BACKGROUND OF THE INVENTION

1. Field of the Invention

[0001] This invention relates generally to a system and method for setting the slip in a torque converter of a vehicle and, more particularly, to a system and method for providing a minimum torque converter slip in response to changes in engine speed and transmission gears so as to minimize vehicle driveline vibrations and provide good fuel economy.

2. Discussion of the Related Art

[0002] Internal combustion engine vehicles that employ automatic transmissions typically include a torque converter positioned between the engine and the transmission of the vehicle. A torque converter is a fluid coupling device typically including an impeller coupled to an output shaft of the engine and a turbine coupled to the input shaft of the transmission. The torque converter uses hydraulic fluid to transfer rotational energy from the impeller to the turbine. Thus, the torque converter can disengage the engine crank shaft from the transmission input shaft during vehicle idling conditions to enable the vehicle to stop and/or to shift gears.

[0003] The rotational speed of the impeller relative to the turbine in the torque converter is typically different so that there is a converter slip therebetween. Because large slips between the engine output and the transmission input significantly affect the fuel economy of the vehicle, some vehicles employ a torque converter clutch (TCC) for controlling or reducing the slip between the engine and the transmission. The TCC can also mechanically lock the impeller at the output of the engine to the turbine at the input of the transmission so that the engine and transmission rotate at the same speed. Locking the impeller to the turbine is generally only used in limited circumstances because of various implications.

[0004] Thus, a TCC generally has three modes. A fully locked mode as just described, a fully released mode and a controlled slip mode. When the TCC is fully released, the slip between the impeller and the turbine of the torque converter is only controlled by the hydraulic fluid therebetween. In the slip mode, the TCC controls the pressure of hydraulic fluid in the torque converter so that the slip between the torque converter impeller and the turbine can be set so that is does not exceed a predetermined slip.

[0005] Various engine torque perturbations, engine pulses and other engine noises, generally in the range of 30-300 Hz, can be passed through the torque converter from the engine to the transmission and onto the vehicle dhveline, which are felt by the vehicle occupants as shaking or vibrations of the vehicle. Typically, these engine pulses and perturbations are more easily passed through the torque converter as the amount of slip between the engine and the transmission is reduced. Thus, for those times when the TCC is locked or has set the slip in the torque converter between the engine and the transmission to be very low, such engine vibrations are typically passed through to the vehicle drive-train. These types of engine disturbances and noise vary depending on the engine speed and the transmission gear.

SUMMARY OF THE INVENTION

[0006] In accordance with the teachings of the present invention, a method is disclosed for adjusting the slip of a torque converter provided between an engine and a transmission of a vehicle in real-time, where the converter slip is set by a torque converter clutch. A sensor at an output of the transmission is used to determine vibrations transmitted through the torque converter to the dhveline of the vehicle. The sensor signal from the sensor is sent to a controller where it is converted to the frequency domain. If the amplitude of the frequency signal exceeds a predetermined threshold, then the algorithm increases the converter slip until the frequency vibrations are reduced below the threshold.

[0007] Additional features of the present invention will become apparent from the following description and appended claims, taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 is a block diagram showing various drive-train components of a vehicle;

[0009] Figure 2 is a flow chart diagram showing a process for adjusting the torque converter slip in real-time as a function of engine speed, transmission gear and engine torque so as to reduce vibrations, according to an embodiment of the present invention;

[0010] Figure 3 is a flow chart diagram showing a process for adjusting the torque converter slip in real-time as a function of engine speed, transmission gear and engine torque so as to reduce vibrations, according to another embodiment of the present invention; and

[0011] Figure 4 is a flow chart diagram showing a process for adjusting the torque converter slip in real-time as a function of engine speed, transmission gear and engine torque so as to reduce vibrations, according to another embodiment of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS [0012] The following discussion of the embodiments of the invention directed to a method for adjusting a slip for a torque converter between a vehicle engine and transmission is merely exemplary in nature, and is in no way intended to limit the invention or its applications or uses.

[0013] Figure 1 is a block diagram of various power-train components of a vehicle 10. The power-train components include an engine 12 and a transmission 14. An output shaft of the engine 12, represented by line 16, is coupled to one end of a torque converter 18, and an input shaft of the transmission 16, represented by line 20, is coupled to an opposite end of the torque converter 18. As discussed above, the torque converter 18 transfers rotational energy from the engine 12 to the transmission 14 using hydraulic fluid so that the engine 12 can be disengaged from the transmission 14 when necessary. A TCC 22 sets a torque converter slip in the torque converter 18 between the engine 12 and the transmission 14, as discussed above. In this diagram, engine output power is depicted as engine rotational speed N _E measured in revolutions per minute (RPM) and engine torque T _E measured in Newton-meters. Likewise, the speed of the transmission 14 at its input is represented by transmission input speed Ni and transmission torque Ti . The torque slip in the torque converter 18 is defined as N _E - Ni An output shaft of the transmission 14, represented as line 28, is coupled to a dhveline 30 of the vehicle 10 that distributes the engine power to the vehicle wheels (not shown) in a manner that is well understood to those skilled in the art. The speed of the output shaft 28 of the transmission 14 is represented as N ₀ and the torque of the output shaft 28 of the transmission 14 is represented at T ₀ .

