JP6515371B2 - Electric power steering device - Google Patents

Description

  The present invention relates to an improved technique of an electric power steering apparatus that applies an assist torque corresponding to a steering torque to a steering system.

  In the electric power steering apparatus, the steering torque generated on the steering wheel is detected by a torque sensor, the electric motor generates an auxiliary torque corresponding to the steering torque, and the driver's burden is caused by adding the auxiliary torque to the steering torque. To reduce

  A general electric power steering apparatus comprises a column shaft connected to a steering wheel, a pinion shaft connected to the column shaft via two universal joints and an intermediate shaft, and a rack and pinion mechanism on the pinion shaft. And an auxiliary torque mechanism for adding an auxiliary torque to a steering torque generated in the steering wheel.

  Thus, the pinion shaft is connected to the column shaft via the two universal joints and the intermediate shaft in order to increase the degree of freedom of the arrangement of the electric power steering apparatus with respect to the vehicle body. A steering apparatus having such two universal joints and an intermediate shaft is known, for example, in Patent Document 1.

  In a steering apparatus known in Patent Document 1, a first universal joint, an intermediate shaft, a second universal joint, and a pinion shaft are connected to a column shaft in this order. The intermediate shaft intersects the column shaft at a crossing angle. The pinion shaft intersects with the intermediate shaft at a crossing angle.

  Each of the universal joints is constituted by a Cardan-type universal shaft joint which is a kind of unequal-speed universal joint. The variable speed universal joint is widely used because it is relatively inexpensive. However, even if the angular velocity on the input side is uniform, the angular velocity on the output side is unequal in speed. For this reason, two universal joints and an intermediate shaft are combined. By shifting the phase of the second universal joint by 90 ° with respect to the phase of the first universal joint, the angular velocity of the pinion shaft can be made approximately constant.

  In general, the following two types of assist torque application types of the electric power steering apparatus are known.

  In the first addition type, the steering torque of the column shaft is detected by a torque sensor, and the assist torque generated by the electric motor is added to the column shaft based on the steering torque. In the first addition type, when so-called combined torque in which the assist torque is added to the steering torque is transmitted from the column shaft to the pinion shaft, the unequal velocity (unevenness) phenomenon of the unequal-speed universal joint is generated. There is an impact. For this reason, in order to enhance the steering feeling of the electric power steering apparatus, it is necessary to make the angular velocity of the pinion shaft approximately equal by providing two unequal-speed universal shaft joints having different phases.

  In the second addition type, the steering torque of the pinion shaft is detected by a torque sensor, and the assist torque generated by the electric motor based on the steering torque is added to the pinion shaft or the rack shaft. In the second addition type, when the steering torque is transmitted from the column shaft to the pinion shaft, there is an influence of the unequal speed (unevenness) phenomenon of the unequal-speed universal joint. Since the detected steering torque fluctuates due to the influence of the unequal speed (waviness) phenomenon, the assist torque generated by the electric motor also fluctuates based on the steering torque. For this reason, in order to enhance the steering feeling of the electric power steering apparatus, it is necessary to make the angular velocity of the pinion shaft approximately equal by providing two unequal-speed universal shaft joints having different phases.

  Therefore, for example, in view of the arrangement of the electric power steering apparatus with respect to the vehicle body, two universal joints may be used to make the angular velocity of the pinion shaft substantially constant even if only one universal joint is required. And an intermediate shaft. This is disadvantageous in reducing the cost and weight of the electric power steering apparatus.

Patent No. 4271176 gazette

  An object of the present invention is to provide a technology capable of further enhancing the steering feeling of the electric power steering apparatus while achieving cost reduction and weight reduction of the electric power steering apparatus.

