Linear actuator

A linear actuator for generating a thrust force for relatively displacing an outer tube and an inner tube in an axial direction includes a rod standing in an axial center part of the inner tube, a plurality of permanent magnets held side by side in an axial direction by the rod, a plurality of coils facing the permanent magnets, and a holder that is fixed to the outer tube and holds the plurality of coils. The holder includes a tubular coil holding portion that is provided in an annular space formed between the rod and the inner tube and holds the coils. A clearance is formed between the outer periphery of the coil holding portion and the inner periphery of the inner tube.

TECHNICAL FIELD

This invention relates to a linear actuator.

BACKGROUND ART

A damping linear actuator for damping the roll of a vehicle is disclosed in JP2005-106242A.

The linear actuator disclosed in JP2005-106242A includes an outer tube, an inner tube slidably inserted into the outer tube and a rod standing from a bottom portion of the outer tube and sliding contact with the inner periphery of the inner tube. The inner tube is supported by a bearing mounted on the inner periphery of an opening of the outer tube and a bearing mounted on the outer periphery of the rod.

The linear actuator includes a plurality of annular permanent magnets held side by side in an axial direction on the outer periphery of the inner tube and a plurality of coils held on the inner periphery of the outer tube and facing the permanent magnets. The direction and magnitude of a current flowing in each coil are controlled to generate a thrust force for relatively displacing the outer tube and the inner tube in the axial direction, thereby damping the roll of a vehicle.

SUMMARY OF THE INVENTION

In the linear actuator disclosed in JP2005-106242A, the inner tube is supported by the bearings mounted on the inner periphery of the outer tube and the outer periphery of the rod. Thus, the inner tube may be strained form the bearings as a base point by being subjected to a load acting in a radial direction. In such a case, this strain may be transferred to the permanent magnets held on the outer periphery of the inner tube to break the permanent magnets.

This invention has been designed in consideration of these problems, and an object thereof is to provide to provide a linear actuator capable of a stable operation even upon being subjected to a load acting in a radial direction.

The present invention provides a linear actuator for generating a thrust force for relatively displacing an outer tube and an inner tube slidably inserted into the outer tube in an axial direction. The linear actuator includes a rod standing in an axial center part of the inner tube, a plurality of permanent magnets held side by side in an axial direction by the rod, a plurality of coils facing the permanent magnets; and a holder that is fixed to the outer tube and holds the plurality of coils, wherein, the holder includes a tubular coil holding portion that is provided in an annular space formed between the rod and the inner tube and holds the coils, and a clearance is formed between the outer periphery of the coil holding portion and the inner periphery of the inner tube.

EMBODIMENTS OF THE INVENTION

Hereinafter, an embodiment of the present invention is described with reference to the drawings.

A linear actuator100according to the embodiment of the present invention is described with reference toFIG. 1.

The linear actuator100is a damping linear actuator to be provided in automotive vehicles, railroad vehicles, buildings and the like.

The linear actuator100includes an outer tube1, an inner tube2slidably inserted into the outer tube1, and a rod3standing in an axial center part of the inner tube2. The outer tube1and the inner tube2are bottomed tubular members.

The linear actuator100includes a field magnet4composed of a plurality of permanent magnets40held side by side in an axial direction in the rod3, a plurality of coils50facing the field magnet4, and a holder5fixed to the outer tube1and configured to hold the coils50, and generates a thrust force for relatively displacing the outer tube1and the inner tube2in the axial direction.

The holder5includes a tubular coil holding portion51for holding the coils. The coil holding portion51is provided in an annular space7formed between the outer periphery of the rod3and the inner periphery of the inner tube2. Further, a clearance8is formed between the outer periphery of the coil holding portion51and the inner periphery of the inner tube2.

Each component part of the linear actuator100is described in detail below.

The linear actuator100is coupled to two relatively movable members, e.g. a vehicle body and a movable body, via devises60,61respectively provided on the outer surfaces of bottom portions of the outer tube1and the inner tube2.

In this embodiment, the outer tube1and the holder5for holding the coils50fixed to the outer tube1are a stationary element. Further, the inner tube2, the rod3standing in the axial center part of the inner tube2and a rod guide6provided on a tip end part of the rod3are a movable element.

The linear actuator100damps vibration input to the vehicle body by relatively moving the stationary element and the movable element.

