JPH0429582B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an electric power steering device equipped with a fail-safe mechanism.

(Prior art) In recent years, it has been installed on the steering shaft of automobiles.
It has an input shaft that connects to the steering wheel side and an output shaft that connects to the front wheels.It is an electric type that is configured to detect the required torque between the input shafts according to the load when operating the steering wheel, and activate the built-in electric motor to assist the steering torque. A power steering device is proposed. This electric power steering device generally includes an electromagnetic clutch between the rotating shaft and the output shaft of the electric motor, and the operation of the electric motor is controlled by a signal detected by a torque detector. This makes it possible to effectively transmit torque to the output shaft.

(Problems to be Solved by the Invention) As described above, in a control circuit that outputs a control signal based on a torque detector and its output signal, an electric motor that generates auxiliary torque and an output torque of the electric motor are connected to an output shaft. If the transmitting electromagnetic clutch is configured to be controlled together, if an abnormality occurs in the torque detector etc. and a detection signal is output, the electric motor will operate even though no steering torque is applied to the input shaft, and the electromagnetic clutch will be activated. The clutch is in the connected state and only auxiliary torque is generated on the output shaft.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an electric power steering device configured such that when no steering torque is applied to the input shaft, even if the electric motor operates, its rotational torque is not transmitted to the output shaft. It is something.

(Means for Solving the Problems) The present invention provides an electric power steering device in which relative rotational displacement is achieved between an input shaft, an intermediate shaft, and a first torsion bar, and between an intermediate shaft and an output shaft by a second torsion bar. In addition to connecting possible
A first torque detection section that detects steering torque based on the magnitude of relative rotational displacement between the input shaft and the intermediate shaft, and a second torque detection section that detects steering torque based on the magnitude of relative rotational displacement between the intermediate shaft and the output shaft. The electric motor is controlled by the output of the first torque detecting section, and the on/off of the clutch means is controlled by the output of the second torque detecting section.

(Function) According to the above configuration, the clutch means is turned on only when the steering torque is separately detected for the first torque detection section that outputs a signal that is the basis of operation control of the electric motor that generates the auxiliary torque. Since the second torque detection section is provided, even if the electric motor is operated in a state where there is no steering torque, this rotational torque can be prevented from being transmitted to the output shaft. Then, the first torque detection section detects the relative rotational displacement between the input shaft and the intermediate shaft set by the first torsion bar, and similarly detects the second
Since the torque detection section detects the steering torque based on the relative rotational displacement between the intermediate shaft and the output shaft set by the second torsion bar, it is easy to make the detection characteristics of these torque detection sections different, allowing for more precise control. can be done.

(Example) An example of the present invention will be described below with reference to the drawings.

Figure 1 is a longitudinal cross-sectional view of the electric power steering device, with the cut plane bent at 90 degrees at the center line.

In FIG. 1, reference numeral 1 denotes a cylindrical case, and an input shaft 2, an intermediate shaft 3, and an output shaft 4 are arranged along the axis of the case 1. The input shaft 2 and the intermediate shaft 3, and the intermediate shaft 3 and the output shaft 4 are connected by first and second torsion bars 5 and 6, respectively. A DC motor 7 is built in the center of the case 1, magnets 8 are fixed at symmetrical positions on the inner surface of the case, and bearings 10 and 1 are mounted on the intermediate shaft 3.
Reference numerals 1 and 12 indicate a rotatably provided cylindrical shaft; 13 an armature winding fixedly attached to the cylindrical shaft 9; 14 a commutator;
5 is a brush that supplies power to the armature winding 13. A first torque detection section 16 is built into the small diameter portion of the case 1 on the right side in FIG. 1, and a planetary gear reduction mechanism 17 and a multi-plate clutch mechanism 18 serving as clutch means are built into the left side portion.

