque to the upper steering shaft 16 of the steering unit 12.

  Further, the power steering device 10 has an electronic control device 50. The electronic control unit 50 functions as a control unit that controls the assist torque, as will be described in detail later, by controlling the rotational torque of the electric motor 42. The electronic control unit 50 receives signals indicating the steering angle θ and the steering torque T from a steering angle sensor 52 and a torque sensor 54 provided on the upper steering shaft 16, respectively. The electronic control device 50 also receives a signal indicating the vehicle speed V from the vehicle speed sensor 56.

  The electronic control device 50 includes a CPU, a ROM, a RAM, and an input / output port device, which are connected to each other via a bidirectional common bus. The ROM stores a control program, a map, and the like, which will be described later. You may remember. Further, the steering angle sensor 52 and the torque sensor 54 detect the steering angle θ and the steering torque T, respectively, with the case of steering in the left turn direction of the vehicle as positive.

  The microcomputer of the electronic control unit 50 calculates the target assist torque Tat according to the flowcharts shown in FIGS. 2 and 3 based on the steering angle θ, the steering torque T, and the vehicle speed V, and the power based on the target assist torque Tat. The steering unit 46 is controlled. Note that the control according to the flowchart shown in FIG. 2 is repeatedly executed at predetermined time intervals when an ignition switch (not shown) is on.

  First, in step 10, a signal indicating the steering angle θ detected by the steering angle sensor 52 is read. In step 20, based on the steering torque T and the vehicle speed V, from the map shown in FIG. 5, the target basic assist torque is increased as the magnitude of the steering torque T increases and decreases as the vehicle speed V increases. Tab is calculated.

  In step 30, based on the absolute value of the steering angle θ and the vehicle speed V, the target friction torque Tft is calculated from the map shown in FIG. As shown in FIG. 6, the target friction torque Tft is calculated so as to increase as the absolute value of the steering angle θ increases and to increase as the vehicle speed V increases.

  As shown in FIG. 10, when the vehicle speed V is higher than the first vehicle speed reference value Vc1 (positive constant), the self-aligning torque Tsat increases as the absolute value of the steering angle θ increases. Therefore, in order to reduce the steering force in the region where the steering angle θ is large and improve the steering stability, the target friction torque Tft is calculated as a larger value as the steering angle θ is larger as described above. Is done. Further, the self-aligning torque Tsat increases as the vehicle speed V increases. Therefore, the higher the vehicle speed V is, the lower the steering force required during medium / high speed traveling is improved and the steering stability is improved, and the target friction torque Tft is reduced as described above to reduce the steering resistance during low speed traveling. The higher V is, the larger the value is calculated.

  When step 30 is completed, the control proceeds to step 70 where the target steering angle θt is calculated according to the flowchart shown in FIG. Note that the target steering angle θt and the target additional friction torque Tct described later are also calculated with the left turn direction being positive.

In step 80, the target additional friction torque Tct is calculated according to the following equation (1) based on the steering angle θ and the target steering angle θt. The gain K in the following equation (1) is a positive value and is the same as the gain K used in the calculation of the target steering angle θt in step 70 (see the description of step 73 described later). As can be seen from the following equation (1), the sign of the target additional friction torque Tct, that is, the direction of action thereof, is determined by the magnitude relationship between the steering angle θ and the target steering angle θt.
Tct = K (θt−θ) (1)

  In step 90, the target additional friction torque Tctf is subjected to low-pass filter processing to calculate the target additional friction torque Tctf after low-pass filter processing from which high-frequency noise components have been removed.

  Regarding the calculation of the target basic assist torque Tab and the target additional friction torque Tctf after the low-pass filter processing in the above steps 10 to 90, refer to Japanese Patent Application Laid-Open No. 2009-126244 concerning the application of the present applicant if necessary. .

  In step 100, it is determined whether or not the vehicle speed V is equal to or lower than a second vehicle speed reference value Vc2 (a positive constant smaller than the first vehicle speed reference value Vc1). When a positive determination is made, control proceeds to step 120, and when a negative determination is made, control proceeds to step 110.

