Vehicle control device

Abstract

To achieve both improvement of the durability of a continuously variable transmission and securing of the runnability of a vehicle, as compared with the case where upshift control is performed uniformly.SOLUTION: When an input rotation speed of a continuously variable transmission is equal to or higher than a predetermined rotation speed, which is set based on a predetermined correlation between the input rotation speed and inertia torque that is inputted to the continuously variable transmission by rapid reduction of rotation speed of drive wheels and at which it is necessary to suppress the inertia torque, upshift control is performed for controlling a speed change ratio of the continuously variable transmission to a high vehicle speed side, and therefore, when the inertia torque becomes relatively large in the case where a vehicle travels on a road surface where the drive wheels tend to spin, the input rotation speed of the continuously variable transmission is reduced by upshift of the continuously variable transmission, and the inertia torque inputted when the rotation speed of the drive wheels rapidly reduces is suppressed actually. Further, when the inertial torque becomes relatively small, upshift of the continuously variable transmission is not performed, and driving torque is easily secured.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a control device for a vehicle equipped with a continuously variable transmission in which a transmission element is wound between a primary pulley and a secondary pulley. [Background technology]

[0002] Control devices for vehicles equipped with a continuously variable transmission (CVT), which forms part of a power transmission path between a power source and drive wheels and has a transmission element wound between a primary pulley and a secondary pulley, are well known. For example, Patent Document 1 discloses a control device for an automatic transmission. Patent Document 1 discloses that upshift control is performed to protect the CVT by changing the gear ratio of the CVT to a higher vehicle speed when the vehicle is traveling on a low-friction road surface, thereby improving durability of the CVT by suppressing large inertia torque input to the CVT when the drive wheels are locked from a spinning state. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-210059 Summary of the Invention [Problem to be solved by the invention]

[0004] However, if upshift control is uniformly performed while traveling on road surfaces where the drive wheels are likely to spin in order to improve the durability of the continuously variable transmission, there is a possibility that upshift control will be performed even when the vehicle is in a traveling state where there is no need to protect the continuously variable transmission. Therefore, there is room for improvement in terms of achieving both improved durability of the continuously variable transmission and ensuring the vehicle's driving performance, for example, power performance.

[0005] The present invention was made against the background of the above circumstances, and its purpose is to provide a vehicle control device that can achieve both improved durability of the continuously variable transmission and ensure the driving performance of the vehicle, compared to when uniform upshift control is performed. [Means for solving the problem]

[0006] The gist of a first invention is (a) a control device for a vehicle having a continuously variable transmission that forms part of a power transmission path between a power source and drive wheels and has a transmission element wound between a primary pulley and a secondary pulley, (b) including a gear change control unit that performs upshift control to control the gear ratio of the continuously variable transmission to a higher vehicle speed when the vehicle is traveling on a road surface on which the drive wheels are likely to spin, compared to when the vehicle is traveling on a road surface on which the drive wheels are unlikely to spin, and (c) the gear change control unit performs the upshift control when the input rotational speed of the continuously variable transmission is equal to or higher than a predetermined rotational speed at which the inertia torque needs to be suppressed, the predetermined rotational speed being set based on a predetermined correlation between the input rotational speed and the inertia torque input to the continuously variable transmission due to a sudden decrease in the rotational speed of the drive wheels. [Effects of the Invention]

[0007] According to the first aspect of the present invention, when the input rotation speed of the continuously variable transmission is equal to or higher than a predetermined rotation speed at which inertia torque needs to be suppressed, the predetermined rotation speed being set based on a predetermined correlation between the input rotation speed and the inertia torque input to the continuously variable transmission due to a sudden decrease in the rotation speed of the drive wheels, upshift control is performed to control the gear ratio of the continuously variable transmission to the high vehicle speed side. Therefore, when the inertia torque becomes relatively large when the vehicle is traveling on a road surface on which the drive wheels are likely to spin, the input rotation speed of the continuously variable transmission is reduced by upshifting, and the inertia torque input when the rotation speed of the drive wheels actually decreases suddenly is suppressed. Furthermore, even when the vehicle is traveling on a road surface on which the drive wheels are likely to spin, when the inertia torque becomes relatively small, upshifting of the continuously variable transmission to suppress the inertia torque is not performed, making it easier to ensure a drive torque suited to the traveling conditions. Therefore, compared to when uniform upshift control is performed when the vehicle is traveling on a road surface where the drive wheels are likely to spin, it is possible to achieve both improved durability of the continuously variable transmission and ensure the vehicle's driving performance. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a diagram illustrating a schematic configuration of a vehicle to which the present invention is applied, and is also a diagram illustrating main parts of control functions and control systems for various controls in the vehicle. [Figure 2] FIG. 10 is a diagram showing an example of a predetermined correlation between an input shaft rotation speed and an input shaft inertia torque caused by a sudden decrease in drive wheel speed. [Figure 3] This is a flowchart explaining the main parts of the control operation of the electronic control device, and is a flowchart explaining the control operation for achieving both improved durability of the continuously variable transmission and ensuring the drivability of the vehicle compared to when uniform upshift control is performed. DETAILED DESCRIPTION OF THE INVENTION

