EP0286203A1

EP0286203A1 - Vacuum cleaner

Info

Publication number: EP0286203A1
Application number: EP88300779A
Authority: EP
Inventors: Richard B. Kosten
Original assignee: Black and Decker Inc
Current assignee: Black and Decker Inc
Priority date: 1987-04-06
Filing date: 1988-01-29
Publication date: 1988-10-12

Abstract

A vacuum cleaner (10) includes a telescoping handle (22) having a plurality of resilient pads (106, 116) for preventing vibration and motion of the handle (22) with respect to the remainder of the vacuum cleaner. All elements of the vacuum cleaner are mounted on a single frame (34). A power unit (12) includes two halves which are mounted on the frame (34) from opposite sides. A socket (26) at a lower end of the frame (34) receives the lower end (38) of a substantially rigid dust bowl (14). The upper end (30) of the dust bowl (14) includes a gasket (50) maintained in face-sealing contact with a lower surface (32) of the power unit (12). A latch assembly (123) in the frame (34) includes a locking dog (128) urged into locking entry in one of two openings (117, 119) in the telescoping handle shaft (22). A pair of ramp teeth (134) enter corresponding limit ramps (125, 127) when an attempt is made to extend the handle (22) beyond its normal extension. This prevents further extension but mating ramp surfaces (144, 148) permit retraction to one of the normal locking positions.

