Abstract:
A deployable nozzle for a rocket engine, the nozzle including at least a stationary divergent segment and a movable divergent segment that is coaxial about the stationary divergent segment and configured to move along the stationary divergent segment from a retracted position towards a deployed position. The deployable nozzle further includes a transverse stiffener that is prestressed in tension and that extends transversely relative to the movable divergent segment in a vicinity of a downstream end of the movable divergent segment between at least two points at a periphery of an inside wall of the movable divergent segment.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a deployable nozzle for a rocket engine, and more particularly but not exclusively, to a deployable nozzle for a top-stage engine of a rocket, and to a rocket engine including such a nozzle. In the meaning of the invention, a nozzle is a duct of a rocket engine through which combustion gas is ejected. 
     BACKGROUND OF THE INVENTION 
     A known deployable nozzle for a rocket engine comprises at least a stationary divergent segment and a movable divergent segment that is coaxial about the stationary divergent segment and suitable for moving along the stationary divergent segment from a retracted position towards a deployed position. 
     That type of deployable nozzle is generally fabricated in such a manner that its walls are as thin as possible, within limits set by mechanical strength and ability to withstand high temperature, in order to reduce its weight and thus optimize the performance of the engine on which it is mounted. Nevertheless, the movable divergent segment is particularly flexible while it is in the retracted position, such that the vibration to which it is subjected can lead to high levels of mechanical loading that can degrade it to such an extent as to prevent it from operating properly. For example, while the nozzle is retracted between two stages of a rocket, the vibration to which it is subjected during launching of the rocket can crack or even break the movable divergent segment. 
     An object of the present invention is to remedy the above-mentioned drawbacks, at least in part. 
     SUMMARY OF THE INVENTION 
     The invention achieves this object by providing a deployable nozzle of the above-specified type further comprising a transverse stiffener that is prestressed in tension and that extends transversely relative to the movable divergent segment in the vicinity of a downstream end of the movable divergent segment between at least two points at the periphery of an inside wall of the movable divergent segment. 
     The stationary and movable divergent segments, and more generally the deployable nozzle, define an axial direction. The movable divergent segment moves along the axial direction while extending around the stationary divergent segment. The stationary divergent segment is for attaching to a point that is stationary relative to the movable divergent segment. Upstream and downstream for the deployable nozzle are defined relative to the flow direction of combustion gas through the nozzle. Since the stationary and movable segments are both divergent, the sections of their upstream ends are smaller than the sections of their downstream ends. It can be understood that in the retracted position (or folded position), the downstream end of the movable divergent segment is closer to the downstream end of the stationary divergent segment than is the upstream end of the movable divergent segment. Conversely, in the deployed position (or extended position), the upstream end of the movable divergent segment is closer to the downstream end of the stationary divergent segment than is the downstream end of the movable divergent segment. 
     The “vicinity” of the downstream of the movable divergent segment is defined as being the environment of the movable divergent segment that extends axially over 10% of the total axial extent of the movable divergent segment either way from its downstream end; the portion of the movable divergent segment that extends axially over 10% of the total axial extent of the movable divergent segment from the downstream end naturally being included. Consequently, this segment portion is referred to as the “downstream end portion”. The terms “vicinity” and “end portion” apply equally to the upstream end, and also to the stationary divergent segment, and more generally to the nozzle. 
     It can be understood that the stiffener extends between two distinct inside points of the downstream end portion of the movable divergent segment. By arranging the stiffener in this way, the space it occupies in the environment of the deployable nozzle is small, so it does not constitute any hindrance while the divergent segments are retracted. This is particularly advantageous when the nozzle is located between two stages of a rocket. In addition, this position for the stiffener serves to ensure that the stiffener does not hinder deployment of the nozzle. Furthermore, still because of this positioning, the stiffener does not impede the flow of combustion gas through the nozzle when the engine starts or is operating. 
     Since the stiffener is prestressed in tension, the at least two points are coupled together so that their relative movements due to vibration are limited or even prevented. In particular, the resonant modes of lobes of the ovalization type, three lobes, four lobes, etc., of the movable divergent segment are blocked, or their deformation amplitudes are limited. Furthermore, the stiffener is advantageously more flexible than the movable divergent segment such that the resonant vibrations of the stiffener do not generate additional force in the vicinity of said points. 
