192 clutches and power-stop control – Field responsive frictional media type
Reexamination Certificate
1999-12-29
2001-09-18
Lorence, Richard M. (Department: 3681)
192 clutches and power-stop control
Field responsive frictional media type
C192S052400, C417S319000
Reexamination Certificate
active
06290043
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
This invention relates to the field of clutches for a compressor in an air conditioning system. More particularly, the invention pertains to such a clutch having soft start characteristics.
2. Description of the Prior Art
A compressor for an air conditioning system of an automobile typically includes a clutch to enable disengagement of the compressor during periods in which no air conditioning is desired. During demand situations, the clutch is engaged so that the compressor compresses the refrigerant in a known manner. Prior art clutches typically are of an electromagnetic friction clutch construction. A compressor typically is driven by a V-groove pulley assembly supported by a bearing pressed onto the body of the compressor. The pulley is driven by the automotive accessory drive belt.
Prior art clutches typically include an armature affixed to the splined shaft of the compressor via a bolt. A stationary wire coil assembly is press-fit to the compressor housing. The armature is normally separated by a small air gap from the pulley face by a spring mechanism, so that the clutch is normally disengaged. Automotive voltage is applied to the coil to engage the clutch, normally having a nominal value of 14.4 volts. Upon application of this voltage, the current in the coil increases from zero on a time scale related to the inductive time constant of the clutch, typically
150
milliseconds. The current induces magnetic flux to flow in the pulley, across the air gap, and into the armature. When the magnetic flux density reaches a critical level, the attractive force between the armature and the pulley becomes large enough to overcome the spring force holding the armature away from the pulley. The armature is then rapidly drawn into contact with the pulley, suddenly initiating torque transfer to the compressor and causing the compressor shaft to begin to rotate. When the shaft speed matches the pulley speed, the torque then reaches a steady-state level that is a function of pulley speed, cooling demand, and other vehicle operational characteristics.
When such a prior art clutch is engaged, undesirable effects can occur, including stumble, surge, and noise. Stumble is a longitudinal vehicle vibration induced by the sudden change in engine torque demand which occurs upon compressor engagement. Surge is a lurch that occurs when the clutch is disengaged. Noise is generated as the armature of the electromagnetic friction clutch is rapidly driven into contact with the clutch pulley during engagement. These effects of rapid compressor engagement are objectionable to the vehicle occupants and may contribute to premature failure of compressor components. Previous efforts to overcome these concerns include using passive mechanical means, such as mating slots or other structures provided in the pulley and armature, which are said to reduce the rate of increase of magnetic force. An example of this is illustrated in U.S. Pat. No. 4,749,073 to Olden.
Another attempt to reduce these concerns includes the insertion of an elastomeric coupling between the armature and compressor shaft to damp transients encountered during engagement and operation, as shown in U.S. Pat. No. 5,219,273 to Chang. Other attempts to reduce these concerns include electronic controls of the clutch current in an attempt to produce soft-start coupling, as described in U.S. Pat. No. 4,509,091 to Booth and U.S. Pat. No. 4,567,975 to Roll. These patents disclose a method of generating a time-varying clutch current. These methods draw the armature initially to the pulley, but allow the pulley to slip. The clutch current is increased smoothly to gradually increase the level of torque transfer and decrease the slip until a state of complete engagement is reached. These methods permit slip, which causes the electromagnetic friction clutch surfaces to become burnished over time, reducing the ability of the clutch to transfer torque.
It would therefore be desirable to provide a clutch which softens the engagement of an air conditioning compressor, but which does not cause excessive wear of the clutch friction surfaces.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide, in an air conditioning compressor a clutch having a soft start which does not experience excessive wear.
An advantage of the use of a clutch according to the present invention is that the air conditioning system will have less objectionable noise and vibration. A second advantage is that, by reducing the objectionable characteristics of such a system, one may cycle the clutch more frequently and thereby maximize fuel efficiency and optimally control the temperature of the passenger compartment.
Further advantages include having the ability to operate the compressor at high speeds. With conventional clutches, operation at high engine RPMs causes undesirable noise. With a clutch according to the present invention, the clutch may be slipped, permitting lower RPM operation for a given input speed.
The present invention concerns an electromagnetic clutch for an air conditioning compressor housed in a compressor housing having a drive shaft extending from the housing and being rotatable about an axis of rotation. The clutch includes a generally cylindrical driving member having an axis of rotation and a peripheral annular first frictional surface, an annular driven member extending about the driving member and having an axis of rotation coaxial with the driving member axis of rotation, the driven member having an annular second frictional surface positioned radially adjacent the first frictional surface to form an annular space therebetween, a quantity of flowable magnetic material provided in the annular space, a magnetic coil positioned adjacent the annular space and control means connected to the magnetic coil for supplying electrical power from a power supply to energize the magnetic coil. When the driven member is attached to the compressor shaft, the driving member is rotatably mounted on the compressor housing and the magnetic coil is fixed to the compressor housing, the driving member can be rotated without rotating the driven member. When the control means applies electrical power to the magnetic coil, magnetic flux is created in the annular space polarizing the magnetic material and frictionally coupling the first and second frictional surfaces to cause the driving member to rotate the driven member. The control means can pulse width modulate the supplied power for “soft” starting and/or stopping of the compressor.
REFERENCES:
patent: 4849120 (1989-07-01), Price et al.
patent: 4898266 (1990-02-01), Garrett et al.
patent: 4967887 (1990-11-01), Annacchino et al.
patent: 5469947 (1995-11-01), Anzai et al.
patent: 5816372 (1998-10-01), Carlson et al.
patent: 5985168 (1999-11-01), Phule
Cohen Alex David
Elie Larry D.
Ginder John M.
Harte Shane A.
Khetarpal Vipen
Lorence Richard M.
Shelton Larry I.
Visteon Global Technologies Inc.
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