Patent Application
20130313048
This disclosure is related to hydraulic control systems for direct drive transmissions.
The statements in this section merely provide background information related to the present disclosure. Accordingly, such statements are not intended to constitute an admission of prior art.
Hydraulic systems for a transmission in a vehicle can lubricate and cool the transmission by communicating a hydraulic fluid from a sump to at least one of a plurality of subsystems of a hydraulic circuit. In battery electric vehicles, the transmission can include a direct drive transmission. Direct drive transmissions do not include gear selection systems utilizing torque transfer devices that are hydraulically activated and deactivated. Therefore, failure conditions including fluid leakage resulting in low fluid levels and hydraulic fluid blockage within the hydraulic circuit will not have any impact on the ability of the transmission to provide output torque for driving the vehicle. However, failure conditions can result in transmission components not being adequately cooled and lubricated. Damage to the transmission components can occur if such failure conditions are not addressed.
It is known, for example, to monitor hydraulic fluid levels within hydraulic control systems by measuring the fluid level within a sump. It is further known, for example, to utilize pressure sensors placed throughout a hydraulic control system to detect hydraulic fluid blockage. Such sensors and measuring devices can add to cost and limit packaging constraints within hydraulic control systems.
Method for detecting a fault condition in a vehicular hydraulic circuit during a drive cycle using an electric pump includes monitoring an actual pump torque and monitoring a desired pump torque. A current confidence factor is determined based on the actual pump torque and the desired pump torque. An average confidence factor is iteratively calculated based on the current confidence factor and previously determined confidence factors.
The average confidence factor is compared to a fault condition threshold.
An absence of the fault condition in the hydraulic circuit is detected when the average confidence factor is at least the fault condition threshold, and
a presence of the fault condition in the hydraulic circuit is detected when the average confidence factor is less than the fault condition threshold.
One or more embodiments will now be described, by way of example, with reference to the accompanying drawings, in which:
Referring now to the drawings, wherein the showings are for the purpose of illustrating certain exemplary embodiments only and not for the purpose of limiting the same,
The supply line 28 is in fluid communication with a cooler supply line 36 to distribute the hydraulic fluid 12 to the cooler subsystem 42 and a one-way spring bypass valve 44 disposed in parallel with the cooler subsystem 42. The cooler subsystem 42 is a subsystem of the hydraulic circuit 11 and may include an oil cooler to reduce the temperature of the hydraulic fluid 12. The one-way spring bypass valve 44 allows hydraulic fluid 12 to bypass the cooler subsystem 42 in the event of inadequate cooler flow. The one-way spring bypass valve 44 is set at a predetermined pressure and if the pressure of the hydraulic fluid 12 in the cooler supply line 36 exceeds this pressure, the one-way spring bypass valve 44 opens momentarily to increase the flow of hydraulic fluid 12. Both the cooler subsystem 42 and the one-way spring bypass valve 44 are in fluid communication with a lubrication supply line 46. Embodiments are envisioned where the cooler subsystem 42 and the one-way spring bypass valve 44 are omitted. The lubrication supply line 46 distributes the hydraulic fluid 12 to the lubrication and temperature management subsystem 48. The lubrication and temperature management subsystem 48 is a subsystem of the hydraulic circuit 11 and generally includes various fluid lines, passages, and other components used to deliver the hydraulic fluid 12 to various components within the transmission to lubricate and manage temperature of the various components. The hydraulic fluid 12 then communicates back to the sump 14.
The operation of the hydraulic control system 10 includes operating the electric motor 18 to drive the pump 16 via an output shaft 17. A control module 5 is utilized for controlling the speed of the electric motor 18 to control pump speed and pump torque of the pump 16. Therefore, the control module 5 can command the electric motor 18 to control the pump torque to achieve a desired pump torque corresponding to a pump speed request.
Control module, module, control, controller, control unit, processor and similar terms mean any one or various combinations of one or more of Application Specific Integrated Circuit(s) (ASIC), electronic circuit(s), central processing unit(s) (preferably microprocessor(s)) and associated memory and storage (read only, programmable read only, random access, hard drive, etc.) executing one or more software or firmware programs or routines, combinational logic circuit(s), input/output circuit(s) and devices, appropriate signal conditioning and buffer circuitry, and other components to provide the described functionality. Software, firmware, programs, instructions, routines, code, algorithms and similar terms mean any controller executable instruction sets including calibrations and look-up tables. The control module has a set of control routines executed to provide the desired functions. Routines are executed, such as by a central processing unit, and are operable to monitor inputs from sensing devices and other networked control modules, and execute control and diagnostic routines to control operation of actuators. Routines may be executed at regular intervals, for example each 3.125, 6.25, 12.5, 25 and 100 milliseconds during ongoing engine and vehicle operation. Alternatively, routines may be executed in response to occurrence of an event.
