Automatic transmission control system

Abstract

To accurately control hydraulic pressure of a friction fastening element, considering a reduction in a friction coefficient of the friction fastening element when in a slip state.SOLUTION: A controller 200 in an automatic transmission control system is configured to: calculate a friction coefficient of a friction fastening element, when the friction fastening element is in a slip state, based on hydraulic pressure applied to the friction fastening element, a temperature of oil supplied to the friction fastening element, a differential rotation speed between an input side friction plate and an output side friction plate in the friction fastening element, and a friction surface temperature in the friction fastening element; control the hydraulic pressure based on the friction coefficient and demand torque for a vehicle; calculate shear stress acting on the friction fastening element by subtracting a temperature dependent term determined in accordance with the friction surface temperature from a speed dependent term determined in accordance with the differential rotation speed; and calculate the friction coefficient based on the shear stress. A contribution ratio of the speed dependent term with respect to the shear stress is larger than the contribution ratio of the temperature dependent term with respect to the shear stress.SELECTED DRAWING: Figure 8

Description

Technical Field

[0001] The present invention relates to a control system for an automatic transmission having friction engagement elements.

Background Art

[0002] Conventionally, in a vehicle, an automatic transmission including a plurality of friction engagement elements that can take a engaged state, a released state, and a slip state, and forming a plurality of gear stages by changing the friction engagement elements to be engaged among them, a hydraulic pressure adjustment mechanism that adjusts the hydraulic pressure applied to the friction engagement elements, and a controller configured to control the hydraulic pressure applied from the hydraulic pressure adjustment mechanism to the friction engagement elements is known.

[0003] For example, Patent Document 1 describes such a control system for an automatic transmission. Specifically, Patent Document 1 describes a technique of calculating a pressing force corresponding to a required transmission torque to be applied to a friction engagement element, correcting this pressing force based on a map defining the characteristics of the friction coefficient of the friction engagement element and the differential rotational speed (the rotational speed difference between the input-side friction plate and the output-side friction plate of the friction engagement element), and controlling the hydraulic pressure applied to the friction engagement element based on the corrected pressing force. Note that the pressing force corresponds to the load applied to the friction engagement element and has a magnitude corresponding to the hydraulic pressure applied to the friction engagement element.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Generally, the transmission torque of a friction fastening element is controlled via the hydraulic pressure applied to the friction fastening element. The control value of this hydraulic pressure is calculated from the required torque from the driver (which uniquely corresponds to the required transmission torque to be applied to the friction fastening element) and the friction coefficient of the friction fastening element. Therefore, in order to achieve highly accurate transmission torque control, it is desirable to accurately grasp the friction coefficient. However, since the friction coefficient is affected by various factors such as the load of the friction fastening element, the differential rotation speed, and the oil temperature, it is difficult to obtain an accurate value. In this regard, the technique described in Patent Document 1 mentioned above calculates the friction coefficient in consideration of the differential rotation speed of the friction fastening element.

[0006] Here, the friction coefficient of the friction fastening element tends to decrease when the friction fastening element is in a slip state. This is considered to be due to the increase in the friction surface temperature of the friction fastening element in the slip state. However, the technique described in Patent Document 1 mentioned above does not consider the decrease in the friction coefficient due to such an increase in the friction surface temperature, and thus cannot obtain an accurate friction coefficient.

[0007] The present invention has been made to solve the above-described problems of the prior art, and an object thereof is to provide a control system for an automatic transmission that can accurately control the hydraulic pressure of a friction fastening element in consideration of the decrease in the friction coefficient of the friction fastening element when it is in a slip state.

Means for Solving the Problems

[0008] In order to achieve the above object, the present invention provides a control system for an automatic transmission mounted on a vehicle, comprising: an automatic transmission including friction engaging elements including an input-side friction plate and an output-side friction plate, the friction engaging elements being switchable by hydraulic pressure to which a fastening state, a release state, and a slip state are imparted; a hydraulic pressure adjusting mechanism configured to adjust the hydraulic pressure applied to the friction engaging elements; and a controller configured to control the hydraulic pressure applied from the hydraulic pressure adjusting mechanism to the friction engaging elements in order to adjust the transmission torque of the friction engaging elements. The controller calculates the friction coefficient of the friction engaging elements based on the hydraulic pressure applied to the friction engaging elements, the oil temperature of the oil supplied to the friction engaging elements, the differential rotational speed between the input-side friction plate and the output-side friction plate in the friction engaging elements, and the friction surface temperature in the friction engaging elements when the friction engaging elements are at least in a slip state, controls the hydraulic pressure based on the friction coefficient and the required torque to be generated in the vehicle, calculates the shear stress acting on the friction engaging elements by subtracting the temperature-dependent term defined according to the friction surface temperature from the speed-dependent term defined according to the differential rotational speed, and calculates the friction coefficient based on the shear stress. The contribution degree of the speed-dependent term with respect to the shear stress is larger than the contribution degree of the temperature-dependent term with respect to the shear stress.

