WO2008087506A2 - A linear electro-mechanical actuator for a parking brake - Google Patents

A linear electro-mechanical actuator for a parking brake Download PDF

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Publication number
WO2008087506A2
WO2008087506A2 PCT/IB2007/055283 IB2007055283W WO2008087506A2 WO 2008087506 A2 WO2008087506 A2 WO 2008087506A2 IB 2007055283 W IB2007055283 W IB 2007055283W WO 2008087506 A2 WO2008087506 A2 WO 2008087506A2
Authority
WO
WIPO (PCT)
Prior art keywords
screw
reduction unit
transmission unit
parking brake
electric motor
Prior art date
Application number
PCT/IB2007/055283
Other languages
French (fr)
Other versions
WO2008087506A3 (en
Inventor
Ettore Berutti
Enrico Di Stefano
Original Assignee
Aktiebolaget Skf
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Aktiebolaget Skf filed Critical Aktiebolaget Skf
Publication of WO2008087506A2 publication Critical patent/WO2008087506A2/en
Publication of WO2008087506A3 publication Critical patent/WO2008087506A3/en

Links

Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60T—VEHICLE BRAKE CONTROL SYSTEMS OR PARTS THEREOF; BRAKE CONTROL SYSTEMS OR PARTS THEREOF, IN GENERAL; ARRANGEMENT OF BRAKING ELEMENTS ON VEHICLES IN GENERAL; PORTABLE DEVICES FOR PREVENTING UNWANTED MOVEMENT OF VEHICLES; VEHICLE MODIFICATIONS TO FACILITATE COOLING OF BRAKES
    • B60T13/00—Transmitting braking action from initiating means to ultimate brake actuator with power assistance or drive; Brake systems incorporating such transmitting means, e.g. air-pressure brake systems
    • B60T13/02—Transmitting braking action from initiating means to ultimate brake actuator with power assistance or drive; Brake systems incorporating such transmitting means, e.g. air-pressure brake systems with mechanical assistance or drive
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60T—VEHICLE BRAKE CONTROL SYSTEMS OR PARTS THEREOF; BRAKE CONTROL SYSTEMS OR PARTS THEREOF, IN GENERAL; ARRANGEMENT OF BRAKING ELEMENTS ON VEHICLES IN GENERAL; PORTABLE DEVICES FOR PREVENTING UNWANTED MOVEMENT OF VEHICLES; VEHICLE MODIFICATIONS TO FACILITATE COOLING OF BRAKES
    • B60T11/00—Transmitting braking action from initiating means to ultimate brake actuator without power assistance or drive or where such assistance or drive is irrelevant
    • B60T11/04—Transmitting braking action from initiating means to ultimate brake actuator without power assistance or drive or where such assistance or drive is irrelevant transmitting mechanically
    • B60T11/046—Using cables
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60T—VEHICLE BRAKE CONTROL SYSTEMS OR PARTS THEREOF; BRAKE CONTROL SYSTEMS OR PARTS THEREOF, IN GENERAL; ARRANGEMENT OF BRAKING ELEMENTS ON VEHICLES IN GENERAL; PORTABLE DEVICES FOR PREVENTING UNWANTED MOVEMENT OF VEHICLES; VEHICLE MODIFICATIONS TO FACILITATE COOLING OF BRAKES
    • B60T17/00—Component parts, details, or accessories of power brake systems not covered by groups B60T8/00, B60T13/00 or B60T15/00, or presenting other characteristic features
    • B60T17/18—Safety devices; Monitoring
    • B60T17/22—Devices for monitoring or checking brake systems; Signal devices
    • B60T17/221—Procedure or apparatus for checking or keeping in a correct functioning condition of brake systems
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
    • F16H—GEARING
    • F16H35/00—Gearings or mechanisms with other special functional features
    • F16H2035/005—Gearings or mechanisms preventing back-driving

