Dual Camshaft Phase Control Assembly

Abstract

The present disclosure employs a pair of camshafts for intake valves. A first phase controller is installed at a first end of the first intake camshaft connecting to the crankshaft. A second phase controller is installed at a second end of the first intake camshaft connecting to the second intake camshaft. Each phase controller can adjust phase angle accordingly to modify intake valve timing and intake valve lift. This set up is duplicated for the exhaust valves to modulate exhaust valve timing and exhaust valve lift. First and second camshafts are connected via a series of levers, which merges the rotations of both camshafts into one. The phase controllers can be differential gear sets, epicyclical gear sets, or a combination thereof.

Claims

1. A dual camshaft phase control assembly comprising: a first phase controller connecting a crankshaft and a first end of a first camshaft, wherein the first phase controller comprises a first gear system to modulate phase relations between the crankshaft and the first camshaft; a second phase controller connecting a second end of the first camshaft and a second end of a second camshaft, wherein the second phase controller comprises a second gear system to modulate phase relations between the first and second camshafts; and means to combine rotational output of the first and the second camshafts.

2. The dual camshaft phase control assembly of claim 1, wherein the first gear system further comprises a first set of differential bevel gears with: a pair of input and output gears to receive and to transmit torque from the crankshaft which in turn drive the first camshaft; a pair of control and spider gears in meshed relations with the input and output gears; and an actuator, driven by a first control module in communication with a vehicle's central computing system, to rotate the control gear to modulate phase relations between the crankshaft and the first camshaft.

3. The first gear system of claim 2, wherein the input gears, the output gears, the actuator, and the first control module are arranged in a serial fashion sharing a common rotational axis with the first camshaft.

4. The first gear system of claim 2, wherein the first control module drives the output gear via a spur gear.

5. The dual camshaft phase control assembly of claim 1, wherein the second gear system further comprises a second set of differential bevel gears with: a pair of input and output gears to receive and to transmit torque from the first camshaft which in turn drive the second camshaft; a pair of control and spider gears in meshed relations with the input and output gears; and an actuator, driven by a second control module in communication with the vehicle's central computing system, to rotate the control gear to modulate phase relations between the first and second camshafts.

6. The second gear system of claim 5, wherein the input gears, the output gears, the actuator, and the second control module are arranged in a serial fashion sharing a common rotational axis with the second camshaft.

7. The second gear system of claim 5, wherein the second control module drives the output gear via a spur gear.

8. The dual camshaft phase control assembly of claim 1, wherein the first gear system further comprises a first set of epicyclical gears with: a sun gear, in gear mesh with a plurality of planet gears, to receive and to transmit torque from the crankshaft which in turn drives the first camshaft; a ring gear to encapsulate the planet gears via gear mesh; and a spur gear to drive the ring gear to modulate phase relations between the crankshaft and the first camshaft as instructed by a first control module, which is in communication with a vehicle's central computing system.

9. The first gear system of claim 8, wherein the sun gear shares a common rotational axis with the first camshaft.

10. The dual camshaft phase control assembly of claim 1, wherein the second gear system further comprises a second set of epicyclical gears with: a sun gear, surrounded by a plurality of planet gears via gear mesh, to receive and to transmit torque from the first camshaft which in turn drive the second camshaft; a ring gear to encapsulate the planet gears via gear mesh; and a spur gear to drive the ring gear to modulate phase relations between the first and the second camshafts as instructed by a second control module, which is in communication with a vehicle's central computing system.

11. The second gear system of claim 10, wherein the sun gear shares a common rotational axis with the second camshaft.

12. The dual camshaft phase control assembly of claim 1, wherein the crankshaft and the first camshaft are connected via a belt.

13. The dual camshaft phase control assembly of claim 1, wherein the means to combine rotational output of the first and the second camshafts further comprises: a plurality of levers each with a first section configured to be in contact with a first camshaft lobe, a second section in connection with the first section and configured to be in contact with a second camshaft lobe; and a cam prominent which drives an engine valve.

14. The means to combine rotational output of the first and the second camshafts of claim 1 further employs a plurality of levers, arranged at a pre-determined interval apart from one another, operating in conjunction with the first and the second camshafts lobes to drive a plurality of engine valves via corresponding cam prominents.

