Model-based torque converter control

Abstract

A method of controlling hydraulic pressure to a torque converter is provided. The method includes: determining a slip error from a target slip value and a measured slip; integrating said slip error; determining a state space feedback control matrix for said measured slip; determining a state space feedback control matrix for said integrated slip error; and controlling pressure based on said state space feedback control matrix for said measured slip and said state space feedback control matrix for said integrated slip error.

Description

FIELD

The present invention relates to control systems and methods for torque converters.

BACKGROUND

The term “road-to-lab-to-math” describes the effort to reduce the amount of on-road testing and replace it with laboratory testing of components and subsystems. Road-to-lab-to-math simulates the functionality of vehicle component on a computer. The simulation uses mathematical models that make evaluation more precise and more representative of in-use conditions.

Alternatively, on-road testing of prototype vehicles can be very expensive; not only because of the costs of the vehicles themselves, but also because they comprise many prototype subsystems. Should one of these subsystems fail, the other subsystems cannot be tested without it. By bringing these subsystems and components to the laboratory, this interdependence of available hardware is eliminated. For example, it is now possible to evaluate a prototype transmission without a prototype engine being attached to it, so engine problems need not affect the transmission test schedule. Alternatively, it is also possible to verify the prototype transmission for compatibility with engines that may not yet be prototyped or even fully designed. Once the prototype is verified in the lab, it can be integrated into the vehicle.

SUMMARY

Accordingly, a method of controlling hydraulic pressure to a torque converter is provided. The method includes: determining a slip error from a target slip value and a measured slip; integrating said slip error; determining a state space feedback control matrix for said measured slip; determining a state space feedback control matrix for said integrated slip error; and controlling pressure based on said state space feedback control matrix for said measured slip and said state space feedback control matrix for said integrated slip error.

In other features, a torque converter control simulation system is provided. The system includes a controller model including: a converter control module that integrates a slip error and determines an apply pressure value and a release pressure value based on state space feedback control including said integrated slip error and received signals including an engine torque signal, an engine speed signal, a turbine speed signal, a target slip signal and a measured slip signal; and a hydraulic control module that determines a pressure signal based on said apply pressure and said release pressure. The system also includes a plant model including: a hydraulic module that simulates a hydraulic flow of a solenoid and a valve based on a state space representation of the solenoid and the valve; and a mechanical module that simulates the mechanical functions of a torque converter based on torque relationships within the torque converter.

Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:

FIG. 1 is a functional block diagram illustrating a vehicle including a torque converter system;

FIG. 2 is a block diagram illustrating a torque converter control system;

FIG. 3A is a diagram illustrating a mechanical system of the torque converter control system;

FIG. 3B is a diagram illustrating a torque relationships within the mechanical system of the torque converter control system;

FIG. 4 is a diagram illustrating a hydraulic system of the torque converter control system;

FIG. 5 is a bond graph of the hydraulic system;

FIG. 6 is a state space representation of the hydraulic system; and

FIG. 7 is an exemplary model in Matlab form illustrating the converter control module.

DETAILED DESCRIPTION

The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. For purposes of clarity, the same reference numbers will be used in the drawings to identify similar elements. As used herein, the term module refers to an application specific integrated circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or group) and memory that executes one or more software or firmware programs, a combinational logic circuit, and/or other suitable components that provide the described functionality.

Referring now to FIG. 1, before determining a mathematical model of a particular vehicle component, it is necessary to understand its function in the vehicle and its interaction with other components. FIG. 1 illustrates a vehicle 10 that includes a conventional torque converter system. An engine 12 combusts an air and fuel mixture to produce drive torque. Air is drawn into an intake manifold 14 through a throttle 16. The throttle 16 regulates mass air flow into the intake manifold 14. Air within the intake manifold 14 is distributed into cylinders 18. Although six cylinders 18 are illustrated, it can be appreciated that the engine can have a plurality of cylinders including, but not limited to, 2, 3, 5, 6, 8, 10, 12 and 16 cylinders.

Torque from the engine 12 is supplied to a transmission 20 through a torque converter (TC) system shown generally at 22. The TC system 22 includes a torque converter 24, a hydraulic pump 26, a solenoid 28, and a valve 30. The hydraulic pump 26 is driven by the engine 12 to selectively supply pressurized fluid to the torque converter 24 through the solenoid 28 and the valve 30. A duty cycle is commanded by a controller 32 to the solenoid 28 that controls the valve 30 in order to vary the supply of pressurized fluid to the torque converter 24. A slip rate of the torque converter 24 is varied based on control of the pressurized fluid.

