GB2033534A

GB2033534A - Combined elastomeric spring and fluid damper

Info

Publication number: GB2033534A
Application number: GB7934851A
Authority: GB
Original assignee: Gould Inc
Current assignee: Gould Inc
Priority date: 1978-10-13
Filing date: 1979-10-08
Publication date: 1980-05-21
Also published as: DE2941118C2; DE2941118A1; FR2438769A1; AU524030B2; JPS5554740A; IT7950546A0; IT1120864B; JPS6321051B2; GB2033534B; BR7906549A; FR2438769B1; CA1127191A; AU5101679A

Abstract

A spring/damper comprises inner and outer members (12, 14) connected by an elastomeric shear spring (16) and having a main fluid chamber (26) defined therebetween which communicates with a second fluid chamber (36) in the inner member through a restricted orifice (40). There is an elastomeric bladder (42) within the second fluid chamber which is chargeable with gas. There may also be axially-spaced circumferential wear rings (60) on the bladder (42) to minimize bladder abrasion against the inner wall of the inner member (12). An elastomeric ring (64) attached to the inner member (12) within the main fluid chamber engages the outer member when the damper bottoms out and this seals the restricted orifice (40) against flow of fluid therethrough from the main fluid chamber (26) to the second fluid chamber (36). The restricted orifice (40) includes an elastomeric restrictor having a yieldable flap (130) covering a passage (112) for blocking flow therethrough in one direction while providing flow in a reverse direction. <IMAGE>

Description

SPECIFICATION Viscous spring damper Background of the invention The present invention relates generally to shock absorbers. More particularly, it relates to shock absorbers of the type which use both an elastomeric shear spring and flow of fluid through a restricted orifice for absorbing shock and dissipating energy.

Known shock absorbers of the type described include those disclosed in U.S. Pat. No. 2,818,249 issued December31, 1957 to Boschi, U.S. Pat. No.

3,658,314 issued April 25, 1972, to Luzsicza, and, British Pat. No. 1,148,515 issued April 16,1969 to Moulton. In the British patent, a force transmitting member deforms a diaphragm for transmitting force through a fluid to an elastomeric shear spring. The fluid flows through an orifice covered by yieldable flaps which provide one-way flow. The Luzsicza device has a piston separating a gas pressure chamber from a fluid chamber and a bumper is mounted on the bottom of the outer member for limiting telescoping movement of the inner and outer members. It is necessary to machine the cylinder for the piston in order to provide good sealing and smooth piston movement. Maintaining effective seals on the piston over long periods of time is very difficult.The Boschi device includes a bladder in an inner chamber but there is no way to selectively charge the bladder with variable gas pressure. The bladder would also wear rapidly if the cylinder in which it moves is not smooth.

Summary of the invention The present invention concerns the provision of an expandable and contractible elastomeric bladder for separating a gas chamber from a fluid chamber in a viscous spring damper, and for varying the spring rate of the damper, calibrating the damper or leveling a load supported thereby.

In another aspect, the invention concerns the provision of a viscous spring damper with first and second outer members connected with opposite end portions of an inner member by first and second elastomeric shear springs having different deformation characteristics.

In still another aspect, the present invention concerns the location of a bumper ring on an end wall of the inner member for sealing againstthe inner surface of an outer member to block further flow of fluid through an orifice from the main fluid chamberto a second fluid chamber.

Afurther aspect of the invention concerns the provision of a simplified and efficient elastomeric restrictor for providing non-linear flow through the orifice between the main fluid chamber and the second fluid chamber.

It is a principal object of the present invention to provide an improved viscous spring damper having improved operating characteristics.

It is another object of the invention to provide an improved viscous spring damper having an improved bladder construction for separating a gas chamber from a fluid chamber.

It is another object of the invention to provide an improved viscous spring damper having a plurality of different stages with different damping characteristics.

It is also an object of the invention to provide a viscous spring damper with an improved stop bumper.

It is an additional object of the invention to provide an improved restrictor valve for providing fluid flow between variable volume fluid chambers in avis- cous spring damper.

