Linear actuator comprising 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 comprises 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 as a single part from a plastic material comprising a liquid crystal polymer and polytetrafluoroethylene, and in that the screw pitch (Pv) of the threaded section (36) is between 1.25 mm and 1.75 mm.

Description

[0001] DESCRIPTION OF A LINEAR ACTUATOR WITH A RELIORATED ACTUATOR ROD

[0002] Technical field of the invention

[0003] The present invention relates to a linear stepper actuator.

[0004] The invention relates more particularly to a linear stepper actuator of the type used in an air inlet valve housing for a heat engine.

[0005] Technical background

[0006] A linear stepper actuator typically comprises a housing, a stator assembly within the housing with a series of windings around a main axis, and a rotor assembly comprising at least one permanent magnet, which is 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 the rotor assembly to rotate. The actuator also includes an actuator rod extending along the main axis, which is fixed against rotation and has a threaded section adapted for screwing into a threaded section of the rotor assembly, so that rotation of the rotor assembly causes linear movement of the actuator rod along the main axis.

[0007] When such an actuator is used for an internal combustion engine air inlet valve housing, the free axial end of the actuator rod is fitted with a needle element which is intended to close or open a secondary air duct, in particular to control engine idle speed during a cold start.

[0008] Previously, the actuator rod was made of metal. However, for reasons of cost and weight, it was proposed to make the actuator rod from plastic material, specifically using polytetrafluoroethylene (PTFE).

[0009] In practice, when using plastic actuator rods, failures have been observed on some actuators. Specifically, a sticking or jamming phenomenon frequently occurs, meaning the needle remains pressed against the secondary air duct inlet, preventing the actuator rod from retracting, despite commands being sent to the actuator.

[0010] Therefore, there is a need to address this reliability issue.

[0011] Summary of the invention

[0012] The invention proposes a linear stepper actuator comprising:

[0013] - a case,

[0014] - a stator assembly arranged in the casing and equipped with a series of windings around a main axis,

[0015] - 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,

[0016] - 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,

[0017] - a needle element which is arranged at a free axial end called 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.

[0018] According to other features of the invention:

[0019] - the screw pitch is between 1.45mm and 1.55mm;

[0020] - the screw pitch is equal to 1.5mm;

[0021] - the threaded section has threads that are generally crenellated in shape.

[0022] The invention also proposes a valve assembly comprising:

[0023] - 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.

[0024] Brief description of the figures

[0025] Other features and advantages of the invention will become apparent upon reading the detailed description that follows, for which reference should be made to the accompanying drawings in which:

[0026] [Fig.1] is a schematic axial cross-sectional view which represents a valve assembly equipped with a linear stepper actuator in accordance with the teachings of the invention;

[0027] [Fig.2] is a schematic axial cross-sectional view that represents the linear stepper actuator of Figure 1;

[0028] [Fig.3] is a side view which represents the actuator rod which equips the linear stepper actuator of figure 1;

[0029] [Fig.4] is a schematic perspective view which represents a portion of the threaded section of the actuator rod in Figure 3 in order to illustrate the serrated shape of the threads.

[0030] Detailed description of the invention

[0031] In the description that follows, identical, similar or analogous elements will be designated by the same reference numbers.

[0032] Figure 1 shows a set of valves 10 designed to regulate the air supply to a heat engine.

[0033] 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.

[0034] The main body 12 includes a secondary duct 18, parallel to the main duct 14, which allows the section of main duct 12 equipped with the damper 16 to be bypassed. In Figure 1, the white arrows F1 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.

[0035] The valve assembly 10 includes a linear stepper actuator 20 which is mounted here in a housing 22 of the main body 12.

[0036] The linear stepper actuator 20, which is shown in an enlarged view in Figure 2, comprises a housing 24 which contains a stator assembly 26 and a rotor assembly 28, the rotor assembly 28 being mounted for rotation inside the stator assembly 26 around a main longitudinal axis A1.

[0037] The stator assembly 26 is provided with a series of windings 30 around the main longitudinal axis A1 and around the rotor assembly 28.

[0038] The rotor assembly 28 includes at least one permanent magnet 32.

[0039] The rotor assembly 28 is mounted to rotate relative to the stator assembly 26 so that, when the windings 30 are energized, a magnetic field is generated and causes the rotor assembly 28 to rotate.

[0040] The stepper linear actuator 20 comprises an actuator rod 34 extending along the main longitudinal axis A1. 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 A1.

[0041] In the following description, we will use, as a non-limiting example, a back-to-front orientation along the main longitudinal axis A1, which corresponds to a left-to-right orientation when considering figures 1, 2, and 3.

[0042] The actuator rod 34 is provided at its front axial end with a needle element 40 suitable for closing 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 A1 so that the actuator rod 34 and the needle element 40 are coaxial with the axis of the secondary conduit 18.

[0043] In Figure 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.

[0044] Figure 3 shows in more detail the actuator rod 34 with its needle element 40, and Figure 4 shows part of the threaded section 36.

[0045] 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).

[0046] According to an advantageous embodiment example, the liquid crystal polymer is Vectra® A430 marketed by the company Celanese.

[0047] 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.

[0048] According to an advantageous embodiment, the threaded section 36 has threads 44 generally in the shape of crenellations, as illustrated by Figure 4. The threads 44 here have a profile close to a rectangular profile, with a summit part 46 forming a plateau and edges 48, on either side of the summit part 46, slightly rounded.

[0049] An improved reliability and responsiveness of the linear stepper actuator 20 was observed with the slotted threads 44 and by increasing the pitch Pv from 1 mm to 1.5 mm. With a Pv pitch of 1 mm, blockages of the actuator rod 34 occurred, whereas with a Pv pitch of 1.5 mm, no blockages were observed.

[0050] The actuator rod 34 is preferably manufactured by plastic injection molding. LEGEND

[0051] 10: Valve assembly

[0052] 12: main body

[0053] 14: Main conduit

[0054] 16: panel

[0055] 18: secondary conduit

[0056] 20: Linear stepper actuator

[0057] 22: Housing

[0058] 24: case

[0059] 26: stator assembly

[0060] 28: rotor assembly

[0061] 30: windings

[0062] 32: permanent magnet

[0063] 34: Actuator rod

[0064] 36: threaded section

[0065] 38: threaded section

[0066] 40: point element

[0067] 42: Inlet port

[0068] 44: nets

[0069] 46: summit section

[0070] 48: edges

[0071] A1: main longitudinal axis

[0072] F1: Main airflow

[0073] F2: Secondary airflow

[0074] PV: no screws

Claims

DEMANDS 1. Stepper linear actuator (20) comprising: - a case (24), - a stator assembly (26) arranged in the housing (24) and equipped with a series of windings (30) around a main axis (A1), - a rotor assembly (28) which includes at least one permanent magnet (32) and which is mounted for rotation relative to the stator assembly (26) around the main axis (A1) so that, when the windings (30) are energized, a magnetic field is generated to cause rotation of the rotor assembly (28), - an actuator rod (34) which extends along the main axis (A1), which is blocked in rotation and which includes a threaded section (36) adapted to cooperate by screwing with a tapped section (38) of the rotor assembly (28) so that a rotation of the rotor assembly (28) causes a linear displacement of the actuator rod (34) along the main axis (A1), - 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 1.25mm and 1.75mm.

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. Step-by-step 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) having a main conduit (14) whose opening is controlled by the pivoting of a flap (16) and having 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) so 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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