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  Grinding wheel spindleUSPTO Application #: 20060286908Title: Grinding wheel spindle Abstract: A spindle for a grinding wheel which is to grind re-entrant cams on camshafts is described, comprising a drive motor, a shaft extending from the motor at the end of which is mounted a grinding wheel, and a rigid elongate casing extending from the motor and encasing the shaft. The length of the shaft and casing is selected to be at least as long as the axial length of cam shafts to be ground by the wheel. The shaft is carried in three hydrostatic bearings. One bearing is located near the grinding wheel at the end of the rigid casing remote from the motor. The assembly increases the shaft stiffness and its resistance to bending. A second bearing is located at the inboard end of the shaft and the third bearing is located within the motor at the far end of the shaft. The length of the rotor-bearing part is shorter than the external part of the shaft, which is constructed so that the stiffness and the support of the shorter part of the shaft dictate that the bending resonance of the longer external part is above the critical spindle rotational frequency. The motor housing is symmetrical and includes a water cooling jacket in which water follows a helical path around the motor, to avoid cooling one side of the motor more than another. The spindle is constructed to be axisymmetrical, so that any heat generated within the bearings dissipates radially and uniformly into the surrounding material. Oil is supplied under pressure to the bearings by a pump from a reservoir to which oil returns from the bearings. The oil is heated in each bearing and the heated oil drains into lower regions of the enclosure formed by the shaft casing and motor housing. The lower regions of this enclosure constitute a separate oil collection box mounted so as not to strain the shaft. A thermal barrier is provided between the upper and lower regions of the enclosure. During assembly the internal bores of two of the bearings are initially aligned and the third bearing is adjusted radially to bring all three bores into alignment. (end of abstract)
Agent: Barnes & Thornburg LLP - Chicago, IL, US Inventors: James Andrew Chaundler, Walter Maximillian Markus Knuefermann USPTO Applicaton #: 20060286908 - Class: 451181000 (USPTO) Related Patent Categories: Abrading, Machine, Rotary Tool, Rotary Cylinder, Internal, Abrading Crank-pin The Patent Description & Claims data below is from USPTO Patent Application 20060286908. Brief Patent Description - Full Patent Description - Patent Application Claims
BACKGROUND [0001] Automotive engine designers have realised that a better performing engine can be achieved by modification of the camshaft lift profile. Thus the profile of that part of the cam which controls the actual opening and closing of the valve, is modified from a conventional flat or convex shape so as to possess a concave region. A camshaft of this type is known as having a re-entrant profile. [0002] This type of profile manifests itself on the cam lobe as a depression in the lift/closure flank of the cam, which can only be produced with a grinding wheel whose external radius is the same as, or more preferably smaller than, the minimum radius of the cam form. Non re-entrant cam profiles can of course be ground with wheels of unlimited radius. [0003] A number of issues are faced when designing grinding wheel spindles for this task; [0004] 1. Due to the small grinding wheel diameter, the spindle speed has to be proportionally higher to maintain a satisfactory wheel surface speed. [0005] 2. The grinding wheel must be capable of reaching the base circle diameter of each cam lobe, and in particular a cam lobe at the end of a camshaft remote from the spindle housing, while allowing the tips of other lobes to rotate clear of the spindle body is situated parallel to the camshaft. Therefore the spindle shaft is restricted in diameter to allow this clearance. [0006] It is therefore necessary for the rotating shaft to be long, to be of small diameter and to be able to run at high rotational speeds. [0007] Spindle design considerations dictate that the first resonant bending mode for a rotating shaft should reside beyond the maximum spindle rotating frequency. This arises from the observation that as spindle speed approaches its resonant frequency, resonance can be excited and spindle performance will be affected, often to the point of failure. [0008] Hitherto this problem has usually been avoided by arranging that the resonant frequency of the spindle is as high as possible. Conventionally this has been achieved by using shafts which are short in axial length and have as large a diameter as is practical. [0009] This is the very antithesis of the requirements for a grinding wheel spindle which is adapted to grind re-entrant cam profiles. SUMMARY OF INVENTION [0010] According