According to the invention of claim 1, a column shaft connected to the steering wheel, a pinion shaft connected to the column shaft, a rack shaft connected to the pinion shaft via the rack and pinion mechanism, and An electric power steering apparatus, comprising: an auxiliary torque mechanism for adding an auxiliary torque to a steering torque generated in a steering wheel;
The auxiliary torque mechanism includes a torque sensor that detects the steering torque generated in the steering wheel, an electric motor that generates the auxiliary torque based on the steering torque detected by the torque sensor, and the electric motor. And an auxiliary torque transmission mechanism for transmitting the auxiliary torque to any one of the rack shaft and the pinion shaft, wherein the connection configuration between the column shaft and the pinion shaft is a connection by only a single universal joint, The single universal joint is constituted by an unequal-speed universal joint, the torque sensor is disposed on a steering column for rotatably supporting the column shaft, and the steering wheel is in a neutral position. Steering ratio is smaller than the steering ratio at the other steering angle position As will be constant, an electric power steering apparatus characterized by phase is set in the non-uniform speed form universal joint with respect to the column shaft is provided.

  In the invention according to claim 1, the pinion shaft is connected only by a single universal joint to the column shaft rotatably supported by the steering column. The universal joint is constituted by an inconstant speed universal joint. Therefore, even if the angular velocity of the column shaft is constant, the angular velocity of the pinion shaft is unequal.

  On the other hand, in the invention according to claim 1, the torque sensor is disposed on the steering column. That is, the torque sensor is disposed at a steering torque upstream (close to the steering wheel) than the universal joint in the steering system from the steering wheel to the steering wheel. For this reason, the torque sensor is not influenced by the inherent characteristics of the universal joint, for example, the unequal velocity (waviness) phenomenon of the universal joint. As a result, the detection accuracy of detecting the steering torque by the torque sensor can be enhanced.

  Furthermore, in the invention according to claim 1, the electric motor generates the assist torque based on the high-precision steering torque detected by the torque sensor. The value of the auxiliary torque becomes a more accurate value without being affected by the inherent characteristics of the universal joint, for example, the unequal speed (waviness) phenomenon of the universal joint. Further, the auxiliary torque is transmitted to either the rack shaft or the pinion shaft by the auxiliary torque transmission mechanism. That is, the assist torque is added to the steering torque downstream of the universal joint in the steering system. For this reason, the transmission of the auxiliary torque to the steering system is not affected by the inherent characteristics of the universal joint, for example, the unequal velocity (waviness) phenomenon of the universal joint.

  By the way, the "steering torque" itself transmitted from the column shaft to the pinion shaft through the universal joint is affected by the inherent characteristics of the universal joint, for example, the unequal velocity (waviness) phenomenon of the universal joint. However, the assist torque transmitted to either the rack shaft or the pinion shaft is generally relatively larger than the steering torque. Therefore, it is possible to suppress, as much as possible, the fluctuation of the combined torque in which the assist torque is added to the steering torque, that is, the wave phenomenon of the so-called combined torque.

  As described above, although the connection point between the column shaft and the pinion shaft is only one so-called single joint, the detection accuracy of the steering torque by the torque sensor is enhanced. Moreover, the accurate assist torque that follows the change in the steering torque generated in the steering wheel can be quickly applied from the assist torque mechanism to the steering torque downstream of the steering system. The steering torque by the driver can be finely assisted by the assist torque. Therefore, the steering feeling of the electric power steering apparatus can be further enhanced.

  Moreover, since the column shaft and the pinion shaft are connected only by a single universal joint, the number of parts of the connecting member can be reduced. Furthermore, the single universal joint can be constituted by a relatively inexpensive unequal speed universal joint. Therefore, the cost and weight of the electric power steering apparatus can be reduced.

In the invention according to claim 1 , the unequal speed type relative to the column shaft can be set so that the steering ratio when the steering wheel is in the neutral position is smaller than the steering ratio when the steering wheel is at the other steering angle position The phase of the shaft joint (single universal joint) is set.

