JP3377865B2 - Electric power steering device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rack and pinion type power steering control device. 2. Description of the Related Art In a conventional example shown in FIGS. 3, 4 and 5, a stub shaft 1 is linked to a handle H, and a pinion shaft 3 is provided.
To form a pinion 3a, and the pinion 3a
Are engaged with the rack 4 a formed on the rack shaft 4. The stub shaft 1 and the pinion shaft 3 are
The shafts 1 and 3 are connected via a torsion bar 8 so that the shafts 1 and 3 can rotate relative to each other while twisting the torsion bar 8. The stub shaft 1 and the pinion shaft 3 are respectively provided with driven gears 9 and 1.
0 is rotatably provided, and a pair of driven bevel gears 9 and 10 are meshed with a drive bevel gear 11 shifted by 90 degrees with respect to the axis thereof. Therefore, when the drive bevel gear 11 rotates, the two driven bevel gears 9, 10
Will rotate in opposite directions. The drive bevel gear 11 is linked via a speed reducer 6 to an electric motor 7 having a constant rotation in one direction, and the electric motor 7 is connected to a battery 5 which is a power supply source. Further, the pair of driven gears 9, 10
Between them, a tubular movable body 12 is fitted so as to straddle both the stub shaft 1 and the pinion shaft 3. The movable body 12 is connected to the stub shaft 1 by straight spline connection, and to the pinion shaft 3 by helical spline connection. That is, the tip portion of the stub shaft 1 is defined as a straight spline shaft portion 17, and the straight spline shaft portion 1
7, a straight spline portion 18 formed on one side of the movable body 12 is engaged. Further, the tip of the pinion shaft 3 is a helical spline shaft 19,
A helical spline portion 20 formed on the other side of the movable body 12 is engaged with the helical spline shaft portion 19. The movable body 12 has a helical spline connection to the stub shaft 1 and a pinion shaft 3
May be connected by a straight spline. A first clutch mechanism 13 is provided on the movable body 12 and one driven bevel gear 9 as described above, and a second clutch mechanism 14 is provided between the movable body 12 and the other driven bevel gear 10. Next, the operation of the conventional example will be described. Now, when the stub shaft 1 is rotated by turning the handle H, the rotational force is transmitted to the pinion shaft 3 via the torsion bar 8. However, since the pinion shaft 3 is hard to rotate due to the resistance on the tire side, the stub shaft 1 rotates relatively to the pinion shaft 3 while twisting the torsion bar 8. Thus, the stub shaft 1
Is rotated, the movable body 12 also rotates integrally therewith. However, since the two shafts 1 and 3 rotate relative to each other as described above, the movable body 12 moves in the axial direction according to the lead of the helical spline shaft 19. At this time, the greater the resistance on the tire side, the greater the relative rotation amount between the shafts 1 and 3 and the greater the amount of movement of the movable body 12 in the axial direction. However, the moving direction of the movable body 12 is the stub shaft 1
It depends on the direction of rotation. For example, when the handle H is turned to the right, the stub shaft 1 rotates in the direction of arrow A1, and the movable body 12 moves upward in FIG. 5 to connect the first clutch mechanism 13. Conversely, when you turn the handle H to the left,
The stub shaft 1 rotates in the direction of arrow A2,
The movable body 12 moves downward in FIG.
Connect. When the first clutch mechanism 13 is connected, the driving bevel gear 11 linked to the electric motor 7 is turned by an arrow A
In this case, the movable body 12 rotates together with the driven bevel gear 9 in the A1 direction. When the movable body 12 rotates in the direction of arrow A1 in the state where the first clutch mechanism 13 is connected in this way, the stub shaft 1 and the pinion shaft 3 integrally rotate in the direction of arrow A1 via the movable body 12.
In other words, the pinion shaft 3 is rotated by the driving force of the electric motor 7 to move the rack shaft 4 and power assist the steering force. Also, contrary to the above, the second
When the clutch mechanism 14 is connected, the movable body 12
Rotates with the driven gear 10 in the direction of arrow A2.