[0009] In an embodiment of the present invention, the primary pulley, which is an input pulley, and the secondary pulley, which is an output pulley, each have, for example, a fixed sheave, a movable sheave, and a hydraulic actuator that applies thrust to change the groove width between the fixed sheave and the movable sheave. The vehicle is equipped with a hydraulic control circuit that independently controls pulley oil pressure as hydraulic oil supplied to the hydraulic actuator. This hydraulic control circuit may be configured to generate pulley oil pressure as a result by controlling the flow rate of hydraulic oil to the hydraulic actuator. Such a hydraulic control circuit controls the thrust (= pulley oil pressure × pressure-receiving area) of the primary pulley and the secondary pulley, thereby performing gear shift control to prevent slippage of the transmission elements and achieve a target gear shift. The transmission elements may be, for example, an endless annular compression-type power transmission belt having an endless annular hoop and elements, which are thick-walled plate-like blocks connected in a thickness direction along the hoop, or a tension-type power transmission belt comprising an endless annular link chain in which ends of alternately stacked link plates are connected to each other by connecting pins. The continuously variable transmission is a well-known belt-type continuously variable transmission, and in a broad sense, the concept of this belt-type continuously variable transmission also includes a chain-type continuously variable transmission.

[0010] Furthermore, the speed ratio (also called gear ratio) of the continuously variable transmission or the like is "rotational speed of the rotating member on the input side / rotational speed of the rotating member on the output side." For example, the speed ratio of the continuously variable transmission is "rotational speed of the primary pulley / rotational speed of the secondary pulley." The high side of the speed ratio is the high vehicle speed side where the speed ratio is small. The low side of the speed ratio is the low vehicle speed side where the speed ratio is large. For example, the lowest speed ratio is the speed ratio on the lowest vehicle speed side, which is the lowest vehicle speed side, and is the maximum speed ratio where the speed ratio is the largest value.

[0011] The power source is, for example, an engine such as a gasoline engine or a diesel engine that generates power by burning fuel. The vehicle may also be equipped with a rotating machine or the like as the power source in addition to or instead of the engine.

[0012] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. [Example]

[0013] Fig. 1 is a diagram illustrating the schematic configuration of a vehicle 10 to which the present invention is applied, and also illustrates the main parts of the control functions and control systems for various controls in the vehicle 10. In Fig. 1, the vehicle 10 is equipped with an engine 12 that functions as a power source, drive wheels 14, and a power transmission device 16 provided in a power transmission path between the engine 12 and the drive wheels 14.

[0014] The engine 12 is a known internal combustion engine such as a gasoline engine, a diesel engine, etc. An electronic control device 90 (described later) controls an engine control device 50 including a throttle actuator, a fuel injection device, an ignition device, etc., provided in the vehicle 10, thereby controlling the engine torque Te, which is the output torque of the engine 12.

[0015] The power transmission device 16 includes a torque converter 20, a turbine shaft 22, a forward / reverse switching device 24, an input shaft 26, a continuously variable transmission 28, an output shaft 30, a reduction gear mechanism 32, a differential gear 34, and other components housed within a case 18, which is a non-rotating member attached to the vehicle body. The power transmission device 16 also includes left and right drive shafts 36 connected to the differential gear 34. The input side of the torque converter 20 is connected to the engine 12. The turbine shaft 22 is a rotating member that connects the output side of the torque converter 20 to the input side of the forward / reverse switching device 24. The input shaft 26 is a rotating member that connects the output side of the forward / reverse switching device 24 to the input side of the continuously variable transmission 28. The output shaft 30 is a rotating member that connects the output side of the continuously variable transmission 28 to the input side of the reduction gear mechanism 32. The output side of the reduction gear mechanism 32 is connected to the differential gear 34. In the power transmission device 16, the power output from the engine 12 is transmitted to the drive wheels 14 via a torque converter 20, a forward / reverse switching device 24, a continuously variable transmission 28, a reduction gear mechanism 32, a differential gear 34, and a drive shaft 36 in this order. When no particular distinction is made, the power is also referred to as driving force, torque, and force.

[0016] The torque converter 20 includes a pump wheel 20p connected to the engine 12 and a turbine wheel 20t connected to a turbine shaft 22. The torque converter 20 is a fluid transmission device that transmits power from the engine 12 to the turbine shaft 22 via fluid. The torque converter 20 includes an LU clutch 38 as a direct-coupled clutch that connects the pump wheel 20p and the turbine wheel 20t, i.e., that connects the input and output rotary members of the torque converter 20. The LU clutch 38 is a known lock-up clutch.

