JP2016155418A - Steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve a good steering feeling by reducing flutter vibrations to be inputted to a steering handle.SOLUTION: A rack supporting mechanism 20 stored in a guide housing 7b formed in a rack shaft housing 7 has an adjust spring 24 that energizes a rack shaft guide 22 by set pressure F0 and an adjust piston 25 that contacts a backside of the adjust spring 24; and when a rack assist pressure control unit 36 determines that a steering handle 4 is in the vicinity of a neutral position, supplies assist pressure Fr to a hydraulic chamber 7e formed in the guide housing 7b to assist pressing force against a rack shaft 8 of the rack shaft guide 22. This causes friction force μ between the rack shaft 8 and a pinion 5a to increase and flutter vibrations to be inputted to the steering handle 4 to be reduced, so as to achieve a good steering feeling.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a steering device that reduces flutter vibration that is reversely input to a rack shaft housing, rattling noise generated at a meshing portion between a rack and a pinion, and the like.

  External forces including various vibration components are reversely input to the steering system while the vehicle is running. Such reverse inputs are transmitted to the steering shaft via the rack shaft and the steering gear box that constitute the steering device. This causes a so-called steering vibration.

  Typical examples of the steering vibration include flutter vibration and rattling noise. The flutter vibration is a minute vibration in which the steering handle is swung in the circumferential direction in small increments due to tire imbalance, and appears remarkably in high-speed running. On the other hand, the rattling noise is a hammering sound caused by backlash at the meshing portion of the rack and the pinion due to vibrations reversely input from the road surface when traveling on a rough road.

  Since this flutter vibration and rattling noise give the driver an unpleasant feeling, various techniques for reducing it have been proposed. A typical technique is to suppress the rattling noise by applying high friction to the axial movement of the rack shaft in the steering gear box or the rotation of the pinion shaft, and steering with flutter vibration. What suppresses transmission to the shaft side is known.

  However, if the friction in the steering gear box is increased, the return of the steering wheel is deteriorated, so that it is necessary to perform tuning for each vehicle type, and complicated work is required.

  As a countermeasure against this, it is conceivable to perform return control of the steering wheel by the electric power steering device, but there is a possibility that the normal steering feeling is deteriorated.

  On the other hand, for example, in Patent Document 1 (Japanese Patent Application Laid-Open No. 2005-219539), when a frequency component due to flutter vibration is detected in high-speed traveling, an assist signal for canceling the frequency component is supported by a motor that drives the electric power steering. A technique is disclosed in which the electric power steering is attenuated by adding to the current and driving the electric power steering in a direction in which flutter vibration cancels.

JP 2005-219539 A

  However, in the technique disclosed in the above-mentioned document, flutter vibration is attempted to be attenuated by resonating the electric power steering device in the opposite phase, but this cancel control detects frequency components due to flutter vibration. Therefore, control delay is likely to occur, and there is a limit to efficiently attenuating flutter vibration. Furthermore, since it cannot be applied to a hydraulic power steering device, there is a problem of poor versatility.

  Furthermore, with the technique disclosed in the above-described document, it is not possible to suppress the rattling noise that occurs during rough road traveling or the like.

  In view of the above circumstances, the present invention can reduce rattling noise and flutter vibration transmitted to the steering handle with good responsiveness, and can obtain a good steering feeling. An object of the present invention is to provide a steering apparatus that can be applied to the power steering apparatus of the present invention and can obtain high versatility.

  The present invention includes a pinion shaft connected to a steering handle and having a pinion, a rack shaft having a rack meshed with the pinion, a rack shaft housing that houses the rack shaft and supports the rack shaft slidably, And a rack shaft support mechanism having a biasing member that presses the rack shaft toward the pinion with a preset set pressure, and further includes a rack assist pressure that presses the biasing member in the rack axis direction. And a rack assist pressure calculating means for setting the assist pressure generated by the assist means based on the parameter detected by the driving condition detecting means for detecting the driving condition of the vehicle.

  According to the present invention, the rack assist means for applying the rack assist pressure to the biasing member that presses the rack shaft toward the pinion side provided in the rack shaft support mechanism is provided, and this rack assist pressure is set in the driving state of the vehicle. Since it is set based on the parameter detected by the operating state detecting means for detecting the rack, by generating the rack assist pressure in an area where flutter vibration and rattling noise are likely to occur, the pressing force on the rack shaft pinion is reduced. As a result, the rattling noise and flutter vibration can be reduced with good responsiveness, and a good steering feeling can be obtained.

  Further, since the structure is such that the urging member is assisted, it can be applied to both electric and hydraulic power steering devices, and high versatility can be obtained.

Overall schematic diagram of the power steering device when the steering handle is in a neutral state II-II sectional view of FIG. Configuration diagram of rack assist pressure control unit Characteristic diagram showing friction force set corresponding to the steering angle indicating the amount of movement of the rack shaft The flowchart which shows the rack assist pressure control routine by 1st Example. (A) is a conceptual diagram of a pinion meshing rack position setting table, (b) is a conceptual diagram of a rack assist pressure setting table. Flowchart showing a rack assist pressure control routine according to the second embodiment. (A) is an explanatory view of rack assist pressure set according to the rack load, and (b) is a conceptual diagram of the rack assist pressure setting table. Flowchart showing a rack assist pressure control routine according to the third embodiment. (A) is a conceptual diagram of a pinion meshing rack position correction gain setting table, (b) is a conceptual diagram of a torque correction gain setting table, and (c) a characteristic diagram showing a change in frictional force with respect to a steering angle. Flowchart showing a rack assist pressure control routine according to the fourth embodiment. (A) is a conceptual diagram of a rack position correction gain setting table, (b) is a conceptual diagram of a rack load correction gain setting table, and (c) is a characteristic diagram showing a change in frictional force with respect to a steering angle. Flowchart showing a rack assist pressure control routine according to the fifth embodiment. (A) is a conceptual diagram of a lateral acceleration correction gain setting table, (b) is a conceptual diagram of a wheel speed correction gain setting table, and (c) is a characteristic diagram showing a change in frictional force with respect to lateral acceleration.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the present embodiment, an electric power steering device will be described as an example of the power steering device.

  As shown in FIG. 1, the electric power steering apparatus 1 has a steering shaft 2 rotatably supported on a vehicle body frame via a steering column (not shown), and one end of the electric power steering device 1 extends toward the driver's seat. The other end is extended to the engine room side. A steering handle 4 is fixed to the end of the steering shaft 2 on the driver's seat side, and a steering pinion shaft (hereinafter referred to as “pinion”) is provided on a steering gear box 6 described later at an end extending to the engine room side. A pinion housing 7a that rotatably supports a shaft 5) is provided.

  A steering gear box 6 extending in the vehicle width direction left and right is disposed in the engine room. The steering gear box 6 has a rack shaft housing 7, and a rack shaft 8 is supported in the rack shaft housing 7 so as to be slidable back and forth in the axial direction. Further, the rack 8a formed on the rack shaft 8 is engaged with the pinion 5a formed on the pinion shaft 5 to form a rack and pinion type steering gear mechanism.

