Contactless sensing of a fluid-immersed electric motor

Abstract

A method and system for measuring rotor position or velocity in an electric motor disposed in hydraulic fluid. The system comprises a contactless position sensor that measures electric motor rotor via magnetic, optical, or other means through a diaphragm that is permeable to the sensing means but impervious to the hydraulic fluid. An electronic sensor is positioned outside the operating fluid, whereas the motor is located in the fluid volume.

Claims

1. A system comprising; an active suspension system in a vehicle interposed between a wheel mount and a vehicle body, the active suspension system comprising: an actuator body; a hydraulic pump in fluid communication with the actuator body; a contactless position sensor; an electric motor at least partially immersed in hydraulic fluid and coupled to the hydraulic pump, the electric motor comprising a rotor with a sensor target wherein the contactless position sensor senses an angular position of the rotor; a diaphragm that isolates the contactless position sensor from the hydraulic fluid; an energy source; and a controller in electrical communication with the contactless position sensor, and wherein the controller sources energy from the energy source for use by the electric motor to control the active suspension at least partially based on the sensed angular position of the rotor.

2. The system of claim 1, wherein the electric motor is a BLDC motor, and wherein in response to the sensed angular position of the rotor the controller commutates the electric motor to create at least one of a torque and velocity characteristic in the motor.

3. The system of claim 2, wherein creating at least one of a torque and velocity characteristic in the motor creates a force from the active suspension system.

4. The system of claim 2, wherein the response to the sensed angular position of the rotor comprises the controller applying a vehicle dynamics algorithm that uses at least one of rotor velocity, active suspension actuator velocity, actuator position, actuator velocity, wheel velocity, wheel acceleration, and wheel position to control operation of the electric motor using the sensed angular position of the rotor.

5. The system of claim 2, wherein the response to the sensed angular position of the rotor comprises the controller applying a hydraulic ripple cancellation algorithm to control operation of the electric motor using the sensed angular position of the rotor.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) The accompanying drawings are not intended to be drawn to scale. In the drawings, each identical or nearly identical component that is illustrated in various figures may be represented by a like numeral. For purposes of clarity, not every component may be labeled in every drawing. In the drawings:

(2) FIG. 1 is a cross section of an integrated pump motor and controller assembly in accordance with the prior art.

(3) FIG. 2 is a cross section of an integrated pump motor and controller comprising a motor rotor contactless position sensor and controller assembly.

(4) FIG. 2A is a detail view of the BLDC motor rotor position sensor, sensing magnet and diaphragm.

(5) FIG. 3 is a cross section of an alternate embodiment of a hydraulic pump, BLDC motor containing a motor rotor position sensor and controller assembly.

(6) FIG. 3A is a detail view of the alternate embodiment of the BLDC motor rotor position sensor, sensing magnet and diaphragm.

(7) FIG. 4 is a cross section of the integrated pump motor and controller comprising a motor rotor position sensor and controller assembly using an annular type source magnet.

DETAILED DESCRIPTION

(8) In certain applications, an electric motor is used to provide torque and speed to a hydraulic pump to provide force and velocity to a hydraulic actuator, and conversely, the hydraulic pump may be used as a motor to be used to back-drive the electric motor as a generator to produce electricity from the force and velocity inputted into the actuator.

(9) For reasons of performance and durability, these electric motors are of the BLDC type and may be mounted inside a housing, close coupled with the pump, where they may be encased in the working fluid under high pressure. In order to provide adequate hydraulic system performance, accurate control of the torque and speed of the BLDC motor is required, which may require a rotary position sensor for commutation. Although rotary position sensors for BLDC motor commutation/control currently exist, certain applications, such as the use in active suspension actuators or high performance aerospace actuators, for example, are particularly challenging due to the fact that the BLDC motor may be mounted inside a housing, where it is encased in the working fluid under high pressures.