[0017] The power transmission device 16 includes a mechanical oil pump 40 connected to the pump impeller 20p. The oil pump 40 is driven to rotate by the engine 12, and supplies hydraulic oil OIL to a hydraulic control circuit 52 provided in the vehicle 10, which serves as the source pressure of hydraulic oil pressure for controlling the speed change of the continuously variable transmission 28, generating belt clamping pressure in the continuously variable transmission 28, switching the control states of a forward clutch C1 and a reverse brake B1 (described later), and switching the control state of the LU clutch 38. The control states of the forward clutch C1, the LU clutch 38, and the like are operating states such as an engaged state, a slip state, and a released state.

[0018] The forward / reverse switch device 24 includes a double-pinion planetary gear set 24p, a forward clutch C1, and a reverse brake B1. The planetary gear set 24p is a differential mechanism having three rotating elements: a sun gear 24s, a carrier 24c, and a ring gear 24r. The sun gear 24s is connected to the turbine shaft 22. The carrier 24c is connected to the input shaft 26. The ring gear 24r is selectively connected to the case 18 via the reverse brake B1. The carrier 24c and the sun gear 24s are selectively connected via the forward clutch C1. The forward clutch C1 and the reverse brake B1 are both known hydraulic wet-type friction engagement devices that are frictionally engaged by their respective hydraulic actuators. The control states of the forward clutch C1 and the reverse brake B1 are switched by changing the torque capacity using the adjusted hydraulic oil pressure supplied from the hydraulic control circuit 52. In the forward / reverse switching device 24, when the forward clutch C1 is engaged and the reverse brake B1 is released, a forward power transmission path is formed in the power transmission device 16. When the reverse brake B1 is engaged and the forward clutch C1 is released, a reverse power transmission path is formed in the power transmission device 16. When both the forward clutch C1 and the reverse brake B1 are released, the power transmission device 16 is placed in a neutral state in which power transmission is disabled.

[0019] The continuously variable transmission 28 includes a primary pulley 60 with a variable effective diameter connected to the input shaft 26, a secondary pulley 62 with a variable effective diameter connected to the output shaft 30, and a transmission belt 64 wound around the pulleys 60, 62 as a transmission element. The continuously variable transmission 28 is a known belt-type continuously variable transmission in which power is transmitted via friction between the pulleys 60, 62 and the transmission belt 64, and transmits power from the engine 12 to the drive wheels 14. In this manner, the continuously variable transmission 28 is a continuously variable transmission that forms part of the power transmission path between the engine 12 and the drive wheels 14. The friction force is also referred to as clamping pressure, and is also referred to as belt clamping pressure. This belt clamping pressure is the belt torque capacity Tcvt, which is the torque capacity of the transmission belt 64 in the continuously variable transmission 28.

[0020] The primary pulley 60 includes a fixed sheave 60a connected to the input shaft 26, a movable sheave 60b that is non-rotatable relative to the fixed sheave 60a about the axis of the input shaft 26 but movable in the axial direction, and a hydraulic actuator 60c that applies a primary thrust Wpri to the movable sheave 60b. The primary thrust Wpri is the thrust of the primary pulley 60 (= primary pressure Ppri × pressure-receiving area) that changes the V-groove width between the fixed sheave 60a and the movable sheave 60b. In other words, the primary thrust Wpri is the thrust of the primary pulley 60 that is applied by the hydraulic actuator 60c to clamp the transmission belt 64. The primary pressure Ppri is a hydraulic pressure supplied to the hydraulic actuator 60c by the hydraulic control circuit 52 and is the pulley hydraulic pressure that generates the primary thrust Wpri. The secondary pulley 62 includes a fixed sheave 62a connected to the output shaft 30, a movable sheave 62b that is movable in the axial direction but not rotatable relative to the fixed sheave 62a around the axis of the output shaft 30, and a hydraulic actuator 62c that applies a secondary thrust Wsec to the movable sheave 62b. The secondary thrust Wsec is the thrust (= secondary pressure Psec × pressure-receiving area) of the secondary pulley 62 that changes the width of the V-groove between the fixed sheave 62a and the movable sheave 62b. In other words, the secondary thrust Wsec is the thrust of the secondary pulley 62 that is applied by the hydraulic actuator 62c to clamp the transmission belt 64. The secondary pressure Psec is a hydraulic pressure supplied to the hydraulic actuator 62c by the hydraulic control circuit 52 and is the pulley hydraulic pressure that generates the secondary thrust Wsec.

