JPH07223548A - Torque transmission mechanism - Google Patents

Abstract

PURPOSE:To realize the sure clutch operation with the simple constitution, as for a torque transmission mechanism which is suitably used for a motor- driven type power steering device. CONSTITUTION:A torque transmission mechanism 1 which is arranged on a power steering device 2 and carries out the auxiliary steering by transmitting the output torque of a motor 21 to a steering shaft 4, is equipped with a steering side shaft connected with the steering shaft 4 through a reduction gear 18 and an output side shaft which has a fitting groove for the fitting with the steering side shaft inside, and transmits the driving torque generated by the motor 21 to the steering side shaft through the fitting part. The thermal expansion rate of the material which constitutes the output side shaft is set larger than the thermal expansion rate of the material which constitutes the steering side shaft.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a torque transmission mechanism,
Particularly, the present invention relates to a torque transmission mechanism suitable for use in an electric power steering device.

[0002]

2. Description of the Related Art A general power steering system has a structure in which hydraulic pressure is used to assist the steering wheel operating force. Therefore, the power steering device includes a hydraulic pump driven by the engine and an actuator (for example, a hydraulic cylinder or the like) that drives the steering gear with the hydraulic pressure supplied by the hydraulic pump.

In the power steering device using this hydraulic pressure, it is necessary to dispose a hydraulic pump, a hydraulic cylinder, etc. around the steering in the engine room of the automobile. In order to arrange the engine, a considerably large space is required in the engine room, and even if it is not, the narrow engine room is further narrowed, which causes the maintainability such as maintenance and inspection to be significantly deteriorated.

On the other hand, for the purpose of miniaturization and reduction of energy loss, there has been proposed a device which directly drives a steering gear by using an electric motor as an actuator, but in reality, control of the electric motor is complicated. Has not yet been put to practical use.

Therefore, while an electric motor is provided as an actuator, the electric motor is connected to a steering gear via a transmission and an electromagnetic clutch, and the electric motor and the electromagnetic clutch are controlled in accordance with the operating state to make the energy compact. A power steering device having high efficiency and excellent steering and safety has been provided (Japanese Patent Laid-Open No. 64-41468).

The power steering device disclosed in the above publication detects the load of the electric motor and releases the electromagnetic clutch when the load is in an overload state of a predetermined value or more,
As a result, the electric motor is prevented from heating and burning.

[0007]

However, in the torque transmission mechanism provided in the above conventional power steering apparatus, an electromagnetic clutch for interrupting torque transmission must be provided, and the electromagnetic clutch is an electromagnetic solenoid, a plurality of gears,
Since it is composed of many parts such as a rotation restricting mechanism that restricts the rotation of the gear by the operation of the electromagnetic solenoid when the torque is cut off, the structure is complicated, the cost is high, and the device shape becomes large. there were.

In the above power steering device,
In order to open the electromagnetic clutch when the motor is overloaded, a motor overcurrent detector for detecting that an overcurrent flows through the motor is provided, and the motor overcurrent detector supplies it to the clutch controller 14. It is necessary to install software (logic) for driving the electromagnetic solenoid on the basis of the received signal, which also causes a problem that both the software and hardware configurations are complicated.

The present invention has been made in view of the above points, and an output side for transmitting a driving torque generated by a steering shaft connected to a steering member and an electric motor to a steering shaft via a fitting portion. An object of the present invention is to provide a torque transmission mechanism capable of realizing a reliable clutch operation with a simple structure by configuring the shaft and the shaft with members having different thermal expansion coefficients.

[0010]

In order to solve the above problems, the present invention is characterized by taking the following means.

According to another aspect of the present invention, there is provided a torque transmission mechanism arranged in a power steering device for transmitting an output torque of an electric motor to a steering member to perform an auxiliary steering, the steering side being connected to the steering member. The shaft and an annular shape form a fitting portion inside which the steering-side shaft is fitted. The drive torque generated by the electric motor is transmitted to the steering-side shaft through the fitting portion. And a coefficient of thermal expansion of a material forming the output side shaft is set to be larger than a coefficient of thermal expansion of a material forming the steering side shaft.

According to a second aspect of the invention, in the torque transmission mechanism according to the first aspect, it is determined based on the motor drive current value that the output side shaft and the steering side shaft have been disengaged. A disengagement detection means and an energization control means for stopping energization to the electric motor when it is determined that the output side shaft and the steering side shaft are disengaged from each other are provided. is there.

