Continuously variable transmission (CVT) selection under transient driving conditions

Abstract

A system for selecting a manual transmission input gear during transient driving conditions (10) of a motor vehicle (14), comprising: a vehicle transmission (12); a motor (16) connected to the transmission (12), a torque converter (18) connected to the transmission (12), and a differential (20) providing a drive output; a control unit (34) in communication with the motor (16) and the gearbox (12); a switching device in communication with the control unit (34) which provides a manual selection by an operator of the motor vehicle (14) between a park mode, a reverse mode, a neutral mode, a drive mode and a manual mode; where, at the time of entering manual mode, a predicted gear is frozen close to an actual gear; wherein the transmission (12) defines a continuously variable transmission, CVT (12), comprising a first pulley (26) connected to an input shaft (22) and a second pulley (28) rotatably driven by a belt slidably connected to the first pulley (26) and the second pulley (28); furthermore comprising a range of pulley ratios divided into several bins that independently define successive segments of a total range of ratios of the CVT (12); furthermore comprising a bin center identified for any one of the several bins; wherein the predicted gear defines a predicted gear ratio and the actual gear defines a real CVT ratio, wherein the predicted gear ratio is frozen at the bin center of each of the multiple bins that are close to the real gear ratio at the time of entering manual mode, defined as approximately one to two bins away from the real gear ratio at the time of entering manual mode.

Description

[0001] The present disclosure relates to motor vehicle transmissions and the manual selection of operating modes by the operator during vehicle operation.

[0002] In vehicles with continuously variable transmissions (CVTs), the driver can typically switch from automatic to manual shift mode by selecting a manual shift option (M) on a transmission selector. The common manual shifting operation of CVT transmissions is also known as tap-up-tap-down (TUTD) mode and involves an initialization algorithm that freezes the variator ratio to a desired ratio determined by a steady-state driving ratio map. The operator typically expects the transmission variator ratio to freeze at the operator's desired ratio. However, it has been observed that when the algorithm freezes to the desired variator ratio using data from a steady-state driving ratio map, excessive transmission shifting can occur after entering TUTD mode upon accelerator pedal depression or lift-off.

[0003] JP 3 218 962 B2 describes a manual shift control device for setting a target gear ratio of a continuously variable transmission to one of several preset gear positions based on a signal from a manual shift command device operated by the driver. The device includes a shift mode switching device for selectively switching between an automatic shift control device and the manual shift control device.

[0004] DE 10 2013 104 331 B4 describes a vehicle control unit. The vehicle control unit provides an automatic mode that automatically determines a gear ratio depending on the vehicle's operating state, and also provides a temporary manual mode that, upon driver input, selects any one of several predefined gear ratios and automatically switches to automatic mode depending on the vehicle's operating state.When an operating mode is switched from automatic mode to temporary manual mode by a downshift operation that changes a gear ratio to a lower gear ratio in a transmission, and an engine speed is lower than a reference speed predetermined depending on a vehicle speed, the vehicle control unit selects any of the predetermined gear ratios such that the engine speed is equal to or higher than the reference speed.

[0005] DE 698 17 468 T2 describes a transmission ratio control device for controlling a continuously variable transmission for a motor vehicle.

[0006] While current continuously variable transmission control systems fulfill their purpose, there is therefore a need for a new and improved system and procedure for selecting a manual transmission input gear during transient driving conditions of a motor vehicle. DESCRIPTION

[0007] According to the invention, a system for selecting a manual transmission input gear during transient driving conditions of a motor vehicle comprises a transmission in a motor vehicle. An engine is connected to the transmission. A torque converter is connected to the transmission, and a differential provides drive power. A control unit is connected to the engine and the transmission. A shift device is connected to the control unit and allows a motor vehicle operator to manually select between the operating modes Park, Reverse, Neutral, Drive, and Low or Manual (PRNDL). Upon entering manual mode, a predicted gear close to an actual gear is locked in.

[0008] The transmission defines a continuously variable transmission (CVT) with a first pulley connected to the input shaft and a second pulley rotatably driven by a belt slidably connected to the first and second pulleys.

[0009] A range of pulley ratios is divided into multiple bins, which independently define successive segments of a total range of CVT ratios.

[0010] Furthermore, a bin center is identified for each of the several bins.

