Method for controlling an automated dual clutch of a hydraulic clutch actuation system

Abstract

Method for controlling an automated dual clutch of a hydraulic clutch actuation system, in which two partial clutches (12, 19) of the dual clutch are actuated by a hydrostatic clutch actuator (4, 6, 7) on the basis of a clutch characteristic curve, wherein a clutch torque is set over an actuation path of the respective partial clutch (12, 19), wherein during a sniffing process of a hydraulic section (7, 9, 11) of the clutch actuation system (1) a touch point of the clutch characteristic curve of the respective sniffing partial clutch (12) changes, which is corrected, characterized in that to correct the touch point of an inactive partial clutch (12) a correction factor is determined which depends on a pressure that occurs during the sniffing process of the inactive partial clutch (12) at an active partial clutch (19) and is transmitted to the inactive partial clutch (12).

Description

[0001] The invention relates to a method for controlling an automated double clutch of a hydraulic clutch actuation system, in which two partial clutches of the double clutch are each actuated by a hydrostatic clutch actuator based on a clutch characteristic curve, wherein a clutch torque is adjusted via an actuation path of the respective partial clutch, wherein during a sniffing process of a hydraulic section of the clutch actuation system, a sensing point of the clutch characteristic curve of the respective sniffing partial clutch changes, which is corrected.

[0002] In automated clutch applications, torque accuracy is crucial for a vehicle's smooth starting and shifting. Knowledge of the clutch torque is based on a travel-to-torque relationship known as the clutch characteristic curve, which can be shifted, scaled, or distorted by appropriate corrections. For hydrostatically engaged clutches, the hydrostatic distance must be modulated accordingly or taken into account in the clutch characteristic curve.

[0003] The special feature of hydrostatically engaged clutches is that the expansion and contraction of a hydraulic fluid present in a clutch actuator of the clutch actuation system causes the position between a slave cylinder and the clutch actuator to change significantly over time. This has fundamental consequences: Due to its inhomogeneity, the temperature of the hydraulic fluid in the hydraulic path between the clutch actuator and the slave cylinder cannot be determined. Therefore, the shift in the clutch characteristic curve must be continuously detected. Furthermore, due to the large volume expansion, the expansion / contraction of the hydraulic fluid must be compensated for, which requires a sniffing process in the clutch actuator.

[0004] DE 10 2011 102 906 A1 discloses a method for controlling an automated dual clutch, in which the dual clutch comprises two sub-clutches arranged in a drive train of a vehicle between at least one prime mover and a transmission. The two sub-clutches of the dual clutch are arranged in a clutch bell housing, with each sub-clutch being assigned a hydrostatic clutch actuator. The clutch actuator contains a master cylinder having a snifting bore by means of which the master cylinder can be connected to an expansion tank. During operation of the sub-clutch of the dual clutch, the hydraulic volume of the hydraulic fluid sealed off in the hydrostatic system is equalized via the open snifting bore.The master piston contained in the master cylinder is retracted far enough that the sniffer hole is released and pressure equalization can take place in the expansion tank.

[0005] From the as yet unpublished DE 10 2015 210 175 A1 a method for controlling an automatically actuated friction clutch is known, in which a clutch torque is transmitted by a hydrostatic release system on the basis of a clutch characteristic curve, wherein at a sniffing position a touch point of the clutch characteristic curve which changes depending on sniffing processes is continuously corrected by means of a compensation value.

[0006] Unlike dry clutches, temperature does not tend to cause significant changes in the air gap in wet clutches. However, a significant change occurs in dual clutches due to the crosstalk between one sub-clutch and the other sub-clutch, which is known as the crosstalk effect. This means that when one sub-clutch is actuated, the entire operating range of the other sub-clutch shifts. This effect is due to the mechanical guidance of both sub-clutches on a plate carrier and a clutch cover.

[0007] The invention is based on the object of specifying a method for controlling an automated double clutch of a hydraulic clutch actuation system, in which shifts in the clutch characteristic curve are compensated both by the crosstalk of one partial clutch to the other partial clutch and by the sniffing process.

[0008] According to the invention, the object is achieved in that, to correct the contact point of an inactive partial clutch, a correction factor is determined which depends on a pressure that occurs at an active partial clutch during the sniffing process of the inactive partial clutch and crosstalks to the inactive partial clutch. By taking into account the crosstalk of the active partial clutch to the inactive partial clutch, the clutch characteristic curve of the inactive partial clutch is shifted towards higher travels, ensuring a more precise setting of a contact point of the inactive partial clutch even after a sniffing process. Advantageously, after the sniffing process of the inactive partial clutch, a long-term contact point is set, which is corrected using the correction factor. The long-term contact point is known per se.However, since this is not constant due to the combination of the sniffing process of the inactive partial clutch and the crosstalk of the pressure from the active partial clutch to the inactive partial clutch, this long-term sensing point is advantageously corrected using the correction factor. This results in an almost accurate sensing point of the inactive partial clutch and a precise clutch torque derived from the sensing point of the clutch characteristic curve.

