CN107035786B - Method for reducing noise during clutch engagement - Google Patents

Abstract

The present invention provides a method for reducing noise when a clutch is engaged by a method and system for driving an accessory shaft from a pulley driven by a drive member in a vehicle. Wherein, the driving method comprises the following steps: energizing the electromagnetic unit by passing a selected voltage/current through the electromagnetic unit; using the energized electromagnetic unit to draw the armature into engagement with the friction surface, which in turn causes engagement of the clutch, which in turn operatively connects the pulley to the accessory shaft, wherein the voltage/current transmitted through the electromagnetic unit is selected such that a speed of the armature when engaged with the friction surface remains below a selected speed, wherein the selected speed is selected such that a sound level of an impact to the friction surface when the armature is engaged with the friction surface is substantially inaudible in a passenger compartment of the vehicle.

Description

Method for reducing noise during clutch engagement

Cross reference to related applications

This application claims the benefit of U.S. provisional patent application No. 62/204,365 filed on 12/8/2015.

Technical Field

The present disclosure relates to clutch drives, and in particular to control systems to control associated clutch mechanisms.

Background

Clutches are useful devices for controlling the operable connection between a driving element, such as an engine crankshaft in a vehicle, and a driven element, such as an accessory in a vehicle, for example, a supercharger, alternator, water pump, or any other suitable accessory. However, many clutches currently suffer from a number of problems.

Of particular note, audible contact sounds may emanate from the clutch assembly, such as when strong mechanical contact is made between operatively associated surfaces. Audible contact sounds are often noticeable during idle operating conditions and may add to the overall noise, vibration, and harshness (NVH) profile of the vehicle.

It would be advantageous to provide a clutch that at least partially addresses one or more of these issues.

Disclosure of Invention

In one aspect, a method for driving an accessory shaft from a pulley driven by a drive member in a vehicle is provided. The method comprises the following steps: energizing the electromagnetic unit by passing a selected current through the electromagnetic unit; an energized electromagnetic unit is used to pull the armature into engagement with the friction surface, which in turn causes engagement of the clutch, which in turn operatively connects the pulley to the accessory shaft. The current transmitted through the electromagnetic unit is selected such that a speed of the armature when engaged with the friction surface remains below a selected speed, wherein the selected speed is selected such that a sound level of an impact to the friction surface when the armature is engaged with the friction surface is substantially inaudible in a passenger compartment of the vehicle.

According to another aspect, provided is a system for driving an accessory shaft from a pulley driven by a drive member in a vehicle. The system includes an electromagnetic unit, an armature, a clutch, and a control system. The control system is programmed to transmit a selected current through the electromagnetic unit to draw the armature into engagement with the friction surface, which in turn causes engagement of the clutch, which in turn operatively connects the pulley to the accessory shaft. The current transmitted through the electromagnetic unit is selected such that a speed of the armature when engaged with the friction surface remains below a selected speed, wherein the selected speed is selected such that a sound level of an impact to the friction surface when the armature is engaged with the friction surface is substantially inaudible in a passenger compartment of the vehicle.

Drawings

The foregoing and other features and advantages will be apparent from the following description of the present disclosure as illustrated in the accompanying drawings. The accompanying drawings, which are incorporated herein and form a part of the specification, further serve to explain the principles of the disclosure and to enable a person skilled in the pertinent art to make and use the disclosure. The figures are not drawn to scale.