[0011] The predicted gear defines a predicted ratio, and the actual gear defines an actual ratio of the CVT. The predicted gear ratio is frozen at the bin center of any one of the multiple bins that is close to the actual gear ratio at the time of entering manual mode, defined as approximately one to two bins away from the actual gear ratio at the time of entering manual mode.

[0012] In another aspect of the present disclosure, an offset is added to the CVT real ratio at the time of entering manual mode.

[0013] In another aspect of the present disclosure, the offset is based on a rate of change of the real ratio and is retrieved from a memory in a calibratable lookup table.

[0014] In another aspect of the present disclosure, the transmission is defined as a planetary gear set comprising a sun gear, a ring gear, and a carrier assembly. In yet another aspect of the present disclosure, a clutch and a brake are provided which, when selectively actuated, provide one of the modes: park mode, reverse mode, neutral mode, drive mode, and manual mode, with the clutch driving the differential.

[0015] In another aspect of the present disclosure, the predicted gear is frozen at the time of entering manual mode; and an offset is added to the actual gear, the offset being based on a rate of change of the actual gear and retrieved from a memory in a calibratable lookup table.

[0016] According to several aspects, a procedure for selecting a continuously variable transmission with manual mode input ratio during transient driving conditions of a motor vehicle includes: Providing a continuously variable transmission (CVT) in a motor vehicle connected to an engine; controlling the engine and CVT using a controller; positioning a switching device in communication with the controller that enables an operator of the motor vehicle to select between a park mode, a reverse mode, a neutral mode, a drive mode, and a manual mode; dividing a range of CVT ratios into multiple bins that independently define successive segments of the range of ratios; and freezing a predicted CVT ratio at the time of entering manual mode in a midpoint of one of the multiple bins close to an actual CVT ratio.

[0017] In another aspect of the present disclosure, the method further includes adding an offset to the CVT real ratio at the time of entering manual mode.

[0018] In another aspect of the present disclosure, the method further includes the calculation of the offset using a rate of change of the CVT real ratio.

[0019] In another aspect of the present disclosure, the method further comprises retrieving the offset from a memory in a calibratable lookup table.

[0020] In another aspect of the present disclosure, the method further includes the fact that the center of one of the several bins is close to the CVT real ratio and the bin center is about one to two bins away from the CVT real ratio at the time of entering manual mode.

[0021] In another aspect of the present disclosure, the method further comprises connecting a first pulley to an input shaft and rotatably driving a second pulley by means of a belt which is slidably connected to the first pulley and the second pulley.

[0022] In another aspect of the present disclosure, the method further comprises connecting a torque converter to the CVT and providing a differential for a drive output for the motor vehicle.

[0023] In one example, a procedure for selecting an input gear for a manual transmission mode during transient driving conditions of a motor vehicle includes: switching a PRNDL shift device into a manual mode to engage a continuously variable transmission (CVT) in a manual mode; applying an offset to a real ratio of the CVT; rounding the real ratio to the nearest bin ratio midpoint in one direction of the shift to improve shift consistency; and determining whether a calculated input ratio causes a shift beyond a requested or desired ratio.

[0024] In another aspect of the present disclosure, the method further comprises retrieving the offset from a lookup table stored in memory and basing the offset on a rate of real ratio change.

[0025] In another aspect of the present disclosure, the method further comprises entering manual mode at the calculated input ratio if the calculated input ratio does not cause a shift beyond the desired ratio; and entering manual mode at the desired ratio if the calculated input ratio causes a shift beyond the desired ratio.

[0026] Further areas of application will become apparent from the description presented here. It goes without saying that the description and specific examples serve only for illustration and are not intended to limit the scope of this disclosure. FIGURE DESCRIPTION Fig. Figure 1 is a diagram of a system and procedure for selecting a transmission action mode input gear during transient driving conditions of a continuously variable transmission according to an exemplary aspect; Fig. 2 is an end view of a pulley and chain arrangement of the system of Fig. 1; Fig. Figure 3 is a diagram of engine and transmission power using the system and method of Fig. 1; Fig. 4 is a flowchart showing the steps for carrying out the procedure of Fig. 1 are shown; and Fig. 5 is a diagram of a system similar to Fig. 1 is used for a planetary gear. DETAILED DESCRIPTION

[0027] The following description is merely exemplary and is not intended to limit the present disclosure, application or use.

