Controlling a CVT transmission ratio change during a sudden vehicle stop

Abstract

Vehicle (10) with a continuously variable transmission (CVT) (14), wherein the CVT (14) comprises: an input element (13); an output element (15); a primary variator disc (18) that is operable to receive an input torque; a secondary variator disc (20) which is operable to generate an output torque (T O ) to transfer, wherein the primary and secondary variator discs (18, 20) are applied to a respective primary and secondary pressure (P) P , P S ) address; a first and second speed sensor (S P , S S ), which are operable to a respective rotational speed (ω P , ω S ) of the primary and secondary variator disc (18, 20); and a controller (50) in conjunction with the first and second speed sensors (S P , S S ), which is programmed to: Receiving the measured rotational speeds (ω)P , ω S , n P ) the primary and secondary variator disc (18, 20) from the first and second speed sensors (S P , S S ); Calculating a current speed ratio (SR) of the CVT (14) over a threshold CVT speed ratio using the measured speeds (ω) P , ω S , n P ); Comparing the calculated current speed ratio (SR) with a plurality of calibrated threshold ratios (K1, K2, K3) during a sudden stop event of the vehicle (10) (S107, S108, S109); and Selective execution of one of a plurality of CVT control actions (CA #1, CA #2, CA #3, CA #4, CA #6, CA #7) after the calculated current speed ratio (SR) falls below the threshold CVT speed ratio during the sudden stop event, wherein the executed CVT control action (CA #1, CA #2, CA #3, CA #4, CA #6, CA #7) is determined by which of the plurality of calibrated threshold ratios (K1, K2, K3) is exceeded by the calculated current speed ratio (SR) after the calculated current speed ratio (SR) falls below the threshold CVT speed ratio, and the measured speeds (ω P , ω S , n P ) depends (S112, S114, S113, S115, S119, S121).

Description

[0001] The present disclosure relates to gear ratio control of a continuously variable transmission during a sudden vehicle stop.

[0002] A continuously variable transmission (CVT) is a type of powershift transmission capable of achieving fine variability between a highest and lowest possible speed ratio. Unlike conventionally geared transmissions, which use one or more planetary gear sets and multiple rotating and braking friction clutches to achieve a discrete gear ratio, a CVT uses a system of variable-diameter discs, known as a variator assembly, to achieve a transition anywhere within a calibrated range of speed ratios.

[0003] A typical variator assembly comprises two variator pulleys connected by an endless rotating drive member, such as a chain or belt. The drive member rides in a variable-width gap defined by the tapered faces of mating half-pulleys of the pulleys. One of the pulleys is typically connected to an engine crankshaft to act as a driving, primary pulley. The other pulley is connected to a CVT output shaft to act as a driven / secondary pulley. One or more gear sets might be used on the input and / or output sides of the variator assembly, depending on the design. To change a CVT speed ratio, a shifting force is applied to the primary pulley and / or secondary pulley via one or more pulley actuators.The sliding force effectively squeezes the pulley halves together to change the width of the gap between the tapered pulley faces. Changing the pulley size, also known as the pitch radius, causes the drive component to run higher or lower within the gap. This, in turn, changes the effective diameters of the variator pulleys and thus the CVT's speed ratio.

[0004] DE 11 2010 005 399 T5 discloses a control device for a continuously variable transmission. A control device for a continuously variable transmission, the continuously variable transmission comprising a primary pulley to which a driving force of an internal combustion engine is input, a secondary pulley coupled to a vehicle wheel, and a belt wound around the pair of pulleys to transmit the driving force. The control device controls a hydraulic pressure to be supplied to each of the pulleys to change a wrap radius of the belt on each of the pulleys, and performs feedback control of the hydraulic pressure of the primary pulley based on the actual gear ratio calculated based on a rotational speed of each of the pulleys and a target gear ratio.The control device comprises: a speed sensor for detecting a speed of at least a part of a power transmission system from the internal combustion engine to the wheel, wherein when the speed is less than a first reference value, the control device executes lower limit hydraulic control for regulating the hydraulic pressure of the primary pulley to a lower limit hydraulic pressure capable of setting a gear ratio to a maximum gear ratio, when the speed is equal to or exceeds the first reference value, the control device regulates the hydraulic pressure of the primary pulley to a higher hydraulic pressure than the lower limit hydraulic pressure, and when the speed is equal to or exceeds a second reference value that is greater than the first reference value, the control device executes the feedback control.The aim is to circumvent the inaccuracy of speed measurement by speed sensors at low speeds by increasing the speeds.

