Abstract:
An apparatus ( 5 ) for the deep rolling of recesses ( 4 ) and radii of crankshafts ( 1 ). The deep rolling is accomplished with the aid of deep-rolling rollers ( 8 ) which, during revolution of the crankshaft ( 1 ), penetrate into the recesses ( 4 ) or radii of the crankshaft ( 1 ) under application of a deep-rolling force and at an angle of approximately 35° and bring about a deformation in the crankshaft ( 1 ) itself. According to the invention, the depth of penetration of the deep-rolling rollers ( 8 ) in the crankshaft ( 1 ) is measured in the radial direction and the magnitude of the deep-rolling force is regulated as a function of the measured penetration depth in such a fashion that in the course of at least one revolution of the crankshaft ( 1 ) a plastic deformation corresponding to a predefined rolling depth is obtained at least at one of the two recesses ( 4 ) or radii of a relevant journal bearing ( 2 ) after the deep rolling.

Description:
RELATED APPLICATIONS 
     This invention claims priority to German Application No. 10126064.4, filed May 28, 2001. 
     BACKGROUND OF THE INVENTION 
     The invention relates to a method and apparatus for deep rolling recesses and radii on crankshafts according to the features of the preamble of the main claim. 
     The deep rolling of crankshafts is accomplished by means of deep-rolling rollers which are pressed with a predefined force into the recesses and radii which respectively laterally delimit the bearings of a crankshaft. A method, a machine or tools for deep rolling the radii and recesses of crankshafts are disclosed, for example, in EP 0 683 012 A1 and also in EP 0 661 137 B1 and EP 0 299 111 B1. In the known methods using the known machines the crankshaft material is plasticized to a depth of approximately 1 mm with the aid of deep-rolling rollers which are rotatably supported in the deep-rolling tool. In this case, residual compressive stresses build up tangentially around the rolling radius of the deep-rolling rollers, which reduce the formation of cracks at the critical points of the transition of the bearing pin to the cheek of the crankshaft during operation of the crankshaft under bending stress and thus appreciably enhance the fatigue strength of a crankshaft. The quality of any deep rolling is of decisive importance for the service life of a crankshaft. With higher torques and higher engine performance, especially with the widespread use of diesel engines, the requirements for crankshafts are becoming increasingly demanding. In consequence, the industry has moved towards making the deep rolling of crankshafts increasingly critical and with increasingly higher precision. So far it is known that deep rolling force can be carried out with a predefined deep rolling force. However, adhering to the deep-rolling force alone is not able to compensate for the spreads in the strength of the crankshaft material or the inaccuracies introduced into the crankshaft during the pre-processing of the crankshaft, especially during cutting and, if appropriate, hardening. Errors in the pre-processing at recesses or radii on a crankshaft to be deep-rolled are not detected by the known methods where a pre-defined deep-rolling force is adhered to. 
     A method for strengthening workpiece surfaces has also been disclosed in DE 195 11 882 A1. The known method can be applied to crankshaft processing. In this case, the workpiece surface is measured during the strengthening process and controlled variables for setting/changing tool parameters are derived from the measured results. The depth of penetration of the deforming tool into the workpiece surface is especially determined. A deep-rolling roller applying a corresponding pressing force penetrates into the material and thus produces ridges on both sides of the penetrating deep-rolling roller depending on the flow behavior of the work piece material. The actual penetration depth of the deep-rolling roller is then obtained from the difference in the ridges. The surface contour can then be measured in various different ways, for example, mechanically, pneumatically, hydraulically, acoustically, electromagnetically, electrocapacitatively or electronically using suitably acting sensors. 
     A disadvantage of the known method is the indirect recording of the penetration depth via the ridges on both sides of the penetrating deep-rolling roller. Such ridges are sometimes not present at all or are so little defined that they can barely be measured. This is especially the case, for example, with the ridges at the transitions to both sides of recesses on crankshafts which lie in respectively different planes. Experience has shown that the accuracy with which the ridges can be measured is not sufficient to make reliable statements on the depth of penetration of the deep-rolling roller into the crankshaft. Instead of this, it is substantially more favorable to directly follow the path of the deep-rolling roller, whether in the radial direction or in the axial direction of movement relative to the crankshaft, or in both directions of movement at the same time. 
     In industrial practice, the situation may also arise where individual deep-rolling rollers of a machine have a shorter service life compared with the other deep-rolling rollers and prematurely fail. With the means known so far, it is difficult or completely impossible to detect such premature failure of the deep-rolling tool. The industry has thus managed so far by randomly checking the rolled radii or recesses of crankshafts using clip-on instruments which are applied manually. 