Further, according to the third aspect of the present invention, the first member formed in an annular shape is fitted into the first member, and the frictional force generated at the fitting portion of the first member causes frictional force. A torque transmission mechanism including a second member that transmits torque from a first member, wherein either the first member or the second member is formed of a member having a large coefficient of thermal expansion. In addition, the other is formed of a member having a small coefficient of thermal expansion.

[0014]

The above-mentioned means operate as follows.

According to the first aspect of the present invention, the steering shaft is fitted to the fitting portion formed on the output shaft, whereby the drive torque generated by the electric motor from the output shaft to the steering shaft. Can be transmitted.

When the electric motor is overloaded, the electric motor heats up, so the heat generated by the electric motor is transferred to the output side shaft. The coefficient of thermal expansion of the material forming the output-side shaft is set to be larger than the coefficient of thermal expansion of the material forming the steering-side shaft, so that the output-side shaft undergoes large thermal expansion with respect to the steering-side shaft. Thereby, the fitting of the output side shaft and the steering side shaft in the fitting portion is released,
The torque transmission from the output side shaft to the steering side shaft is blocked, and it is possible to prevent an excessive steering force from being applied to the steering member, and it is possible to improve safety.

According to the invention of claim 2, claim 1
In the torque transmission mechanism described above, when the fitting release detecting means determines that the fitting between the output side shaft and the steering side shaft has been released, the energization controlling means stops energizing the electric motor. Unnecessary energization of the motor is prevented and damage to the electric motor can be prevented.

Further, according to the invention of claim 3, the first member is formed into an annular shape, and the second member is fitted into the first member, whereby the first member and the second member are fitted. Is applied to the first member and the second member by making the torque transmission between the first member and the second member different from each other in the coefficient of thermal expansion of the first member and the coefficient of thermal expansion of the second member. Since the torque can be transmitted and released between the first member and the second member according to the generated heat, the torque can be transmitted and released between both members with a simple configuration.

[0019]

Embodiments of the present invention will now be described with reference to the drawings.

FIG. 1 shows a power steering device 2 to which a torque transmission mechanism 1 according to an embodiment of the present invention is applied. In the figure, 3 is a steering wheel,
It is fixed to the upper end of the steering shaft 4. Further, the power steering device 2 according to the present embodiment adopts a rack and pinion system, so that the lower end of the steering shaft 4 is connected to the rack and pinion type steering gear 5.

The steering gear 5 is composed of a pinion 6 arranged coaxially with the steering shaft 4 and a rack 7 meshing with the pinion 6. Therefore, when the driver rotationally operates the steering wheel 3, the steering shaft 4 rotates and the pinion 6 also rotates accordingly. It is displaced in the directions of the middle arrows A1 and A2. Further, tie rods 8 and 9 are connected to both sides of the rack 7, and a ball joint 10 connected to a suspension mechanism (not shown) in which tires are arranged at the tip of each tie rod 8 and 9. 11 is provided.

The pinion 6 and the rack 7 are the case 1
It is configured to be stored in the racks 2 and 13 and also the rack 7
Dust seal 1 at the connecting position between the tie rods 8 and 9.
4 and 15 are arranged. This allows
Dust is prevented from entering the meshing position between the pinion 6 and the rack 7 and the connecting position between the rack 7 and the tie rods 8 and 9.

A steering sensor 16 is provided at a predetermined position on the steering shaft 4. The steering sensor 16 is configured to detect a rotational torque generated on the steering shaft 4 when the driver rotates the steering wheel 3 and the steering wheel 3. The steering signal detected by the steering sensor 16 is transmitted to the power steering computer. In this embodiment, the engine control unit 17 (hereinafter referred to as the ECU) also serves as a power steering computer.

Further, a speed reducer 18 is arranged at a predetermined position on the steering shaft 4. The speed reducer 18 is composed of, for example, a pair of straight bevel gears 19 and 20, and is configured to obtain deceleration corresponding to the number of teeth of each gear 19 and 20. A pair of straight bevel gears 19, 20
Of these, one of the bevel gears 19 is disposed on the steering shaft 4, and the other of the bevel gears 2 is
0 is connected to an electric motor 21 (hereinafter, simply referred to as a motor) via a torque transmission mechanism 1 which is a main part of the present invention. By driving the motor 21 and transmitting the rotational force thereof to the steering shaft 4 via the torque transmission mechanism 1 and the speed reducer 18, the operating force of the steering wheel 3 can be power assisted.