[0009] In one embodiment, a travel offset of the inactive partial clutch is used as the correction factor, which is determined from the difference between two travel displacements of the inactive partial clutch. The first travel displacement of the inactive clutch occurs when the pressure of the active partial clutch changes from a first value to a second value, and the second travel displacement occurs when the pressure of the active partial clutch changes from the second value to a third value during the sniffing process of the inactive clutch. With the setting of the inactive partial clutch to higher travels selected in this way, the slave cylinder is pressed towards a stop with a reduced force of the diaphragm spring during the sniffing process.

[0010] In one embodiment, the correction factor for different pressures is stored in a map determined on a test bench. Since in this map, each clutch travel point of the inactive partial clutch can be assigned a pressure of the active partial clutch, the correction factor can be easily determined from the map if the pressure of the active partial clutch is known.

[0011] In one variant, the pressure of the active partial clutch, which is applied to the inactive partial clutch during the sniffing process and which crosses over to it, is determined at an optimal operating point of the active partial clutch. This ensures that the design of the inactive partial clutch's sniffing process is always based on the most probable pressure applied to the active partial clutch.

[0012] In a further development, after determining the correction factor, adaptation of a shift in the long-term characteristic curve of the inactive clutch is prevented. This prevents errors in setting the contact point.

[0013] In another variant, the priority of the sniffing process is reduced after the correction factor has been determined. Since this prevents an immediately subsequent sniffing process, sources of error are also minimized.

[0014] In one embodiment, in the event of significant crosstalk between the pressure occurring in the active partial clutch and the inactive partial clutch, the shift in the clutch characteristic curve of the inactive partial clutch is learned only at a reduced, preferably halved, speed. This allows the feedback variable for the characteristic curve shift to be determined particularly reliably.

[0015] Advantageously, a wet clutch is used as the partial clutch. The proposed method is particularly suitable for wet, directly actuated clutches with a hydrostatic travel distance, and is particularly suitable for hydrostatically engaged clutches.

[0016] The invention permits numerous embodiments. One of these will be explained in more detail with reference to the figures shown in the drawing.

[0017] They show: Fig. 1 a schematic structure of a hydraulic clutch actuation system, Fig. 2 a schematic diagram of a double clutch, Fig. 3 a simplified elasticity model of the double clutch, Fig. 4 a schematic diagram of a crosstalk effect on the inactive partial clutch, Fig. 5 a schematic diagram of a crosstalk and sniffing process compensation during the characteristic curve shift of the inactive partial clutch to the pressure applied to the active partial clutch, Fig. 6 an embodiment of the method according to the invention.

[0018] In Fig. Figure 1 schematically illustrates the structure of an automatic clutch actuation system 1 using a schematically illustrated hydrostatic clutch actuator (HCA) as used in vehicles. The hydraulic clutch actuation system 1 comprises a control unit 3 on the master side 2, which controls an electric motor 4, which in turn drives a transmission 5 to convert the rotational movement of the electric motor 4 into a translational movement of a piston 6, which is mounted for axial movement within a master cylinder 7. The electric motor 4, the piston 6, and the master cylinder 7 form the hydrostatic clutch actuator.If a rotary movement of the electric motor 4 causes a change in the position of the piston 6 in the master cylinder 7 along the clutch travel to the right, the volume of the master cylinder 7 is changed, whereby a pressure p is built up in the master cylinder 7, which is transmitted via a pressure medium 8 in the form of a hydraulic fluid via a hydraulic line 9 to the slave side 10 of the hydraulic clutch actuation system 1. The length and shape of the hydraulic line 9 is adapted to the installation space of the vehicle. On the slave side 10, the pressure p of the pressure medium 8 in a slave cylinder 11 causes a change in travel, which is transmitted to a clutch 12 in order to actuate it. The master cylinder 7, the hydraulic line 9 and the slave cylinder 11 form the hydraulic path.

[0019] The pressure p in the master cylinder 7 on the master side 2 of the hydraulic clutch actuation system can be determined by a sensor 13. The sensor 13 is preferably a pressure sensor. The distance s traveled by the clutch actuator 4, 6, 7 is determined by a second sensor 14, which is designed as a travel sensor and measures the distance traveled by the piston 6 in the master cylinder 7. The sensors 13, 14 are connected to the control unit 3.