     From the difficulties and disadvantages described previously, the object for the invention is to further improve the deep rolling of radii and recesses of crankshafts in order to achieve in particular a uniform product result and to detect in good time and eliminate any errors which have crept into the process from the preceding processing of the workpiece. In this way, the improvement should be attainable without additional expenditure and in an economical fashion. In particular, already existing equipment such as crankshaft deep-rolling machines and crankshaft deep-rolling tools as well as inherently known measuring and regulating equipment should be used to implement and the deep rolling without any substantial changes. 
     SUMMARY OF THE INVENTION AND ADVANTAGES 
     The present invention proposes an apparatus and method with which the penetration depth is measured continuously in the radial direction of the deep-rolling rollers of a deep-rolling tool and the magnitude of the deep-rolling force is regulated as a function of the measured penetration depth such that in the course of the deep-rolling operation at the recesses or radii of a journal bearing after deep rolling there is maintained a plastic deformation which corresponds to a pre-defined rolling depth. 
     In a similar fashion, errors which have been introduced into the crankshaft during the pre-processing, whether as a result of cutting or as a result of hardening, are detected. For this purpose there is used a measuring tool which has a structure identical to a deep-rolling tool. Before the actual beginning of the deep-rolling operation measuring rollers are inserted into the recesses of the journal bearings under a low applied force. The axial spreading of the measuring rollers which takes place during the penetration is recorded and determined as the measured value for the quality of the pre-processing. Sensors which record the axial distance between individual measuring rollers and the adjacent oil collars of the crankshaft are used for this purpose. 
     The known method of deep rolling the recesses and radii of crankshafts with a pre-defined rolling depth is now improved by achieving a specific rolling depth depending on the particular state of the radii or recesses of the crankshaft to be deep-rolled and suitably varying the deep-rolling force to achieve this rolling depth. 
     The apparatus can implement such a method using a single deep-rolling roller of a deep-rolling tool but the resulting penetration depth of both deep-rolling rollers usually used on a deep-rolling tool can also be measured. In addition, the resulting axial displacement of the measuring rollers of a measuring tool can be recorded. Several devices are suitable for measuring the penetration depth of the deep-rolling rollers or the displacement of the measuring rollers of a measuring tool in the axial direction and the particular selection is in each case within the measures of the relevant technical specialist. 
     The penetration depths of the deep-rolling rollers of a deep-rolling tool or the displacements of the measuring rollers of a measuring tool measured using sensors are fed to a computer, saved in the computer, converted into operands and the deep-rolling force is regulated accordingly. The usual procedure involves first rolling the crankshaft at a low and constant applied force before the actual deep rolling and, after the deep-rolling at the deep-rolling force, evaluating the difference between the measured values, which is obtained from the penetration depths at the applied force and the deep-rolling force and then determining the penetration depth using a correspondingly evaluated operand. Such an operand is advantageously suitable for determining the errors which occur during the pre-processing of the crankshaft, whether as a result of cutting or as a result of hardening or damage to the deep-rolling rollers themselves. 
     The present invention provides a radial intermediate space between the guide roller for the deep-rolling rollers and the journal bearing of the crankshaft there is provided a sensor which measures the penetration depth of the deep-rolling roller in the recesses and radii of the crankshaft. The sensor is connected to a computer which saves the measured values of the penetration depth and converts them into operands, where the computer is again connected to a plurality of control elements of which at least one controls the revolution of the crankshaft and at least one other controls the loading of the pressure-medium cylinder which the pressure medium as a function of the revolution of the crankshaft and the evaluated computer operands to produce the deep-rolling force. 
     Sensors can be arranged in various measuring planes along the equipment arms. In addition to the possibility of determining the penetration depth of the deep-rolling rollers into the crankshaft in the radial direction, provided that the two measuring rollers of a measuring tool configured as a deep-rolling tool are inclined at an angle of approximately 35° within the measuring rolling tool, it is also possible to determine the axial spreading of the measuring rollers accompanying the penetration of the measuring rollers with the aid of sensors. 
     Inductive sensors, triangulation sensors which function optically, digital path-measuring sensors, potentiometers or ultrasound sensors are suitable as sensors. The choice of the most suitable sensor in each case lies with the relevant technical specialist. In this case, it is envisaged that triangulation sensors which operate with laser beams can also be used. Both digital path-measuring sensors and capacitative potentiometers can be constructed as devices which measure by the eddy current method. Preferably, the particular sensors have at least tenfold resolution with a measuring range of approximately 1 mm, where the measured value of the rolling depth lies between 0.1 and 0.9 mm. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is explained subsequently with reference to several examples of embodiment. The drawings which are respectively highly simplified, not to scale and predominantly schematic, are as follows: 
     FIG. 1 is a front view of a deep-rolling tool; 
     FIG. 2 shows the arrangement of a deep-rolling tool inside a single deep-rolling device; 
     FIG. 3 is a schematic diagram of the measuring directions; 
     FIG. 4 shows the measurement of an axial displacement by measuring rollers of a measuring tool; 
     FIG. 5 is a side view of the measuring arrangement in FIG. 2; 
     FIG. 6 shows different measuring planes along an equipment arm; 
     FIG. 7 is a schematic diagram showing the attachment of sensors; 
     FIG. 8 is a swivellable measuring apparatus; 
     FIG. 9 is an apparatus for measuring different rolling depths; 
     FIG. 10 is a deep-rolling device with a displacement pickup. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In the Figures those parts which directly relate to the crankshaft are respectively made particularly identifiable by shading. Control systems are shown by broken lines. 