     It can be understood that the greater the number of points connected together by the stiffener, the greater the number of resonant modes that are blocked. For example, when the nozzle forms a body of revolution about the axial direction, a stiffener that extends between twelve points that are uniformly distributed angularly around the axial direction serves to block the first five resonant modes of vibration (i.e. the lower-frequency resonant modes) of the movable divergent segment. 
     Thus, since the first resonant modes in vibration of the movable divergent segment are blocked, the external vibration to which it is subjected does not excite those resonant modes. Consequently, the higher energy resonance phenomena that are associated with the lower frequency resonant modes that are blocked by the stiffener disappear. The higher frequency resonance phenomena present lower energy and present little or no risk of deteriorating the movable divergent segment. 
     Consequently, since the mechanical stresses due to vibration in the movable divergent segment of the deployable nozzle of the invention are smaller than in the movable divergent segment of prior art deployable nozzles, the walls of the movable divergent segment of the nozzle of the invention may be thinner than the walls of the movable divergent segment of the prior art, while withstanding an equivalent vibration spectrum. This reduction in thickness enables the nozzle of the invention to be lighter than prior art nozzles and thus enables the performance of the engine on which it is mounted to be improved. 
     Advantageously, the transverse stiffener extends in a transverse plane of the movable divergent segment. 
     A transverse plane is a plane perpendicular to the axial direction of the movable divergent segment. This improves blocking of the first resonant modes of the movable divergent segment. 
     In a variant, the stiffener comprises at least one tie extending diametrically and having two ends, each end being connected to a point of the periphery of the inside wall of the movable divergent segment. 
     A tie that extends diametrically is a tie that directly connects together two points of the periphery of the inside wall of the movable divergent segment that are opposite each other about the central axis of the movable divergent segment, the tie intersecting the axis, and with this applying regardless of the shape of the cross-section of the movable divergent segment. Preferably, the cross-section of the movable divergent segment is circular. The tie then extends along a diameter of the circular section. Such a tie is easier to install and its prestress in tension is easier to adjust than a tie that does not extend diametrically. Preferably, the stiffener has three ties all extending diametrically and each having two ends, each end of each tie being connected to a respective point of the periphery of the inside wall of the movable divergent segment. This serves to improve blocking of the first vibration mode. 
     In another variant, the stiffener comprises at least two ties extending radially from a primary central body. 
     A tie that extends radially is a tie that extends from the central body arranged on the central axis of the movable divergent segment towards a point on the inside periphery of the inside wall of the movable divergent segment, with this applying regardless of the shape of the cross-section of the movable divergent segment. Thus, a radial tie presents a first end connected to the central body and a second end connected to the wall of the movable divergent segment. Preferably, the cross-section of the movable divergent segment is circular. The tie then extends along a radius of the circular section, or in a variant it extends like the spokes of a bicycle wheel (i.e. without being directed through the central geometrical axis of the movable divergent segment, but towards the periphery of a central axis presenting a certain diameter). It should be observed that the central body is said to be “primary” relative to a central body that is described below and that is said to be “secondary”. Preferably, the stiffener has at least three ties extending radially from a primary central body. This makes it possible to improve the blocking of the first vibration modes. 
     Advantageously, the stiffener comprises adjustment means for adjusting the prestress tension. 
     By using the means for adjusting the prestress in tension, it is possible to apply predetermined and controlled levels of prestress. By way of example, the prestress means may comprise a tensioner that is adjustable by means of a screw thread system. 
     Advantageously, the stiffener comprises at least one cord made of polymer fibers. 
     A polymer fiber cord is light in weight. Thus, the added weight constituted by the stiffener compared with the remainder of the nozzle is small relative to the weight of the nozzle. This makes it possible to avoid penalizing the efficiency of the engine to which the nozzle is fastened. It can be understood that the cord acts as a tie. Furthermore, a cord occupies little space so the obstruction constituted by the transverse stiffener in the movable divergent segment is negligible relative to the total section of the movable divergent segment and it does not disturb the jet of combustion gas, in particular when igniting the engine to which the deployable nozzle is fastened. Each tie preferably comprises a polymer fiber cord. Advantageously, the stiffener has at least three polymer fiber cords. 