Brief description of the drawing Figure 1 is a cross-sectional elevational view of a viscous spring damper constructed in accordance with the present invention; Figure 2 is a cross-sectional elevational view of the damper of Figure 1 in a telescoped condition; Figure 3 is a graph showing how it is possible to vary the initial spring rate of the damper of Figure 1; Figure 4 is a graph showing the deflection characteristics of the damper of Figure 1; Figure 5 is a cross-sectional elevational view of another embodiment; Figure 6 is a cross-sectional elevational view of still another embodiment; Figure 7 is a cross-sectional elevational view of a restrictor valve taken generally on line 7-7 of Figure 1; Figure 8 is a cross-sectional elevational view similarto Figure 7 and showing slow flow through the restrictor valve;; Figure 9 is a view similar to Figure 8 and showing fast flow through the restrictor valve; Figure 10 is a cross-sectional elevational view of another embodiment of a restrictor valve; Figure 11 is a cross-sectional elevational view similar to Figure 10 and showing flow in one direction through the restrictor valve; and, Figure 12 is a cross-sectional elevational view similar to Figure 10 and showing flow through the restrictor valve in an opposite direction.

Description of the preferred embodiments of the invention Figure 1 shows a viscous spring damper including an inner member 12 connected with an outer member 14 by an elastomeric shear spring 16 which is bonded to the surfaces of the inner and outer members. Outer member 14 includes an outer tube 20 secured to a cap 22. A main fluid chamber 26 is defined between inner and outer members 12 and 14, and elastomeric shear spring 16. A plug 28 is positioned in an opening in cap 22 after a desirable quantity of fluid is introduced into main fluid chamber 26. References to a fluid in this application are meant to define a liquid, such as hydraulic fluid.

Inner member 12 includes an outwardly extending mounting flange 30 and an elongated cup-like portion including an end wall 32 having a peripheral wall 34 extending therefrom to enclose an elongated second fluid chamber 36. Orifice means generally indicated at 40 is provided for transferring fluid between fluid chambers 26 and 36.

An elongated expandable and contractible elas tomeric bladder 42 is positioned within second fluid chamber 36, and has a circumferential mounting flange 44 secured between a circumferential shoulder on the inner member 12 and a cap member 48 which is press fit or otherwise suitably secured to inner member 12. Cap member 48 has valve means in the form of an air check valve 50 mounted thereon for selectively charging bladder 42 with variable gas pressure. Bladder 42 is shaped to generally conform with the shape of second fluid chamber 36, and includes a bladder end wall 54 facing end wall 32, and a bladder peripheral wall 56 facing inner member peripheral wall 34.

Bladder 42 has a plurality of spaced wear means thereon for minimizing abrasion of the bladder. This makes it possible to omit machining of the interior of second fluid chamber 36. The wear means may take many different forms and, in one arrangement, comprises a plurality of axially-spaced outwardly projecting circumferential rings 60 integral with bladder periperal wall 56. Bladder end wall 54 may also be substantially thicker than the remainder of the bladder to provide abrasion resistance. When bladder 42 expands and contracts it rubs against the interior of inner member end wall 32 and peripheral wall 34, and wear means 60 minimizes any danger of rupturing the bladder.Rings 60 are sufficiently close together, and the bladder wall therebetween is sufficiently thick, to prevent the bladder from bulding outwardly between adjacent rings into contact with the surface of inner member peripheral wall 34.

Circumferential rings 60 also trap hydraulic fluid therebetween for maintaining lubricant along the peripheral wall of bladder 42 to further minimize abrasion thereof.

Bumper stop means in the form of an elastomeric ring 64 is attached to inner member end wall 32 within main fluid chamber 26. Ring 64 may be attached to end wall 32 in any suitable manner, including mold bonding, mechanical fasteners or a chemical adhesion.

The viscous spring damper may be used as a shock absorber on vehicles, or on machinery supports or the like. When used on vehicles, inner member 12 is connected with the vehicle body, while outer member 14 is connected to the vehicle axle.

Relative telescoping axial movement between inner and outer members 12, 14 stresses elastomeric shear spring 16, and varies the volumes of fluid chambers 26,36 while fluid is transferred therebetween through orifice means 40. This action absorbs shock and dissipates energy in a known manner.