[0021] In the continuously variable transmission 28, a hydraulic control circuit 52 driven by an electronic control device 90 (described later) regulates and controls the primary pressure Ppri and the secondary pressure Psec, thereby controlling the primary thrust Wpri and the secondary thrust Wsec. As a result, in the continuously variable transmission 28, the V-groove width of each pulley 60, 62 is changed to change the loop diameter (= effective diameter) of the transmission belt 64, changing the speed ratio γ (= input shaft rotation speed Nin / output shaft rotation speed Nout), and controlling the belt clamping pressure so as not to cause slippage of the transmission belt 64. In other words, by controlling the primary thrust Wpri and the secondary thrust Wsec, belt slippage of the transmission belt 64 is prevented, and the speed ratio γ of the continuously variable transmission 28 is set to the target speed ratio γtgt. The input shaft rotation speed Nin is the input rotation speed of the continuously variable transmission 28, and is the rotation speed of the input shaft 26, and is equivalent to the rotation speed of the primary pulley 60. The output shaft rotation speed Nout is the output rotation speed of the continuously variable transmission 28 , the rotation speed of the output shaft 30 , and is the same as the rotation speed of the secondary pulley 62 .

[0022] In the continuously variable transmission 28, when the primary pressure Ppri is increased, the V-groove width of the primary pulley 60 is narrowed and the gear ratio γ is reduced. Reducing the gear ratio γ means that the continuously variable transmission 28 is upshifted. On the other hand, in the continuously variable transmission 28, when the primary pressure Ppri is decreased, the V-groove width of the primary pulley 60 is widened and the gear ratio γ is increased. Reducing the gear ratio γ means that the continuously variable transmission 28 is downshifted. Note that in the continuously variable transmission 28, belt slippage is prevented by the primary thrust force Wpri and the secondary thrust force Wsec, and the target gear ratio γtgt is realized by the interrelationship between the primary thrust force Wpri and the secondary thrust force Wsec; the target gear change is not realized by only one thrust force. In accordance with the interrelationship between the primary pressure Ppri and the secondary pressure Psec, the thrust ratio τ (=Wsec / Wpri), which is the ratio between the primary thrust Wpri and the secondary thrust Wsec, is changed, thereby changing the gear ratio γ of the continuously variable transmission 28. The thrust ratio τ is the ratio of the secondary thrust Wsec to the primary thrust Wpri. For example, the larger the thrust ratio τ, the larger the gear ratio γ, i.e., the more the continuously variable transmission 28 is downshifted.

[0023] The vehicle 10 is equipped with a wheel brake device 54. The wheel brake device 54 includes a brake master cylinder and a cylinder actuator (not shown) that generate brake hydraulic pressure. Each wheel, including the drive wheels 14 and the non-driven wheels (not shown), is equipped with a wheel brake 56. If the vehicle 10 is an all-wheel drive vehicle, the non-driven wheels are drive wheels. The wheel brake device 54 is a brake device that applies wheel braking torque, which is a braking torque generated by the wheel brakes 56, to the wheels in accordance with a command from an electronic control device 90 (described later). The wheel brake device 54 supplies brake hydraulic pressure to wheel cylinders (not shown) provided in each wheel brake 56 in response to, for example, the driver's depression of the brake pedal. In the wheel brake device 54, under normal conditions, master cylinder hydraulic pressure generated by the brake master cylinder and corresponding to the brake operation amount Bra is supplied to the wheel cylinders as brake hydraulic pressure. On the other hand, in the wheel brake device 54, for example, when the ABS (Anti-lock Brake System) function, TRC (Traction Control) function, VSC (Vehicle Stability Control) function, vehicle speed control, automatic driving control, automatic brake control function, etc. are operating, brake hydraulic pressure of a magnitude corresponding to the wheel braking torque required for each control is supplied to the wheel cylinder in order to generate wheel braking torque. The brake operation amount Bra is a signal that corresponds to the brake pedal depression force and indicates the magnitude of the brake pedal depression operation by the driver, i.e., the magnitude of the brake operation.

[0024] The ABS is a system that controls the brake hydraulic pressure of each wheel to prevent the wheels from locking, in order to ensure the stability of the vehicle 10 during braking due to sudden braking operations or braking on slippery road surfaces. The TRC is a system that controls the brake hydraulic pressure and driving force of the drive wheels 14 to suppress slippage of the drive wheels 14 and ensure driving force appropriate to road surface conditions, in order to ensure the stability of the vehicle 10 during starting / accelerating on slippery road surfaces or accelerating while cornering. The VSC is a system that controls the brake hydraulic pressure and driving force of each wheel to mitigate rear wheel or front wheel skid, in order to ensure stability in the turning direction of the vehicle 10.

