ELECTRIC LINEAR MOTION ACTUATOR AND ELECTRIC BRAKE SYSTEM

• US 20130048443A1
• Filed: 04/27/2011
• Published: 02/28/2013
• Est. Priority Date: 05/14/2010
• Status: Active Grant

• Current Assignee: NTN Corporation
• Original Assignee: NTN Corporation
• Inventors: Muramatsu, Makoto, Yamasaki, Tatsuya, Eguchi, Masaaki, Goto, Tomomi
• Granted Patent: US 9,145,940 B2
• Time in Patent Office: Days
• US Class Current: 188/72.1
• CPC Class Codes: F16D 2121/24 using motors
• CPC Class Codes: F16D 2125/40 Screw-and-nut
• CPC Class Codes: F16D 2125/48 with parallel stationary axes, e.g. spur gears
• CPC Class Codes: F16D 2127/06 Locking mechanisms, e.g. acting on actuators, on release mechanisms or on force transmission mechanisms
• CPC Class Codes: F16D 2129/08 Electromagnets
• CPC Class Codes: F16D 65/18 adapted for drawing members together , e.g. for disc brakes
• CPC Class Codes: F16H 25/2021 with means for avoiding overloading
• CPC Class Codes: F16H 25/2252 Planetary rollers between nut and screw
• CPC Class Codes: Y10T 74/18568 Reciprocating or oscillating to or from alternating rotary
• CPC Class Codes: Y10T 74/18576 including screw and nut

Abstract

An electric brake system is proposed which includes an electric linear motion actuator and can generate the required braking force with high accuracy. A load sensor (30) is provided in a motion converting mechanism of the actuator which converts the rotary motion of a rotary shaft (4) to which the rotation of an electric motor (2) is transmitted to linear motion of an outer ring member (5) as an output member. The load sensor (30) detects the pushing force with which the outer ring member (5) linearly drives a driven member. With this arrangement, if the driven member is a braking member of an electric brake system, it is possible to directly detect the braking force applied by the driven member and thus to accurately generate the required braking force.

Claims

1. An electric linear motion actuator comprising a motion converter mechanism for converting a rotary motion of a rotor shaft of an electric motor, or a rotary motion of a rotary member to which the rotation of the rotor shaft is transmitted to a linear motion of an output member for linearly driving a driven member, wherein the driven member is configured to be pushed by a front side of the output member, characterized in that a load sensor is mounted in the motion converter mechanism, the load sensor being configured to detect a pushing force with which the output member pushes the driven member when the driven member is linearly driven by the output member.

2. The electric linear motion actuator of claim 1, further comprising a heat insulator protecting the load sensor.

3. The electric linear motion actuator of claim 2, wherein the heat insulator is disposed between the load sensor and a component part of the motion converter mechanism which is in contact with the load sensor without the heat insulator.

4. The electric linear motion actuator of claim 1, wherein the load sensor is one of a load cell, a piezoelectric sensor, a semiconductor load sensor and a magnetostrictive load sensor.

5. The electric linear motion actuator of claim 1, wherein the motion converter mechanism comprises a rotary shaft member which is one of the rotor shaft of the electric motor and a rotary shaft which comprises said rotary member, an outer ring member provided around the rotary shaft member and fitted in a radially inner surface of a housing, a plurality of planetary rollers rotatably supported by a carrier so as to be disposed between the rotary shaft member and the outer ring member, the planetary rollers being configured to revolve around the rotary shaft member while rotating about axes of the individual planetary rollers when the rotary shaft member rotates, wherein a helical rib is formed on a radially inner surface of the outer ring member and each of the planetary rollers has on its radially outer surface circumferential grooves which are equal in pitch to the helical rib or a helical groove which is equal in pitch to, and different in lead angle from, the helical rib, said helical rib being engaged in the circumferential grooves or the helical grooves of the respective planetary rollers, whereby the motion converter mechanism converts the rotary motion of the rotary shaft member to linear motion of one of the outer ring member and the carrier as the output member for linearly driving the driven member, thereby linearly moving the outer ring member and the carrier relative to each other.

6. The electric linear motion actuator of claim 5, wherein the carrier is prevented from moving axially, and the outer ring member is fitted in the housing so as to be rotationally fixed to the housing and slidable relative to the housing, whereby the outer ring member serves as the output member for linearly driving the outer ring member.

7. The electric linear motion actuator of claim 6, wherein the load sensor is provided on a rear side of the outer ring member as the output member, which is opposite to the front side of the outer ring member, which pushes the driven member.

8. The electric linear motion actuator of claim 7, wherein the load sensor is disposed between a thrust bearing axially supporting a rear side of the carrier, which receives a reaction force of the pushing force of the outer ring member, and a backup member supporting a rear side of the thrust bearing.

9. The electric linear motion actuator of claim 7, wherein the load sensor is disposed between a backup member supporting a rear side of the carrier, which receives a reaction force of the pushing force of the outer ring member, through a thrust bearing and a stopper restricting the movement of the backup member in a rearward direction.

10. An electric brake system including an electric linear motion actuator for converting a rotary motion of an electric motor to a linear motion of an output member, thereby linearly driving a braking member, whereby the linearly driven braking member is pressed against a braked member, characterized in that the electric linear motion actuator is the electric linear motion actuator of claim 1.

11. The electric linear motion actuator of claim 2, wherein the load sensor is one of a load cell, a piezoelectric sensor, a semiconductor load sensor and a magnetostrictive load sensor.

12. The electric linear motion actuator of claim 3, wherein the load sensor is one of a load cell, a piezoelectric sensor, a semiconductor load sensor and a magnetostrictive load sensor.

