Method and controller for controlling output torque of a propulsion unit

• US 8,447,491 B2
• Filed: 07/05/2010
• Issued: 05/21/2013
• Est. Priority Date: 07/07/2009
• Status: Active Grant

• Current Assignee: Volvo Lastvagnar AB (Volvo AB)
• Original Assignee: Volvo Lastvagnar AB (Volvo AB)
• Inventors: Templin, Peter
• Primary Examiner(s): CHEUNG, CALVIN K
• Application Number:
  US13/382,531
• Publication Number:
  US 20120101705A1
• Time in Patent Office: 1,051 Days
• Field of Search: 701/99, 701/110
• US Class Current: 701/99
• CPC Class Codes: B60W 30/20 Reducing vibrations in the driveline

Abstract

Method for controlling output torque (T_eng) of a propulsion unit in a vehicle powertrain including driven wheels drivingly connected to the propulsion unit via a mechanical transmission with a drive shaft, wherein the method including the steps of registering driver torque demand (T_d) for vehicle propulsion, registering propulsion unit rotational speed (ω_e), and controlling the output torque (T_eng) of the propulsion unit to asymptotically follow the driver torque demand (T_d) using a closed-loop linear-quadratic regulator (LQR) based controller (9) having the driver torque demand (T_d) and the propulsion unit rotational speed (ω_e) as input data, in order to minimize driveline oscillations.

Claims

1. A method for controlling output torque (T_eng) of a propulsion unit in a vehicle powertrain comprising driven wheels drivingly connected to the propulsion unit via a mechanical transmission with a drive shaft, the method comprising:

registering a driver torque demand (T_d) for vehicle propulsion;

registering a propulsion unit rotational speed (ω

_e);

controlling the output torque (T_eng) of the propulsion unit to asymptotically follow the driver torque demand (T_d) using a closed-loop linear-quadratic regulator (LQR) based controller having the driver torque demand (T_d) and the propulsion unit rotational speed (ω

_e) as input data, in order to minimize oscillations;

receiving, via the closed-loop LQR based controller, a full state vector information ({circumflex over (x)}) from a state observer based on at least the propulsion unit rotational speed (ω

_e);

generating, via the closed-loop LQR based controller, a controller torque demand (T_f) used for the controlling of the output torque (T_eng) of the propulsion unit based on the driver torque demand (T_d) and the full state vector information ({circumflex over (x)}),

and wherein the controlling of the output torque (T_eng) of the propulsion unit is realized by regulating at least the following three performance index components of the controller to zero;

a time derivative of a drive shaft torque ({dot over (T)}_shaft) of the drive shaft;

an integrated difference (x_u) between the driver torque demand (T_d) and the controller torque demand (T_f); and

a current difference between the driver torque demand (T_d) and the controller torque demand (T_f).

2. The method according to claim 1, wherein the state observer is based on a Loop Transfer Recovery (LTR) design, and the state observer is adapted to generate the full state vector information ({circumflex over (x)}) based on at least the propulsion unit rotational speed (ω

_e) and the controller torque demand (T_f).

3. The method according to claim 1, wherein the full state vector information ({circumflex over (x)}) includes as a state variable at least a drive shaft torsion angle (θ

_S).

4. The method according to claim 1, wherein the step of registering the driver torque demand (T_d) for vehicle propulsion comprises the steps of:

translating an accelerator pedal position into the driver torque demand (T_d);

deriving a torque reference set point (T_r) from the driver torque demand (T_d) by comparing the driver torque demand (T_d) with at least one active torque limitation, and setting the torque reference set point (T_r) to a minimum torque value out of torque values of a comparison;

supplying the torque reference set point (T_r) to the closed-loop LQR based controller as the driver torque demand (T_d).

5. The method according to claim 1, wherein the step of generating the controller torque demand (T_f) used for controlling the output torque (T_eng) of the propulsion unit comprises the steps of:

generating a compensated torque (T_e) by the closed loop LQR based controller;

comparing the compensated torque (T_c) with at least one active torque limitation, and;

setting the controller torque demand (T_f) to a minimum torque value out of torque values of a comparison.

6. The method according to claim 1, comprising taking backlash into account in the method for controlling the output torque (T_eng) of the propulsion unit by the following step:

in case the powertrain backlash will be traversed, providing an intermediate torque hold value (U_rhold) that a requested torque (T_d, T_r) may not exceed until a contact mode is reached, in order to limit acceleration shocks following the traversing of the backlash.