     Preferably, the cord is made of aramid fibers (or Kevlar, registered trademark, fibers) or the equivalent. The term “equivalent” covers a fiber cord presenting a coefficient of thermal expansion, a melting or vaporization temperature, stiffness, and sensitivity to creep that are of the same order of magnitude as a cord made of aramid fibers. For example, the cord could equally well be made of polyester fibers. 
     A cord of aramid or equivalent fibers presents the advantage of not creeping, i.e. of being insensitive to creep, while presenting satisfactory traction stiffness. Thus, the tension prestress in such a cord varies little or not at all over time. Furthermore, this aramid fiber cord presents a small coefficient of thermal expansion. Thus, the tension prestress in such a cord varies little or not at all, even when the cord is subjected to temperature variations, e.g. when the nozzle is mounted on an engine arranged between cryogenic stages. 
     Furthermore, such a cord melts and decomposes in a few seconds under the effect of the hot combustion gas ejected by the engine. Thus, when the nozzle is deployed and the engine to which it is fastened is in operation, the decomposition of the cords of the stiffener serve to avoid impeding the ejection of combustion gas from the nozzle. In addition, the fact that the cord disintegrates under the effect of heat makes it possible to avoid ejecting solid pieces when the nozzle is deployed and the engine is operating, thereby avoiding any risk of damaging the engine itself, or for example the upper stage to which is attached or the lower stage from which it has just been released. 
     Advantageously, the stiffener comprises fastener means for fastening to the movable divergent segment and secured to said movable divergent segment. 
     Since they are secured to the movable divergent segment, the fastener means are not ejected from the nozzle, e.g. when the cord melts and disintegrates, and as a result they do not present any risk of causing damage by being thrown out, e.g. towards the engine of the upper stage or of the lower stage. 
     Advantageously, the fastener means do not extend inside the movable divergent segment. Thus, the fastener means do not disturb the flow of combustion gas. 
     Advantageously, in the retracted position, the stiffener cooperates with the downstream end portion of the stationary divergent segment. 
     It can be understood that the stiffener cooperates directly or via one or more intermediate part(s) with the stationary divergent segment. This makes it possible, particularly, but not exclusively, to block resonant modes of the rigid body in tilting and in moving the movable divergent segment radially relative to the stationary divergent segment. This further reduces vibration and the risk of damage to the movable divergent segment, and reduces the risk of collision between the movable divergent segment and the stationary divergent segment. 
     Advantageously, the stationary divergent segment and the movable divergent segment present, in the vicinity of their downstream ends, complementary centering means that cooperate with each other in the retracted position. 
     The complementary centering means serve firstly to hold the movable divergent segment in position relative to the stationary divergent segment, and secondly to block radial movements in translation and/or tilting movements of the movable divergent segment relative to the stationary divergent segment, and in particular to block resonant modes of the rigid body. 
     In an embodiment, the stiffener carries an annular centering skirt that cooperates with a downstream end portion of the stationary divergent segment in the retracted position by mutually engaging therewith. 
     It can be understood that in this embodiment the complementary means are formed firstly by the annular skirt and secondly by the downstream end portion of the stationary divergent segment. For example, the skirt is adapted to fit closely to the downstream end portion of the stationary divergent segment. In the retracted position, the prestress of the stiffener enables the stiffener to keep the skirt engaged with the downstream end portion of the stationary divergent segment, and possibly also to maintain contact between them. 
     Advantageously, the skirt cooperates with an inside wall of the end portion of the stationary divergent segment. The skirt is preferably made of material that is light (compared with the weight of the deployable nozzle) and that melts or vaporizes easily under the effect of the hot combustion gas. For example, the skirt may be made of rigid foam and/or it may present a honeycomb internal structure. Such a skirt may be made for example out of polyurethane foam or out of an epoxy resin composite material for the outer walls and out of polypropylene for the honeycomb internal structure. 
     In another embodiment, the stiffener has at least two ties extending radially from a primary central body, and the downstream end of the stationary divergent segment carries a secondary central body with which the primary central body cooperates in the retracted position by mutual engagement therewith. 
     In this embodiment, it can be understood that the complementary centering means are formed firstly by the primary central body and secondly by the secondary central body. For example, the primary central body and the secondary central body cooperate by tenon-and-mortice type mutual engagement. 