[0005] DE 101 25 317 A1 discloses a shift control device for a continuously variable transmission of a vehicle. When the temperature of an actuating fluid in an actuator is low, a lower limit value of the target input speed is set. The lower limit value is greater than a lower limit value set for a normal temperature of the actuating fluid. A target input speed is calculated from the driving state of the vehicle, for example, based on the degree of operation of an accelerator pedal, the vehicle speed, etc. If the target input speed is lower than the lower limit value, the target input speed is set to the lower limit value. As a result of control including the above steps, a gear ratio becomes relatively high before the vehicle stops.Therefore, even if the gear ratio change rate is low, the gear ratio can be brought close to or to the maximum value before the vehicle stops. Thus, reductions in the gear ratio change rate due to low temperature of the actuator actuating fluid can be compensated or eliminated.

[0006] Disclosed herein is an example vehicle including an internal combustion engine, a continuously variable transmission (CVT), and a controller programmed to control a speed ratio of the CVT in a particular manner during / after a sudden stop of the vehicle. The CVT includes an endless rotatable drive member and a variator assembly of the type specified above. During the sudden stop event of the vehicle, the pulley speeds will quickly reach a low threshold speed before a calibrated minimum CVT speed ratio can be achieved. The controller is therefore programmed to execute steps of an associated control method and ultimately command appropriate control actions with respect to the CVT during such a sudden stop event, i.e., at any time when the variator pulley speeds are sufficiently low that the variator pulley speeds cannot be accurately measured.

[0007] It is the object of the present invention to provide a vehicle with a continuously variable transmission that ensures optimal starting of the vehicle after a sudden stop event.

[0008] This object is achieved by a vehicle having the features of claim 1.

[0009] Advantageous embodiments are specified in the dependent claims.

[0010] The invention is described below by way of example with reference to the drawings: Fig. 1 is a schematic diagram of an exemplary vehicle having a continuously variable transmission (CVT) and a controller programmed to control the CVT during a sudden stop event of the vehicle as set forth herein. Fig. 2 is a flowchart illustrating an exemplary embodiment of a method for controlling the speed ratio of the Fig. 1 during the sudden stop event. Fig. 3 is a timing diagram of varying amplitudes of different vehicle parameters illustrating a control action in which the CVT ratio is estimated or extrapolated to a calibrated minimum ratio, with time on the x-axis and amplitude on the y-axis. Fig. 4 is a timing diagram of changing amplitudes of different vehicle parameters illustrating a control action in which the CVT speed ratio is kept constant, with time on the x-axis and amplitude on the y-axis. Fig. Figure 5 is a timing diagram of varying amplitudes of different vehicle parameters illustrating a further control action in which the CVT ratio is adjusted to a calibrated minimum ratio at a faster rate than that used in Fig. 4, with time on the x-axis and amplitude on the y-axis.

[0011] With reference to the drawings, in which like reference numerals correspond to the same or similar components throughout the several figures, Fig. 1, a vehicle 10 is shown schematically. The vehicle 10 includes a torque-generating device 12, which is shown as an exemplary internal combustion engine (E), but which may also be embodied as an electric machine or other suitable device operable to produce output torque. For consistency of illustration, the torque-generating device 12 will be described below as an engine 12, without limiting the scope to such a construction.

[0012] The vehicle 10 also includes a continuously variable transmission (CVT) 14 and a controller (C) 50. As will be described in detail below with reference to the flowchart of Fig. 2 and with additional reference to the timing diagrams of the Fig. 3-5, the controller 50 is programmed to calculate a current speed ratio of the CVT 14 and to perform other actions with respect to the CVT 14 during a sudden stop event of the vehicle 10, i.e., any event in which speeds of a primary and secondary variator pulley 18 and 20 are too low for accurate measurement.