[0009] In the present invention configured as described above, the controller calculates the shear stress acting on the friction engaging elements from the speed-dependent term defined according to the differential rotational speed of the friction engaging elements and the temperature-dependent term defined according to the friction surface temperature of the friction engaging elements and having a smaller contribution degree than the speed-dependent term, and calculates the friction coefficient based on this shear stress. As a result, by considering the state of the friction surface temperature of the friction engaging elements in the slip state, the friction coefficient can be accurately obtained, and the hydraulic pressure can be accurately controlled based on this friction coefficient. As a result, when the friction engaging elements are in the slip state, the transmission torque can be stably controlled.

[0010] In the present invention, preferably, the controller calculates the velocity-dependent term by multiplying a value corresponding to the differential rotational speed by a first coefficient, and calculates the temperature-dependent term by multiplying a value corresponding to the friction surface temperature by a second coefficient. The first coefficient is set to a value larger than the second coefficient, whereby the contribution degree of the velocity-dependent term to the shear stress is larger than the contribution degree of the temperature-dependent term to the shear stress. According to the present invention configured as described above, since the contribution degrees of the velocity-dependent term and the temperature-dependent term to the shear stress are accurately considered, a more accurate friction coefficient can be obtained.

[0011] In the present invention, preferably, the controller is configured to set the first coefficient and the second coefficient to larger values as the hydraulic pressure applied to the friction fastening element increases. According to the present invention configured as described above, by taking into account the hydraulic pressure dependence of the first coefficient and the second coefficient, a more accurate friction coefficient can be obtained.

[0012] In the present invention, preferably, the controller is configured to calculate the frictional heat generated in the friction fastening element from the frictional force corresponding to the calculated friction coefficient and the differential rotational speed, and calculate the friction surface temperature based on the frictional heat. In the present invention configured as described above, since it is difficult to detect the friction surface temperature with a sensor, the controller calculates the friction surface temperature. In this case, since the controller calculates the friction surface temperature based on the frictional heat generated in the friction fastening element, an accurate friction surface temperature can be obtained.

[0013] In the present invention, preferably, the controller calculates the friction coefficient based on the frictional force obtained by adding the boundary frictional force acting on the friction fastening element corresponding to the shear stress and the fluid frictional force acting on the friction fastening element separately from the boundary frictional force, and calculates the boundary frictional force and the fluid frictional force based on the surface distance between the input-side friction plate and the output-side friction plate in the friction fastening element in the slip state. According to the present invention configured as described above, by taking into account the boundary friction force and the fluid friction force according to the surface-to-surface distance, a more accurate friction coefficient can be obtained.

Advantages of the Invention

[0014] According to the control system of the automatic transmission according to the present invention, by taking into account the decrease in the friction coefficient of the friction engagement element when in the slip state, the hydraulic pressure of the friction engagement element can be accurately controlled.

Brief Description of the Drawings

[0015]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Modes for Carrying Out the Invention

[0016] Hereinafter, with reference to the accompanying drawings, a control system for an automatic transmission according to an embodiment of the present invention will be described.

[0017] [Basic Configuration] First, with reference to FIGS. 1 to 4, the basic configuration of the control system for the automatic transmission according to this embodiment will be described. FIG. 1 is a schematic configuration diagram of the automatic transmission according to this embodiment, FIG. 2 is a engagement table of the friction engagement elements of the automatic transmission according to this embodiment, FIG. 3 is a schematic configuration diagram of the friction engagement elements and the hydraulic adjustment mechanism according to this embodiment, and FIG. 4 is a block diagram showing the electrical configuration of the control system for the automatic transmission according to this embodiment.

[0018] As shown in FIG. 1, the automatic transmission 1 has an input shaft 2 as an input member of the automatic transmission 1 to which engine output is input via a torque converter or the like (not shown). On the input shaft 2, first, second, and third planetary gear sets (hereinafter referred to as "first, second, and third gear sets") 10, 20, and 30 are arranged from the drive source side (the right side in the figure).

[0019] On the input shaft 2, as friction engagement elements for switching the power transmission paths constituted by the first to third gear sets 10, 20, and 30, a low clutch 40 and a high clutch 50 that selectively transmit power from the input shaft 2 to the gear sets 10, 20, and 30 sides, and LR (low reverse) brakes 60, 26 brakes 70, and R35 brakes 80 that fix predetermined rotating elements of the respective gear sets 10, 20, and 30 are arranged in this order from the drive source side. Hereinafter, when these clutches and brakes (40 to 80) are used without distinction, they will be simply referred to as "friction engagement elements" without symbols.

[0020] The first, second, and third gear sets 10, 20, and 30 are each composed of a sun gear 11, 21, 31, a plurality of pinions 12, 22, 32 meshing with these sun gears 11, 21, 31, carriers 13, 23, 33 supporting these pinions 12, 22, 32 respectively, and ring gears 14, 24, 34 meshing with the pinions 12, 22, 32.

[0021] And the sun gear 11 of the first gear set 10 and the sun gear 21 of the second gear set 20 are coupled and connected to the inner rotating member 41 of the low clutch 40. Also, the carrier 23 of the second gear set 20 is connected to the inner rotating member 51 of the high clutch 50. Further, the input shaft 2 is directly connected to the sun gear 31 of the third gear set 30.