     FIG. 1 shows the sequence for deep rolling a crankshaft  1 . The crankshaft  1  has a journal bearing  2 , for example, for a main bearing or a connecting-rod bearing. In the direction of the longitudinal axis of the crankshaft  1 , shown, for example, by the dot-dash line  3  running parallel to the longitudinal axis, the journal bearing  2  is delimited on each side by recesses  4 . As can be seen clearly in FIG. 1, the two recesses  4  have an axial distance apart which corresponds to the width of the journal bearing  2 . According to the selected representation in FIG. 1, the recesses  4  are processed using a deep-rolling tool  5 . The deep-rolling tool  5  consists of a tool housing  6  in which a guide roller  7  is supported rotatably about the axis  3 . A deep-rolling roller  8  penetrates into each of the recesses  4 , wherein the two deep-rolling rollers  8  are spread outwards preferably at an angle of approximately 35° to the vertical and are supported inside the tool housing  6  on guide surfaces  9  of the guide roller  7 . 
     As a result of the action of the deep-rolling rollers  8  on the recess  4 , tangential residual compressive stresses shown by the arrows  10  appear inside the crankshaft  1  at the bottom of the recess  4 . The bottom of the recesses  4  is indicated by the arrow  11 ; the arrow  12  indicates the rolling radius which in crankshafts for engines of passenger cars may be between 1.2 and 1.9 mm. 
     In the present example, a sensor  14  is located in the radial spacing between the outer circumference  13  of the guide roller  7  and the journal bearing  2  of the crankshaft  1 . The sensor  14  is connected to the housing  6  at a suitable point and measures the radial distance between the outer circumference  13  of the guide roller  7  and the journal bearing  2  of the crankshaft  1 . The sensor  14  can, for example, be an eddy current sensor in miniature form. The sensor  14  is shown again in FIG.  2 . Here, for example, it is located on an equipment arm  15  of a deep-rolling device  17  having the two equipment arms  15  and  16 . 
     As already mentioned, a single deep-rolling machine has a plurality of such deep-rolling devices  17  corresponding to the number of journal bearings  2  to be processed. The two equipment arms  15  and  16  are hinge-connected one to the other at a common pivot point  18  in a scissors fashion. Each of the first outer ends  19  and  20  of the two equipment arms  15  and  16  holds corresponding parts of a deep-rolling tool  5 . Thus, for example, at the first outer end  19  of the equipment arm  15  is attached the tool housing  6  with the guide roller  7  and on the opposite first outer end  20  of the second equipment arm  16  is attached a casing  21  with the two supporting rollers  22 . The crankshaft  1  is located in between deep-rolling rollers  8  and support rollers  22 . According to the representation in FIG. 2, the sensor  14  is attached both to the equipment arm  15  and to the tool housing  6 . 
     Between the two second outer ends  23  and  24  of the equipment arms  15  and  16  there is located a pressure-medium cylinder  25 . This pressure-medium cylinder  25  produces the deep-rolling force which is required to deep roll the recesses  4  of the crankshaft  1 . The signal from the sensor  14  is transferred, for example, to a computer  53 , where it is saved, converted into an operand, and fed to a regulator  54  which regulates the supply of the pressure medium to the pressure-medium cylinder  25 . The computer  53  and regulator  54  are equipment familiar to the relevant technical specialist. 
     FIG. 3 shows the change in distance  26  of the deep-rolling roller  8  to the bearing surface  2  of the crankshaft  1  in the radial direction. Here only the change in distance  26  of the two deep-rolling rollers  8  is recorded jointly, which each individually undergo a change in their position during the deep-rolling process in the direction of the two arrows  27 . It can be seen from FIG. 3 that the two arrows  27  can each be resolved into one component in the vertical direction corresponding to the arrow  26  and one component  28  in the direction of the axis of rotation  3 . 