When the movable body 12 rotates in the direction of arrow A2 with the second clutch mechanism 14 connected as described above, the stub shaft 1 and the pinion shaft 3 integrally rotate in the direction of arrow A2 via the movable body 12. Also in this case, the electric motor 7
The pinion shaft 3 is rotated by the driving force to move the rack shaft 4 to assist the steering force. In this conventional example, although not shown, the electric motor 7 is configured to start rotating as soon as the ignition switch is turned on. Further, the electric motor 7 may be configured to detect the rotation of the handle and rotate. In the device having such a configuration, the electric motor 7 as a drive source is selected based on the maximum output torque T required by the power steering device. However,
The output torque of the electric motor 7 varies depending on the load acting on it. When the steering torque is small and the clutch is not connected, the load on the electric motor 7 is small, and the motor output torque of the electric motor 7 is small, but the rotation speed is high. At this time, the maximum motor rotation speed of the electric motor 7 reaches near N. Conversely, the greater the load, the greater the output torque, but this time the number of revolutions will be lower. This characteristic is indicated by the straight line a in FIG. FIG. 3 shows the characteristic of the motor output torque-rotational speed when the power supply source is a general battery 5 with a constant output voltage. [0008] As described above, in the conventional apparatus, when an electric motor is selected based on a required maximum output torque T, when the load acting on the electric motor is minimum, the electric motor is replaced. For example, when the output torque is minimum, the rotation speed of the electric motor 7 becomes higher than necessary. As described above, if the rotation speed of the electric motor increases, the rotation speed of the speed reducer naturally increases, which causes a problem that noise increases. Further, when the electric motor rotates at a high speed, the motor brush and the like are quickly consumed, and the life of the electric motor is shortened. An object of the present invention is to provide an electric power steering apparatus that ensures a required maximum output torque and prevents the motor rotation speed from becoming higher than the required maximum rotation speed even when the output torque is minimum. . According to the present invention, a stub shaft connected to a handle and a pinion shaft formed with a pinion meshing with a rack are connected by a torsion bar, while a drive bevel gear and a drive bevel gear are connected. The drive bevel gear includes a pair of driven bevel gears facing each other while meshing with each other while shifting the direction of the axis by 90 degrees.
Each of the stub shaft and the pinion shaft is projected between opposed portions of the pair of driven gears, and both shafts are rotatable with respect to the pair of driven gears. In between, there is provided a movable body that straddles a stub shaft and a pinion shaft, and this movable body makes a straight spline connection with one shaft and a helical spline connection with the other shaft, while the movable body and one A first clutch mechanism is provided between the driven bevel gear and a second clutch mechanism is provided between the movable body and the other driven bevel gear, and the driving bevel gear is connected to an electric motor via a speed reducer. The electric motor is based on an electric power steering device connected to a power supply source. Assuming the above device, the present invention
A rotation speed sensor connected to the electric motor, and a control device connected to the rotation speed sensor, the control device includes:
It is characterized in that the voltage applied from the power supply source to the electric motor is controlled so that the motor speed does not exceed the required maximum speed. According to the present invention, as described above, the rotation speed of the electric motor can be detected by the rotation speed sensor, and the detection result can be fed back to the control device. Then, the voltage applied to the electric motor is controlled so that the rotation speed of the electric motor does not become higher than the required maximum rotation speed. As described in the prior art, when the battery 5 with a constant applied voltage is used, there is a characteristic between the motor output torque and the rotation speed of the electric motor 7 as shown in FIG. .
However, in actuality, considering the maximum turning speed of the steering wheel H and the reduction ratio of the conventional reduction gear 6, the assist force is small.
That is, the high rotation range where the motor output torque is small is an unnecessary high rotation range. Therefore, in this embodiment, the control device 15 is controlled so that the rotation speed of the electric motor 7 does not become higher than necessary.
Thus, the voltage applied to the electric motor 7 is controlled. The lower the required value of the maximum number of revolutions N1 of the electric motor 7, the lower the noise of the speed reducer, and the longer the life of each part. However, this required maximum rotational speed N1
If the steering wheel turning speed is too low,
May be higher than the rotation speed of the electric motor 7 obtained through the control, and the assist force may not be able to keep up. Considering the above, the required maximum number of rotations of the electric motor 7 is set to N1. In this embodiment, when the motor rotation speed N1 reaches a certain rotation speed via the speed reducer 6, N1 is set while considering that this rotation speed does not become lower than the steering wheel rotation speed that can be actually steered by the driver. It was determined as the required maximum speed. FIG. 1 is a mechanism diagram of an embodiment of the present invention.