[0022] Also, the ring gear 14 of the first gear set 10 and the carrier 23 of the second gear set 20 are coupled, and an LR brake 60 is disposed between them and the transmission case 3. Also, the ring gear 24 of the second gear set 20 and the carrier 33 of the third gear set 30 are coupled, and a 26 brake 70 is disposed between them and the transmission case 3. Further, an R35 brake 80 is disposed between the ring gear 34 of the third gear set 30 and the transmission case 3. And an output gear 4 as an output member of the automatic transmission 1 for outputting the output of the automatic transmission 1 to the driving wheel (not shown) side is connected to the carrier 13 of the first gear set 10.

[0023] The automatic transmission 1 configured as described above forms the 1st to 6th speeds in the D range and the reverse speed in the R range as shown in FIG. 2 by variously combining the engagement states of the low clutch 40, high clutch 50, LR brake 60, 26 brake 70, and R35 brake 80.

[0024] Each friction fastening element includes a plurality of inner friction plates arranged inside, an outer friction plate arranged outside the plurality of inner friction plates, a piston for fastening these plurality of friction plates, and a fastening hydraulic pressure chamber to which a fastening hydraulic pressure for pressing the piston toward the friction plate side is supplied. Depending on the power transmission state, one of the inner friction plate and the outer friction plate becomes the input-side friction plate and the other becomes the output-side friction plate.

[0025] Subsequently, with reference to FIG. 3, a partial configuration of each friction fastening element and a hydraulic pressure adjustment mechanism (in other words, a hydraulic circuit) 100 that controls the fastening and release of the friction fastening element will be described by taking the high clutch 50 as an example.

[0026] The high clutch 50 includes at least one inner friction plate 52 engaged with the outer peripheral surface of the cylindrical portion of the inner rotating member 51, at least one outer friction plate 54 engaged with the outer peripheral surface of the cylindrical portion of the outer rotating member 53, and a piston 55 for pressing the inner friction plate 52 and the outer friction plate 54.

[0027] The inner friction plate 52 and the outer friction plate 54 are alternately arranged in the axial direction. The piston 55 is arranged so as to be rotatable around the axis of the input shaft 2 and slidable in the axial direction. By sliding in the axial direction, the piston 55 presses the inner friction plate 52 and the outer friction plate 54 in the axial direction to fasten them to each other. The sliding of the piston 55 is controlled by the supply and discharge of oil to and from the fastening hydraulic pressure chamber 56.

[0028] A solenoid valve 101 as a control valve that constitutes a part of the hydraulic pressure adjustment mechanism 100 for controlling the supply and discharge of oil supplied to the fastening hydraulic pressure chamber 56 is connected to the fastening hydraulic pressure chamber 56. Line hydraulic pressure regulated to a fastening hydraulic pressure according to a command signal from a controller 200 (see FIG. 4) described later is supplied to the hydraulic pressure chamber 56 via the solenoid valve 101. The line pressure is regulated to a value according to the accelerator opening degree, engine speed, etc., with the hydraulic pressure generated by a mechanical oil pump 62 rotationally driven by the engine 61 etc. as the original pressure.

[0029] Note that the present invention is not limited to the application to the automatic transmission 1 shown in FIG. 1 etc. (this automatic transmission 1 is an example of the application target of the present invention), and it is applicable to automatic transmissions of various configurations including friction engagement elements that operate by hydraulic pressure.

[0030] Subsequently, as shown in FIG. 4, the automatic transmission 1 includes a hydraulic pressure adjustment mechanism 100 for selectively supplying a line pressure for fastening to the above-described friction engagement element to realize the above-described gear stage. This hydraulic pressure adjustment mechanism 100 includes a plurality of solenoid valves (SV) 101 for shift control, specifically, a first solenoid valve 101, a second solenoid valve 101, a third solenoid valve 101... (hereinafter, when these are used without distinction, they are simply referred to as "solenoid valve 101"). By the solenoid valve 101, the flow and hydraulic pressure of the oil supplied from the oil pump 62 (see FIG. 3) to the hydraulic pressure adjustment mechanism 100 are controlled, and the hydraulic pressure supplied to the fastening hydraulic pressure chamber is adjusted. As a result, the friction engagement element is fastened by the supply of oil to the fastening hydraulic pressure chamber, while the friction engagement element is released by the discharge of oil from the fastening hydraulic pressure chamber. Further, by controlling the hydraulic pressure in the fastening hydraulic pressure chamber of the friction engagement element, the fastening state, release state, and slip state of the friction engagement element, as well as the degree of fastening (fastening ratio) in the slip state, are controlled.

[0031] The plurality of solenoid valves 101 of the hydraulic pressure adjustment mechanism 100 are controlled by the controller 200. The controller 200 includes one or more microprocessors 200a as a central processing unit (CPU) that executes a program, a memory 200b configured by, for example, a RAM (Random Access Memory) and a ROM (Read Only Memory) that stores programs and data, and an input / output bus or the like that performs input / output of electrical signals. Note that the controller 200 is configured by, for example, an ECU (Electronic Control Unit) or a TCM (Transmission Control Module).

