Patent Application
20110262266
The present disclosure relates to exhaust gas-driven turbochargers having a variable-geometry member for regulating the flow of exhaust gas through the turbine. The disclosure relates in particular to a linear actuator for effecting movement of the variable-geometry member.
Turbochargers for internal combustion engines often include some type of variable-geometry member for regulating exhaust gas flow through the turbine so as to provide a greater degree of control over the amount of boost provided to the engine by the turbocharger. Such variable-geometry members can include variable vane arrangements, waste gates, sliding pistons, etc.
Linear actuators are frequently employed for providing the motive force to move the variable-geometry member of the turbocharger. An actuator rod or shaft of the actuator is mechanically coupled to the variable-geometry member. Examples of such linear actuators include pneumatic actuators operated by vacuum derived from the engine's intake system.
In order to accurately control the position of the variable-geometry member, typically a sensor assembly is incorporated in the linear actuator for sensing the position of the actuator rod along the nominal displacement path of the actuator rod. One type of sensor assembly comprises a permanent magnet and a Hall effects sensor. The magnet is housed within the movable part of the actuator that imparts movement to the actuator rod. The sensor is disposed in the fixed part of the actuator, proximate the magnet. The nominal displacement path of the actuator rod is usually coincident with the longitudinal axis of the actuator rod. However, often the actual movement of the actuator rod is not a pure translation along the longitudinal axis of the rod, but also includes some amount of rotation of the rod about one or more axes that are not parallel to the longitudinal axis. This complex movement of the actuator rod complicates the accurate sensing of the actuator rod position by the sensor assembly.
Others have tried to address this problem by providing a guiding structure for the actuator rod. The guiding structure surrounds and contacts the actuator rod and constrains it to pivot about a fixed pivot point that is proximate the sensor. The magnet is contained in a part of the rod adjacent the sensor. The objective of this arrangement is to keep the radial spacing between the magnet and the sensor constant regardless of whether the rod is purely translating or undergoing a complex translation and rotation movement. One drawback of this approach is that the guiding structure exerts frictional forces on the actuator rod as it slides, and therefore the actuator force must overcome the frictional force before the rod will move. The sliding contact between the guiding structure and the actuator rod also causes wear of these surfaces, which in turn leads to increasing “slop” over time, so the guiding structure gradually loses its effectiveness at keeping the magnet-to-sensor spacing constant.
The present disclosure concerns a linear actuator for a variable-geometry member of a turbocharger. The linear actuator includes a sensor assembly whose accuracy does not depend on keeping the magnet-to-sensor spacing constant. Accordingly, the sensor assembly is able to cope with complex movements of the actuator rod (or, more generally, the movable portion of the actuator) without impairment to the accuracy of position detection. Furthermore, the actuator does not require any guiding structure that contacts the part that houses the magnet, so friction and wear are eliminated or at least substantially reduced.
In accordance with one embodiment described herein, a turbocharger for an internal combustion engine comprises a compressor wheel and a turbine wheel mounted on a common shaft, the compressor wheel being disposed in a compressor housing and the turbine wheel being disposed in a turbine housing, the turbine housing defining passages for receiving exhaust gas, directing the exhaust gas to the turbine wheel, and discharging the exhaust gas from the turbine housing. The turbocharger further includes a variable-geometry member operable to regulate flow of exhaust gas through the turbine housing, and a linear actuator coupled with the variable-geometry member and operable to cause movement of the variable-geometry member.
The linear actuator comprises a fixed portion and a movable portion, the movable portion being coupled with the fixed portion by a coupling arrangement that permits the movable portion to undergo generally linear movement relative to the fixed portion in a direction generally parallel to a longitudinal axis so as to cause movement of the variable-geometry member. The coupling arrangement also permits the movable portion to undergo rotational movement, within limits set by the coupling arrangement, about at least one axis that is non-parallel to the longitudinal axis. The actuator includes a sensor assembly comprising a permanent magnet fixedly mounted on the movable portion and a sensor fixedly mounted relative to the fixed portion and adjacent to the magnet. The generally linear and rotational movements of the movable portion cause movement of the magnet relative to the sensor, and that movement of the magnet has components along at least two orthogonal axes.
The sensor is operable to sense magnetic flux density components of the magnet along multiple orthogonal axes. A position of the magnet along the longitudinal axis is determinable from these magnetic flux density components.
In a particular embodiment described herein, the sensor assembly includes a magnet carrier that defines an internal cavity in which the magnet is disposed. The sensor assembly also includes a sensor housing that defines an internal cavity in which the sensor is disposed. The coupling arrangement of the actuator is configured to allow the generally linear and rotational movements of the movable portion while preventing contact between the outer surface of the magnet carrier and the outer surface of the sensor housing. Thus, during normal operation, there is always space between the outer surfaces of the magnet carrier and the sensor housing, so friction and wear of these surfaces are eliminated.
More generally, the actuator is free of any guiding structure that would contact the outer surface of the magnet carrier to guide movement thereof as the movable portion undergoes the generally linear and rotational movements.
In the embodiment described herein, the fixed portion of the actuator comprises an enclosure, and the movable portion of the actuator includes a diaphragm within the enclosure, the enclosure and diaphragm cooperating to define an interior chamber capable of supporting a fluid pressure differential across the diaphragm. The actuator further comprises a spring biasing the diaphragm in a direction opposite the fluid pressure differential across the diaphragm, whereby in the absence of such a fluid pressure differential the spring biases the diaphragm against a first stop defining a first extreme position of the movable portion.
In the described embodiment of the actuator, the portion of the sensor housing in which the sensor is contained extends into the interior chamber and is offset to one side of the longitudinal axis, and the magnet is located on the longitudinal axis.