  As shown in FIG. 10, the self-aligning torque Tsat when the absolute value of the steering angle θ is the maximum value θmax allowed by the steering mechanism 20 decreases as the vehicle speed V decreases. The second vehicle speed reference value Vc2 is a vehicle speed at which the self-aligning torque Tsat becomes 0 when the absolute value of the steering angle θ is the maximum value θmax. Therefore, the second vehicle speed reference value Vc2 may be obtained, for example, experimentally as the maximum value of the vehicle speed V at which the self-aligning torque Tsat becomes a negative value when the absolute value of the steering angle θ increases. Note that the range of the steering angle θ in which the self-aligning torque Tsat is a negative value is expanded toward the side closer to 0 as the vehicle speed V is lower. Therefore, the reference value θc (the steering angle θ at which the self-aligning torque Tsat becomes 0 when the vehicle speed V is equal to or less than the second vehicle speed reference value Vc2) decreases as the vehicle speed V decreases.

  In step 110, a map of gain Kt for correcting the target additional friction torque Tct is selected from the plurality of maps shown in FIG. 7 in accordance with the vehicle speed V, and gain based on the absolute value of the steering angle θ. Kt is calculated.

  In step 120, a map of gain Kt for correcting the target additional friction torque Tct is selected from the plurality of maps shown in FIG. 8 according to the vehicle speed V, and gain based on the absolute value of the steering angle θ. Kt is calculated.

  The gain Kt shown in FIG. 8 has a corrected target additional friction torque Tctf, which will be described later, which is the same as the sign inversion value of the negative self-aligning torque Tsat shown in FIG. It may be determined experimentally, for example, to be substantially the same as the value converted to a positive value.

  In step 130, the corrected target additional friction torque Tctfa is calculated as the product Tctf · Kt of the corrected target additional friction torque Tctfa and the gain Kt.

  In step 140, the target assist torque Tat is calculated as the sum Tab + Tctfa of the target basic assist torque Tab and the corrected target additional friction torque Tctfa.

  In step 150, the power steering unit 46 is controlled based on the target assist torque Ta so that the assist torque Ta of the power steering unit 46 becomes the target assist torque Ta.

  Next, the calculation of the target steering angle θt in step 70 will be further described with reference to the flowchart shown in FIG.

  First, in step 71, it is determined whether or not the initialization of the target steering angle θt has been completed, that is, whether or not this time is the first control. When an affirmative determination is made, control proceeds to step 73, and when a negative determination is made, control proceeds to step 72.

  In step 72, the target steering angle θt is initialized by setting the target steering angle θt to the current steering angle θ. Note that the initial value of the target steering angle θt may be zero.

  In step 73, the deviation upper limit Δ is calculated as the product Tft · K of the target friction torque Tft calculated in step 30 and the gain K. Since the target friction torque Tft and the gain K are positive values, the deviation upper limit value Δ is also a positive value. The gain K may be an arbitrary fixed value determined in consideration of the rigidity of the steering system. However, when the gain K is lower than the torsional rigidity of the portion of the steering system having the lowest rigidity (generally, the portion of the torsion bar incorporated in the upper steering shaft 16), the steering wheel 14 Even if the steering wheel is rotated, the steering angle of the steered wheel cannot be set to the steering angle corresponding to the target steering angle θt. Therefore, the gain K is preferably higher than the torsional rigidity of the part having the lowest rigidity of the steering system.

  In step 74, it is determined whether or not the steering angle θ is larger than the sum θt + Δ of the target steering angle θt and the deviation upper limit value Δ, that is, whether or not the target steering angle θt needs to be reduced and corrected. Done. When a negative determination is made, control proceeds to step 76, and when an affirmative determination is made, the target steering angle θt is corrected to a value θ−Δ obtained by subtracting the deviation upper limit value Δ from the steering angle θ in step 75. The

  In step 76, it is determined whether or not the steering angle θ is smaller than the difference θt−Δ between the target steering angle θt and the deviation upper limit value Δ, that is, whether or not the target steering angle θt needs to be increased. Is determined. When a negative determination is made, the control proceeds to step 80, and when an affirmative determination is made, the control is corrected to a value θ + Δ obtained by adding the deviation upper limit value Δ to the steering angle θ in step 77. The

  For the calculation of the target steering angle θt, refer to the above Japanese Patent Application Laid-Open No. 2009-126244 if necessary.

