VELOCITY CONTROL OF EXHAUST VALVE ACTUATION

TECHNICAL FIELD

The subject invention relates to a method and apparatus for controlling actuation movement of an exhaust valve to reduce noise and improve durability.

BACKGROUND OF THE INVENTION

Noise attenuation valves are often used in vehicle exhaust systems to reduce noise generated during vehicle operation. A noise attenuation valve typically includes a flapper valve mounted on a shaft that pivots the flapper valve within an inlet tube formed within an exhaust component, such as a muffler for example. The flapper valve has a disc shaped body that rotates within the inlet tube to vary exhaust gas flow area. The shaft is coupled to a solenoid with a linkage assembly. A controller controls the solenoid to rotate the shaft via the linkage assembly. As the shaft rotates, the flapper valve varies the exhaust gas flow area as needed to attenuate noise.

One disadvantage with this traditional configuration is that components in the noise attenuation valve and solenoid generate operational noise. For example, movement of the linkage assembly and rotation of the shaft can generate noises due to slack and clearance between the components.

Additionally, operational movement of the solenoid generates undesired noise. The solenoid includes a plunger that is coupled to the linkage assembly. When the solenoid is electrically actuated, an electronic voltage is used to generate a magnetic force that pulls the plunger in a first direction to position the flapper valve at a desired position. The plunger can move until a travel limit stop is reached. The velocity at which the plunger moves, and the force at which the travel limit stop is contacted, can generate undesirable noise. Further, when the electronic voltage is cut-off, a spring forces the plunger in a second direction, opposite of the first direction, to return the flapper valve to an initial position. This quick release of the plunger also generates undesirable noise and increases wear rates of associated exhaust valve components.

Thus, it is desirable to provide a method and apparatus for controlling movement of the actuator for an exhaust valve that reduces operational noises and reduces wear rates.

SUMMARY OF THE INVENTION

The subject invention provides an exhaust valve assembly with a control that varies actuation power levels by using pulse width modulation (PWM) to reduce operational noises. The exhaust valve assembly includes a valve body supported on a shaft for rotation within an exhaust component. The shaft is coupled to an actuator that moves between an actuation position and a release position. A controller controls the actuator to rotate the shaft to move the valve body. The controller uses PWM to vary velocity of the plunger for at least one of an actuation event or a release event to reduce noise generated during actuator movement.

In one example the controller provides a controlled release. The controller generates an initial power level when releasing the actuator and generates a subsequent power level that is different than the initial power level when moving the actuator to a fully released position. By controlling release velocity, operational noises are significantly reduced as the actuator is moved from the actuation position to the release position. In another example the controller provides a controlled actuation. During initial movement of the actuation the controller generates a low power level, then power is increased during primary actuation, and then power is reduced as the actuator reaches an end of travel position, i.e. a maximum actuation position. The controller could also vary power during both actuation and release as the actuator moves back and forth between the actuation position and the release position.

In one example, the actuator comprises a solenoid with a plunger. The control actuates the solenoid to move the plunger in a first direction to move the solenoid to the actuation position. The solenoid includes a resilient return member that moves the plunger in a second direction opposite of the first direction when moving the solenoid to the release position. During actuation and/or release, the controller supplies at least a first voltage to the solenoid to generate a first magnetic force level and a second voltage to the solenoid to generate a second magnetic force

level that is different than the first magnetic force level. The use of a variable magnetic force during actuation reduces noise generated during actuation. Further, the use of a varied magnetic force in combination with the resilient return member controls movement of the plunger toward a fully released position to reduce operational noise.

These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a schematic view of an exhaust system with a valve actuation control assembly incorporating the subject invention.

Figure 2 is a perspective view of a valve actuator and control incorporating the subject invention. Figure 3 is a graph indicating Force Levels vs. Time for actuator release.

Figure 4 is a graph indicating Velocity vs. Time during a release event. Figure 5 is a graph indicating a controlled actuation event.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An exhaust system 10 is shown in Figure 1. The exhaust system 10 includes an exhaust component 12, such as an inlet tube for a muffler for example, that directs the flow of exhaust gases from an engine (not shown). A noise attenuation valve 14 is positioned within the exhaust component 12 to reduce noise generated during vehicle operation. The noise attenuation valve 14 can be configured as an electric or vacuum type valve.

In the example shown, the noise attenuation valve 14 includes a flapper valve body 16 mounted on a shaft 18 that pivots the flapper valve body 16 within the exhaust component 12 about an axis 20. The flapper valve body 16 is usually a discshaped body and rotates within the exhaust component 12 to vary exhaust gas flow area, however, other valve configurations could also be used.

The shaft 18 is supported on a bushing assembly 22 that provides a bearing surface as the shaft 18 rotates relative to a housing 24. The shaft 18 is coupled by a

linkage assembly 26 to an actuator 28, which controls movement of the shaft 18. As the shaft 18 rotates, the flapper valve body 16 varies the exhaust gas flow area as needed to attenuate noise. A controller 30 controls movement of the actuator 28. In the example shown, the actuator 28 is a solenoid 32 that includes a plunger 34 that is coupled to the shaft 18 by the linkage assembly 26 (see Figure 2).

