Patent Application
20100087999
The present invention relates generally to motor vehicle powertrains, and more specifically to methods for detecting end-of-fill at a clutch in an automatic transmission, and devices for practicing the same.
Most automatic transmissions used in contemporary motor vehicles, such as the modern-day automobile, include a number of gear elements, generally in the nature of epicyclic planetary gear sets, for coupling the transmission's input and output shafts. Traditionally, a related number of hydraulically actuated torque establishing devices, such as clutches and brakes (the term “torque transmitting device” used hereinafter to refer to both clutches and brakes), are selectively engageable to activate the aforementioned gear elements for establishing desired forward and reverse speed ratios between the transmission's input and output shafts. The speed ratio is defined as the transmission input speed divided by the transmission output speed. Thus, a low gear range has a high speed ratio, whereas a high gear range has a lower speed ratio.
Shifting from one forward speed ratio to another is performed in response to engine throttle and vehicle speed, and generally involves releasing one or more “off-going” clutches associated with the current or attained speed ratio, and applying one or more “on-coming” clutches associated with the desired or commanded speed ratio. To perform a “downshift”, the transmission transitions from a low speed ratio to a high speed ratio. The downshift is accomplished by disengaging a clutch associated with the lower speed ratio, and contemporaneously engaging a clutch associated with the higher speed ratio, thereby reconfiguring the gear set to operate at the higher speed ratio. Shifts performed in the above manner are termed clutch-to-clutch shifts, and require precise timing in order to achieve high quality shifting.
The quality of a shift operation (e.g., a downshift or an upshift) depends upon the cooperative operation of several functions, such as pressure changes within the clutch apply chambers and the timing of control events. The engagement of a hydraulic clutch generally consists of two primary stages: the fill mode and the pressure modulation mode. In the fill mode, the clutch volume is rapidly filled with hydraulic fluid. In the pressure modulation mode, the pressure within the clutch volume is carefully modulated to ensure proper and full engagement of the clutch. After a predetermined time, the rate of filling is generally dropped to avoid pressure spikes when end-of-fill is reached.
Detecting end-of-fill at the clutch is extremely critical in controlling automatic transmissions, and prolonging transmission operational life expectancy. Variations in manufacturing tolerances in each transmission, changes due to component wear, inordinate piston stroke, variations in transmission fluid quality and temperature, fluid leakage, etc., will inherently affect clutch fill time. If the proper fill time is not known or accurately estimated, the controller may inadvertently “underfill” or “overfill” the clutch when attempting to modulate clutch pressure to fully engage the clutch. An “underfill” condition may result in “engine flare”—a sudden spike in engine speed, which leads to quicker wear of the clutch friction material. An “overfill” condition may result in “transmission tie-up”—inadvertent simultaneous engagement of both on-coming and off-going clutches, which deteriorates shift-feel, and may cause a shock load to the powertrain and the vehicle.
Adaptive control techniques, which estimate the fill times or fill volumes of the various clutches over a predetermined number of shifts involving each clutch, help to ameliorate some of the variability attributable to manufacturing tolerances, temperature, wear, and so on. Some prior art approaches, in an attempt to predict end-of-fill, use transmission input and output speed sensors to approximate underfill and overfill conditions. The time delay used to estimate clutch fill is adjusted based upon the transmission input speed. However, transient changes, that is, changes in the operating conditions that the controller has not adapted to, will affect the shift quality. Furthermore, a transient condition will have a negative effect on the fill time for the next shift without the transient condition.
In another attempt to more accurately predict end-of-fill, additional flow sensing valves or hydraulic pressure sensors may be used to detect pressure differentials at predetermined locations in the transmissions electro-hydraulic control system. The spool of the flow sensing valve, for example, closes a switch in response to a pressure differential that signals the end-of-fill condition. In a similar respect, a pressure detection switch that monitors hydraulic pressure may be used to predict the end of fill condition.
According to one embodiment of the present invention, an improved method is provided for determining when a fluidly actuated torque transmitting device, such as a hydraulic clutch, in a power transmission is substantially filled with fluid—e.g., reaches an end-of-fill condition. The transmission has an electrically activated solenoid in operative communication with the torque transmitting device, and operable to regulate the same. The method includes: monitoring the active current being drawn by the solenoid during clutch fill—e.g., measuring the actual current, and determining a filtered current therefrom; detecting if an aberration occurs in the active current during clutch fill; and producing an end-of-fill signal in response to an aberration in the current.
