LINEAR ACTUATOR WITH AN IMPROVED ACTUATOR ROD

Abstract

The present invention relates to a linear stepper actuator (20) comprising: - a housing (24), - a stator assembly (26), - a rotor assembly (28), - an actuator rod (34) which includes a threaded section (36), - a needle element (40) which is arranged at a free axial end, referred to as the front end, of the actuator rod (34), characterized in that the actuator rod (34) and the needle element (40) are made in one piece from a plastic material comprising a liquid crystal polymer and polytetrafluoroethylene, and in that the thread pitch (Pv) of the threaded section (36) is between 1.25 mm and 1.75 mm. Figure 2 for the abstract.

Description

Title of the invention: LINEAR ACTUATOR COMPRISING AN IMPROVED ACTUATOR ROD Technical field of the invention

[0001] The present invention relates to a linear stepper actuator.

[0002] The invention relates more particularly to a linear stepper actuator of the type used in an air inlet valve housing for a heat engine. Technical background

[0003] A linear stepper actuator generally comprises a housing, a stator assembly disposed within the housing and equipped with a series of windings around a main axis, and a rotor assembly comprising at least one permanent magnet and mounted for rotation relative to the stator assembly about the main axis such that, when the windings are energized, a magnetic field is generated to cause rotation of the rotor assembly. The actuator also includes an actuator rod extending along the main axis, which is rotationally fixed and has a threaded section adapted to engage by screwing with a tapped section of the rotor assembly so that rotation of the rotor assembly causes linear displacement of the actuator rod along the main axis.

[0004] When such an actuator is used for an internal combustion engine air inlet valve housing, the free axial end of the actuator rod is provided with a needle element which is intended to close or open a secondary air duct, in particular to control the engine idle speed during a cold start.

[0005] Previously, the actuator rod was made of metal. However, for reasons of cost and weight, it has been proposed to make the actuator rod out of plastic material, in particular using polytetrafluoroethylene (PTFE).

[0006] In practice, when using actuator rods made of plastic material, failures have been observed on some actuators. Indeed, a sticking or jamming phenomenon frequently occurs, meaning that the needle remains pressed against the inlet of the secondary air duct, making it impossible to retract the actuator rod, despite the control instructions transmitted to the actuator.

[0007] There is therefore a need to remedy this reliability problem. Summary of the invention

[0008] The invention proposes a linear stepper actuator comprising: - a housing, - a stator assembly arranged in the casing and equipped with a series of windings around a main axis, - a rotor assembly comprising at least one permanent magnet and mounted for rotation relative to the stator assembly around the main axis such that, when the windings are energized, a magnetic field is generated to cause rotation of the rotor assembly, - an actuator rod extending along the main axis, which is blocked in rotation and which includes a threaded section adapted to cooperate by screwing with a tapped section of the rotor assembly so that a rotation of the rotor assembly causes a linear displacement of the actuator rod along the main axis, - a needle element which is arranged at a free axial end, referred to as the front end of the actuator rod, characterized in that the actuator rod and the needle element are made in one piece from a plastic material comprising a liquid crystal polymer and polytetrafluoroethylene, and in that the thread pitch of the threaded section is between 1.25mm and 1.75mm.

[0009] According to other features of the invention:

[0010] - the screw pitch is between 1.45mm and 1.55mm;

[0011] - the screw pitch is equal to 1.5mm;

[0012] - the threaded section has threads that are generally crenellated in shape.

[0013] The invention also proposes a valve assembly comprising: - a main body equipped with a main conduit whose opening is controlled by the pivoting of a flap and equipped with a secondary conduit parallel to the main conduit, - a linear stepper actuator according to one of the preceding characteristics, which is mounted on the main body so that, in an extreme forward position of the actuator rod, the needle element closes an inlet orifice of the secondary conduit and, in an extreme rear position of the actuator rod, the needle element is clear of the inlet orifice of the secondary conduit. Brief description of the figures

[0014] Other features and advantages of the invention will become apparent upon reading the detailed description that follows, for an understanding of which reference should be made to the accompanying drawings in which:

[0015] [Fig-1] is a schematic axial cross-sectional view which represents a valve assembly equipped with a step-by-step linear actuator conforming to the teachings of the invention;

[0016] [Fig.2] is a schematic axial cross-sectional view which represents the linear stepper actuator of [Fig.1];

[0017] [Fig.3] is a side view which represents the actuator rod which equips the linear stepper actuator of the [Fig.1];

[0018] [Fig. 4] is a schematic perspective view representing a portion of the threaded section of the actuator rod of [Fig. 3] to illustrate the serrated shape of the threads. Detailed description of the invention

[0019] In the description that follows, identical, similar or analogous elements will be designated by the same reference numerals.

[0020] In [Fig.1], a set of valves 10 intended to regulate the air supply to a heat engine is shown.

[0021] The valve assembly 10 comprises a main body 12 equipped with a main conduit 14 whose opening is controlled by the pivoting of a flap 16, or butterfly.

[0022] The main body 12 includes a secondary conduit 18, parallel to the main conduit 14, which allows the section of main conduit 12 equipped with the flap 16 to be short-circuited.

[0023] On [Fig.1], the white arrows Fl represent the main airflow passing through the main duct 14 and the grey arrows F2 represent the secondary airflow passing through the secondary duct 18.

[0024] The valve assembly 10 includes a linear stepper actuator 20 which is mounted here in a housing 22 of the main body 12.