[0013] The controller 50 is also programmed to send disc pressure control signals (arrow P CC) to the primary and secondary variator pulleys 18 and 20 during / after a sudden stop event in which a programmed / calibrated minimum CVT speed ratio optimal for launch, hereinafter referred to as a first threshold ratio (k1), is not reached, and to communicate a speed ratio uncertainty condition to another controller, e.g., an engine control module (ECM) 150, via a status signal (arrow 11) after such a sudden stop event. The controller 50 also selectively estimates the current CVT speed ratio under certain operating conditions when the speeds ω P and ω S the primary and secondary discs, as determined by respective disc speed sensors S P and S Sare determined below a second threshold ratio (k2) which exceeds the first threshold ratio (k1), but at which the disc speeds ω P and ωs are still below a sensor resolution or a threshold for an accurate measurement.

[0014] As is known in the art, the accuracy or resolution of speed sensors, such as the speed sensors S P and S S, at low speeds, may be relatively low, and it may therefore be difficult to accurately calculate the current CVT ratio during and after a sudden stop event of the vehicle 10. The controller 50 is therefore programmed with the first, second, and third threshold ratios (k1, k2, k3) via programming of a memory (M) of the controller 50, e.g., in a lookup table. The controller 50 determines whether these calibrated thresholds are reached during the sudden stop event upon crossing or dropping below a calibrated speed ratio indicative of a last known valid calculated measurement. Such a value may be determined offline and stored in the memory (M) and can be expected to vary based on the design of the particular sensors S used. P , S Sas well as the vehicle platform, the torque converter, and the variator geometry. The ideal situation is that the first threshold ratio (k1) is reached before the primary and secondary discs 18 and 20 have stopped rotating. No additional control actions are required if this result occurs. However, if this result does not occur, the controller 50 instead performs one of a number of different possible control actions with respect to the CVT 14 depending on the calculated current speed ratio (SR), where SR=ωSωP, and the disk speeds, or more precisely, depending on whether the primary and secondary disks 18 and 20 have stopped rotating or not. A method 100 and the various conditions for the control actions are described below with reference to the Fig. 2-5 executed.

[0015] With reference to the exemplary vehicle 10 of Fig. 1, the engine 12 includes an output shaft / crankshaft 13. The crankshaft 13 is connected to the CVT 14, which in turn includes an output shaft 15. The output shaft 15 ultimately delivers output torque (arrow T O) to a set of drive gears 16. The CVT 14 includes the primary variator pulley 18 connected to and driven by the crankshaft 13, the secondary variator pulley 20 connected to the output shaft 15, and a continuously rotating drive member or CVT belt 22. The term "belt," as used herein, refers to any closed / endless loop of rubber and / or metal suitable for transmitting torque from the primary variator pulley 18 to the secondary variator pulley 20, including a loop of chain or a conventional rubber and metal CVT drive belt. For simplicity, the term "belt" will be used hereinafter to refer to any suitable endless rotatable member.

[0016] The primary and secondary variator pulleys 18 and 20 each comprise mating halves 19 and 21, respectively, with respective tapered end surfaces 23 and 25 defining a variable-width gap 26. The belt 22 is positioned in the gap 26 and rides on the tapered end surfaces 23 and 25 when the engine 12 rotates the primary pulley 18 at engine speed (N E ), which is thus the input speed / primary speed (ω P ) of the primary disk 18. The secondary disk 20 rotates at the second speed (ω S ). As mentioned above, both disc speeds (ω P , ω S ) via the sensors S P and S S measured and reported to the controller 50, for example as signals via a controller area network or other suitable channels.