The motor 21 has a built-in motor drive circuit.
Connected to the driver 22
Drive current I₂The rotation is controlled by
Has been. Further, the driver 22 is connected to the ECU 17 described above.
It is connected. The ECU 17 sends from the steering sensor 16.
Steering wheel based on the received torque signal
Optimal motor 21 for power assisting the operating force of 3
Supply current value I ₁To calculate this current value I₁Electric
Flow command value I₁Is transmitted to the driver 22. driver
22 is a drive current I of the motor 21.₂From the ECU 17
Received current command value I₁Drive current control to approach
I do.

Here, the torque transmission mechanism 1 will be described by enlarging it in FIG. As shown in the figure, the torque transmission mechanism 1 includes a steering side shaft 23 connected to a steering shaft 4 serving as a steering member via a reduction mechanism 18, and an output side shaft 24 connected to an output shaft of a motor 21. It is configured. In this embodiment, the output shaft 24 is integrated with the output shaft of the motor 21.

The output side shaft 24 is connected to the motor 21 (not shown in FIG. 2) at the right end in the figure,
A cylindrical fitting groove 25 is formed at the left end portion to have an annular shape. On the other hand, the steering shaft 23 is provided with a straight bevel gear 20 constituting the reduction mechanism 18 at the left end in the figure, and the right end is fitted into a fitting groove 25 formed in the output shaft 24. It has been configured.

Further, paying attention to the material of the shafts 23 and 24, the steering side shaft 23 is formed of a material having a small coefficient of thermal expansion (for example, ceramic),
The output side shaft 24 is the steering side shaft 23.
It is formed of a material (for example, copper) having a larger coefficient of thermal expansion than that of the above.

By configuring the torque transmission mechanism 1 as described above, when the torque transmission mechanism 1 is heated, since the output side shaft 24 is made of a material having a large coefficient of thermal expansion, large thermal expansion occurs. On the other hand, since the steering-side shaft 23 is made of a material having a small coefficient of thermal expansion, even if the torque transmission mechanism 1 is heated, thermal expansion as much as the output-side shaft 24 does not occur.

As a matter of course, due to the thermal expansion of the output side shaft 24, the diameter dimension of the fitting groove 25 formed in the output side shaft 24 also increases, and accordingly, the output side shaft 24 and the steering side. Shaft 23
The mating force between and decreases. Finally, the steering-side shaft 23 becomes freely rotatable in the fitting groove 25 (i.e., loosely fitted), and the output-side shaft 24
Torque cannot be transmitted from the steering wheel to the steering shaft 23.

That is, the torque transmission mechanism 1 functions as a clutch mechanism for transmitting and releasing the torque from the output side shaft 24 to the steering side shaft 23 according to the amount of heating applied. Further, the torque transmission mechanism 1 is
As described above, the columnar steering-side shaft 23,
Since the fitting groove 25 is formed, it has a simple configuration including only the output-side shaft 24 that has an annular shape.
The product cost of the torque transmission mechanism 1 can be kept extremely low.

Further, by appropriately selecting the materials of the steering shaft 23 and the output shaft 24, that is, the combination of the thermal expansion coefficients of the shafts 23 and 24, the torque transmission and the torque transmission cancellation between the shafts 23 and 24 can be performed. The timing to perform can be set arbitrarily.

Here, it is assumed that an overload is applied to the motor 21 and the motor 21 generates heat. When an overload is applied to the motor 21 and the motor 21 generates heat, the generated heat is conducted from the motor 21 to the output side shaft 24. In the configuration of the present embodiment, since the output side shaft 24 is made of a material having a large coefficient of thermal expansion as described above, the heat of the motor 21 is conducted to the output side shaft 24 and thermally expanded, so that the steering side Tokule transmission between the shaft 23 and the output side shaft 24 is released. That is, when an overload is applied to the motor 21, the transmission of the tokule between the steering shaft 23 and the output shaft 24 is released.