Description

BACKGROUND OF THE INVENTION

The present invention relates to housewares, and more particularly to vacuum cleaners.
Vacuum cleaners are almost indispensable houseware appliances for household cleaning. Such cleaners are most commonly powered by AC power from an external source. Generally, they consist of a fan or blower operative to produce a partial vacuum at an intake. Air sucked in by the partial vacuum passes through a filter bag whereby dirt particles are removed from the air stream. The filtered air is returned to the environment.
The above externally powered vacuum cleaners tend to be large and heavy. Thus, certain types of cleaning which is adapted to vacuum cleaning is not conveniently performed with them. In addition, the need for an external power source limits their use to areas where such external power sources are available.
A relatively new class of vacuum cleaner solves the problems of size, weight and power availability. Such a new class, disclosed in U.S. Patent No. 4,209,875, the disclosure of which is incorporated herein by reference, is exemplified by a cordless, hand-held, vacuum cleaner sold under the trademark Dust Buster by the Black and Decker Corporation. The cordless condition is achieved by an internal rechargeable battery in the vacuum cleaner capable of being recharged between uses.
Hand-held vacuum cleaners cannot be used on certain surfaces such as, for example, floors without requiring the user to stoop over. Consequently, a vacuum cleaner adapted for cleaning a floor without stooping appears to extend the advantages of cordless vacuuming.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an improved vacuum cleaner.
Accordingly, therefore, there is provided by the present invention a vacuum cleaner characterized by a frame, a power unit mounted on the frame for providing a suction, a dust bowl sealably connected to the power unit for application of said suction inside said dust bowl, means communicating with said dust bowl for applying said suction from said dust bowl to a surface to be vacuumed, a handle shaft telescopically connected to said frame, and resilient means between said frame and said handle shaft for taking up any clearances therebetween.
Preferably said resilient means comprises one or more resilient pads, such as resilient vibration snubbers.
Preferably the handle shaft is telescopically mounted to slide inside the frame which may comprise an elongate hollow member.
In a preferred embodiment of the invention, there is provided a vacuum cleaner having a telescoping handle and a plurality of resilient pads for inhibiting vibration and motion of the handle with respect to the remainder of the vacuum cleaner. All elements of the vacuum cleaner are mounted on a single frame. A power unit includes two halves which are mounted on the frame from opposite sides. A socket at a lower end of the frame receives the lower end of a substan tially rigid dust bowl. The upper end of the dust bowl includes a gasket maintained in face-sealing contact with a lower surface of the power unit. A latch assembly in the frame includes a locking dog urged into locking entry in one of two openings in the telescoping shaft. A pair of ramp teeth enter corresponding limit ramps when an attempt is made to extend the handle beyond its normal extension. This prevents further extension but mating ramp surfaces permit retraction to one of the normal locking positions.
According to another aspect of the invention, there is provided a vacuum cleaner comprising: a frame, a power unit mounted on the frame, a dust bowl sealable to the power unit, means on the frame for applying a suction from the dust bowl to a surface, a telescoping shaft, means for permitting the telescoping shaft to telescope to at least first and second positions in the frame, and resilient means between the frame and the telescoping shaft for taking up clearances therebetween.
According to a further aspect of the invention, there is provided a latch for a telescoping shaft in a vacuum cleaner comprising: first and second locking nooks in the telescoping shaft, a latch assembly, the latch assembly including a locking dog fittable into either of the first and second locking nooks for locking the telescoping shaft into one of first and second positions, at least one ramp tooth on the latch assembly, at least one limit ramp in the shaft, the at least one limit ramp being disposed in a position related to the second locking nook reachable by the at least one ramp tooth when the telescoping shaft is extended beyond its maximum extension, the at least one limit ramp including first means cooperating with the at least one ramp tooth for preventing extension of the telescoping shaft more than a predetermined amount beyond the maximum extension, and the at least one limit ramp and the at least one ramp tooth including second means for permitting extension of the shaft to be reduced from the predetermined amount beyond the maximum extension to the maximum extension.
According to yet another aspect of the invention, there is provided a vacuum cleaner comprising: a frame, a power unit at a first end of the frame, a socket at a second end of the frame, a swivelling floor tool swivellably affixed to the socket, a substantially rigid dust bowl, means at a first end of the dust bowl for producing a first substantially air-tight seal with the socket, means at a second end of the dust bowl for providing a second substantially air-tight seal with the power unit, and the socket and the swivelling floor tool including means for providing a substantially air-tight passage for air between the socket and a vacuum port in the swivelling floor tool, whereby a vacuum created in the power unit is communicated to a surface adjacent the vacuum port and the surface is cleaned.