[0017] The width of the gap 26 can be varied by moving the mating halves 19 and / or 21 to change the current speed ratio of the CVT 14. Therefore, the vehicle 10 comprises Fig. 1 a respective first and second variator actuator 28 and 30, which are each responsive to a primary and secondary pressure (arrows P P or P S ), which has corresponding disc pressure sensors (S PP , S PS ) are measurable to move the respective primary and secondary variator discs 18 and 20 towards each other. A return spring (not shown) or other return mechanism within each of the variator discs 18 and 20 moves the variator discs 18 and 20 away from each other when the respective primary and secondary pressure (P P , P S ) is drained. Although it is in Fig. 1 for ease of illustration, an exemplary embodiment of the first and second actuators 28 and 30 comprises a hydraulic piston / cylinder system, although other linear actuators, such as electromechanical devices or pneumatic pistons, may be used.

[0018] The first actor 28 of Fig. 1 acts on a movable one of the associated halves 19 of the primary variator disc 18 in response to the application of the primary pressure (arrow P P ). Similarly, the second actuator 30 acts on a movable one of the mating halves 21 of the secondary variator disc 20 in response to the secondary pressure (arrow P S ). Line pressure (arrow P L) may be supplied to the CVT 14 via a fluid pump 32 as shown, wherein the fluid pump 32 draws fluid 33, such as oil, from a sump 34 and circulates the fluid 33 to the CVT 14 via hoses, fittings, and other suitable fluid conduit (not shown). In one possible embodiment, the line pressure (arrow P L ) equal to the secondary pressure (P S ). However, other embodiments can be considered in which the primary and secondary pressure (arrows P P or P S ) regardless of the line pressure (arrow P L ) are.

[0019] The controller 50 may be embodied as one or more computing devices having a memory (M). The controller 50 may include, but is not limited to, hardware components such as a processor (P), circuitry including a timing circuit, an oscillator, analog-to-digital circuitry, digital-to-analog circuitry, proportional-integral-derivative (PID) control logic, a digital signal processor, and any necessary input / output devices and other signal conditioning and / or signal buffering circuitry. The memory (M) may include tangible, non-transitory memory, such as read-only memory, e.g., magnetic, solid-state, flash, and / or optical memory, as well as sufficient amounts of electrically erasable programmable read-only memory, and the like. Steps embodying the method 100 may be recorded in the memory (M) and executed by the processor (P) in the overall control of the vehicle 10.

[0020] The controller 50, which is connected to the first and second actuators 28 and 30, receives a set of control inputs (arrow CC E ) as part of the procedure 100 described below. The control inputs (arrow CC E ) can adjust the vehicle speed N 10 , as detected by one or more wheel or transmission output speed sensors S 10 reported, calculated or measured, the disc speeds (ω P , ω S ) and an output torque request (arrow T REQ ). As is known in the art, the output torque requirement (arrow T REQ) is typically determined by actions of a driver of the vehicle 10, such as a current throttle request, braking levels, gear state, and the like. The vehicle 10 may include optional paddle shifters 35, as shown in phantom, so that the driver of the vehicle 10 requests a shift via a push of one of the paddle shifters 35. With such a construction, movement of the paddle shifters 35 generates a requested shift signal (arrow RS) as part of the set of control inputs (arrow CC I ).

[0021] With reference to Fig. 2, an exemplary embodiment of the method 100 begins at step S102, wherein the controller 50 of Fig. 1 the vehicle speed N 10 determined. Step 102 may involve measuring the vehicle speed N 10 via the speed sensor / speed sensors S 10for example, a wheel speed sensor or a transmission output speed sensor. The sensor S S in the exemplary embodiment of Fig. 1 may measure a transmission output speed, which is the speed of the output element 15. The method 100 proceeds to step S104 once the vehicle speed N 10 transmitted to the controller 50 or otherwise made available to it.

[0022] At step S104, the controller 50 next determines whether vehicle conditions (COND) indicate a sudden stop event of the vehicle 10. Such conditions may include braking levels and / or a rate of change of a vehicle speed (N 10 ), for example, a threshold rate of change in the speed of the output member 15. The method 100 proceeds to step S105 if the vehicle 10 has suddenly stopped or is about to do so, and otherwise repeats step S104.