15. The dual camshaft phase control assembly of claim 1, wherein the first and the second camshafts are substantially parallel lengthwise.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The present disclosure, in accordance with one or more various embodiments, is described in detail with reference to the following figures. The drawings are provided for purposes of illustration only and to merely depict typical or exemplary embodiments of the invention. These drawings are provided to facilitate the reader's understanding of the invention and shall not be considered limiting of the breadth, scope, or applicability of the invention. It should be noted that for clarity and ease of illustration these drawings are not necessarily made to scale.

[0025] Some of the figures included herein illustrate various embodiments of the invention from different viewing angles. Although the accompanying descriptive text may refer to such views as top, bottom or side views, such references are merely descriptive and do not imply or require that the invention be implemented or used in a particular spatial orientation unless explicitly stated otherwise.

[0026] FIG. 1 is a schematic drawing of an internal combustion engine with sets of phase control mechanism to continuously modify variable valve timing, as well as variable valve lift for both intake and exhaust valves, according to some embodiments of the present disclosure.

[0027] FIG. 2 is a schematic drawing of using 4 differential gear sets as phase control mechanisms, according to some embodiments of the present disclosure. This figure also illustrates one of possible installations among crankshaft, camshafts, cylinders, phase control gear sets, actuators, and control center.

[0028] FIG. 3 is an enlarged view of an area near 32 of FIG. 2, illustrating a differential gear set connecting Camshaft 41 and 42 on a second end.

[0029] FIG. 4 illustrates a top and a side view of Camshaft 41 and 42 with differential gear sets installed on both ends

[0030] FIG. 5 illustrates a perpendicular sectional view of dual camshafts, profiles of cam lob orientations, a lever, and their relation to the valve attached.

[0031] FIG. 6 illustrates a perpendicular sectional view of dual camshafts in a different arrangement with a different type of lever.

[0032] FIG. 7 is a diagram illustrating the relation between crank angle (in degrees) and valve lift (in millimeter)

[0033] FIG. 8 illustrates cam lobe profiles (controlling valve lift) in degrees of phase shift with crank angles as used in FIG. 7

[0034] FIG. 9 is a schematic of a possible installation arrangement among a sprocket (driven by crankshaft), a differential gear set for phase shift, and phase shift control box, according to some embodiments of the present disclosure.

[0035] FIG. 10 is a schematic of another possible installation arrangement of a differential gear set and its phase shift control box.

[0036] FIG. 11 offers an explosive view of FIG. 10 with main parts disassembled for illustration purpose

[0037] FIG. 12 is a schematic drawing of using 2 epicyclical gear sets as phase control mechanisms, according to some embodiments of the present disclosure.

[0038] FIG. 13 offers an explosive view of an epicyclical gear set from FIG. 12 with main parts disassembled for illustration purpose

[0039] FIG. 14 is a schematic of a dual cam system with an epicyclical gear set installed on one end, and a differential gear set installed on the other end.

[0040] FIG. 15 illustrates a side view of an epicyclical gear set with its control box. Rotational relations among various parts of the gear set is marked for demonstrating mechanisms of introducing phase shift

[0041] FIG. 16 illustrates an exemplary combined camshaft lobe profiles as it drives a lever.

[0042] FIG. 17 illustrates a perpendicular sectional view of dual camshafts' profiles of a sequence of cam lob orientations when the phase angle between first and second camshafts remains at zero.

[0043] FIG. 18 illustrates a perpendicular sectional view of dual camshafts' profiles of a sequence of cam lob orientations when the phase angle between first and second camshafts is adjusted to a none-zero value.

[0044] FIG. 19 is a chart to compare the present disclosure with prior art.

[0045] The figures are not intended to be exhaustive or to limit the invention to the precise form disclosed. It should be understood that the invention can be practiced with modification and alteration, and that the invention be limited only by the claims and the equivalents thereof.

DETAILED DESCRIPTION OF THE OF THE INVENTION

[0046] From time-to-time, the present disclosure is described herein in terms of example environments. Description in terms of these environments is provided to allow the various features and of the invention to be portrayed in the context of an exemplary application. After reading this description, it will become apparent to one of ordinary skill in the art how the invention can be implemented in different and alternative environments.