  The left and right ends of the rack shaft 8 protrude from the end of the rack shaft housing 7, and a tie rod 9 is connected to the end, and a tie rod end 10 integrated with the tie rod 9 is connected to the ball joint 11. The knuckle arm 13 extends from the steering knuckle 12. The steering knuckle 12 rotatably supports a steering wheel (left and right front wheels) 14 and is supported by a vehicle body frame (not shown) via a front arm 16 so as to be steerable. The connecting portion between the rack shaft 8 and the tie rod 9 is covered with a dust boot 21 attached to the rack shaft housing 7.

  An electric motor 19 is connected to the pinion shaft 5 through an assist transmission mechanism 18, and the steering torque applied to the steering handle 4 is assisted by the electric motor 19. Accordingly, when the driver operates the steering handle 4 to rotate the steering shaft 2 and the pinion shaft 5, the rack shaft 8 moves in the left-right direction by the rotation of the pinion shaft 5, and the steering knuckle 12 rolls by the movement. Then, the steered wheel 14 is steered in the left-right direction, and the steering torque at that time is assisted by the electric motor 19.

  Further, the rack 8a is provided at a position deviated to one side with respect to the rack shaft 8 (the right side in FIG. 1). When the steering handle 4 is in the neutral position (steering angle = 0), the center of the rack 8a is approximately It is meshed with a pinion 5 a provided on the pinion shaft 5. A rack shaft support mechanism 20 is provided on the side facing the pinion 5a with the rack shaft 8 interposed therebetween, in the upper part in the figure. The rack shaft support mechanism 20 supports the rack shaft 8 so as to be slidable in the axial direction, and presses the rack 8a against the pinion 5a.

  As shown in FIG. 2, the rack shaft support mechanism 20 is mounted on a rack shaft guide housing (hereinafter abbreviated as “guide housing”) 7 b that is formed to protrude from the rack shaft housing 7. The guide housing 7b is formed at a position facing the pinion 5a with the rack shaft 8 interposed therebetween.

  In this guide housing 7b, a rack shaft guide accommodating chamber 7d and a hydraulic chamber 7e as an operating chamber are formed in a concentric cylindrical communication with each other, and the inner diameter of the hydraulic chamber 7e is the inner diameter of the rack shaft guide accommodating chamber 7d. Accordingly, a step portion 7f is formed at the boundary between the rack shaft guide accommodating chamber 7d and the hydraulic chamber 7e. The rack shaft guide housing chamber 7d is opened to the rack shaft 8 side, while the base end of the hydraulic chamber 7e is opened to the outside.

  The rack shaft support mechanism 20 has a cylindrical rack shaft guide 22, and the rack shaft guide 22 is housed in the rack shaft guide housing chamber 7 d so as to be able to advance and retract. The rack shaft guide 22 is formed with a rack shaft sliding contact surface 22a having a semicircular cross section for supporting the rack shaft 8 so as to be slidable back and forth in the axial direction. Note that a lubricant such as grease is filled between the rack shaft sliding contact surface 22 a and the surface of the rack shaft 8.

  Further, a spring accommodating recess 22b is formed on the surface of the rack shaft guide 22 opposite to the rack shaft sliding contact surface 22a, and a seal groove 22c is formed on the circumference of the rack shaft guide 22. A seal ring (not shown) such as an O-ring (not shown) is attached to the seal groove 22c, and the sealing performance between the outer periphery of the rack shaft guide 22 and the inner wall of the rack shaft guide storage chamber 7d is maintained.

  Further, an assist piston 25 is interposed between the rack shaft guide 22 and the stepped portion 7f of the rack shaft guide accommodating chamber 7d. A seal groove 25a is formed on the outer periphery of the assist piston 25, and a seal member (not shown) that seals between the inner wall of the rack shaft guide storage chamber 7d is mounted in the seal groove 25a.

  Further, an adjustment spring 24 as an urging member is interposed between the assist piston 25 and a spring accommodating recess 22 b formed in the rack shaft guide 22. The assist piston 25 moves back and forth according to the differential pressure between the hydraulic pressure introduced into the hydraulic chamber 7e and the spring pressure of the adjustment spring 24. When the spring pressure is higher than the hydraulic pressure, the assist piston 25 moves to the hydraulic chamber 7e side and is hooked on the stepped portion 7f.

  The rack shaft guide 22 urges the rack shaft 8 in the direction of the pinion 5a by the rack shaft sliding contact surface 22a formed on the rack shaft guide 22 by the urging force of the adjusting spring 24. In a state where the assist piston 25 is hooked on the stepped portion 7f, the adjustment spring 24 is set so as to press the rack shaft 8 through the rack shaft guide 22 with a preset set pressure F0 (see FIG. 4). Yes. Accordingly, even when no hydraulic pressure is supplied to the hydraulic chamber 7e, the rack shaft 8 is pressed in the direction of the pinion 5a by the urging force (set pressure F0) from the rack shaft guide 22.

  A sealing cap 23 is fastened and fixed to the opening of the hydraulic chamber 7e via a seal member 26. The sealing cap 23 is provided with an oil passage 23a having one end opened to the hydraulic chamber 7e and the other end opened outward, and is fixed to the outer opening of the oil passage 23a. One end of an oil passage 32 provided in a hydraulic assist circuit 31 as rack assist means is communicated with the hydraulic nipple 27. The hydraulic assist circuit 31 regulates the hydraulic pressure supplied to the hydraulic chamber 7e and applies assist pressure to the assist piston 25. The other end of the oil passage 32 faces an oil pan 33 that stores oil. An oil pump 34 is interposed downstream thereof.

  A drain oil passage 32a whose downstream end faces the oil pan 33 is connected to the middle of the oil passage 32 provided on the downstream side of the oil pump 34, and a pressure regulating variable valve 35 is connected to the drain oil passage 32a. Is intervening. The variable valve 35 is a normally open type, and its opening degree is controlled by a drive signal output from the rack assist pressure control unit 36 shown in FIG. 2, and is supplied from the oil pump 34 to the hydraulic chamber 7e of the rack shaft support mechanism 20. The hydraulic pressure is adjusted.

  As shown in FIG. 3, the rack assist pressure control unit 36 is mainly configured by a well-known microcomputer having a CPU, a ROM, a RAM, an input interface, an output interface, and the like (not shown). An operation state as an operation state detection means, which is a general term for various sensors that detect the operation state of the vehicle required when setting the rack assist pressure for the rack shaft 8 on the input interface side of the rack assist pressure control unit 36. A detection sensor 37 is connected. A variable valve 35 is connected to the output interface side.

  The rack assist pressure control unit 36 first obtains the steering angle θs based on various parameters detected by the driving state detection sensor 37, and the steering angle θs is within a predetermined region on the left and right sides of the neutral position (θs = 0). In some cases, the variable valve 35 is driven to supply hydraulic pressure to the hydraulic chamber 7e of the rack shaft support mechanism 20 to assist the urging force against the rack shaft guide 22.

