Patent Publication Number: US-10322490-B2

Title: Method and device for producing non-cylindrical bores with at least one recess by honing

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a process chain for machining an initially cylindrical bore by honing tools as well as to the corresponding honing tools. 
     The manufacturers of motor vehicles are faced with the permanent task of continuously reducing the fuel consumption of their vehicle fleet furnished with reciprocating piston engines. In reciprocating piston engines, the friction between the piston or the piston rings, on the one hand, and the cylinder bore plays a great part in the internal friction losses up to about 35%. Therefore, the reduction of friction in the area of the cylinder bore provides a significant potential for reducing the fuel consumption. 
     An approach for reducing the friction between piston and cylinder bore is form honing, developed by the applicant, that is disclosed in detail in EP 2 170 556 B1. In this method, the deviations from the geometry of a cylinder that are caused by clamping actions during assembly and/or thermal expansions of the cylinder bore are equalized in that complementary elevations or depressions are formed during form honing. This method is very effective and is used successfully in the production of various reciprocating piston engines. 
     DE 10 2013 204 714 A1 discloses a honing method by means of which the cylinder bore of an internal combustion engine is provided with a bottle shape. A shape in which the cylinder bore has two cylindrical sections that have a different diameter is referred to as bottle shape. The section with the smaller diameter is provided in the area of the cylinder head while the section with the greater diameter is provided in the area of the crankshaft. Between these areas, a truncated cone-shaped transition area is formed which occupies approximately 5% to 20% of the bore length. 
     DE 103 581 50 A1 discloses a method with which two sections of different hardness that are sequentially arranged in axial direction of a cylinder bore can be machined. This method and the corresponding tool are in particular advantageously employed when the cylinder bore is hardened in sections thereof and, as a consequence, the hardened section and section that is not hardened must be honed in a different way. 
     From this publication it is known to design the cylinder bore at its open end, i.e., where later on the cylinder head is mounted, such that a counterbored bore results. This is graphically illustrated in  FIG. 6  of this publication. A slight widening in the upper section of the cylinder bore is referred to as a counterbore. In this context, this widening only applies to the uppermost quarter of the cylinder bore. 
     A further approach for reducing the friction between piston rings and cylinder running surface provides widening of the cylinder bore at the end that is located in the vicinity of the crankcase. This end is also referred to in the following as “bottom end”. The later published DE 10 2015 109 609 discloses a process chain for widening (cylinder) bores at their bottom end. For this purpose, relatively short honing stones are employed. 
     In order to reduce the pump losses of internal combustion engines, the cylinders of internal combustion engines of the newest generation have one or more recesses at their bottom end. These recesses reduce the pump losses. However, they lead to the honing process being carried out with an interrupted cut. The tools known from the prior art with short honing stones that are suitable for widening a bore cannot be used in bores with a recess because the short honing stones have the tendency to cant when they “travel across” the recess. 
     The invention has the object to provide honing methods, a process chain as well as suitable honing tools for performing the methods which allow for the inexpensive and reproducible manufacture of widened cylinder bores with at least one recess. This widening is referred to also as “conical honing”. 
     In this context, the desired geometry of the “cylinder bore” is a cylindrical section with an adjoining conically widened end. Possibly, the bore also comprises one or two additional cylindrical sections. A truncated cone-shaped (cylinder) bore in the meaning of the invention is a bore whose diameter changes continuously across more than half of the length, preferably at least ¾ of the length of the cylinder bore. Ideally, the truncated cone occupies more than 85%, in some cases even 100%, of the length of the cylinder bore. 
     SUMMARY OF THE INVENTION 
     This object is solved according to the invention by a tool comprising a tool body comprising several honing stones and characterized in that two or more honing stones are arranged on a common shell. 
     The tool according to the invention is characterized in that two, three, or four or even five honing stones are arranged on a common shell. The honing stones which are arranged adjacent to each other on the shell in circumferential direction of the honing tool cover an angle range of the bore to be machined of, for example, 30° or 50° and are connected to each other more or less rigidly. When such a group of short honing stones now travels across a recess in the bore to be machined, wherein the width of the recess is smaller than the circumferential range that a shell or the honing stones arranged adjacent to each other on the shell covers, canting of the honing stones in the area of the recess is effectively avoided. 
     As a result of this, it is possible to design the honing stones to be very short and to produce a conicity or widening of the bore even where the recess is located. 
     Because canting of the short honing stones when traveling across the recess is reliably prevented by the arrangement according to the invention of several honing stones on one shell that is bridging the recess, the stock removal rate of the honing tool according to the invention is very high even for widening or plateau honing of bores with recesses. 