According to one aspect of this embodiment, the method also includes initiating clutch fill mode prior to monitoring the active current. Initiating clutch fill mode includes commanding a high current and/or a high fluid pressure. Ideally, fill mode also includes monitoring clutch fill time. To this regard, the method preferably also includes determining if the fill time is greater than a threshold fill time. In this instance, monitoring the active current draw of the solenoid during clutch fill is executed in response to the fill time being greater than the threshold fill time.
According to another aspect of this particular embodiment, detecting if an aberration occurs includes determining a change in instantaneous velocity of the solenoid armature. To this regard, detecting if an aberration occurs preferably also includes determining if the change in instantaneous velocity is greater than a threshold change in armature velocity. Determining a change in instantaneous velocity is preferably based, at least in part, upon the inductance and resistance of the solenoid.
In accordance with another embodiment of the present invention, an improved method for detecting an end-of-fill condition at a hydraulic clutch in an automatic transmission is provided. The transmission has at least one electromagnetic solenoid. Each solenoid has an armature that is circumscribed by a coil, and movable in response to current flowing through the coil. The solenoid fluidly communicates a pressurized fluid source, such as a hydraulic pump and fluid reservoir, with the clutch apply volume, whereby the end-of-fill condition corresponds to the clutch apply volume being pressurized to a predetermined end-of-fill pressure by the solenoid.
The method of this embodiment includes: initiating clutch fill mode by commanding a high current to the solenoid, whereby a high fluid pressure is delivered to the clutch apply volume from the pressurized fluid source; monitoring clutch fill time; determining if the fill time is greater than a threshold fill time; monitoring the active current being drawn by the solenoid during clutch fill mode in response to the fill time being greater than the threshold fill time; detecting if an aberration occurs in the active current being drawn by the solenoid; and stopping distribution of fluid to the hydraulic clutch in response to the current aberration.
In accordance with one aspect of this embodiment, monitoring an active current includes measuring the actual current being drawn by the solenoid, and processing the actual current to determine a filtered (e.g., average) current.
In accordance with another aspect, detecting if an aberration occurs in the active current draw includes determining a change in instantaneous velocity of the solenoid armature. To this regard, detecting if an aberration occurs also includes determining if the change in instantaneous velocity is greater than a threshold change in armature velocity. Ideally, determining the change in instantaneous velocity is based upon certain solenoid parameters, which include, for example, the inductance, slope of inductance as a function of armature position, and resistance of the solenoid.
According to yet another embodiment of the present invention, a control apparatus for regulating activation of a hydraulic clutch in an automatic transmission is provided. The control apparatus includes a variable force solenoid (VFS) having a coil in operative communication with a transmission current source. The solenoid also includes a spool that operates to selectively fluidly communicate a pressurized fluid source with the clutch apply volume. An armature is connected to the spool, and circumscribed by the coil, whereby the armature operates to transition between a first and a second position in response to current flowing through the coil. A controller is in operative communication with the solenoid, and operates, at least in part, to control the movement of the armature. A sensor is in operative communication with both the solenoid and the controller. The sensor is configured to continuously monitor the current draw of the solenoid, and transmit signals indicative thereof to the controller.
The controller is programmed and configured to selectively initiate clutch fill mode by commanding a high current to the solenoid coil, whereby a high fluid pressure is delivered to the clutch apply volume from the pressurized fluid source through the solenoid. The controller is also programmed and configured to monitor the clutch fill time, and determine if the fill time is greater than a threshold fill time. If so, the controller is further programmed and configured to measure and monitor the active draw of current by the solenoid during clutch fill mode. In addition, the controller is programmed and configured to detect if an aberration occurs in the active current, and to stop distribution of fluid to the hydraulic clutch in response to the current aberration. Detecting if an aberration occurs includes determining a change in instantaneous velocity of the solenoid armature.
According to one aspect of this embodiment, the solenoid is in direct fluid communication with the hydraulic clutch. To this regard, the solenoid is preferably a high-flow, direct acting variable force solenoid (VFS) that is operable to control both clutch fill and clutch modulation. It is also desired that the sensor which monitors solenoid current draw is a closed-loop current controller.
The above objects, features, and advantages, and other objects, features, and advantages of the present invention will be readily apparent from the following detailed description of the preferred embodiments and best mode for carrying out the present invention when taken in connection with the accompanying drawings and appended claims.