The controller 32 determines the duty cycle based on inputs received from the torque converter 24, the engine 12, the transmission 20, and/or other control modules within the controller 32. The inputs include: an engine speed signal received from and engine speed sensor 34 or determined by an engine speed control module; a turbine speed signal received from an turbine speed sensor 36 or determined by a turbine speed control module; an engine torque signal determined by an engine torque control module; and a slip signal determined from a slip module.

In order to mathematically model the torque converter control system a controller model and a plant model are developed. The controller model simulates the method of controlling the torque converter. The plant model simulates the torque converter as it is mechanically functioning. In an exemplary embodiment, the torque converter system can be broken down into two sub-systems, a hydraulic system and a mechanical system. The hydraulic system includes the solenoid 28 and the valve 30. The mechanical system includes the torque converter 24. A plant model 40 and a controller model 42 can be defined for each sub-system. In FIG. 2, the controller model 42 includes a converter control module 44 and a hydraulic control module 46. The plant model 40 includes a hydraulic module 48 and a mechanical module 50.

Referring now to FIGS. 3A and 3B. FIG. 3A illustrates the physical characteristics of the mechanical system in more detail. A torque converter 24 consists of three elements a turbine 52, a stator 54, and a pump 56. The pump (P) 56 is the input (drive) member. The pump 56 receives power from the engine. The turbine (T) 52 is the output (driven) member. The turbine 52 is connected to the transmission 20 (FIG. 1). The stator (ST) 54 assembly is the reaction member or torque multiplier. The stator (ST) 54 is supported on a one way clutch (C) 58 also referred to as the torque converter clutch (TCC), which operates as an overrunning clutch and permits the stator 54 to rotate freely in one direction and lock in the opposite direction. Engine inertia (I_m) is 60 supplied to the torque converter 24. Torque converter inertia (I_conv) 62 is supplied to the transmission 20 (FIG. 1). The rotational speed of the engine 12 (FIG. 1) is represented by E_S. The rotational speed of the turbine 52 is represented by T_S.

FIG. 3B illustrates the torque relationships between the elements of the torque converter 24. Based on the torque relationships, the mechanical system can be modeled mathematically by the following two equations:

$\begin{array}{cc}{I}_m·\frac{E_S}{t}=C_m-C_p-C_t\mathrm{and}& \left(1\right)\\ I_{\mathrm{conv}.}\frac{T_S}{t}=C_t+C_T.& \left(2\right)\end{array}$

Where C_m represents Engine torque and C_e represents input torque. C_t represents torque transmitted to the wheels by the TCC. C_p represents pump torque and C_T represents turbine torque. Equations 1 and 2 can be used by the mechanical module 50 (FIG. 2) to model the torque converter mechanical system.

Referring now to FIG. 4, the flow of the hydraulic system is shown in more detail. The mechanical system is commanded by the hydraulic system through the TCC. Apply and release pressure (P_apply and P_release) are commanded by a regular apply signal (Reg_Apply) 64 and a TCC solenoid signal (TCC_VBS) 66. P_apply 68 and P_release 70 drive the TCC and create an amount of slippage through the fluid coupling. Based on a bond graph of the hydraulic system shown in FIG. 5 and a state space representation shown in FIG. 6, an input/output equation representing the hydraulic system can be:

{dot over (x)}=A.x+B.u

y=C.x   (3)

Where x represents a system state vector, u represents an input vector, and y represents an output vector. Equation 3 is used by the hydraulic module 48 (FIG. 2) to model the hydraulic system.

Referring back to FIG. 2, control methods are provided by the converter control module 44 and the hydraulic control module 46 in order to regulate slip, where slip equals engine speed minus turbine speed:

Slip=E_S−T_S.   (4)

Regulating slip provides a more efficient transfer of engine torque to the transmission 20 (FIG. 1). The converter control module 44 receives a turbine speed signal 72, an engine speed signal 74, an engine torque signal 76, a target slip signal 78 and a measured slip signal 80 as input. Based on the inputs 72-80, the converter control module 44 computes P_apply 82 and P_release 84 pressure in an attempt to eliminate the error between the measured slip and the target slip. The hydraulic control module 46 determines an appropriate TCC pressure signal 86 from the difference between P_apply 82 and P_release 84 pressure.