The first torque detection section 16 is constituted by a differential transformer 19 in this embodiment. 19A is a primary coil 19a fixed to the inner surface of the case and two secondary coils 19b, 19b provided on both sides of the primary coil 19a.
The coil part 19B consists of the input shaft 2 and the intermediate shaft 3.
This is a movable iron core that moves in the axial direction in response to the direction and magnitude of the angular difference when a relative angular difference occurs due to the torsion of the torsion bar 5. 1
The control circuit 20 provides an alternating current signal to the secondary coil 19a, and the output signals of the secondary coils 19b, 19b are provided to the control circuit 20, where the signals are processed. Based on this signal processing, the control circuit 20 supplies armature current to the electric motor 7 in order to generate the required auxiliary torque.

The planetary gear reduction mechanism 17 also includes a first sun gear 21 formed at the left end of the cylindrical shaft 9, three planetary gears 22, a carrier member 23 that pivotally supports the planetary gears 22, and a cylindrical portion of the carrier member 23. A second sun gear 24, three planetary gears 25, a second carrier member 26 which supports the planetary gears 25 and is rotatably supported on the intermediate shaft 3 by a bearing 26, and has internal teeth. and a ring gear 27.

The multi-plate clutch mechanism 18 includes the carrier member 26 and a carrier member 2 fixed to the output shaft 4.
8. Clutch plates 29 and 30 are engaged with the carrier member 26 and rotate together with it, while clutch plates 31 and 32 are engaged with the carrier member 28 and rotated together with it. For example, three holes are formed in the outer clutch plate 32, and a pushing member 33 and a sphere 34 are provided in the holes, and the sphere 34 is pressed by a clutch disk 35 fixed to the intermediate shaft 3. . The clutch disk 35 is formed with a tapered recess 36, which is deepest at the center, as shown in FIG. 2, at a location where the sphere 34 comes into contact. In this structure, when a relative angle difference occurs between the intermediate shaft 3 and the output shaft 4 due to the torsion of the torsion bar 6, the sphere 34 is pushed in the direction A by the clutch disk 35, and the clutch plates 29, 30, 31, 32 becomes connected.

The input shaft 2 is rotatably provided with a bearing 37, and its outer end 2a is connected to the handle. Intermediate shaft 3
is rotatably provided by bearings 10, 11 and a bearing 38 interposed between the cylindrical shaft 9 and the cylindrical shaft 9. The left end of the input shaft 2 and the right end of the intermediate shaft 3 are engaged with each other with a predetermined gap due to the uneven relationship. The output shaft 4 has bearings 39,3
It is rotatably provided at 9, and its outer end is connected to the load side. At the left end of the intermediate shaft 3 and the right end of the output shaft 4, two uneven engaging portions 40 having a predetermined gap are provided, as shown in FIG. 40a is a concave portion, and 40b is a convex portion.

In FIG. 1, 41 is a long bolt for assembling the case 1, and 42 is a lid that supports the bearings 39, 39 and is provided at the left end of the case 1.

Next, the operation of the electric power steering device having the above configuration will be explained.

When a steering torque is applied to the input shaft 2 and a load is applied to the output shaft 4, torsion occurs between the input shaft 2 and the intermediate shaft 3 and between the intermediate shaft 3 and the output shaft 4 against the torsion bars 5 and 6. arise. When a relative angle difference occurs between the input shaft 2 and the intermediate shaft 3 due to twisting of the torsion bar 5, this angle difference is detected by the first torque detection section 16, and a detection signal is sent to the control circuit 20. Based on this detection signal, the control circuit 20
obtains the required armature current and supplies it to the motor 7. The electric motor 7 is supplied with an armature current via a brush 15 and a commutator 14, and generates a required auxiliary torque. The rotational torque of the electric motor 7 is transmitted via a planetary gear reduction mechanism 17. On the other hand, when a relative angle difference occurs between the intermediate shaft 3 and the output shaft 4 due to twisting of the torsion bar 6, the tapered recess 36 of the clutch disk 35 pushes the sphere 34, and the clutch plates 29, 30, 31, and 32 are crimped. , the multi-plate clutch mechanism 18 is in the connected state. As a result, the auxiliary rotational torque output from the electric motor is reduced to a predetermined rotational speed by the speed reduction mechanism 17 and transmitted to the output shaft 4 via the multi-plate clutch mechanism 18. The above operation occurs no matter which direction the input shaft 2 is rotated.

