# US 10,245,949 B2 · Method for operating a motor vehicle including an all-wheel drive that can be enabled and disabled by determining an angular acceleration of components, which are uncoupled when the all-wheel drive is disabled

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- Number: US 10,245,949 B2
- Document ID: US10245949B2
- Status: Granted
- Kind: B2
- Application number: 15/524,639
- Filed: 2015-11-06
- Published: 2017-11-30
- Granted: 2019-04-02
- Earliest claimed: 2014-11-06
- Assignees: Audi AG
- Applicants: Audi AG
- Inventors: Dieter Weidemann; Heiko Hanickel; Florian Kolb; Hans Jörg Brühl
- Web page: https://patentgrep.com/patent/US10245949B2

## CPC

- B60K 23/0808: {for varying torque distribution between driven axles, e.g. by transfer clutch}
- B60K 23/08: for changing number of driven wheels {, for switching from driving one axle to driving two or more axles (B60K17/3515 takes precedence)}
- F16H 61/12: Detecting malfunction or potential malfunction, e.g. fail safe (in control of hydrostatic gearing F16H61/4192) {; Circumventing or fixing failures}
- B60K 2023/0825: {for adding torque to the front wheels}
- B60K 2023/0833: {for adding torque to the rear wheels}
- B60Y 2400/42: Clutches or brakes
- B60Y 2400/421: Dog type clutches or brakes
- B60K: ARRANGEMENT OR MOUNTING OF PROPULSION UNITS OR OF TRANSMISSIONS IN VEHICLES; ARRANGEMENT OR MOUNTING OF PLURAL DIVERSE PRIME-MOVERS IN VEHICLES; AUXILIARY DRIVES FOR VEHICLES; INSTRUMENTATION OR DASHBOARDS FOR VEHICLES; ARRANGEMENTS IN CONNECTION WITH COOLING, AIR INTAKE, GAS EXHAUST OR FUEL SUPPLY OF PROPULSION UNITS IN VEHICLES
- F16H: GEARING
- B60Y: INDEXING SCHEME RELATING TO ASPECTS CROSS-CUTTING VEHICLE TECHNOLOGY

## Abstract

A method for operating a motor vehicle including an all-wheel drive that can be enabled and disabled, and a drive train including two clutches actuated by a control unit for enabling and disabling the all-wheel drive, and components rotating between the two clutches, which components are driven when the all-wheel drive is enabled and are uncoupled from the remaining drive train when the all-wheel drive is disabled. In order to allow early detection of defects and, in particular, bearing defects of the rotating components, and to determine the applied drag torque even without knowing the oil temperature, in one embodiment, when the all-wheel drive is disabled, the rotational speed (n) of at least one of the uncoupled components is measured in a time interval, and an angular acceleration of the uncoupled components is determined therefrom.

## Claims

### Claim 1

A method for operating a vehicle, wherein the vehicle comprises:
an all-wheel drive configured to be enabled and disabled, and a drive train with two clutches actuated by a control unit configured to enable and disable the all-wheel drive, and a plurality of components configured to rotate between the two clutches, the plurality of components configured to be driven when the all-wheel drive is enabled and configured to be uncoupled from the remaining drive train when the all-wheel drive is disabled, wherein the method comprises:
when the all-wheel drive is disabled, measuring the rotational speed (n) of at least one of the plurality of uncoupled components in a time interval and determining an angular acceleration (a) of the uncoupled components.

### Claim 2 (depends on 1)

The method according to claim 1, further comprising indicating a defect when the determined angular acceleration (a) fails to meet or exceeds a predetermined critical threshold value.

### Claim 3 (depends on 1)

The method according to claim 1, further comprising calculating a drag torque (DT) on the basis of the determined angular acceleration (α) and a moment of inertia or mass moment of inertia (J) of the plurality of uncoupled components.

### Claim 4 (depends on 3)

The method according to claim 3, wherein the drag torque (DT) is calculated for a plurality of different rotational speeds (n) measured in the time interval.

### Claim 5 (depends on 3)

The method according to claim 3, wherein the drag torque (DT) is calculated according to the relationship
DT=J×α+DecTconst−AccTconst
where J is the moment of inertia or mass moment of inertia and a is the angular acceleration of the uncoupled components, where DecTconst is a constant decelerating torque, and AccTconst is a constant accelerating torque.

### Claim 6 (depends on 3)

The method according to claim 3, wherein the torque for acceleration is pilot-controlled as a function of the calculated drag torque (DT) upon the next active acceleration of the uncoupled components.

### Claim 7 (depends on 6)

The method according to claim 6, wherein the pilot control of the torque for accelerating the uncoupled components is only carried out as a function of the calculated drag torque (DT) when the period of time between the measurements of the rotational speed (n) of at least one of the uncoupled components and the engagement of the all-wheel drive is less than a predetermined period of time.

### Claim 8 (depends on 3)

The method according to claim 3, wherein the calculated drag torque (DT) is compared to a stored reference drag torque (DTref) and, as a result, a conclusion is drawn about a wear-induced or wear-compensated component of the drag torque (DT).

### Claim 9 (depends on 8)

The method according to claim 8, further comprising determining a current oil temperature in an axle drive from the wear-compensated component of the drag torque (DT).