  When the steering handle 4 is in the vicinity of the neutral position, such as on a straight road on a highway, the driver only feels the steering handle 4 lightly, so flutter vibration is likely to be felt. On the other hand, when avoiding a front obstacle or making a sudden lane change during high-speed driving, the driver turns the steering wheel against the restoring force (self-aligning torque) applied to the steering wheel 4, so flutter vibration is generated. I don't feel strong.

  On the other hand, rattling noise is generated when traveling on rough roads, and is hardly generated when traveling on roads such as paved roads.

  Therefore, the range in which the driver feels flutter vibration is limited to a steering angle region in which the steering handle 4 swings left and right in straight travel, and the rattling noise can be dealt with during rough road travel.

  In the present embodiment, the hydraulic pressure supplied from the oil pump 34 to the hydraulic chamber 7e of the rack shaft support mechanism 20 is regulated by the variable valve 35, and as shown in FIG. A rack assist pressure Fr (= basic rack assist pressure F1) is applied in a region (θL−θR) where the driver feels flutter vibration strongly with the neutral position (θs = 0) as the center. As a result, in the steering gear box 6, the frictional force μ when moving the rack shaft 8 in the axial direction increases, and transmission of flutter vibration to the steering handle 4 side is reduced.

  In this embodiment, for the sake of convenience, the left steering of the steering handle 4 is represented as + and the right steering is represented as-, and the above-described region (θL-θR) is represented as a neutral region (θL-θR) for convenience. ). The neutral region (θL−θR) is a region in which the driver feels flutter vibration strongly for each vehicle type by simulation or the like.

  On the other hand, as a countermeasure against rattling noise, first, a rough road is determined, and when it is determined that the road is rough, a rack assist pressure Fr to be applied to the rack shaft 8 is set according to the traveling state, and the rack assist pressure Fr is When the basic rack assist pressure F1 is set, the rack shaft guide 22 is strongly pressed against the pinion 5a over the set pressure F0.

  As described above, according to the present embodiment, the region where the flutter vibration and the rattling noise are likely to be generated is determined by the parameters such as the vehicle speed Vs and the rack position θs. Therefore, the flutter transmitted to the steering handle 4 is determined. Vibration and rattling noise can be reduced with good responsiveness. In addition, since the rack assist pressure Fr is applied to the rack shaft guide 22 to suppress the transmission of flutter vibration, the present invention can be applied to both electric and hydraulic power steering devices.

  By the way, there are various parameters for detecting a region where the driver strongly feels flutter vibration and rattling noise, and the calculation processing is different for each parameter. In the following, assist control corresponding to the parameter to be detected will be specifically described according to each flowchart for each embodiment.

[First embodiment]
5 and 6 show a first example of the present embodiment. In this embodiment, a vehicle speed sensor that detects the vehicle speed Vsp and a steering angle sensor that detects the steering angle θs of the steering handle 4 are employed as the driving state detection sensor 37, and the rack shaft 8 is based on the parameters detected by these sensors. Is set to the rack assist pressure Fr to be applied.

  The rack assist pressure control unit 36 according to this embodiment sets the rack assist pressure Fr according to the rack assist pressure control routine shown in FIG. In this routine, first, in step S1, the vehicle speed Vsp of the host vehicle detected by the vehicle speed sensor and the steering angle θs of the steering handle 4 detected by the steering angle sensor are read.

  Next, in step S2, the vehicle speed Vsp is compared with a preset high speed determination vehicle speed Vsph. The high speed determination vehicle speed Vsph is obtained in advance based on a simulation or the like in a region where flutter vibration occurs during straight traveling, and is set to about 100 to 140 [Km / h], for example.

  If the vehicle speed Vsp is equal to or higher than the high speed determination vehicle speed Vsph (Vsph ≦ Vsp), it is determined that it is necessary to take measures against flutter vibration, and the process proceeds to step S3. If the vehicle speed Vsp is less than the high speed determination vehicle speed Vsph (Vsph> Vsp), it is determined that it is not necessary to take measures against flutter vibration, and the routine is exited as it is.

  Thereafter, when the routine proceeds to step S3, the amount of movement from the pinion meshing rack position Pr, that is, the neutral position of the rack shaft 8, is referred to the pinion meshing rack position setting table shown in FIG. Ask for. The processing in this step corresponds to the rack position calculation means of the present invention.

  The pinion meshing rack position Pr is the rack position where the pinion 5a is meshed, that is, the rack position where the rack shaft sliding contact surface 22a of the rack shaft guide 22 is in sliding contact, and the neutral position (θs = 0) is a reference. Is substantially proportional to the steering angle θs. Therefore, the pinion meshing rack position Pr can also be obtained by a linear expression from the steering angle θs and a preset inclination.

  Next, the process proceeds to step S4, where the rack assist pressure Fr is set based on the pinion meshing rack position Pr with reference to the rack assist pressure table shown in FIG. The processing in this step corresponds to the rack assist pressure calculating means of the present invention.

  In this rack assist pressure table, a neutral area (PrL-PrR), which is a rack position area where the driver feels flutter vibration strongly with the neutral position (Pr = 0) of the rack 8a as the center, is previously determined for each vehicle type by simulation or the like. Is set to seek. Accordingly, the neutral region (PrL-PrR) represented by the amount of movement of the rack shaft 8 corresponds to the neutral region (θL-θR) described above when converted to the handle angle θs.

  Further, the rack assist pressure Fr in the neutral region (PrL-PrR) is set to the basic rack assist pressure F1. This basic rack assist pressure F1 is a pressure higher than the set pressure F0 that presses the rack 8a of the rack shaft 8 against the pinion 5a to such an extent that the driver does not feel flutter vibration strongly. Is set.

  Further, the rack assist pressure Fr in the region deviating from the neutral region (PrL-PrR) is set to zero. Therefore, when Fr = 0, no drive signal is output from the rack assist pressure control unit 36 to the variable valve 35, the variable valve 35 is normally open, and the rack shaft guide 22 is set at the set pressure F0 from the adjustment spring 24. The rack shaft 8 is pressed.

  By pressing the rack shaft 8 against the pinion 5a with the basic rack assist pressure F1, it is possible to reduce transmission of flutter vibration input to the steering gear box 6 to the steering handle 4 side.

  Next, the process proceeds to step S5, a drive signal (not output when Fr = 0) corresponding to the rack assist pressure Fr (= 0 or F1) set in step S4 is output to the variable valve 35, and the routine is exited.

  The variable valve 35 adjusts the amount of oil returned from the drain oil passage 32a to the oil pan 33 in accordance with the drive signal from the rack assist pressure control unit 36, for example, when a drive signal corresponding to the basic rack assist pressure F1 is input. The hydraulic pressure (basic rack assist pressure F1) supplied to the hydraulic chamber 7e of the rack shaft support mechanism 20 is generated.

  Then, as shown in FIG. 2, the hydraulic pressure of the basic rack assist pressure F1 flows into the hydraulic chamber 7e of the rack shaft support mechanism 20, presses the assist piston 25, and the adjustment spring 24 is moved in advance via the assist piston 25. The difference (F1-F0) from the set pressure F0 that has been set is compressed, and the spring pressure of the adjustment spring 24 is increased to the basic rack assist pressure F1.