Now, assume that the torque detection section 16 outputs a signal related to torque even though no steering torque is applied to the input shaft 2. Then, the control circuit 20 performs signal processing in the same manner as described above, and operates the electric motor 20 in accordance with the detected torque. However,
Since no steering torque is applied to the input shaft 2, there is no relative angular difference between the intermediate shaft 3 and the output shaft 4, thereby keeping the multi-plate clutch mechanism 18 in a disconnected state. Therefore, even if the electric motor 7 generates rotational torque, it will not be transmitted to the output shaft 4.

Since the spring constants of the torsion bars 5 and 6 can be adjusted separately, the detection characteristics of the torque detection units 16 and 43 can also be easily varied, and the optimum detection characteristics can be set for controlling the electric motor 7 and clutch mechanism 18. .

As described above, according to the above structure, the intermediate shaft 3 is provided separately, the intermediate shaft 3 and the output shaft 4 are connected by the torsion bar 6, and the clutch disk 35, the sphere 34, and the pushing member 33 are provided, and the input shaft 2 is used for steering. A second torque detection section 43 is provided which can determine whether or not torque is applied, and the action of this torque detection section 43 selects whether or not the multi-disc clutch mechanism 18 is connected. As a result, when steering torque is not applied to the input shaft 2, even if the electric motor 7 rotates, its output torque is not transmitted to the output shaft 4.

Note that the uneven engagement portion 40 between the intermediate shaft 3 and the output shaft 4
is a mechanism that can ensure that both shafts are connected in any case.

In the above embodiment, since it is not necessary to use an electromagnetic clutch, the device can be made smaller and lighter.

As another embodiment, in an electric power steering device equipped with an electromagnetic clutch, the on/off state of the electromagnetic clutch corresponding to the second torque detection section 43 is
It is also possible to provide an electrical switch section for determining the off state.

(Effect of the invention) As is clear from the above explanation, according to the present invention,
Even if a failure occurs in the electrical system and the electric motor is activated, the output torque of the electric motor can be prevented from being transmitted to the output shaft unless steering torque is applied.
Since the first torque detection section and the second torque detection section detect steering torque based on the rotational displacement set by different torsion bars, the detection characteristics of these torque detection sections can be set separately, resulting in more precise control.

[Brief explanation of drawings]

FIG. 1 is a longitudinal cross-sectional view of an electric power steering device according to an embodiment of the present invention, FIG. 2 is a view of the main part as viewed from the direction of the arrow in FIG. 1, and FIG. 3A is a view as seen from the direction of the arrow in FIG. Figure 3B is a diagram of the main part of Figure 3A.
FIG. In the drawing, 2 is an input shaft, 3 is an intermediate shaft, 4 is an output shaft, 7 is an electric motor, 16 is a first torque detection section, 17
18 is a planetary gear reduction mechanism, 18 is a multi-plate clutch mechanism,
20 is a control circuit, and 43 is a second torque detection section.

Claims (1)

[Claims] 1. It has an input shaft, an intermediate shaft, and an output shaft, and connects an electric motor, the input shaft, and the intermediate shaft so that they can be relatively rotationally displaced by a first torsion bar, and controls the relative rotational displacement between the input shaft and the intermediate shaft. A first torque detection section detects steering torque based on the magnitude of the steering torque, and a second torsion bar connects the intermediate shaft and output shaft so that the intermediate shaft and the output shaft can rotate relative to each other. a second torque detection section that detects steering torque based on the magnitude of relative rotational displacement; a control circuit that drives the electric motor based on the output signal of the first torque detection section; and a control circuit that is interposed between the electric motor and the output shaft. An electric power steering device characterized in that the clutch means is brought into a connected state by the detection of steering torque by the second torque detection section.