As aforementioned, direct drive transmissions do not include gear selection systems utilizing torque transfer devices that are hydraulically activated and deactivated. Accordingly, fluid leakage resulting in low fluid levels and hydraulic fluid blockage within the hydraulic circuit will not have any impact on the ability of the transmission to provide output torque for driving the vehicle. However, such failure conditions (e.g., fluid leakage resulting in low fluid levels and hydraulic fluid blockage) can result in transmission components not being adequately cooled and lubricated. Damage to the transmission components can occur if such failures in the hydraulic circuit 11 go undetected.
The torque module 52 monitors an actual pump torque 64, TP, that may be measured at the output shaft 17 of the electric motor 18 that drives the pump 16. However, this disclosure is not limited to measuring the actual pump torque 64 at the output shaft 17 and can be obtained and measured by other methods. A current pump speed can also be monitored at the output shaft 17. TP 64 is input to the comparison unit 56. A desired torque module 54 receives a pump speed request 65 and determines a desired pump torque 66, TP
The comparison unit 56 determines a torque deviation 68 based on comparing TP 64 and TP
The confidence module 58 determines a current confidence factor 70 as a function of the torque deviation 68 at a current pump speed during a current iteration. The confidence module can include a look-up table for determining the current confidence factor 70 associated with the torque deviation 68 at the current pump speed. The current confidence factor 70 includes a factor ranging between and including zero (“0”) and one (“1”). A confidence factor of “1” relates to a highest level of confidence that the torque deviation 68 at the current pump speed is acceptable. For instance, a confidence factor of “1” would correspond to no torque deviation between the actual pump torque and the desired pump torque. A confidence factor of “0” relates to a lowest level of confidence that the torque deviation 68 at the current pump speed is acceptable. For instance, a confidence factor of “0” would correspond to an unacceptable or impermissible torque deviation between the actual pump torque and the desired pump torque. The confidence factor associated with a torque deviation at a given pump speed can be predetermined during calibration, and obtained using the look-up table, to act as a tolerance for fluctuating torque deviations. As will become apparent, the current confidence factor 70 enables the allowance of some deviation in TP 64 from TP
The EWMA filter 60 receives the confidence factor 70 between and including “0” and one “1.” The EWMA filter 60 is a statistical filter that can be utilized to iteratively calculate an average confidence factor based on the current confidence factor and an average confidence factor calculated in an immediately preceding iteration. Even more specifically, the EWMA filter 60 can be utilized to iteratively calculate the average confidence factor based on a weighted average between the current confidence factor and the average confidence factor calculated in the immediately preceding iteration. A relationship between the average confidence factor, the current confidence factor 70 and the average confidence factor calculated in the immediately preceding iteration may be expressed as follows:
i=CFi*w+
wherein
The fault condition detection module 62 compares
If
A presence of a fault condition in the hydraulic circuit can be detected only when
The failure condition determination module 76 receives the designated output 74 indicating the absence (e.g., pass-flagged) or presence (e.g., fault-flagged) of a detected fault condition during each iteration of the controller. As aforementioned, a pass-flagged designated output also indicates the presence of a detected acceptance condition. The failure condition determination module 76 includes a counter for monitoring a plurality of detected fault conditions during a current drive cycle. Likewise, the counter (or a separate counter) of the failure condition determination module 76 monitors a plurality of detected acceptance conditions during the current drive cycle. In an exemplary embodiment, the drive cycle may is initiated in response to a key-on event and terminated in response to a key-off event. The plurality of detected fault conditions can be compared to a failure condition threshold and the plurality of detected acceptance conditions can be compared to a pass condition threshold. If the plurality of detected fault conditions exceed the failure condition threshold, a failure condition 78 can be determined. If the plurality of detected acceptance conditions exceed the pass condition threshold, a pass condition 77 can be determined. Hence, the counter(s) within the failure condition determination module 76 can incrementally count the designated output 74 from each iteration, designating one of a fault-flagged and a pass-flagged average confidence factor, and compare the sum of the designated outputs 74 designated as fault-flagged to the failure condition threshold and compare the sum of the designated outputs 74 designated as pass-flagged to the pass condition threshold. In an exemplary embodiment, the failure condition threshold corresponds to a maximum number of average confidence factors designated as fault-flagged allowed during a drive cycle (e.g., current drive cycle) before a failure condition is determined.