[0032] As shown in FIG. 4, detection signals are input into the controller 200 mainly from an accelerator opening sensor 201, an engine speed sensor 202, a vehicle speed sensor 203, a hydraulic pressure sensor 204, an oil temperature sensor 205, an input rotation speed sensor 206, and an output rotation speed sensor 207. The accelerator opening sensor 201 detects the accelerator opening corresponding to the operation of the accelerator pedal by the driver. The engine speed sensor 202 detects the rotation speed of the engine 61. The vehicle speed sensor 203 detects the speed (vehicle speed) of the vehicle. The hydraulic pressure sensor 204 detects the hydraulic pressure applied to the friction engagement element. The oil temperature sensor 205 detects the oil temperature (hydraulic oil) of the oil supplied to the friction engagement element. The input rotation speed sensor 206 and the output rotation speed sensor 207 detect the rotation speeds of the input-side friction plate and the output-side friction plate of the friction engagement element, respectively. The hydraulic pressure sensor 204, the input rotation speed sensor 206, and the output rotation speed sensor 207 are provided for each of the five friction engagement elements (40, 50, 60, 70, 80). That is, for each of the five friction engagement elements, the hydraulic pressure, the rotation speed of the input-side friction plate, and the rotation speed of the output-side friction plate are detected.

[0033] Based on the detection signals of the above sensors 201 to 207, the controller 200 supplies a control signal to the hydraulic pressure adjustment mechanism 100 (each solenoid valve 101) to control the hydraulic pressure applied to each friction engagement element. For example, the controller 200 adjusts the transmission torque of each friction engagement element by controlling the hydraulic pressure applied to each friction engagement element. In this embodiment, the details of the hydraulic pressure control performed by the controller 200 on each friction engagement element will be described later.

[0034] [Hydraulic Pressure Control Method] Next, the hydraulic control method performed by the controller 200 in the present embodiment will be specifically described. In the present embodiment, when the friction engagement element is in a slip state (during slip continuation), the controller 200 controls the hydraulic pressure of the friction engagement element so that the transmission torque of the friction engagement element is maintained constant. In this case, the controller 200 obtains the friction coefficient of the friction engagement element, and obtains the control value of the hydraulic pressure to be applied to the friction engagement element from this friction coefficient and the required torque from the driver (corresponding to the required transmission torque to be applied to the friction engagement element).

[0035] Here, in order to realize highly accurate transmission torque control, it is desirable to accurately grasp the friction coefficient. However, the friction coefficient is affected by various factors such as the hydraulic pressure (load) applied to the friction engagement element, the differential rotation speed, and the oil temperature. Therefore, it is difficult to obtain an accurate value. Thus, in the present embodiment, the controller 200 obtains the friction coefficient of the friction engagement element based on the hydraulic pressure applied to the friction engagement element, the oil temperature of the oil supplied to the friction engagement element, the differential rotation speed between the input-side friction plate and the output-side friction plate in the friction engagement element, and the friction surface temperature in the friction engagement element.

[0036] First, with reference to FIG. 5, a hydraulic control method according to a comparative example for comparison with the present embodiment will be described. As shown in FIG. 5, the comparative example creates a μ map to be applied according to the load, differential rotation speed, and oil temperature of the friction engagement element in consideration of the fact that the friction coefficient (μ) of the friction engagement element changes depending on these factors, and obtains the friction coefficient from this μ map. Then, the comparative example obtains the pressing force (pressing load) to be applied to the friction engagement element by dividing the required transmission torque (corresponding to the driver's required torque) by this friction coefficient, and obtains the hydraulic pressure corresponding to this pressing force. Further, the comparative example corrects the hydraulic pressure thus obtained using F / B control, and uses the corrected hydraulic pressure as the hydraulic control value. Specifically, in F / B control, the hydraulic pressure is corrected by a value obtained by adding a proportional term and an integral term corresponding to the differential rotation speed of the friction engagement element.

[0037] However, such comparative examples determine the coefficient of friction without considering the decrease in the coefficient of friction when the friction fastening element is in a slip state, that is, the decrease in the coefficient of friction due to the increase in the friction surface temperature, as described in the problems to be solved by the above invention. Although this decrease in the coefficient of friction can be absorbed to some extent by F / B control, in the comparative example, due to the integral term of this F / B control, the follow-up speed of the transmission torque of the friction fastening element becomes slow, and the controllability of the hydraulic pressure tends to deteriorate.

[0038] Here, with reference to FIG. 6, the decrease in the coefficient of friction due to the increase in the friction surface temperature will be specifically described. FIG. 6 schematically shows the peeling and re-adsorption of the molecular film formed by the ATF (Automatic Transmission Fluid) additive in the oil (lubricating oil) according to the differential rotation speed and the friction surface temperature of the friction fastening element. As shown in FIG. 6, when the differential rotation speed (speed) increases, the molecular film tends to peel off. In this case, the coefficient of friction increases. On the other hand, when the friction surface temperature increases, the molecular film tends to re-adsorb. In this case, the coefficient of friction decreases. From this, in the present embodiment, the controller 200 obtains the coefficient of friction in consideration of the friction surface temperature of the friction fastening element.