The above, and other objects, features and advantages of the present invention will become apparent from the following description read in conjunction with the accompanying drawings, in which like reference numerals designate the same elements.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a perspective view of a vacuum cleaner according to an embodiment of the invention;
Fig. 2 is a side view of the vacuum cleaner of Fig. 1 with its dust bowl moved aside and its floor tool partly disassembled. A support assembly is also shown adjacent the vacuum cleaner;
Fig. 3 is a side view of the frame of the vacuum cleaner with all elements except the handle and shaft removed;
Fig. 4 is a view taken in the direction IV-IV in Fig. 3;
Fig. 5 is a cross section taken along V-V in Fig. 4;
Fig. 6 is a view of the telescoping shaft of the preceding figures removed from the frame;
Fig. 7 is a cross section taken along VII-VII in Fig. 3 showing the telescoping shaft in its fully retracted position;
Fig. 8 is a cross section corresponding to Fig. 7 but showing the telescoping shaft in an intermediate position;
Fig. 9 is a fractional view of a portion of the locking mechanism of Figs. 7 and 8;
Fig. 10 is a view corresponding to Figs. 7 and 8 showing the telescoping shaft in its over-extended and blocked position; and
Fig. 11 is an electrical schematic diagram of the vacuum cleaner and its support assembly.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to Fig. 1, there is shown, generally at 10, a vacuum cleaner according to an embodiment of the invention. A power unit 12, containing a conventional electric motor and fan (not shown) draws air through a dust bowl 14 operatively connected at its lower end to a swivelling floor tool 16. Air exits power unit 12 through a plurality of louvers 18 in power unit 12 after being filtered in a conventional filter element in dust bowl 14. An electric switch 20 controls the application of electric power to power unit 12.
Although the present invention is equally applicable to an externally powered and an internally (battery) powered embodiment, for concreteness, an internally powered embodiment of the invention is assumed. The electric motor and fan in power unit 12 and the filtering element in dust bowl 14 are conventional and are fully detailed in the referenced patent. Thus, further description thereof is omitted.
A telescoping shaft 22, having a hand grip portion 24 at an extremity thereof, supports and guides vacuum cleaner 10 with a lower surface of swivelling floor tool 16 in contact with a floor (not shown). As will be more fully detailed hereinafter, telescoping shaft 22 is provided with means for permitting it to telescope between a minimum to a maximum length whereby compactness for storage is provided as well as convenient length for use in cleaning a floor without stooping.
A socket 26, swivellably affixed to swivelling floor tool 16, receives and seals a forward end 28 of dust bowl 14. An upper end 30 of dust bowl 14 is held in face-to-face abutment with a lower face 32 of power unit 12. A latch 34ʹ ensures that, once dust bowl 14 is installed in the position shown, it remains in such position.
Referring now to Fig. 2, wherein dust bowl 14 is displaced and swivelling floor tool 16 is partially disassembled for clarity of illustration, a frame 34 provides the principal support for all elements of vacuum cleaner 10. Socket 26 is seen to extend at right angles from frame 34. A cavity 36 in socket 26 permits insertion of a mating part 38 extending forward from forward end 28. A curved surface 40 in socket 36 supports a sealing pad 42 surrounding an air duct 44 which passes into a generally cylindrical swivel member 46. A curved forward surface 48 on mating part 38 is shaped to seat in a sealing manner against sealing pad 42. It will be noted that upper end 30 and lower face 32 are disposed at equal angles with respect to a longitudinal axis of frame 34. A gasket 40, surrounding a filter element 52 in a downstream end of dust bowl 14, is moved into sealing engagement with lower face 32 to provide a closed sealing figure on lower face 32, whereby a sealed air path is created between power unit 12 and air duct 44.
A latch button 54, about which more will be discussed later, protrudes through a side of a channel 56 at the rear of power unit 12. A pair of support openings 58 (only one of which is shown, the other is disposed in a symmetrical location on the hidden side of power unit 12) provide means for entry of a mating pair of support horns 60 (only the nearer of which is shown) of a support assembly 62. Support assembly 62 may include means for positioning an electrical connector 64 enterable into support opening 58 for providing charging power to batteries internal to power unit 12. As will be more fully detailed later, a connector assembly (not shown) within support opening 58 cooperates with electrical connector 64 to disconnect the internal motor in power unit 12 when vacuum cleaner 10 is mounted for support and charging on support assembly 62.