[0028] Referring to Fig. 1 are a system and a method for selecting a manual transmission mode input gear during transient driving conditions 10 according to several aspects directed to a powertrain with a continuously variable transmission (CVT) 12 in a motor vehicle 14. It is noted and described in detail below that the system and method for selecting a manual transmission input gear during transient driving conditions 10 can also be applied to other transmission designs, such as a multi-gear planetary gear set.

[0029] In addition to the CVT 12, the drive train comprises a motor 16, a torque converter 18, and a differential 20. The torque converter 18 includes an impeller (I) driven by the motor 16, a turbine (T) capable of delivering power via an input shaft 22, and a stator (S) that provides the torque multiplication of the torque converter 18 in a known manner. The input shaft 22 is driven by an input drive element 24, which is connected to an input pulley or first pulley 26 of the CVT 12.

[0030] The CVT 12 also has an output pulley or second pulley 28, which is connected to the first pulley 26 by a belt or chain 30. The chain 30 can be constructed in a known manner from a plurality of steel blocks held together by several steel bands. The belt 30 is held under tension between the first pulley 26 and the second pulley 28, so that a friction drive is achieved between the first pulley 26 and the second pulley 28 in a known manner.The first pulley 26 and the second pulley 28 each have a movable side disc and a fixed side disc, so that the operating diameter of the belt 30 between the first pulley 26 and the second pulley 28 can be adjusted, thereby changing a ratio between the input drive element 24 and an output shaft 32 which is connected to the differential 20 which provides a drive output for the motor vehicle 14.

[0031] Referring to Fig. 2 and back again Fig. 1. The diameter of the first pulley 26 and the second pulley 28 is controlled in a known manner by a control unit 34, which may include an electronic processor or a digital computer and a memory 36 in combination with a hydraulic control system in a hydraulic pump (not shown). These systems are generally known, so a more detailed description is not considered necessary for the person skilled in the art to understand the operation of the CVT 12.

[0032] The terms controller, control module, module, control unit, control device, processor and similar terms used herein refer to one or more combinations of application-specific integrated circuits (ASICs), electronic circuits, central processing units, e.g. microprocessors and associated non-transitory memory components in the form of memory and storage devices, including but not limited to read-only memory, programmable read-only memory, random access memory, hard disk drives and the like.A non-transitory memory component is capable of storing machine-readable instructions in the form of one or more software or firmware programs or routines, combinational logic circuits, input / output circuits and devices, signal conditioning and buffer circuits, and other components that can be accessed by one or more processors to provide a described functionality.

[0033] Input / output circuitry and devices include analog-to-digital converters and related equipment that monitor inputs from sensors, either at a preset sampling frequency or in response to a triggering event. Software, firmware, programs, instructions, control routines, code, algorithms, and similar terms refer to all sets of instructions executable by controllers, including calibrations and lookup tables. Individual controllers execute control routine(s) that provide desired functionality, including monitoring inputs from sensor devices and other networked controllers, and executing control and diagnostic instructions to manage the operation of one or more actuators. The routines can be executed at regular intervals, such as at predetermined microsecond intervals, during operation.

[0034] Alternatively, routines can be executed in response to the occurrence of one or more triggering events. Communication between controllers and between controllers, actuators, and / or sensors can occur via a direct wired connection, a networked communication bus connection, a wireless connection, or another suitable communication link. Communication includes the exchange of data signals in any suitable form, such as electrical signals over a conductive medium, electromagnetic signals exchanged through the air, optical signals exchanged via fiber optics, and the like. Data signals can include signals representing sensor inputs, signals representing actuator commands, and communication signals between controllers.

[0035] When the CVT 12 is engaged by a clutch 38, the input or first pulley 26 is adjusted by the control unit 34 to achieve a minimum forward radius 40. As is common with CVT control, the output or second pulley 28 is controlled in relation to the movement of the input or first pulley 26. The input or first pulley 26 is therefore subjected to sufficient pressure to ensure that the first pulley 26 and the second pulley 28 achieve their desired diameters. Tension on the belt 30, along with the pressure exerted on the first pulley 26, allows for the adjustment of the second pulley 28, thus providing the correct operating diameter. By setting the minimum forward radius 40 in the first pulley 26, an overall ratio for the CVT 12 is established.When the CVT 12 is switched into overdrive by engaging the clutch 38, the input or first pulley 26 is adjusted by the regulator 34 to achieve a maximum forward radius 42.