     Advantageously, the stationary divergent segment includes a transverse stiffener prestressed in tension comprising at least two ties extending radially in the vicinity of a downstream end of the stationary divergent segment, between at least two points of the periphery of an inside wall of the stationary divergent segment from the secondary central body. 
     With the stiffener of the stationary divergent segment blocking the first resonant modes of vibration of the stationary divergent segment, this correspondingly increases the reliability of the deployable nozzle. 
     Advantageously, in order to reduce the mass added by the stiffener(s), the primary central body and/or the secondary central body should be made of material that is light in weight (compared with the weight of the deployable nozzle). Advantageously, in order to avoid ejecting solid pieces, the primary central body and/or the secondary central body should be made of a material that melts or vaporizes easily under the effect of the hot combustion gases. For example, the primary body and/or the secondary body should be made of aramid fibers or of polyamide (or nylon) fibers). 
     The invention also provides a rocket engine including at least one deployable nozzle of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention and its advantages can be better understood on reading the following detailed description of various embodiments of the invention given as non-limiting examples. The description refers to the accompanying drawings, in which: 
         FIG. 1  shows a first embodiment of the deployable nozzle of the invention in the retracted position; 
         FIG. 2  shows the  FIG. 1  deployable nozzle seen looking in the axial direction along arrow II of  FIG. 1 ; 
         FIG. 3  shows the  FIG. 1  deployable nozzle in the deployed position; 
         FIG. 4  shows the  FIG. 1  deployable nozzle fitted with an annular centering skirt; 
         FIG. 5  shows a second embodiment of the deployable nozzle of the invention, shown in part; 
         FIG. 6  shows the  FIG. 5  deployable nozzle seen looking in the axial direction along arrow VI of  FIG. 5 ; 
         FIG. 7  shows a fastener of the stiffener of the  FIG. 5  deployable nozzle; and 
         FIG. 8  shows a third embodiment of the deployable nozzle of the invention, shown in part. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       FIG. 1  shows a first embodiment of a deployable nozzle of the invention for a rocket engine, the nozzle being shown in the retracted position. The deployable nozzle  10  comprises a stationary divergent segment  12  and a movable divergent segment  14 , and it extends along an axis X (or axial direction X). The stationary and movable divergent segments are frustoconical in shape about the axis X. The movable divergent segment  14  slides along the axis X and is coaxial about the stationary divergent segment  12 . The stationary divergent segment  12  presents a coupling portion  121  fastened to the outlet of a propulsion chamber  200  of a rocket engine. Combustion gas flows in the deployable nozzle  10  from the propulsion chamber  200  via the coupling portion  121 . Thus, the upstream end  12   a  of the stationary divergent segment  12  is arranged beside the coupling portion  121 , while the downstream end  12   b  of the stationary divergent segment  12  is arranged remote therefrom. In the same manner, the upstream end  12   a  of the movable divergent segment  14  is arranged beside the coupling portion  121  while the downstream end  14   b  of the movable divergent segment is arranged remote therefrom. 
     A transverse stiffener  16  extends in a transverse plane of the movable divergent segment  14  perpendicular to the axis X, in the vicinity of its downstream end  14   b.  With reference to  FIG. 2 , the stiffener  16  comprises three aramid fiber cords  16   a  extending diametrically so as to form three ties. The cords  16   a  are angularly equidistant. Thus, in this example, each cord is spaced at 60° (sixty degrees of angle) from the adjacent cords. Each cord  16   a  has two ends, these two ends connecting together two diametrically opposite points of the inside wall of the movable divergent segment  14 . In a variant, the stiffener  16  could comprise only one, two, or more than three cords  16   a.    
     With reference to  FIG. 3 , the deployable nozzle  10  is shown in the deployed position, the engine (not shown) is in operation, and the stiffener  16 , represented by dashed lines, has been melted by the hot combustion gas from the engine. 