The outer tube1includes a small-diameter tubular portion10which has an opening1ainto which the inner tube2is to be inserted and with the inner periphery of which the inner tube2slides contact, a large-diameter tubular portion11which extends coaxially with the small-diameter tubular portion10, and a bottom portion12which closes an end opening of the large-diameter tubular portion11and on the outer surface of which the clevis60is provided. The bottom portion12is bolted to an end part of the large-diameter tubular portion11.

The small-diameter tubular portion10and the large-diameter tubular portion11have an equal outer diameter, and the inner diameter of the small-diameter tubular portion10is smaller than that of the large-diameter tubular portion11. An annular step portion13is formed on a boundary between the inner peripheries of the small-diameter tubular portion10and the large-diameter tubular portion11.

An annular first bearing14sliding contact with the outer periphery of the inner tube2is provided on the inner periphery of the opening1aof the outer tube1.

The inner tube2includes a tubular movable portion20, the outer periphery of which slides contact with the first bearing14provided on the outer tube1, and a bottom portion22which closes an end opening of the tubular movable portion20and on the outer surface of which the clevis61is provided.

A jaw portion20ahaving a large outer diameter is formed on the outer periphery of a tip end side of the tubular movable portion20. An annular second bearing24sliding contact with the inner periphery of the outer tube1is provided on the jaw portion20a.

Since the inner tube2is supported via the first bearing14and the second bearing24, it can slide relative to the outer tube1while sufficient rigidity is ensured against a load acting in a radial direction.

The rod3includes a tubular portion31and cap members32,33for closing openings on both ends of the tubular portion31. One cap member32is linked to the center of the bottom portion22of the inner tube2. The other cap member33is linked to the center of the rod guide6sliding contact with the inner periphery of the outer tube1. In this way, a base end part of the rod3is fixed to the bottom portion22of the inner tube2and the rod guide6is provided on a tip end part thereof. The rod3is provided to movably penetrate through a hollow part in the axial center of the substantially tubular holder5.

The field magnet4composed of the plurality of permanent magnets40arranged side by side in the axial direction is accommodated in a hollow part inside the rod3. In this way, the permanent magnets40are held side by side in the axial direction in the rod3. By this, even if a load acts on the inner tube2in a radial direction to strain the inner tube2, that strain is not transferred to the rod3, whereby breakage of the permanent magnets40due to the transfer of the strain of the inner tube2to the permanent magnets40can be prevented.

The permanent magnets40are formed into rods and so magnetized that an N pole and an S pole appear in the axial direction. The adjacent permanent magnets40are accommodated side by side in the axial direction in the rod3with the same poles facing each other. Yokes41are provided between the adjacent permanent magnets40.

Instead of being formed into rods, the permanent magnets40may be formed into rings and held on the outer periphery of the rod3. In such a case, the permanent magnets40may be so configured that the inner and outer peripheries are polarized and may be so arranged that N poles and S poles alternately appear along the axial direction of the rod3. Further, it is not always necessary to provide the yokes41.

By providing the rod guide6on the tip end part of the rod3, the tip end side of the rod3can be prevented from shaking in radial directions when the rod3moves in the axial direction in the outer tube1according to a displacement of the inner tube2relative to the outer tube1. That is, the roll of the rod3can be prevented.

In this way, the rod guide6prevents the rod3from rolling to interfere with the holder5when the linear actuator expands and contracts. Thus, a distance between the permanent magnets40accommodated in the rod3and the coils50held in the holder5can be kept constant. Accordingly, axial misalignment between the permanent magnets40and the coils50is prevented and the linear actuator100can stably generate a thrust force. If the permanent magnets40are configured to be held on the outer periphery of the rod3, the rod guide6prevents the permanent magnets40from interfering with the holder5.

The holder5includes the tubular coil holding portion51for holding the plurality of coils50facing the permanent magnets40on the inner periphery, and a flange portion52fixed to the step portion13of the outer tube1via a bolt53. The flange portion52has a function of restricting any further movement by the contact with an end part of the inner tube2.

The coil holding portion51moves back and forth in the annular space7formed between the rod3and the inner tube2according to a relative displacement of the outer tube1and the inner tube2. Further, the predetermined clearance8is present between the outer periphery of the coil holding portion51and the inner periphery of the inner tube2. This can prevent the transfer of a strain to the coil holding portion51even if a load acts on the inner tube2in a radial direction to strain the inner tube2.