Outer member 14 has an end wall 66 opposite inner member end wall 32. When the inner and outer members are substantially fully telescoped, bumper stop ring 64 engages the inner surface of outer member end wall 66 as shown in Figure 2. With ring 64 durrounding orifice means 40 in radially outwardly spaced relationship thereto, engagement of ring 64 with the inner surface of outer member 14 seals main fluid chamber 26 against further flow of fluid through orifice means 40 into second fluid chamber 36. This provides a hydraulic lock, and a significant amount of the load is supported on the hydraulic fluid trapped within main fluid chamber 26. This results in a very high final spring rate.

The initial spring rate of the viscous spring damper may be varied by varying the gas pressure within the bladder 42. The damping characteristics of the damper may also be calibrated by varying the gas pressure within bladder 42. In addition, a vehicle having the damper installed thereon may be leveled undervarying loads by varying the gas pressure within bladder 42.

Figure 3 shows a graph with a telescoping deflection between inner and outer members 12,14 plotted on the abscissa, and deflecting compressive load plotted on the ordinate. The initial spring rate of the device is represented by the steep straight line extending along A-B. This initial spring rate may be varied by varying the gas pressure within bladder 42.

For example, the dotted line showing of Figure 1 shows bladder 42 in a fully expanded condition so it is pressurized to a pressure greater than the pressure within main fluid chamber 26. As the damper is loaded, it is initially very stiff because fluid cannot be transferred from main fluid chamber 26 to second fluid chamber 36 through orifice means 40. When the load reaches point B, the bladder begins to contract as fluid is transferred to chamber 36 from chamber 26 and the damper will deflect along the curve B-C. The point at which the damper deflects along a smoother low slope curve B-C may be varied by varying the precharge gas pressure within blad der 42. Loading of the damper in extension by loads tending to axially separate members 12, 14 is represented by lines A-D.A hydraulic lock is formed and provides a high spring rate in extension limited only by the elastic quality of the elastomeric shear spring and by the vapor pressure of the fluid. This is a desirable characteristic for good cornering stability.

If the precharge gas pressure within bladder 42 is made substantially equal to the pressure in main fluid chamber 26, a much lower initial spring rate will result. In the manufacture of dampers of the type described, the deflection characteristics of elastomeric shear spring 16 will vary due to differences in the rubber or other material used. Therefore, it is possible to calibrate each damper by varying the gas pressure within bladder 42 to correspond with the deflection characteristics of the elastomeric shear spring in each particular dampen With bladder 42 fully expanded as shown in shadow lines in Figure 1, bladder end wall 54 seals orifice means 40 to prevent flow of fluid therethrough until pressure acting on bladder 42 is sufficient to slightly compress same.

Figure 4 is a graph showing the general deflection characteristics of the elastomeric shear spring, the hydraulic damper, and the combined deflection characteristics. Deflection is plotted on the abscissa, while load is plotted on the ordinate. Curve 70 shows that the hydraulic damper has a very low initial spring rate. Curve 72 shows that the elastomeric shear spring has a relatively high initial spring rate but then deflects very rapidly after an initial stiffness is overcome. The combined deflection curve indicated at 74 shows that it is possible to achieve a relatively high initial spring rate at 76 which merges into a relatively soft characteristic 78 in load range 80, and then a final high spring rate 82 achieved by pressurizing the bladder and sealing the orifice means against flow therethrough as described with reference to Figure 2.Varying the initial gas pressure within bladder 42 makes it possible to vary portion 76 of curve 74. When a vehicle is loaded, it is also possible to vary the gas pressure within bladder 42 in order to change the load range 80.

Figure 5 shows another embodiment wherein inner and outer members 12a, 14a are connected by an elastomeric shear spring 1 6a having bumper stop ring 64a formed integrally therewith. This eliminates an extra part along with the need to assemble same.

In other respects, the viscous spring damper of Figure 5 operates in the same manner as explained with reference to Figure 1. The other features and characteristics of the damper described in Figure 1 may also be included in the damper of Figure 5. Main fluid chamber 26a communicates with second fluid chamber 36a through orifice means 40a. Bladder 42a is secured within inner member 12a by a cap member 48a having gas valve 50a secured thereto.