The actuator 28 typically rotates or pivots the shaft 18 via the linkage assembly 26 back and forth between travel limit stops 36. When a voltage is applied to the solenoid 32, a magnetic force is applied to the plunger 34 that pulls the plunger 34 in an axial direction along axis A toward the right as shown in Figure 2. This rotates the linkage assembly 26 in a clockwise direction until the rightmost travel limit stop 36 is reached. The solenoid 32 in Figure 2 is shown in a "closed" or "actuation" position in Figure 2.

When electric voltage is removed from the solenoid 32, a resilient return spring 38 forces the plunger 34 to move to the left as shown in Figure 2. This rotates the linkage assembly 26 in a counter-clockwise direction and places the solenoid in a "release" or "unactuated" position. The linkage assembly 26 rotates until the leftmost travel limit stop 36 is reached.

The velocity at which the actuation of solenoid 32 occurs can generate undesirable noises. Further, the velocity at which the return spring 38 releases the solenoid to return the plunger 34 to an initial or unactuated position can also generate noise. Additionally, the velocity at which components hit the travel limit stops 36 can affect component durability and further generate noise.

To reduce these operational noises and to improve component durability, the controller 30 varies the power, e.g. voltage/current, during at least one of actuation and release to provide finely controlled movement of the plunger 34. The controller 30 applies a first voltage level actuating the plunger 34 and applies a second voltage level when releasing the plunger 34. During release and actuation, multiple voltage variations could be generated by the controller 30. By controlling voltage levels during release of the solenoid 32, the return spring 38 still returns the plunger 34 to the release position, but the time period during which this event occurs is longer than if the return spring 38 was used by itself. Further, the force at which the release occurs is also significantly less than if the return spring 38 were used alone.

Figure 3 shows an example of a force level vs. time for actuator release comparing use of the return spring 38 alone and using the return spring 38 in combination with a reduced operational voltage. The line at 50 indicates a force level for the return spring 38 alone. In this example, the force level is at 100% of the maximum current required for one second and then immediately drops to a 0% force level. The line at 52 indicates a force level for the return spring 38 in combination with a reduced operational voltage. In the example shown, the force level is at 100% of the maximum current required for just under 1 second and then drops to approximately 50% for another 1.5 seconds where the force level then drops to 0%.

Figure 4 shows an example of velocity vs. time for actuator release. The line at 60 indicates a velocity over time for the return spring 38 alone. In this example, the velocity starts out at 0 for just over 1 second and reaches a maximum velocity level indicated at 20 at a time of about 1.7 seconds, and then immediately drops back to 0. The line at 62 indicates a velocity over time for the return spring 38 in combination with a reduced operational voltage. In this example, the velocity starts out at 0 for just over 1 second and then reaches a maximum velocity level indicated at 10 until just over 2 seconds have passed from initiation of release, and then drops back to 0. While Figures 3 and 4 show force and velocity levels during release, it should be understood that the controller 30 could also vary power during actuation to slow movement of the plunger 34 just prior to reaching a travel limit stop 36 as shown at 70 in Figure 5.

As shown in Figure 5, during initial movement of the actuation the controller 30 generates a low power level, then power is increased during primary actuation, and then power is reduced as the actuator 28 reaches an end of travel position, i.e. a maximum actuation position. In the example shown, current is initially at 30% of the maximum force, then increases to 100% a mid-actuation, and then decreases from 100% down to 10% at an end of actuation. This further assists in reducing operational noises during valve actuation. It should be understood that the current levels and time periods shown in Figure 5 are just one example configuration, and that other current and time period combinations could be used as needed.

Also, the examples shown in Figures 3 and 4 for the return spring 38 in combination with a reduced voltage are just one example configuration. It should be understood that the force levels, time intervals, and velocities could be varied to other levels, and additionally multiple variations could also occur between a fully applied position and a fully released position, or vice-versa.

The controller 30 controls movement of the plunger 34 by using pulse width modulation (PWM). A voltage is applied in a series of pulses generated by ON and OFF events. When OFF there is no voltage applied, and when ON a level of voltage is applied as desired. Typically, this voltage level can be up to 12 volts. These pulses or excitation voltages can be ON and OFF for different time percentages to achieve different duty cycles as needed. Frequency of switching between ON and OFF events of the duty cycles is also modulated as needed. An upper bound of frequency can be as high as 100,000 Hertz. A lower bound of frequency is dictated by system response requirements. Typically, this lower bound would not be lower than 100 Hertz.

In the subject invention, PWM is used to control movement of the solenoid 32. In the solenoid 32, magnetic force is proportional to power flowing through the solenoid 32. By varying voltage, the velocity and force level for movement of the plunger 34 is easily controlled to very precise movements. This reduces operational noises and improves component durability.

The controller 30 can use PWM to only control plunger movement during actuation or to only control plunger movement during release. The controller 30 could also vary power during both actuation and release as the plunger moves between the actuation position and the release position. The force and velocity levels at which the controller 30 moves the plunger 34 can be tuned or varied for different vehicle applications. Further, the force and velocity levels can be tuned or varied on a specific vehicle in response to vehicle input parameters such as road speed, engine speed, throttle position, braking, stereo volume, etc. Finally, it should be understood that while the subject control system is shown as being used in a noise attenuation valve 14 positioned in an inlet tube for a

muffler, the control system could be used for valves located in other exhaust components.

Although a preferred embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.