[0020] Furthermore, the master cylinder 7 has a sniffer bore 16, which, when open, connects the pressure medium 8 to a compensating reservoir 15. This is necessary to compensate for any volume expansion of the pressure medium 8 due to temperature changes or air bubbles. During this process, the pressure medium 8 returns to ambient pressure and is available for a subsequent clutch operation. This is initiated when the piston 6 of the master cylinder 7 moves back to the right, whereby the sniffer bore 16 is closed by the piston 6, and the sniffer process is terminated.

[0021] In this illustration, the hydraulic clutch actuation system 1 is shown schematically for only one clutch 12. In the case of a dual-clutch system, the second partial clutch is actuated analogously. Actuation is effected by the slave cylinder 11, which acts on the second partial clutch via a disc spring 17, which is sealed off by a pressure chamber 18. The first and second partial clutches 12, 19 are supported by a disk carrier 20 and a clutch cover 21 ( Fig. 2). This, together with the volume expansion of the pressure medium 8, defines the stiffness of the pressure characteristic curve.

[0022] In the following, a directly actuated wet double clutch will be considered, in which the effect occurs that the active partial clutch 19 applies pressure to the inactive partial clutch 12 due to the mechanical connection via the plate carrier 20 and the clutch cover 21, which leads to a shift in the clutch characteristic curve of the inactive partial clutch 12. In connection with Fig. 3 and Fig. This effect, which is called the crosstalk effect, will be explained in Chapter 4. In Fig. Figure 3 shows a simplified elasticity model of a dual clutch 12, 19, in which the individual mechanical elements are represented as springs. The sub-clutches 12, 19, which are controlled by the slave cylinder 11, are connected to a position 23 of the clutch actuator or master cylinder 7 via a spring 22, which describes a volume expansion of the hydraulic path 7, 9, 11 and the slave cylinder 11. The volume expansion of the pressure medium 8 occurs during the sniffing process. Furthermore, a stop 24 of the slave cylinder 11 is present. The position of the slave cylinder 11 is further connected to a spring representing the pressure pot 18, which in turn correlates with the disc spring 17 and with a pad spring 25, which moves to a stop 26. Both the springs of the first and the springs of the second partial clutch 12, 19 are connected to the spring 27 of the clutch cover 21 and the plate carrier 20.

[0023] In Fig. 4, only the inactive partial clutch 12 is considered in two states Z1, Z2. The active partial clutch 19, which shifts the inactive partial clutch 12 at its operating point, is only indicated in this illustration by the arrow P. It is assumed that neither the inactive nor the active partial clutch 12, 19 transmit any torque (state Z1). The inactive partial clutch 12 is influenced by the crosstalk effect during the sniffing process. The restoring force of the slave cylinder 11 is reduced and thus influences the clutch characteristic curve of the inactive partial clutch 12 during the sniffing process. As a result, the inactive partial clutch 12 is compressed by the crosstalk pressure applied to the active partial clutch 19, which transmits torque (state Z2). This creates a different equilibrium state because the elasticity of the individual springs changes non-linearly.The touch point of the clutch characteristic curve of the inactive partial clutch 12, at which the partial clutch 12 begins to transmit a torque in the active state, does not return to an original long-term touch point after the sniffing process, which therefore has to be corrected.

[0024] In Fig. Figure 5 shows a schematic diagram of a characteristic curve shift of the clutch characteristic of the inactive clutch 12 during crosstalk and sniffing process compensation. This shows a characteristic curve shift of the inactive partial clutch 12 versus the pressure of the active partial clutch 19. The linear straight lines P5, P10, P20 and P40 indicate the characteristic curve shifts of the inactive partial clutch 12 when only the crosstalk effect occurs, i.e. the pressure of the active partial clutch 19 crosstalks to the inactive partial clutch 12 through the mechanical connection via clutch cover 21 and plate carrier 20. For example, the characteristic curve P20 illustrates a characteristic curve shift of the inactive partial clutch 12 during the crosstalk effect during the last sniffing process at a pressure of 20 bar applied to the active partial clutch 19. Accordingly, the numbers 5, 10 and 40 represent the corresponding pressure in bar applied to the active partial clutch 19.Curve K, shown in dash-dotted lines, shows a clutch characteristic curve that occurs when, in addition to the crosstalk effect, a sniffing process has also occurred on the inactive partial clutch 12. This clutch characteristic curve (curve K) is non-linear, which is why more volume of the pressure medium 8 is processed in the hydraulic system. As a result, the pressure rises earlier and the long-term touch point shifts into negative ranges.

