Add-on brake system

An add-on brake system includes a housing accommodating a linear actuator including: an electric motor having a rotor and a stator; a nut arrangement coupled to the rotor; a linear threaded plunger associated having a first end linearly protruding from one end of the arrangement and a second end linearly protruding from an opposite end thereof; an inboard brake pad coupled to the housing; and an outboard brake pad associated with the second end, oriented transverse to the plunger. The plunger has an initial unclamped position in which the second end protrudes to an extent n1 from the other end of the arrangement, yielding a spacing S1 between the inboard and outboard brake pads, and a final clamped position in which the second end protrudes to an extent n2>n1 from the other end of the arrangement, yielding a spacing S2<S1 between the pads.

PRIORITY CLAIM

This application claims priority from Israel Patent Application No. 241966 filed on Oct. 8, 2015, which is incorporated herein, in its entirety, by this reference.

TECHNOLOGICAL FIELD

The presently disclosed subject matter relates to brake systems for vehicles, in particular for an air vehicle.

BACKGROUND

It is well known in the field of aviation to provide air vehicles, including aircraft and other airborne vehicles, with a brake system, configured for stopping the air vehicle during its taxiing when on the ground.

Calipers are a common brake arrangement, used also in air vehicle, in which two brake pads are configured for clamping therebetween a portion of the wheel (or an element fixedly associated therewith), thereby preventing it from rotating, effectively stopping the air vehicle.

Hydraulic systems can also be substituted by electromechanical systems which can weigh less and require less maintenance. One example of such a mechanical system is a geared caliper system in which an arrangement of gears associated with an electric motor replacing the hydraulic actuation.

Such electromechanical brake systems can incorporate a powerful motor allowing the brake system to be incorporated in large-scale aircrafts. An example of this is disclosed in US2014/0000993 which relates to an electromechanical brake system includes a base carrier provided with a pair of pad plates for application of pressure to a disc, a caliper housing supported by the base carrier to be movable forward and backward to apply pressure to the pad plates, a pressing member including a ball nut installed at the caliper housing to convert rotational motion into rectilinear motion to apply pressure to the pad plates and a ball screw coupled to the ball nut, a force sensor installed at the ball nut to sense load produced by the ball nut, a motor to produce rotational force to operate the pressing member, and a speed reducer connected to a rotating shaft of the motor to transfer driving force to the pressing member, wherein the speed reducer may be adapted to change a reduction ratio depending on presence of load sensed by the force sensor.

In general, the replacement of hydraulic systems with mechanical/electric systems is performed in other avionic systems other than the brakes. One such example is provided in the research paper “Analysis of Electro-Mechanical Actuator Systems in More Electric Aircraft Applications” by Mohsen Torabzadeh-Tari, KTH Electrical Engineering, ISBN 91-7178-0998.

GENERAL DESCRIPTION

In accordance with a first aspect of the subject matter of the present application, there is provided an add-on brake system for a vehicle, for example an air vehicle, for example an aircraft, is configured for clamping a wheel disc thereof, said add-on brake system comprising:a housing accommodating a direct-drive linear actuator comprising:an electric motor constituted by a rotor and a statora nut arrangement fixedly and directly coupled to the rotor and configured for revolving therewith;a linear threaded plunger associated with the nut arrangement for being driven thereby in a linear direction upon the revolution of the latter, said plunger having a first end linearly protruding from one end of the nut arrangement and a second end linearly protruding from an opposite end of the nut arrangement;at least one inboard brake pad fixedly coupled to the housing;at least one outboard brake pad associated with the second end of the linear threaded plunger, oriented transverse to the linear threaded plunger and configured for being driven thereby in the linear direction;

said linear threaded plunger being configured for assuming an initial unclamped position in which the second end protrudes to a first extent n1from the other end of the nut arrangement, yielding a first spacing S1between the inboard and outboard brake pads, and a final, clamped position in which the second end protrudes to a second extent n2>n1from the other end of the nut arrangement, yielding a second spacing S2<S1between the inboard and outboard brake pads, allowing clamping said wheel disc.

The electric motor can be of a brushless type motor, based on magnetic flux and induction between electromagnets of the stator and permanent magnets of the rotor as known per se.

It is noted that since the inboard brake pad is fixedly associated with the housing, the distance between the housing and the inboard brake pad remains constant throughout the operation of the add-on brake system.

The nut arrangement can have a maximal linear extension H between the first end and second end thereof, and said linear threaded plunger has a maximal linear extension L between its respective ends, so that L/H<1.5, and wherein n1, n2<H/4.

The nut arrangement can be a ball-nut type, comprising a plurality of balls constituting the threads of the nut, configured for engaging the matching threads of the linear threaded plunger.