[0047] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as is commonly understood by one of ordinary skill in the art to which this invention belongs. All patents, applications, published applications and other publications referred to herein are incorporated by reference in their entirety. If a definition set forth in this section is contrary to or otherwise inconsistent with a definition set forth in applications, published applications and other publications that are herein incorporated by reference, the definition set forth in this document prevails over the definition that is incorporated herein by reference.

[0048] The present disclosure, in some embodiments thereof, relates to a variable valve timing mechanism for an internal combustion engine. More specifically, it comprises at least one set of phase control assembly adapted to operate with dual camshafts. The phase control assemblies can independently and continuously modify both intake and exhaust valve timing and valve lift, optimized for various running conditions of the engine.

[0049] Referring to FIGS. 14, the present disclosure employs two camshafts, 41 & 42 (FIG. 2), arranged in parallel to each other to control intake valves. A separate pair of camshafts, 43 & 44, in similar configurations is designated to control exhaust valves. A phase control assembly refers to a pair of gear sets installed on both ends of a pair of camshafts. For instance, in FIG. 1, an epicyclical gear set 91 and a differential gear set 22 are installed on both ends of a pair of camshafts 41 and 42 to control intake valves, and to modify their phase relations according to engine needs. Another pair of phase control assembly, comprising gear sets 93 and 24, modifies phase relations of camshafts 43 and 44, which control exhaust valves.

[0050] FIG. 2 illustrates another exemplary embodiment with engine casing removed for a better view of the assemblies. Differential gear sets 21 and 22 are installed on both ends of camshafts 41 and 42, which controls intake valves. Another set of differential gears 23 and 24 are installed on both ends of camshafts 43 and 44, which controls exhaust valves.

[0051] Camshafts 41 and 43 can be driven directly by crankshaft 51 via a chain or a belt in meshed relations with gears connecting gear sets 21 and 23. Camshafts 42 and 44 can be driven indirectly by crankshaft 51 via ring gears, in meshed relations with camshafts 41 and 43, and also connecting gear sets 22 and 24.

[0052] Camshafts Sensor 01 measures crankshaft angle. Sensors 02 and 03 measure intake camshafts' angle (41 and 42) respectively. Sensors 04 and 05 measure exhaust camshaft's angle respectively (43 and 44). All sensor measurements are taken in real time, and their output signals are constantly transmitted to an automobile's main computer.

[0053] Each differential gear set comprises a control shaft installed coaxially at the end of a camshaft, and can be independently adjusted via an actuator to change its phase (or angular) relations with the camshaft. Actuator 31 rotates control shaft 11 of differential gear set 21 to advance or to retard phase relations between crankshaft and first intake camshaft 41. Actuator 32 rotates control shaft 12 of differential gear set 22 to advance or to retard phase relations between first intake camshaft 41 and second intake camshaft 42. Actuator 33 rotates control shaft 13 of differential gear set 23 to advance or to retard phase relations between crankshaft and first exhaust camshaft 43. Actuator 34 rotates control shaft 14 of differential gear set 24 to advance or to retard phase relations between first exhaust camshaft 43 and second exhaust camshaft 44.

[0054] FIG. 3 illustrates an enlarged perspective view of differential phase control gear set 22, which connects intake camshafts 41 and 42, as in one of possible embodiments of the present disclosure. The main components of this differential gear sets are: first bevel gear 64, second bevel gear 65, spider gear 66, control gear 67, and ring gear 62 attached to a housing 63. Rotation propagating from first intake camshaft 41 drives end gear 61, which in turn drives ring gear 62, which further in turn drives second intake camshaft 42. Since housing 63 is welded onto ring gear 62, they both rotate around axis 120. Within housing 63, first and second bevel gears 64 and 65 are in gearmesh with spider gear 66 and control gear 67. First and second bevel gears 64 and 65 thus rotate around their axis 110, which allow the housing to rotate round axis 120 while in gearmesh with spider gear 66 and control gear 67 at the same time.

[0055] Note that gears 66, 67, 64, and 65 do not need to be identical, so long as the differential and phase change functionalities are preserved. Parameters, such as sizes and scale, are not drawn in proportion, and can take different values based on an engine's particular needs. Figures are for exemplary illustration purpose only. Variations are acceptable for different gear mesh angle, ratio, whether to use straight bevel teeth or spiral bevel teeth etc.