  As a result, when the position of the rack 8a formed on the rack shaft 8 with respect to the pinion 5a is in a neutral region (PrL-PrR) in which the driver strongly feels flutter vibration, the rack 8a of the rack shaft 8 becomes the pinion 5a. On the other hand, since it is strongly pressed by the basic rack assist pressure F1, as shown in FIG. 4, the frictional force μ when trying to move the rack shaft 8 in the axial direction increases. Therefore, it is difficult for flutter vibration from the left and right steering wheels 14 to be transmitted to the steering handle 4, and it is necessary to grip the steering handle 4 firmly even when the vehicle is traveling on a straight road on a highway at high speed. There is no, and a good steering feeling can be obtained. Since the frictional force μ depends on the spring pressure for compressing the adjustment spring 24, the optimum frictional force μ can be obtained for each vehicle type by adjusting the basic rack assist pressure F1.

  On the other hand, when driving on an expressway, the steering handle 4 was cut beyond the neutral region (PrL-PrR) to turn on a curve with a relatively small curvature such as an obstacle avoidance operation, a sudden lane change, or a junction. In this case, the rack assist pressure Fr is set to 0 in step S4. Therefore, the variable valve 35 is normally opened, the hydraulic pressure in the hydraulic chamber 7e is discharged from the drain oil passage 32a, and the assist piston 25 is retracted by the urging force of the adjustment spring 24, and is hooked on the step portion 7f. The spring pressure of 24 is returned to the set pressure F0. As a result, the frictional force μ is returned to the normal value, so that the return after turning the steering handle 4 is not hindered, and in this case, a good steering feeling can be obtained.

  Thus, in the present embodiment, the spring pressure in the neutral region (PrL-PrR) in which the driver strongly feels flutter vibration is set to the basic rack assist pressure F1 that is higher than the set pressure F0. Therefore, the steering gear box 6 The internal frictional force μ is increased, and flutter vibration that is reversely input from the steering wheel 14 side to the steering gear box 6 is hardly transmitted to the steering handle 4 side. On the other hand, when the steering handle 4 is turned beyond the neutral region (PrL-PrR), the spring pressure of the adjustment spring 24 is returned to the set pressure F0.

  As a result, even if flutter vibration occurs while traveling on a highway at high speed, it is difficult to transmit the vibration to the steering wheel 4 in straight traveling, and a good steering feeling can be obtained. When a proper steering operation is performed, the spring pressure returns to the set pressure F0, so that the steering wheel return is not hindered and a good steering feeling can be obtained.

  Further, since the basic rack assist pressure F1 is generated by hydraulic pressure, the basic rack assist pressure F1 can be finely adjusted for each vehicle even after shipment. Furthermore, since the hydraulic control circuit is provided in the rack shaft support mechanism 20, it can be applied to both electric and hydraulic power steering devices, and high versatility can be obtained.

  In the present embodiment, the amount of movement from the pinion meshing rack position Pr, that is, the neutral position of the rack shaft 8, is not limited to the steering angle θs detected by the steering angle sensor, but the rotation angle for detecting the rotation angle of the electric motor 19. You may make it obtain | require based on the parameter detected with the displacement sensor which detects the stroke (movement amount) of a sensor or the rack shaft 8. FIG. Therefore, each of these sensors corresponds to the movement amount detecting means of the present invention.

[Second Embodiment]
7 and 8 show a second example of the present embodiment. In the first embodiment described above, the rack assist pressure Fr is set based on the pinion meshing rack position Pr. However, in this embodiment, based on the load (rack load) Lr generated when the rack shaft 8 is slid, The corresponding rack position is estimated and the rack assist pressure Fr is set.

  When the driver turns the steering handle 4 at high speed, the rack load Lr shows a large value because the self-aligning torque from the steering wheel 14 side is applied to the rack shaft 8 as a reaction force. On the other hand, in a state where the vehicle is traveling at a high speed on a straight path, the rack load Lr is small because the steering handle 4 is in a substantially neutral state.

  Therefore, by detecting the rack load Lr, a neutral region (θL−θR) as shown in FIG. 4 can be estimated. In this embodiment, a vehicle speed sensor that detects the vehicle speed Vsp and a load sensor that detects a load (rack load) Lr generated when the rack shaft 8 is slid are used as the driving state detection sensor 37. Based on the detected parameter, the rack assist pressure Fr to be applied to the rack shaft guide 22 is set. The load sensor for detecting the rack load Lr may directly detect the load applied to the rack shaft 8, but is obtained by detecting the shaft torque acting on the steering shaft 2 and the pinion shaft 5. There may be.

  The rack assist pressure control unit 36 according to this embodiment sets the rack assist pressure Fr according to the rack assist pressure control routine shown in FIG. In this routine, first, in step S11, the vehicle speed Vsp of the host vehicle detected by the vehicle speed sensor and the rack load Lr detected by the load sensor are read.

  Next, the process proceeds to step S12, where the vehicle speed Vsp is compared with a preset high speed determination vehicle speed Vsph. When the vehicle speed Vsp is equal to or higher than the high speed determination vehicle speed Vsph (Vsph ≦ Vsp), it is determined that it is necessary to take flutter vibration countermeasures. Proceed to step S13. If the vehicle speed Vsp is less than the high speed determination vehicle speed Vsph (Vsph> Vsp), it is determined that it is not necessary to take measures against flutter vibration, and the routine is exited as it is.

  In step S13, the rack load Lr is compared with a preset neutral region determination threshold Lo. Incidentally, the processing in this step corresponds to the rack load determining means of the present invention.

  As shown in FIG. 8A, the neutral region determination threshold Lo is based on the rack load Lr as to whether or not the rack position Pr meshed with the pinion 5a is in the neutral region (PrL-PrR). Is a threshold value to be determined. Since the load applied to the rack shaft 8 increases as the absolute value of the handle angle θs increases from the neutral position, the neutral region (PrL−PrR) is estimated based on the neutral region determination threshold Lo (absolute value). be able to. Therefore, the neutral region determination threshold Lo (absolute value) is set corresponding to the boundary of the neutral region (PrL-PrR).

  If Lr ≦ Lo, it is determined that the pinion meshing rack position Pr is in the neutral region (PrL-PrR), the process proceeds to step S14, and the rack assist pressure Fr is set to the basic rack assist pressure F1 (Fr ← F1). The process proceeds to step S16. On the other hand, when Lr> Lo, it is determined that the pinion meshing rack position Pr is out of the neutral region (PrL-PrR), the process branches to step S15, the rack assist pressure Fr is set to 0 (Fr ← 0), and step S16. Proceed to

  When the process proceeds from step S14 or step S15 to step S16, a drive signal corresponding to the rack assist pressure Fr is output to the variable valve 35, and the routine is exited.

  As a result, as in the first embodiment described above, the hydraulic pressure corresponding to the basic rack assist pressure F1 is supplied into the hydraulic chamber 7e of the rack shaft support mechanism 20 by the operation of the variable valve 35. On the other hand, when the rack assist pressure Fr is set to 0, the variable valve 35 is normally open, the hydraulic pressure in the hydraulic chamber 7e is drained, and the rack shaft guide 22 is moved to the rack shaft by the set pressure F0 of the adjustment spring 24. 8 is pressed toward the pinion 5a.