[0036] With further reference to Fig. 1. The CVT 12 can be operated in communication with the controller 34 by means of selections made using a switching device 44, which allows a manual selection by an operator of the motor vehicle 14 between a park, reverse, neutral, drive, and low or manual (PRNDL) operating mode. The switching commands are transmitted via the controller 34 and control the operation of the CVT 12, including a gear ratio defined by the position of the belt 30 on the first pulley 26 and the second pulley 28, which is shifted by a change in hydraulic system pressure. Operation in drive mode provides an essentially infinite selection of gear ratio values ​​within a predetermined, hardware-limited range as the drive belt 30 shifts to different positions on the first pulley 26 and the second pulley 28.Specific shift points are therefore neither provided for in Drive mode nor perceptible to the operator. The vehicle speed is controlled, as is generally known, via the pedal positions of an accelerator and a brake pedal (not shown).

[0037] CVT 12 pulley ratios can be defined as follows. An actual ratio is defined as an actual CVT ratio produced by the pulley positions at any given moment. A requested or desired ratio is defined as a driver-requested ratio based on pedal position and vehicle speed, and which can be changed based on several elements, including a selected drive mode, such as Sport mode; aggressive driving with high accelerator pedal pressure during rapid pedal movements; transmission protection modes, including operation at high transmission temperature, during uphill or downhill driving; the driver's PRNDL selection, such as Manual; and the like.A target transmission ratio is defined as a transmission ratio calculated for a safe operating condition and a hardware-capable state of the gearbox, based on a difference between the actual transmission ratio and the target transmission ratio, whereby the system pressure is controlled such that the pulley positions are changed in a ramp-like manner in the direction of the target transmission ratio.

[0038] To achieve gear ratio changes, predefined shift maps stored in memory are typically used. An optimal shift map or gear ratio selection is based on vehicle speed, pedal inputs, and other factors. Known optimal CVT shift maps are developed or optimized based on steady-state driving conditions, where the conditions reflect slow or steady pedal changes. A shift map based on steady-state driving may not correspond to the driving condition desired by the driver or to the condition that occurs during a non-steady-state operating condition when the driver selects tap-up-tap-down (TUTD) or manual mode.A new method for selecting a ratio for manual mode input during transient driving operation is desired to improve input time, safety, and hardware durability. Transient driving operation is defined here as operation in which the desired ratio does not correspond to the actual ratio, and the commanded ratio actively follows a desired ratio requirement.

[0039] To improve the accuracy and speed of gear changes during transient driving for the CVT 12 in manual mode, the system and procedure for selecting an input gear for manual transmission mode during transient driving conditions 10 provide a range of pulley or variator ratios divided into multiple “bins” that independently define successive segments of a total range of ratios or gears of the CVT 12. For example, the total range of ratios can be specified with six, seven, eight, or more bins that individually define successive ratio ranges of the CVT 12. The successive bins can also correspond to individual gears, such as first gear, second gear, third gear, and so on.

[0040] According to several aspects, the selection of manual mode, also known as tap-up-tap-down (TUTD) mode, can be made by the operator during a period of rapid pedal movement changes, for example, to decelerate the vehicle 14 while driving downhill or to accelerate the vehicle 14 while driving uphill or during an overtaking maneuver, when additional control of vehicle speed, acceleration rate, or deceleration rate by the operator is desired. Upon entering TUTD or manual mode, it is therefore initially assumed that the CVT 12 is not in a gear ratio requested or desired by the operator, since the actual gear ratio at the time of entry may be several gear ranges away from the desired gear ratio, depending on the pedal position.To enable a consistent entry into TUTD or manual mode, according to the present disclosure, when the operator selects manual mode, a predicted real ratio is determined based on a predicted value of the real ratio in the near future, e.g., by using a Kalman filter or by calculating the real ratio as a function of the rate of change of the real ratio at the time of entry into manual mode. Determining the predicted real ratio in this way allows the transmission to maintain the frozen initial TUTD input ratio more quickly and consistently, while being less noticeable to the operator, as it also mitigates the impact of the real ratio exceeding the frozen input ratio.