     The tool according to the invention is of a very compact configuration because, due to the arrangement of several honing stones on a shell, the number of components is relatively minimal. In particular, the tool length is relatively short and, moreover, the tool according to the invention requires only a minimal idle travel past the bore to be machined so that the tool can be used even when tight space conditions are present, for example, because the the bearing seat of a crankcase occupies space. 
     In order for the honing stones of the tool according to the invention, which serve for conical honing of a section of a cylindrically pre-honed bore, to be centered in the best possible way in the pre-honed bore, on the tool body of the honing tool several guide bars are formed. These guide bars are axially spaced apart relative to the honing stones so that the guide bars center the honing tool in the cylindrical part of the pre-honed bore and, at a certain spacing thereto, another part of the initially cylindrical bore is conically widened. 
     It is possible that the guide bars and/or the honing stones are radially feedable. Then, a best-possible guiding of the honing tool in the bore and the desired widening of the bore can be achieved. 
     The feed action of the honing stones is realized in that on the shells feed ramps are formed and in that these feed ramps are interacting with a feed cone. 
     Alternatively, it is possible that the honing stones are rigidly connected with the shells or are connected pendulously with the shells. Due to the pendulous support of the honing stones on the shells, an even better contact of the honing stones on the surface of the bore to be machined is achieved. Despite of this, canting of individual honing stones in the recess of the bore to be machined is prevented. 
     In order to be able to monitor and control the process of conical widening during machining, air gauging nozzles are arranged on the honing tool. These air gauging nozzles can be preferably integrated into a guide bar. This simplifies the manufacture and it makes it possible, independent of the honing stones and their wear, to detect the geometry and dimensions of the conically widened bore. 
     The method according to the invention for widening the bore comprises the steps of: placing the honing stones of the honing tool against the bore, honing the bore with decreasing stroke, wherein a lower reversing point UP of the honing tool remains substantially unchanged. This means that the part of the bore which is located at the lower reversing point UP of the honing tool is machined more frequently by the honing stones than the areas of the bore that are more remote from the lower reversing point UP. Therefore, here the increase of the diameter is greater than in the area of the upper reversing point. As a result, the initially cylindrical bore widens more and more toward the lower reversing point. Honing of the bore with decreasing stroke is terminated according to the invention as soon as the upper reversing point OP has reached a predetermined OP 2  (OP=OP 2 ). 
     It has been found that in this way an initially cylindrical bore can be converted to a slightly conical bore in sections thereof. The method according to the invention can be designed to be very simple and reliable and is possible in this context to produce a bore whose contour line is approximated to a truncated cone in sections thereof. 
     Alternatively, widening of a part of the cylindrical bore can also be performed by a method for making conical a cylindrical bore in areas or sections thereof that comprises the following steps: 
     Placing the guide bars of the honing tool against the bore to be machined, conically honing a part of the bore wherein a feeding force with which the honing stones are forced against the bore is controlled as a function of a position of the honing tool in the bore. 
     With this method, a good action of making conical or widening of the initially cylindrical bore is also achieved. It has been found to be advantageous when the feeding force increases with increasing spacing of the honing tool from a reversing point. It is possible that the feeding force increases linearly, progressively, or even degressively with increasing spacing of the honing tool from a reversing point. In this way, it is possible to compensate effects that lead to a deviation from the desired truncated cone-shaped form of the bore. However, it is also possible to create targeted deviations from a geometric ideal truncated cone shape. For example, the bore in the area of the lower reversing point can be particularly wide in regard to the diameter so that the bore produced according to the method of the invention is widened—greatly exaggerated—like the bell of a trombone. A stiffness of the bore wall which changes locally across the length of the bore can be compensated by a locally changing feed action. 
     It has further been found to be advantageous when the feed action of the honing tool is realized only when the honing tool is in the vicinity of the lower reversing point UP. The lower reversing point is the area of the bore which has the greatest diameter after performing the method according to the invention. The feed action of the honing tool can only be carried out, for example, when the honing tool is located between the predetermined terminal value UP2 and the lower reversing point UP. OP 2  is the point within the travel stroke which is met for all continuously shortened strokes. Within the travel OP 2 -UP the honing tool is incrementally fed. OP 2  is thus the stroke position of the upper reversing point of the smallest stroke and thus also of the last stroke of the machining cycle. This spacing OP 2 -UP is the smallest commonly traveled travel interval all strokes. Accordingly, the honing stone for each stroke is fed uniformly independent of its length. 
     These embodiments of the method according to the invention have the advantage that firstly the feed action over the entire honing process is independent of the stroke of the honing tool and therefore can be controlled well with respect to control technology 
     Also, it leads to an improved geometry of the finish machined conical bore because “collapse” of the bore in the area of the lower reversing point UP can be prevented as much as possible. In this way, a “bottle shape” of the bore with two cylindrical sections and a short truncated cone-shaped intermediate area can be avoided. 