       FIG. 4  shows a variant in the deployed position of the  FIG. 1  deployable nozzle, in which the stiffener  16  carries a single-piece annular centering skirt  18  of rigid polyurethane foam. The skirt  18  extends axially along the axis X and is frustoconical in shape. The diameter of the upstream end  18   a  of the skirt  18  is less than the diameter of the downstream end  12   b  of the stationary divergent segment  12 , while the diameter of the downstream end  18   b  of the skirt  18  is greater than the diameter of the downstream end  12   b  of the stationary divergent segment  12 . Thus, along its axial extent, the skirt  18  penetrates in part inside the stationary divergent segment  12  and its outside wall cooperates with the inside wall of the stationary divergent segment  12  by bearing thereagainst. The stiffener  16  holds the skirt  18  against the stationary divergent segment  12 . As shown in  FIG. 4 , this thrust causes the cords  16   a  to flex. The skirt  18  is supported by the cords  16   a.  For this purpose, the cords  16   a  pass through the skirt  18 , through the thickness thereof, via holes  18   c,  the cords  16   a  being capable of sliding in the holes  18   c.    
       FIG. 4  is a detailed view of the fastener  17  of the cords  16   a  to the movable divergent segment  14 . Each fastener  17  comprises a hook  17   a  with a base that is threaded and has a nut  17   b  screwed thereon to present a shoulder for cooperating with the outside wall of the movable divergent segment  14  by bearing thereagainst. Each end of the cords  16   a  is fastened to a hook  17   a  via a loop  16   b.  By using the nut  17   b,  it is possible to adjust the radial position of the hook  17   a,  and thus to adjust the tension in the cord  16   a.  In combination, the hook  17   a  and the nut  17   b  serve to secure the fastener  17  to the movable divergent segment  14 . Thus, the fasteners  17  form means for fastening the stiffener  16  to the movable divergent segment  14 , while the nuts  17   b  form means for adjusting the tensioned prestress in the stiffener  16 . 
       FIGS. 5 and 6  show a second embodiment of the deployable nozzle of the invention, in the retracted position. Portions that are common with the first embodiment are not described again and they are given the same reference signs. 
     The deployable nozzle  110  has a first transverse stiffener  116  arranged in the vicinity of the downstream end  14   b  of the movable divergent segment  14 , and a second transverse stiffener  120  arranged in the vicinity of the downstream end  12   b  of the stationary divergent segment  12 . The first stiffener  116  extends in a transverse plane of the movable divergent segment  14 , i.e. a plane that is perpendicular to the axis X, while the second stiffener  120  extends in a transverse plane of the stationary divergent segment  12 , i.e. a plane that is perpendicular to the axial direction X. The first stiffener  116  has three aramid fiber cords  116   a  forming three radial ties. Each cord  116   a  has two ends, namely a first end connected to a primary central body  116   b  made of aramid fibers and a second end connected to a point at the periphery of the inside wall of the movable divergent segment  14 . Likewise, the second stiffener  120  has three aramid fibers cords  120   a  forming three radial ties. Each cord  120   a  presents two ends, namely a first end connected to a secondary central body  120   b  of rigid synthetic material such as nylon, and a second end connected to a point of the periphery of the inside wall of the stationary divergent segment  12 . Naturally, in a variant, the first and/or second stiffener could have two radial cords or more than three radial cords. The cords  116   a  and  120   a  extend along radii respectively of the movable and the stationary divergent segments  14  and  12 . 
     The primary central body  116   b  is a body of revolution about the axis X, and it presents an axially-projecting rod and an annular portion that extends radially and that has the cords  116   a  fastened thereto. The secondary central body  120   b  is a body of revolution about the axis X presenting an axial central hole and an annular portion that extends radially and that has the cords  120   a  fastened thereto. The rod of the primary central body  116   b  cooperates with the central hole of the secondary central body  120   b  by engaging therein. Thus, when the deployable nozzle is in the retracted position, as shown in  FIG. 5 , the rod of the primary central body  116   b  is engaged in the hole in the secondary central body  120   b.  When the nozzle moves into its deployed position, the movement in translation of the movable divergent segment  12  downstream along the direction X disengages the rod of the primary central body  116   b  from the hole in the secondary central body  120   b.  Naturally, in a variant, the rod could be arranged on the secondary central body while the hole is arranged in the primary central body. In yet another variant, a plurality of rods could engage respectively in a plurality of holes in the retracted position. 