7. The method according to claim 6, comprising

including backlash angle (θ

_b) as a state variable in the full state vector information ({circumflex over (x)});

determining if the powertrain is in a negative side contact mode, a positive side contact mode, or a non-contact mode, based on state mode transition conditions;

determining if the powertrain backlash will be traversed;

determining the intermediate torque hold value (U_rhold);

controlling the output torque (T_eng) of the propulsion unit by means of an optimal control law of the closed loop LQR based controller in a contact mode, and controlling the output torque (T_eng) of the propulsion unit by means of an open-loop control during the non-contact mode.

8. The method according to claim 7, wherein the state mode transition conditions are based on a backlash angle (θ

_b), a time derivative of the backlash angle ({dot over (θ

)}_b), and the drive shaft torque (T_shaft).

9. The method according to claim 8, wherein the state mode transition condition or conditions for determining when the goes from:

the negative site contact mode to the non-contact mode is when the drive shaft torque (T_shaft)>

0;

the positive side contact mode to the non-contact mode is when the drive shaft torque (T_shaft)<

0;

the non-contact mode to the negative side contact mode are when the backlash angle (θ

_b)=−

α and

the time derivative of the backlash angle ({dot over (θ

)}_b)<

0; and

the non-contact mode to the positive side contact mode are when the backlash angle (θ

_b)=α and

the time derivative of the backlash angle ({dot over (θ

)}_b)>

0,

wherein the backlash angle (θ

_b) is limited by −

α

≦

θ

_b≦

α

.

10. The method according to claim 6, wherein the intermediate torque hold value (U_rhold) is determined by numerical optimization based on at least an estimate of a time derivative of the backlash angle ({dot over (θ

)}_b) at a time instance when an opposing side of the powertrain backlash is reached.

11. A propulsion unit torque controller for controlling output torque (T_eng) of a propulsion unit in a vehicle powertrain comprising driven wheels drivingly connected to the propulsion unit via a mechanical transmission with a drive shaft, wherein the controller is a closed-loop linear-quadratic regulator (LQR) based controller, and the closed loop LQR based controller is arranged to control the output torque (T_eng) of the propulsion unit by the following steps:

registering a driver torque demand (T_d) for vehicle propulsion;

registering a propulsion unit rotational speed (ω

_e);

controlling the output torque (T_eng) of the propulsion unit to asymptotically follow the driver torque demand (T_d) having the driver torque demand (T_d) and the propulsion unit rotational speed (ω

_e) as input data, in order to minimize oscillations,

wherein the dosed loop LQR based controller is arranged to;

receive a full state vector information ({circumflex over (x)}) from a state observer based on at least the propulsion unit rotational speed (ω

_e);

generate a controller torque demand (T_f) used for controlling an output torque (T_eng) of the propulsion unit based on the driver torque demand (T_d) and the full state vector information ({circumflex over (x)}), and

wherein the closed loop LQR based controller is arranged to control the output torque (T_eng) of the propulsion unit by regulating the following three performance index components of the controller to zero;

a time derivative of a drive shaft torque ({dot over (T)}_shaft) of the drive shaft;

an integrated difference (x_u) between the driver torque demand (T_d) and the controller torque demand (T_f); and

a current difference between the driver torque demand (T_d) and the controller torque demand (T_f).

12. The propulsion unit torque controller according to claim 11, wherein the closed loop LQR based controller is arranged to take backlash into account when controlling the output torque (T_eng) of the propulsion unit by:

in case powertrain backlash will be traversed, providing an intermediate torque hold value (U_rhold) that a requested torque (T_d, T_r) may not exceed until a contact mode is reached, in order to limit acceleration shocks following the traversing of the backlash.

13. The propulsion unit torque controller according to claim 12, comprising

including a backlash angle (θ

_b) as a state variable in the full state vector information ({circumflex over (x)});

determining if the powertrain is in a negative side contact mode, a positive side contact mode, or a non-contact mode, based on state mode transition conditions;

determining if the powertrain backlash will be traversed;

determining the intermediate torque hold value (U_rhold);

controlling the output torque (T_eng) of the propulsion unit by means of optimal control law of the closed loop LQR based controller in contact mode, and controlling the output torque (T_eng) of the propulsion unit by means of open-loop control during non-contact mode.