Patent Application
20170234755
This disclosure relates to the field of vehicle controls. More particularly, the disclosure pertains to a method of calibrating a torque sensor.
Many vehicles are used over a wide range of vehicle speeds, including both forward and reverse movement. Some types of engines, however, are capable of operating efficiently only within a narrow range of speeds. Consequently, transmissions capable of efficiently transmitting power at a variety of speed ratios are frequently employed. Transmission speed ratio is the ratio of input shaft speed to output shaft speed. When the vehicle is at low speed, the transmission is usually operated at a high speed ratio such that it multiplies the engine torque for improved acceleration. At high vehicle speed, operating the transmission at a low speed ratio permits an engine speed associated with quiet, fuel efficient cruising.
A common type of automatic transmission includes a gearbox capable of alternately establishing a fixed number of power flow paths, each associated with a fixed speed ratio. The gearbox includes a number of shift elements such as clutches and brakes. A particular power flow path is established by engaging a particular subset of the shift elements. To shift from one power flow path to another power flow path with a different speed ratio, one or more shift elements must be released while one or more other shift elements must be engaged. Some shift elements may be passive devices such as one way clutches, while other shift elements engage or disengage in response to commands from a controller. For example, in many automatic transmissions, the shift devices are hydraulically controlled friction clutches or brakes. The controller regulates the torque capacity of the shift element by regulating an electrical current to a solenoid, which adjusts a force on a valve which, in turn, adjusts a pressure in a hydraulic circuit.
Most transmissions are equipped with a launch device. When the vehicle is stationary or moving very slowly, the gearbox input speed is less than the minimum operating speed of the engine. A launch device transmits torque from the engine to the gearbox input while permitting the engine to rotate at an acceptable speed. A common launch device is a torque converter which includes an impeller driven by the engine and a turbine driving the gearbox input. Torque is transferred from the impeller to the turbine hydro-dynamically. Many torque converters also include a hydraulically controlled lock-up clutch that couples the impeller to the turbine, bypassing the hydro-dynamic power transfer path to improve efficiency at higher vehicle speeds. Other transmissions use an actively controlled launch clutch as a launch device.
A modern automatic transmission is controlled by a microprocessor which adjusts the torque capacity of each shift element, including any lock-up clutch, at regular intervals. At each interval, the controller gathers information indicating the driver's intent, such as the positions of the shifter (PRNDL), the accelerator pedal, and the brake pedal. The controller also gathers information about the current operating state of the vehicle, engine, and transmission, such as the speed of various elements and the torque transmitted by various elements. Using this information, the controller determines whether to maintain the currently established power flow path or to shift to a different power flow path. If the controller decides to shift to a different power flow path, the controller then adjusts the torque capacities of the off-going shift elements and the on-coming shift elements in a coordinated manner in order to make the transition as smoothly as possible.
The capability to shift smoothly depends on the ability to accurately determine operating state of the vehicle from sensor inputs. Various noise factors complicate this by influencing the relationship between the sensed quantity and the sensor output. These noise factors include environmental conditions such as temperature, component wear over time, and part-to-part variability in the manufacturing process. Methods which measure and compensate for these noise factors improve the ability to accurately determine operating state and therefore improve the ability to control the transmission.
A method of manufacturing transmission includes fabricating a plurality of shafts and sensors, testing each of the shafts and sensors, assembling the transmissions, and entering compensation data into controllers based on the test results. Each shaft has a magnetized section adapted for use with a magneto-elastic torque sensor. Each production shaft is tested with a master torque sensor, which may be either a pre-selected torque sensor with known sensitivity or may be an alternative magnetic flux sensing instrument. Similarly, each production sensor is tested with a master shaft, which may be either a pre-selected shaft with known magnetic signature or may be an alternative device that emits a known magnetic signature. The testing may produce characterizing data such as average zero torque electrical output and a metric of electrical output variability with respect to rotational position. The characterizing data may be utilized to identify a range for each shaft and a range for each sensor which are then used to select the compensation data to be entered into each controller.
Embodiments of the present disclosure are described herein. It is to be understood, however, that the disclosed embodiments are merely examples and other embodiments can take various and alternative forms. The figures are not necessarily to scale; some features could be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention. As those of ordinary skill in the art will understand, various features illustrated and described with reference to any one of the figures can be combined with features illustrated in one or more other figures to produce embodiments that are not explicitly illustrated or described. The combinations of features illustrated provide representative embodiments for typical applications. Various combinations and modifications of the features consistent with the teachings of this disclosure, however, could be desired for particular applications or implementations.
Transmission 12 establishes various power flow paths having different speed ratios by selectively engaging and disengaging a number of shift elements. Controller 30 adjusts the torque capacity of on-coming and off-going friction clutches during shift events. For some types of transmissions, such as dual clutch transmissions, controller 30 also continuously adjusts the torque capacity of one of more clutches to launch the vehicle from a stationary position. Controller 30 may utilize signals from transmission 12, such as input and output speed and torque sensors. Controller 30 may also send control signals to engine 10 to adjust the torque output of the engine.