Figure 6 shows another arrangement wherein inner member 1 2b has first and second outer members 90, 1 4b connected thereto by first and second elastomeric shear springs 92, 16b. First outer member 90 also defines the load transfer member for transferring the load to the damper. In this embodiment first elastomeric shear spring 92 has less stiffness than second shear spring 16b, although other shear spring combinations can be used. Bladder 42b is shown as being formed integral with first shear spring 92. However, it will be recognized that bladder 42b can be formed separately from first shear spring 92 and secured to the open end of inner member 12b by a cap member having a large central opening for providing free communication therethrough with the interior of the bladder.Gas valve 50b extends through first outer member 90 for communication with a gas chamber 94 which also communicates freely with the interior of bladder 42b. As the damper is loaded, first outer member 90 deflects downwardly in Figure 6 while first elastomeric shear spring 92 deforms. This action also increases the gas pressure within gas chamber 94 and bladder 42b. When first outer member 90 substantially bottoms out, the load is transferred through inner member 12b to second elastomeric shear spring 16b which then operates in the same manner as described with reference to Figure 1.

In the arrangement of Figure 6, the orifice means is shown as including a large central opening 102, and bladder 42b has an integral elongated restrictor projection 104 extending through the opening. Restrictor projection 104 varies in size along its length to vary the size of opening 102 in accordance with the expanded and contracted condition of bladder 42b.

In the arrangement shown, restrictor projection 104 is shown as increasing in size from bladder 42b to the free end of projection 104. Thus, as the damper is loaded and deflects, with resulting collapse of bladder 42b, the size of opening 102 decreases so that a higher spring rate will progressively result as deflection proceeds. Obviously, the size of projection 104 may be reversely varied if so desired. It will also be recognized that instead of having projection 104, the bladder of Figure 6 can be the same as the bladder in Figure 1. Fluid is transferred between main and second fluid chambers 26b, 36b as the volume thereof varies during deflection of the damper. It is also possible to provide the damper of Figure 6 without using a bladder.Instead of using a conventional hydraulic fluid, a gel-like liquid which does not trap or form the gas could be substituted.

Figures 7-9 show a valving arrangement for the orifice connecting the two fluid chambers. A plurality of first flow passages are defined by a plurality of circumferentially-spaced holes 112 arranged in a circular pattern through end wall 32 outwardly of a central restrictor mounting hole 114. An elastomeric restrictor includes a central stem 116 tightly received through mounting hole 114. A hollow rivet including a hollow stem 118 and a flange 120 at one end extends centrally through restrictor stem 116 and has a retaining washer 122 secured to its other end.

Washer 122 is secured to rivet stem 118 with restrictor stem 118 under compression to provide an enlargement 124. The other end of restrictor stem 116 has an enlargement in the form of a yieldable circular flap 130 covering holes 112 and being yieldable away from end wall 32 to provide nonlinear flow from the main fluid chamber to the second fluid chamber as shown in Figures 8 and 9.

Figure 8 shows elastomeric flap 130 deflected upwardly to provide slow upward flow, while Figure 9 shows flap 130 deflected further upwardly to provide fast flow. Return flow takes place through the return passage defined by hollow rivet stem 118. This provides linearflowfrom the second fluid chamber back to the main fluid chamber. Instead of using a hollow rivet for securing the elastomeric restrictor in place, it will be recognized that it is possible to provide an integral central return hole through the elastomeric restrictor and to provide an enlarged snap head on the stem for snapping through mounting hole 114.

Figures 10-12 show another arrangement wherein a plurality of first flow holes 140 are arranged in a circular pattern outwardly of restrictor mounting hole 142. A plurality of second flow holes 144 are arranged in a circular pattern outwardly of first flow holes 140. An elastomeric restrictor has a small circular yieldable flap 146 covering first flow holes 140 and a large circular yieldable flap 148 covering second flow holes 144. The restrictor is made in two pieces, with each piece having a flap 146, 148 thereon and a portion of a stem received in mounting hole 142 to define a restrictor mounting stem 150. A rivet 152 which may or may not be hollow is provided for securing the elastomeric restrictor in place. Large flap 148 has a plurality of holes 154 therethrough aligned with first flow holes 140 to provide flow through large flap 148 to first flow hole 140. Large flap 148 blocks flow in one direction through second flow holes 144 while allowing flow therethrough in a reverse direction as shown in Figure 12. Small flap 146 blocks flow through first flow holes 140 in the reverse direction while providing flowtherethrough in the one direction as shown in Figure 11. Flow through first flow holes 140 in the one direction takes place by having the fluid flow through holes 154 in large flap 148.