  Then, as shown in FIG. 8A, the neutral region partitioned by the neutral region determination threshold Lo on the rack shaft 8 becomes the basic rack assist pressure F1 higher than the set pressure F0, as shown in FIG. Further, the frictional force μ when the rack shaft 8 is moved in the axial direction increases. As a result, an increase in the frictional force μ makes it difficult for flutter vibration from the left and right steering wheels 14 to be transmitted to the steering handle 4, and a good steering feeling can be obtained.

  As described above, in this embodiment, the neutral position of the steering handle 4 is estimated based on the rack load. Therefore, in addition to the effects of the first embodiment described above, there is no need to detect the rack position and the steering angle. For example, if the rack load is detected using an existing shaft torque sensor that detects the shaft torque of the steering shaft 2, the cost can be reduced by sharing the parts.

  In this embodiment, the rack load Lr detected by the load sensor and the neutral region determination threshold Lo are compared to define the neutral region (PrL-PrR). Using an axial pressure sensor that detects the axial pressure of the tie rod 9 connected to the shaft 8, the neutral pressure (PrL−PrR) is determined by comparing the axial pressure detected by the axial pressure sensor with the neutral region determination threshold value. You may make it demarcate. Therefore, the load sensor and the axial pressure sensor correspond to the rack load detecting means of the present invention.

[Third embodiment]
9 and 10 show a third example of the present embodiment. In the first and second embodiments described above, when the steering handle 4 and the rack shaft 8 are in the neutral region (PrL-PrR), the rack assist pressure Fr is uniformly set to the basic rack assist pressure F1. However, in the present embodiment, the rack assist pressure Fr is variably set according to the operation state of the steering handle 4 of the driver.

  In the present embodiment, as the driving state detection sensor 37, a vehicle speed sensor for detecting the vehicle speed Vsp, a steering angle sensor for detecting the steering angle θs, and a steering torque Tq applied to the steering handle 4 from the shaft torque of the steering shaft 2 and the like are detected. A shaft torque sensor as a torque detecting means is employed, and a rack assist pressure Fr to be applied to the rack shaft guide 22 is set based on parameters detected by the sensors.

  The rack assist pressure control unit 36 according to this embodiment sets the rack assist pressure Fr according to the rack assist pressure control routine shown in FIG.

  In this routine, first, in step S21, the vehicle speed Vsp of the host vehicle detected by the vehicle speed sensor and the steering angle θs of the steering handle 4 detected by the steering angle sensor are read, and further the steering shaft 2 detected by the shaft torque sensor. Is read as steering torque Tq.

  Next, the process proceeds to step S22, where the vehicle speed Vsp is compared with a preset high speed determination vehicle speed Vsph. If the vehicle speed Vsp is equal to or higher than the high speed determination vehicle speed Vsph (Vsph ≦ Vsp), it is determined that flutter vibration countermeasures need to be taken. Proceeding to step S23, if the vehicle speed Vsp is less than the high speed determination vehicle speed Vsph (Vsph> Vsp), it is determined that it is not necessary to take countermeasures against flutter vibration, and the routine is directly exited.

  Proceeding to step S23, it is checked whether or not the steering angle θs is in the neutral region (θL−θR) shown in FIG. 4. If it is in the neutral region (θL−θR) (θR ≦ θs ≦ θL), step S24 is performed. Proceed to On the other hand, if it is out of the neutral region (θL−θR) (θs <θR or θL <θs), the process branches to step S25, the rack assist pressure Fr is set to 0 (Fr ← 0), and the process goes to step S29. Jump.

  When the process proceeds from step S23 to step S24, the pinion meshing rack position Pr is set based on the steering angle θs with reference to the pinion meshing rack position setting table shown in FIG. 6A of the first embodiment. The pinion meshing rack position Pr may be obtained by a linear expression from the steering angle θs and a preset inclination, as in the first embodiment.

  Next, the process proceeds to step S26, and based on the pinion meshing rack position Pr, the position correction gain corresponding to the rack position with which the pinion 5a meshes with reference to the pinion meshing rack position correction gain setting table shown in FIG. Set Gr. Note that the processing in steps S24 and S26 corresponds to the position correction gain calculation means of the present invention.

  In this pinion meshing rack position correction gain setting table, the position correction gain Gr at the neutral position is set to 0 [%], from which the steering angle increases as the amount of movement of the rack 8a meshing with the pinion 5a increases from side to side. Even when θs is in the neutral region (θL−θR), a position correction gain Gr that increases is set.

  Thereafter, the process proceeds to step S27, where the torque correction gain Gt is set based on the steering torque Tq with reference to the torque correction gain setting table shown in FIG. The process in step S27 corresponds to the torque correction gain calculation means of the present invention.

  This torque correction gain table has a characteristic in which a torque correction gain Gt that decreases as the absolute value of the steering torque Tq increases from 100 [%] when the steering torque Tq is 0 [Nm] is set. Therefore, when the driver turns the steering wheel 4, the torque correction gain Gt gradually becomes a low value. In addition, when the driver weakens the gripping force on the steering handle 4 at the time of switching back, the steering handle 4 is returned with a restoring force (self-aligning torque), so that the steering torque Tq becomes almost 0 [%]. still. The torque correction gain Gt is set to 0 [%] near the left and right boundaries of the torque correction gain Gt.

Next, the process proceeds to step S28, where the rack assist pressure Fr is set to
Fr ← F1-ΔFr · Gr · Gt
Calculate from Here, ΔFr is the rack assist pressure change amount, and is calculated from, for example, the difference between the rack assist pressures Fr obtained until the previous calculation. The processing in this step corresponds to the rack assist pressure calculating means of the present invention.

  Thereafter, when the process proceeds from step S25 or step S28 to step S29, a drive signal corresponding to the rack assist pressure Fr is output to the variable valve 35, and the routine is exited.

  In this embodiment, the basic rack assist pressure F1 is set as a basic value, and the rack assist pressure change amount ΔFr is subtracted by a gain-corrected value to set the rack assist pressure Fr. Therefore, FIG. As shown in FIG. 4, when the driver turns the steering handle 4 in any direction from the neutral position, the position correction gain Gr is 0 [%] at the first neutral position, so the rack assist pressure Fr is the basic rack assist. It is set by the pressure F1 (Fr ← F1). Thereafter, when the steering handle 4 is steered, the rack assist pressure Fr decreases according to the correction gains Gr and Gt set at that time. Thereafter, when the absolute value of the steering torque Tq exceeds a predetermined value, the torque correction gain Since Gt is set to 0 [%], the rack assist pressure Fr is set again at the basic rack assist pressure F1 (Fr ← F1).

  On the other hand, if the driver turns the steering wheel 4 and then loosens the gripping force, the steering torque Tq becomes 0 [%] and the torque correction gain Gt becomes 100 [%]. As shown by the broken line in FIG. 10 (c), the pressure is lowered to the vicinity of the set pressure F0. As a result, even when the steering handle 4 is in the neutral region (θL-θR), the steering wheel return is not hindered and a good steering feeling can be obtained.