Definitions

  • the present invention relates to a linear electromechanical actuator, in particular for a parking brake of a motor vehicle, comprising an electric motor, a screw mechanism and a gear reduction unit interposed between the electric motor and the screw mechanism.
  • an actuator for the parking brake must be irreversible (or "non-backdrivable"), i.e. it must be able to maintain the braking force imparted in the absence of a release command, hi other words, as a result of the friction between the movable parts of the actuator, the output rod must be able to maintain the position reached until a new operating command is given.
  • the screw mechanisms proposed hitherto for actuating parking brakes generally make use of friction screw mechanisms in an attempt to achieve a compromise between the requirement for "irreversibility” and a “direct” efficiency which is acceptable in terms of friction, hi this context, the expression “direct efficiency” is understood as meaning the efficiency obtained by operating the electric motor, while “indirect efficiency” indicates the efficiency obtained by operating the actuator output member.
  • the maximum direct efficiency which can be obtained with the friction screw mechanisms is in the order of 35- 40%. hi order to achieve a performance above this level it is necessary to use screw mechanisms which, however, are not irreversible or risk becoming so during the working life of the actuator, resulting in instability and incorrect functioning of the system.
  • U.S. patent No. 6,655,507 describes a screw actuator for a parking brake comprising an electric motor and a ball screw.
  • the actuator requires an electromechanical brake in order to maintain the position reached by the ball screw when no power is supplied by the electric motor.
  • the object of the invention is to provide an actuator which combines a high direct efficiency with the requirement for irreversibility, or negative indirect efficiency, without the addition of auxiliary devices for preventing undesirable movements of the output screw when no commands are given by the electric motor.
  • the actuator 10 designates overall a linear electromechanical actuator according to the invention, for operating the parking brakes (not shown) of a motor vehicle.
  • the actuator 10 includes an electric motor 20 which, by means of an epicyclic reduction unit 30 with spur gears and an associated ball screw 40, imparts linear movements to a component C for connection to the parking brakes by means of a Bowden cable (not shown).
  • the assembly formed by the epicyclic reduction unit 30 and the ball screw forms the transmission unit of the actuator.
  • the electric motor 20 is preferably a direct current permanent-magnet motor which is able to rotate selectively in both directions of rotation depending on the command signal received from an electronic control module (not shown).
  • the motor 20 rotationally drives, by means of a pair of spur gears 21, 31, a planet wheel carrier 32 mounted rotatably about an axis x coinciding with the actuating axis of the screw mechanism 40 and parallel to the axis X 1 of the electric motor.
  • Two bearings 51 are situated between the planet wheel carrier 32 and a tubular support portion 52 of the casing 50 of the actuator.
  • Designated 33 are the planet wheels of the reduction unit, which are mounted on cylindrical pivot pins 34.
  • the planet wheels mesh with a first fixed sun gear 35 mounted on the support 52 and with a second sun gear 36 rotationally integral with the screw nut 41 of the ball screw 40. Rotation of the screw nut 41 causes the displacement of a screw or threaded rod 42 along the axis x and, consequently, the connection component C connected to the screw 42.
  • the ball screw 40 is per se a reversible mechanism with a high mechanical performance
  • the epicyclic reduction unit has a negative "indirect" efficiency when no commands are given by the electric motor. This special feature means that the transmission unit is generally irreversible, while offering a suitable direct performance able to produce high actuating forces for the brake.
  • the epicyclic reduction unit owing to its characteristic feature of irreversibility, also performs the function of an actuator locking device, avoiding the costs associated with an additional locking device, as discussed in the introduction.

Landscapes

  • Engineering & Computer Science (AREA)
  • Transportation (AREA)
  • Mechanical Engineering (AREA)
  • Physics & Mathematics (AREA)
  • Fluid Mechanics (AREA)
  • Braking Arrangements (AREA)
  • Braking Systems And Boosters (AREA)

Abstract

A transmission unit for a linear electromechanical actuator, in particular for a parking brake, comprises: a non-backdrivable irreversible epicyclic reduction unit (30) capable of receiving a rotary movement from an electric motor (20), a reversible screw mechanism (40), preferably a ball screw, with a screw nut (41) which can be rotationally driven by means of the epicyclic reduction unit (30) about a longitudinal axis (x) and an output screw (42) translatable along said axis as a result of the rotation of the screw nut.

