Abstract:
Apparatus and a method for testing for improper assembly of moving parts features the use of a plurality of vibration sensors placed on predetermined locations of an external surface of a device housing the moving parts. A computing element analyses the sensor outputs to determine whether an assembly error exists, the nature of the error and its location within the device.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to methods and apparatus for testing for the proper assembly of components of apparatus having moving parts. More particularly, the invention pertains to methods and apparatus for determining the proper assembly of automotive engine blocks, including the internal moving parts of such blocks. 
     While moving down an assembly line, automotive engines may be subject to assembly errors, either by human operators or by automated equipment. Traditionally, two of the most commonly encountered assembly errors for engine components are reversed piston heads and missing connecting rod bearings. 
     FIG. 1 depicts the cross-section of an engine block  100  showing a crankshaft  106  having a center line of rotation  104  and the connecting rod  108  and its associated piston head  110  for one cylinder  102  of the engine. If piston head  110  is installed incorrectly- that is, upside down, then head  110  will lie at an angle to the longitudinal center line of the cylinder, thereby creating a “slap” condition which is obviously detrimental to proper functioning of the engine once it is fully assembled and started. The slap condition arises from head  110  improperly contacting the cylinder wall at points  111  and  112 . 
     Similarly, if during the assembly process , a bearing between crankshaft  106  and connecting rod  108  is omitted, connecting rod  108  and its associated piston head  110  will not operate as intended. Rather pronounced knocking vibrations will result from the connecting rod having too much “play” during its stroke, due to the absence of the bearing. 
     In conventional assembly processes, assembly errors such as those discussed above have been discovered either “the hard way” by starting the fully assembled engine and suffering the consequences, by use of complicated and expensive optical inspection systems, or by labor-intensive manual inspection. 
     Therefore, there is seen to be a need in the art for an automated, yet relatively simple method and apparatus for determining whether proper assembly of a device having moving internal parts, such as an automotive internal combustion engine, has taken place. 
     SUMMARY OF THE INVENTION 
     Accordingly, a plurality of vibration sensors are arranged in a predetermined positional pattern in contact with a device under test. The output of each of the sensors is electrically coupled to a computing element. A coupling device couples a source of motive power so as to cause movement of assembled movable parts within the device. While the source is moving the movable parts at a predetermined rate, vibrations in the device under test are converted to electrical signals by the array of sensors and forwarded to the computing element for conversion into digital signatures. The computer utilizes a method to analyze the digital signatures to determine whether the engine has been assembled correctly. If an assembly error is detected by the computing element, the method functions further to identify both the type of assembly error and the location or locations within the device where the assembly error has occurred. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     The objects and features of the invention will become apparent from a reading of a detailed description, taken in conjunction with the drawing, in which: 
     FIG. 1 is a cross sectional view of a portion of an engine block demonstrating incorrect piston installation; 
     FIG. 2 is a functional block diagram showing an end view of a test station and the engine block to be tested; 
     FIG. 3 is a functional block diagram showing a view taken along arrow  3  of FIG. 2 of the test station of FIG. 2; 
     FIG. 4 is a view taken along arrow  4  of FIG. 3 of a mounting plate for two of the sensors used in the test station of FIGS. 2 and 3; 
     FIG. 5 is a flowchart setting forth the procedure by which the type and location of engine assembly error is determined in accordance with the principles of the invention; and 
     FIG. 6 is a top view of a typical V-8 engine setting forth the numerical designation of the cylinders in relation to four vibration sensors positioned on the engine. 
    
    
     DETAILED DESCRIPTION 
     As discussed briefly above, FIG. 1 shows a cylinder  102  in which the associated piston head  110  has been inserted upside-down. Under this condition, the incorrect installation results in the piston contacting the cylinder at points  111  and  112 , which will create a knocking or slapping condition as the piston head follows its associated connecting rod  108  along its stroke path. Likewise, when a bearing normally lying between the crankshaft  106  and connecting rod  108  is missing, a relatively violent knock condition will exist. We have discovered that the vibrations initiated by either or both of these assembly errors may be utilized in deriving information as to the nature and location of the assembly fault 
     With reference to FIGS. 2 and 3, test station  200  receives at least partially assembled engine blocks  100  transported to the station by a conveyor  250 . Upon arrival at station  200 , engine  100  is lifted from conveyor  250  by means not shown so as to isolate engine  100  from any noise and vibrations emanating from other positions along the conveyor belt. This action results in an isolation gap  230  between block  100  and conveyor  250 . Next, pneumatic cylinders  384   a  and  384   b  move mounting plates  186   a  and  186   b , respectively, toward opposite ends of engine block  100  to place four sensors  220   a ,  220   b ,  220   c  and  220   d  in contact with predetermined locations on the external surfaces of engine block  100 . Additionally, mounting plate  186   b  moves a drive coupling element  382  into engagement with crankshaft  380  (having an axis of rotation at  210  of FIG. 2) of engine  100 , thereby coupling shaft  380  to the drive shaft of electric servo motor  370 . 