FIG. 1 is a side cross-sectional view of a clutch assembly associated with an accessory according to an embodiment of the present invention;

FIG. 2a is an exploded perspective view of the clutch assembly shown in FIG. 1;

FIG. 2b is another exploded perspective view of the clutch assembly shown in FIG. 1;

FIG. 3 is a side cross-sectional view of the clutch assembly shown in FIG. 1, with the clutch assembly in a disengaged position;

FIG. 4 is a side cross-sectional view of the clutch assembly shown in FIG. 1, with the clutch assembly in an engaged position;

FIGS. 5a and 5b are enlarged exploded perspective views of a portion of the clutch assembly shown in FIG. 1;

FIG. 6 is a schematic diagram of a portion of a control system;

FIG. 7 is a flow chart illustrating a method of controlling the clutch assembly shown in FIG. 1;

FIG. 8a is a graph showing a voltage/current profile for a momentary on/off actuation sequence;

FIG. 8b is a graph showing a voltage/current profile for a pulse width modulated on/off actuation sequence;

FIG. 9 is a graph showing a series of ramp profiles (based on increasing time periods) to be tested to determine an optimal activation time period;

FIG. 10 is a graph showing the relationship between ramp profile to be tested and loudness for activation and deactivation of command signals;

FIG. 11a is a graph showing the sound pressure profile of the instantaneous on/off actuation sequence;

FIG. 11b is a graph showing the sound pressure profile of a pulse width modulated on/off actuation sequence;

FIG. 12a is a graph illustrating an exemplary standard thermal management algorithm as may be applied to a switchable water pump;

FIG. 12b is a graph illustrating a modified thermal management algorithm as may be applied to a switchable water pump, wherein the number of SWP activation events is reduced; and

fig. 13 is a graph showing activation command signals, PWM signals, and resultant forces on the armature with gradually changing duty cycles of voltage and current to the armature.

Detailed Description

Specific embodiments of the present disclosure are now described with reference to the drawings, wherein like reference numbers indicate identical or functionally similar elements. The following detailed description is merely exemplary in nature and is not intended to limit the disclosure or the application and uses of the disclosure. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding technical field, background, brief summary or the following detailed description.

Clutch assembly

Referring to FIG. 1, an exemplary clutch assembly 10 is shown. The clutch assembly 10 is adapted for selectively transmitting power from a drive member, such as a belt, timing belt, chain, gear, or any other suitable drive member (not shown), to the accessory 20. The clutch assembly 10 may be mounted to an accessory housing 22 (as illustrated in fig. 1), and the clutch assembly 10 is operable to selectively connect a drive member to a shaft 24 of the accessory 20. The shaft 24 is rotatable about an axis a. The accessory 20 may be any suitable accessory, such as a supercharger, alternator, water pump, fan, air conditioning compressor, power steering pump, vacuum pump, air compressor, hydraulic motor, power take-off, or backup generator.

Referring now to fig. 2a to 4, the clutch assembly 10 includes first and second clutch members 30, 32, both of which clutch members 30, 32 are rotatable about axis a, a wrap spring clutch 34, an armature 36, an actuator 38 and an electromagnetic unit 40. The clutch assembly 10 may be constructed of relatively few components and the clutch assembly 10 can be used to selectively transmit power from the drive member to the accessory 20 with very little power.

The clutch assembly 10 is movable from the disengaged position shown in fig. 3 to the engaged position shown in fig. 4 by transmitting magnetic flux from the electromagnetic unit 40 through the first clutch member 30, the armature 36 and back into the electromagnetic unit 40. The clutch assembly 10 may be referred to as engaged when the clutch assembly 10 is in the engaged position, and the clutch assembly 10 may be referred to as disengaged or not engaged when the clutch assembly 10 is in the disengaged position.

The first clutch member 30 is driven by a drive member such as a belt, timing belt, chain, gear, or any other suitable drive member. The drive member itself may be driven by any suitable means, for example by the crankshaft of an engine in a vehicle. In the illustrated embodiment, the first clutch member 30 includes a pulley (pulley)42, but may also include some other member, such as a sprocket, a gear, or any other suitable member. The first clutch member 30 may be made of any suitable material, such as a suitable steel. The first clutch member 30 may be rotatably supported on a stationary member 44 via one or more bearing members 46, which stationary member 44 may be referred to as an electromagnetic unit support member. In this embodiment, two bearing members 46 are provided, the two bearing members 46 being ball bearings, however any other suitable type of bearing member may be used.