Although additional flow openings and a flap valve are shown in Figure 6, it will be recognized that it is possible to omit such openings and the flap valve and to use only the projection 104 and hole 102. For features of the invention useable independently of the specific stop bumper, such bumper can be located between a vehicle body and axle or in other locations.

While there have been described what are at present considered to be the preferred embodiments of this invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is, therefore, aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

Claims

1. Aviscousspring damper including inner and outer members connected by an elastomeric shear spring such as to provide a main fluid chamber between said members, said chamber communicating with a second chamber in said inner member through restricted orifice means, said members being relatively movable for stressing said shear spring and varying the volumes of said chambers while effecting fluid flow therebetween through said orifice means, an expandable and contractible gas chargeable elastomeric bladder in said second chamber, and valve means for charging said bladder with gas to a selected pressure.

2. The viscous spring damper of claim 1 wherein said bladder is engageable with the wail of said second chamber and includes a plurality of spaced integral wear means extending outwardly therefrom for protecting said bladder against abrasion.

3. The viscous spring damper of claim 1 wherein said inner member has an end wall through which said orifice means extends and includes an elongated peripheral wall extending from said end wall in a direction away from said main chamber, said second chamber being defined within said end wall and peripheral wall, and said bladder being constructed to generally conform to the shape of said second chamber by having a bladder end wall facing said inner member end wall and a bladder peripheral wall facing said inner member peripheral wall.

4. The viscous spring damper of claim 3 including a plurality of spaced outwardly extending integral wear means on said bladder for preventing abrasion thereof.

5. The viscous spring damper of claim 4 wherein said wear means comprises a plurality of axiallyspaced circumferential rings extending outwardly from said bladder peripheral wall.

6. The viscous spring damper of claim 1 wherein said inner member has an end wall separating said chambers and said orifice means is in said end wall, and said bladder being movable into engagement with said end wall for closing said orifice means.

7. The viscous spring damper of claim 1 wherein said inner and outer members have end walls facing one another in spaced relationship, bumper stop means extending from said end wall on said inner member toward said end wall on said outer member for engaging said end wall on said outer member to limit telescoping movement of said members.

8. The viscous spring damper of claim 7 wherein said orifice means is in said end wall of said inner member and said bumper stop means comprises a bumper ring surrounding said orifice means, en gagement of said bumper ring with said end wall of said outer member preventing flow of fluid from said main chamber to said second chamber through said orifice means.

9. The viscous spring damper of claim 7 wherein said bumper stop means is integral with said elastomeric shear spring.

10. The viscous spring damper of claim 1 where in said inner member has opposite end portions and one of said end portions is connected with said outer member by said elastomeric shear spring which defines a second stage shear spring, and a load transmitting member connected with the other of said end portions by a first stage elastomeric shear spring.

11. The viscous spring damper of claim 10 wherein said bladder is integral with said first stage elastomeric shear spring.

12. The viscous spring damperofclaim 10 wherein said load transmitting member includes a variable volume third chamber communicating with the interior of said bladder.

13. The viscous spring damper of claim 1 wherein said orifice means includes an enlarged central orifice and further including an elongated restrictor projection on said bladder extending through said central orifice, said projection varying in crosssectional size along its length for varying the size of said central orifice in accordance with the expanded and collapsed condition of said bladder.

14. The viscous spring damper of claim 1 wherein said restricted orifice means includes passages in said inner memberfor establishing communication between said chambers, an elastomeric restrictor attached to said inner member and having a yieldable flap in one of said chambers covering said passages, said flap blocking fluid flow through said passages from said one chamber to the other chamber and being yieldably displaceable away from said inner member for providing flow through said passages from said other chamber to said one chamber, and additional passage means for providing fluid flow from said one chamber to said other chamber.

15. The viscous spring damper of claim 1 wherein said restricted orifice means includes at least one passage through said inner member for establishing communication between said chambers, an elastomeric restrictor attached to said inner member and having a yieldable flap in said second chamber covering said passage for blocking fluid flow through said passage from said second chamber to said main chamber while providing reverse flow by deflecting away from said passage, and an additional passage for providing flow from said second chamber to said main chamber.

