METHOD FOR HANDLING DRIVETRAIN TOLERANCES

This invention relates generally to vehicle drivetrains and, more particularly, to handling drivetrain tolerances.

Modern vehicles have geometric tolerances that create mechanical play within a vehicle's drivetrain. The mechanical play can be caused by tolerances between various interacting components in the drivetrain. The mechanical play caused by the tolerances can cause noise, also known as clunk, during transitions between torque direction (positive or negative) in the drivetrain.

One implementation of a method for handling tolerances in a vehicle drivetrain includes detecting a request for a change in direction of the output torque of a propulsion system coupled to the drivetrain. The output rotational speed of a transmission in the vehicle is first increased for a predetermined time. Then output rotational speed of the transmission is decreased until the output rotational speed of the transmission reaches a predetermined contact speed. Increasing and decreasing the output rotational speed of the transmission bridges over the tolerances in the drivetrain resulting from the change in direction of the torque faster than conventional methods that usually simply decrease transmission output speed until impact.

In another implementation, the method includes detecting a request for a change in the direction in an output torque of a propulsion device coupled to the drivetrain. A profile is determined to bridge over tolerances in the vehicle drivetrain within a predetermined time by controlling the output rotational speed of a transmission

coupled to the propulsion device. The profile is executed by controlling the output rotational speed of the transmission using an electric motor coupled to the transmission. In yet another implementation, a method for handling tolerances in a drivetrain of a hybrid electric vehicle having a transmission and an electric motor includes detecting a driver request for a directional change in torque. The electric motor is controlled to increase the rotational speed of an output shaft on the transmission for a predetermined time. The rotational speed of the output shaft is decreased until the rotational speed of an output of the transmission reaches a predetermined contact speed and the tolerances in the drivetrain have been bridged over. The vehicle is then operated at the requested torque.

The following detailed description of preferred embodiments and best mode will be set forth with regard to the accompanying drawings, in which:

FIG. 1 is a is a schematic view of an embodiment of a drivetrain system in a vehicle;

FIG. 2 is a flow chart illustrating a method of handling drivetrain tolerances in a vehicle;

FIG. 3 is a graph illustrating, in general fashion, the effects of a prior art method of handling drivetrain tolerances in a vehicle by slowing down the velocity of a torque direction change;

FIG. 4 is a graph illustrating, the effects of the method of handling drivetrain tolerances in a vehicle of FIG. 2; and

FIG. 5 is a graph illustrating, in general fashion, a profile generated by the method of FIG. 2.

Referring in more detail to the drawings, FIG. 1 illustrates a vehicle generally shown at 10, such as a hybrid electric vehicle. The vehicle 10 includes a drivetrain generally indicated at 12 coupled to wheels 14 to propel the vehicle 10. The drivetrain 12 can include an internal combustion engine 16 for providing mechanical power for the vehicle 10, a transmission 18 for transferring the mechanical power to the wheels 14, an electric motor 20 for converting electrical energy to mechanical power and vice versa, a differential 22 for transferring power to the wheels, and a number of shafts connecting the drivetrain components to one another. It is also possible to have more than one electric motor. For example, the transmission 18 can include an input shaft 24, an output shaft 26 and a countershaft 28 interacting with a number of gears. The internal combustion engine 16 can be coupled to the input shaft 24 of the transmission 18 via a clutch or spring damper 30 or combination. The electric motor 20 can also be coupled to the input shaft 24, the output shaft 26, or the countershaft 28 of the transmission. The output shaft 26 connects the transmission 18 to the differential 22. The differential 22 is connected to the wheels 14 via axles 32 to transmit rotational force from the output shaft 26 to the wheels. The arrangement of the drivetrain 12 may vary from that shown in FIG. 1. For example, the vehicle 10 may be front wheel drive, real wheel drive or all wheel drive vehicle. Moreover, the arrangement of the engine 16 and electric motor 20 with the transmission 18 may also vary.

FIG. 2 illustrates an implementation of a method 100 for handling tolerances in a vehicle drivetrain. For example, the method 100 can be implemented using the drivetrain 12 described above. In general, the method 100 includes determining tolerances in the drivetrain 12 and receiving a trigger to indicate a change in torque direction. A change in torque direction may include a change from positive torque to negative torque or vice versa. Positive torque may include torque applied to the

wheels via the drivetrain 12 to increase or maintain wheel speed. Negative torque may include torque applied to the wheels to slow the wheel speed, such as when braking or coasting. When the vehicle is coasting, the transmission 18 may apply resistance to the rotation of the wheels 14 through the drivetrain 12 and thus gradually slow the wheel speed.