     The method according to the invention for producing a largely truncated cone-shaped bore from an initially cylindrical bore can be integrated in mass production in a process chain for form machining of cylindrical bores wherein this process chain comprises pre-honing of the bore. In this context, a first honing tool or first honing stones of a honing tool can be used. Pre-honing of the bore has the task of manufacturing a completely cylindrical bore with uniform size and uniform surface and of achieving a very good geometric precision of the bore. 
     In the next step, the non-cylindrical forming of the bore, for example, with a cylindrical and an adjoining conical bore section, is carried out. 
     In a further step, the bore, made conical, is finish honed so that the desired surface quality and property of the conical bore is reached. This can also be done in a multi-step process as plateau or spiral slide honing in a tool with appropriate separation of the cutting action. In this context, basic roughness depth and plateau roughness depth can be generated as superimposed profile structure. Further advantages and advantageous embodiments of the invention can be taken from the following drawings, their description, and the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       It is shown in: 
         FIG. 1 : a schematic illustration of an initially cylindrical bore that by means of the method according to the invention has been made conical; 
         FIG. 2 : the first process step “cylindrical pre-honing”; 
         FIG. 3 : the first alternative of the second process step “conical form honing”; 
         FIG. 4 : the second alternative of the second process step “conical form honing”; 
         FIG. 5 : the process step 3.1 “producing the oil retaining roughness”; 
         FIG. 6 : the process step 3.2 “producing the plateau”; 
         FIG. 7 : an isometric illustration of a honing tool according to the invention for performing the second process step; 
         FIG. 8 : a longitudinal section of the honing tool of  FIG. 7 ; 
         FIG. 9 : a cross-section of the honing tool of  FIG. 7  at the level of the honing shells; 
         FIG. 10 : the honing tool with double feed action for performing the third process step “plateau honing”; 
         FIG. 11 : a longitudinal section of the tool of  FIG. 10 ; 
         FIG. 12 a    and  FIG. 12 b   : cross sections of the tool of  FIG. 10  along the lines E-E and F-E; and 
         FIG. 13 : a variant of the honing tool for plateau honing. 
         FIG. 14 : an isometric illustration of the comb-like embodied shells according to the invention, and 
         FIG. 15 : a schematic illustration for illustrating the meshing of the shells according to the invention. 
     
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     In  FIG. 1 , a cylinder bore with a diameter D 0  and a bore length L is schematically illustrated. 
     The diameter D 0  refers to the diameter of the cylindrical “top” end of the bore. The bottom end of the bore is conically widened by approximately 15-40 micrometer in radial direction. 
     At the bottom end of the cylinder bore a recess A with a height H 0  and a width B is indicated. 
     The object of the method according to the invention is to manufacture a bore which at the bottom end has at least one recess A with the width B and at least thereat is conically widened and thereat has a diameter greater than D 0 . 
     The contour line of the conically honed bore is identified by  1  in  FIG. 1 . In principle, it is true for all Figures that same reference characters are used for the same components or processes and only the differences are explained, respectively. 
     In  FIG. 2 , preparation of the bore for the widening according to the invention or conical honing is schematically illustrated. The bore to be machined must be prepared so that this machining process can be performed reproducibly, quickly, and inexpensively. In a machining step which is carried out prior to the actual process chain, a bore is introduced into the workpiece. This can be realized, for example, by fine boring, rough honing, or pre-honing. This process step is indicated in  FIG. 2  by the reference character  3 ′. The desired cylindrical bore is indicated in the block  3 ′ by the lines  4 . The blank in which the bore is introduced is indicated by dashed lines  6 . 
     In a block  5 , the first process step of the process chain according to the invention is schematically illustrated. This first process step is also referred to in the following as “pre-honing”. It concerns a conventional honing process by means of which the afore described cylindrical bore produced beforehand by fine boring is further improved with regard to geometry, diameter, and surface. Pre-honing can be carried out with a conventional honing tool whose honing stones are furnished, for example, with diamond as abrasive material. The stroke for cylindrical pre-honing is constant. This fact is shown in the central part of the block  5  by a diagram which illustrates the stroke length H across the honing duration t hon . The cylindrical pre-honing is terminated as soon as an in-process measurement has detected that the nominal value of the bore diameter has been reached. 
     After the end of the first process step “cylindrical pre-honing”, a bore is thus provided whose geometry corresponds very precisely to a cylinder. Also, all cylinder bores in a series production exhibit a very similar surface structure and the diameter of the bores of one series have only a very minimal variance. This makes it possible to carry out the following process step, “conical honing”, with a minimal series variance and reproducible results in an efficient and reliable way. 