More specifically, the hydraulic control module 46 calculates the commanded TCC pressure P_Tcc 86 from a hydraulic filter. The hydraulic filter takes into account the state space representation of the hydraulic system (FIG. 6) and the fact that the response time of the hydraulic system is fast, while aiming to assure a null static error between the desired and the output (dP=P_apply−P_release) pressure. The pre-filter uses the input dP and a line pressure P_LINE to compute P_TCC 86 by solving equation (3) provided {dot over (x)}=0. The mathematical model can be shown as:

$\begin{array}{cc}{P}_{\mathrm{TCC}}=\frac{\frac{x_1}{C_1}+F_0+A_1*P_{\mathrm{reg}}}{\mathrm{Areg}*{\mathrm{coeffP}}_{\mathrm{LINE}}\mathrm{correction}}.& \left(5\right)\end{array}$

Where x₁ is the position of the valve. C₁ is the capacity of the valve. F₀ is the nominal feedback force of the valve. A_reg is the area of the valve on the intput side. A₁ is the area of the valve on the output side. P_reg is the regulated pressure that is output from the valve. coeffP_linecorrection is a line coefficient factor that compensates the difference between commanded and actual line pressure.

The converter control module 44 controls slip based on the first mechanical equation of the torque converter (equation 1). Substituting the following equation for pump torque C_p:

C _p =A*E _S ² +B*E _S *T _S +C*T _S ²   (6)

and the following equation for transmitted torque C_t:

C _t =dP*nAr*μ(E_S,T_S),   (7)

the first mechanical equation becomes:

$\begin{array}{cc}{I}_m*\frac{E_S}{t}=C_m+A*E_S^2+B*E_S*T_S+C*T_S^2-\mu \left(E_S,T_S\right)*\mathrm{nAr}*\mathrm{dP}.& \left(8\right)\end{array}$

Given the non-linearity of the mechanical system, two variable substitutions can be made based on the pump torque equation in order to obtain a linear system. Provided z=E_S−E_S1 where E_S1 and E_S2 are solutions of the pump torque equation (6) and u=1/z, the mathematical model becomes:

$\begin{array}{cc}\frac{u}{t}=-\frac{A}{I_m}-\frac{A}{I_m}*\left(E_{S1}-E_{S2}\right)*u+\frac{\left[\mu \left(E_S,T_S\right)*\mathrm{nAr}*\mathrm{dP}-C_m\right]}{I_m}*u^2.& \left(9\right)\end{array}$

In order to develop an efficient torque converter control method that is robust against variation of engine torque, a friction coefficient and/or pure delay, state space feedback control including an integral action is implemented. FIG. 7 is a Matlab model illustrating the torque converter control method. Slip error is calculated from a pre-determined target slip U_Target 78 and a measured slip U_Slip 80 that is output from the plant model 50. An integrator 90 applies an integration to slip error (U_Target−U_Slip). A TCC pressure is then determined from state space feedback matrices Rcons 92 representing a correction for the input order and Ru 94 representing a correction for the pressure command.

The mathematical models used to generate the torque converter control method are discussed below. The state space representation matrix of the torque converter is translated from a continuous time to a sampling time, using the following equations:

$\begin{array}{cc}\mathrm{Matrix}=M=-\frac{A}{I_m}*\left(E_{S1}-E_{S2}\right),& \left(10\right)\\ \Phi ={}^{M*T_S},\mathrm{and}& \left(11\right)\\ \Gamma ={\int }_0^{T_S}{}^{M*t}t*B.& \left(12\right)\end{array}$

The matrix in sampling time can be defined as:

$\begin{array}{cc}\Gamma =\frac{{}^{M*T_S}-1}{M}.& \left(13\right)\end{array}$

Where T_S is the sampling time and not turbine speed.

Commanded pressure is determined using the state space feedback matrices and an integral action, where commanded pressure P_TCC equals:

P _TCC=Deptorq+retat_action+intetat_action   (14)

Deptorq is defined as pressure that corrects changes in engine torque. Retat_action is defined as the pressure that corrects an error in the commanded pressure to reach the input target and is shown at 92. Intetat_action is defined as the pressure that ensures zero error in steady state conditions shown at 94.

The following mathematical model represents the pressure that corrects changes in engine torque Deptorq:

$\begin{array}{cc}\mathrm{Deptorq}=\frac{C_m}{\mathrm{nAr}*\mu }& \left(15\right)\end{array}$

Where C_m is engine torque. nAr is a coefficient comprising n number of clutches with a surface area A and a radius r. μ is a friction coefficient.

The following mathematical model represents the pressure that corrects an error in the commanded pressure ret_action:

$\begin{array}{cc}\mathrm{retat\_action}=\frac{I_m}{\mathrm{nAr}*\mu }*r_u*\left(E_S-E_{S1}\right)& \left(16\right)\end{array}$

Where I_m is engine inertia. nAr is a coefficient comprising n number of clutches with a surface area A and a radius r. μ is a friction coefficient. R_u is a correction for the pressure command given by the state space feedback control. E_s is engine speed. E_s1 is a first solution of the pump torque equation (equation 6).