       FIG. 6  shows the azimuth distribution of the cords  116   a  and  120   a  of the first and second stiffeners  116  and  120 . Each of the cords is regularly spaced apart at 120° (one hundred twenty degrees of angle). The cords of the second stiffener  120  are offset in the azimuth direction by 60° (sixty degrees of angle) relative to the cords  116   a  of the first stiffener. More generally, when the first and second stiffeners present the same odd number of cords, the cords of the second stiffener are offset in the azimuth direction so as to extend radially opposite from the cords of the first stiffener. 
       FIG. 7  shows a fastener  117  for attaching the cords  116   a  to the movable divergent segment  14 . The fasteners of the cords  120   a  of the stationary divergent segment  12  are identical. The fastener  117  comprises a bushing  117   a  screwed onto the movable divergent segment  14 . The fastener  117  is thus secured to the movable divergent segment  14 . This bushing  117   a  is tubular and has passing therethrough an endpiece  117   b  that is crimped onto the end of the cord  116   a.  The endpiece  117   b  can slide in the bushing  117   a.  An adjustment nut  117   c  is screwed onto a thread on the endpiece  117   b  and cooperates with the bushing  117   a  by bearing thereagainst, thus making it possible firstly to prevent the endpiece  117   a  from moving in translation towards the inside of the movable divergent segment  14 , and secondly to adjust the tension prestress in the cord  116   a.  A lock nut  117   d  holds the adjustment nut  117   c  in place. A protective cap  117   e  protects the nuts  117   c  and  117   d,  in particular against infiltration of water. The fasteners  117  form means for fastening the stiffener to the movable divergent segment, while the adjustment nuts  117   c  form means for adjusting the tension prestress. 
     Naturally, the fastener  117  of the second embodiment could be used instead of the fasteners  17  of the first embodiment, and vice versa. 
       FIG. 8  shows a third embodiment of the deployable nozzle of the invention. Portions in common with the first and second embodiments are not described again and they are given the same reference sign. 
     The deployable nozzle  210  presents a first transverse stiffener  216  arranged in the vicinity of the downstream end  14   b  of the movable divergent segment  14 , and a second transverse stiffener  220  arranged in the vicinity of the downstream end  12   b  of the stationary divergent segment  12 . The first stiffener  216  extends in a transverse plane of the movable divergent segment  14 , i.e. a plane that is perpendicular to the axial direction X, while the second stiffener  220  extends in a transverse plane of the stationary divergent segment  12 , i.e. a plane that is perpendicular to the axial direction X. 
     In order to compensate for the axial spacing between the downstream end  12   b  of the stationary divergent segment  12  and the downstream end  14   b  of the movable divergent segment  14 , each stiffener has two series of cords connected to a central body, each cord being duplicated. Thus, each central body is offset axially relative to the plane defined by the points to which the stiffeners are connected. 
     Each central body presents two annular portions extending radially and spaced apart axially, a first series of cords being connected to a first annular portion while a second series of cords, duplicating the first series of cords, is connected to the second annular portion. It can thus be understood that two cords extend radially from the primary central body  216   b  or from the secondary central body  220   b  in a common radial plane towards a common point of the inside wall of the movable or stationary divergent segment  14  or  12 . Thus, each stiffener  216  and  220  presents two series of three cords  216   a  and  220   a,  with each cord in one series duplicating a cord in the other series. The azimuth distribution of the cords  216   a  and  220   a  is similar to the distribution of the cords  116   a  and  120   a  of the second embodiment, as shown in  FIG. 6 . Naturally, in a variant, the stiffeners  216  and/or  220  may present two series of two cords or of more than three cords. The cords  216   a  and  220   a  are attached respectively to the movable and stationary divergent segments  14  and  12  by means of fasteners  17  (cf.  FIG. 4 ). Naturally, in a variant, the fasteners  117  (cf.  FIG. 7 ) could replace the fasteners  17 . 
     In the same manner as for the second embodiment, the primary central body  216   b  and the secondary central body  220   b  cooperate by an axial rod engaging in a central hole while the deployable nozzle is in its retracted position, and the rod becomes disengaged from the hole when the deployable nozzle moves into its deployed position. 
     Although the present invention is described with reference to specific embodiments, it is clear that modifications and changes may be carried out on the embodiment without going beyond the general scope of the invention as defined by the claims. In particular, individual characteristics of the various embodiments shown may be combined in additional embodiments. Consequently, the description and the drawings should be considered in an illustrative sense rather than a restrictive sense.