  The column shaft and the pinion shaft are connected by a single unequal speed universal joint. For this reason, the amount of change in the steering angle of the pinion shaft with respect to the amount of change in the steering angle of the column shaft is influenced by the unequal speed (waviness) phenomenon, which is an inherent characteristic of the inconstant speed universal joint. Receive That is, according to the change of the steering angle of the steering wheel, the steering angle of the pinion shaft generates a "wave phenomenon" at the so-called steering angle of the pinion shaft when it greatly changes and when it changes small. For this reason, a change in the stroke of the rack shaft driven by the pinion shaft also generates a wave-like "wave phenomenon" when the change is large and when the change is small.

  The characteristics of the "wave phenomenon" of the unequal-speed universal joint can be combined with the characteristics of the steering ratio to the steering angle by the suspension geometry of a vehicle such as a general passenger car. That is, when the steering angle of the steering wheel is small, since the steering ratio is small, the steered wheels are steered gently, so-called "slow steering". As the steering ratio increases as the steering angle of the steering wheel increases, the steered wheels steer relatively quickly, so-called "quick steer". As described above, in the rack and pinion mechanism, the gear ratio of the rack to the pinion can function in the same manner as the variable ratio type.

It is a schematic diagram of the electric-power-steering apparatus based on Example 1 of this invention. It is explanatory drawing explaining the connection relation of the column shaft shown by FIG. 1, a single universal joint, and a pinion shaft. It is a characteristic view which shows the change of the angular velocity ratio of the universal joint with respect to the steering angle of the column shaft shown by FIG. FIG. 2 is a characteristic diagram showing a characteristic of a steering ratio with respect to a steering angle of the steering wheel shown in FIG. It is a schematic diagram of the electric-power-steering apparatus based on Example 2 of this invention.

  A mode for carrying out the present invention will be described below based on the attached drawings.

  An electric power steering apparatus according to a first embodiment will be described based on the drawings.

  As shown in FIG. 1, the electric power steering apparatus 10 according to the first embodiment is mounted on a vehicle such as an automobile and reduces the driver's burden by adding the assist torque generated by the electric motor 63 to the steering torque. It is Hereinafter, the electric power steering apparatus 10 will be abbreviated as "steering apparatus 10."

  The steering apparatus 10 includes a column shaft 22 connected to a steering wheel 21, a pinion shaft 26 connected to the column shaft 22 by a universal joint 23, and a rack connected to the pinion shaft 26 by a rack and pinion mechanism 27. The shaft 28 and an assist torque mechanism 60 for adding assist torque to the steering torque generated on the steering wheel 21 are included.

  Hereinafter, the steering device 10 will be described in more detail. The steering device 10 comprises a steering system 20 and an assist torque mechanism 60. Hereinafter, the pinion shaft 26 is referred to as “first pinion shaft 26”, and the rack and pinion mechanism 27 is referred to as “first rack and pinion mechanism 27”.

  The steering system 20 is a system from the steering wheel 21 steered by the driver to the steered wheels 33 and 33 (for example, front wheels). More specifically, the steering system 20 connects the first pinion shaft 26 to the steering wheel 21 through the column shaft 22 and the single universal joint 23, and the first rack and pinion to the first pinion shaft 26. A rack shaft 28 is connected via a mechanism 27, and left and right steering wheels 33, 33 are connected to both ends of the rack shaft 28 via left and right tie rods 31, 31 and left and right knuckles 32, 32.

  The column shaft 22 is also referred to as a steering shaft, and is connected to the steering wheel 21, and is accommodated in the steering column 41 and rotatably supported. The steering column 41 is attached to a vehicle body 42 by a steering hanger 43. The steering hanger 43 extends in the vehicle width direction at the front of the vehicle body 42, and both ends thereof are attached to the vehicle body 42. As a result, the steering column 41 is fixed to the vehicle body 42.

  The column shaft 22 comprises a first shaft 22a, a torsion bar 22b and a second shaft 22c. One end of the first shaft 22 a is connected to the steering wheel 21. The other end of the first shaft 22a is connected to one end of the second shaft 22c via the torsion bar 22b. The other end of the second shaft 22 c is connected to the first pinion shaft 26 via a universal joint 23. The column shaft 22 is not limited to the combined structure of the first shaft 22a, the torsion bar 22b and the second shaft 22c, and may be constituted by one shaft.