[0023] Step S105 includes determining whether the CVT 14 is Fig. 1 pressure has been removed (DP). A pressure removal can be easily detected by the controller 50 by determining the on / off state of the engine 12 from Fig. 1 is determined, which is known to the controller 50 about the current ignition state, together with the level of the pressures P P and P S from Fig. 1 relative to corresponding pressure thresholds. When the engine 12 is switched off, a certain drop in fluid pressure should be detected via the disc pressure sensors S PP and S PS from Fig. 1 can be detected. The method 100 proceeds to step S116 if pressure has been removed from the CVT 14, and otherwise proceeds to step S106.

[0024] At step S106, the controller 50 calculates Fig. 1 the current speed ratio of the CVT 14, which is Fig. 2 is abbreviated as “DET SR”. As stated above, the current speed ratio of the CVT 14 is the ratio of the output speed to the input speed of the CVT 14, ie ωSωP.

[0025] The method 100 proceeds to step S107 when the current speed ratio has been determined.

[0026] Step S107 entails comparing the calculated current speed ratio (SR) from step 106 with a calibrated minimum CVT ratio, i.e., the first threshold ratio (k1). The first threshold ratio (k1) is a predetermined / calibrated value that will vary with the design of the vehicle 10. It is a value below which the CVT 14 is considered optimal for launching the vehicle 10. The method 100 is complete when the first threshold ratio (k1) is reached, i.e., no additional control actions are required from the controller 50 outside of launching the vehicle 10, if requested. The method 100 proceeds to step S108 if the current speed ratio (SR) exceeds the first threshold ratio (k1) during / after the sudden stop event.

[0027] Step S108 includes comparing the calculated current speed ratio (SR) from step S106 with the second threshold ratio (k2) and determining whether the calculated current speed ratio is less than the second threshold ratio (k2). The second threshold ratio (k2) is determined by known sensor characteristics of the speed sensors S P and S S from Fig. 1, sampling time, design-specific ride quality criteria, and the like, but is higher than the first threshold ratio (k1) and lower than the third threshold ratio (k3). The method 100 proceeds to step S110 if the current speed ratio of the CVT 14 is less than the second threshold ratio (k2). Otherwise, the method 100 proceeds to step S109.

[0028] At step S109, the controller 50 determines Fig. 1 next checks whether the current speed ratio exceeds the third threshold ratio (k3). Above the third threshold ratio, launch is not enabled, at or below the first threshold (k1) it is considered optimal, and between the second and third ratios (k2, k3) it is possible but not optimal, e.g., may have a less than ideal feel or efficiency. The method 100 proceeds to step S111 if the calculated current speed ratio exceeds the third threshold ratio (k3), and to step S117 if, alternatively, the current speed ratio does not exceed the third threshold ratio (k3).

[0029] Step S110 includes determining whether the absolute disk speeds ω P and ω S , together n P in Fig. 2, not be zero, as in Fig. 2 as n P+For the purpose of method 100, any speed with an absolute value above zero or above a calibrated non-zero value, e.g., 5-10 rpm, may be used. The method 100 proceeds to step S112 if the disk speeds n P not zero and to step S114 if the disk speeds are zero.

[0030] Step S111 is effectively the same as step S110, described directly above. However, step S111 is reached when the calculated current speed ratio of the CVT 14 exceeds the third threshold ratio (k3), while step S110 is reached only when the current speed ratio is less than the second threshold ratio (k2). The method 100 proceeds from step S111 to step S113 when the absolute pulley speeds n Pnot zero, and to step S115 when the disc speeds are zero, ie when discs 18 and 20 have stopped or decelerated below the non-zero lower threshold speed as stated above, so that they have effectively stopped.

[0031] Step S112 includes executing a first control action (CA #1) via the controller 50 with respect to the CVT 14. This step occurs when the current speed ratio of the CVT 14 is less than the second threshold ratio (k2) and the pulley speeds are not zero when falling below the calibrated speed ratio that marks the lower limit of the speed sensor resolution.