[0056] When phase shift is needed either in the advance or in the retard direction between first and second intake camshafts 41 and 42, actuator 32 rotates control shaft 12, which rotates control gear 67 around axis 120 several degrees forward or backward. This additional rotation, whether forward (in addition) or backward (in subtraction), propagates through meshed gears 64, 65, 66, housing 63, and ring gear 62, which drives second intake camshaft 42. The actual amount of phase shift and phase shift timing is controlled by the automobile's main computer system, taken into account various parameters such as engine speed, load, camshaft sensors (02 and 03) readings etc.

[0057] A top and a side view of the dual camshafts with phase control assembly installed are illustrated in FIG. 4, according to one of the embodiments of the present disclosure. In the top view, a phase control differential gear set 21, aimed to modify phase relations between crankshaft and first intake camshaft, further comprises a spur gear 321 in mesh with ring gear 322. A local control module 331, such as an electric motor, drives the actuator 31 to change phase accordingly. A local control module 332 can also be installed in a serial fashion to directly drive actuator 32 without additional spur gears. This exemplary arrangement illustrates that actuators 31 and 32 can be modified to drive different gears of a gear set, so long as the phase change capabilities are comparable. Dimensions and constrains of an engine compartment may very well determine the physical location of a control module and how it is connected to drive the gear sets to modify phase relations.

[0058] FIGS. 5 and 6 illustrates perpendicular sectional views of dual camshafts 41 and 42, and the connections thereof, according to some embodiments of the present disclosure. Axis 511 is defined by connecting the center of camshaft 41 and the tip of its camshaft lobe. Axis 513 is defined by connecting the center of camshaft 42 and the tip of its camshaft lobe respectively. Reference line 512 is drawn to be parallel to Axis 511, thus defines a phase angle 501 between first intake camshaft 41 and second intake camshaft 42. This phase angle can be actively adjusted in either direction by rotating control shaft 12 to modify control gear 67 via differential gear set 22 (FIGS. 2 and 3) installed at a second end of the first and second intake camshafts 41 and 42.

[0059] As both camshafts lobes rotate, it pushes against lever 553, and translate the motion through cam prominent 554 to push onto spring 551, which in turn, lead to the opening and closing of valve 552. FIG. 6 illustrates a different exemplary type of lever 653, where first intake camshaft 641 and second intake camshaft 642 are arranged near ends of lever 653 on opposing sides. Phase angle 601 is defined by axis 613 and reference line 612, which is parallel to axis 611. Rotations of both camshaft lobes push against lever 653, and translate the motion through cam prominent 654 and spring 651 to open and to close valve 652. Levers such as 553 and 653 can be manufactured into different shapes with different profiles, so long as their functionalities are preserved, which is to combine and merge the rotational output of both first and second camshafts.

[0060] First camshaft and second camshaft are connected via a series of levers 553 (FIG. 11), which merges the rotations of both camshafts into one. When camshaft lobes, from both camshafts, are set at an angle (phase angle), the envelope of the combined rotational path drives the levers accordingly. An exemplary camshafts lobes profile combination is illustrated in FIG. 16 as they drive the lever together. The phase angle between the two camshafts are set at 40 degrees, as the combined camshaft lobes rotate from 35 to 70 degrees with respect to a common reference line, it pushes the lever 26.17 mm and 35.85 mm downwards respectively.

[0061] FIGS. 17-18 illustrate several perpendicular sectional views of dual camshafts, profiles of sequences of cam lob orientations when the phase angles between first and second camshafts are set at various zero or none-zero values. In FIG. 17, phase angle between the first and the second camshafts are set at zero degree. First camshaft is driven directly by the crankshaft. An example can be shown in FIG. 3, where rotation of first camshaft 41 (driven by crankshaft) propagates via gears 61, 62, and further onto second camshaft 42. Parameters, such as sizes and scale, are not drawn in proportion, and can take different values based on an engine's particular needs.

[0062] As the crankshaft drives the first camshaft +20 or 20 degrees in FIG. 17, the phase relations between the first and second camshafts remain constant (set at zero). Therefore, an axis passing through the center of the first camshaft and the tip of its cam lobe is parallel to an axis passing through the center of the second camshaft and the tip of its corresponding cam lobe. A mathematical representation of a full rotational cycle is illustrated immediately below, and corresponds to the physical example of the camshafts set at 0, +20, and 20 degrees.