  The pinion meshing rack position Pr may be obtained from the rotation angle of the electric motor 19 or the stroke (movement amount) of the rack shaft 8 as in the first embodiment. It corresponds to the movement amount detection means.

[Fourth embodiment]
11 and 12 show a fourth example of the present embodiment. In the third embodiment described above, the driver's steering situation is detected based on the pinion meshing rack position Pr and the steering torque Tq, but in this embodiment, the driver's steering situation and the rack shaft 8 are detected. The rack assist pressure Fr is variably set based on the applied load.

  That is, the load applied to the rack shaft 8 from the steered wheels 14 is detected while the driver's steering situation and the load applied to the rack shaft 8 are detected and the driver is steering at a fixed steering wheel angle. Detects a state that changes in vibration. And the rack assist pressure Fr according to it is set. In this embodiment, as the driving state detection sensor 37, the same sensors as those of the third embodiment described above are employed.

  The rack assist pressure control unit 36 according to this embodiment sets the rack assist pressure Fr according to the rack assist pressure control routine shown in FIG. In this routine, first, in step S31, the vehicle speed Vsp of the host vehicle detected by the vehicle speed sensor and the steering angle θs of the steering handle 4 detected by the steering angle sensor are read, and further the steering shaft 2 detected by the shaft torque sensor. Is read as steering torque Tq.

  Next, the process proceeds to step S32, where the vehicle speed Vsp is compared with a preset high speed determination vehicle speed Vsph. If the vehicle speed Vsp is equal to or higher than the high speed determination vehicle speed Vsph (Vsph ≦ Vsp), it is determined that it is necessary to take measures against flutter vibration. The process proceeds to step S33, and if the vehicle speed Vsp is less than the high speed determination vehicle speed Vsph (Vsph> Vsp), it is determined that it is not necessary to take countermeasures against flutter vibration, and the routine is directly exited.

  Proceeding to step S33, it is determined whether or not the steering angle θs is in the neutral region (θL−θR) shown in FIG. 4. If it is in the neutral region (θL−θR) (θR ≦ θs ≦ θL), step S34 is performed. Proceed to On the other hand, if it is out of the neutral region (θL−θR) (θs <θR or θL <θs), the process branches to step S35, the rack assist pressure Fr is set to 0 (Fr ← 0), and the process goes to step S41. Jump.

  When the process proceeds to step S34, the pinion meshing rack position Pr is set based on the steering angle θs with reference to the pinion meshing rack position setting table shown in FIG. 6A of the first embodiment, and the process proceeds to step S36.

In step S36, the position change rate dPr is calculated based on the pinion meshing rack position Pr (n-1) obtained in the previous calculation and the pinion meshing rack position Pr obtained this time.
dPr ← (Pr−Pr (n−1)) / Δt
Ask from. Here, Δt is a calculation cycle. Note that the processing in steps S34 and S36 corresponds to the rack position change rate calculating means of the present invention.

  Next, the process proceeds to step S37, and the rack position correction gain GPr is set based on the position change rate dPr with reference to the rack position correction gain setting table shown in FIG. The rack position correction gain GPr is set to 100 [%] at a position where the position change rate dPr is 0 [%]. From this dPr = 0 [%], the absolute value of this position change rate dPr is set to a predetermined value. The characteristic is set such that the decrease starts at the increased position, gradually decreases from there, and is fixed at 0 [%].

  That is, when the position change rate dPr is close to 0 [%] and 0 [%], the driver is not turning the steering handle 4 greatly. Therefore, the steering handle 4 is near the neutral position. Therefore, the rack position correction gain GPr is set to a high value. The processing in this step corresponds to the rack position correction gain calculation means of the present invention.

Thereafter, the process proceeds to step S38, and the load fluctuation rate dLr is calculated based on the steering torque Tq (n-1) obtained at the previous calculation and the steering torque Tq obtained this time.
dLr ← (Tq−Tq (n−1)) / Δt
Ask from. The processing in this step corresponds to the load fluctuation rate calculating means of the present invention.

  In step S39, the rack load correction gain GLr is set based on the load fluctuation rate dLr with reference to the rack load correction gain setting table shown in FIG. The processing in this step corresponds to the rack load correction gain calculation means of the present invention.

  The rack load correction gain GLr is set to 0 [%] at the position of dLr = 0 [%], and the absolute value of the load fluctuation rate dLr increases at a predetermined position from this dLr = 0 [%]. Is set to a characteristic that is gradually increased and fixed at 100 [%].

  Therefore, even if the steering angle of the steering handle 4 is in the neutral range (θL−θR), the rack position correction gain GPr is maintained when the driver is keeping the steering handle 4 at a constant steering angle. Is set to a value close to 100 [%]. On the other hand, if the load input from the left and right steered wheels 14 to the rack shaft 8 changes in vibration in this state, the absolute value of the load fluctuation rate dLr increases.

Next, when proceeding to step S40, the rack assist pressure Fr is set to
Fr ← F1 + ΔFr · GPr · GLt
Calculate from The processing in this step corresponds to the rack assist pressure calculating means of the present invention.

  Thereafter, when the process proceeds from step S35 or step S40 to step S41, a drive signal corresponding to the rack assist pressure Fr is output to the variable valve 35, and the routine is exited.

  In this embodiment, the basic rack assist pressure F1 is set as a basic value, and the rack assist pressure change amount ΔFr is added to the rack position correction gain GPr and the rack load correction gain GLr. Fr is set. Therefore, the position change rate dPr when the steering handle 4 is in the neutral position is close to 100 [%]. However, when the load input from the steering wheel 14 to the rack shaft 8 does not change, the rack load correction gain GLr is It is set to almost 0 [%]. Therefore, as shown in FIG. 12C, the basic rack assist pressure F1, which is a basic value, is set. Even when the driver holds the steering handle 4 at a predetermined steering angle, the position change rate dPr is a value close to 100 [%], but the load input from the steering wheel 14 to the rack shaft 8 does not change. In the state, the rack load correction gain GLr is set to approximately 0 [%].

  On the other hand, for example, when the driver holds the steering handle 4 at a predetermined steering angle and the load input from the steering wheel 14 to the rack shaft 8 changes in vibration, the rack load increases as the fluctuation increases. The correction gain GLr is increased to 100 [%]. Therefore, as shown in FIG. 12 (c), the rack assist pressure Fr becomes higher than the basic rack assist pressure F1, and the pressing force of the rack shaft 8 against the pinion 5a increases accordingly, and the frictional force μ increases. Therefore, transmission of flutter vibration in the direction of the steering shaft 2 is suppressed. Furthermore, it is possible to reduce the occurrence of rattling noise caused by load vibration input from the steering wheel 14 side.

  As described above, in the present embodiment, the driver's steering status based on the position change rate dPr of the pinion meshing rack position Pr and the load fluctuation rate dLr applied to the rack shaft 8 obtained based on the steering torque Tq, and Since the load fluctuation applied to the rack shaft 8 is detected and the pressing force of the rack shaft 8 against the pinion 5a is changed based on this, the steering handle 4 is maintained not only in the neutral position but also at a constant steering angle. Even in a snaked state, transmission of flutter vibration in the direction of the steering shaft 2 and generation of rattling noise can be suppressed.