[0032] Briefly with reference to Fig. 3, a vertical line 60 at t1 marks a time after which the current speed ratio of the DVT 14 cannot be accurately determined. As noted above, the resolution of speed sensors tends to be poorer at lower speeds. Since the controller 50 is Fig. 1 of the current CVT ratio for the optimal control of the CVT 14, specific control steps are taken at step S112 to ensure that the current speed ratio does not exceed the calibrated minimum CVT ratio, ie the first threshold ratio (k1) defined in Fig. 3 is achieved.

[0033] As part of step S112, when the vehicle speed (N 10 ) decreases during the rapid stop event between t0 and t1, the controller 50 commands the disc pressures P P and P Sfor the primary and secondary pulleys 18 and 20, so that the current speed ratio of the CVT 14 reaches the first threshold ratio (k1), for example, in a linear manner as shown, this being achieved via a transmission of the pressure control signals (arrow P CC ) from Fig. 1. The last known valid current speed ratio calculation is made at t1 and is recorded in the memory (M) of the controller 50, and the current speed ratio is estimated or extrapolated after t1 using a set of CVT information. The last estimated / extrapolated value can be used to control the CVT 14 during a subsequent launch of the vehicle 10, as described in Fig. 3 is shown.

[0034] CVT information that can be used to estimate or extrapolate the current CVT speed ratio may include the known return spring characteristics or the design of the pulleys 18 and 20, a temperature of the CVT 14, the specific design of the belt 20, hydraulic properties or limitations, etc. The characteristics will vary with each design and can therefore be calibrated offline and recorded in the memory (M) of the controller 50, which can be accessed by the processor (P) when the current speed ratio reaches line 60 at t1, and thereafter used to estimate the current speed ratio. The controller 50 can determine the transmission state (arrow 11 of Fig. 1) report to the ECM 150 or other controllers required for launch control, indicating the uncertainty of the estimated current speed ratio, and may also temporarily disable the proportional-integral (PI) feedback compensation logic within the controller 50 for feedback compensation during this phase.

[0035] Step S113 includes executing a third control action (CA #3) when the current speed ratio of the CVT 14 is greater than a third threshold ratio (k3) and the pulley speeds are not zero. The pressure commands for this control action are shown in Fig. 5, showing the SR trajectory below the third threshold ratio (k3) prior to t1. The third control action is similar to the first control action of step S112. The last known valid calculated current speed ratio calculation at t1 is recorded in memory (M) of controller 50, and the speed ratio is thereafter estimated or extrapolated using the set of CVT information as noted above.

[0036] Unlike the Fig. 3 is the rate at which the speed ratio changes after t1 in Fig. 5 is reduced more quickly due to the increased nature of the current speed ratio at t1 relative to the third threshold ratio (k3). Launch of the vehicle is not possible / is not enabled above the third threshold ratio (k3), but is possible below the second threshold ratio (k2), albeit not optimal, and so step S113 may entail lowering the speed ratio below the second threshold ratio (k2). As with step S112, the CVT information may be used to determine the current CVT ratio using known return spring characteristics, the design of the discs 18 and 20, and other characteristics of the CVT 14 from Fig. 1, e.g., temperature, the specific design of the belt 22, etc., can be estimated or extrapolated. The controller 50 can report the transmission status (arrow 11) to the ECM 150 or other controllers required for launch control, and can also temporarily disable PI feedback compensation logic during this phase.

[0037] Step S114 of Fig. 2 includes executing a second control action (CA #2) when the current speed ratio is lower than the second threshold ratio (k2) and the disk speeds are zero. This control action is in Fig. 4. In contrast to Fig. 3 and the first control action of step S112, the second control action freezes / maintains the last valid calculated current speed ratio after t1 and freezes the primary and secondary pressure. The vehicle speed N 10continues to decrease until the vehicle 10 stops. As in step S112, the controller 50 reports the CVT state (arrow 11) to the ECT 150 or other controllers required for launch control and temporarily disables the PI logic during this phase. That is, under low-speed conditions, the speed ratio of the CVT 14 cannot be accurately measured and calculated, and therefore, PI feedback compensation does not function well, and as a result, it is temporarily disabled.