Swivelling floor tool 16 includes a floor plate 66 and a cover plate 68 mateable together to sealably encircle cylindrical swivel member 46. Cylindrical swivel member 46 has cylindrical hubs 72 and an outer cylindrical surface 70 centrally disposed at each end thereof (only the outer cylindrical surface 70 at the near end of the member 46 is shown). Cover plate 68 includes a semi-cylindrical sealing surface 74 shaped to seal against an upper portion of outer cylindrical surface 70. A semi-circular guide 76 at each end of semi-cylindrical sealing surface 74 receives a respective cylindrical hub 72. A part-cylindrical sealing surface 78 on floor plate 66 is shaped to seal against a lower portion of outer cylindrical surface 70. A semi-circular guide 80 at each end of part-cylindrical sealing surface 78 forms, with its complementary semi-circular guide 76 on cover plate 68, a complete circle surrounding its respective cylindrical hub 72, thereby providing support and guidance thereof.
An air channel 82 in cover plate 68 extends forward from semi-cylindrical sealing surface 74 toward a front of cover plate 68. A vacuum port 84 in floor plate 66 is disposed below air channel 82. The perimeters of floor plate 66 and cover plate 68 are sealed to each other using any convenient means (not shown), whereby a complete sealed air path is provided between air duct 44 and vacuum port 84. The cylindrical shape of outer cylindrical surface 70, and the complementary shapes of semi-cylindrical sealing surface 74 and part-cylindrical sealing surface 78 permit swivelling floor tool 16 to swivel about an axis of cylindrical swivel member 46. The sealing angular extents of semi-cylindrical sealing surface 74 and part-cylindrical sealing surface 78 are great enough to provide an air seal over the maximum swivel angle permitted by mechanical limits.
A plurality of conventional rollers 86 maybe disposed in a bottom surface of floor plate 66 to provide rolling support for vacuum cleaner 10. In addition, a brush, not shown, may be disposed in the bottom surface of floor plate 66 to aid in loosening dirt.
Referring now to Fig. 3 (which corresponds to Fig. 2 except for the omission of swivelling floor tool 16, support assembly 62 and the removal of power unit 12), frame 34 is seen to extend, unbroken, from socket 26 to an upper end 88. Telescoping shaft 22 is disposed to slide in and out of upper end 88. Thus, frame 34 provides the backbone, and provides mounting, for the entire vacuum cleaner 10. A plurality of attachment loops 90, 92 and 94 are affixed to frame 34 transversely centered in the region thereof occupied by power unit 12, when assembled. Each attachment loop includes a hole 96 therethrough engageable by assembly screws (not shown) employed to assemble power unit 12 thereto.
Referring now also to Fig. 4, frame 34 is seen to be formed of complementary halves 97 and 98 mated together at a central mating line 100. It will be noted that attachment loops 90 (not shown in Fig. 4), 92 and 94 are each made up of a complementary facing pair with a respective hole 96 passing through and aligned with each other. When power unit 12 is assembled onto frame 34 and assembly screws are driven through holes 96, paired alignment between halves 97 and 98, as well as longitudinal stability of power unit 12 with respect to frame 34, is ensured.
One of the problems offered by a telescoping shaft 22, when it is extended, is the long cantilevered length with a correspondingly short portion of telescoping shaft 22 within frame 34 for providing guidance and support thereof. This problem is exacerbated by inevitable clearances required in a manufactured product. Such clearances, especially when combined with a long cantilever and short supporting length, could lead to looseness and a user impression of poor quality.
Referring now also to Fig. 5 (together with Fig. 4), half 97 includes a groove 102 passing therethrough and terminating at mating line 100. A similar groove 104 is disposed in half 98 and terminating at mating line 100 aligned with groove 102. It will be noted that groove 102 and groove 104 pass through their respective portions of attachment loop 94. A resilient vibration snubber 106 is disposed in grooves 102 and 104, passing through attachment loop 94. Resilient vibration snubber 106 is urged into resilient contact with a top surface of telescoping shaft 22 whereby vibration and motion of telescoping shaft 22 normal to its top surface is reduced substantially. A second resilient vibration snubber 108 is disposed in grooves 110 and 112 passing under attachment loop 92 and providing a second position along telescoping shaft 22 at which vibration and motion of telescoping shaft 22 normal to its top surface is prevented.
Referring specifically to Fig. 5, vibration and motion of telescoping shaft 22 normal to its side surface is prevented by one or more pockets 114 within half 97 facing a side surface of telescoping shaft 22. A resilient vibration snubber 116 is compressed into resiliently urged contact with the side surface of telescoping shaft 22 when power unit 12 is assembled onto frame 34. In the preferred embodiment, two pockets 114, each containing a respective resilient vibration snubber 116, are employed. In the foregoing manner, smooth, vibration-free retention of telescoping shaft 22 is provided.