In the disengaged position, the wrap spring clutch 34 is not engaged with the first clutch member 30, and the second clutch member 32 is operatively disengaged from the first clutch member 30 (i.e., the clutch assembly 10 is disengaged). In the engaged position, the wrap spring clutch 34 is radially enlarged into engagement with a radially inner surface 48, shown at 48, of the first clutch member 30, thereby operatively connecting the second clutch member 32 to the first clutch member 30 (i.e., the clutch assembly 10 is engaged).

The wrap spring clutch 34 has a first end 50 (best shown in fig. 5 a), a second end 52 (best shown in fig. 5b), and a plurality of helical coils 54 located between the first and second ends 50, 52. The second clutch member 32 is engaged with the first end 50 of the wrap spring clutch 34 by engagement of the clutch lugs with the helical end face 34 of the first end 50 of the wrap spring clutch 34. The first end 50 of the wrap spring clutch 34 may be retained in a recess 54 (fig. 5b) in the carrier, shown at 56.

The carrier 56 generally assists in maintaining the predetermined shape of the wrap spring clutch 34 and, in particular, assists the wrap spring clutch 34 in resisting undesired deformation during the time that the wrap spring clutch 34 transfers a relatively large torque from the first clutch member 30 to the second clutch member 32.

The carrier 56 may be made of any suitable material, such as plastic, or alternatively a metallic material.

Referring to fig. 3, the carrier 56 is retained in a carrier seat 58 in the second clutch member 32. The carrier 56 is driven in rotation about the axis a by the second clutch member 32 by means of engagement between a plurality of clutch lugs (not shown) on the second clutch member 32 and a plurality of lug slots 60 on the carrier 56. Although the arrangement of two clutch lugs and two lug wells 60 is illustrated, in some embodiments, a single clutch lug/lug well may be provided, or three or more clutch lugs/lug wells may be provided. Instead of providing the clutch lugs on the second clutch member 32 and the lug grooves on the carrier 56, it is also possible to provide the clutch lugs on the carrier 56 and the lug grooves on the second clutch member 32.

Referring to fig. 5b, the carrier 56 also includes a wrap spring clutch seat 62, on which the wrap spring clutch 34 is seated 62. The wrap spring clutch seat 62 terminates in the groove 54. The groove 54 ends at one of the lug slots 60. When the clutch lugs disposed on the carrier seat 58 of the second clutch member 32 are positioned in the lug slots 60, the first end 50 of the wrap spring clutch 34 directly engages one of the clutch lugs. Thus, the second clutch member 32 does not drive the wrap spring clutch 34 through the carrier 56, but directly drives the first end 50 of the wrap spring clutch. This is advantageous in that the helical end face 34a of the first end 50 of the wrap spring clutch 34 directly abuts (and is driven by) a metal surface (i.e., a clutch lug disposed on the carrier seat 58 of the second clutch member 32) rather than abutting the material of the carrier 56, which may be softer than the material of the second clutch member 32 and deformed by the helical end face 34a in the presence of a metal surface between the helical end face 34a and the clutch lug during high torque transmission.

The carrier 56 also includes a first portion 64 of an axially extending wrap spring clutch bearing surface 66. The first portion 64 of the surface 66 supports a portion of a radially inner surface (shown at 68) of the wrap spring clutch 34 (fig. 5 b).

The second clutch member 32 is driven by the first clutch member 30 when the clutch assembly 10 is engaged (fig. 4), and may idle when the clutch 10 is disengaged (fig. 3). The second clutch member 32 is connected to the input shaft 24 of the driven accessory. In the illustrated embodiment, the second clutch member 32 is in the form of a shaft extension.