[0038] Step S115 includes executing a fourth control action (CA #4) when the current speed ratio (SR) is greater than a third threshold ratio (k3) and the pulley speeds are zero. The controller 50 may determine the CVT state (arrow 11 of Fig. 1) and take other necessary action. For example, because the current ratio is too high for launch and the vehicle 10 has stopped, the controller 50 can command depressurization of the CVT 14 to cause a decrease in the speed ratio. In other words, the ratio is reduced by depressurizing the CVT 14 toward the first threshold ratio (k1), allowing launch.

[0039] At step S116, the controller 50 performs a fifth control action (CA #5) if the determination is made at step S105 that pressure has been removed from the CVT 14. When pressure has been removed from the CVT 14, the return force of the return spring in the secondary pulley and possibly the primary pulley moves the pulleys back to the minimum ratio, i.e., the first threshold ratio (k1). Step S116 may involve extrapolating the current speed ratio downward toward the first threshold ratio (k1) starting at t1 of Fig. 3-5, again based on the return spring characteristic and other properties of the CVT 14 as stated above. In one embodiment, the controller 50 may be Fig. 1 may use a timer to count over a calibrated duration indicating that the discs 18 and 20 have moved sufficiently to achieve the minimum or first threshold ratio (k1), or use a model or the like so that the controller 50 is aware that sufficient time has elapsed for the first threshold ratio (k1) to be achieved.

[0040] Step S117 entails determining whether the absolute disk speeds are not zero. If so, the method 100 proceeds to step S119. Alternatively, if the disk speeds are zero, the method 100 proceeds to step S121.

[0041] Step 119 includes executing a sixth control action (CA #6) when the pulleys 18, 20 are rotating and the speed ratio of the CVT 14 exceeds a second threshold ratio (k2) but not the third threshold ratio (k3), as determined in step S117. In this condition, the controller 50 may Fig. 1 try to control the discs 18 and / or 20 to achieve a lower speed ratio via the pressure control signals (arrow P CC ) from Fig. 1, which is essentially as in Fig. 5 shown.

[0042] Step S121 entails executing a seventh control action (CA #7) when the discs are not rotating and the speed ratio of the CVT 14 exceeds the second threshold ratio (k2) but not the third threshold ratio (k3), as determined in step S117. Under this condition, the controller 50 may maintain the current speed ratio as determined in Fig. 4 is shown.

[0043] Using the method 100, the controller 50 is Fig. 1 capable of transmitting the pressure control signals (arrow P CC ) after a sudden stop event in which the calibrated minimum speed ratio / first speed ratio (k1) is not reached. The controller 50 may communicate the uncertainty of the determined ratio after such a stop, such as by transmitting a Boolean value indicating such uncertainty, and may continue to operate via an estimate of the speed ratio. As a result, the vehicle 10 may Fig. 1 be better able to start after a sudden stop event.