Accordingly, even if a load acts on the inner tube2in a radial direction to strain the inner tube2, the strain of the inner tube2is transferred neither to the rod3holding the permanent magnets40nor to the coil holding portion51holding the coils50. Thus, the distance between the permanent magnets40and the coils50is kept constant and the linear actuator100can stably generate a thrust force.

The clearance8may be appropriately set within a range capable of preventing the transfer of the strain of the inner tube2to the coil holding portion51.

The coils50are arranged to be located within an axial length range of the field magnet4and constantly face the field magnet4within a stroke range of the rod3. This prevents a situation where a thrust force generated by the linear actuator100becomes insufficient.

The linear actuator100is equipped with a controller as a control means. The controller controls the magnitude and direction of a current applied to the coils50based on relative position information of the coils50and the permanent magnets40detected by a position sensor (not shown). In this way, a thrust force generated by the linear actuator100and a generation direction of the thrust force are controlled. It should be noted that the thrust force generated by the linear actuator100and the generation direction of the thrust force may be controlled by a controller equipped in the vehicle instead of equipping the linear actuator100with the controller.

Six coils50are shown inFIG. 1. However, the number of the coils50may be set at a number suitable for a thrust force generated by the linear actuator100and an energizing method.

A suction/discharge hole55is formed in the bottom portion12of the outer tube1. Further, the tubular movable portion20of the inner tube2, the flange portion52of the holder5and the rod guide6are formed with communication holes56. When the linear actuator100expands and contracts, air is sucked into and discharged from the linear actuator100through the suction/discharge hole55and air in the linear actuator100moves through the communication holes56. In this way, the linear actuator100smoothly expands and contracts.

The positions and numbers of the suction/discharge hole55and the communication holes56are appropriately selected insofar as the expansion and contraction of the linear actuator are enabled and a volumetric change in the linear actuator100associated with the expansion and contraction can be compensated.

Next, modifications of the embodiment of the present invention are described with reference toFIGS. 2 and 3. The following description is centered on points of difference from the above embodiment and the same components as the linear actuator100according to the above embodiment are denoted by the same reference signs and not described.

First, a linear actuator200shown inFIG. 2is described. In the linear actuator100according to the above embodiment, the devises60,61provided on the both ends of the linear actuator100are respectively coupled to the vehicle body and the movable body. The linear actuator200differs from the linear actuator100in a method for coupling the outer tube1to the vehicle body.

A pair of brackets70including shaft insertion holes70aat positions opposite to each other are provided on the outer periphery of the outer tube1. Supporting shafts71projecting in radial directions of the outer tube1are inserted into the shaft insertion holes70aof the pair of brackets70.

The outer tube1is swingably coupled to the vehicle body via a pair of supporting shafts71. In this way, the outer tube1is coupled to the vehicle body by a trunnion structure. The inner tube2is coupled to the movable body via the clevis61similarly to the linear actuator100.

In the linear actuator200, a mounting length of the linear actuator200can be made shorter than that of the linear actuator100, the both ends of which are coupled via the devises60,61.

In the linear actuator100according to the above embodiment, the flange portion52of the holder5is bolted to the step portion13of the outer tube1. A method for fixing the holder5to the outer tube1is appropriately changed and the linear actuator300includes an example of that.

In the linear actuator300, the holder5is a tubular member composed only of the coil holding portion51for holding the coils50without including the flange portion52. Further, the step portion13protrudes inwardly from the inner periphery of the outer tube1to form an annular stopper portion15. The stopper portion15has a function of restricting any further movement by the contact with an end part of the inner tube2. An end part of the holder5is bolted to the stopper portion15.

According to the embodiment described above, the following functions and effects are achieved.

Since the rod3holding the permanent magnets40stands in the axial center part of the inner tube2, even if a load acts on the inner tube2in a radial direction to strain the inner tube2, that strain does not act on the rod3. Thus, breakage of the permanent magnets40can be prevented.

Further, since the clearance8is present between the coil holding portion51of the holder5and the inner tube2, even if a load acts on the inner tube2in a radial direction to strain the inner tube2, that strain does not act on the coil holding portion51. Thus, a change in the distance between the permanent magnets40and the coils50and the interference of the permanent magnets40and the coils50can be prevented.

It is apparent that the present invention is not limited to the above embodiment and various changes can be made within the scope of the technical concept of the present invention.

With respect to the above description, the contents of application No. 2010-207577, with a filing date of Sep. 16, 2010 in Japan, are incorporated herein by reference.