It should be pointed out that Fig. 5 shows frame 34 as a relatively thick cross section of a resin material. Conventional engineering design would employ suitable cavities and webs to reduce the material used and the consequent weight of the structure. Since such conventional design features are well known to those skilled in the art, and do not comprise an inventive portion of the present disclosure, they are omitted herefrom for simplicity.
Referring now to Fig. 6, telescoping shaft 22 includes a locking nook 117 at an end nearer handle 24 and a similar locking nook 119 near an inner end 121 thereof. A pair of transversely spaced-apart limit ramps 125 and 127 are disposed on telescoping shaft 22 a predetermined distance away from locking nook 119.
Referring now to Fig. 7, telescoping shaft 22 is shown locked in its fully retracted position. A latch cavity 118 in half 98 surrounds an opening 120. An aligned opening 122 in channel 56 permits latch button 54, which forms part of a latch assembly 123, to pass therethrough to an outside position where it is accessible to a user. A pivot 124 is connected to latch button 54 by an integral hinge 126. A locking dog 128 is connected rigidly to pivot 124 by a limit plate 132. Limit plate 132 contacts a surface of latch cavity 118 remote from pivot 124 to limit a maximum amount by which latch button 54 is permitted to protrude through openings 120 and 122. A double ramp limit lock 134, at an end of opening 120 remote from pivot 124, prevents withdrawing telescoping shaft 22 beyond a predetermined distance. Pivot 124 is supported near a surface of telescoping shaft 22 by a pair of fulcrums 135 (only the fulcrum 135 on the far side of latch assembly 123 is shown).
Locking dog 128 is urged through locking nook 117 by the resilient urging of integral hinge 126 to lock telescoping shaft 22 in its fully retracted position shown. In addition, bearing surface 140 is similarly urged into contact with the adjacent surface of telescoping shaft 22.
When latch button 54 is pressed inward, pivot 124, contacting the adjacent surface of telescoping shaft 22, rotates to permit outward motion of locking dog 128, whereby locking dog 128 is moved outward free of locking nook 117 against the resilient urging of integral hinge 126. In this condition, telescoping shaft 22 can be slid outward to an extended position.
Referring now to Fig. 8, telescoping shaft 22 is shown in an intermediate, unlocked, position. Locking dog 128 and double ramp limit lock 134 are urged into sliding contact with the adjacent surface of telescoping shaft 22 due to the support provided to pivots 124 by their respective fulcrums 135, and the resilience of integral hinge 126.
Referring to Figs. 6 and 9, double ramp limit lock 134 includes first and second transversely spaced ramp teeth 136 and 138, each having a bearing surface 140, a locking abutment surface 142 and a sloping ramp surface 144. A center-to-center spacing of ramp teeth 136 and 138 is substantially equal to a center-to-center spacing of limit ramps 125 and 127, and a transverse dimension of each ramp tooth is such that it will fit into its respective limit ramp.
Referring now to Fig. 10, limit ramps 125 and 127 (only limit ramp 127 is shown) are formed by bending inward a tab 146 into the interior of telescoping shaft 22. Tab 146 provides an angled ramp surface 148 disposed at an angle substantially equal to an angle of ramp surface 144. A longitudinal spacing between locking nook 119 and limit ramps 125 and 127 is such that locking dog 128 may enter, and lock into locking nook 119, before ramp teeth 136 and 138 reach their respective limit ramps 125 and 127. Full extension of telescoping shaft 22 is achieved with such locking. If a user presses latch button 54 and attempts to extend telescoping shaft 22 beyond its full extension, the condition shown in Fig. 10 is reached wherein ramp teeth 136 and 138 enter their respective limit ramps 125 and 127. Locking abutment surfaces 142 on ramp teeth 136 and 138 abut ends 150 of their respective limit ramps 125 and 127 whereby further extension is blocked.
Cooperation between angled ramp surfaces 148 and ramp surfaces 144, however, permit telescoping shaft 22 to be moved toward its retracted position. After a short travel in the retracting direction, locking dog 128 is urged into locking nook 119, whereby telescoping shaft 22 becomes locked in its normal full extension.
Referring now to Fig. 11, vacuum cleaner 10 includes a motor-driven blower 152 normally capable of receiving electric power from a battery 154 through an ON OFF switch 156. A normally closed interlock switch 158 is also connected in series with battery power to motor-driven blower 152. A connector 160 in vacuum cleaner 10 mates with a mating connector 162 in support assembly 62 to provide AC power to vacuum cleaner 10. The AC power is rectified by a diode 164 to provide pulsating DC for charging battery 154. A mechanical interlock, represented by a dashed line 166, between connector 160 and interlock switch 158 opens interlock switch 158 whenever vacuum cleaner 10 is installed on support assembly 62. This prevents motor-driven blower 152 from being operated in its charging and storage position on support assembly 62.
Having described preferred embodiments of the invention with reference to the accompanying drawings, it is to be understood that the invention is not limited to those precise embodiments, and that various changes and modifications may be effected therein by one skilled in the art without departing from the scope of the invention as defined in the appended claims.