In response to the trigger, the method 100 accelerates the output of the transmission 18 to bridge over the tolerances in the drivetrain 12. Bridging over the tolerances in the drivetrain 12 involves rotating the drivetrain components through the angular rotation or area of play in which there is relative and not conjoint movement between drivetrain components when a change in torque direction occurs. Before the tolerances are bridged over, the drivetrain 12 cannot transfer torque to the wheels 14 due to the area of play in the drivetrain 12. By accelerating and later decelerating the output of the transmission 18, the tolerances in the drivetrain 12 are bridged over quickly in response to a driver request for a change in torque direction, and hence, clunk and tactile feedback caused by play in the drivetrain 12 are reduced. For example, FIG. 3 shows a graph of a previous method of handling drivetrain tolerances. In response to a driver request for a reversal in torque direction, the output of the transmission 18 may be slowed in order to reduce the amount of clunk when the tolerances are bridged over in the drivetrain 12. But the slowed output can create a delay in the torque response of the drivetrain 12. By slowing down the output of the transmission 18, it takes longer to reach the desired torque output of the drivetrain 12 requested by the driver. As a result, the driver may perceive the response of the vehicle 10 as being sluggish. For example, FIG. 3 shows a torque request by the driver and a corresponding torque response optimized for driver comfort and a quick response. The optimized torque response would be comfortable to the driver but would result in noticeable drivetrain clunk if executed without

impiementing a method for handling drivetrain tolerances. FIG. 3 also shows an actual torque output resulting from slowing the transmission output. The magnitude of the impact upon bridging over the drivetrain tolerances may be reduced, but the resulting torque is delayed. The driver may perceive this delay as a sluggish response from the vehicle's drivetrain 12.

In comparison, the response of method 100 allows the torque output of the drivetrain 12 to track a torque output that the driver desires. An example of the torque output resulting from implementation of method 100 is shown in FIG. 4. FIG. 4 shows a torque request by the driver, a corresponding torque response optimized for driver comfort and quick response, and a torque response output from method 100. The output of the transmission 18 is accelerated in comparison to the wheel speed. Accelerating the output of the transmission 18 bridges over the tolerance in the drivetrain 12 more quickly. The torque response using method 100 substantially tracks the torque response optimized for driver comfort. But unlike the optimized torque response, method 100 results in a reduced perceivable clunk. According to this particular implementation, the method 100 begins at step 110 by determining the drivetrain tolerances. The drivetrain tolerances can be determined through any acceptable method of determining drivetrain tolerances such as engineering calculations, drivetrain simulation models, tolerance measurements on other vehicles of the same or a similar model, and the like. In one implementation, the drivetrain tolerances may be determined by measuring the amount of rotation of the electric motor 20 when the transmission 18 is shifted from reverse to a forward gear or a forward gear to reverse. The drivetrain tolerances may be determined or calculated by determining the amount of rotation of electric motor 18 or a shaft coupled to the electric motor from the time of the shift request until torque is transferred to the wheels 14 in the requested direction. The determination can be

made when the transmission 18 is shifted from a forward gear to reverse or from reverse to a forward gear. The vehicle 10 can determine when the electric motor 20 has bridged over the tolerances by monitoring the amount of power drawn by the electric motor when transitioning between forward and reverse, or vice versa. Once the electric motor 20 has bridged over the tolerances in the drivetrain, the amount of power drawn by the electric motor may increase due to increased loading of the electric motor by the drivetrain. Alternatively, determination of when the tolerances have been bridged over can be done by monitoring for a change in wheel speed, output torque, and the like.

The drivetrain tolerances may be determined once for the vehicle, or alternatively, may be determined periodically, such as after a scheduled number of miles driven, ignition cycles, and the like. The amount of drivetrain tolerance may change over time due to wear on or breaking in of the drivetrain components. Periodic determinations of the drivetrain tolerances may enable the method 100 to monitor and alter as needed the amount of tolerance needed to be bridged over. At step 112, a trigger is received. The trigger indicates a reversal in torque direction such as a change from positive torque to negative torque or negative torque to positive torque. The trigger may be an actual detection of a reversal in torque direction, such as a detection of the rate of torque change, or may be a detection of a driver request for a torque change that could necessitate a reversal in torque direction. For example, the driver may take their foot off the gas pedal while driving, causing a change in torque from a positive torque to a negative torque. In this example, the trigger could include, the detection of the release of the gas pedal, the detection of the rate of change in torque demanded by the driver, or the detection in the rate of torque as a result of the release of the gas pedal.

At step 114, the current wheel speed may be determined. The current wheel speed may be determined via sensors (not shown) at the wheels 14 or by determining the rotational speed of a component coupled with the wheels such as axle 32, differential 22, output shaft 26, or the like.