  The first rack and pinion mechanism 27 comprises a first pinion 27 a provided on the first pinion shaft 26 and a first rack 27 b provided on the rack shaft 28. Of the steering system 20, at least the first pinion shaft 26, the first rack and pinion mechanism 27, and the rack shaft 28 are accommodated in a housing 51 elongated in the vehicle width direction. The rack shaft 28 is slidably supported in the housing 51.

  According to the steering system 20, when the driver steers the steering wheel 21, the left and right steered wheels can be steered by the steering torque via the first rack and pinion mechanism 27 and the left and right tie rods 31, 31. 33, 33 can be steered.

  The auxiliary torque mechanism 60 generates an auxiliary torque based on the steering torque detected by the torque sensor 61 and adds it to the rack shaft 28. The assist torque mechanism 60 includes a torque sensor 61, a control unit 62, the electric motor 63, and an assist torque transmission mechanism 64. That is, the auxiliary torque mechanism 60 adopts a method of directly transmitting the auxiliary torque generated by the electric motor 63 to the rack shaft 28.

  More specifically, the auxiliary torque mechanism 60 generates a control signal at the control unit 62 based on the torque detection signal of the torque sensor 61, and generates an auxiliary torque corresponding to the steering torque by the electric motor 63 based on the control signal. The auxiliary torque generated by the electric motor 63 is transmitted to the second pinion shaft 65 via the auxiliary torque transmission mechanism 64, and the rack shaft is further transmitted from the second pinion shaft 65 via the second rack and pinion mechanism 66. It is a mechanism to transmit to 28.

  The second rack and pinion mechanism 66 comprises a second pinion 66 a provided on the second pinion shaft 65 and a second rack 66 b provided on the rack shaft 28.

  The torque sensor 61 is disposed on the steering column 41 and detects the steering torque generated on the steering wheel 21. That is, the torque sensor 61 detects the steering torque applied to the column shaft 22 and outputs it as a torque detection signal. More specifically, as described above, the first shaft 22a and the second shaft 22c are connected to each other via the torsion bar 22b. Relative torsional displacement occurs between the first shaft 22a and the second shaft 22c according to the magnitude of the steering torque. The torque sensor 61 can detect the steering torque according to the amount of torsional displacement by detecting the relative amount of torsional displacement between the first shaft 22a and the second shaft 22c.

  The torque sensor 61 may be configured as a magnetostrictive torque sensor that detects a change in magnetism that has changed according to the torque generated in the column shaft 22.

  The electric motor 63 generates an auxiliary torque based on the steering torque detected by the torque sensor 61.

  The auxiliary torque transmission mechanism 64 transmits the auxiliary torque generated by the electric motor 63 to the rack shaft 28. The auxiliary torque transmission mechanism 64 is constituted by, for example, a worm gear mechanism. Hereinafter, the auxiliary torque transmission mechanism 64 is appropriately rephrased as a "worm gear mechanism 64".

  The worm gear mechanism 64 comprises a worm shaft 82 connected to a motor shaft 63a of the electric motor 63 by a shaft joint 81, a worm 83 provided on the worm shaft 82, and a worm wheel 84 meshing with the worm 83. The worm wheel 84 is provided on the second pinion shaft 65.

  The auxiliary torque mechanism 60 is disposed in the housing 51. That is, the electric motor 63 and the worm gear mechanism 64 are disposed in the housing 51. More specifically, the electric motor 63 in the auxiliary torque mechanism 60 is assembled to the housing 51, and the worm gear mechanism 64 is accommodated in the housing 51.