13. The electric linear motion actuator of claim 2, wherein the motion converter mechanism comprises a rotary shaft member which is one of the rotor shaft of the electric motor and a rotary shaft which comprises said rotary member, an outer ring member provided around the rotary shaft member and fitted in a radially inner surface of a housing, a plurality of planetary rollers rotatably supported by a carrier so as to be disposed between the rotary shaft member and the outer ring member, the planetary rollers being configured to revolve around the rotary shaft member while rotating about axes of the individual planetary rollers when the rotary shaft member rotates, wherein a helical rib is formed on a radially inner surface of the outer ring member and each of the planetary rollers has on its radially outer surface circumferential grooves which are equal in pitch to the helical rib or a helical groove which is equal in pitch to, and different in lead angle from, the helical rib, said helical rib being engaged in the circumferential grooves or the helical grooves of the respective planetary rollers, whereby the motion converter mechanism converts the rotary motion of the rotary shaft member to linear motion of one of the outer ring member and the carrier as the output member for linearly driving the driven member, thereby linearly moving the outer ring member and the carrier relative to each other.

14. The electric linear motion actuator of claim 3, wherein the motion converter mechanism comprises a rotary shaft member which is one of the rotor shaft of the electric motor and a rotary shaft which comprises said rotary member, an outer ring member provided around the rotary shaft member and fitted in a radially inner surface of a housing, a plurality of planetary rollers rotatably supported by a carrier so as to be disposed between the rotary shaft member and the outer ring member, the planetary rollers being configured to revolve around the rotary shaft member while rotating about axes of the individual planetary rollers when the rotary shaft member rotates, wherein a helical rib is formed on a radially inner surface of the outer ring member and each of the planetary rollers has on its radially outer surface circumferential grooves which are equal in pitch to the helical rib or a helical groove which is equal in pitch to, and different in lead angle from, the helical rib, said helical rib being engaged in the circumferential grooves or the helical grooves of the respective planetary rollers, whereby the motion converter mechanism converts the rotary motion of the rotary shaft member to linear motion of one of the outer ring member and the carrier as the output member for linearly driving the driven member, thereby linearly moving the outer ring member and the carrier relative to each other.

15. The electric linear motion actuator of claim 4, wherein the motion converter mechanism comprises a rotary shaft member which is one of the rotor shaft of the electric motor and a rotary shaft which comprises said rotary member, an outer ring member provided around the rotary shaft member and fitted in a radially inner surface of a housing, a plurality of planetary rollers rotatably supported by a carrier so as to be disposed between the rotary shaft member and the outer ring member, the planetary rollers being configured to revolve around the rotary shaft member while rotating about axes of the individual planetary rollers when the rotary shaft member rotates, wherein a helical rib is formed on a radially inner surface of the outer ring member and each of the planetary rollers has on its radially outer surface circumferential grooves which are equal in pitch to the helical rib or a helical groove which is equal in pitch to, and different in lead angle from, the helical rib, said helical rib being engaged in the circumferential grooves or the helical grooves of the respective planetary rollers, whereby the motion converter mechanism converts the rotary motion of the rotary shaft member to linear motion of one of the outer ring member and the carrier as the output member for linearly driving the driven member, thereby linearly moving the outer ring member and the carrier relative to each other.

16. An electric brake system including an electric linear motion actuator for converting a rotary motion of an electric motor to a linear motion of an output member, thereby linearly driving a braking member, whereby the linearly driven braking member is pressed against a braked member, characterized in that the electric linear motion actuator is the electric linear motion actuator of claim 2.

17. An electric brake system including an electric linear motion actuator for converting a rotary motion of an electric motor to a linear motion of an output member, thereby linearly driving a braking member, whereby the linearly driven braking member is pressed against a braked member, characterized in that the electric linear motion actuator is the electric linear motion actuator of claim 3.

18. An electric brake system including an electric linear motion actuator for converting a rotary motion of an electric motor to a linear motion of an output member, thereby linearly driving a braking member, whereby the linearly driven braking member is pressed against a braked member, characterized in that the electric linear motion actuator is the electric linear motion actuator of claim 4.

19. An electric brake system including an electric linear motion actuator for converting a rotary motion of an electric motor to a linear motion of an output member, thereby linearly driving a braking member, whereby the linearly driven braking member is pressed against a braked member, characterized in that the electric linear motion actuator is the electric linear motion actuator of claim 5.

20. An electric brake system including an electric linear motion actuator for converting a rotary motion of an electric motor to a linear motion of an output member, thereby linearly driving a braking member, whereby the linearly driven braking member is pressed against a braked member, characterized in that the electric linear motion actuator is the electric linear motion actuator of claim 6.

21. An electric brake system including an electric linear motion actuator for converting a rotary motion of an electric motor to a linear motion of an output member, thereby linearly driving a braking member, whereby the linearly driven braking member is pressed against a braked member, characterized in that the electric linear motion actuator is the electric linear motion actuator of claim 7.

22. An electric brake system including an electric linear motion actuator for converting a rotary motion of an electric motor to a linear motion of an output member, thereby linearly driving a braking member, whereby the linearly driven braking member is pressed against a braked member, characterized in that the electric linear motion actuator is the electric linear motion actuator of claim 8.

23. An electric brake system including an electric linear motion actuator for converting a rotary motion of an electric motor to a linear motion of an output member, thereby linearly driving a braking member, whereby the linearly driven braking member is pressed against a braked member, characterized in that the electric linear motion actuator is the electric linear motion actuator of claim 9.