As described above, when an overload is applied to the motor 21, the torque transmission mechanism 1 automatically releases the tokule transmission between the steering shaft 23 and the output shaft 24 by the heat generated by the motor 21. To do. For this reason,
Tokle transmission between the steering-side shaft 23 and the output-side shaft 24 can be released with an extremely simple configuration without using a complicated other configuration such as an electromagnetic clutch, thereby reducing the cost of the torque transmission mechanism 1. be able to. Further, it is possible to prevent the motor 21 from being burnt out and prevent an excessive steering force from being applied to the steering shaft 4, thereby improving safety.

On the other hand, when an overload is applied to the motor 21 as described above, or when the torque transmission by the torque transmission mechanism 1 is released due to some cause of abnormality, the EC
The current command value I transmitted from U17 to the driver 22
_A large difference occurs between ₁ and the drive current value I ₂ supplied from the driver 22 to the motor 21. This is because the steering-side shaft 23 and the output-side shaft 24 are separated from each other, which reduces the load on the motor 21.

As described above, the ECU 2 drives the driver 2
The occurrence of an abnormality can be detected by detecting the difference between the current command value I ₁ sent to _{No. 2} and the drive current value I ₂ supplied from the driver 22 to the motor 21. The abnormality detection processing executed by the ECU 17 incorporated in this embodiment will be described below with reference to FIGS. 3 to 5.

FIG. 3 is a flow chart showing the abnormality detection processing executed by the ECU 17. The abnormality detection process shown in the figure is, for example, a routine process executed every 4 ms.

When the process shown in the figure is started, first in step 10, the driver 22 detects the drive current value I ₂ supplied to the motor 21. Continued Step 12
Then, the absolute value of the difference between the current command value I ₁ transmitted by the ECU 17 itself to the driver 22 and the drive current value I ₂ detected in step 10 is obtained, and whether or not the value is larger than the predetermined value I _s is determined. To judge.

When it is determined in step 12 that the absolute value of the difference between the current command value I ₁ and the drive current value I ₂ is larger than the predetermined value I _s , the steering shaft 23 and the output side are operated as described above. The shaft 24 is separated from the motor 21.
In this case, the motor 21 is overloaded or the torque transmission mechanism 1 is abnormally heated.

Therefore, if a positive determination is made in step 12, the ECU 17 sets the abnormality detection flag F indicating the occurrence of abnormality in step 14 (F = 1). On the other hand, when the negative judgment is made in 12, E
CU17 judges that no abnormality has occurred, and the step 1
In 6, the abnormality detection flag F is reset (F = 0). The abnormality detection processing ends by performing the above processing.

FIG. 4 is a flowchart showing the motor drive processing executed by the ECU 17 based on the detection result of the abnormality detection processing described with reference to FIG. The motor drive process shown in the figure is also a routine process executed every 4 ms, for example.

When the processing shown in FIG.
First, at step 20, in accordance with the steering signal transmitted from the steering sensor 16, the direction in which the driver rotates the steering wheel 3 and the steering shaft 4
The rotational torque T generated in the above is detected. Continued Step 22
Then, based on the rotation direction and the rotation torque T of the steering wheel 3 detected in step 20, the driver 22
Calculate the current command value I ₁ to be transmitted to.

In this embodiment, the map shown in FIG. 5 is used to calculate the current command value I ₁ in step 22. In the map shown in the figure, the horizontal axis represents the rotational torque T detected in step 20, and the vertical axis represents the required current command value I _1. 2
It is the original map. Further, in the map shown in the figure, for example, the rotational torque when the steering wheel 4 is rotated clockwise is the positive direction rotation, and the rotational torque when the steering wheel 4 is rotated counterclockwise is the negative direction rotation. .

Therefore, when the steering wheel 4 is rotated by the clockwise rotation torque (+ T _a ), the current command value I is calculated in step 22 as shown in FIG.
₁ is calculated as I ₁ = + I _a . When the steering wheel 4 is rotated by the counterclockwise rotation torque (-T _b ), the step 2 is performed as shown in FIG.
At 2, the current command value I ₁ is calculated as I ₁ = −I _b .

In the following step 24, the set state of the abnormality detection flag F set in steps 14 and 16 of the abnormality detection processing shown in FIG. 3 is judged. And step 24
When it is determined that the abnormality detection flag F is not set (F = 0), the ECU 17 determines that no abnormality has occurred, advances the processing to step 26, and obtains it in step 22. The current command value I ₁ is output to the driver 22.