[0014] The vehicle 10 also includes a controller 36 intended to represent both an engine controller and a transmission controller. The controller 36 receives a throttle position signal from a vehicle throttle 38, and provides a signal to the engine 12 to provide the necessary engine speed and a signal to the transmission 14 to provide the necessary gear to satisfy the throttle demand. Additionally, depending on the selected engine speed and transmission gear, the controller 36 provides a signal on line 40 to the TCC 22 to set the desired torque converter slip. A sensor 42 measures the output behavior of the transmission 14. In one non-limiting embodiment, the sensor 42 measures the rotational speed of the output shaft 28 of the transmission 14 and sends a speed signal to the controller 36. Suitable examples for the sensor 42 include an encoder, speed sensor, accelerometer, torque sensor, etc.

[0015] The present invention proposes a process for adjusting the torque converter slip in response to changes in engine speed and/or transmission gear and/or engine torque so that the slip is at a desired minimum to conserve fuel, but is not so low where engine pulses and other noise signals are transferred through the torque converter 18 to the driveline 30 and are felt by vehicle occupants. The controller 36 will select the particular slip and transmit it to the TCC 22 on the line 40 for the current engine speed, transmission gear and engine torque based on a pre-populated table that is stored in the controller 36 as a result of vehicle testing or other operations for a minimum torque converter slip that provides good fuel economy and reduced vibration transfer. One process for populating such a table can be found in U.S. Patent Application Serial No. 12/043,499, titled Aggressive Torque Converter Clutch Slip Control Design Through Dhveline Torsional Velocity Measurements, filed March 6, 2008, assignee of this application and herein incorporated by a reference. If the selected torque converter slip for a particular engine speed, transmission gear and engine torque does not provide the desired slip for preventing vibrations from being transferred to the dhveline 30, then the signal from the sensor 42 is used to determine the vibrations in the controller 36, which can then increase the torque converter slip if the vibrations exceed a predetermined threshold.

[0016] Figure 2 is a flow chart diagram 50 showing a method for adjusting the torque converter slip for the reasons discussed above in realtime, i.e., during operation of the vehicle, according to an embodiment of the present invention. The algorithm starts at box 52. At box 54, the algorithm reads the transmission output speed signal from the sensor 42 and fast Fourier transforms the sensor signal at box 56 to convert it to the frequency domain. The algorithm then calculates a transfer torsional value λ _FFT at the output of the transmission 14 in the frequency domain at box 58, which gives an amplitude value. Alternatively, the torsional amplitude could be determined by passing the transmission output sensor signal from the sensor 42 through a bandpass filter. The algorithm then determines whether the absolute value of the transfer torsional value λ _FFT of the transmission output speed is greater than a set torsional value λ _{engine speed gear} , scaled by a factor a, at decision diamond 60. The set torsional value λ _{engine speed gear} is provided in a look-up table for each desirable combination of engine speed, transmission gear and engine torque.

[0017] If the transfer torsional value λ _FFT is greater than the set torsional value λ _{engine speedι gear} for the specific engine speed and gear that the vehicle is currently in, the algorithm then determines whether the transfer torsional value λ _FFT is greater than the set torsional value λ _{engine speed gear} at decision diamond 62, otherwise it returns to detecting the transmission output speed at the box 54. If the transfer torsional value λ _FFT is greater than the set torsional value λ _{engine speed gear} for the current engine speed and gear at the decision diamond 62, meaning that significant vibrations are being transferred through the dhveline 30, the algorithm will increase the torque converter slip at box 64 for that location in the look-up table. If the transfer torsional value λ _FFT is not greater than the set torsional value λ _{engine speed gear} for the current engine speed and gear at the decision diamond 62, meaning the torque converter slip is not the best for fuel economy, then the algorithm will decrease the torque converter slip at box 66 to minimize the slip value for that location in the look-up table. The new torque converter slip from the boxes 64 and 66 based on the engine speed, transmission gear and engine torque is then stored in the slip table at box 64 and replaces the previous slip value.

[0018] The process of the flow chart diagram 52 offers one embodiment for changing the values in the torque converter slip table in realtime during vehicle operation. In other embodiments, other processes can be incorporated for changing the torque converter clutch slip for the various engine speeds, transmission gears and engine torques. Figure 3 is a flow chart diagram 70 showing another process for adjusting the slip table in realtime, according to another embodiment of the present invention, where like elements to the flow chart diagram 52 are identified by the same reference number. Particularly, instead of determining whether the transfer torsional value λ _FFT is greater than or equal to the set torsional value λ _{engine speed gear} , the system employs a feedback controller at box 72 that computes how much the slip should increase or decrease based on various vehicle parameters.

[0019] Figure 4 is a flow chart diagram 80 showing another process for determining a minimum torque converter clutch slip in real-time based on engine speed, transmission gear and engine torque, according to another embodiment of the present invention, where like elements to the flow chart diagram 52 are identified by the same reference numeral. In this embodiment, the transfer torsional value λ _FFT at the box 58 is sent to a feedback controller box 82 that calculates an error between the transfer torsional value λ _FFT and a predetermined threshold reference value that can be a function of gear state, engine speed and engine torque. Based on the feedback, the feedback controller determines how much the torque converter slip should be increased or decreased for the transmission gear, engine speed and engine torque combination in the look-up table.

[0020] The foregoing discussion discloses and describes merely exemplary embodiments of the present invention. One skilled in the art will readily recognize from such discussion and from the accompanying drawings and claims that various changes, modifications and variations can be made therein without departing from the spirit and scope of the invention as defined in the following claims.