The second clutch member 32 is mounted to the input shaft 24 as follows: the second clutch member 32 has a shaft mounting portion 70, the shaft mounting portion 70 having a cross-sectional shape that mates with the accessory input shaft 24 and rotationally fixes the second clutch portion 32 with the accessory input shaft 24. In the illustrated embodiment, the shaft mounting portion 70 is splined in cross-section (i.e., the shaft mounting portion 70 is splined) and interlocks with corresponding splines on the input shaft 24. The second clutch member 32 also includes an input shaft bore 72, the input shaft bore 72 receiving a threaded fastener 74 that passes through the input shaft bore 72 and threadingly engages an input shaft bore 76 in an end of the input shaft 24, thereby axially securing the second clutch member 32 to the input shaft 24.

To use the threaded fastener 74 and install it in the input shaft 24, a hole 78 is provided in the first clutch member 30. After installation of the first and second clutches, the cap 80 may be inserted into the bore 78 of the first clutch member 30.

The actuator 38, armature 36, wrap spring clutch 34 and carrier 56 are operatively engaged with one another. More specifically, the armature 36 is rotatably operatively connected with the second end 52 of the wrap spring clutch 34 (i.e., via the actuator 38 in the illustrated embodiment), the actuator 38 is rotatably operatively connected with the armature 36, the carrier 56 is rotatably operatively connected with the first end 50 of the wrap spring clutch 34 and the carrier 56 is rotatably operatively connected with the second clutch member 32.

Since the actuator 38, armature 36, wrap spring clutch 34, and carrier 56 are mounted to the second clutch 32, the actuator 38, armature 36, wrap spring clutch 34, and carrier 56 are stationary when the clutch assembly 10 is disengaged. Thus, when the clutch 10 is disengaged, the accessories 20 operatively associated with the second clutch 32 are stationary.

The actuator 38 is axially held in place at one end by an actuator retainer 80 and at the other end by a carrier retainer 82, wherein the actuator retainer 80 is secured to the second clutch 32 (e.g., by press-fitting) and the carrier retainer 82 is secured to the second clutch 32 (e.g., by press-fitting).

The electromagnetic unit 40 includes an electromagnet 84 and an electromagnetic unit housing 86. The electromagnetic unit housing 86 is connected to the electromagnetic unit support member 44 (i.e., the clutch housing 44) by any suitable means, such as by fasteners, press fit, stacking, etc.

When the first clutch member 30 is rotating and the second clutch 32 is stationary, the wrap spring clutch 34, the actuator 38, and the armature 36 are stationary with the second clutch 32. When it is desired to engage the clutch assembly 10 (i.e., to place the clutch in an engaged position to operatively connect the first clutch 30 to the second clutch 32), the electromagnetic unit 40 is energized, creating a magnetic flux in the first clutch 30. The magnetic flux draws the armature 36 axially into engagement with the friction surface 30a on the first clutch 30 with sufficient force to frictionally decelerate the armature 36 and the second end 52 of the wrap spring clutch 34 relative to the first end 50 of the wrap spring clutch 34. This movement of the second end 52 of the wrap spring clutch 34 radially expands the wrap spring clutch 34 into engagement with the wrap spring clutch engagement surface 48 of the first clutch member 30, thereby operatively connecting the first clutch member 30 with the second clutch member 32.

When the electromagnetic unit 40 is de-energized, there is no more magnetic flux in the first clutch member 30, or there may be a small amount of residual magnetic flux in the first clutch member 30. Thus, the engagement force between the armature 36 and the first clutch member 30 is greatly reduced, and can be reduced to zero without any residual magnetic flux in the first clutch member 30. Thus, the bias of the wrap spring clutch 34 urging the wrap spring clutch 34 toward its free state will overcome any frictional forces present between the armature 36 and the friction surface 30a of the first clutch member 30, and will therefore cause the wrap spring clutch 34 to contract and thus retract from the inner surface 48 of the first clutch member 30, thereby operatively disconnecting the first clutch 30 from the second clutch 32. The clutch assembly 10 may thus be referred to as "normally disengaged". This provides a failsafe feature such that the clutch assembly 10 does not drive the accessories 20 in the event that the clutch assembly 10 fails and the driving of the accessories 20 is undesirable or dangerous.