  In this embodiment, instead of the steering angle θs detected by the steering angle sensor, the rotation angle of the electric motor 19 or the stroke (movement amount) of the rack shaft 8 may be used as a parameter. Further, instead of the steering torque Tq detected by the shaft torque sensor, a load for sliding the rack shaft 8 or a parameter for detecting the axial force of the tie rod 9 may be used.

[Fifth embodiment]
13 and 14 show a fifth embodiment of the present invention. In the fourth embodiment described above, the rack assist pressure Fr is variably set in accordance with the driver's steering situation and the load fluctuation rate applied to the rack shaft 8, but in this embodiment, the vehicle running situation and road surface situation are determined. Accordingly, the rack assist pressure Fr is variably set.

  In this embodiment, as the driving state detection sensor 37, a lateral acceleration sensor as a lateral acceleration detection means for detecting a lateral acceleration Gy acting on the vehicle body, a wheel speed sensor as a wheel speed detection means for detecting the wheel speed of each of the four wheels. And the rack assist pressure Fr applied to the rack shaft guide 22 is set based on the parameters detected by the sensors.

  The rack assist pressure control unit 36 according to this embodiment executes arithmetic processing according to the rack assist pressure control routine shown in FIG.

  That is, in this routine, first, in step S51, the lateral acceleration Gy acting on the vehicle body detected by the lateral acceleration sensor and the wheel speed Vs detected by the wheel speed sensor are read. In this embodiment, the lateral acceleration Gy is represented as + for left turn and-for right turn. A wheel speed sensor is provided on each of the rotating shafts of the four wheels, and reads the detected wheel speed Vs of each wheel. Only one wheel speed Vs described in step S51 is described as a representative. Accordingly, the processing in step S54 shown below is calculated for each of the read four wheel speeds Vs, and the largest wheel speed change rate dVs is read in step S55 described later.

Thereafter, when proceeding to step S52, the lateral acceleration change rate dGy is calculated based on the lateral acceleration Gy read this time and the lateral acceleration Gy (n-1) obtained at the previous calculation.
dGy ← (Gy−Gy (n−1)) / Δt
Ask from. The processing in this step corresponds to the lateral acceleration change rate calculating means of the present invention.

  In step S53, the lateral acceleration correction gain Ggy is set based on the lateral acceleration change rate dGy with reference to the lateral acceleration correction gain table shown in FIG. The processing in this step corresponds to the lateral acceleration correction gain calculating means of the present invention.

  In this lateral acceleration correction gain table, the lateral acceleration correction gain Ggy is set to 0 [%] until the absolute value of the lateral acceleration change rate dGy increases by a predetermined value, and then gradually increased and fixed to 100 [%]. Set to characteristics. Accordingly, when the vehicle is traveling straight, the lateral acceleration change rate dGy is almost 0 [%], so the lateral acceleration correction gain Ggy is also set to 0 [%], and the absolute value of the lateral acceleration Gy during turning is set. As the value increases, the lateral acceleration correction gain Ggy also increases.

Thereafter, the process proceeds to step S54, where the wheel speed change rate dVs is calculated based on the wheel speed Vs read this time and the wheel speed Vs (n-1) obtained at the previous calculation.
dVs ← (Vs−Vs (n−1)) / Δt
Ask from. As described above, the wheel speed change rate dVs is obtained for all four wheels. The processing at this step corresponds to the wheel speed change rate calculating means of the present invention.

  Then, when the process proceeds to step S55, the wheel speed change rate dVs having the largest absolute value is extracted from the wheel speed change rates dVs for each wheel, and based on the wheel speed change rate dVs, FIG. The wheel speed correction gain GVs is set with reference to the wheel speed correction gain table shown in FIG. The processing in this step corresponds to the wheel speed correction gain calculation means of the present invention.

  In this wheel speed correction gain table, the wheel speed correction gain GVs is set to 0 [%] until the absolute value of the wheel speed change rate dVs is increased by a predetermined value, and then gradually increased and fixed to 100 [%]. It has characteristics.

  Accordingly, when the vehicle is traveling on a paved road, the four wheels are in contact with the road surface, so the wheel speed change rate dVs of the four wheels does not change greatly, and the wheel speed correction gain GVs is 0 [%]. A value close to. On the other hand, when one of the wheels slips on the rough road, the wheel speed change rate dVs of the wheel changes greatly, and the wheel speed correction gain GVs increases.

Thereafter, when the process proceeds to step S56, the rack assist pressure Fr is
Fr ← F1 + ΔFr · Ggy · GVs
Calculate from The processing in this step corresponds to the rack assist pressure calculating means of the present invention.

  Thereafter, the process proceeds to step S57, where a drive signal corresponding to the rack assist pressure Fr is output to the variable valve 35, and the routine is exited.

  In this embodiment, the basic rack assist pressure F1 is set as a basic value, and the rack assist pressure change amount ΔFr is added with a value obtained by correcting the gain by the lateral acceleration correction gain Ggy and the wheel speed correction gain GVs. Fr was set. Therefore, when the lateral acceleration change rate dGy and the wheel speed change rate dVs are both small, such as when traveling on a paved straight road, at least one of the correction gains Ggy and GVs is set to 0 [%]. The rack assist pressure Fr is set to the basic rack assist pressure F1 (Fr = F1). Further, when traveling on a paved curved road, the lateral acceleration change rate dGy changes greatly, but the wheel speed change rate dVs of each wheel does not change greatly. Therefore, the rack assist pressure Fr is set to the basic rack assist pressure F1. (Fr = F1).

  On the other hand, if the wheel slips during driving on a rough road, the wheel speed change rate dVs (absolute value) of the slipped wheel increases, and if the vehicle runs on a continuous curved road in that state, the absolute value of the lateral acceleration change rate dGy also increases. growing. Then, as indicated by the solid line in FIG. 14 (c), as the absolute value of the lateral acceleration Gy increases, the rack assist pressure Fr increases, and the frictional force when attempting to move the rack shaft 8 in the axial direction. μ increases. As a result, not only the steering handle 4 can be prevented from wobbling when traveling on a rough road, but also the rattling noise generated due to the backlash at the meshing portion between the rack shaft 8 and the pinion 5a can be reduced.

  As described above, in this embodiment, the traveling state of the vehicle is examined based on the lateral acceleration change rate dGy acting on the vehicle body and the wheel speed change rate dVs of each wheel, and the rack shaft 8 is connected to the pinion 5a during the rough road traveling. Since the rack assist pressure Fr to be pressed to the side is increased, the steering handle 4 can be prevented from wobbling not only in the neutral position but also in the steered state. it can. Furthermore, the rattling noise generated at the meshing portion between the rack shaft 8 and the pinion 5a can be reduced.