(10) An electric motor/generator may be applied in an active suspension system to work cooperatively with a hydraulic motor to control movement of a damper in a vehicle wheel suspension actuator. The electric generator may be co-axially disposed and close coupled with the hydraulic motor, and it may generate electricity in response to the rotation of the hydraulic motor, while also facilitating rotational control of the hydraulic motor by applying torque to deliver robust suspension performance over a wide range of speeds and accelerations. It may be desirable to precisely control the electric motor/generator. To achieve precise control, precise rotor position information may be needed. In particular, determining the position of the rotor relative to the stator (the windings) is important to precisely control currents passing through the windings based on the rotor position for commutation. To precisely and dynamically control the currents through the windings (depending on where the rotor is in its rotation, what direction it is turning, its velocity, and acceleration), a fairly precise reading of rotor position is required. To achieve precisely determining the rotor position, a sensor is used. By applying position determination algorithms that are described below, a low cost sensor (e.g. with accuracy of one degree) may be used. Rotor position may also be used for a variety of reasons other than that for commutation. For example, position may be used for determining fluid flow velocity from the coupled hydraulic motor. Also, the motor controller may be applied in an active suspension that senses wheel and body events through sensors, such as a position sensor or body accelerometer, etc., and senses the rotational position of the rotor with the position sensor and in response thereto sources energy from the energy source for use by the electric motor to control the active suspension. In embodiments the response to the position sensor comprises a vehicle dynamics algorithm that uses at least one of rotor velocity, active suspension actuator velocity, actuator position, actuator velocity, wheel velocity, wheel acceleration, and wheel position, wherein such value is calculated as a function of the rotor rotational position. Another such use of the rotary position sensor may be for the use in a hydraulic ripple cancellation algorithm; positive displacement hydraulic pumps and motors typically produce a pressure pulsation, or ripple, that is in relation to its rotational position. This pressure pulsation can produce undesirable noise and force pulsations in downstream actuators, etc. Since the profile of the pressure pulsation can be determined relative to the pump position, and hence the rotor and hence the source magnet position, it is possible for the controller to use an algorithm that can vary the motor current and hence the motor torque based upon the rotor position signal to counteract the pressure pulsations, thereby mitigating or reducing the pressure pulsations, reducing the hydraulic noise and improving the performance of the system.

(11) In some configurations described herein, portions of the BLDC motor (or the complete BLDC motor) may be submerged in hydraulic fluid. This may present challenges to sensing a precise position of the rotor. Therefore, a magnetic target (source magnet) attached on the rotor shaft may be detected by a sensor disposed so that it is isolated from the hydraulic fluid. One such arrangement may include disposing a sensor on a dry side of a diaphragm that separates the fluid from the sensor. Because magnetic flux passes through various materials, such as a nylon, plastic or aluminum etc., it is possible to use such materials for a diaphragm so that the sensor can read the rotor position while keeping the sensor out of the fluid. While a low cost magnetic sensor may provide one-degree resolution with one to two degrees of linearity, which may be sufficient simply for determining rotor position, to precisely control the currents flowing through the windings, additional information about the rotor may be needed, such as acceleration of the rotor. One approach would be to use a more accurate sensor, although this increases costs and may not even be practical when the rotor is immersed in fluid. Therefore, a filter that correlates velocity with position may be utilized. The filter may perform notch filtering with interpolation of any filtered positions. By performing notch filtering, harmonics of the filtered frequency are also filtered out, thereby improving results. By using a combination of filtering, pattern sensing, and on-line auto-calibration, precise calibration steps during production or deployment are eliminated, thereby reducing cost, complexity, and service issues. Methods and systems of rotor position sensing may include magnetically sensing electric generator rotor position of a fluid immersed electric generator shaft through a diaphragm. Other methods and systems may include processing the sensed position data to determine rotor acceleration with a low-cost magnetic sensor. Other methods may include processing a series of sensor target detections with at least one of a derivative and integration filter and an algorithm that uses velocity over time to determine position and acceleration of the rotor. Other methods may include detecting the magnetic sensor target each time it passes proximal to the rotary position sensor, resulting in a series of detections that each represent a full rotation of the rotor and then detecting electric motor voltages and/or currents to determine a rotor velocity (as is known in the art of sensorless control of a BLDC motor by measuring the back EMF in the undriven coils to infer the rotor position), then processing the series of detections with an algorithm that calculates rotor position by integrating rotor velocity and resetting absolute position each time the magnetic sensor target passes the magnetic sensor.