Control system

With respect to fig. 6, the clutch assembly 10 is operatively associated with the control system 100 to allow control of activation and deactivation of the clutch assembly 10. In particular, the control system 100 is used to control engagement of the wrap spring clutch 34 with the first clutch member 30. The control system 100 comprises a PCB 110 with a processor 115 and a memory 120 and a driver 125 for providing current to the electromagnetic unit 40. The control system 100 also incorporates a suitable communication link 130 into the vehicle's CAN data bus 135 and a power connection into the vehicle's battery (not shown). The communication link 130 may be provided as a wired connection or may be provided as a wireless link via any suitable wireless protocol, such as Zigbee. The control system 100 may be housed in an Engine Control Unit (ECU) or in a separate dedicated housing. The control system 100 may be located within the accessory 20. For example, the control system 100 may be housed within a housing provided for the electromagnetic unit 40. Typically, the control system 100 is positioned in a manner that protects it from mechanical damage and elements. As shown, the control system 100 is provided as part of an Engine Control Unit (ECU) 105.

It should be understood that the PCB 110 may include a voltage monitoring unit 140, a CAN message translator 145, and a PWM module 150 thereon. The CAN message translator 145 is used to receive messages from and send messages to the CAN data bus 135 of the vehicle. PWM module 150 is used to generate PWM signals that control the voltage/current profile sent to electromagnetic unit 40. Instead of the CAN message translator 145, a similar device configured to communicate over a different type of network (e.g., LIN) may be used. The control system 100 may include any suitable additional components, such as zener diodes and/or other diodes, that facilitate deenergizing the electromagnetic units, such as in a controlled manner.

Control algorithm

The control algorithm executed by the control system 100 is shown as a flow chart in fig. 7, with fig. 7 showing inputs and outputs to different parts of the control system. The control algorithm executed by the control system 100 may be referred to as the method 200 and may be stored in a memory of the control system such that the control system 100 is programmed to perform the activation/deactivation of the clutch assembly 40. The method is shown at 200 and begins at 202. At step 204, a management algorithm programmed into the ECU, such as a thermal management algorithm provided for the water pump, generates an activation command. The generation of the activate command by the thermal management algorithm will depend on various factors. For example, the activation command may be triggered based on feedback information received from various sensors placed at selected locations of the operating environment (i.e., thermal profile) of the contact engine. The activation command may also be triggered according to a predetermined activation profile for a detected operating condition, such as an idle operating condition, a cruise operating condition, or a high speed operating condition. The control system 100 may provide the ability to check selected parameters before activating the electromagnetic unit. Thus, at step 206, the selected parameters are checked, relating to the state of the engine, the voltage at the battery (not shown) of the vehicle, and any other suitable parameters. At step 208, the control system 100 determines whether to allow activation of the clutch 10 based on the checked parameters. For example, if the battery does not have sufficient charge to maintain the necessary current to the electromagnetic unit 40 for a sufficient amount of time, the processor 115 may determine that the clutch is not allowed to be engaged, in which case, at step 210, the control system 100 reports to the engine ECU 105 that the clutch assembly 10 will not be engaged. If activation is allowed, an activation command from the thermal management algorithm is transmitted to the drive control algorithm at step 212. At step 214, the actuator control algorithm instructs the control actuator 125 to energize the electromagnetic unit 40 of the clutch assembly 10.

As previously described, when the electromagnetic unit 40 is energized, a magnetic flux is generated in the first clutch member 30. The magnetic flux draws the armature 36 axially into engagement with the friction surface 30a of the first clutch 30 with sufficient force to frictionally decelerate the armature 36 and the second end 52 of the wrap spring clutch 34 relative to the first end 50 of the wrap spring clutch 34. This movement of the second end 52 of the wrap spring clutch 34 radially expands the wrap spring clutch 34 into engagement with the wrap spring clutch engagement surface 48 of the first clutch member 30, thereby operatively connecting the first clutch member 30 with the second clutch member 32.