     This type of recording can be seen from FIG.  4 . As they penetrate into the recesses  4  of the crankshaft  1 , the measuring rollers  38  of a measuring tool  57  at the same time undergo a spreading in the axial direction  28 . As for a deep-rolling tool  6 , the two measuring rollers  38  of the measuring tool  57  are led laterally in cages  33  (FIG.  5 ). In order to determine the axial displacement of the measuring rollers  38  of the measuring tool  57 , there are provided sensors  29  which, for example, determine the size of a spacing  30  between the measuring rollers  38  and the oil collars  31  of a crankshaft  1 . The axial position of the measuring rollers  38  before the deep rolling operation makes it possible to identify errors in the pre-processing of the crankshaft  1 , i.e., recesses  4  recessed to different depths. The displacement of the measuring rollers  38  during deep rolling makes it possible to identify different rolling depths, e.g. as a consequence of different hardenings in the vicinity of the recesses  4  and thus serves to monitor the process. There is an arrangement corresponding to FIG. 4 where the conditions for attaching sensors  29  to the tool housing  40  of a measuring tool  57  are particularly favorable. In addition, a force sensor  32  can also complete the measuring device  57  which, if necessary, also acts together with a path sensor (not shown) by means of which the path  34  covered by the recess  4  during a revolution of the crankshaft  1  is recorded. The force sensor  32  is, for example, connected via a control line  55  to the supply line  56  via which the pressure medium is supplied to the pressure-medium cylinder  25 . The respective magnitude of the deep rolling force is determined and monitored via this possible method of recording the working pressure also familiar to the relevant technical specialist. 
     FIG. 6 shows a sensor  35  similar to the sensor  14  which records the radial change in distance between the two first outer ends  19  and  21  of the two equipment arms  15  and  16 . In addition to the arrangement at the outer ends  19  and  20 , sensors comparable to the sensor  35  can also be attached in the measuring planes  36 . Here also the suitable choice of measuring planes  36  is left to the relevant technical specialist. For the particular arrangement it is merely desireable that the measured quantity being sought has tenfold resolution. 
     An enlarged view substantially corresponding to FIG. 6 is reproduced in FIG.  10 . Here a holder  58  is attached between the outer end  20  and the pivot point  18  on the inside of the equipment arm  15 . From the holder  58  projects a measuring sensor  59 , for example, an inductive displacement pickup, directed towards the equipment arm  16 . The measuring sensor  59  can record the distance between the two equipment arms  15  and  16  with high accuracy and is thus suitable for recording the depth of penetration of the deep-rolling roller  8  into the crankshaft  1  without any gaps. The measuring signal passes via a measurement line  60  to the computer  53  which commands the regulator  54  which for its part loads the pressure-medium cylinder  25  via the supply lines  56 . The measuring sensor  59  records the penetration depth of the deep-rolling roller  8  with an accuracy of ±0.01 mm in the measurement range. 
     FIG. 7 shows the schematic attachment  37  of a sensor  14  to a tool housing  40 . Instead of the deep-rolling rollers  8 , in the representation shown in FIG. 7 there are provided measuring rollers  38  whose size and configuration is comparable to the deep-rolling rollers  8  in FIG.  1 . The measuring rollers  38  are also supported by a guide roller  39  inside a tool housing  40 . FIG. 7 shows a swivellable measuring device  41 . Another representation of such a swivellable measuring device  41  is also shown in FIG.  8 . The swiveling of the measuring device  41  is accomplished, for example, via a small pressure-medium cylinder  42 . The two devices  41  shown in FIGS. 7 and 8 are purely measuring devices. These are swiveled into the appropriate journal bearing  2  of a crankshaft  1  as soon as the deep-rolling tools  6  to  8  have been brought out of engagement and are then used to monitor the deep-rolling process. If the equipment  42  is suitably configured and attached, e.g. on the equipment arm  15 , the depth of penetration  26  of the deep-rolling rollers  8  can also be measured during the deep rolling and the deep rolling force produced via the pressure-medium cylinder  25  can also be regulated as with the sensor  14  integrated in the deep-rolling tool  6 . 
     Another different measuring device is shown in FIG.  9 . Here the measuring apparatus consists of two guide rollers  43  and  44  divided in half axially. These two half-rollers  43  and  44  are each rotatably supported in a housing  45 . On these are supported measuring rollers  46  and  47  which each penetrate into recesses  48  and  49  of a crankshaft  1 . As can be seen from FIG. 9, the recesses  48  and  49  are of different depth, corresponding to different rolling depths. Sensors  50  are again connected to the housing  45  via attachments  51  similar to the attachments  37  in FIG.  7 . The device as shown in FIG. 9 is also swivellable and is used for simultaneous measurement of the different rolling depths  48  and  49 . Here it is envisaged that the two halves  43  and  44  of a guide roller  52  can move in the radial direction relative to the crankshaft  1 . To each of the axes of rotation assigned to the guide rollers  43  and  44  is connected a sensor  50 , for example, an eddy current sensor, which determines the displacement of the system relative to the journal bearing  2 .