  When traveling on a paved straight road or curved road such as an expressway, the lateral acceleration change rate dGy and the wheel speed change rate dVs of each wheel are set to values close to 0%. . Therefore, since the rack assist pressure Fr is fixed at the basic rack assist pressure F1, transmission of flutter vibration in the direction of the steering shaft 2 can be suppressed. In this case, the present embodiment and the first embodiment described above are combined and switched to the control of the first embodiment at the time of running on the paved road, so that both the paved road running and the bad road running are good. A steering feeling can be obtained.

  The present invention is not limited to the above-described embodiment. For example, the assist means is provided with linear motion means such as a linear actuator instead of the hydraulic assist circuit 31, and the assist pressure is directly applied to the assist piston 25 by the linear motion means. You may make it provide.

  The wheel speed Vs may be an average value of four wheels. Furthermore, the wheel speed sensor may detect only the wheel speed Vs of a representative wheel (for example, the front wheel closest to the steering handle 4) among the four wheels. Alternatively, the wheel speed sensor may detect the wheel speeds of the left and right wheels of the drive wheel in the case of two-wheel drive.

1 ... Electric power steering device,
4 ... Steering handle,
5a ... pinion,
6 ... Steering gear box,
7 ... Rack shaft housing,
7a ... pinion housing,
7b ... guide housing,
7d: Rack shaft guide storage chamber,
7e ... hydraulic chamber,
8a ... rack,
14 ... Steering wheel,
22 ... Rack shaft guide,
24 ... Adjust spring,
25 ... assist piston,
31. Assist circuit,
32a ... Drain oil passage,
34 ... Oil pump,
35 ... Variable valve for pressure regulation,
36 ... Rack assist pressure control unit,
37 ... Driving state detection sensor,
dGy: lateral acceleration change rate,
dLr: Load fluctuation rate,
dPr: Position change rate,
dVs ... Wheel speed change rate,
F0 ... Set pressure,
F1 ... Basic rack assist pressure,
Fr: Rack assist pressure,
Ggy: Lateral acceleration correction gain,
GLr: Rack load correction gain,
GPr: Rack position correction gain,
Gr: Position correction gain,
Gt: Torque correction gain,
GVs: Wheel speed correction gain,
Gy ... Lateral acceleration,
Lo: neutral region determination threshold,
Lr ... rack load,
Pr: Pinion meshing rack position,
(ΘL−θR), (PrL−PrR)... Neutral region,
Tq: Steering torque,
Vs ... wheel speed,
Vsp ... Vehicle speed,
Vsph ... High speed judgment vehicle speed,
ΔFr: rack assist pressure change amount,
θs ... steering angle,
μ… friction force

Claims (6)

A pinion shaft connected to the steering handle and having a pinion;
A rack shaft having a rack meshed with the pinion;
A rack shaft housing for accommodating the rack shaft and supporting the rack shaft slidably;
In a steering apparatus comprising: a rack shaft support mechanism having a biasing member that presses the rack shaft toward the pinion with a preset set pressure;
Furthermore,
Rack assist means for applying a rack assist pressure for pressing the biasing member in the rack axial direction;
A steering apparatus, comprising: a rack assist pressure calculating means for setting an assist pressure generated by the assist means based on a parameter detected by a driving condition detecting means for detecting a driving condition of a vehicle. The operating state detection means is a movement amount detection means for detecting the movement amount of the rack shaft,
And rack position calculating means for obtaining a rack position meshing with the pinion based on the movement amount of the rack shaft detected by the movement amount detecting means,
The rack assist pressure calculating means sets the assist pressure generated by the assist means when the rack position obtained by the rack position calculating means is in a preset neutral region centered on a neutral position. The steering apparatus according to claim 1. The operating state detecting means is a rack load detecting means for detecting a load generated when the rack shaft is slid,
Furthermore, it has rack load determination means for comparing the load detected by the rack load detection means with a preset threshold value,
2. The steering according to claim 1, wherein the rack assist pressure calculating unit sets an assist pressure generated by the assist unit when the rack load determining unit determines that the rack load is equal to or less than the threshold value. 3. apparatus. The driving state detection means is a movement amount detection means for detecting a movement amount of the rack shaft and a torque detection means for detecting a steering torque applied to the steering handle,
Furthermore,
A rack position meshing with the pinion is obtained based on the movement amount detected by the movement amount detection means, and the neutral position is 0 based on the rack position, and the position increases from there depending on the movement amount of the rack position. Position correction gain calculating means for calculating a correction gain;
Based on the steering torque detected by the torque detection means, the torque correction gain calculating means for obtaining a torque correction gain that becomes 1 near 0 and decreases as the steering torque increases;
The rack assist pressure calculation means adds a value obtained by correcting the rack assist pressure change amount obtained for each calculation cycle with the position correction gain and the torque correction gain to a basic rack assist pressure set in advance. The steering apparatus according to claim 1, wherein an assist pressure generated by the assist means is set. The driving state detection means is a movement amount detection means for detecting a movement amount of the rack shaft and a torque detection means for detecting a steering torque applied to the steering handle,
Furthermore,
Rack position change rate calculating means for obtaining a rack position change rate from a rack position meshed with the pinion obtained based on the movement amount detected by the movement amount detecting means;
Based on the rack position change rate obtained by the rack position change rate calculating means, the rack obtains a rack position correction gain that is 1 when the rack position change rate is 0 and decreases according to the rack position change rate. Position correction gain calculation means;
Load fluctuation rate calculation means for obtaining a load fluctuation rate from the steering torque detected by the torque detection means;
Rack load correction gain calculation for obtaining a rack load correction gain that is 0 when the load fluctuation rate is 0 based on the load fluctuation rate obtained by the load fluctuation rate calculating means and that increases from the load fluctuation rate according to the load fluctuation rate. Means,
The rack assist pressure calculation means adds a value obtained by correcting the rack assist pressure change amount obtained at each calculation cycle by the rack position correction gain and the track load correction gain to a preset basic rack assist pressure. The steering device according to claim 1, wherein an assist pressure generated by the assist means is set. The driving state detecting means is a lateral acceleration detecting means for detecting a lateral acceleration acting on the vehicle body and a wheel speed detecting means for detecting a wheel speed,
Furthermore,
Lateral acceleration change rate calculating means for obtaining a lateral acceleration change rate based on the lateral acceleration detected by the lateral acceleration detecting means;
Based on the lateral acceleration change rate obtained by the lateral acceleration change rate calculating means, the lateral acceleration change rate is 0 when the lateral acceleration change rate is 0, and a lateral acceleration correction gain that increases according to the lateral acceleration change rate is obtained therefrom. Acceleration correction gain calculation means;
A wheel speed change rate calculating means for obtaining a wheel speed change rate from the wheel speed detected by the wheel speed detecting means;
Based on the wheel speed change rate obtained by the wheel speed change rate calculation means, the wheel speed change gain is 0 when the wheel speed change rate is 0, and a wheel speed correction gain that increases in accordance with the wheel speed change rate is obtained therefrom. Speed correction gain calculation means,
The rack assist pressure calculating means adds a value obtained by correcting the rack assist pressure change amount obtained at each calculation cycle by the lateral acceleration correction gain and the wheel speed correction gain to a preset basic rack assist pressure. The steering device according to claim 1, wherein an assist pressure generated by the assist means is set.

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