[0025] In Fig.Figure 6 shows an example of determining the clutch characteristic curve of the inactive partial clutch 12 during a sniffing process with an active crosstalk effect. At point A, at a pressure of 20 bar in the active partial clutch 19, a sniffing process takes place in the inactive partial clutch 12. The pressure in the active partial clutch 19 is then reduced from 20 bar to 10 bar, whereby the inactive partial clutch 12 moves from point A on the characteristic curve P20 to point B. At this pressure of 10 bar in the active partial clutch 19, another sniffing process is triggered in the inactive partial clutch 12, whereby the inactive partial clutch 12 is raised to the clutch characteristic curve P10 (from point B to point C). Point C represents a path point of the clutch characteristic curve of the inactive partial clutch 12, which occurs when the active partial clutch 19 has a pressure of 10 bar.Subsequently, the pressure of the active partial clutch 19 is increased to 40 bar, whereby the inactive partial clutch 12 moves from point C to point D. At point D, another sniffing process occurs on the inactive partial clutch 12 at a pressure of 40 bar, which is applied to the active partial clutch 19. The clutch characteristic curve of the inactive partial clutch 12 shifts from point D to point E.

[0026] From the travel distances traveled by the inactive partial clutch 12 between points B and C and points D and E, a travel difference is calculated, resulting in a clutch offset, which is used to correct the long-term touch point. This travel difference is used as a correction factor for the long-term touch point, so that even under these conditions, the correct touch point, which corresponds to the actual conditions of the dual clutch, is known for the clutch characteristic curve of the inactive partial clutch 12. This corrected touch point is used when the inactive partial clutch transitions to the active clutch state. List of reference symbols 1 clutch actuation system 2 Encoder side 3 Control unit 4 electric motor 5 gearboxes 6 pistons 7 master cylinders 8 Pressure Means 9 Hydraulic line 10 Recipient side 11 slave cylinder 12 Inactive partial coupling 13 Sensor 14 Sensor 15 expansion tank 16 sniffer bore 17 Disc spring 18 Pressure cooker 19 Active partial clutch 20 slat carriers 21 Clutch cover 22 spring 23 positions 24 stops 25 pad spring 26 stop

Claims

[1] Method for controlling an automated double clutch of a hydraulic clutch actuation system, in which two partial clutches (12, 19) of the double clutch are each actuated by a hydrostatic clutch actuator (4, 6, 7) based on a clutch characteristic curve, wherein a clutch torque is set via an actuation path of the respective partial clutch (12, 19), wherein during a sniffing process of a hydraulic section (7, 9, 11) of the clutch actuation system (1), a touch point of the clutch characteristic curve of the respective sniffing partial clutch (12) changes, which is corrected, characterized by in that, in order to correct the sensing point of an inactive partial clutch (12), a correction factor is determined which depends on a pressure which occurs at an active partial clutch (19) during the sniffing process of the inactive partial clutch (12) and which spills over to the inactive partial clutch (12). [2] Method according to claim 1, characterized bythat after the sniffing process of the inactive partial coupling (12) a long-term sensing point is set, which is corrected with the correction factor. [3] Method according to claim 1 or 2, characterized by that a path offset of the inactive partial clutch (12) is used as a correction factor, which is determined from a difference between two path displacements of the inactive partial clutch (12), wherein the first path displacement of the inactive partial clutch (12) occurs when the pressure of the active partial clutch (19) changes from a first value to a second value and the second path displacement occurs when the pressure of the active partial clutch (19) changes from the second value to a third value during the sniffing process of the inactive partial clutch (12). [4] Method according to claim 1, 2 or 3, characterized by that the correction factor for different pressures is stored in a map which is determined on a test bench. [5] Method according to at least one of the preceding claims, characterized by that the pressure of the active partial clutch (19), which is applied to the inactive partial clutch (12) during the sniffing process and which is transferred to the latter, is determined at an optimal operating point of the active partial clutch (19). [6] Method according to at least one of the preceding claims, characterized by that after the correction factor has been determined, an adaptation of a shift in the long-term characteristic curve of the inactive partial clutch (12) is prevented. [7] Method according to at least one of the preceding claims, characterized by that after the correction factor has been determined, the priority of the sniffing process is reduced. [8] Method according to at least one of the preceding claims, characterized bythat in the event of a strong crosstalk of the pressure occurring in the active partial clutch (19) on the inactive partial clutch (12), the shift of the clutch characteristic curve of the inactive partial clutch (12) is learned only at a reduced speed. [9] Method according to at least one of the preceding claims, characterized by that a wet clutch is used as the partial clutch (12, 19).

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