  When the occupant steers the steering wheel 21, the column shaft 22 rotates with the steering wheel 21. The rotation generates a steering torque on the column shaft 22. The steering torque is detected by the torque sensor 61. The controller 62 operates the electric motor 63 based on the detected steering torque. As the electric motor 63 operates, the assist torque is transmitted to the rack shaft 28 through the worm gear mechanism 64, the second pinion shaft 65 and the second rack and pinion mechanism 66.

  According to the steering device 10, the steering wheels 33 and 33 can be steered by the rack shaft 28 by the combined torque obtained by adding the assist torque of the electric motor 63 to the steering torque of the driver.

  Here, the connection relationship between the column shaft 22, the universal joint 23, and the first pinion shaft 26 will be described in detail. As mentioned above, the connection configuration between the column shaft 22 and the first pinion shaft 26 is a direct connection by only a single universal joint 23. That is, the universal joint 23 is used alone.

  As shown in FIG. 2 (a), the single universal joint 23 is constituted by a cardan-type universal shaft joint (cardan joint) which is a kind of unequal-speed universal shaft joint. The Cardan type universal joint is also referred to as a hook joint, a cross joint, or a universal joint. More specifically, the universal joint 23 (cardan-type universal shaft joint 23) includes a substantially U-shaped first yoke 91 connected to the column shaft 22 and an approximately U connected to the first pinion shaft 26. And a cruciform member 93 connecting the pair of yokes 91 and 92 to each other.

  The center line S2 of the first pinion shaft 26 intersects with the center line S1 of the column shaft 22 at an intersection angle α. In this case, the crossing angle α between the two axes 22 and 26 is not 0 ° (α ≠ 0).

  Now, when the column shaft 22 rotates 90 degrees from the state shown in FIG. 2A, the cruciform member 93 also rotates. The cruciform member 93 is restrained by the first pinion shaft 26. For this reason, the inclination of the cruciform member 93 changes and changes to the state of FIG. 2 (b). When the column shaft 22 continues to rotate further, the cruciform member 93 repeats the state of FIG. 2 (a) and the state of FIG. 2 (b) every 90 °. At this time, even if the column shaft 22 rotates at a constant speed, the rotational speed (angular velocity) of the first pinion shaft 26 does not become equal.

Assuming that the rotation angle θ (steering angle θ) of the column shaft 22 and the crossing angle is α, the angular velocity ω1 and the first pinion shaft 26 when the column shaft 22 rotates at a constant angular velocity ω1. It is generally known that there is a relationship between the angular velocity ratio rω expressed by the following equation (1) with the angular velocity ω2 of.
rω = ω2 / ω1 = cos α / (1−sin ² θ · sin ² α) (1)

  The characteristic of the above equation (1) is represented by FIG. FIG. 3 is a characteristic diagram showing changes in the angular velocity ratio rω with respect to the steering angle θ, where the horizontal axis is the steering angle θ of the column shaft 22 and the vertical axis is the angular velocity ratio rω. According to FIG. 3, the following can be understood. That is, in the case of the intersection angle α = 0, the angular velocity ratio rω is always constant regardless of the steering angle θ. In the case of the crossing angle α ≠ 0, the angular velocity ratio rω increases at the steering angle θ = 0 to 90 °, and rω decreases at θ = 90 to 180 °. This is repeated every 180 degrees of the steering angle θ. The swing width of the angular velocity ratio rω is more remarkable as the crossing angle α is larger.

  Based on the above points, in Example 1, the steering ratio Rs (not shown) when the steering wheel 21 shown in FIG. 1 is in the neutral position is the steering ratio Rs when the steering wheel 21 is at another steering angle position. The phase of the cardan-type free shaft joint 23 with respect to the column shaft 22 is set so as to be smaller than the above.

  Here, “steering ratio Rs” means the steering angle θ (not shown) of the steering wheel 21, that is, the steering angle θ of the column shaft 22, and the turning angle β (not shown) of the steered wheels 33, 33 It is a value divided by the turning angle β, and also referred to as a steering angle ratio Rs.