The linear threaded plunger can also comprise a restricting member, configured for preventing the plunger from rotating about its axis, whereby revolution of the nut arrangement about the plunger restricts the displacement of the plunger only to the linear direction.

The restricting member can be associated with the housing in a manner preventing revolution of the plunger. Specifically, the restricting member can be a pin having a first end associated with the plunger and a second end received within a channel formed in the housing and preventing revolution of the pin. The channel can extend in the longitudinal direction, wherein, when said plunger displaces in the linear direction, the pin travels together with the plunger, its second end sliding within the channel of the housing.

In effect, the brake system of the present application provides a compact, light-weight add-on module which can be easily mounted onto the wheel disc of a small-scale air vehicles, for example small-scale aircraft (e.g., drone, light UAV etc.), without significantly increasing the width dimensions of the wheel area throughout its operation.

Since the add-on brake system of the present application is configured for small-scale air vehicles, for example small-scale aircrafts, the amount of power required for arresting the wheeled disc is also considerably lower, the use of the add-on brake system becomes applicable.

Furthermore, the compactness of the add-on brake system according to at least one example of the presently disclosed subject matter can allow for mounting two or more such brake system onto a single wheel of an air vehicle, for example an aircraft, thereby providing a modular assembly based on power requirements concerning braking.

It is also to be noted that the add-on system according to at least one example of the presently disclosed subject matter can be provided on other types of vehicles, and not just air vehicles, wherein such vehicles have at least one wheel that includes a wheel disc.

It is also appreciated that using a ball-nut arrangement provides a high level of precision when driving the linear threaded plunger, as opposed to geared motors. This allows a wiser consumption of electricity and power, making the entire brake system more efficient.

According to another aspect of the subject matter of the present application there is provided an air vehicle, for example an aircraft, comprising at least one wheel having a wheel disc, and having assembled thereto an add-on brake system according to the previous aspect of the present application, receiving said wheel disc between the inboard and outboard brakes pads thereof.

In operation, in the first, loose position, neither of the brake pads are in contact with the wheel disc. In this position, the housing is disposed at a distance M1from the wheel disc.

The add-on brake system is slidingly mounted onto the wheel of the air vehicle, and configured for performing a displacement in the linear direction during its operation. Specifically, from the above initial unclamped position (also referred to herein as the loose position), revolution of the nut causes linear displacement of the plunger, so that the second end thereof associated with the outboard brake pad displaces the latter towards the wheel disc.

The outboard brake pad displaces linearly towards the wheel disc until it engages it, thereby bringing the add-on brake system into an intermediate brake position (also referred to herein as a first clamped position). In this position, the outboard brake pad is flush against an external surface of the wheel disc, the inboard brake pad is still spaced from an internal surface of the wheel disc, and the housing is still at a distance M1from the when disc.

From the intermediate brake position, further revolution of the nut arrangement entails further linear displacement of the linear threaded plunger. However, since the outboard brake pad is restricted from further linear movement (abutting the external surface of the wheel disc), this resulting effect causes the entire housing, along with the nut arrangement and the inboard brake pad, to linearly displace in the opposite direction, bringing the inboard brake pad closer to the internal surface of the wheel disc.

Upon abutment of the inboard brake pad with the internal surface of the wheel disc, the add-on brake system reaches its second clamped position (also referred to herein as the final clamped position). In this position, the wheel disc is firmly clamped between the inboard and outboard brake pads, and the housing is disposed at a distance M2>M1from the wheel disc.

DETAILED DESCRIPTION

Attention is first drawn toFIGS. 1A and 1B, in which an add-on brake system is shown, generally designated with reference numeral1, and comprising a housing10, a mounting arrangement30, an inboard brake pad assembly50, and an outboard brake pad assembly60. The add-on brake system is configured for being fixedly mounted onto a wheel of an air vehicles, for example an aircraft (seeFIGS. 3A to 3C), and has a spacing S between the brake pad assemblies50,60configured for receiving therein a disc element of the wheel.

Turning now toFIG. 2, the housing10is shown accommodating a linear actuator assembly in the form of a brushless motor comprising a stator80, a rotor70associated with the stator80and configured for being revolved thereby, a nut arrangement73(shownFIG. 4B) fixedly associated with the rotor70and a linear threaded plunger20engaged with the nut arrangement to be linearly driven thereby. The rotor70is supported on both sides by bearings90.

It is also observed that the motor has a width M in cross-section and the nut housing has a width H, symmetrically aligned. However, the plunger20protrudes to an extent nLon an inner end21Ithereof from the left end of the nut housing, and to an extent nRon an outer end21Othereof from the right end of the nut housing.