The sensor can comprise a multi-axis Hall effects sensor.
In the described embodiment, the magnet carrier includes a hollow generally cylindrical portion in which the magnet is disposed, the generally cylindrical portion having a proximal end proximate the sensor and an opposite distal end remote from the sensor, the magnet carrier further including a generally disk-shaped portion joined to the distal end of the generally cylindrical portion.
The spring in the described embodiment comprises a coil spring disposed generally concentrically about the magnet carrier, and the generally disk-shaped portion of the magnet carrier defines a surface contacted by one end of the coil spring.
The magnet carrier can include a plastic portion and a metal portion, the plastic portion including the generally cylindrical portion that houses the magnet, the metal portion defining the surface contacted by the coil spring.
The movable portion of the actuator can include a generally cup-shaped member having an open end located relatively closer to the sensor and a closed end defined by a bottom wall located relatively farther from the sensor. The disk-shaped portion of the magnet carrier contacts an inner surface of the bottom wall of the generally cup-shaped member.
Having thus described the disclosure in general terms, reference will now be made to the accompanying drawings, which are not necessarily drawn to scale, and wherein:
The turbocharger and actuator now will be described more fully hereinafter with reference to the accompanying drawings in which some but not all possible embodiments are shown. Indeed, the turbocharger and actuator may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Like numbers refer to like elements throughout.
A turbocharger and actuator according to one embodiment are depicted in
The unison ring 52 is rotated by a mechanical linkage (not visible in
The present disclosure concerns in particular the design of the actuator 60, and therefore the present description will focus on the actuator.
The cup-shaped member 90 of the actuator is disposed with its closed bottom wall against the upper surface of the diaphragm 80 and its open end facing upwardly. The coil spring 100 is disposed substantially concentrically with respect to the cup-shaped member 90 and has one end engaged against the bottom wall of the cup-shaped member 90 and its opposite end engaged against an inner surface of the upper housing part 72 (although the turn of the coil spring that engages the housing part 72 cannot be seen in the cross-section of
The actuator includes a fluid passage (not visible in
The actuator rod 62 passes through a ring-shaped gimbal 120 that keeps the portion of the rod within the gimbal generally centered relative to the actuator housing but permits the rod to undergo some degree of pivoting about axes transverse to the longitudinal axis of the rod. This pivoting ability is necessary because as a result of the characteristics of the variable-geometry mechanism to which the distal end of the rod 62 is connected, the rod 62 in some turbochargers will not purely translate parallel to its longitudinal axis, but will undergo a complex motion made up primarily of a translation component parallel to the longitudinal axis but also including a secondary rotation component about at least one axis that is not parallel to the longitudinal axis of the rod. This complex motion of the actuator rod 62 is also imparted to the cup-shaped member 90 because of the substantially rigid connection therebetween. This in turn complicates the accurate sensing of the actuator position, as further described below.
The actuator 60 also includes a sensor assembly 130 for sensing the position of the actuator rod 62 along the nominal longitudinal axis A of the actuator (
The sensor housing 132 includes a socket portion 140 for receiving a plug (not shown). The socket portion 140 houses three electrically conductive pins 142 that are electrically connected to the sensor 134. The plug includes three receptacles that respectively receive the three pins 142, and conductors of the plug carry signals on the pins to a processor (e.g., the vehicle ECU, not shown) that processes the signals to determine the actuator position from the signals.
The magnet carrier 150 comprises a plastic portion 152 and a metal portion 156. The plastic portion 152 includes a hollow generally cylindrical portion 158 that contains the permanent magnet 154, which has a solid generally cylindrical configuration. The magnetic pole of the permanent magnet is substantially coincident with the central longitudinal axis of the cylindrical portion 158 of the magnet carrier. The plastic portion 152 also includes a generally disk-shaped portion 160 joined to the distal (lower) end of the generally cylindrical portion 158. The metal portion 156 of the magnet carrier sits atop the upper surface of the disk-shaped portion 160, and comprises a generally annular member such as a metal washer, the purpose of which will become apparent below.
When the sensor assembly 130 is installed in the actuator 60 as shown in
The sensor 134 can comprise a multi-axis Hall effects sensor. A suitable sensor, for example, is available from Melexis N. V. of Belgium, as part number MLX90333, although the invention is not limited to any particular model or type of sensor. The sensor is operable to detect components of magnetic flux density of the magnet 154 along at least two mutually orthogonal axes. For example, when the sensor comprises a generally planar chip comprising a multi-axis Hall effects sensor, the flux density in a direction normal to the plane of the chip (i.e., along a Z-axis) can be denoted Bz, and the flux density components along the two mutually orthogonal X- and Y-axes in the plane of the chip can be denoted Bx and By. The sensor can be operable to measure these flux density components and to output two signals that are respectively representative of the Bx and By flux density components. The sensor can be arranged in the actuator such that one of the X- and Y-axes is substantially parallel to the nominal longitudinal axis A (which lies in the plane 4-4 indicated in
It can be seen that the member 90 and the magnet carrier 150 move in a substantially unguided manner, in the sense that there is no structure that contacts the outer surface of the magnet carrier 150 to try to keep it at a constant radial spacing distance from the sensor 134. The magnet carrier 150 and actuator rod 62 are free to undergo complex translational-rotational movements, within limits dictated by the coupling arrangement (which includes the gimbal 120) that couples the movable portion with the fixed portion of the actuator. This is possible because of the use of the multi-axis sensor 134 that is capable of detecting and accounting for such complex movements of the magnet 154. It would not be possible with the single-axis types of Hall effects sensors that are commonly employed in linear actuators.
Many modifications and other embodiments of the inventions set forth herein will come to mind to one skilled in the art to which these inventions pertain having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the inventions are not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.