  When the steering angle θ of the steering wheel 21 is small, since the steering ratio Rs is small, the steered wheels 33 and 33 are steered gently, so-called "slow steering". Since the steering ratio Rs increases as the steering angle θ of the steering wheel 21 increases, the steered wheels 33, 33 steer relatively rapidly, so-called "quick steering".

  In FIG. 4A, the horizontal axis is the steering angle θ of the steering wheel 21 and the vertical axis is the steering ratio Rs. The characteristics of the steering ratio Rs with respect to the steering angle θ “by change of the angular velocity ratio rω of the steering wheel 21” FIG. 6 is a characteristic diagram represented based on the characteristics shown in FIG. 3 above.

  Specifically, as shown in FIG. 3, when the steering wheel 21 is at the neutral position, that is, when the steering angle θ is 0 ° (θ = 0 °), the angular velocity ratio rω has the lowest value. Then, every time the steering angle θ changes by 180 °, the value of the angular velocity ratio rω increases or decreases, that is, “waves” in a wave shape. As a result, as shown in FIG. 4 (a), the value of the steering ratio Rs also increases or decreases, that is, "waves" in a wave shape. When the angular velocity ratio rω becomes the lowest value, the steering ratio Rs becomes the lowest value Rmi.

  In the first embodiment, as shown in FIG. 4A, the steering ratio Rs is set to the minimum value Rmi when the steering wheel 21 is at the neutral position, that is, when the steering angle is 0 ° (θ = 0 °). doing.

  In other words, the steering ratio Rs when the steering wheel 21 is in the neutral position (θ = 0 °) is more than the steering ratio Rs when the steering wheel 21 is at another steering angle position (eg, 0 ° <θ <180 °). The phase of the cardan-type free shaft joint 23 with respect to the column shaft 22 is set such that the setting is small (Rs = Rmi). For example, when the steering wheel 21 is in the neutral position, the phase of the cardan-type free shaft joint 23 is set to the phase shown in FIG. 2 (a). Here, the phase of the cardan-type universal joint 23 refers to the rotational direction of the second yoke 92 with respect to the first yoke 91, that is, the phase of the cruciform member 93.

  By the way, as shown in FIG. 4 (b), it is known that the characteristic of the steering ratio Rs with respect to the steering angle θ is obtained by the suspension geometry (geometrical arrangement of suspension links) of a vehicle such as a general passenger car. ing. FIG. 4B is a characteristic diagram showing the characteristics of the steering ratio Rs with respect to the steering angle θ by “suspension geometry”, where the horizontal axis is the steering angle θ of the steering wheel 21 and the vertical axis is the steering ratio Rs.

  According to FIG. 4B, the value of the steering ratio Rs is the smallest when the steering wheel 21 is in the neutral position (θ = 0 °), and the steering angle at which the right or left steering is performed from the neutral position. It can be seen that as θ increases, it increases.

  A combined characteristic of the characteristic shown in FIG. 4 (a) and the characteristic shown in FIG. 4 (b) is shown in FIG. 4 (c). FIG. 4C is a characteristic diagram showing the characteristics of the steering ratio Rs with respect to the “as a whole vehicle” steering angle θ, where the horizontal axis is the steering angle θ of the steering wheel 21 and the vertical axis is the steering ratio Rs. .

  According to FIG. 4C, the value of the steering ratio Rs is the smallest when the steering wheel 21 is in the neutral position (θ = 0 °), and the steering angle at which the right or left steering is performed from the neutral position. It can be seen that as θ increases, it increases substantially in stages.

  As described above, the connection configuration between the column shaft 22 and the first pinion shaft 26 shown in FIG. 1 is a connection by only a single universal joint 23, whereby the first and second rack and pinion mechanisms are provided. At 27, 66, the gear ratio of the racks 27b, 66b with respect to the pinions 27a, 66a can function in the same way as the variable ratio type. Here, in the “variable ratio type”, the gear ratios of the racks 27b and 66b with respect to the pinions 27a and 66a are made smaller when the steering wheel 21 is in the neutral position, and become larger as the steering angle becomes larger. is there.