[0039] Also, in this embodiment, the controller 200 is configured to obtain the friction coefficient based on the fluid frictional force and the boundary frictional force acting on the friction fastening element. Here, with reference to FIG. 7, the fluid frictional force and the boundary frictional force acting on the friction fastening element will be specifically described. FIG. 7 schematically shows the friction phenomenon occurring in the friction fastening element in the slip state. As shown in FIG. 7, the fluid frictional force is the frictional force caused by the lubricating oil on the slip surface of the input-side friction plate and the output-side friction plate (corresponding to the driven plate and the friction material, respectively) in the friction fastening element. Also, the boundary frictional force is the frictional force caused by the partial contact (microscale contact due to roughness protrusions) between the input-side friction plate and the output-side friction plate. The sum of the reaction forces due to these fluid frictional force and boundary frictional force balances the load applied to the friction fastening element. In other words, the fluid frictional force and the boundary frictional force act so as to share the load. From such a perspective, in this embodiment, the controller 200 starts from the distance (distance between surfaces) between the opposing surfaces of the input-side friction plate and the output-side friction plate, obtains the fluid frictional force and the boundary frictional force, and obtains the friction coefficient from the frictional force obtained by adding these.

[0040] Next, with reference to FIG. 8, the hydraulic control method according to this embodiment will be specifically described. As shown in FIG. 8, the controller 200 first obtains the load of the friction fastening element corresponding to the hydraulic pressure detected by the hydraulic pressure sensor 204, the differential rotational speed obtained from the rotational speeds detected by the input rotational speed sensor 206 and the output rotational speed sensor 207 respectively, and the oil temperature detected by the oil temperature sensor 205. Then, the controller 200 obtains the distance between surfaces corresponding to the load based on these load, differential rotational speed, and oil temperature. For example, considering that an oil film is formed between the surface roughnesses of the input-side friction plate and the output-side friction plate on the slip surface of the friction fastening element, the controller 200 obtains the distance between surfaces from the median value of these surface roughnesses. Note that the differential rotational speed is not limited to being obtained from the input rotational speed sensor 206 and the output rotational speed sensor 207, and may be obtained from the input and output rotational speeds of the automatic transmission 1 and the internal gear configuration.

[0041] The fluid frictional force is defined by the contact area of the oil in the friction coupling element and the fluid shear stress according to the above surface distance (fluid frictional force = contact area of oil × fluid shear stress). Here, the contact area of the oil is the area obtained by subtracting the true contact area, which is the contact area at the microscale due to the roughness protrusions in the friction coupling element, from the apparent contact area in the friction coupling element. Further, the fluid frictional force depends on the oil temperature and the differential rotational speed, and has a load dependence according to the surface distance. Therefore, the controller 200 obtains the fluid frictional force using a model (for example, a 3D - CFD model) defined based on the dependencies of these parameters.

[0042] Also, the boundary frictional force is defined by the true contact area in the friction coupling element and the boundary shear stress according to the above surface distance (boundary frictional force = true contact area × boundary shear stress). Here, it has been confirmed that the true contact area has a load dependence. Also, it has been confirmed that the boundary shear stress has a dependence on the differential rotational speed and the friction surface temperature. Therefore, in the present embodiment, the controller 200 obtains the boundary shear stress using the following formula (1). τ = A + B·ln(V) - C·T Formula (1)

[0043] In Formula (1), “τ” represents the boundary shear stress, “A”, “B”, and “C” represent coefficients (A, B, C > 0), “V” represents the differential rotational speed, and “T” represents the friction surface temperature. “B·ln(V)” is a speed - dependent term defined to multiply the value (ln(V)) corresponding to the differential rotational speed V by the coefficient B (corresponding to the first coefficient), and represents the peeling model of the molecular film formed by the above - mentioned ATF additive. “C·T” is a temperature - dependent term defined to multiply the friction surface temperature T by the coefficient C (corresponding to the second coefficient), and represents the re - adsorption model of the molecular film formed by the above - mentioned ATF additive. Therefore, the controller 200 obtains the boundary shear stress τ using the value obtained by subtracting the temperature - dependent term from the speed - dependent term from Formula (1). As is clear from Formula (1), the relationship between the boundary shear stress τ and the friction surface temperature T is represented linearly.

[0044] Further, the controller 200 sets the coefficient B to a value larger than the coefficient C (B > C). As a result, the contribution degree of the speed-dependent term to the boundary shear stress τ is larger than the contribution degree of the temperature-dependent term to the boundary shear stress τ. Further, the controller 200 sets each of the coefficients A, B, and C to a larger value as the load applied to the friction fastening element, that is, the hydraulic pressure, increases. This is because the boundary shear stress τ has a dependency not only on the differential rotation speed V and the friction surface temperature T but also on the hydraulic pressure (load). Note that appropriate values of the coefficients A, B, and C are set in advance through experiments, simulations, or the like.