16. The viscous spring damper of claim 15 wherein said additional passage is through said elastomeric restrictor.

17. The viscous spring damper of claim 1 wherein said restricted orifice means includes a plurality of passages through said inner member for establishing communication between said chambers, an elastomeric restrictor attached to said inner member and having afirstyieldableflap in said main chamber for blocking flow from said main chamber to said second chamber through certain of said passages while providing reverse flow and a second yieldable flap in said second chamber for blocking flow from said second chamber to said main chamber through the remainder of said passages while providing reverse flow.

18. A viscous spring damper comprising: an inner member having opposite end portions connected with first and second outer members by first and second elastomeric shear springs, a main fluid chamber between said inner member and said second outer member, a second fluid chamber in said inner member, and restricted orifice means for establishing communication between said chambers.

19. The viscous spring damperofclaim 18 including an expandable and contractible elastomeric bladder in said second chamber, and valve means for selectively charging said bladder with gas pressure.

20. The viscous spring damperofclaim 19 wherein said bladder is integral with said first elastomeric shear spring.

21. The viscous spring damper of claim 18 wherein said first elastomeric shear spring has a lower spring rate than said second elastomeric shear spring.

22. The viscous spring damper of claim 21 including an expandable and contractible elastomeric bladder in said second chamber, valve means for selectively charging said bladder with gas pressure, and a variable volume gas chamber between said first and inner members communicating with the interior of said bladder, said gas chamber varying in volume during relative movement between said first and inner members for varying the gas pressure in said bladder.

23. In a viscous spring damper including inner and outer members connected by an elastomeric shear spring and having a main fluid chamber therebetween communicating with a second chamber in said inner member through restricted orifice means, said members being relatively movable for stressing said shear spring and varying the volumes of said chambers while effecting fluid flowtherebe- tween through said orifice means, elastomeric bumper means in said main chamber engageable between said members for limiting relative telescoping movement thereof, the improvement comprising: said bumper means being attached to said inner member and being in the form of a ring surrounding said orifice means in outwardly spaced relationship thereto, said ring being engageable with said outer member to close said orifice means against communication with said main chamber.

24. The viscous spring damper of claim 23 wherein said bumper means is integral with said elastomeric shear spring.

25. A viscous spring damper comprising: inner and outer members connected by an elastomeric shear spring and having a main fluid chamber therebetween communicable with a second fluid chamber in said inner member through restricted orifice means, said members being relatively movable for stressing said shear spring and varying the volumes of said chambers while transferring fluid therebetween through said orifice means, said inner member having an end wall with said orifice means therein, said orifice means including a plurality of flow holes in said end wall positioned in spacedapart relationship in a generally circular pattern around a central restrictor mounting hole, an elastomeric restrictor having a central stem tightly received through said mounting hole, enlargements on said stem on opposite sides of said end wall for retaining said stem in said mounting hole, one of said enlargements comprising a yieldable circular flap covering said flow holes for blocking flow therethrough in one direction while providing non linearflowtherethrough in a reverse direction, and a central hole through said stem and enlargements for providing substantially linearflowtherethrough in said one direction.

26. viscous spring damper comprising: inner and outer members connected by an elastomeric shear spring and having a main fluid chamber therebetween communicable with a second fluid chamber in said inner member through restricted orifice means, said members being relatively movable for stressing said shear spring and varying the volumes of said chambers while transferring fluid therebetween through said orifice means, said inner member having an end wall with said orifice means therein, said orifice means including a plurality of first flow holes in said end wall positioned in spaced-apart relationship in a generally circular pattern around a central restrictor mounting hole, a plurality of second flow holes in said end wall positioned in spaced-apart relationship in a generally circular pattern outwardly of said first flow holes, an elastomeric restrictor having a central stem tightly received through said mounting hole, said restrictor having a large yieldable flap on one side of said end wall covering said second flow holes for blocking flowtherethrough in one direction while providing flow in a reverse direction, said restrictor having a smaller yieldable flap on the opposite side of said end wall covering said first flow holes for blocking flowtherethrough in said reverse direction while providing flowtherethrough in said one direction, and passages through said large flap for providing flow therethrough in said one direction to said first flow holes.

27. The viscous spring damper of claim 26 wherein said restrictor is formed in two pieces each having one of said flaps thereon and a portion of said stem.

28. Aviscousspring damper substantially as hereinbefore described with reference to the accompanying drawings.