Method for calibrating an actuator of an all-wheel drive clutch

A method for calibrating an actuator of an all-wheel drive clutch in a motor vehicle to accommodate for wear in the actuator and/or in the clutch, the motor vehicle transmitting at least part of a drive torque permanently to a primary axle and a part of the drive torque is optionally transmitted through the clutch to a secondary axle, the method comprising:

• calculating a desired clutch torque (MD) to be transmitted through the clutch to the secondary axle based on predetermined driving state parameters;
• determining a control signal for the actuator based on the desired clutch torque (MD) in accordance with a first desired clutch torque/control signal relationship having a first characteristic (K);
• determining a clutch slip value (Δn) that corresponds to a difference in rotary speed between the primary axle and the secondary axle;
• determining a reference secondary axle torque (MrefSA) that corresponds to a proportion of the drive torque transmitted to the secondary axle when the clutch slip value (Δn) is substantially zero;
• comparing the clutch slip value (Δn) to a threshold value (Thresh);
• comparing the desired clutch torque (MD) with the reference secondary axle torque (MrefSA);
• checking torque increase conditions by determining whether the clutch slip value (Δn) is larger than the threshold value (Thresh) and whether the desired clutch torque (MD) is larger than the reference secondary axle torque (MrefSA);
• changing the first desired clutch torque/control signal relationship to a second desired clutch torque/control signal relationship having a second characteristic (K′) in dependence on a result of the comparisons, wherein the first desired clutch torque/control signal relationship is changed to the second desired clutch torque-control signal relationship in the sense of an increase in the proportion of the driving torque transmitted to the secondary axle through the clutch when the torque increase conditions are satisfied;
• and
• using the second desired clutch torque/control signal relationship to determine the control signal for the actuator upon subsequent actuation of the clutch.

A method for calibrating an actuator of an all-wheel drive clutch of a motor vehicle to accommodate for wear in the actuator and/or in the clutch, the motor vehicle transmitting at least part of a drive torque permanently to a primary axle and a part of the drive torque is optionally transmitted through the clutch to a secondary axle, the method comprising:

• calculating a desired clutch torque (MD) to be transmitted through the clutch to the secondary axle based on predetermined driving state parameters;
• determining a control signal for the actuator based on the desired clutch torque (MD) in accordance with a first desired clutch torque/control signal relationship having a first characteristic (K);
• determining a clutch slip value (Δn) that corresponds to a difference in rotary speed between the primary axle and the secondary axle;
• determining a reference secondary axle torque (MrefSA) that corresponds to a proportion of the drive torque transmitted to the secondary axle when the clutch slip value (Δn) is substantially zero;
• comparing the clutch slip value (Δn) to a threshold value (Thresh);
• comparing the desired clutch torque (MD) with the reference secondary axle torque (MrefSA);
• determining an actual clutch slip value (Δnreal) that corresponds to a difference between the speed of the primary axle and the speed of the secondary axle;
• determining a tire tolerance compensated clutch slip value (Δncomp) that corresponds to a difference between the speed of the primary axle and the speed of the secondary axle while taking account of a property difference of the wheels of the primary axle and the wheels of the secondary axle;
• determining a value for the reference secondary axle torque (MrefSA) that corresponds to the proportion of the driving torque that is transmitted to the secondary axle when the tire compensated clutch slip value (Δncomp) is substantially zero;
• and
• checking torque increase conditions by determining whether the actual clutch slip value (Δnreal) is larger than a first threshold value (Thresh1), whether the tire tolerance compensated clutch slip value (Δncomp) is larger than a second threshold value (Thresh2), and whether the desired clutch torque (MD) is larger than the reference secondary axle torque (MrefSA);
• changing the first desired clutch torque/control signal relationship to a second desired clutch torque/control signal relationship having a second characteristic (K′) in dependence on a result of the comparisons;
• and
• using the second desired clutch torque/control signal relationship to determine the control signal for the actuator upon subsequent actuation of the clutch;
• wherein the first desired clutch torque/control signal relationship is changed to the second desired clutch torque/control signal relationship in the sense of an increase in the proportion of the driving torque transmitted to the secondary axle through the clutch when the torque increase conditions are satisfied.

A method for calibrating an actuator of an all-wheel drive clutch of a motor vehicle having at least a part of a driving torque permanently transmitted to a primary axle and a part of the driving torque optionally transmitted to a secondary axle by the clutch, the method comprising:

• calculating a desired clutch torque (MD) on the basis of driving state parameters;
• determining a control signal for the actuator from the desired clutch torque in accordance with a preset desired clutch torque/control signal relationship;
• determining a clutch slip value (Δn) that corresponds to a difference between a speed of the primary axle and a speed of the secondary axle;
• determining a reference secondary axle torque (MrefSA) that corresponds to a proportion of the driving torque that is transmitted to the secondary axle and for which a clutch slip value (Δn) of substantially zero is expected;
• comparing the clutch slip value (Δn) with a threshold value (Thresh) and comparing the desired clutch torque (MD) with the reference secondary axle torque (MrefSA);
• determining an actual clutch slip value (Δnreal) that corresponds to a difference between the speed of the primary axle and the speed of the secondary axle;
• determining a tire tolerance compensated clutch slip value (Δncomp) that corresponds to a difference between the speed of the primary axle and the speed of the secondary axle while taking account of a property difference of the wheels of the primary axle and the wheels of the secondary axle;
• determining a value for the reference secondary axle torque (MrefSA) that corresponds to the proportion of the driving torque that is transmitted to the secondary
• axle for which a tire compensated clutch slip value (Δncomp) of substantially zero is expected;
• checking torque increase conditions by determining whether the actual clutch slip value (Δnreal) is larger than a first threshold value (Thresh1), whether the tire tolerance compensated clutch slip value (Δncomp) is larger than a second threshold value (Thresh2), and whether the desired clutch torque (MD) is larger than the reference secondary axle torque (MrefSA);
• and
• changing the desired clutch torque/control signal relationship in dependence on a result of the comparisons, wherein the desired clutch torque/control signal relationship is changed in the sense of an increase in the proportion of the driving torque transmitted to the secondary axle if the torque increase conditions are satisfied;
• using the changed desired clutch torque/control signal relationship to determine the control signal for the actuator upon subsequent actuation of the clutch.