     In principle, it is possible to make conical the bore in two different ways in accordance with the invention. In  FIG. 3 , a first alternative of the second process step “conical honing” is illustrated in a block  7 . In the left part of the block  7 , the transition from the cylindrical bore  9 , illustrated in dashed lines, into the desired conical bore  11  is shown schematically and greatly exaggerated. At the center of the block  7 , the temporal sequence of the second process step “conical honing” is schematically illustrated. In this context, the stroke length H of the honing tool is plotted against the time t. Each stroke of the honing tool has two reversing points, i.e., a lower reversing point UP and an upper reversing point OP. The maximum stroke length H max  traveled in the second process step is determined in block  7  by the upper reversing point OP 1  and the lower reversing point UP. The maximum stroke length H max  determines the length of the conically widened portion of the bore at the bottom end thereof. 
     The second process step begins with one or a few strokes with constant stroke length wherein the stroke length H is the travel from OP 1 -UP. At the point in time t 1  when the honing stones have contacted the bore to be machined, which at this point in time is still cylindrical, the stroke length H is reduced stepwise. It is a characteristic feature of the method according to the invention that a reversing point, preferably the lower reversing point UP, remains unchanged and the upper reversing point OP is reduced step-by-step until a predetermined limit value OP 2  is reached. Thereafter, the process step  2  ends. 
     Control of the stroke H of the honing tool by an incremental reduction of the stroke length with identical lower reversing point UP has the result that the bore at its bottom end is provided with the desired truncated cone-shaped or a conical contour surface. 
     The method according to the invention is very precise and requires only little time because, when the predetermined limit value OP 2  for the upper reversing point is reached, the honing operation is terminated. 
     This is an important advantage in comparison to the method disclosed in DE 10 2013 204 714 A1. Here, a conventional machining phase still follows which is characterized by a constant stroke at reduced stroke length. 
     It has been surprisingly found that with the method according to the invention, that comprises in the end only two stages, a very good quality of bores made conical or of conical bores can be produced in a short period of time. 
     The second process step according to the second alternative illustrated in  FIG. 3  is either performed with time control or as a function of the number of the performed strokes of the honing tool. 
     In  FIG. 4 , a second alternative of the second process step 7 “conical honing” is illustrated. 
     In this second alternative of the second process step 7, the feed action of the honing stones  13  is realized as a function of the position of the honing tool in the bore to be machined. This means that at the top end of the bore, in the vicinity of the upper reversing point OP  1 , the honing stones are fed less far than at the lower reversing point UP. This relationship is illustrated in a diagram in which the feed action Z is illustrated as a function of the position of the honing tool in the form of a line  15  (=line through origin). This linear correlation is of course only exemplary. It is also possible to predetermine a progressive or degressive correlation between feed action Z and the position of the honing tool between upper reversing point OP and lower reversing point UP and to control the feed action of the honing tool accordingly. 
     It is also possible to change the characteristic line of feed action during machining. In this way, it is possible to make the load of the honing tool  13  more uniform and to avoid excessive stress. 
     The second process step 7 can thus be performed with time control (see  FIG. 3 ) or stroke control (see  FIG. 4 ). 
     For both alternatives it is possible to hone not only conical bores; it is instead also possible to generate a bottle shape of the bores and, as needed, to carry out counterboring of the cylindrical bore at the top end of the bore and/or at the bottom end of the bore. 
     The second alternative requires a honing tool that is suitable for form honing and that enables the position-dependent feed action of the honing stones. 
     In  FIGS. 5 and 6 , the third processing step “plateau honing” is illustrated. Plateau honing comprises two partial steps, i.e., “producing the oil retaining roughness” (partial step 3.1) and “producing the plateau” (partial step 3.2). 
     The feeding force which results from feed action “Z” is constant across the stroke in both partial steps 3.1 and 3.2, respectively. However, in “producing the oil retaining roughness” (partial step 3.1) a greater feeding force is employed than in “producing the plateau” (partial step 3.2). When “producing the oil retaining roughness” (partial step 3.1) or both partial steps 3.1 and 3.2 are carried out with a high stroke speed, then the honing structures are positioned at an acute angle relative to each other and one speaks then of spiral slide honing. This type of producing the oil retaining roughness is also encompassed by the partial step 3.1. The partial steps 3.1 and 3.2 can be realized with the position-dependent feed action as well as with individual spring-loaded honing stones. In both cases, an equidistant guiding of the honing stones is realized relative to the truncated cone-shaped bore formed beforehand in step 2. 
     Further details of the process control are disclosed in the later published DE 10 2015 209 609 of the same applicant. Reference is being had herewith to this application and the contents of this application is incorporated by reference into the contents of the present application. 