[0025] The vehicle 10 further includes an electronic control unit 90 that includes a control device for the vehicle 10. The electronic control unit 90 includes a so-called microcomputer equipped with, for example, a CPU, RAM, ROM, an input / output interface, etc., and the CPU executes various controls of the vehicle 10 by performing signal processing in accordance with programs stored in the ROM in advance while utilizing the temporary storage function of the RAM. The electronic control unit 90 includes computers for engine control, clutch control, transmission control, etc. as necessary.

[0026] The electronic control device 90 receives various signals (for example, an engine rotation speed Ne which is the rotation speed of the engine 12, a turbine rotation speed Nt which is the rotation speed of the turbine shaft 22, an input shaft rotation speed Nin, an output shaft rotation speed Nout corresponding to the vehicle speed V, a rotation speed of the left and right drive wheels 14 and a rotation speed of the left and right drive wheels 14) based on detection values ​​of various sensors provided in the vehicle 10 (for example, an engine rotation speed sensor 70, a turbine rotation speed sensor 72, an input rotation speed sensor 74, an output rotation speed sensor 76, each wheel speed sensor 78, an accelerator opening sensor 80, a throttle valve opening sensor 82, a brake sensor 84, an acceleration sensor 86, a yaw rate sensor 88, etc.). The vehicle 10 also supplies various signals, such as wheel speeds Nw, Nwdl, Nwdr, Nwsl, and Nwsr, which are the rotational speeds of the wheels including the non-driven wheels (not shown), accelerator opening θacc, which is the driver's accelerator operation amount indicating the magnitude of the driver's acceleration operation, throttle valve opening θth, which is the opening of the electronic throttle valve, brake-on signal Bon, which is a signal indicating the state in which the brake pedal for operating the wheel brakes is being operated by the driver, brake operation amount Bra, longitudinal acceleration Gx of the vehicle 10, lateral acceleration Gy of the vehicle 10, and yaw rate Ryaw, which is the rotational angular velocity around the vertical axis of the vehicle 10. The wheel speeds Nwdl and Nwdr are drive wheel speed Nwd, which is the rotational speed of the drive wheels 14, and the wheel speeds Nwsl and Nwsr are non-driven wheel speed Nws, which is the rotational speed of the non-driven wheels (not shown).

[0027] The electronic control device 90 outputs various command signals (for example, an engine control command signal Se for controlling the engine 12, a CVT hydraulic control command signal Scvt for controlling the shifting of the continuously variable transmission 28 and the belt clamping pressure, etc., a CB hydraulic control command signal Scb for controlling each of the forward clutch C1 and the reverse brake B1, an LU hydraulic control command signal Slu for controlling the LU clutch 38, a brake control command signal Sbra for controlling the wheel braking torque, etc.) to each device (for example, the engine control device 50, the hydraulic control circuit 52, the wheel brake device 54, etc.) provided in the vehicle 10.

[0028] The electronic control unit 90 includes an engine control means, i.e., an engine control section 92, and a gear change control means, i.e., a gear change control section 94 in order to realize various controls in the vehicle 10.

[0029] The engine control unit 92 outputs an engine control command signal Se to the engine control device 50 to control the engine 12 so as to obtain the required engine torque Te.

[0030] Specifically, the engine control unit 92 calculates the amount of driving demanded by the driver for the vehicle 10 by, for example, applying the accelerator opening θacc and the vehicle speed V to a driving demand map. The driving demand map is a relationship for calculating the driving demand that is determined experimentally or by design and stored in advance, i.e., a predetermined relationship. The driving demand is, for example, a required driving torque Trdem [Nm] at the drive wheels 14. The driving demand may also be, for example, a required driving force Frdem [N] at the drive wheels 14 or a required output shaft torque at the output shaft 30. The engine control unit 92 outputs an engine control command signal Se to the engine control device 50 to control the engine 12 so as to obtain an engine torque Te that realizes the required driving torque Trdem, taking into account transmission loss, auxiliary load, the gear ratio γ of the continuously variable transmission 28, etc.

[0031] The shift control unit 94 outputs a CVT hydraulic control command signal Scvt to the hydraulic control circuit 52 to control the primary pressure Ppri and the secondary pressure Psec so as to achieve the target gear ratio γtgt of the continuously variable transmission 28 while preventing belt slippage of the continuously variable transmission 28, thereby performing gear changes of the continuously variable transmission 28.