The application of full voltage from the battery, i.e., the momentary switching of the electromagnetic unit 40, has the effect of subjecting the clutch assembly 10 to a relatively fast ramp-up time for the engagement between the armature 36 and the friction surface 30a of the first clutch member 30 and between the wrap spring clutch 34 and the wrap spring clutch engagement surface 48 on the first clutch member 30. It has been found that sudden on/off voltage/current applications result in high speed armature movement. Thus, the engagement between the contact surfaces generates an audible contact sound (i.e., a clicking sound) upon activation of the electromagnetic unit 40. This undesirable audible contact sound can be particularly noticeable during idle operating conditions.

It should be appreciated that the clutch assembly may be subject to varying sub-optimal operating conditions, such as high temperatures (100 ℃ to 120 ℃) and low voltages (9V to 10V). To compensate, the clutch assembly may be configured to operate in worst case conditions, i.e., the clutch assembly is configured such that the reduced current flowing through the electromagnetic unit 40 is still sufficient to pull the armature 36 under suboptimal conditions. However, this approach has the disadvantage that excessive armature speed may result due to excessive voltage/current under normal operating conditions, which may generate excessive force and high mechanical shock upon activation, which may increase the undesirable audible contact sound associated with activation of the electromagnetic unit 40.

The driver control algorithm used by control system 100 allows for soft actuation of the clutch assembly to reduce the audible contact sound when electromagnetic unit 40 is activated. This can be achieved by: by limiting (i.e., clipping) the voltage/current deliverable by the control system to a level equivalent to the worst-case condition, the activation force and mechanical shock are reduced. For example, the driver control algorithm may limit the activation voltage (from an average 14 volt activation voltage under normal engine operating conditions) to 10 volts in order to reduce the armature speed and therefore reduce high mechanical impact forces.

The driver control algorithm may also be configured to modify the activation voltage/current profile using pulse width modulation to deliver the activation voltage/current with a more gradual slope compared to a non-pulse width modulated activation sequence. A more gradual slope to the activating voltage/current results in a slower armature speed, thereby reducing the activating force and mechanical shock. The slower armature speed is selected to achieve an inaudible or sufficiently quiet sound level of the mechanical impact based on a pre-selected threshold set by, for example, the vehicle manufacturer's requirements for harshness (NVH).

The value of the voltage/current resulting from step 214 (fig. 7) is transmitted to PWM module 150 (fig. 6), and PWM module 150 outputs a pulse width modulated signal (referred to as a PWM signal) to control driver 125, which in turn pulse width modulates the voltage or current to electromagnetic unit 40 based on the PWM signal from PWM module 150. The PWM signal is selected to produce a ramp voltage/current profile as compared to the instantaneous on/off profile. In view of fig. 8a, fig. 8a shows the voltage and current profiles (curves 195 and 196) for an on/off actuation sequence. The instantaneous on/off actuation sequence exhibits an instantaneous voltage application and a steep current profile, resulting in fast armature speed and high mechanical impact force. In contrast, a pulse width modulated on/off actuation sequence according to an embodiment of the present disclosure is shown in fig. 8 b. The pulse width modulated voltage and current (profiles represented by curves 197 and 198) exhibit a gradual ramp profile, resulting in a slower armature speed compared to the algorithm curves 195 and 196 in fig. 8 a. The voltage and current profiles shown in fig. 8b result in slower armature speed and reduced mechanical impact force at impact compared to the profiles shown in fig. 8a, so that less noise is generated by the armature when not driven by the voltage and current shown in fig. 8a, but by the voltage and current shown in fig. 8 b.