[0045] The controller 200 obtains the friction coefficient of the friction fastening element, that is, the friction characteristic, from the frictional force obtained by adding the fluid frictional force and the boundary frictional force described above, and then controls the hydraulic pressure in the same manner as in the comparative example. That is, the controller 200 divides the required transmission torque corresponding to the accelerator opening detected by the accelerator opening sensor 201 by the friction coefficient to obtain the pressing force to be applied to the friction fastening element, corrects the hydraulic pressure corresponding to this pressing force by F / B control according to the differential rotation speed of the friction fastening element, and controls the friction fastening element with the corrected hydraulic pressure.

[0046] Further, the controller 200 calculates the frictional heat generated in the friction fastening element from the frictional force and the differential rotation speed obtained as described above, and obtains the friction surface temperature based on the frictional heat. Specifically, the controller 200 obtains the current friction surface temperature by applying the calorific value corresponding to the frictional heat to the friction surface temperature obtained in the previous calculation process (it is only necessary to keep the history of the friction surface temperature obtained in the past). Then, the controller 200 obtains the surface-to-surface distance and the frictional force described above using the friction surface temperature thus obtained, that is, feeds back the friction surface temperature to the calculation of the surface-to-surface distance and the frictional force. By doing so, the friction surface temperature that sequentially changes according to the friction state is considered in each calculation.

[0047] Next, with reference to FIG. 9, the method for obtaining the coefficients A, B, and C in the formula (1) for obtaining the above-mentioned boundary shear stress τ will be described. FIG. 9 shows, in order from the top, the accelerator opening (corresponding to the required torque), the hydraulic pressure, the torque (the solid line indicates the transmitted torque, and the dashed line indicates the engine torque), the differential rotational speed, the friction coefficient, and the friction surface temperature. Each graph shown in FIG. 9 is obtained by reproducing the hill-hold scene with a chassis roller using a vehicle in which the friction fastening element starts in a slip state (the vehicle speed at this time is 0). Also, the vehicle torque (T cl ) is detected by the chassis roller, and the friction surface temperature (T) is detected by a thermocouple installed in the friction fastening element.

[0048] First, the vehicle torque T cl is expressed by formula (2) from the tire torque T tire and the coefficient α1, and the hydraulic pressure P cl is expressed by formula (3) from the vehicle torque T cl , the friction coefficient μ cal and the coefficient α2. The friction coefficient μ cal is expressed by formula (4) from the frictional force F cal and the pressing force (pressing load) N in . Also, the frictional force (boundary frictional force) F cal is expressed by formula (5) from the true contact area A r and the boundary shear stress τ. T cl = T tire ·α1 Formula (2) P cl =(T cl / μ cal )·α2 Formula (3) μ cal = F cal / N in Formula (4) F cal = A r ·τ Formula (5)

[0049] From the above-mentioned formula (1) and formulas (3) to (5), the hydraulic pressure P cl is expressed by formula (6). And A r and N inSince it can be regarded as a coefficient depending on hydraulic pressure, Equation (6) is transformed into Equation (7). Furthermore, Equation (7) is transformed into Equation (8), and Equation (8) is transformed into Equation (9). Equation (9) is an equation in which the vehicle torque T cl is replaced by the accelerator opening O. P cl ={T cl / (A + B·ln(V) - C·T)}·(N in / A r )·α3 Equation (6) P cl ={T cl / (A + B·ln(V) - C·T)}·α4 Equation (7) A + B·ln(V) - C·T = (T cl / P cl )·α4 Equation (8) A + B·ln(V) - C·T + (O / P cl )·α5 = 0 Equation (9)

[0050] By substituting the accelerator openings O1 to O4, differential revolutions V1 to V4, and friction surface temperatures T1 to T4 obtained at the same hydraulic pressure into Equation (9), the following four simultaneous equations can be established. Therefore, by solving this system of simultaneous equations, the coefficients A, B, C, and α5 to be applied at a certain hydraulic pressure can be obtained. And if such calculations are performed for various hydraulic pressures, the coefficients A, B, C, and α5 to be applied according to the hydraulic pressure can be defined. A + B·ln(V1) - C·T1 + (O1 / P cl )·α5 = 0 A + B·ln(V2) - C·T2 + (O2 / P cl )·α5 = 0 A + B·ln(V3) - C·T3 + (O3 / P cl )·α5 = 0 A + B·ln(V4) - C·T4 + (O4 / P cl )·α5 = 0

[0051] [Function and Effect] Next, with reference to FIGS. 10 and 11, the operation and effects of the control system of the automatic transmission according to the present embodiment will be described. FIG. 10 is a time chart showing the results of the hydraulic control method (the method shown in FIG. 5) according to a comparative example for comparison with the present embodiment, and FIG. 11 is a time chart showing the results of the hydraulic control method (the method shown in FIG. 8) according to the present embodiment. As described above, in both the comparative example and the present embodiment, when the friction engagement element is in a slip state, the hydraulic pressure of the friction engagement element is controlled based on the friction coefficient obtained by calculation so that the transmission torque is maintained constant.