The present invention is described herein in the context of an electro-hydraulic control system for a multi-ratio automatic transmission. The portion of the electro-hydraulic control system shown in
Referring to the drawings, wherein like reference numbers refer to like components throughout the several views, a portion of an electro-hydraulic control system for a power transmission is schematically illustrated in
The hydraulic clutch 12 includes an apply piston 22 slidably disposed inside of a piston chamber 24 (also referred to herein as “apply volume”) defined by a piston housing 26. The clutch apply volume 24, through piston housing 26, is in direct fluid communication with the solenoid 20 by a clutch feed path, which is defined at least partially by first hydraulic conduit 28. The piston 22 is urged into a disengaged position (as seen in
The hydraulic clutch 12 is shown in
The clutch assembly shown in
With continuing reference to
A spool valve, indicated generally at 54 in
The valve body 56 has a clutch feed passage 66, a supply passage 68, a feedback passage 70, and an exhaust port 72. The clutch feed passage 66 (also known as “control pressure”) fluidly communicates the spool valve body 56 with the piston housing 26 via first hydraulic conduit 28. In a similar respect, the supply passage 68 (also known as “line pressure”) fluidly communicates the spool valve body 56 with the pump 16 via second hydraulic conduit 74, generally through a line pressure regulator valve (not shown herein). In addition, the feedback passage 70 is in fluid communication with the clutch feed passage 66 via third hydraulic conduit 76. The feedback passage 70 is used by the solenoid 20 to regulate output pressure from clutch feed passage 66. Finally, the exhaust port 72 is fluidly connected to the reservoir 18 or a backfill pressure circuit (not explicitly illustrated herein) to maintain a very low pressure (generally less than 5 psi) to keep the circuits filled with fluid even when the clutch 12 is disengaged.
According to the embodiment of
The solenoid 20 also operates to modulate pressure to the hydraulic clutch 12. That is, the current flow through the primary electromagnetic coil 44 can be manipulated to moving the armature 50 to intermittent positions between the clutching and declutching positions. Specifically, when the clutch pressure is being regulated, the clutch feed passage 66 is selectively open to the supply passage 68, and the feedback passage 70 is used to regulate the solenoid position.
The electronic portion of the control system 10 is primarily defined by the ECU 14, which is depicted in
A method of detecting an end-of-fill condition at a hydraulic clutch in an automatic transmission in accordance with a preferred embodiment of the present invention is depicted in block diagram format in
Looking to
Step 101 also includes monitoring the clutch fill time—“Begin Timer (t)”, and determining, in step 103, if and when the fill time (t) is greater than a threshold fill time (tth). When the clutch fill process is started (e.g., step 101), there is a step change in the current command to the solenoid 20.
If the clutch fill time (t) does exceed the threshold fill time (tth), the method 100 responds, in step 105, by measuring and monitoring the active current being drawn by the solenoid 20 during clutch fill mode (e.g., using sensor 78). Monitoring the active current being drawn by the solenoid 20 preferably includes measuring the actual current 80A, and processing the actual current 80A using a standard signal filter, such as, but certainly not limited to, a Kalman filter, a Butterworth filter, a low-pass or high-pass filter, etc., to determine the filtered current 80B.
Contemporaneous therewith, or after step 105, the method 100 then includes detecting if an aberration or irregularity occurs in the active current drawn by the solenoid 20 during clutch fill. One such aberration is shown for explanatory purposes at 88 in
According to step 107 of
{dot over (x)}=(V−L(di/dt)−iR)/(iL′(x))
Detecting end-of-fill at the clutch 12 in accordance with the present invention removes the need for pressure switches that are required in some prior art methodologies, resulting in space and cost savings. The present invention is also independent of clutch volume, which may change over time as indicated above, as well as transmission input and output speeds, which vary from shift-to-shift under different transient operating conditions.
In step 109, the method 100 includes determining if the change in instantaneous velocity ({dot over (x)}) is greater than a threshold change in armature velocity ({dot over (x)}th). Due to inherent noise in measuring the instantaneous velocity ({dot over (x)}), there will always be some calculated change in the velocity of the armature 50 even during steady state conditions. To eliminate the possibility of a premature end-of-fill signal, and capture only the change when the armature moves after fill, the method 100 includes the threshold value ({dot over (x)}th), which is determined by the amount of noise in the system measurements. If the change in instantaneous velocity ({dot over (x)}) is not greater than the threshold change in armature velocity ({dot over (x)}th), the method 100 returns to step 105. If the change in instantaneous velocity ({dot over (x)}) is greater than the threshold change in armature velocity ({dot over (x)}th), the method 100 will produce an end-of-fill signal, and command stoppage of the distribution of fluid to the hydraulic clutch 12 at step 111.
The method 100 of the present invention preferably includes at least steps 101-111. However, it is within the scope and spirit of the present invention to omit steps, include additional steps, and/or modify the order presented in
While the best modes for carrying out the invention have been described in detail, those familiar with the art to which the instant invention relates will recognize various alternative designs and embodiments for practicing the invention within the scope of the appended claims.