     Motor  370  is then started and brings crankshaft  380  up to a predetermined rotational speed, for example 120 rpm. At this point, if there are any assembly errors involving the connecting rod bearings or piston heads of motor  100 , knock-like vibrations will be detected by each of the sensors  220   a , 220   b ,  220   c  and  220   d . (It will be understood that sensor  220   d  is not visible in the views of FIGS. 2 and 3.) Assembly irregularities will thus be manifested at the output of the sensors as a series of noise spikes or “clicks”. Stored program computer  360  collects the analog outputs from sensors  220   a-d  via data buses  390   a , 390   b ,  390   c  and  390   d , respectively. Analog to digital converter card  362  associated with computer  360  converts the sensor outputs to digital signal signatures for analysis by computer  360  via the methods of this invention to be described below. 
     Sensors  220   a-d  may comprise any mechanical- to -electrical transducer capable of converting mechanical vibrations to electrical signals. In a preferred embodiment, sensors  220   a-d  comprise accelerometers, such as the model no. 353B65, commercially available from PCB Piezotronics, Inc. of Depew, N.Y. Alternatively, sensors  220   a-d  could comprise piezoelectric devices or conventional microphones. Other types of equivalent transducers may be selected by those of ordinary skill in the art. 
     FIG. 4 depicts a front elevational view of mounting plate  186   a  of FIG.  3 . Accelerometer sensors  220   a  and  220   b  are shown mounted in the center of triangular plates  402  and  404  attached to plate  186   a . It is to be understood, however, that mounting portions for the sensors could be an integral part of mounting plate  186   a . Preferably, the sensors are spring loaded in their mounting positions to assure proper physical contact with the engine block upon movement by pneumatic cylinders  384   a  and  384   b  of the plates  186   a  and  186   b  into engaging position wit h the engine block  100 . 
     Due to the positioning of the accelerometer sensors  220   a-d  with respect to the engine block  100 , the amplitude of the vibrational spikes or clicks will vary from sensor to sensor, depending upon the location(s) of the assembly error(s). This fact is utilized by an analysis method in computer  360  in determining the nature of any assembly error and its location within engine block  100 . A preferred location of the sensors is at the ends of the engine block at positions externally adjacent to cooling water channels formed in the interior of the block. 
     FIG. 5 sets forth a flow chart diagram for a method of determining whether the engine has been assembled properly, and, if not, the nature of the assembly error and its location. With reference to FIG. 5, the routine starts at block  501  and proceeds to block  503  where data from the four vibration sensors  220   a-d  (FIGS. 2-4) is collected, and the sampled and digitized outputs thereof are placed in four linear arrays of data. A sampling rate of 10,000 samples/second has been found to produce acceptable results. 
     The data collection at block  503  continues by examining each array for the maximum and minimum digital sample values in each array. The minimum value in each array is subtracted from the maximum value in the same array to obtain a “span” for each sensor output. Hence the span value for each sensor represents the maximum sensor output signal excursion for that sensor. 
     Next, the array with the greatest signal transition, or span P 1 , is compared to a predetermined limit value, or threshold T 1 , at decision block  505 . If the maximum span value P 1  is greater than the predetermined limit T 1 , then the routine recognizes that the sensed vibration levels are abnormally high, thereby indicating that an assembly error has occurred. If the maximum span P 1  is less than the predetermined amount T 1 , then the routine passes to block  507 , and the test is completed with an indication that the engine has been successfully assembled. 
     When the predetermined limit has been exceeded, the routine proceeds to decision block  509 , where the amount by which the maximum span value exceeds a second predetermined noise value T 2  is compared to a predetermined percentage of full-scale. If this excess value is greater than the predetermined percentage of full-scale, then the routine proceeds to block  511  to be described below. If the span value excess is not greater than the predetermined percentage of full-scale, then the rutine proceeds to block  517 , where it is determined that a piston has been installed backwards, leading to the above-described piston slap condition. 