       FIG. 7  shows an embodiment of a honing tool  31  according to the invention in a perspective illustration in detail. 
     The honing tool  31  comprises a honing body  33  and a receptacle  35  with which the honing tool  31  can be coupled to a spindle, not illustrated, of a conventional honing machine. 
     The connection of the honing tool  31  with the spindle can be realized, for example, by a double joint (cardanic) drive rod. A rigid connection between the honing tool  31  and the spindle is possible also. In a vertically operating honing machine, the cardanic connection to the spindle is preferred. In a horizontally operating honing machine, the rigid connection is preferred. 
     The honing machine can be designed, for example, with a conventional double feed system wherein the cutting rates and radial feed positions for different honing methods (e.g., plateau honing, spiral slide honing or conventional honing) can be automatically controlled. 
     In conventional honing process (also referred to as oscillating honing), honing is performed by rotation of the honing tool  31  with multiple stroke repetitions. 
     For widening the bottom end of a cylindrical bore (see  FIG. 1 ) in accordance with the second step of the process chain according to the invention, a cutting bar group  37  is provided on the honing tool  31 . The honing stones of the cutting bar group  37  are relatively short in axial direction. In this way, widening of the bottom end of the cylindrical bore (see  FIG. 1 ) is facilitated or is even made possible in this way. 
     The honing tool  31  according to the invention exhibits the special feature that several honing stones  37  are arranged on a shell, respectively, and are fixedly connected to it. This will be explained in more detail infra in connection with  FIG. 9 . 
     The honing tool  31  comprises also the guide bars  39 . The guide bars  39  center the honing tool  31  in the cylindrical (top) part of the bore (see  FIG. 1 ). 
     The guide bars  39  are comprised of metallic material, e.g., hard metal or of sintered diamond coatings which either have a wear-resistant smooth surface or have a rough, cutting, machining, surface. Then the guide bars  39  at the same time also act as honing stones for the cylindrical part of the bore. 
     The guide bars  39  and the honing stones  37  are arranged in axial position in sequence and so as not to overlap. As an alternative to the illustrated honing stones  37 , the shells can be provided across the entire surface area with abrasive material, for example, diamond grains, by means of galvanic bonding. 
     The guide bars  39  can be radially fed in order to achieve a play-free contact on the cylindrical part of the bore to be machined. In this way, a very good centering action of the tool  31  in the bore across a great axial length is achieved. As a result of this, a very good coaxial alignment of conical (bottom) and cylindrical (top) part of the bore is achieved. 
     It is also possible to attach the guide bars  39  on the tool body  33  so as to be non-feedable. They are then ground to a diameter such that a certain clearance is formed between the pre-processed bore and the guide bars  39 . 
     In this way, a guiding of the honing tool  31  in the bore is achieved also, in particular with the precision of the clearance between the guide bars and the pre-machined bore. 
     The clearance between the guide bars  39  and the pre-machined bore has an effect on the quality of guiding of the honing tool  31  in the bore. 
     The guide bars  39  are longer than the honing stones  37 . In this way, a constant good guiding action of the honing tool  31  during the second processing step 2 “conical form honing” is ensured. 
     The tool receptacle  35  is preferably of a double joint configuration, so that the honing tool  31  can center itself and align within the bore when the guide bars  39  are moved radially outwardly into contact at the cylindrical part of the bore. However, also rigid tool receptacles and tool receptacles with only one joint have been tested successfully. 
     It has been found to be advantageous to provide at least one air gauging nozzle  41  in the tool body  33  and between honing stones  37  and guide bars  39  in axial direction. These air gauging nozzles  41  enable in-process measurement of the developing conical shape of the bottom part of the bore. 
     Honing can be done with the swelling stroke or with the dynamic EMF within the axial working range of the shells or of the honing stones where the conicity is produced. 
       FIG. 8  shows a section of the tool  31  in which the expandable guide bars  39  are recognizable. In this context, a feed tube  43  actuates two groups of feed cones  45  which move the guide bars  39  radially in outward direction when the feed tube  43  in  FIG. 8  is moved downwardly relative to the tool  31 . The guide bars  39  are mounted on support bars  40  which at their radial inner “end” have two conical feed surfaces  47  which are spaced apart from each other. These feed surfaces  47  interact with the feed cones  45  in a generally known manner. 
     Springs  49  secure the guide bars  39  as well as the honing stones  37  against falling out. 
     Feeding of the honing stones  37  is realized similar to feeding of the guide bars  39 . A feed rod  51  is guided through the feed tube  43 . It is connected to a feed cone  53 . When the feed rod  51  in  FIG. 8  is relatively moved in the tool  31  in downward direction, the honing stones  37  are fed radially in outward direction. The conical feed surfaces  57  (see  FIG. 9 ) of the honing stones  37  which are located on honing shells  55  and are interacting with the feed cone  53  are not visible in the longitudinal section according to  FIG. 8 . 