(12) By using a single target magnet attached to the center of the rotor shaft the magnet length and the associated back iron of the rotor need only extend to the length required so as to achieve the maximum possible torque of the motor, not extending further so as to provide rotor magnet length for sensing with Hall effect sensors. This will reduce the required inertia of the rotor assembly as compared to prior art approaches. One such arrangement locates the target magnet about the center of the rotor shaft by a non-magnetic, light-weight component that not only allows for the flux of the target magnet to adequately penetrate the non-magnetic diaphragm, but also reduces the rotating inertia of the rotor assembly, thereby improving the responsiveness and performance of the system.

(13) Turning now to the figures, FIGS. 2 and 2A the integrated pump motor and controller comprising a motor rotor position sensor and controller assembly 6-202 is shown. In the embodiment of FIG. 2, a rotary position sensor 6-204, that measures the rotational position of a source magnet 6-206 and is protected from the working hydraulic fluid 6-208 under pressure that is contained within the housing 6-210, is shown. In the embodiment shown, the rotary position sensor may be a contactless type sensor, wherein the rotary position sensor comprises of an array of Hall effect sensors that are sensitive to magnetic flux in the axial direction relative to the axis of rotation of the source magnet and can sense the flux of a diametrically magnetized two-pole source magnet to determine absolute position and a relative position. The array of Hall effect sensors may be connected to an on-board microprocessor that can output the absolute position and a relative position signal as a digital output. This type of sensor allows for a degree of axial compliance of the sensor to the source magnets as well as for radial mis-alignment of the source magnet to the sensor without degrading sensor output performance, thereby allowing the sensor to operate under normal manufacturing tolerances for position and rotation. This type of sensor may comprise of an on-board temperature sensor that can correct for errors due to temperature variance.

(14) In the embodiment shown, the first port 6-214 of the hydraulic pump 6-210 is in fluid connection with the fluid 6-208 that is contained within the housing 6-210 and the first fluid connection port 6-214. Therefore the pressure of the fluid 6-208 is at the same pressure as the first port of the pump 6-212. The second port of the hydraulic pump 6-212 is in fluid connection with the second fluid connection port 6-216. Depending upon the use of the integrated pump motor and controller assembly 6-202, the first and second fluid connection port may the inlet and outlet of the hydraulic pump, and vice versa, and the first and second fluid connection port may be at high or low pressure or vice versa. As such, the fluid 6-208 contained in the housing 6-210 could be at the maximum working pressure of the pump. In certain applications, such as active suspension actuators or aerospace actuators for example, this could reach 150 BAR or above. It is therefore necessary to protect the rotary position sensor 6-204 from such pressures. Although prior teaches that Hall effect sensors can be protected from working system pressure by encasing them in an EPOXY molding for example, this type of arrangement is typically suitable for low pressure systems, as it would be impractical to encapsulate the sensor deep enough inside of the EPOXY molding so that the strain induced upon the relatively week structure of EPOXY did not act upon the sensor resulting in its failure. As such, in the embodiment shown in FIG. 2, the rotary position sensor 6-204 is protected from the pressure of the fluid 6-208 by a sensor shield or diaphragm 6-218. The sensor shield 6-218 is located within a bulkhead 6-220, in front of the sensor. The sensor shield 6-218 is exposed to the pressure of the hydraulic fluid 6-208. As shown in FIG. 2, the sensor shield is sealed to the bulkhead by means of a hydraulic seal 6-222 (although an elastomeric seal is disclosed, a mechanical seal or adhesive etc. may be used, and the technology is not limited in this regard) such that the hydraulic fluid cannot pass by the sensor shield. The bulkhead 6-220 is sealed to the housing 6-210. A small air gap 6-224 exists between the sensor shield and the sensor so that any deflection of the sensor shield, due to the hydraulic fluid pressure acting on it, does not place any load onto the sensor itself. The sensor shield 6-218 is constructed of a non-magnetic material so that the magnetic fluxes of the source magnet 6-206 can pass through the sensor shield unimpeded. The sensor shield may be constructed from many types of non-magnetic material, such as aluminum or an engineered performance plastic etc., and the technology is not limited in this regard. An example of the selection criteria for the sensor shield material being that it is preferably able to contain the pressure of the fluid 6-208 without failure, it preferably does not deflect enough under pressure so that it will contact the rotary position sensor causing failure of the sensor, it preferably does not impede the magnetic flux of the source magnet so as to create sensing errors, and it is preferably cost effective for the application. The rotary position sensor 6-204 may be adequately shielded from other external magnetic fluxes such as that from the magnets 6-226 on the motor rotor 6-228 or from the motor stator windings 6-230, so as not impair its ability to accurately sense the position of the magnetic flux of the source magnet. In the embodiment shown the rotary position sensor 6-204 may be shielded from these disturbing magnetic fluxes by the bulkhead 6-220. The bulkhead 6-220 may be constructed from a material, such as steel, for example, that tends to prevent errant magnetic fluxes from passing through to the rotary position sensor.