[0041] For example, if manual mode is selected when the CVT 12 is currently operating in a real ratio that defines a second bin ratio, which can also be defined as second gear, and the operator changes a pedal position indicating a desire to shift into a seventh bin ratio, which can be defined as seventh gear, a shift into the seventh bin ratio can take 5 to 7 seconds. The gear ratio changes, or shifts from second to seventh gear, using the known steady-state conditions can result in poor performance in reaching the overall shift point. According to the present disclosure, as mentioned above, in order to enable a consistent entry into TUTD or manual mode when the operator selects manual mode, a predicted real ratio is determined based on a predicted value of the real ratio in the near future, e.g.,This can be achieved by using a Kalman filter or by calculating the real ratio as a function of the rate of change of the real ratio at the time of entering manual mode. Depending on several factors, the predicted real ratio can be chosen based on a bin mean that is close to or "near" the real ratio at the time of entering manual mode. A predicted real ratio "near" the initial bin or the real gear ratio can be approximately one to two bins away from the real bin ratio.

[0042] For example, if the actual ratio is the second bin ratio, the bin ratio "close" to the actual ratio could be the third or fourth bin ratio. By predicting the actual ratio at the time of entering manual mode, faster and smaller shifts can be achieved, resulting in a shift time of less than 5 to 7 seconds, with the smaller shifts being less noticeable to the operator. The final switch to the seventh bin, if requested by the operator, can then be achieved manually, for example, via a push button or paddle shifter.

[0043] With further reference to Fig. 1. The selection of the ratio for freezing a TUTD or manual input ratio is based on the actual CVT ratio, which is adjusted by adding a predetermined offset 45, instead of using a desired pulley or variator ratio based on steady-state driving conditions, as is known. The actual CVT ratio defines the ratio at which the CVT 12 actually operates when switching to manual mode. The offset 45 is added to the CVT actual ratio to prevent overshoot. The offset 45 is retrieved from memory 36 in a calibratable lookup table and is based on a rate of change of the actual ratio.

[0044] It should be noted that the actual gear ratio may be rounded to the nearest bin gear center in one shift direction to improve the consistency of the first shift performed after entering TUTD mode. If a calculated input gear ratio would cause the pulleys to shift beyond the desired ratio, the desired ratio will be used as the input gear ratio.

[0045] With reference to Fig. 3 and again on Fig. 1 and Fig. Figure 2 shows a diagram 46 displaying several operating values, including a vehicle speed 48 over time and an engine speed 50 over time, and provides a comparison of the entry into TUTD mode using the known desired ratio method versus the system and method of the present disclosure. An accelerator pedal change 52 is made for which a TUTD entry ratio 54 would historically be obtained using a desired ratio 56. When using the system and method for selecting an input gear for the manual transmission mode during transient driving conditions 10 according to the present disclosure, an actual ratio 58 is used instead of the desired ratio 56 to determine a TUTD entry ratio 60. The TUTD entry ratio reduces the shift time into TUTD mode by approximately 2.0 to 2.5 seconds for the example shown.

[0046] With reference to Fig. 4 and again onto the Fig. 1, Fig. 2 to Fig. 3 is an algorithm that performs the process steps 62 of the present disclosure, is activated via a calibration, and the motor vehicle 14 has a TUTD mode. To operate the present system, in a switching step 64, the operator first switches the PRNDL switching device 44 to the L or Manual position. In an application step 66, if the operator selects the manual mode, a predicted real ratio is determined based on a predicted value of the real ratio in the near future, e.g., by using a Kalman filter or by applying an offset 45 to the real ratio as a function of a rate of change of the real ratio at the time of entering manual mode.

[0047] Offset 45 is calibratable and applied to the actual ratio to prevent overshoot. Offset 45 is retrieved from a lookup table stored in memory 36 and is based on a rate of change of the gear ratio. In a rounding step 68, the predicted actual gear ratio is rounded to the nearest bin gear center point in one shift direction to improve shift consistency. In a determination step 70, it is determined whether the calculated TUTD input ratio causes a shift beyond the desired ratio.