  As will be understood from the above description, in step 20, the target basic assist torque Tab as a basic control amount for reducing the driver's steering burden is calculated, and in steps 30 to 130, the steering feeling is improved. The corrected target additional friction torque Tctfa as a hysteresis control amount is calculated. In step 140, the target assist torque Tat is calculated as the sum of the target basic assist torque Tab and the corrected target additional friction torque Tctfa. In step 150, the power steering unit 46 is controlled based on the target assist torque Tat. The

  In particular, in a situation where the vehicle speed V is less than or equal to the reference value Vc2 and the self-aligning torque Tsat may be a negative value, an affirmative determination is made in step 100, and the map shown in FIG. Thus, the gain Kt is calculated. Further, in step 130, the corrected target additional friction torque Tctf is calculated as a product Tctf · Kt of the target additional friction torque Tctf after the low-pass filter processing and the gain Kt.

  As described above, the gain Kt shown in FIG. 8 is such that the corrected target additional friction torque Tctf is substantially the same as the sign inversion value of the negative self-aligning torque Tsat shown in FIG. Is set. Therefore, in a situation where the vehicle speed V is equal to or less than the reference value Vc2 and the absolute value of the steering angle θ is very large, which is equal to or greater than the reference value θc, it counters the negative self-aligning torque Tsat that urges the steering wheel 14 in the increased direction. Frictional torque can be generated. Therefore, in a situation where the vehicle speed is very low and the steering angle is very large, it is possible to prevent the self-aligning torque from becoming negative and increase the steering reaction force during steering. Thus, the steering feeling can be improved as compared with the conventional case.

  For example, as indicated by a two-dot chain line in FIG. 11, in a situation where the vehicle speed V is very low and the absolute value of the steering angle θ is very large, ie, the reference value θc or more, the self-aligning torque Tsat is a negative value. Corresponding to the above, the return torque Tre at the time of the increase is also a negative value. In other words, the return torque Tre acts in the increasing direction. Therefore, in the case of the conventional power steering apparatus, the return torque Tre changes as indicated by the broken line with respect to the steering indicated by the arrow.

  On the other hand, according to the first embodiment, since the negative self-aligning torque Tsat is canceled out by the friction torque, the return torque Tre at the time of increase in the region where the self-aligning torque Tsat becomes negative is 0. In other words, it is possible to avoid the return torque Tre acting in the direction of increasing. In the case of the first embodiment, the return torque Tre changes with respect to the steering indicated by the arrow, for example, as indicated by the solid line in FIG.

[Second Embodiment]
FIG. 4 is a flowchart showing an assist torque control routine in the second embodiment of the power steering apparatus 10 according to the present invention. In FIG. 4, the same step number as the step number shown in FIG. 2 is assigned to the same step as the step shown in FIG.

  In this second embodiment, when step 20 is complete, control proceeds to step 40. In step 40, as in step 100 of the first embodiment, it is determined whether or not the vehicle speed V is equal to or lower than the second reference value Vc2. When an affirmative determination is made, control proceeds to step 60, and when a negative determination is made, control proceeds to step 50.

  In step 50, a map for calculating the target friction torque Tft is selected from a plurality of maps shown in FIG. 6 based on the vehicle speed V, and based on the absolute value of the steering angle θ from the selected map. A target friction torque Tft is calculated. In this case, since the vehicle speed V is higher than the reference value Vc2, the map for the low vehicle speed is not selected from the plurality of maps shown in FIG.

  In step 60, a map for calculating the target friction torque Tft is selected from a plurality of maps shown in FIG. 9 based on the vehicle speed V, and based on the absolute value of the steering angle θ from the selected map. A target friction torque Tft is calculated. Note that, in the plurality of maps shown in FIG. 9, the sign of the negative self-aligning torque Tsat shown in FIG. 10 is inverted to a positive value in a region where the absolute value of the steering angle θ is larger than the reference value θc. Corresponds to the specified value.