(15) In the embodiment shown in FIG. 2, the rotary position sensor 6-204 is mounted directly on the motor controller printed circuit board (PCB) 6-232. The PCB 6-232 is supported in a controller housing 6-234 that forms a sensing compartment that is free from the working fluid 6-208. The source magnet 6-206 may be located in a magnet holder 6-236 that locates the source magnet coaxially with the BLDC motor rotational axis and the rotary position sensor axis, and in close axial proximity to the sensor shield 6-218. The source magnet and magnet holder are operatively connected to the BLDC motor rotor 6-228. In the embodiment shown the magnet holder 6-236 is constructed of a non-magnetic material so as not to disturb the magnetic flux of the source magnet 6-206. In the highly dynamic application of an active suspension actuator, where there are rapid rotational accelerations and reversals of the motor rotor it is preferable to reduce the inertia of the rotating components and for this reason the magnet holder may be constructed of a light weight, non-magnetic material, such as aluminum, or an engineered performance plastic, etc.

(16) In FIG. 3 an alternative embodiment of an integrated pump motor controller 6-302 is shown. This embodiment is similar to that of the embodiment of FIG. 2 with the exception that the rotary position sensor is mounted remotely from the motor controller PCB, and the sensor is electrically connected to the motor controller via wires 6-304. This arrangement may be advantageous when locating the motor controller in the proximity of the rotary position sensor and source magnet is not practical.

(17) Referring to FIGS. 3 and 3A, a rotary position sensor 6-306 is located in a sensor body 6-308 via a sensor holder 6-310. The sensor body and sensor are held in rigid connection to the housing 6-312, and there is a seal 6-314 between the housing and the sensor body. The sensor body is constructed of a magnetic material (such as steel for example) so as to shield the sensor from external unwanted magnetic fluxes (from the BLDC motor rotor magnets or from the stator windings for example) that may degrade the sensor accuracy. In the embodiment shown, the sensor is located coaxially with the rotational axis of the BLDC motor rotor axis. A source magnet 6-316 is located in a magnet holder 6-318 that locates the source magnet coaxially with the BLDC motor rotational axis and the sensor axis, and in close axial proximity to a sensor shield 6-320. The source magnet and magnet holder are operatively connected to the BLDC motor rotor. The sensor shield is constructed so that it has a thin wall section that allows the face of the source magnet to be located close to the working face of the sensor so as to provide sufficient magnetic flux strength to penetrate the sensor so as to provide accurate position signal. The sensor shield 6-320 is exposed to the pressure of the ambient hydraulic fluid. As shown in FIG. 3A, the sensor shield is sealed to the bulkhead by means of a hydraulic seal 6-322 (although an elastomeric seal is disclosed, a mechanical seal or adhesive etc. could be used, and the technology is not limited in this regard) such that the hydraulic fluid cannot pass by the sensor shield. A small air gap exists between the sensor shield and the sensor so that any deflection of the sensor shield, due to the hydraulic fluid pressure acting on it, does not place a load onto the sensor itself. The sensor shield is constructed of a non-magnetic material so that the magnetic fluxes of the source magnet can pass through the sensor shield unimpeded.