One known type of torque sensor is based on materials that have magnetic properties which change in response to shear strain. When a shaft transmits torque, the surface of the shaft deflects in shear. For a given shaft geometry, the surface shear strain is proportional to the torque transmitted by the shaft. A magneto-elastic torque sensor produces an electrical signal that varies in response to the change in the magnetic field. A controller can estimate the transmitted torque by processing the electrical signal. Such a torque sensor is described in U.S. Pat. No. 6,698,299.
Several factors, in addition to shaft torque, influence the electrical signal generated by the sensor 40. These other factors are collectively known as noise factors. Accurately determining shaft torque requires measures to minimize and/or compensate for these factors. The noise factors include temperature and part-to-part variability of the shaft and the sensor components. One way to compensate for temperature is to test the sensor and shaft at a variety of known shaft torques and known temperatures to produce a map indicating shaft torque as a function of voltage and temperature. Using this map, the controller measures the voltage and temperature and looks up a corresponding torque value, interpolating as necessary.
Ideally, the testing that generates the map would be performed with the actual sensor and shaft used in the transmission. In that way, the map would also compensate for part-to-part variability of the shaft and sensor manufacturing processes. In practice, this may be impractical. The shafts and sensors may be manufactured by different suppliers and not paired to one another until the transmission is assembled. Once the transmission is assembled, it may be impractical to run the testing on every transmission at the necessary variety of known temperatures and known shaft torques.
At 62, the sensor manufacturer fabricates a production sensor. At 64, the sensor manufacturer assembles the production sensor to the master shaft and runs tests. Since this testing is performed on every sensor, cost may dictate a less comprehensive set of controlled temperatures and controlled torques than the testing used to produce the master mapping. The result of this testing is a sensor mapping. Differences between the sensor mapping and the master mapping are attributable to part-to-part variability of the sensor manufacturing process. Similarly, at 66 and 68, a production shaft is fabricated and tested with the master sensor to produce a shaft mapping. When the production sensor and shaft are shipped to the transmission manufacturer, the sensor and shaft mapping are also transmitted to the transmission manufacturer. Alternatively, data that characterizes the difference between the sensor or shaft mapping and the master mapping may be transmitted. In a mass production environment, the shafts and sensors are marked or otherwise individually identified so that each unit is associated with a particular corresponding mapping.
Once a particular shaft and sensor are paired by the transmission manufacturer, the transmission manufacturer combines the master mapping, the shaft mapping, and the sensor mapping at 70 to produce a production mapping. One way to accomplish this is to compute differences between the master mapping and the sensor and shaft mappings respectively and add these differences to the master mapping. After the transmission is assembled at 72, the production mapping is entered into the transmission controller at 74. This production mapping at least partially compensates for the part-to-part variability of the sensor and the shaft. If there is interaction between the sensor variability and shaft variability, the production mapping does not capture that interaction. Also, if the sensor and shaft mappings are produced at the component manufacturing facility, the production mapping does not compensate for any changes that may occur while the components are in transit.
The process may be modified to compensate for changes in shaft magnetization that occur in transit by doing the shaft mapping at the assembly facility using a portable tester like the tester illustrated in
While no torque is applied to the shaft, the shaft may be rotated by rotating shaft 92. Test controller 86 measures and records the electric current at a number of different shaft rotational positions. If the maximum and/or minimum current are outside of a specification, the shaft may be discarded or returned for rework. This data may be processed to generate scalar values characterizing the average zero torque electrical output and the variability of zero torque electrical output as a function of rotational position. This testing may be repeated with a known torque applied to the exposed end of the shaft to characterize the rate of change of voltage with respect to torque. The tester may also include a temperature sensor to record the temperature at which the test results are taken. The test results may be shifted to compensate for temperature differences using temperature sensitivity data derived from the master mapping.
Similarly, at 104 and 106, N shafts representing the anticipated spectrum of shaft variability are tested with a master sensor to generate a set of N reference shaft mappings. A master sensor may be an actual sensor unit which is pre-selected for a known sensitivity to magnetic flux magnitude and spatial profiles. Alternatively, it may be a magnetic flux sensing instrumentation with adequate sensitivity to magnitude and spatial profiles to classify the magnetized shafts. The shaft testing may be simplified for a reduced shaft map to characterize magnetic behaviors only under selected conditions that are sufficient for the purpose of shaft classification. At 108, each selected sensor is tested with each selected shaft to generate M×N production mappings. As in
Then, at 114, the production mapping corresponding to the closest matches is entered into the controller. The testing performed at 108 to create the production mappings may be much more thorough than the testing performed at steps 102, 106, 110, and 112. To further increase the accuracy, the mapping entered into the controller may be modified based on the difference between the sensor mapping and the reference sensor mapping and/or the difference between the shaft mapping and the reference shaft mapping.
While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms encompassed by the claims. The words used in the specification are words of description rather than limitation, and it is understood that various changes can be made without departing from the spirit and scope of the disclosure. As previously described, the features of various embodiments can be combined to form further embodiments of the invention that may not be explicitly described or illustrated. While various embodiments could have been described as providing advantages or being preferred over other embodiments or prior art implementations with respect to one or more desired characteristics, those of ordinary skill in the art recognize that one or more features or characteristics can be compromised to achieve desired overall system attributes, which depend on the specific application and implementation. As such, embodiments described as less desirable than other embodiments or prior art implementations with respect to one or more characteristics are not outside the scope of the disclosure and can be desirable for particular applications.