The PWM module 150 is configured to generate a ramped voltage/current for on and off activation commands. The ramped voltage/current is generated by subjecting the voltage/current to a series of increasing duty cycles (during an on command) or decreasing duty cycles (during an off command) for a set period of time. Examples of such increased duty cycles and decreased duty cycles are shown in fig. 13. Curve 300 represents an activate command signal. Curve 302 represents the PWM signal (voltage or current) and curve 304 represents the force acting on the armature 36. At time T0, the activate command signal (curve 300) is off and accordingly, the PWM signal (curve 302) output from the PWM module 150 is zero. At time T1, the activate command signal (curve 300) is switched on (on). The times T2, T3, and T4 represent the starting points of successive time periods in which the duty cycle of the voltage or current is incremented (represented by the PWM signal curve 302). Due to the increasing duty cycle, the armature force (curve 304) increases at a selected slope. At time T5, the PWM signal (curve 302) remains on. At time T6, the activate command signal (curve 300) is switched off. Times T7 and T8 represent the starting points of successive time periods in which the duty cycle of the voltage or current is decreasing (represented by PWM signal curve 302). At time T9, the PWM signal remains off.

As shown in fig. 9, a series of ramp profiles (based on varying PWM duty cycles) are implemented. It will be appreciated that reducing the duty cycle will slow the armature speed.

The relationship between the ramp profile to be tested and the loudness for activating and deactivating the command signal is shown in fig. 10. It is apparent that increasing the time period for the pulse width modulated on/off actuation sequence results in a decrease in measured loudness from the clutch pack. In other words, when the activated/deactivated voltage/current is delivered at a lower slope, the noise level measured from the clutch assembly is reduced.

Based on the above, the control system 100 is configured to deliver pulse width modulated voltage/current over a time period of 1 to 2 milliseconds. In some embodiments, the pulse width modulated voltage/current may be applied for a time period of 1 millisecond to 1.5 milliseconds. Considering fig. 11a, fig. 11a shows the sound pressure profile of the instantaneous on/off actuation sequence. In contrast, in fig. 11b, the sound pressure profile for the pulse width modulated on/off actuation sequence is for a period of 1 to 1.5 milliseconds. It is evident that the ramp voltage/current reduces the audible contact sound to a level close to the background noise, thereby improving the NVH profile of the vehicle.

As previously stated, the generation of the activate command by the thermal management algorithm will depend on various factors. For example, the activation command may be triggered based on feedback information received from various sensors disposed at selected locations that access the operating conditions (i.e., thermal profile) of the engine. The activation command may also be triggered according to a predefined activation profile of a detected operating condition (e.g., an idle operating condition, a cruise operating condition, or a high speed operating condition), wherein the accessory 20 is a water pump, in particular a Switchable Water Pump (SWP), and the SWP thermal management algorithm may periodically activate/deactivate the SWP to simulate a variable cooling stage flow. Higher switching frequencies are more efficient in achieving faster engine heat engines and provide improved fuel economy. The frequency of SWP activation will have an impact on the audible contact sound, especially during vehicle idling, and therefore the improvements mentioned herein with respect to the pulse width modulated voltage/current used to energize the electromagnetic unit 40 can be combined with a regulated thermal management algorithm. For example, an exemplary standard thermal algorithm such as that shown in fig. 12a may be modified to that shown in fig. 12b, wherein the number of SWP activation events is reduced, particularly during vehicle idle (i.e., when vehicle speed is zero).

Thus, by providing the control system 100 and associated algorithms described above, the clutch assembly 10 may be configured for soft actuation, i.e., the activation/deactivation of the electromagnetic unit 40 is subject to a ramped voltage/current profile achieved through pulse width modulation. The ramping voltage/current produces a reduced armature speed and produces a reduced mechanical impact force. Accordingly, the audible contact sound is reduced, particularly under idle conditions.

It should be appreciated that while the clutch assembly 10 has been described as having a wrap spring clutch 34 to effect torque transfer from the first clutch member 30 to the second clutch assembly 32, other clutch configurations may be implemented. Thus, the control system 100 and associated algorithms may be applied to clutch assemblies having alternative clutch mechanisms.