(18) The source magnet holder 6-318 is constructed of a low density, non-magnetic material, such as aluminum or an engineered performance plastic etc. so as not to degrade the source magnetic flux strength and to reduce rotational inertia. The sensor wires 6-304 are sealed to the sensor body (by means of a hydraulic seal, mechanical seal, or adhesive etc.) so as to protect the rotary position sensor from the environment.

(19) In an alternative embodiment as shown in FIG. 4 the source magnet 6-402 is of an annular type and the rotary position sensor 6-404 is mounted eccentrically to the rotor rotational axis and a and senses the flux of the source magnet 6-402 through the non-magnetic sensor shield 6-406. The functioning and arrangement of this configuration is similar to that as disclosed in the embodiments of FIGS. 2 and 3. This arrangement may be advantageous by offering finer sensing resolution without a significant increase in cost due to the increased number of poles in the annular source magnet.

(20) In an arrangement similar to the embodiment of the Hall effect rotary position sensor shown in FIG. 4, an alternative embodiment is to use an optical rotary position sensor that measures the rotational position of a reflective disc which is protected from the working hydraulic fluid under pressure in a similar manner to that described in the embodiment of FIG. 4, wherein the optical rotary position sensor comprises of a light transmitter/receiver and a reflective disc.

(21) In this embodiment the Hall effect rotary position sensor is replaced by a light transmitter/receiver is mounted onto the controller PCB located off-axis with the rotational axis of the BLDC motor. A sensor shield is located in front of the light transmitter and receiver and is exposed to the hydraulic fluid under pressure in the housing. The sensor shield is sealed such that the hydraulic fluid does not enter the sensor cavity. The sensor shield is constructed of an optically clear material such as an engineered plastic or glass etc., so that the light source can pass through the sensor shield unimpeded. A small air gap exists between the sensor shield and the light transmitter and receiver so that any deflection of the sensor shield, due to the hydraulic fluid pressure acting on it, does not place a load onto the light transmitter and receiver itself. The annular type source magnet as shown in the earlier embodiment FIG. 4 is replaced in this embodiment by reflective disc that is drivingly connected to, and coaxial with, the BLDC motor, and that is located near the light transmitter and receiver so that light emitted from the light transmitter is reflected back to the light receiver via the optically clear sensor shield.

(22) The reflective disc may contain markings so as to produce a reflected light signal as the disc rotates; the light transmitter receiver then reads this signal to determine the BLDC motor position. From this position motor speed and acceleration can also be determined. The wavelength of light source used is such it can pass through the sensor shield, the oil within the valve and any contaminants contained within the oil, unimpeded, so that the light receiver can adequately read the light signal reflected from the reflective disc.

(23) Although the embodiments of FIGS. 2, 3 and 4 refer to an electric motor rotary position sensor for use in certain types integrated electric motors and hydraulic pumps for use in high performance actuators, these embodiments can also be incorporated into any electric motor-hydraulic pump/motor arrangement whereby the electric motor is encased in the working fluid (as in compact hydroelectric power packs etc.), and the inventive methods and systems are not limited in this regard.

(24) Although the embodiments show the use of a rotary Hall effect position sensor and optical rotary position sensor, various other types of rotary position sensor, such as encoders, potentiometers, fiber optic and resolvers etc. may be accommodated in a similar manner, for example the Hall effect rotary position sensor could be replace by a metal detector and the source magnet could be replaced by a an element that is adapted to be detected thru the non-metallic sensor shield or the rotary position sensor could be a radio frequency detector and the sensor target be adapted detectable by the sensor and as such, the patent is not limited in this regard.

(25) As sensor technology progresses, it may be possible to use a rotary position sensor that can withstand a high fluid pressure, temperature environment with external magnetic fields, and as such could be incorporated to sense the rotational position of a suitable sensor target, and the patent is not limited in this regard.

(26) While the present teachings have been described in conjunction with various embodiments and examples, it is not intended that the present teachings be limited to such embodiments or examples. On the contrary, the present teachings encompass various alternatives, modifications, and equivalents, as will be appreciated by those of skill in the art. Accordingly, the foregoing description and drawings are by way of example only.