On the other hand, when it is determined in step 24 that the abnormality detection flag F is set (F = 1), the ECU 17 causes the torque transmission mechanism 1, the power steering device 2, or a device in the vicinity thereof to operate. When it is determined that an abnormality has occurred, the process proceeds to step 28, the current command value (I ₁ = 0) is output to the driver 22 so that the power supply to the motor 21 is stopped, and the abnormality provided on the front panel, for example. Turn on the alarm lamp to notify the occurrence.

As a result, the driver can detect the occurrence of the above-mentioned abnormality, and the safety can be improved. Further, the above-mentioned abnormality detection processing and motor driving processing can be realized by software processing based on the output signal from the sensor that constitutes the torque transmission mechanism 1.
It does not increase the processing of CU17.

In the above-described embodiment, since the output shaft 24 is connected to the motor 21 as a heating element, the output shaft 24 is formed with the fitting groove 25 and has a large coefficient of thermal expansion. An example is shown in which the steering side shaft 23 is made of a material, has a shape that can be fitted into the fitting groove 25, and is made of a material having a small coefficient of thermal expansion.

However, the constitutional relationship between the output side shaft 24 (first member) and the steering side shaft 23 (second member) is not necessarily limited to the constitution of the above-mentioned embodiment, but the first member. Alternatively, the coefficient of thermal expansion and the fitting structure may be appropriately selected in consideration of which of the second members is provided with the heating element.

[0050]

As described above, according to the present invention, the following various effects can be realized.

According to the first aspect of the present invention, when the electric motor is overloaded, the heat generated by the electric motor releases the fitting between the output side shaft and the steering side shaft at the fitting portion, and the output side shaft is released. The torque transmission from the shaft to the steering shaft is automatically cut off. Therefore, despite the simple structure, torque transmission can be reliably cut off when the electric motor is overloaded, and an excessive steering force can be prevented from being applied to the steering member. It is possible to improve the sex.

According to the second aspect of the present invention, when the fitting release detecting means determines that the fitting between the output side shaft and the steering side shaft is released, the energization control means energizes the electric motor. Since the electric motor is stopped, unnecessary electric power supply to the electric motor is prevented and damage to the electric motor can be prevented.

Further, according to the third aspect of the invention, it is possible to transmit and release the torque between the first member and the second member with a simple structure.

[Brief description of drawings]

FIG. 1 is a main part configuration diagram showing a power steering device 2 to which a torque transmission mechanism according to an embodiment of the present invention is applied.

FIG. 2 is an enlarged perspective view showing a torque transmission mechanism.

FIG. 3 is a flowchart showing an abnormality detection process executed by an ECU.

FIG. 4 is a flowchart showing a motor drive process executed by the ECU based on the detection result of the abnormality detection process described with reference to FIG.

FIG. 5 is a diagram showing a map used to calculate a current command value I ₁ in step 22.

[Explanation of symbols]

 1 Torque Transmission Mechanism 2 Power Steering Device 2 Steering Wheel 4 Steering Shaft 5 Steering Gear 6 Pinion 7 Rack 8, 9 Tie Rod 16 Steering Sensor 17 ECU 18 Reducer 21 Motor 22 Driver 23 Steering Side Shaft 24 Output Side Shaft 25 Fitting Groove

Claims (3)

[Claims] 1. A torque transmission mechanism provided in a power steering device for transmitting an output torque of an electric motor to a steering member to perform auxiliary steering, wherein a steering shaft connected to the steering member and an annular shape. By forming a fitting portion for fitting the steering side shaft therein, and transmitting the driving torque generated by the electric motor to the steering side shaft via the fitting portion. And a thermal expansion coefficient of a material forming the output side shaft is set to be larger than a thermal expansion coefficient of a material forming the steering side shaft. 2. The torque transmission mechanism according to claim 1, further comprising a disengagement detection means for determining, based on a motor drive current value, that the engagement between the output side shaft and the steering side shaft has been released. A torque transmission mechanism comprising: energization control means for stopping energization of the electric motor when it is determined that the output side shaft and the steering side shaft are disengaged from each other. 3. A first member formed in an annular shape and fitted in the first member, and the friction force generated at a fitting portion between the first member and the first member causes A torque transmission mechanism including a second member for transmitting torque, wherein one of the first member and the second member is formed of a member having a large coefficient of thermal expansion, and the other is formed of a heat. A torque transmission mechanism characterized by being formed of a member having a small expansion coefficient.