[0048] If the response to determination step 70 is a NO signal 72, the TUTD mode is entered in a basic input step 74 with the calculated TUTD input ratio. If the response to determination step 70 is a YES signal 76, the TUTD mode is entered with a desired ratio in an alternative input step 78. The predicted actual gear ratio at input is rounded to the nearest bin gear center to improve the consistency of the first circuit executed in TUTD mode. The target gear ratio is chosen as the input gear ratio when the TUTD mode is entered under steady-state conditions. The target gear ratio is selected upon entering TUTD mode by using the current actual gear ratio and its rate of change instead of the desired gear ratio.

[0049] Referring to Fig. 5 and back again Fig.Section 1 defines the system and method of this disclosure as a concept also applicable to a multi-stage transmission such as a planetary gear automatic transmission. For example, the CVT 12 can be converted into a planetary gear 80, and a shift speed of the gears of the multi-stage planetary gear 80 can replace the shift speed of the ratios identified above for use with the CVT 12. For the planetary gear 80, the above step of retrieving and applying the offset 45 can be omitted, allowing an actual shift operation to be completed while subsequent planned shift operations are aborted by freezing on an reached or commanded gear instead of a desired gear upon entering TUTD mode. In this way, the system and method of this disclosure can be applied to various transmission designs.

[0050] The planetary gear set 80 comprises a sun gear 82, a ring gear 84, and a carrier assembly 86. The carrier assembly includes a carrier ring gear 88 on which several pinions 90 are rotatably mounted. The ring gear 84 has a hub section 92, which forms a partial housing for a clutch 94. When engaged, the clutch 94 allows the sun gear 82 to be connected to the ring gear 84. The carrier assembly 86 is connected to the fluid-operated multi-disc brake 96, which, when actuated or engaged, holds the carrier assembly 86 in place, thereby creating an inverse relationship between the sun gear 82 and the ring gear 84. The clutch 94 and the brake 96 are fluid-operated friction devices of known design and familiar to those skilled in the art in the field of power transmission. The clutch 94 is connected to the output shaft 32.It should be noted that the sun gear 82, the ring gear 84 and the support assembly 86 may be connected in various formats, which have been identified above within the scope of this disclosure.

[0051] A system and method for selecting a transmission action mode input gear during transient driving conditions, as disclosed herein, offers several advantages. These include a system and method that uses a combination of a real variator ratio, a desired variator ratio, and a rate of change of the real variator ratio to determine the ratio to be frozen at during the break-in period.

Claims

[1] A system for selecting a manual transmission input gear during transient driving conditions (10) of a motor vehicle (14), comprising: a vehicle transmission (12); a motor (16) connected to the transmission (12), a torque converter (18) connected to the transmission (12), and a differential (20) providing a drive output; a control unit (34) in communication with the motor (16) and the gearbox (12); a switching device in communication with the control unit (34) which provides a manual selection by an operator of the motor vehicle (14) between a park mode, a reverse mode, a neutral mode, a drive mode and a manual mode; where, at the time of entering manual mode, a predicted gear is frozen close to an actual gear; wherein the transmission (12) defines a continuously variable transmission, CVT (12), comprising a first pulley (26) connected to an input shaft (22) and a second pulley (28) rotatably driven by a belt slidably connected to the first pulley (26) and the second pulley (28); furthermore comprising a range of pulley ratios divided into several bins that independently define successive segments of a total range of ratios of the CVT (12); furthermore comprising a bin center identified for any one of the several bins; wherein the predicted gear defines a predicted gear ratio and the actual gear defines an actual CVT ratio, wherein the predicted gear ratio is frozen at the bin center of each of the multiple bins that are close to the actual gear ratio at the time of entering manual mode, defined as approximately one to two bins away from the actual gear ratio at the time of entering manual mode. [2] The system according to claim 1, which further includes an offset which is added to the real CVT ratio at the time of entering manual mode. [3] The system according to claim 2, wherein the offset is based on a rate of change of the real ratio and is retrieved from a memory in a calibratable lookup table. [4] The system according to claim 1, wherein the transmission (12) defines a planetary gear transmission (80) with a sun gear (82), a ring gear (84) and a support assembly (86). [5] The system according to claim 4, which further comprises a clutch (94) and a brake (96) which, when selectively actuated, provide for one of the modes park mode, reverse mode, neutral mode, drive mode and manual mode, wherein the clutch (94) also drives the differential (20). [6] The system according to claim 4, wherein: the predicted gear is frozen at an entry time into manual mode, and An offset is added to the actual gait, where the offset is based on a rate of change of the actual gait.

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