     This type of feed action is known to any person of skill in the art and therefore requires no detailed explanation. 
     In  FIG. 9  a cross section of the tool  31  along the line G-G is illustrated. 
     This illustration shows the feed cone  53  well. Since the feed cone in the area of the section plane is bored hollow, the feed rod  51  is not visible. Well illustrated are a total of six shells  55  uniformly distributed about the circumference which each support five honing stones  37 . 
     For reasons of clarity, the five honing stones  37  only on one shell are provided with reference characters. 
     Radially inwardly, conical feed surfaces  57  are extending which interact in a generally known way with the feed cone  53 . The shells  55  are rigid so that therefore also the five honing stones  37  arranged on a shell  55  are positioned fixedly relative to each other. 
     In the present embodiment, six shells  55  are present so that the five honing stones  37  arranged on a shell  55  cover approximately a circumferential angle of 60°. 
     When now this circumferential angle of approximately 60° is correlated with the width B of the recess A in  FIG. 1 , it is apparent that the circumferential area which is covered by the five honing stones  37  must be greater than the width B of the recess A in  FIG. 1 . Then it is ensured that always at least one honing stone  37  of a shell is not located in the area of the recess A but is guided on the bore wall. As a result of this, due to the rigid connection of the five honing stones  37  by the shell  55 , the other honing stones which are positioned across the recess A are also secured against canting. 
     Accordingly, by means of the tool according to the invention it is possible to conically widen a cylindrical bore in sections thereof even when in the area in which conically widening is to take place a recess is located which would make difficult guiding of the honing stones  37 . 
     The conical widening by means of the tool according to the invention is as efficient as other methods known in the prior art for widening bores without recesses. 
     The tool according to the invention is also not more expensive in its manufacture because significant cost advantages result by combining several honing stones on a shell  55 . 
     In  FIG. 10 , a honing tool  59  is illustrated that is suitable for performing the third process step, i.e., honing of the area of the bore that has been previously made conical or widened. Use of this tool  59  independent of the described process chain is possible also. The preferred use concerns machining of bores with recesses A in the bore to be machined. Depending on the employed feed mode or stroke mode, cylindrical, truncated cone-shaped or conical bores can be produced or further processed. 
     In a tool body  61  guide bars  63  are arranged. In the guide bars  63  air gauging nozzles  65  are integrated. The air gauging nozzles  65  are arranged at the bottom end of the guide bars  63  which is opposite the receptacle  66 . In other words: The air gauging nozzles  65  are located in immediate vicinity of the honing stones  67  and  69 . 
     In the illustrated embodiment, three honing stones  67  and three honing stone  69  are combined to a group, respectively. The honing stones  67  and  69  alternate about the circumference of the honing tool  59 . In axial direction, the honing stones  67  and  69  are positioned at the same level, i.e., below the guide bars  63 . 
     The honing stones  67  and  69  are coated with different abrasive materials because they effect the two partial steps of plateau honing, i.e., the partial step 3.1 (see  FIG. 5  “producing the oil retaining roughness”) and the partial step 3.2 (see  FIG. 6  “producing the plateau”). 
     In order to prevent canting of the groups of honing stones  67  or  69  upon traveling across the recess A (see  FIG. 1 ), at least two groups  67 . 1  or  67 . 2  are arranged on a shell. The same holds true also for the second group of honing stones  69 . 1  or  69 . 2 . 
     It is also possible that three groups of honing stones  67  are arranged on a common shell and correspondingly also three groups of honing stones  69 . 3  are arranged on a shell. 
     Important in connection with the invention is that canting of the honing stones  67  or  69  is avoided in this way, similar to the honing tool according to  FIGS. 7 and 8 . 
       FIG. 10  illustrates well the shells  71  which support the honing stone groups  67 . 1 ,  67 . 2 , and  67 . 3 . 
     Coaxially arranged thereto is a further shell  73  which supports the honing stone groups  69 . 1 ,  69 . 2 , and  69 . 3 . 
     Against rotation and loss, the shells  71  or  73  are secured by an end member  75  which is screwed to the tool body  61 . As a whole, distributed about the circumference there are three shells  71  and three shells  73  and correspondingly nine honing stone groups  67  and nine honing stone groups  69 . For reasons of clarity, only one shell  71  and  73  as well as three honing stone groups  67 . 1 ,  67 . 2 , and  67 . 3  as well as  69 . 1 ,  69 . 2  and  69 . 3  are illustrated in  FIG. 10 . 