[0032] Specifically, the shift control unit 94 calculates the target input shaft rotation speed Nintgt by applying the accelerator opening θacc and the vehicle speed V to, for example, a shift map, which is a predetermined relationship. The shift map is a relationship for calculating the target input shaft rotation speed Nintgt that is determined experimentally or by design and stored in advance, i.e., a predetermined relationship. The shift control unit 94 calculates the target gear ratio γtgt (=Nintgt / Nout) based on the target input shaft rotation speed Nintgt. The shift control unit 94 calculates the estimated turbine torque Tte (=Tee×t; t is the torque ratio of the torque converter 20) based on the estimated engine torque Tee. The turbine torque Tt is the torque input to the continuously variable transmission 28. The shift control unit 94 calculates the thrust ratio τ based on the target gear ratio γtgt and the estimated turbine torque Tte, for example, using a thrust ratio map, to achieve the target gear ratio γtgt while preventing belt slippage. The thrust ratio map is a relationship for determining the thrust ratio τ that is experimentally or design-based and stored in advance, i.e., a predetermined relationship. The shift control unit 94 calculates a target primary thrust Wpritgt and a target secondary thrust Wsectgt to achieve this thrust ratio τ. The shift control unit 94 converts the target primary thrust Wpritgt and the target secondary thrust Wsectgt into a target primary pressure Ppritgt (= Wpritgt / pressure-receiving area) and a target secondary pressure Psectgt (= Wsectgt / pressure-receiving area), respectively. The shift control unit 94 outputs a CVT hydraulic control command signal Scvt to the hydraulic control circuit 52 to control the primary pressure Ppri and the secondary pressure Psec so as to obtain the target primary pressure Ppritgt and the target secondary pressure Psectgt. For convenience, the above description of the shift control of the continuously variable transmission 28 has focused on thrust for maintaining a constant target gear ratio γtgt. During a speed change transition of the continuously variable transmission 28, the thrust to achieve a target upshift or a target downshift is added to this constant-hold thrust.

[0033] Here, when the vehicle 10 is traveling on a road surface where the drive wheels 14 are prone to spinning, i.e., slipping, the drive wheel speed Nwd may be suddenly reduced after the drive wheels 14 begin to slip. In this case, there is a risk that a large inertia torque may be input to the continuously variable transmission 28. If an inertia torque exceeding the belt torque capacity Tcvt is input, belt slippage may occur, which may reduce the durability of the power transmission belt 64 and lead to a reduction in the durability of the continuously variable transmission 28. The inertia torque input to the continuously variable transmission 28 due to a sudden decrease in the drive wheel speed Nwd is, for example, the inertia torque on the input shaft 26 that accompanies the sudden decrease in the drive wheel speed Nwd, i.e., the input shaft inertia torque Tint.

[0034] A road surface on which the drive wheels 14 are likely to slip is one on which the drive wheels 14 are likely to slip, such as a low-friction road (i.e., a low μ road) with an extremely low coefficient of friction, such as a snowy or icy road, or a rough road such as a corrugated or unpaved road. The drive wheel speed Nwd may be suddenly reduced, for example, when the vehicle 10 transitions from a low μ road to a high-friction road (i.e., a dry road) with a high coefficient of friction, when the brakes are applied while the drive wheels 14 are slipping (i.e., tire slip), or when tire slip occurs while traveling on a rough road and then grips. When traveling on a rough road such as a corrugated road, tire slip and grip may occur repeatedly within a short period of time.

[0035] Upshifting the continuously variable transmission 28 can suppress an increase in the input shaft rotation speed Nin and suppress the input shaft inertia torque Tint that accompanies a sudden decrease in the drive wheel speed Nwd. When the vehicle 10 is traveling on a road surface on which the drive wheels 14 are likely to spin, the transmission control unit 94 performs upshift control CTup to control the gear ratio γ of the continuously variable transmission 28 to a higher vehicle speed compared to when the vehicle 10 is traveling on a road surface on which the drive wheels 14 are unlikely to spin. The upshift control CTup suppresses the input shaft inertia torque Tint to suppress a decrease in durability of the continuously variable transmission 28, and therefore also serves as a protective control to protect the continuously variable transmission 28. The transmission control unit 94 performs the upshift control CTup by setting a target gear ratio γtgtup for upshift control that is smaller by a predetermined amount than the target gear ratio γtgt in the normal gear shift control CTsh, which performs gear shift control of the continuously variable transmission 28 using, for example, the above-mentioned gear shift map or thrust ratio map. The predetermined amount is a predetermined change amount of the speed ratio for suppressing the input shaft inertia torque Tint that accompanies a sudden decrease in the drive wheel speed Nwd compared to, for example, normal speed change control CTsh.

[0036] It has been discovered that the input shaft inertia torque Tint that accompanies a sudden decrease in drive wheel speed Nwd becomes relatively large when the input shaft rotation speed Nin is relatively high. For this reason, if upshift control CTup is uniformly performed to prevent a decrease in the durability of the continuously variable transmission 28 while the vehicle is traveling on a road surface on which the drive wheels 14 are likely to spin, the continuously variable transmission 28 will be upshifted even when the input of a large input shaft inertia torque Tint is unlikely to occur, which could result in a decrease in the driving performance, for example, the power performance, of the vehicle 10.