[0052] First, referring to FIG. 10, the comparative example will be described. FIG. 10 shows, in order from the top, hydraulic pressure, torque, friction coefficient, and differential rotation speed. Specifically, in FIG. 10, graph G11 shows the hydraulic pressure applied to the friction engagement element, graph G12 shows the transmission torque of the friction engagement element, graph G13 shows the torque capacity (corresponding to the applied hydraulic pressure) corresponding to the maximum static friction force of the friction engagement element, graph G14 shows the input torque from the engine 61 to the automatic transmission 1 corresponding to the driver's required torque, graph G15 shows the friction coefficient obtained by the comparative example, graph G16 shows the actual friction coefficient, graph G17 shows the differential rotation speed of the friction engagement element, and graph G18 shows the target differential rotation speed. Also, during the period from time T11 to T12 and after time T13, it is assumed that the friction engagement element is set in a slip state (slip control). Since the torque capacity corresponds to the maximum static friction force, the smaller of the torque capacity and the input torque is adopted as the transmission torque of the friction engagement element.

[0053] In the comparative example, as shown by reference sign A11, it can be seen that torque loss occurs where the transmitted torque is much lower than the input torque (graphs G12, G13, G14). The reason for this is as follows. As shown in graphs G15 and G16, during the period from time T11 to T12, the friction coefficient obtained by the comparative example deviates significantly from the actual friction coefficient. This is because the actual friction coefficient decreases due to the increase in the friction surface temperature of the friction engagement element in the slip state, but in the comparative example, the friction coefficient is obtained without considering such a friction surface temperature. As a result, in the comparative example, the necessary hydraulic pressure that should be applied according to the actual friction coefficient is not applied (the applied hydraulic pressure is smaller than the required one), and due to the decrease in the torque capacity, torque loss occurs where the transmitted torque is much lower than the input torque. According to such a comparative example, as shown by reference sign A12, it takes time for the transmitted torque to stabilize. Also, in the comparative example, due to the F / B integral term during the previous slip control (FIG. 5), a deviation in the friction coefficient as shown by reference sign A13 remains, and as a result, as shown by reference sign A14, excessive torque loss occurs at the start of the next slip control.

[0054] Subsequently, referring to FIG. 11, the present embodiment will be described. FIG. 11 shows, in order from the top, hydraulic pressure, torque, friction coefficient, and differential rotational speed. Specifically, in FIG. 11, graph G21 shows the hydraulic pressure applied to the friction engagement element, graph G22 shows the transmitted torque of the friction engagement element, graph G23 shows the torque capacity of the friction engagement element, graph G24 shows the input torque from the engine 61 to the automatic transmission 1, graph G25 shows the friction coefficient obtained according to the present embodiment, graph G26 shows the actual friction coefficient, graph G27 shows the differential rotational speed of the friction engagement element, and graph G28 shows the target differential rotational speed. Also, it is assumed that the friction engagement element is set in a slip state during the period from time T21 to T22 and after time T23 (slip control).

[0055] According to this embodiment, as shown in graphs G25 and G26, it can be seen that the obtained friction coefficient substantially matches the actual friction coefficient. That is, according to this embodiment, it can be said that a friction coefficient that accurately reproduces the decrease in the friction coefficient due to the increase in the friction surface temperature of the friction fastening element has been obtained. As a result, according to this embodiment, as shown by reference sign A21, it can be seen that torque dropout is suppressed, and as shown by reference sign A22, the time until the transmitted torque stabilizes is shortened. In addition, according to this embodiment, as shown by reference sign A23, it can be seen that the stability of the differential rotation speed of the friction fastening element is improved. Furthermore, according to this embodiment, as shown by reference sign A24, it can be seen that excessive torque dropout caused by the F / B integral term is suppressed as compared with the comparative example.

[0056] Summarizing the above, in this embodiment, when the friction fastening element is at least in a slip state, the controller 200 calculates the friction coefficient of the friction fastening element based on the hydraulic pressure applied to the friction fastening element, the oil temperature of the oil supplied to the friction fastening element, the differential rotation speed between the input-side friction plate and the output-side friction plate in the friction fastening element, and the friction surface temperature in the friction fastening element, controls the hydraulic pressure based on the friction coefficient and the required torque to be generated in the vehicle, calculates the shear stress acting on the friction fastening element by subtracting the temperature-dependent term defined according to the friction surface temperature from the speed-dependent term defined according to the differential rotation speed, and is configured to calculate the friction coefficient based on the shear stress, and the contribution degree of the speed-dependent term to the shear stress is larger than the contribution degree of the temperature-dependent term to the shear stress. According to such an embodiment, by considering the state of the friction surface temperature of the friction fastening element in the slip state, the friction coefficient can be accurately obtained, and the hydraulic pressure can be accurately controlled based on this friction coefficient. As a result, when the friction fastening element is in a slip state, the transmitted torque can be stably controlled, specifically, the transmitted torque can be maintained constant.