     In  FIG. 11 , a longitudinal section of the tool  59  according to  FIG. 10  is illustrated. 
     This tool also has a double feed action for the shells  73  and for the shells  71 , respectively. The feed rod  77  and the feed cone  79  are surrounded by a feed tube  81  as well as a further feed cone  83 . The feed cones  79  and  83  interact with complementary feed ramps  85  of the shells  71  as well as a feed ramp  87  of the shells  73  in a generally known way. 
     As can be seen in  FIG. 11 , the honing stones  67  and  69  are at the same level. However, in  FIG. 11  the shells  73  project less far in downward direction than the shells  71 . At the same time, the shell  71  begins in axial direction father downward than the shell  73 . In this way, it is possible to provide a penetration or cutout for the respective other shell so that the shells  73  with their correlated feed ramps  87  reaches the feed cone  79  and the shells  71  with reaches with their feed surfaces  85  the feed cone  83 . 
     Here also, the honing stones  67  and  69  are secured by spring rings  49  in contact against the feed cone  79  or  83 . In  FIGS. 14 and 15 , the shells  71  and  73  and their intermeshing are illustrated. 
     In  FIG. 12 a    and  FIG. 12 b   , two cross sections of the tool according to  FIG. 11  are illustrated. 
     The section along the line F-F shown in  FIG. 12 b    illustrates well the shells  73  which support the honing stone groups  69 . 1  to  69 . 3  as well as the feed ramp  87  and the feed cone  79  which is coupled with the feed rod  77 . 
     The section along the line E-E shown in  FIG. 12 a    illustrates well the shells  71  which support honing stones  67 . 1 ,  67 . 2 , and  67 . 3 . Further, it is illustrated well that radially inwardly, in extension of the shells  71 , the feed surfaces  85  interact with the feed cone  83 . 
     The shells  71  as well as the shells  73  cover almost 120° of the circumference so that also for this tool it is ensured that the honing stones  67 . 1 ,  67 . 2 , and  67 . 3  will not cant when they rest above a recess A as illustrated in  FIG. 1 . 
     In  FIG. 13 , a second embodiment of a honing tool  59  according to the invention is illustrated in longitudinal section which is suitable to perform the “plateau honing” with the partial processes  3 . 1  and  3 . 2 . 
     The feed rod  77  comprises a feed cone  79  which effects with complementary feed ramps  87  of the shell  71  a radial feed action of the support bars  91  when the feed rod  77  is displaced, for example, by a non-illustrated electromechanical feed action of the honing machine in axial direction relative to the tool body  61 . In this embodiment, the support bars  91  support the honing stones  67 . 
     In a corresponding manner, the feed tube  81  is coupled with a feed cone  83  which, together with complementary feed ramps  85  of the the shell  73 , effects a radial feed action of the support bars  93  and thus also of the honing stones  69  when the feed tube  83  is controlled appropriately. 
       FIG. 13  further illustrates well that in the shells  71  and  73  as well as the support bars  91  and  93  two bores  95  are provided, respectively, in which spiral springs  97  are arranged. Two spiral springs  97  each are supported at one end against the base of the bores  95  in the shells  71  or  73  as well as with the other end in the support bars  91  and  93 . On the radially outwardly arranged area of the support bars  91  and  93 , the honing stones  67 ,  69  are attached. 
     As an alternative to the aforementioned spiral springs, other springs can be used also, for example, also possible are constructions with leaf springs, plate springs, bending joints or with elastically yielding components. 
     Perpendicular to the drawing plane in  FIG. 13 , bearing bolts  99  are arranged in the support bars  91  and  93 . The bearing bolts  99  interact with grooves  103 , hardly visible in  FIG. 13 , in the feed ramps  85 ,  87  in such a way that the support bars  91 ,  93  in axial direction cannot be displaced relative to the feed ramps  85 ,  87 . At the same time, the support bars  91 ,  93  can perform a pendulous compensation movement whose axis of rotation coincides with the longitudinal axis of the bearing bolt  99 . In this way it is possible that the honing stones  67 ,  69 , in accordance with the conicity of the bore  101  to be machined, will become slantedly positioned. As a result of this, the honing stones  67 ,  69  are forced across their entire length uniformly and with constant force against the cylinder bore  101  to be processed. 
     In this way, in every area of the cylinder bore the same surface is thus achieved in the end by machining with the honing tool according to the invention. 
     In order for the support bars  91 ,  93  not to be forced as a result of the force of the spiral springs  97  radially outwardly out of the tool body  61 , a frame  105  is screwed on radially outwardly on the feed ramps  85 ,  87 . 
     The construction of these pendulously supported honing stones  67 ,  69  corresponds mostly to the construction disclosed in patent DE 10 2010 032 453 whose contents is herewith incorporated by reference into the contents of the present patent application. 