     Once it has been determined that a piston has been improperly installed at block  517 , the routine proceeds to decision block  519 . At decision block  519 , the sensor output having the greatest span P 1  is compared to the sensor output having the next greatest span P 2 . If the difference between these two spans is greater than a predetermined percentage of full-scale, than the routine proceeds to block  525  and indicates that a piston nearest the ends of the engine block, or an “outside” piston is involved. If the greatest and next greatest spans fail the comparison test set forth in decision block  519 , then the routine proceeds to block  521 , where an indication is generated that a piston furthest away from the four sensors, or an “inside piston” is involved. 
     Whether an inside or outside piston is involved, the routine then winds up at block  527 , where the location of the cylinder is determined using the relative magnitudes or spans of the signals of the vibration sensor having the greatest output and vibrations of the sensor having the next greatest output. 
     Once the specific cylinder location is determined, as described below, the routine exits at  529  with an indication that the engine has been improperly assembled, and the location of the assembly error. 
     Returning to decision block  509  of FIG. 5, if the sensor output having the greatest span magnitude is greater than the predetermined noise limit T 2  by a predetermined percentage of full-scale, then the routine proceeds to block  511 , and indicates that a connecting rod bearing is missing. 
     From block  511  the routine will then proceed to decision block  513  where the greatest span value P 1  is compared to the next greatest span value P 2 . If this comparison results in a difference greater than a predetermined percentage of fullscale the routine proceeds to block  515  and indicates that an outside piston is involved in the assembly error. If the comparison to the predetermined percentage of full-scale leads to the result that the difference is less than the percentage of full-scale, than the routine proceeds to block  523  where an inside piston is indicated to be the source of the assembly error. 
     Once the determination of whether an inside or an outside piston is involved has been made, the routine proceeds to block  527 , where, again, the specific cylinder involved in the assembly error is determined by analyzing the span, or maximum amplitude excursion of various sensor signals. 
     The determination of the location of the assembly fault at block  527  of FIG. 5 is best understood by considering the top view of a typical V-8 engine block  100  of FIG.  6 . With reference to FIG. 6, the four vibration sensors  220   a-d  are shown mounted at opposite ends of engine  100 . Cylinders  1 ,  3 ,  5  and  7  are located at the left hand of the V, and cylinders  2 ,  4 ,  6  and  8  are positioned as shown at the right hand of the V. 
     Knowing the relative positions of cylinders  1  through  8 , the routine set forth in FIG. 5 utilizes the relative maximum amplitude of the signals from sensors  220   a-d  to determine the location of the assembly fault. “Inside cylinders” are those furthest from either end of engine  100 - namely, cylinders  3 ,  5 ,  4  and  6 . “Outside cylinders” are those nearest to the vibration sensor array at either end of engine  100 - namely, cylinders  1 ,  2 ,  7  and  8 . 
     The method of block  527  of FIG. 5, knowing the pattern of inside and outside cylinders, utilizes the relative magnitudes, or spans, of the four sensors  220   a-d  to pinpoint the cylinder or cylinders in which an assembly problem has occurred. 
     If the sensor with the greatest span value is to  200   a  and the method of FIG. 5 has determined that an inside cylinder is involved, then the routine identifies the location of the problem as cylinder  3 , since cylinder  3  is the closest inside cylinder to sensor  220   a . Similarly, if the sensor with the greatest span value is  220   b , then cylinder  5  is the location of the assembly error. If sensor  220   c  yields the greatest span value, then cylinder  4  is the location of the assembly error. Finally, if sensor  220   d  as the greatest span value, then cylinder  6  is the location of the assembly fault. 
     In a similar manner, if the routine of FIG. 5 determines that an outside cylinder is the location of an assembly error, then the routine will associate the sensor with the maximum value with a corresponding cylinder, as follows. If the sensor  220   a  has the maximum span, then cylinder  1  is the location of the assembly error. If sensor  220   b  has a maximum span value, then cylinder  7  is the location of the fault. If sensor  220   c  has the greatest span value, then cylinder  2  is the location of the assembly error. Finally, if censored  220   d  has the greatest span value, then the routine knows that cylinder  8  is the location of the assembly error. 
     The invention has been described with reference to an exemplary embodiment for the sake of example only. The scope and spirit of the invention is to be determined from a proper interpretation of the appended claims.