At step 1 16, time required to reach the target torque is determined. The target torque is the resulting output torque of the drivetrain 12 in response to the driver's torque demand. The time to reach the target torque may be determined based upon a function of the change in torque from the current torque to the target torque. A larger difference between the current torque and the target torque can increase the amount of time required to reach that target torque. Additionally, the time required can be based upon a function of the current wheel speed. The time required to reach the target torque can be used to determine a maximum amount of time available to bridge over the tolerances in the drivetrain 12 when changing torque direction. At step 118, a profile is generated for bridging over the tolerances in the drivetrain 12. The profile determines a target for the rotational speed of the output shaft 26 of the transmission 18 while the drivetrain tolerances are bridged over. By determining the rotational speed of the output shaft 26, the profile provides a target rotational speed for the output shaft to bridge over the tolerances in the drivetrain 12 within the time determined in step 116. Bridging over the tolerances within the time determined in step 116 provides a quick response to the driver's demand for a change in torque direction. In one implementation, the rotational speed of the output shaft 26 of the transmission 18 is controlled throughout the profile by the electric motor 20. To bridge over the tolerances within the time determined in step 116, the profile may begin by increasing the rotational speed of the output shaft 26. Accelerating the output shaft 26 bridges over the tolerances in the drivetrain 12 quickly by spinning the output shaft 26 at a rotational speed faster than the current wheel speed. The

difference in speeds between the output shaft 26 and the wheel speed causes the drivetrain components to rotate through the tolerances or play between the components.

The profile also decelerates the output shaft 26 rotational speed to, for example, reduce the clunk that occurs at the point the drivetrain tolerances have been bridged over. The output shaft 26 can be decelerated until its rotational speed generally matches the wheel speed at a predetermined contact speed. The matched speeds of the output shaft 26 and the wheel speed may be within an acceptable range of each other, taking into account tolerances of the drivetrain 12, the electric motor 20, and the like.

An example of a profile is shown in FIG. 5. The profile in FIG. 5 shows a rotational speed of the output shaft 26 of the transmission 18 over time and the wheel speed. The area between the rotational speed of the output shaft 26 and the wheel speed is equivalent to the drivetrain tolerances determined in step 110. As the profile is executed, the output shaft 26 is spun through the driveline tolerances. The profile also shows discrete steps performed by the electric motor 20 to execute the profile. The length of time of each step can depend upon the time required to update the output of the electric motor 20. The number of steps executed within the profile can vary depending upon the amount of time determined in step 116 and the amount of time required to update the output of the electric motor 20.

Another example of a profile is shown in FIG. 4. FIG. 4 shows the wheel speed and the output speed of the output shaft 26 of the transmission 18. The area 34 between the output shaft rotational speed and the wheel speed is the tolerance or play in the drivetrain 12. In one implementation, the profile can be determined based on the amount of rotation of the electric motor 20 or the output shaft 26 required to bridge over the tolerances in the drivetrain 12. The profile is calculated to complete the

rotation within the time determined in step 116. in one implementation, the profile may be generated by determining the number of steps that may be taken within the predetermined time for the electric motor 20 to bridge over the tolerances in the drivetrain and determining the output of the electric motor for each step. A determination can be made as to whether the electric motor 20 has sufficient torque to complete the profile within the pre-determined time. If the motor 20 does not have sufficient torque to execute the profile, the rates of acceleration and deceleration can be adjusted to comply with the electric motor's 20 capabilities. The time to complete the profile can also be adjusted to compensate for the electric motor's 20 capabilities. At steps 120 and 122, the profile generated at step 118 is executed. At step 120, execution of the profile may begin by increasing the rotational speed of the output shaft 26. The electric motor 20 may drive the output shaft 26 of the transmission 18. The output rotational speed can be increased until it reaches a peak 36 indicated at the profile. The rotational speed of the electric motor 18, the input shaft 24, and/or the output shaft 26 of the transmission 18 can be monitored to determine whether the rotational speed complies with the profile generated at step 118. The output speed of the electric motor 20 can be adjusted to compensate for any differences between the actual speed of the output shaft 26 and the profile.

At step 122, the output shaft 26 is decelerated. The deceleration in the output shaft 26 follows the acceleration in the rotational speed of the output shaft as determined by the profile. As can be seen in FIG. 4, the speed of the output shaft 26 decelerates until it generally matches the wheel speed. The speeds should match at about the same time that the tolerances of the drivetrain 12 are bridged over. Matching the output shaft 26 rotational speed and the wheel speed reduces or eliminates the perceivable clunk when the tolerances of the drivetrain 12 are bridged over by

reducing the impact when the drivetrain components engage. Once engaged, the drivetrain components are able to transmit torque to the wheels 14. At step 124, the vehicle 10 is operated at the desired or requested torque. At this point, the wheel speed is accelerated or decelerated by the internal combustion engine 16 and/or the electric motor 20 based on the driver's request. If the driver's request was to increase the vehicle torque the vehicle 10 may be operated to increase the torque from the internal combustion engine 16 and/or the electric motor 20. Likewise, the driver request was to decrease the vehicle torque, the electric motor 20 and/or the internal combustion engine 16 may decrease the torque through the drivetrain 12.

While certain preferred embodiments have been shown and described, persons of ordinary skill in this art will readily recognize that the preceding description has been set forth in terms of description rather than limitation, and that various modifications and substitutions can be made without departing from the spirit and scope of the invention. The invention is defined by the following claims.