  In the present invention, the auxiliary torque mechanism 60 is limited to the configuration in which the auxiliary torque generated by the electric motor 63 is transmitted from the worm gear mechanism 64 to the rack shaft 28 via the second pinion shaft 65. is not. That is, the auxiliary torque mechanism 60 only needs to transmit the auxiliary torque generated by the electric motor 63 to either the rack shaft 28 or the pinion shaft 26. For example, the auxiliary torque mechanism 60 can be configured to change the worm gear mechanism 64 into a “ball screw” and transmit the auxiliary torque directly to the rack shaft 28 by the ball screw.

  Further, as in the second embodiment shown in FIG. 5, the auxiliary torque mechanism 60 can be configured to directly transmit the auxiliary torque to the first pinion shaft 26 (pinion shaft 26) by the worm gear mechanism 64. It is.

  An electric power steering apparatus according to a second embodiment will be described with reference to FIG. FIG. 5 is represented corresponding to FIG. The electric power steering apparatus 10A of the second embodiment is the electric power steering apparatus 10 of the embodiment except that the assist torque mechanism 60 shown in FIGS. 1 to 4 is changed to the assist torque mechanism 60A shown in FIG. The same reference numerals are assigned and the description is omitted.

  Specifically, the worm wheel 84 of the auxiliary torque mechanism 60A of the second embodiment is provided on the first pinion shaft 26. Therefore, the second pinion shaft 65 and the second rack and pinion mechanism 66 shown in FIG. 1 are unnecessary. The second embodiment exhibits the same effect as the first embodiment.

  It is as follows when the description of Example 1 and 2 is put together. The pinion shaft 26 is connected only by a single universal joint 23 to a column shaft 22 rotatably supported by the steering column 41. The universal joint 23 is constituted by an inconstant speed universal joint. Therefore, even if the angular velocity of the column shaft 22 is uniform, the angular velocity of the pinion shaft 26 is unequal.

  On the other hand, in the first and second embodiments, the torque sensor 61 is disposed on the steering column 41. That is, the torque sensor 61 is disposed in the steering system 20 at a steering torque upstream (closer to the steering wheel 21) than the universal joint 23. For this reason, the torque sensor 61 is not influenced by the influence of the inherent characteristics of the universal joint 23, for example, the unequal velocity (waviness) phenomenon of the universal joint 23. As a result, the detection accuracy of detecting the steering torque by the torque sensor 61 can be enhanced.

  Furthermore, the electric motor 63 generates an assist torque based on the high-precision steering torque detected by the torque sensor 61. The value of the auxiliary torque becomes a more accurate value without being affected by the inherent characteristics of the universal joint 23, for example, the uneven velocity (waviness) phenomenon of the universal joint 23. Further, the auxiliary torque is transmitted to either the rack shaft 28 or the pinion shaft 26 by the auxiliary torque transmission mechanism 64. That is, the assist torque is added to the steering system 20 at a steering torque downstream of the universal joint 23. Therefore, the transmission of the auxiliary torque to the steering system 20 is not affected by the inherent characteristics of the universal joint 23, for example, the unequal velocity (waviness) phenomenon of the universal joint 23.

  By the way, the "steering torque" itself transmitted from the column shaft 22 to the pinion shaft 26 through the universal joint 23 is affected by the inherent characteristics of the universal joint 23. For example, the unequal speed (swelling) phenomenon of the universal joint 23. Affected by However, the assist torque transmitted to either one of the rack shaft 28 and the pinion shaft 26 is generally relatively larger than the steering torque. Therefore, it is possible to suppress, as much as possible, the fluctuation of the combined torque in which the assist torque is added to the steering torque, that is, the wave phenomenon of the so-called combined torque.