[0025] The linear stepper actuator 20, which is shown in an enlarged view in [Fig. 2], comprises a housing 24 containing a stator assembly 26 and a rotor assembly 28, the rotor assembly 28 being rotatably mounted inside the stator assembly 26 about a longitudinal main axis AL

[0026] The stator assembly 26 is provided with a series of windings 30 around the main longitudinal axis Al and around the rotor assembly 28.

[0027] The rotor assembly 28 includes at least one permanent magnet 32.

[0028] The rotor assembly 28 is mounted to rotate relative to the stator assembly 26 so that that, when the windings 30 are energized, a magnetic field is generated and causes the rotor assembly 28 to rotate.

[0029] The stepper linear actuator 20 comprises an actuator rod 34 extending along the main longitudinal axis AL. The actuator rod 34 is mounted to be rotationally locked and has a threaded section 36 adapted to engage by screwing with a tapped section 38 of the rotor assembly 28. Thus, any rotation of the rotor assembly 28 causes a linear displacement of the actuator rod 34 along the main longitudinal axis AL.

[0030] In the remainder of the description, we will use, by way of non-limiting agreement, an orientation from back to front along the main longitudinal axis Al, which corresponds to an orientation from left to right when considering figures 1, 2, and 3.

[0031] The actuator rod 34 is provided at its front axial end with a needle element 40 adapted to close an inlet orifice 42 of the secondary conduit 18. According to the example shown, the secondary conduit 18 extends partly along the longitudinal axial direction Al so that the actuator rod 34 and the needle element 40 are coaxial with the axis of the secondary conduit 18.

[0032] On [Fig. 1], the needle element 40 and the actuator rod 34 are shown in dashed line in the extreme rear position, and in dashed line in the extreme front position, or closing position of the inlet orifice 42.

[0033] In [Fig.3], the actuator rod 34 with its needle element 40 is shown in more detail, and in [Fig.4] a part of the threaded section 36.

[0034] In accordance with the teachings of the invention, the actuator rod 34 and the needle element 40 are made in one piece from a plastic material comprising a liquid crystal polymer and polytetrafluoroethylene (PTFE).

[0035] According to an advantageous embodiment, the liquid crystal polymer is Vectra® A430 marketed by Celanese.

[0036] In combination with this specific choice of plastic material, the thread pitch Pv of the threaded section 36 is between 1.25 mm and 1.75 mm, preferably between 1.45 mm and 1.55 mm. Advantageously, the thread pitch Pv is approximately 1.5 mm.

[0037] According to an advantageous embodiment, the threaded section 36 comprises threads 44 generally in the form of crenellations, as illustrated by [Fig.4]. The threads 44 here have a profile close to a rectangular profile, with a summit portion 46 forming a plateau and edges 48, on either side of the summit portion 46, slightly rounded.

[0038] An improved reliability and responsiveness of the linear stepper actuator 20 was observed with slotted threads 44 and by increasing the pitch Pv from 1 mm to 1.5 mm. With a pitch Pv of 1 mm, blockages of the actuator rod 34 occur, whereas with a pitch Pv of 1.5 mm, no blockages are observed.

[0039] The actuator rod 34 is preferably made by plastic injection in a mold.

[0040] LEGEND

[0041] 10: valve assembly 12: main body 14: Main conduit 16: panel 18: secondary conduit 20: Linear stepper actuator 22: Housing 24: case 26: stator assembly 28: rotor assembly 30: windings 32: permanent magnet 34: Actuator rod 36: threaded section 38: threaded section 40: point element 42: Inlet port 44: nets 46: summit section 48: edges Al: main longitudinal axis Fl: Main airflow F2: Secondary airflow PV: no screws

Claims

Demands

1. A stepper linear actuator (20) comprising: - a housing (24), - a stator assembly (26) disposed in the housing (24) and provided with a series of windings (30) about a main axis (Al), - a rotor assembly (28) comprising at least one permanent magnet (32) and mounted for rotation relative to the stator assembly (26) about the main axis (Al) such that, when the windings (30) are energized, a magnetic field is generated to cause rotation of the rotor assembly (28), - an actuator rod (34) extending along the main axis (Al), which is rotationally fixed and which has a threaded section (36) adapted to cooperate by screwing with a tapped section (38) of the rotor assembly (28) such that rotation of the rotor assembly (28) causes linear displacement of the actuator rod (34) along the main axis (Al),- a needle element (40) which is arranged at a free axial end called the front end of the actuator rod (34), characterized in that the actuator rod (34) and the needle element (40) are made in one piece from a plastic material comprising a liquid crystal polymer and polytetrafluoroethylene, and in that the thread pitch (Pv) of the threaded section (36) is between 1.25 mm and 1.75 mm.

2. Stepper linear actuator (20) according to the preceding claim, characterized in that the screw pitch (Pv) is between 1.45mm and 1.55mm.

3. Stepper linear actuator (20) according to the preceding claim, characterized in that the screw pitch (Pv) is equal to 1.5mm.

4. Stepper linear actuator (20) according to any one of the preceding claims, characterized in that the threaded section (36) has threads (44) that are generally in the form of crenellations.

5. Valve assembly (10) comprising: - a main body (12) provided with a main conduit (14) whose opening is controlled by the pivoting of a flap (16) and provided with a secondary conduit (18) parallel to the main conduit (14), - a linear stepper actuator (20) according to any one of claims 1 to 3, which is mounted on the main body (12) such that, in an extreme forward position of the actuator rod (34), the needle element (40) closes an inlet orifice (42) of the secondary conduit (18) and, in an extreme rear position of the actuator rod (34), the needle element (40) is clear of the inlet orifice (42) of the secondary conduit (18).

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