Straight-cut motor shaft with pinned eccentric

Abstract

An electro-hydraulic pump assembly for a controlled braking system utilizes an eccentric pump drive apparatus including a pump drive shaft having a first end thereof adapted for attachment of an eccentric, and an eccentric attached to the first end of the pump drive shaft. The pump drive shaft defines a centerline thereof, and a bore extending from a first end of the shaft parallel to and displaced an offset distance from the centerline. The eccentric includes a drive element and a stem extending from the drive element for a press fit into the bore of the shaft. The bore extends into the shaft beyond the end of the stem of the eccentric, forming a void inside the shaft for balancing the shaft so that no counterweights need to be added to the eccentric drive apparatus. The pump drive shaft and eccentric are fabricated from straight-cut cylindrical stock by simple turning, drilling, and cylindrical grinding operations.

We claim:  
     
         1 . An eccentric pump drive apparatus comprising: 
 a pump drive shaft having a first end thereof adapted for attachment of an eccentric; and    an eccentric attached to the first end of the pump drive shaft.    
     
     
         2 . The eccentric pump drive apparatus of  claim 1  wherein the eccentric is attached to the first end of the shaft with a press fit.  
     
     
         3 . The eccentric pump drive apparatus of  claim 1  wherein: 
 the shaft defines a centerline thereof and a bore extending from the first end of the shaft parallel to and displaced an offset distance from the centerline; and  
 the eccentric includes drive element thereof and a stem extending from the drive element for a press fit into the bore of the shaft.  
 
     
     
         4 . The eccentric pump drive apparatus of  claim 3  including a motor rotor attached to the shaft.  
     
     
         5 . The eccentric pump drive apparatus of  claim 3  further including a bearing on the drive element of the eccentric.  
     
     
         6 . The eccentric pump drive apparatus of  claim 5  including a motor rotor attached to the shaft.  
     
     
         7 . The eccentric pump drive apparatus of  claim 5  wherein the bearing is a needle bearing press fitted onto the drive element.  
     
     
         8 . The eccentric pump drive apparatus of  claim 7  wherein the eccentric includes a flange at the distal end thereof for retaining the bearing on the drive element of the eccentric.  
     
     
         9 . The eccentric pump drive apparatus of  claim 3  wherein the eccentric defines a mass offset from the centerline of the shaft, and the bore includes a portion thereof extending into the shaft a distance beyond the stem to such a length from the first end of the shaft that the eccentric pump drive apparatus is rotationally balanced about the centerline of the shaft.  
     
     
         10 . The eccentric pump drive apparatus of  claim 9  including a motor rotor attached to the shaft.  
     
     
         11 . The eccentric pump drive apparatus of  claim 9  wherein the eccentric and bearing define a mass offset from the centerline of the shaft, and the portion of the bore extending into the shaft extends a distance beyond the stem to such a length from the first end of the shaft that the eccentric pump drive apparatus is rotationally balanced about the centerline of the shaft, to thereby compensate for the offset mass of the eccentric and bearing.  
     
     
         12 . The eccentric pump drive apparatus of  claim 11  including a motor rotor attached to the shaft.  
     
     
         13 . A pump assembly comprising: 
 an electric motor having a rotor defining an axis of rotation; and    an eccentric pump drive apparatus including a pump drive shaft attached to the rotor for rotation about the axis of rotation and having a first end thereof adapted for attachment of an eccentric, and an eccentric attached to the first end of the pump drive shaft.    
     
     
         14 . The pump assembly of  claim 13  wherein the eccentric is attached to the first end of the shaft with a press fit.  
     
     
         15 . The pump assembly of  claim 13  wherein: 
 the shaft defines a centerline thereof extending along the axis of rotation and a bore extending from the first end of the shaft parallel to and displaced an offset distance from the centerline; and  
 the eccentric includes a drive element thereof and a stem extending from the drive element for a press fit into the bore of the shaft.  
 
     
     
         16 . The pump assembly of  claim 15  wherein the eccentric defines a mass offset from the centerline of the shaft, and the bore includes a portion thereof extending into the shaft a distance beyond the stem to such a length from the first end of the shaft that the eccentric pump drive apparatus is rotationally balanced about the centerline of the shaft.  
     
     
         17 . The pump assembly of  claim 15  wherein the eccentric drive element includes a bearing on the drive element of the eccentric.  
     
     
         18 . The pump assembly of  claim 17  wherein the eccentric and bearing define a mass offset from the centerline of the shaft, and the portion of the bore extends into the shaft a distance beyond the stem to such a length from the first end of the shaft that the eccentric pump drive apparatus is rotationally balanced about the centerline of the shaft, to thereby compensate for the offset mass of the eccentric and bearing.  
     
     
         19 . A method for fabricating an eccentric pump drive apparatus, the method comprising: 
 fabricating a pump drive shaft having a first end thereof adapted for attachment of an eccentric, and    attaching an eccentric to the first end of the pump drive shaft.    
     
     
         20 . The method of  claim 19  wherein the shaft defines a centerline thereof, and the method further comprises: 
 forming a bore in the shaft extending from the first end of the shaft parallel to and displaced an offset distance from the centerline;  
 forming the eccentric to include a drive element thereof and a stem extending from the drive element; and  
 inserting the stem of the eccentric into the bore.  
 
     
     
         21 . The method of  claim 20  wherein the drive element defines a mass, and the method comprises: 
 extending the bore into the shaft a distance beyond the stem to such a length from the first end of the shaft that the eccentric pump drive apparatus is rotationally balanced about the centerline of the shaft.  
 
     
     
         22 . The method of  claim 21  further comprising attaching a motor rotor to the shaft.  
     
     
         23 . The method of  claim 21  further comprising installing a bearing on the drive element of the eccentric.  
     
     
         24 . The method of  claim 23  wherein the eccentric and bearing define a mass offset from the centerline of the shaft, and the method comprises: 
 extending the bore into the shaft a distance beyond the stem to such a length from the first end of the shaft that the eccentric pump drive apparatus is rotationally balanced about the centerline of the shaft.  
 
     
     
         25 . The method of  claim 24  further comprising attaching a motor rotor to the shaft.