[0063] FIG. 18 illustrates two examples where the first and second camshafts are set at 20 and 40 degrees. In other words, an axis passing through the center of the first camshaft and the tip of its cam lobe is at a 20 and a 40 degrees angle with an axis passing through the center of the second camshaft and the tip of its corresponding cam lobe. This is achieved by adjusting actuator 32 as illustrated in FIG. 3 and described in the previous section. A mathematical representation of a full rotational cycle is illustrated immediately below, and corresponds to the physical example of the camshafts set at 0, 20 and 40 degrees. The condition where the angle is set at 0 is carried over from FIG. 17 for reference purpose. If the angles between the first and second camshafts were set at 20 and 40 degrees, the curves will be mirror images of those illustrated in FIG. 18, with respect to the 0 degree curve.

[0064] In FIG. 2, differential gear set 21 is installed between the crankshaft and the first intake camshaft 41 at a first end. A phase change based on the adjustment of control shaft 11 modifies the timing of opening and closing of the intake valve. Differential gear set 22 is installed between the first intake camshaft 41 and the second intake camshaft 42 at an opposing end. A phase change adjustment of control shaft 12 modifies the duration of opening of the intake valve, i.e. how long or short the intake valve stays open. These two gear sets can be adjusted independently of each other. The present disclosure thus provides a mechanism to separately modify intake valve timing and intake valve lift duration.

[0065] In an example illustrated in FIG. 7, crankshaft completes two full rotation cycles, and both first and second intake camshafts complete one full rotation cycle. Crankshaft and first intake camshaft maintain a constant phase relations, while phase angle is modified only between first and second intake camshafts. In other words, intake valve timing remains constant, while intake valve lift duration changes. X-axis represents crank angle (maintained constant with respect to first intake camshaft), and Y-axis represents valve lift (in mm). Different symbols represent degrees of phase shift induced by adjusting control shaft 12 of gear set 22 (FIG. 2). FIG. 8 illustrates corresponding camshaft lobe profiles in terms of phase shift. FIG. 7 demonstrates that higher degrees of phase shift between first and second intake camshafts correspond to longer intake valve duration, i.e., the intake valve stays at maximum lift (fully opened position in mm) longer. FIG. 7 illustrates phase shifts in one direction only. The whole curve will shift to the right, if the phase shifts were desired in the opposition direction. It should be noted that parameters used in the graph are examples for demonstrative purpose only. Different engines or different performance levels can choose different parameter ranges accordingly.

[0066] FIGS. 9-11 illustrate several alternative embodiments of the present disclosure. The phase control assembly comprises at least two phase control gear sets installed on both ends of a pair of camshafts that controls valve timing and its lift duration. Previous embodiments have used intake valves as examples. It should be noted that the same is true for exhaust valves as well.

[0067] FIG. 9 and FIG. 10 illustrates a close up of FIG. 2 with four camshafts 41, 42, 43 (under engine cover), and 44. Camshafts 41 and 42 are designated to modify intake valve timing and intake valve lift duration. Camshafts 43 and 44 are designated to modify exhaust valve timing and exhaust valve lift duration. In FIG. 9, local control modules 931 and 933 are installed on sides of the engine, and are in gear mesh relations with spur gears 941 and 943, which in turn change phase angle between the crankshaft and camshafts 41 and 43 to modulate first intake and first exhaust valve timing. Alternatively, the crankshaft can directly drive both differential gear sets via a belt or chain, as in FIG. 2. In FIG. 10, local control modules 951, 952, 953 and 954 are installed in a serial manner and each drives its corresponding actuators directly to modify phase angels. FIG. 11 illustrates an exemplary explosive view of various parts of the camshaft control module assembly with axis of rotations arranged in one of many possible embodiments.