to the present invention there is provided a spindle for a grinding wheel which is to grind re-entrant cams on camshafts comprising a drive motor, a shaft extending from the motor at the end of which is mounted a grinding wheel, and a rigid elongate casing extending from the motor and encasing the shaft, wherein the length of the shaft and casing is selected to be at least as long as the axial length of cam shafts to be ground by the wheel, the shaft is carried in three bearings each of which is a hydrostatic bearing, and one of the bearings is located near the end of the shaft carrying the grinding wheel so as to be at the end of the rigid casing remote from the motor, thereby to increase the shaft stiffness and increase its resistance to bending. [0011] A second bearing may be located at the inboard end of the external part of the shaft, and the third bearing is located within the motor at the said other end of the shaft. [0012] Typically the shaft is constructed so as to have at least two different diameters, and that part of the shaft which extends within the motor has a greater diameter than does that part of the shaft which extends axially externally therefrom. [0013] The grinding wheel is preferably demountably fixed to the shaft. [0014] The motor is usually an electric motor, and the stator of the motor is preferably secured within a rigid housing. [0015] The non-rotating element of each of the three bearings is preferably secured within either the rigid elongate casing or the rigid motor housing. [0016] According to a preferred aspect of the invention the axial length of the rotor-bearing part of the shaft is shorter than the external part of the shaft, and the shaft is constructed so that the stiffness and the support of the shorter part of the shaft situated between the second and third bearings dictate that the bending resonance of the longer external part is above the critical spindle rotational frequency [0017] Preferably a symmetrical design of housing is employed for the motor. [0018] As already stated, traditionally a grinding wheel spindle shaft has only been supported by two bearings and therefore bearing alignment has not been an issue. However, if three bearings are to be employed, alignment of the three bearings is very important. Where hydrostatic bearings are involved this is a very real problem since typically hydrostatic bearings have radial clearances (and therefore an oil film thickness) of the order of 25 microns, and if vibration is not to be introduced due to misalignment, any adjustment mechanism to achieve alignment needs to be capable of microscopic movements much smaller than the hydrostatic film thickness. [0019] According therefore to another aspect of the present invention, during assembly the internal bores of two of the bearings are initially aligned and then the third bearing is then adjusted radially to bring all three bores into alignment. [0020] However, alignment of the bearings is not restricted to ensuring their alignment during assembly, since at the high speeds required of grinding processes using small wheels, considerable heat can be generated within the bearings, and the spindle can also become heated by heat from the grinding wheel at one end and the electric motor (when under load) at the other end. This can result in variations in the spindle temperature in a non-axisymmetrical manner, resulting in bending due to differential thermal expansion taking place. This can result in misalignment of the spindle shaft and the bearings. This is particularly the case if the differential thermal expansion is occurring in different radial regions of the spindle structure. [0021] Using a Symmetrical Design of Housing for the Motor Assists [0022] Preferably the motor housing includes a water cooling jacket in which water is forced to follow a helical path around the motor, so as to avoid cooling one side of the motor more than another. [0023] Preferably the spindle is constructed to be axisymmetrical, so that any heat generated within the bearings dissipates radially into the surrounding material in a uniform manner, so that in use the spindle housing will tend to warm up and cool down uniformly, and therefore expand and contract uniformly. [0024] In use, oil is supplied under pressure hydrostatic to the bearings by a pump which draws oil from a reservoir to which oil returns from the bearings the oil becomes heated in each bearing and the heated oil drains into lower regions of the enclosure formed by the rigid elongate shaft casing and the motor housing. As a result the lower regions of the enclosure can become heated in use to a higher temperature then the upper regions thereof Continue reading... Full patent description for Grinding wheel spindle Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Grinding wheel spindle patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. 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