In the figure, an electric motor 7 is connected via a control device 15 to a battery 5 which is a power supply source thereof. Further, a rotation sensor 16 is connected to the electric motor 7, and the rotation sensor 16 feeds back the detected rotation speed of the electric motor 7 to the control device 15. Since the configuration other than the above is the same as the conventional one, the same components as those of the conventional example are denoted by the same reference numerals. FIG. 2 shows an operation flowchart of the control device. Let T1 be the maximum motor output torque when the motor output torque is at the required maximum rotation speed N1. In FIG. 2, the motor output torque is the maximum motor output torque T
Consider an area less than one. At this time, if the motor rotation speed fed back to the control device 15 is smaller than the required maximum rotation speed N1, the applied voltage is increased by the control device 15 to maintain the required maximum rotation speed N1.
Conversely, even when the motor rotation speed fed back to the control device 15 is higher than the required maximum rotation speed N1, the control device 15 reduces the applied voltage to maintain the required maximum rotation speed N1. (The above is P1 in FIG. 1.
-P2 region. However, the motor output torque is the maximum motor output torque T
When it is larger than 1, even if the battery voltage is applied to the electric motor 7 at 100%, the rotation speed of the electric motor 7 cannot exceed the motor output torque-rotation speed characteristic a determined by the battery voltage. It decreases according to. (This is the region of P2-P3 in FIG. 2, which is the same as the conventional case. Further, the above-mentioned P1 to P3 are the motor output torque-rotation speed characteristics b of the present embodiment.) According to the present invention, the rotation speed of the electric motor does not become higher than the required maximum rotation speed, so that the consumption of the motor brush and the like can be reduced, and the life of the electric motor is extended. In addition, the number of rotations of the speed reducer does not become unnecessarily high in accordance with the electric motor, the noise can be reduced, and the burden on the speed reducer, the clutch mechanism, the bearing, and the like can be reduced, and the life thereof can be extended. .

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a mechanism diagram of an embodiment of the present invention. FIG. 2 is an operation flowchart of the control device of the present invention. FIG. 3 is a diagram showing motor output torque-revolution speed characteristics of an electric motor when a battery voltage is constant. FIG. 4 is a mechanism diagram of a conventional device. FIG. 5 is a sectional view of a movable case. [Description of Signs] 1 Stub shaft 2 Movable body case 3 Pinion shaft 4 Rack shaft 5 Battery 6 Reducer 7 Electric motor 8 Torsion bar 9 Follower driven gear 10 Follower driven gear 11 Drive bevel gear 12 Movable body 13 First clutch mechanism 14 Second rotation mechanism 15 Control device 16 Rotation sensor H Handle a This is a motor output torque-revolution number characteristic of a conventional electric motor. b is a motor output torque-revolution number characteristic of the electric motor according to the embodiment of the present invention. T Required maximum motor output torque N Maximum motor rotation speed T1 Maximum motor output torque N1 when N1 Required maximum rotation speed

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-6-293266 (JP, A) JP-A-1-94064 (JP, A) JP-A-5-238411 (JP, A) JP-A-2- 124366 (JP, A) JP-A-8-133106 (JP, A) JP-A-7-13651 (JP, U) JP-A-7-19062 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) B62D 5/04 B62D 6/00-6/06

Claims (1)

(57) [Claim 1] A stub shaft connected to a handle and a pinion shaft formed with a pinion engaging with a rack are connected by a torsion bar, while a drive bevel gear and The drive bevel gear includes a pair of driven bevel gears that face each other while shifting the direction of the axis by 90 degrees, and each of the stub shaft and the pinion shaft is connected to an opposing portion of the pair of driven bevel gears. Protruding in between, and, for a pair of driven gears, both shafts are rotatable, and, between the pair of driven gears, a movable body that straddles a stub shaft and a pinion shaft is provided, This movable body has a straight spline connection with one shaft and a helical spline connection with the other shaft. A first clutch mechanism is provided between one driven bevel gear and a second clutch mechanism is provided between the movable body and the other driven bevel gear, and the driving bevel gear is connected to an electric motor via a speed reducer. An electric power steering device connected to a power supply source, the electric motor comprising: a rotation speed sensor connected to the electric motor; and a control device connected to the rotation speed sensor. Number,
An electric power steering apparatus characterized in that a voltage applied from an electric power supply to an electric motor is controlled so as not to exceed a required maximum number of revolutions.