[0068] FIGS. 12-15 illustrate an alternative embodiment where an epicyclical gear set, instead of a differential gear set, is employed to achieve phase control. Epicyclical gear set 91 and 93 are installed between the crankshaft and the first intake camshaft 41 and first exhaust camshaft 43. Gear 991 and 993 are in mesh relations with the crankshaft with a chain or a belt. An exemplary epicyclical gear set, as illustrated in FIG. 13, comprises a sun gear 971 in the center, surrounded by a plurality of planet gears 961 via gear mesh, and a ring gear 962 further encloses all the planet gears via gear mesh. Rotation of the sun gear 971 is directly driven by the crankshaft and propagates to the first intake camshaft 41. When no phase shift is needed, crankshaft angle remains in a constant relation with the camshaft. Phase shift is introduced by rotating the ring gear 962 in either direction, which in turns rotates the planet gears 961 via gear mesh (around their own axis), and thus further drive the sun gear and camshaft 41. A local control module, in some exemplary embodiment, employs a spur gear 941 to introduce phase shift (in either advance or in retard direction) by driving the ring gear 962 via gear mesh. A side view of the epicyclical gear set in FIG. 15 illustrates the rotational relations among the sun, the planet, and the ring gears.

[0069] It should be noted that the effects of phase shift, whether introduced via a differential gear set or via an epicyclical gear set is effectively equivalent. FIG. 14 illustrates an exemplary arrangement where an epicyclical gear set 91 is installed at a first end of an intake camshaft 41, and a differential gear set 22 is installed at a second end of the intake camshafts 41 and second camshaft 42. Depending on feasibility or configuration of an engine compartment, any combination thereof should achieve comparable results as described in the present disclosure. Differential gear set and/or epicyclical gear set are well documented in prior art. Numerous variations of the gear set itself are acceptable so long as its functionalities are preserved for the purpose of the present disclosure.

[0070] While various embodiments of the present disclosure have been described above, it should be understood that they have been presented by way of example only, and not of limitation. Likewise, the various diagrams may depict an example architectural or other configuration for the invention, which is done to aid in understanding the features and functionality that can be included in the invention. The invention is not restricted to the illustrated example architectures or configurations, but the desired features can be implemented using a variety of alternative architectures and configurations. Indeed, it will be apparent to one of skill in the art how alternative functional, logical or physical partitioning and configurations can be implemented to achieve the desired features of the present disclosure. Also, a multitude of different constituent module names other than those depicted herein can be applied to the various partitions.

[0071] Although the invention is described above in terms of various exemplary embodiments and implementations, it should be understood that the various features, aspects and functionality described in one or more of the individual embodiments are not limited in their applicability to the particular embodiments with which they are described, but instead can be applied, alone or in various combinations, to one or more of the other embodiments of the invention, whether or not such embodiments are described and whether or not such features are presented as being a part of a described embodiment. Thus the breadth and scope of the present disclosure should not be limited by any of the above-described exemplary embodiments.

[0072] Terms and phrases used in this document, and variations thereof, unless otherwise expressly stated, should be construed as open ended as opposed to limiting. As examples of the foregoing: the term including should be read as meaning including, without limitation or the like; the term example is used to provide exemplary instances of the item in discussion, not an exhaustive or limiting list thereof; the terms a or an should be read as meaning at least one, one or more or the like; and adjectives such as conventional, traditional, normal, standard, known and terms of similar meaning should not be construed as limiting the item described to a given time period or to an item available as of a given time, but instead should be read to encompass conventional, traditional, normal, or standard technologies that may be available or known now or at any time in the future. Likewise, where this document refers to technologies that would be apparent or known to one of ordinary skill in the art, such technologies encompass those apparent or known to the skilled artisan now or at any time in the future.

[0073] A group of items linked with the conjunction and should not be read as requiring that each and every one of those items be present in the grouping, but rather should be read as and/or unless expressly stated otherwise. Similarly, a group of items linked with the conjunction or should not be read as requiring mutual exclusivity among that group, but rather should also be read as and/or unless expressly stated otherwise. Furthermore, although items, elements or components of the invention may be described or claimed in the singular, the plural is contemplated to be within the scope thereof unless limitation to the singular is explicitly stated.

[0074] The presence of broadening words and phrases such as one or more, at least, but not limited to or other like phrases in some instances shall not be read to mean that the narrower case is intended or required in instances where such broadening phrases may be absent.

[0075] It is appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination or as suitable in any other described embodiment of the invention. Certain features described in the context of various embodiments are not to be considered essential features of those embodiments, unless the embodiment is inoperative without those elements.