Claims

[1] Vehicle (10) with a continuously variable transmission (CVT) (14), the CVT (14) comprising: an input element (13); an output element (15); a primary variator pulley (18) operable to receive an input torque; a secondary variator pulley (20) operable to provide an output torque (T O ), wherein the primary and secondary variator discs (18, 20) are set to a respective primary and secondary pressure (P P , P S ) address; a first and second speed sensor (S P , S S ) which are operable to achieve a respective speed (ω P , ω S ) of the primary and secondary variator pulleys (18, 20); and a controller (50) in connection with the first and second speed sensors (S P , S S ), which is programmed to: Receiving the measured speeds (ω P, ω S , n P ) of the primary and secondary variator discs (18, 20) from the first and second speed sensors (S P , S S ); Calculating a current speed ratio (SR) of the CVT (14) above a threshold CVT speed ratio using the measured speeds (ω P , ω S , n P ); Comparing the calculated current speed ratio (SR) with a plurality of calibrated threshold ratios (K1, K2, K3) during a sudden stop event of the vehicle (10) (S107, S108, S109); and selectively executing one of a plurality of CVT control actions (CA #1, CA #2, CA #3, CA #4, CA #6, CA #7) after the calculated current speed ratio (SR) falls below the threshold CVT speed ratio during the sudden stop event, wherein the executed CVT control action (CA #1, CA #2, CA #3, CA #4, CA #6, CA #7) depends on which of the plurality of calibrated threshold ratios (K1, K2, K3) is exceeded by the calculated current speed ratio (SR) after the calculated current speed ratio (SR) falls below the threshold CVT speed ratio, and the measured speeds (ω P , ω S , n P ) depends (S112, S114, S113, S115, S119, S121). [2] The vehicle (10) of claim 1, wherein the controller (50) is programmed with progressively higher first, second, and third threshold ratios (K1, K2, K3) than the plurality of calibrated threshold ratios, the first threshold ratio (K1) being a calibrated minimum CVT ratio optimal for launching the vehicle (10) after the sudden stop event, the second threshold ratio (K2) being a ratio in which launching the vehicle (10) is possible, and the third threshold ratio (K3) being a ratio above which launching the vehicle (10) is not enabled. [3] The vehicle (10) of claim 2, wherein the plurality of CVT control actions (CA #1, CA #2, CA #3, CA #4, CA #6, CA #7) includes a first control action (CA #1) when the calculated current speed ratio, upon falling below the threshold CVT speed ratio, exceeds the first threshold ratio (K1) and not the second threshold ratio (K2) and the speeds (ω P , ω S ) is not zero, and wherein the first control action (CA #1) comprises estimating a current speed ratio (SR) of the CVT (50) after the calculated current CVT ratio (SR) falls below the threshold CVT speed ratio, and thereafter controlling the primary and secondary pressures (Pp, P R ) until the estimated current speed ratio (SR) reaches the first threshold ratio (K1) (S112). [4] The vehicle (10) of claim 2, wherein the plurality of CVT control actions (CA #1, CA #2, CA #3, CA #4, CA #6, CA #7) includes a second control action (CA #2) when the calculated current speed ratio (SR) exceeds the first threshold ratio (K1) and not the second threshold ratio (K2) upon falling below the threshold CVT ratio and the speeds (ω P , ω S ) be zero, and wherein the second control action (CA #2) is to freeze or maintain the primary and secondary pressure (P P , P S ) (S114). [5] The vehicle (10) of claim 2, wherein the plurality of CVT control actions (CA #1, CA #2, CA #3, CA #4, CA #6, CA #7) includes a third control action (CA #3) when the calculated current speed ratio (SR) exceeds the third threshold ratio (K3) and the speeds (ω P , ω S) is not zero, and wherein the third control action (CA #3) comprises estimating a current speed ratio (SR) of the CVT (10) after the calculated current CVT ratio (SR) falls below the threshold CVT speed ratio, and thereafter controlling the primary and secondary pressures (P P , P S ) so that the estimated current speed ratio (SR) reaches the second speed ratio or the first speed ratio (S113). [6] The vehicle (10) of claim 2, wherein the plurality of CVT control actions (CA #1, CA #2, CA #3, CA #4, CA #6, CA #7) includes a fourth control action (CA #4) when the calculated current speed ratio (SR) exceeds the third threshold ratio (K3) and the speeds (ω P , ω S ) be zero, and wherein the fourth control action (CA #4) comprises a pressure release on the CVT (10) (S115). [7] The vehicle (10) of claim 2, wherein the plurality of CVT control actions (CA #1, CA #2, CA #3, CA #4, CA #6, CA #7), when the calculated current speed ratio (SR) exceeds the second threshold ratio (K2) but not the third threshold ratio (K3) and the speeds are not zero, control the primary and secondary pressures (P P , P S ) to achieve the first threshold ratio (K1) (S119). [8] The vehicle (10) of claim 2, wherein the plurality of CVT control actions (CA #1, CA #2, CA #3, CA #4, CA #6, CA #7) include freezing the primary and second pressures (P P , P S ) when the current CVT speed ratio (SR) exceeds the third threshold ratio (K3) and the speeds (ω P , ω S ) be zero. [9] The vehicle (10) of claim 2, wherein the plurality of CVT control actions (CA #1, CA #2, CA #3, CA #4, CA #6, CA #7) comprise selectively disabling proportional-integral feedback compensation logic.

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