  Steps 70 to 90 and 150 are executed in the same manner as steps 70 to 90 and 150 of the first embodiment, respectively, and when step 90 is completed, the control proceeds to step 140.

  In step 140, the target assist torque Tat is calculated as the sum Tab + Tctf of the target basic assist torque Tab and the target additional friction torque Tctf after the low pass filter process.

  As will be understood from the above description, according to the second embodiment, in step 20, the target basic assist torque Tab as a basic control amount for reducing the driver's steering burden is calculated. In steps 40 to 90, a target additional friction torque Tctf after low pass filter processing as a hysteresis control amount for improving steering feeling is calculated. Further, in step 140, the target assist torque Tat is calculated as the sum of the target basic assist torque Tab and the target additional friction torque Tctf after the low pass filter processing. In step 150, the power steering unit 46 is operated based on the target assist torque Tat. Be controlled.

  In particular, in a situation where the vehicle speed V is less than or equal to the reference value Vc2 and the self-aligning torque Tsat may be a negative value, an affirmative determination is made in step 40, and the map shown in FIG. Thus, the target friction torque Tft is calculated. Further, in steps 70 and 80, the target additional friction torque Tct is calculated based on the target friction torque Tft. In step 90, the target additional friction torque Tctf is low-pass filtered to calculate the final target additional friction torque Tctf. Is done.

  As described above, in the plurality of maps shown in FIG. 9, the negative self-aligning torque Tsat shown in FIG. 10 is a positive value in a region where the absolute value of the steering angle θ is larger than the reference value θc. Corresponds to the value whose sign is inverted. Therefore, as in the case of the first embodiment, in a situation where the vehicle speed V is equal to or less than the reference value Vc2 and the absolute value of the steering angle θ is very large, which is equal to or greater than the reference value θc, the steering wheel 14 is increased. It is possible to generate a friction torque against the negative self-aligning torque Tsat. Therefore, in a situation where the vehicle speed is very low and the steering angle is very large, it is possible to prevent the self-aligning torque from becoming negative and increase the steering reaction force during steering. Thus, the steering feeling can be improved as compared with the conventional case.

  In addition, according to 1st and 2nd embodiment, the magnitude | size of the steering torque T becomes large at the time of switchback steering by increasing a friction torque. However, since the magnitude of the target basic assist torque Tab increases in response to the increase in the magnitude of the steering torque T, the driver's steering burden at the time of switchback steering does not increase excessively.

  Although the present invention has been described in detail with respect to specific embodiments, the present invention is not limited to the above-described embodiments, and various other embodiments are possible within the scope of the present invention. This will be apparent to those skilled in the art.

  For example, in the above-described embodiment, the target assist torque Tat is the target basic assist torque Tab and the friction control amount (the corrected target additional friction torque Tctf in the first embodiment, after the low-pass filter processing in the second embodiment). And the target additional friction torque Tctf). However, as long as the target assist torque Tat includes the friction control amount, the target assist torque Tat is a value including a damping control amount for attenuating a change in steering torque vibration and / or a return control amount for returning the steering wheel 14 to the neutral position. It may be calculated.

  DESCRIPTION OF SYMBOLS 10 ... Power steering apparatus, 12 ... Steering unit, 14 ... Steering wheel, 20 ... Steering mechanism, 46 ... Power steering unit, 50 ... Electronic control unit, 52 ... Steering angle sensor, 54 ... Torque sensor, 56 ... Vehicle speed sensor

Claims (1)

The target friction torque is determined so that the magnitude decreases as the steering angle increases, within a range where the self-aligning torque acting on the steered wheels decreases as the steering angle increases. In a power steering device that applies a friction torque to a steering unit based on the target friction torque,
When the vehicle speed is a vehicle speed at which the self-aligning torque becomes a negative value when the magnitude of the steering angle is equal to or greater than a reference value, the magnitude of the steering angle increases within a range equal to or greater than the reference value. A power steering apparatus configured to determine the target friction torque so as to increase in size.

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