[0037] FIG. 2 is a diagram illustrating an example of a predetermined correlation between the input shaft rotation speed Nin and the input shaft inertia torque Tint associated with a sudden decrease in the drive wheel speed Nwd. In FIG. 2, the higher the input shaft rotation speed Nin, the larger the input shaft inertia torque Tint associated with a sudden decrease in the drive wheel speed Nwd. When the input shaft rotation speed Nin is equal to or greater than a predetermined rotation speed Ninf (see the shaded area in the figure), a large input shaft inertia torque Tint is input, which may reduce the durability of the continuously variable transmission 28. Therefore, the shift control unit 94 may execute the upshift control CTup when the input shaft rotation speed Nin is equal to or greater than the predetermined rotation speed Ninf. The predetermined rotation speed Ninf is a threshold value set based on a predetermined correlation between the input shaft rotation speed Nin and the input shaft inertia torque Tint associated with a sudden decrease in the drive wheel speed Nwd, for example, for determining the range of the input shaft rotation speed Nin in which the input shaft inertia torque Tint needs to be suppressed. As a result, in a region where the input shaft rotation speed Nin is equal to or greater than the predetermined rotation speed Ninf, an increase in the input shaft rotation speed Nin is suppressed, and the input shaft inertia torque Tint can be suppressed. On the other hand, in a region where the input shaft rotation speed Nin is less than the predetermined rotation speed Ninf, the input shaft inertia torque Tint is not input so large that it would be a concern that the durability of the continuously variable transmission 28 would be reduced, so there is no need to suppress the input shaft inertia torque Tint. When the input shaft rotation speed Nin is in a region where it is less than the predetermined rotation speed Ninf, the gear change control unit 94 does not perform the upshift control CTup, but performs the normal gear change control CTsh. As a result, in a region where the input shaft rotation speed Nin is less than the predetermined rotation speed Ninf, the continuously variable transmission 28 is not upshifted more than necessary, and power performance can be ensured.

[0038] When upshift control CTup is performed while the TRC function or VSC function is operating, the gradient of fluctuations in the input shaft rotation speed Nin relative to fluctuations in the vehicle speed V is made gentler. This suppresses fluctuations in the drive torque Tr, preventing sudden changes in the drive torque Tr in response to changes in accelerator operation. This is expected to improve the controllability of the vehicle 10 and also to moderate fluctuations in engine noise by suppressing fluctuations in the input shaft rotation speed Nin. Therefore, it is useful to perform upshift control CTup while the TRC function or VSC function is operating. Note that when the TRC function or VSC function is operating, it can also be considered that the vehicle 10 is traveling on a road surface on which the drive wheels 14 are prone to slip.

[0039] The electronic control device 90 further includes a state determination means, that is, a state determination unit 96, in order to improve the durability of the continuously variable transmission 28 while ensuring the running performance of the vehicle 10.

[0040] The state determination unit 96 determines whether the vehicle 10 is traveling on a road surface on which the drive wheels 14 are likely to spin. The state determination unit 96 determines whether the vehicle 10 is traveling on a road surface on which the drive wheels 14 are likely to spin, for example, based on whether the difference between the average drive wheel speed Nwdav of the left and right drive wheels 14 and the average driven wheel speed Nwsav of the left and right driven wheels (not shown) exceeds a predetermined slip determination threshold for determining that tire slip has occurred. Alternatively, the state determination unit 96 may determine whether the vehicle 10 is traveling on a road surface on which the drive wheels 14 are likely to spin using the wheel slip ratio (=(Nwd-Nws) / Nwd), the rate of change of the drive wheel speed Nwd, the outside air temperature, the road surface temperature, the longitudinal acceleration Gx, etc. Alternatively, the state determination unit 96 determines whether the TRC function or the VSC function is operating.

[0041] If the state determination unit 96 determines that the vehicle 10 is traveling on a road surface on which the drive wheels 14 are likely to spin, or if it determines that the TRC function or the VSC function is operating, it determines whether the input shaft rotation speed Nin is equal to or greater than a predetermined rotation speed Ninf.

[0042] The gear shift control unit 94 performs upshift control CTup when the state determination unit 96 determines that the input shaft rotation speed Nin is equal to or greater than a predetermined rotation speed Ninf. The gear shift control unit 94 performs normal gear shift control CTsh when the state determination unit 96 determines that the vehicle 10 is not traveling on a road surface on which the drive wheels 14 are likely to spin and that the TRC function or the VSC function is not operating. Alternatively, the gear shift control unit 94 performs normal gear shift control CTsh when the state determination unit 96 determines that the input shaft rotation speed Nin is less than the predetermined rotation speed Ninf. A determination by the state determination unit 96 that the vehicle 10 is not traveling on a road surface on which the drive wheels 14 are likely to spin is the same as a determination that the vehicle 10 is traveling on a road surface on which the drive wheels 14 are unlikely to spin.