Claims

1. A vacuum cleaner, characterized by:
a frame (34);
a power unit (12) mounted on the frame (34) for providing a suction;
a dust bowl (14) sealably connected to the power unit (12) for application of said suction inside said dust bowl (14);
means (16), communicating with said dust bowl (14), for applying said suction from said dust bowl to a surface to be vacuumed;
a handle shaft (22) telescopically connected to said frame (34); and
resilient means (106, 116), between said frame (34) and said handle shaft (22), for taking up any clearances therebetween.

2. The vacuum cleaner of Claim 1, characterized in that said resilient means (106, 116) comprises at least one resilient vibration snubber (106).

3. The vacuum cleaner of Claim 1, characterized in that said resilient means (106, 116) comprises first (106) and second (116) resilient means for taking up clearances in two different directions transverse to each other.

4. The vacuum cleaner of Claim 3, characterized in that said first and second means each comprise a resilient pad (106; 116).

5. The vacuum cleaner of Claim 4, characterized in that said handle shaft is of rectangular cross-section and said first means (106) engages one side of the rectangular cross-section and said second means (116) engages an adjacent side thereof.

6. The vacuum cleaner of Claim 5, characterized in that one (116) of the resilient pads is disposed in a pocket (114) in a side of said frame (34).

7. The vacuum cleaner of Claim 6, characterized in that the other (104) of the resilient pads is disposed through a slot (102, 104) through a wall of said frame (34) and is retained between said handle shaft and an attachment loop (94) extending from said frame (34), said power unit (12) being secured to said attachment loop (94).

8. The vacuum cleaner of any one of the preceding claims, characterized in that said resilient means (106, 116) comprises two resilient vibration snubbers (106, 108) engaged against a common side of said handle shaft (22) and spaced apart in a lengthwise direction of said handle shaft (22), one (106) of these two resilient snubbers (106, 108) being located adjacent an open end (88) of said frame (34), said handle shaft (22) being telescopically slidable inside said frame (34) and extending out through said open end (88).

9. The vacuum cleaner of any one of the preceding claims, characterized in that said handle shaft (22) has first and second nooks (119, 117) therein, and by a latch assembly (123) including a locking dog (128) fittable into either of said first and second locking nooks (119, 117) for locking said telescoping shaft (22) into respective first and second telescopic positions relative to said frame (34), at least one ramp tooth (140) of said latch assembly (123), at least one limit ramp (127) on said shaft (22), said at least one limit ramp (127) being disposed in a position related to said second locking nook (117) reachable by said at least one ramp tooth (140) when said telescoping shaft (22) is extended beyond its maximum extension, said at least one limit ramp (127) including first means (150) cooperating with said at least one ramp tooth (140) for preventing extension of said telescoping shaft (22) more than a predetermined amount beyond said maximum extension, and said at least one limit ramp (127) and said at least one ramp tooth (140) including second means (148, 144) for permitting extension of said shaft (22) to be reduced from said predetermined amount beyond said maximum extension to said maximum extension.

10. The vacuum cleaner of any one of the preceding claims, characterized in that said power unit (12) is located at a first end of said frame (34), a socket (26) is located at a second end of said frame (34), said applying means (16) comprises a swivelling floor tool (16) swivellably affixed to said socket (26), means (38) at a first end (28) of said dust bowl (14) for producing a first substantially air-tight seal with said socket (26), means (50) at a second end (30) of said dust bowl (14) for providing a second substantially air-tight seal with said power unit (12), and said socket (26) and said swivelling floor tool (16) including means (46, 68) for providing a substantially air-tight passage for air between said socket (26) and a vacuum port (84) in said swivelling floor tool (16).

11. A vacuum cleaner, characterized by:
a frame (34);
a power unit (12) at a first end of said frame (34);
a socket (26) at a second end of said frame (34);
a swivelling floor tool (16) swivellably affixed to said socket (26);
a substantially rigid dust bowl (14);
means (38) at a first end (28) of said dust bowl (14) for producing a first substantially air-tight seal with said socket (26);
means (50) at a second end (30) of said dust bowl (14) for providing a second substantially air-tight seal with said power unit (12); and
said socket (26) and said swivelling floor tool (16) including means (46, 68) for providing a substantially air-tight passage for air between said socket (26) and a vacuum port (84) in said swivelling floor tool (16), whereby a vacuum created in said power unit (12) can be communicated to a surface adjacent said vacuum port (84) when said surface is to be cleaned.

12. A latch for a telescoping shaft (22) in a vacuum cleaner (10), characterized by:
first and second locking nooks (119, 117) in said telescoping shaft (22);
a latch assembly (123);
said latch assembly including a locking dog (128) fittable into either of said first and second locking nooks (119, 117) for locking said telescoping shaft (22) into one of first and second positions;
at least one ramp tooth (140) on said latch assembly (123);
at least one limit ramp (127) in said shaft (22);
said at least one limit ramp (127) being disposed in a position related to said second locking nook (117) reachable by said at least one ramp tooth (140) when said telescoping shaft (22) is extended beyond its maximum extension;
said at least one limit ramp (127) including first means (150) cooperating with said at least one ramp tooth (140) for preventing extension of said telescoping shaft (22) more than a predetermined amount beyond said maximum extension; and
said at least one limit ramp (127) and said at least one ramp tooth (140) including second means (148, 144) for permitting extension of said shaft to be reduced from said predetermined amount beyond said maximum extension to said maximum extension.