     In this embodiment of a honing tool  59 , the guide bars are not feedable. 
     In  FIG. 14 , the shells  71  and  73  according to the invention are illustrated in an exploded view. 
     The shell  71  comprises a circular segment-shaped support  107  and a support bar  109 . The support  107  and the support bar  109  are in general manufactured as one piece from a workpiece. It is also conceivable to connect both components to each other by welding or the like. 
     On the radial inner end of the support bar  109  the feed ramp  85  is located that already has been explained before. The support bar  109  passes into a support element  111  which supports the honing stones  67 . 
     In this embodiment, in addition to the support bar  109  further support elements  111  are formed at the ends of the support  107 . The honing stones  67  which belong to the shell  71  are mounted on the support bar  109  or the support elements  111 . In the isometric view of  FIG. 14 , only two support elements  111  are visible; one is covered by the honing stones  67 . 
     Between the support elements  111  or the honing stones  67  arranged thereon, an inner width indicated by the curved double arrow  113  is provided in circumferential direction. 
     The support  107  is connected at one end of the support bars  109  to the latter so that as a whole a comb-like structure results. 
     The shell  73  is in principle of the same configuration as the shell  71 . The important difference resides in that the circular segment-shaped support  117  is arranged on the end of the support bar  119  that is at the top in  FIG. 14  while it is arranged at the bottom end of the support bar  109  in case of the shell  71 . 
     For reasons of clarity, not all honing stones  69  are provided with reference characters. 
     The inner width  113  between the honing stones  67  is greater than a width B 121  of the support elements  121  of the shell  73 . 
     In a corresponding manner, an inner width  123  between the honing stones  69  is greater than a width B 111  of the honing stones  67  of the shell  71 . Because the circular segment-shaped supports  107  and  117  of the shells  71  and  73  is arranged at “oppositely positioned” ends, it is possible that the shells  71  and  73  with the comb-like support elements  111 ,  121  are mounted on the tool body  61  “meshing” with each other (see  FIGS. 10 and 11 ). As a result, the honing stones  67  and  69  are are arranged essentially adjacent to each other on the circumference of the honing tool. This results in a very short constructive length of the honing tool  59 . Also, when machining the bore with this honing tool  59 , only a very short idle travel of the tool past the end of the bore is required. 
     In  FIG. 15  it is again illustrated how the shells  71  and  73  and their honing stones  67 ,  69  are meshing comb-like with each other when they are mounted on the honing tool  59  (see  FIG. 10 ).  FIG. 15  is a somewhat simplified illustration which however illustrates well the principle according to the invention of comb-like meshing shells  71  and  73 . In order to illustrate this principle, the inner widths  113  and  123  are also indicated. 
     It should be noted that in the honing tool  59  the following combinations are possible: 
     Variant 1: 
     shell  71 : pendulous support of the honing stones  67   
     shell  73 : pendulous support of the honing stones  69   
     Variant 2: 
     shell  71 : rigid connection of the honing stones  67   
     shell  73 : rigid connection of the honing stone  69   
     Variant 3: 
     shell  71 : pendulous support of the honing stones  69   
     shell  73 : rigid connection of the honing stones  69   
     Variant 4: 
     shell  71 : rigid connection of the honing stones  67   
     shell  73 : pendulous support of the honing stones  69   
     On the basis of the afore described constructive features of the honing tools according to the invention, the process chain according to the invention can be performed with the following process steps listed once more: 
     1. Cylindrical pre-honing with conventional honing technology for producing a cylindrical starting state with defined roughness for further bore machining. 
     2. The second operation machines the cylindrical bore to the desired bore form with a cylindrical section and an adjoining conical section. This can be done with pre-published methods such as swelling stroke or dynamic stepped feed action. 
     3. The third machining stage characterizes a smoothing operation with which, for example, a spiral slide honing with a plateau profile is generated. As in conventional plateau honing or spiral slide operations, here also a double feed action tool is used. This means that two shell sets with three shells each are furnished with different honing stones and are feedable independent of each other. 
     In process step 2 the honing tool whose honing stones are arranged on shells are guided in the cylindrical portion of the bore which ensures a coaxial position of the conical part relative to the cylindrical section. 
     For the third process step, a shell tool is proposed which has two different shell sets which are arranged in the tool body in the same axial position. In this way, coverage of large surface area bore interruptions as well as functionally proper plateau honing with absolutely identical honing angle of is achieved in the partial steps 3.1 “producing the oil retaining roughness” and 3.2 “producing a plateau”. 
     Moreover, the tools for the second and third operations are designed for air gauging so that the resulting conicity can be monitored constantly in the process.