Description

A linear electro-mechanical actuator for a parking brake
The present invention relates to a linear electromechanical actuator, in particular for a parking brake of a motor vehicle, comprising an electric motor, a screw mechanism and a gear reduction unit interposed between the electric motor and the screw mechanism.
In an actuator of this kind, rotary movement imparted to the rotor of the electric motor is reduced by the reduction unit and converted by the screw mechanism into a linear movement of a threaded rod or output screw which, pulling a Bowden cable, applies a braking force to the parking brakes of the vehicle. Considered as a whole, an actuator for the parking brake must be irreversible (or "non-backdrivable"), i.e. it must be able to maintain the braking force imparted in the absence of a release command, hi other words, as a result of the friction between the movable parts of the actuator, the output rod must be able to maintain the position reached until a new operating command is given.
The screw mechanisms proposed hitherto for actuating parking brakes generally make use of friction screw mechanisms in an attempt to achieve a compromise between the requirement for "irreversibility" and a "direct" efficiency which is acceptable in terms of friction, hi this context, the expression "direct efficiency" is understood as meaning the efficiency obtained by operating the electric motor, while "indirect efficiency" indicates the efficiency obtained by operating the actuator output member. The maximum direct efficiency which can be obtained with the friction screw mechanisms is in the order of 35- 40%. hi order to achieve a performance above this level it is necessary to use screw mechanisms which, however, are not irreversible or risk becoming so during the working life of the actuator, resulting in instability and incorrect functioning of the system.
U.S. patent No. 6,655,507 describes a screw actuator for a parking brake comprising an electric motor and a ball screw. The actuator requires an electromechanical brake in order to maintain the position reached by the ball screw when no power is supplied by the electric motor.
The object of the invention is to provide an actuator which combines a high direct efficiency with the requirement for irreversibility, or negative indirect efficiency, without the addition of auxiliary devices for preventing undesirable movements of the output screw when no commands are given by the electric motor.
These and other objects and advantages, which will be understood more clearly in the following, are achieved by a transmission unit and by an actuator having the features set forth in the accompanying claims.
The structural and functional features of a preferred, but non-limiting embodiment of the invention will now be described. Reference is made to the accompanying drawing which is a schematic cross-sectional view of an actuator according to the invention.
In the drawing, 10 designates overall a linear electromechanical actuator according to the invention, for operating the parking brakes (not shown) of a motor vehicle. The actuator 10 includes an electric motor 20 which, by means of an epicyclic reduction unit 30 with spur gears and an associated ball screw 40, imparts linear movements to a component C for connection to the parking brakes by means of a Bowden cable (not shown). The assembly formed by the epicyclic reduction unit 30 and the ball screw forms the transmission unit of the actuator.
The electric motor 20 is preferably a direct current permanent-magnet motor which is able to rotate selectively in both directions of rotation depending on the command signal received from an electronic control module (not shown). The motor 20 rotationally drives, by means of a pair of spur gears 21, 31, a planet wheel carrier 32 mounted rotatably about an axis x coinciding with the actuating axis of the screw mechanism 40 and parallel to the axis X1 of the electric motor. Two bearings 51 are situated between the planet wheel carrier 32 and a tubular support portion 52 of the casing 50 of the actuator. Designated 33 are the planet wheels of the reduction unit, which are mounted on cylindrical pivot pins 34. The planet wheels mesh with a first fixed sun gear 35 mounted on the support 52 and with a second sun gear 36 rotationally integral with the screw nut 41 of the ball screw 40. Rotation of the screw nut 41 causes the displacement of a screw or threaded rod 42 along the axis x and, consequently, the connection component C connected to the screw 42. While the ball screw 40 is per se a reversible mechanism with a high mechanical performance, the epicyclic reduction unit has a negative "indirect" efficiency when no commands are given by the electric motor. This special feature means that the transmission unit is generally irreversible, while offering a suitable direct performance able to produce high actuating forces for the brake.
It will be appreciated that the epicyclic reduction unit owing to its characteristic feature of irreversibility, also performs the function of an actuator locking device, avoiding the costs associated with an additional locking device, as discussed in the introduction.
Whilst it is not desired to be bound to any specific theory in this connection, experimental tests carried out by the Applicant have shown that the factor which plays a decisive part in ensuring the irreversibility of the epicyclic reduction unit 30 is the sliding friction which develops at the interface between the planet wheels and the pivot pins of the planet wheel carrier. Li particular, the tests carried out by the Applicant have shown that excellent results may be obtained if the planet wheels 33 and the pivot pins 34 are made of steel which has undergone a surface hardening treatment.
It is understood that the invention is not limited to the embodiment described and illustrated here, which is to be regarded as an example; instead the invention may be subject to modifications regarding the form and arrangement of parts and constructional and functional details, for example as regards the number of teeth which determines the different transmission ratios of the gears of the epicyclic reduction unit.