  As described above, although the connection point between the column shaft 22 and the pinion shaft 26 is only one so-called single joint, the detection accuracy of the steering torque by the torque sensor 61 is enhanced. Moreover, the accurate assist torque following the change in the steering torque generated in the steering wheel 21 can be quickly applied downstream of the steering torque of the steering system 20 from the assist torque mechanism 60. The steering torque by the driver can be finely assisted by the assist torque. Therefore, the steering feeling of the electric power steering device 10, 10A can be further enhanced.

  In addition, since the column shaft 22 and the pinion shaft 26 are connected only by the single universal joint 23, the number of parts of the connecting member can be reduced. Furthermore, the single universal joint 23 can be configured by a relatively inexpensive unequal speed universal joint. Accordingly, cost reduction and weight reduction of the electric power steering device 10, 10A can be achieved.

  Furthermore, the unequal-speed universal shaft with respect to the column shaft 22 is set such that the steering ratio Rs when the steering wheel 21 is in the neutral position is smaller than the steering ratio Rs when the steering wheel 21 is at the other steering angle position. The phase of the joint 23 (single universal joint 23) is set.

  The column shaft 22 and the pinion shaft 26 are connected by a single unequal speed universal joint 23. For this reason, with respect to the amount of change in the steering angle of the column shaft 22, the amount of change in the steering angle of the pinion shaft 26 is an inherent characteristic of the unequal-speed universal joint 23, unequal speed (swell) Affected by the phenomenon. That is, according to the change of the steering angle θ of the steering wheel 21, the steering angle of the pinion shaft 26 generates a “wave phenomenon” at the steering angle of the pinion shaft 26 when it greatly changes and when it changes small. . For this reason, the change in the stroke of the rack shaft 28 driven by the pinion shaft 26 also generates a wave-like "wave phenomenon" at the time of the large change and the time of the small change.

  The characteristics of the “wave phenomenon” of the unequal-speed universal joint 23 can be combined with the characteristics of the steering ratio Rs with respect to the steering angle θ by the suspension geometry of a vehicle such as a general passenger car. That is, when the steering angle θ of the steering wheel 21 is small, since the steering ratio Rs is small, the steered wheels 33, 33 are steered gently, so-called "slow steering". Since the steering ratio increases as the steering angle θ of the steering wheel 21 increases, the steered wheels 33, 33 steer relatively quickly, so-called "quick steer". As described above, in the rack and pinion mechanism 27, the gear ratio of the rack 27b to the pinion 27a can be the same as that of the variable ratio type.

  The electric power steering device 10, 10A of the present invention is suitable for use in a passenger car.

10 electric power steering device 10A electric power steering device 20 steering system 21 steering wheel 22 column shaft 23 universal joint 26 pinion shaft (first pinion shaft)
27 Rack and Pinion Mechanism (First Rack and Pinion Mechanism)
28 Rack shaft 41 Steering column 60 Auxiliary torque mechanism 60A Auxiliary torque mechanism 61 Torque sensor 63 Electric motor 64 Auxiliary torque transmission mechanism

Claims (1)

A column shaft connected to a steering wheel, a pinion shaft connected to the column shaft, a rack shaft connected to the pinion shaft via a rack and pinion mechanism, and an auxiliary torque to a steering torque generated in the steering wheel An electric power steering apparatus including an assist torque mechanism for adding
The auxiliary torque mechanism includes a torque sensor that detects the steering torque generated in the steering wheel, an electric motor that generates the auxiliary torque based on the steering torque detected by the torque sensor, and the electric motor. An auxiliary torque transmission mechanism for transmitting the auxiliary torque to any one of the rack shaft and the pinion shaft;
The connection configuration between the column shaft and the pinion shaft is connection by only a single universal joint,
The single universal joint is constituted by an unequal speed universal joint.
The torque sensor is disposed on a steering column for rotatably supporting the column shaft .
The phase of the unequal-speed universal joint with respect to the column shaft is set so that the steering ratio when the steering wheel is in the neutral position is smaller than the steering ratio when the steering wheel is at the other steering angle position. An electric power steering apparatus characterized by being set .

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