In response to the determined failure condition 78 in the hydraulic circuit, the control module 5 may execute a control action. The control action can include recording a diagnostic trouble code corresponding to the determined failure condition 78. Further, the control action can include displaying a message corresponding to the failure condition 78. The displayed message can include a service warning displayed upon an instrument panel or a human machine interface within the vehicle. If the plurality of detected fault conditions exceeding the failure condition threshold are all positive fault-flags having a value of “1,” the determined failure condition 78 is indicative of insufficient hydraulic fluid levels within the hydraulic circuit 11. Similarly, if the plurality of detected fault conditions exceeding the failure condition threshold are all negative fault-flags each having a value of “(−1),” the determined failure condition 78 is indicative of hydraulic fluid blockage within the hydraulic circuit. It will be appreciated that when a failure condition has been determined, components within the transmission (e.g., direct drive transmission) may not be adequately cooled and lubricated even though the transmission is still capable of providing motive torque. Failure to service the failure condition can result in damage to the transmission components.
In an exemplary embodiment of the present disclosure, the counter within the failure condition determination module 76 is reset during a subsequent drive cycle if the plurality of detected fault conditions does not exceed the failure condition threshold. However, when a failure condition is determined when the plurality of detected fault conditions exceed the failure condition threshold, the failure condition can be maintained at the initiation of the subsequent drive cycle. During the subsequent drive cycle, the plurality of detected acceptance conditions can be monitored by the counter within the failure condition determination module 76. The plurality of detected acceptance conditions during the subsequent drive cycle can be compared to the pass condition threshold. The maintained failure condition that was determined in the previous drive cycle can be reset if the plurality of detected acceptance conditions exceed the pass condition threshold during the subsequent drive cycle.
In an alternative embodiment, the utilization of determining a confidence factor is not required for determining a failure condition in the hydraulic circuit 11. With reference to the HCFD controller 200 of
In the alternative embodiment,
The flowchart 300 starts at block 302 and proceeds to block 304. Block 304 monitors an actual pump torque and monitors a desired pump torque during a current drive cycle. The current drive cycle can be initiated in response to a key-on event and terminated in response to a key-off event. The desired pump torque includes a target pump torque required to achieve a pump speed request for maintaining desired flow characteristics of hydraulic fluid for providing lubrication and temperature management within the hydraulic circuit. The flowchart proceeds to block 306.
Block 306 determines a current torque deviation based on a deviation in the actual pump torque from the desired pump torque. The flowchart 300 proceeds to block 308. Block 308 iteratively calculates an average torque deviation based on a weighted average between the current torque deviation and an average torque deviation calculated in an immediately preceding iteration. An exponentially weighted moving average filter can be utilized to iteratively calculate the average torque deviation. The average torque deviation can be calculated utilizing Eq. [1], wherein the term “torque deviation” replaces the term “confidence factor.” The flowchart proceeds to block 310.
Block 310 designates the average torque deviation as one of flagged and un-flagged. Specifically, the average torque deviation calculated in block 308 is compared to a fault condition threshold. The average torque deviation is designated as flagged when the average torque deviation is greater than the fault condition threshold. The average torque deviation is designated as un-flagged when the average torque deviation is not greater than the fault condition threshold. The average torque deviation designated as flagged can include the average torque deviation having a positive flag, wherein the positive flag can correspond to a detected fault condition in the average torque deviation indicative of insufficient hydraulic fluid levels within the hydraulic circuit. Likewise, the average torque deviation designated as flagged can include the average torque deviation having a negative flag, wherein the negative flag can correspond to a detected fault condition in the average torque deviation indicative of hydraulic fluid blockage within the hydraulic circuit. The flowchart proceeds to block 312.
Block 312 determines a failure condition in the hydraulic circuit when a plurality of average torque deviations designated as flagged exceed a failure condition threshold. Each flagged average torque deviation can be monitored utilizing a counter. The failure condition threshold can correspond to a maximum number of average torque deviations designated as flagged allowed during a drive cycle before a failure condition is determined. If the fault condition is determined, a failure output 313 can execute a control action including at least one of recording a diagnostic trouble code corresponding to the determined failure condition and displaying a message corresponding to the determined failure condition.
The disclosure has described certain preferred embodiments and modifications thereto. Further modifications and alterations may occur to others upon reading and understanding the specification. Therefore, it is intended that the disclosure not be limited to the particular embodiment(s) disclosed as the best mode contemplated for carrying out this disclosure, but that the disclosure will include all embodiments falling within the scope of the appended claims.