Claims

1. A transmission unit for a linear electromechanical actuator, in particular for a parking brake, comprising: a gear reduction unit (30) able to receive a rotary movement from an electric motor (20), a screw mechanism (40) comprising a first threaded member (41) which can be rotationally driven by means of the reduction unit (30) about a longitudinal axis (x) and a second threaded output member (42) displaceable along said axis as a result of the rotation of the first threaded member; characterized in that the screw mechanism (40) is a backdrivable mechanism, and the reduction unit (30) includes an epicyclic reduction unit with spur gears, where the epicyclic reduction unit is a non-backdrivable irreversible mechanism.
2. A transmission unit according to Claim 1, characterized in that the epicyclic reduction unit comprises a plurality of rotatable planet wheels (33) mounted so as to rotate with sliding friction on respective pivot pins (34) of a planet wheel carrier (32).
3. A transmission unit according to Claim 2, characterized in that the planet wheels (33) and the pivot pins (34) are made of steel.
4. A transmission unit according to Claim 1, characterized in that the screw mechanism (40) is a ball screw, wherein the first threaded member (41) is a rotatable screw nut and the second threaded member (42) is a translatable screw.
5. A linear electromechanical actuator, in particular for a parking brake, including an electric motor (20) and a transmission unit (30, 40) according to any one of Claims 1 to 4.
PCT/IB2007/055283 2007-01-19 2007-12-21 A linear electro-mechanical actuator for a parking brake WO2008087506A2 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
ITTO2007A000031 2007-01-19
IT000031A ITTO20070031A1 (en) 2007-01-19 2007-01-19 LINEAR ELECTROMECHANICAL ACTUATOR OF A PARKING BRAKE.

Publications (2)

Publication Number Publication Date
WO2008087506A2 true WO2008087506A2 (en) 2008-07-24
WO2008087506A3 WO2008087506A3 (en) 2008-09-12

Family

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Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/IB2007/055283 WO2008087506A2 (en) 2007-01-19 2007-12-21 A linear electro-mechanical actuator for a parking brake

Country Status (2)

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IT (1) ITTO20070031A1 (en)
WO (1) WO2008087506A2 (en)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2014003274A1 (en) * 2012-06-26 2014-01-03 주식회사 미래브이씨 Electrically-powered parking brake apparatus for mid-size and large commercial vehicles
US20150148185A1 (en) * 2013-11-27 2015-05-28 Flowinn (Shanghai) Industrial Co., Ltd. Linear Travel Structure of Electrical Operating Device

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6655507B2 (en) 2001-01-26 2003-12-02 Honda Giken Kogyo Kabushiki Kaisha Electrically operated parking brake apparatus

Family Cites Families (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE19620463A1 (en) * 1996-05-21 1997-11-27 Bayerische Motoren Werke Ag Parking brake system for automobile
DE19653961A1 (en) * 1996-12-21 1998-06-25 Bosch Gmbh Robert Servo-operated parking brake esp for automobile
DE102004060907B4 (en) * 2004-12-17 2016-07-21 Robert Bosch Gmbh Locking device for locking an automated parking brake of a vehicle

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6655507B2 (en) 2001-01-26 2003-12-02 Honda Giken Kogyo Kabushiki Kaisha Electrically operated parking brake apparatus

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2014003274A1 (en) * 2012-06-26 2014-01-03 주식회사 미래브이씨 Electrically-powered parking brake apparatus for mid-size and large commercial vehicles
US20150148185A1 (en) * 2013-11-27 2015-05-28 Flowinn (Shanghai) Industrial Co., Ltd. Linear Travel Structure of Electrical Operating Device
US9133953B2 (en) * 2013-11-27 2015-09-15 Flowinn (Shanghai) Industrial Co., Ltd. Linear travel structure of electrical operating device

Also Published As

Publication number Publication date
ITTO20070031A1 (en) 2008-07-20
WO2008087506A3 (en) 2008-09-12

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