[0057] Also, in the present embodiment, the controller 200 calculates a speed-dependent term by multiplying a value corresponding to the differential rotational speed by a coefficient B (first coefficient), and calculates a temperature-dependent term by multiplying a value corresponding to the friction surface temperature by a coefficient C (second coefficient). The coefficient B is set to a value larger than the coefficient C, so that the contribution degree of the speed-dependent term to the shear stress is larger than the contribution degree of the temperature-dependent term to the shear stress. Thereby, by accurately considering the contribution degrees of the speed-dependent term and the temperature-dependent term, a more accurate friction coefficient can be obtained.

[0058] Also, in the present embodiment, the controller 200 is configured to set the coefficient B and the coefficient C to larger values as the hydraulic pressure applied to the friction fastening element increases. Thereby, by considering the hydraulic pressure dependence of the coefficient B and the coefficient C, a more accurate friction coefficient can be obtained.

[0059] Also, in the present embodiment, the controller 200 can calculate the frictional heat generated in the friction fastening element from the frictional force corresponding to the calculated friction coefficient and the differential rotational speed, and calculate the friction surface temperature based on the frictional heat. Since it is difficult to detect the friction surface temperature by a sensor, the controller 200 calculates the friction surface temperature. In this case, since the controller 200 calculates the friction surface temperature based on the frictional heat generated in the friction fastening element, an accurate friction surface temperature can be obtained.

[0060] Also, in the present embodiment, the controller 200 calculates the friction coefficient based on the frictional force obtained by adding the boundary frictional force acting on the friction fastening element corresponding to the shear stress and the fluid frictional force acting on the friction fastening element separately from the boundary frictional force, and calculates the boundary frictional force and the fluid frictional force based on the surface distance between the input-side friction plate and the output-side friction plate in the friction fastening element in the slip state. By considering the boundary frictional force and the fluid frictional force according to the surface distance in this way, a more accurate friction coefficient can be obtained.

Explanation of Reference Numerals

[0061] 1 Automatic transmission 40, 50, 60, 70, 80 Friction engagement elements 100 Hydraulic pressure adjustment mechanism 101 Solenoid valve 200 Controller 201 Accelerator opening sensor 204 Hydraulic pressure sensor 205 Oil temperature sensor 206 Input rotation speed sensor 207 Output rotation speed sensor

Claims

1. A control system for an automatic transmission mounted on a vehicle, comprising an automatic transmission including friction engagement elements including an input-side friction plate and an output-side friction plate, the friction engagement elements being switchable by hydraulic pressure to which a fastening state, a release state, and a slip state are imparted; a hydraulic pressure adjustment mechanism configured to adjust the hydraulic pressure applied to the friction engagement elements; a controller configured to control the hydraulic pressure applied from the hydraulic pressure adjustment mechanism to the friction engagement elements so as to adjust the transmission torque of the friction engagement elements; having, the controller, when the friction engagement elements are at least in the slip state, calculates the friction coefficient of the friction engagement elements based on the hydraulic pressure applied to the friction engagement elements, the oil temperature of the oil supplied to the friction engagement elements, the differential rotational speed between the input-side friction plate and the output-side friction plate in the friction engagement elements, and the friction surface temperature in the friction engagement elements, and controls the hydraulic pressure based on the friction coefficient and the required torque to be generated in the vehicle, calculates the shear stress acting on the friction engagement elements by subtracting a temperature-dependent term defined according to the friction surface temperature from a speed-dependent term defined according to the differential rotational speed, and calculates the friction coefficient based on the shear stress, is configured as, a control system for an automatic transmission, characterized in that a contribution degree of the speed-dependent term to the shear stress is larger than a contribution degree of the temperature-dependent term to the shear stress.

2. The controller is configured to calculate the speed-dependent term by multiplying a value corresponding to the differential rotational speed by a first coefficient, and to calculate the temperature-dependent term by multiplying a value corresponding to the friction surface temperature by a second coefficient, the first coefficient is set to a value larger than the second coefficient, whereby a contribution degree of the speed-dependent term to the shear stress is larger than a contribution degree of the temperature-dependent term to the shear stress, The control system of the automatic transmission according to claim 1.

3. The controller is configured to set the first coefficient and the second coefficient to larger values as the hydraulic pressure applied to the friction engagement element increases. The control system of the automatic transmission according to claim 2.

4. The controller is configured to calculate the frictional heat generated in the friction engagement element from the frictional force corresponding to the calculated friction coefficient and the differential rotational speed, and calculate the friction surface temperature based on the frictional heat. The control system of the automatic transmission according to claim 1 or 2.

5. The controller is calculate the friction coefficient based on the frictional force obtained by adding the boundary frictional force acting on the friction engagement element corresponding to the shear stress and the fluid frictional force acting on the friction engagement element separately from the boundary frictional force, calculate the boundary frictional force and the fluid frictional force based on the surface distance between the input-side friction plate and the output-side friction plate in the friction engagement element in the slip state, The control system of the automatic transmission according to claim 1 or 2.

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