[0043] FIG. 3 is a flowchart illustrating the main control operations of the electronic control device 90, which are executed repeatedly, for example, to improve the durability of the continuously variable transmission 28 and ensure the driving performance of the vehicle 10, as compared to when upshift control CTup is uniformly performed.

[0044] 3, first, in step S10 (hereinafter, the term "step" will be omitted) corresponding to the function of the state determination unit 96, it is determined whether the vehicle 10 is traveling on a road surface on which the drive wheels 14 are likely to spin, or whether the TRC function or the VSC function is operating. If the determination in S10 is positive, then in S20, corresponding to the function of the state determination unit 96, it is determined whether the input shaft rotation speed Nin is equal to or greater than a predetermined rotation speed Ninf. If the determination in S20 is positive, then in S30, corresponding to the function of the gear change control unit 94, upshift control CTup is performed. On the other hand, if the determination in S10 is negative, or if the determination in S20 is negative, then in S40, corresponding to the function of the gear change control unit 94, normal gear change control CTsh is performed.

[0045] As described above, according to this embodiment, when the input shaft rotation speed Nin is equal to or greater than the predetermined rotation speed Ninf, the upshift control CTup is performed, and therefore when the input shaft inertia torque Tint associated with a sudden decrease in drive wheel speed Nwd becomes relatively large while the vehicle 10 is traveling on a road surface on which the drive wheels 14 are likely to spin, the input shaft rotation speed Nin is reduced by upshifting the continuously variable transmission 28, thereby suppressing the input shaft inertia torque Tint that is actually input when the drive wheel speed Nwd suddenly decreases. Furthermore, even when the vehicle 10 is traveling on a road surface on which the drive wheels 14 are likely to spin, when the input shaft inertia torque Tint becomes relatively small, the continuously variable transmission 28 does not upshift to suppress the input shaft inertia torque Tint, making it easier to ensure a drive torque Tr suited to the traveling conditions. Therefore, when the vehicle 10 is traveling on a road surface where the drive wheels 14 are likely to spin, it is possible to improve the durability of the continuously variable transmission 28 and ensure the driving performance of the vehicle 10, compared to when the upshift control CTup is uniformly performed.

[0046] Although the embodiments of the present invention have been described in detail above with reference to the drawings, the present invention can also be applied to other embodiments.

[0047] For example, in the above-described embodiment, the flowchart of FIG. 3 may be modified as appropriate, such as not necessarily determining whether the TRC function or the VSC function is operating in S10 of the flowchart of FIG.

[0048] In the above-described embodiment, the torque converter 20 is used as the fluid transmission device, but the present invention is not limited to this. For example, instead of the torque converter 20, another fluid transmission device such as a fluid coupling that does not have a torque amplifying function may be used as the fluid transmission device. Alternatively, the fluid transmission device does not necessarily have to be provided, and may be replaced with, for example, a starting clutch.

[0049] The present invention can also be applied to a vehicle equipped with an automatic transmission in which a plurality of power transmission paths are provided in parallel between a power source and drive wheels, such as a first power transmission path via a gear mechanism and a second power transmission path via a belt-type continuously variable transmission.In short, the present invention can be applied to any vehicle that includes a continuously variable transmission that forms part of the power transmission path between a power source and drive wheels and has a transmission element wound between a primary pulley and a secondary pulley.

[0050] It should be noted that the above is merely one embodiment, and the present invention can be embodied in various forms with various modifications and improvements based on the knowledge of those skilled in the art. [Explanation of symbols]

[0051] 10: Vehicle 12: Engine (power source) 14: Drive wheel 28:Continuously variable transmission 60: Primary pulley 62: Secondary pulley 64: Transmission belt (transmission element) 90: Electronic control device (control device) 94: Transmission control unit

Claims

[Claim 1] A control device for a vehicle including a continuously variable transmission that forms part of a power transmission path between a power source and a drive wheel and has a transmission element wound between a primary pulley and a secondary pulley, a transmission control unit that performs upshift control to control the gear ratio of the continuously variable transmission to a higher vehicle speed side when the vehicle is traveling on a road surface where the drive wheels are likely to spin, compared to when the vehicle is traveling on a road surface where the drive wheels are unlikely to spin, the shift control unit performs the upshift control when the input rotation speed of the continuously variable transmission is equal to or higher than a predetermined rotation speed at which the inertia torque needs to be suppressed, the rotation speed being set based on a predetermined correlation between the input rotation speed and an inertia torque input to the continuously variable transmission due to a sudden decrease in the rotation speed of the drive wheels.

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