With additional reference being made also toFIGS. 4A and 4B, the stator80is30fixedly contained within the housing and comprises a plurality of electromagnet ends82. In operation, when alternating electrical current is passed through the stator80, it entails revolution of the rotor70, owing to the magnetic relationship between the electromagnets82of the stator80and the permanent magnets74of the rotor70. Since the rotor body72is integrally formed or otherwise fixed with the nut housing73, they revolve together under the magnetic force of the stator80.

The rotor70is supported by two ball bearings90allowing it to freely rotate about its axis X, and the nut arrangement73is formed with at least a portion of a ball path77accommodating therein a plurality of balls26, which form the interface between the nut arrangement73and the plunger22. The ball path can be, for example, in a form of a helix about axis X.

In addition, the outer end21Oof the plunger22is formed with a transverse bore29fixedly receiving therein a restricting member28. The head portion of the restricting member28is retained within a narrow portion16Nof the housing10, preventing the restricting member28, and thereby the entire plunger22, from revolving about the central axis X. The plunger22is also formed with at least another portion of a ball path77.

Attention is now drawn toFIGS. 3A to 3C, in which the add-on brake system1is shown mounted onto a wheel assembly2of an air vehicles, for example an aircraft (not shown). The wheel assembly2comprises a fork3articulated to a wheel4, i.e., the wheel4is rotatably mounted to the fork2. The wheel4is provided with a wheel insert5comprising a wheel disc D, fixedly mounted to the wheel4in a manner such that relative rotation between the insert5and the wheel4is prevented.

The add-on brake system1is mounted onto the wheel assembly2so that a peripheral portion of the wheel disc D is received between the inboard and outboard brake pads50,60respectively. The add-on brake system1is slidingly mounted via the mounting arrangement30, and allows the entire add-on brake system1to displace linearly during operation, as will now be explained, with reference toFIGS. 5A to 6C.

As shown inFIGS. 5A and 6A, in the initial unclamped position (also referred to herein as the loose position) of the brake system1, both inboard and outboard brake pads50,60respectively, are spaced from the wheel disc D, having respective gaps g1, g2therefrom. In this position, the housing is disposed at a distance M1from the external surface of the wheel disc D.

Upon actuation of the motor and electrical current passing through the stator80, the rotor70is caused to revolve about its own axis X, thereby revolving therewith the nut arrangement73. This revolution attempts to rotate the plunger22owing to the threaded engagement between the plunger22and the balls26.

However, since the plunger22is restricted from revolving, by the restricting member28, such revolution of the nut arrangement73causes linear displacement of the plunger22, bringing the outboard brake pad60closer to the external surface of the wheel disc, until it reaches the position shown inFIGS. 5B, 6B.

This first clamped position (also referred to herein as the intermediate clamped position) is achieved once the outboard brake pad abuts the external surface of the wheel disc D and is arrested thereby. In this intermediate position, the gap g1is closed (=0), yet the gap g2is still present. It is also noted that in this displacement, the outboard brake pad60moves with respect to the inboard brake pad50and the housing10(moving away from the housing10and closer to the inboard brake pad50).

From this first clamped position, further revolution of the nut arrangement73attempts pushing the plunger2, and subsequently the outboard brake pad60, against the external surface of the wheel disc D. However, since the wheel disc D is fixedly attached to the wheel2, on which the add-on brake system1is mounted, such further advancement of the plunger22with respect to the nut arrangement73causes a linear sliding displacement of the entire housing10, along with the inboard brake pad50, in the opposite direction. Thus, this displacement of the housing results in the inboard brake pad50moving towards the internal surface of the wheel disc D, while the housing moves away from the external wheel disc D.

This operation progresses until the inboard brake pad50abuts the internal surface of the wheel disc D, thereby arresting the inboard brake pad, bringing the add-on brake system1to its second clamped position. In this position, the wheel disc D is tightly clamped between the brake pads50,60, allowing the brake system1to halt an air vehicle, for example an aircraft.

It is noted that during both the initial unclamped position and the first clamped position, the distance of the housing10from the wheel disc D remains constant (M1). It is only during the final stages of operation, in moving from the first clamped position to the second clamped position (also referred to herein as the final clamped position), that this distance changes to M2<M1.

It is observed that throughout the operation of the add-on brake system1, the plunger20only slightly displaces axially, so that it never protrudes from the housing of the nut arrangement to an extent greater than a given ratio. In particular, the arrangement is such that the L/H<1.5, and each of the extends nL, nRare smaller than H/4, providing a compact arrangement of the motor.

Those skilled in the art to which this presently disclosed subject matter pertains will readily appreciate that numerous changes, variations, and modifications can be made without departing from the scope of the presently disclosed subject matter, mutatis mutandis.