While various embodiments have been described, it should be understood that they have been presented by way of illustration and example only of the disclosure, and not limitation. It will be apparent to persons skilled in the relevant art that various changes in form and detail can be made therein without departing from the spirit and scope of the disclosure. Thus, the breadth and scope of the present disclosure should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents. It should also be understood that each feature of each embodiment discussed herein, and each reference listed herein, may be used in combination with the features of any other embodiment. All patents and publications discussed herein are incorporated by reference in their entirety.

Claims (12)

1. A method for driving an accessory shaft from a pulley driven by a drive member in a vehicle, the method comprising:

a. energizing an electromagnetic unit by passing a selected voltage/current through the electromagnetic unit;

b. using the energized electromagnetic unit to draw an armature into engagement with a friction surface with a force sufficient to cause engagement of a wrap spring clutch, which in turn operatively connects the pulley to the accessory shaft, and the wrap spring clutch is decoupled from the armature and the electromagnetic unit,

wherein the voltage/current transmitted through the electromagnetic unit is selected such that a speed of the armature when engaged with the friction surface remains below a selected speed, wherein the selected speed is selected such that a sound level of an impact to the friction surface when the armature is engaged with the friction surface is substantially inaudible in a passenger compartment of a vehicle,

wherein the voltage/current transmitted through the electromagnetic unit at least one of: ramping up at a first selected slope; and ramping down at a second selected slope;

wherein the voltage/current transmitted through the electromagnetic unit is a pulse width modulated voltage/current, wherein pulse width modulation is used to achieve the first selected slope or the second selected slope.

2. The method of claim 1, wherein the voltage/current is clipped when the selected voltage/current is reached.

3. The method of claim 1, wherein the first selected slope is achieved by subjecting the voltage/current to a series of increasing duty cycles over a set period of time.

4. The method of claim 1, wherein the second selected slope is achieved by subjecting the voltage/current to a series of reduced duty cycles over a set period of time.

5. The method of claim 3 or 4, wherein the set period of time is from about 1 millisecond to about 2 milliseconds.

6. The method of claim 3 or 4, wherein the set period of time is from about 1 millisecond to about 1.5 milliseconds.

7. A system for driving an accessory shaft from a pulley driven by a drive member in a vehicle, the system comprising:

an electromagnetic unit;

an armature;

a winding spring clutch; and

a control system programmed to cause a selected voltage/current to be transmitted through the electromagnetic unit so as to draw the armature into engagement with a friction surface with a force sufficient to cause engagement of the wrap spring clutch, which in turn causes the pulley to be operatively connected to the accessory shaft, and the wrap spring clutch to disengage from the armature and the electromagnetic unit,

wherein the voltage/current transmitted through the electromagnetic unit is selected such that a speed of the armature when engaged with the friction surface remains below a selected speed, wherein the selected speed is selected such that a sound level of an impact to the friction surface when the armature is engaged with the friction surface is substantially inaudible in a passenger compartment of a vehicle,

wherein the voltage/current transmitted through the electromagnetic unit at least one of: ramping up at a first selected slope; and ramping down at a second selected slope;

wherein the voltage/current transmitted through the electromagnetic unit is a pulse width modulated voltage/current, wherein pulse width modulation is used to achieve the first selected slope or the second selected slope.

8. The system of claim 7, wherein the voltage/current is clipped when the selected voltage/current is reached.

9. The system of claim 7, wherein the first selected slope is achieved by subjecting the voltage/current to a series of increasing duty cycles over a set period of time.

10. The system of claim 7, wherein the second selected slope is achieved by subjecting the voltage/current to a series of reduced duty cycles over a set period of time.

11. The system of claim 9 or 10, wherein the set period of time is from about 1 millisecond to about 2 milliseconds.

12. The system of claim 9 or 10, wherein the set period of time is from about 1 millisecond to about 1.5 milliseconds.

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