The following mathematical model represents the pressure that ensures zero error in steady state conditions intetat_action:

$\begin{array}{cc}\mathrm{intetat\_action}=\frac{I_m}{\mathrm{nAr}*\mu }*r_{\mathrm{cons}}*\mathrm{error\_u}*{\left(E_S-E_{S1}\right)}^2.& \left(17\right)\end{array}$

Where I_m is engine inertia. nAr is a coefficient comprising n number of clutches with a surface area A and a radius r. μ is a friction coefficient. Rcons is the correction to the input order. Error_u is a difference between a desired slip and a commanded slip. E_s is engine speed. E_s1 is a first solution of the pump torque equation (equation 6).

Those skilled in the art can now appreciate from the foregoing description that the broad teachings of the present invention can be implemented in a variety of forms. Therefore, while this invention has been described in connection with particular examples thereof, the true scope of the invention should not be so limited since other modifications will become apparent to the skilled practitioner upon a study of the drawings, specification, and the following claims.

Claims

1. A method of controlling hydraulic pressure to a torque converter, comprising: determining a slip error from a target slip value and a measured slip;integrating said slip error;determining a state space feedback control matrix for said measured slip;determining a state space feedback control matrix for said integrated slip error; andcontrolling pressure based on said state space feedback control matrix for said measured slip and said state space feedback control matrix for said integrated slip error.

2. The method of claim 1 wherein said controlling pressure further comprises: determining an engine torque correction pressure that corrects changes in engine torque;determining a commanded pressure correction pressure that corrects commanded pressure errors based on said state space feedback control matrix for said measured slip; anddetermining a steady state correction pressure based on said state space feedback control matrix for said integrated slip error.

3. The method of claim 2 further comprising: summing said engine torque correction pressure, said commanded pressure correction, and said steady state correction pressure; andcontrolling pressure based on said summation.

4. The method of claim 2 wherein said engine torque correction pressure (Deptorq) is determined based on engine torque (Cm), a coefficient based on n number of clutches with a surface area A and a radius r (nAr), and a friction coefficient (μ).

5. The method of claim 4 wherein said engine torque correction pressure (Deptorq) is based on:

6. The method of claim 2 wherein said commanded pressure correction is determined based on engine inertia (Im), a coefficient based on n number of clutches with a surface area A and a radius r (nAr), a friction coefficient (μ), a correction based on said state space feedback control matrix for said measured slip (ru), engine speed (Es), and a first solution of pump torque (Es1).

7. The method of claim 6 wherein said commanded pressure correction is determined based on:

8. The method of claim 2 wherein said steady state correction pressure is determined based on engine inertia (Im), a coefficient based on n number of clutches with a surface area A and a radius r (nAr), a friction coefficient (μ), a correction based on said state space feedback control matrix for said integrated slip error (rcons), a difference between desired slip and commanded slip (error_u), engine speed (Es), and a first solution of pump torque (Es1).

9. The method of claim 9 wherein said steady state correction pressure is determined based on:

10. The method of claim 1 further comprising applying a hydraulic filter to said controlled pressure to determine a torque converter pressure signal.

11. The method of claim 10 wherein said hydraulic filter is based on a position of a valve that controls the pressure (x1), a capacity of the valve (C1), a nominal feedback force of the valve (F0), an area of the valve on the intput side (Areg), an area of the valve on the output side (A1), a pressure that is output from the valve (Preg), and a line coefficient factor that compensates a difference between a commanded pressure and an actual line pressure (coeffPlinecorrection).

12. The method of claim 11 wherein said hydraulic filter is based on:

13. A torque converter control simulation system, comprising: a controller model comprising: a converter control module that integrates a slip error and determines an apply pressure value and a release pressure value based on state space feedback control including said integrated slip error and received signals including an engine torque signal, an engine speed signal, a turbine speed signal, a target slip signal and a measured slip signal; anda hydraulic control module that determines a pressure signal based on said apply pressure and said release pressure; anda plant model comprising: a hydraulic module that simulates a hydraulic flow of a solenoid and a valve based on a state space representation of the solenoid and the valve; anda mechanical module that simulates the mechanical functions of a torque converter based on torque relationships within the torque converter.

14. The system of claim 13 wherein said converter control module determines said apply pressure and said release pressure based on computing a summation of an engine torque correction pressure, a commanded pressure correction pressure, and a steady state correction pressure.

15. The system of claim 14 wherein said engine torque correction pressure (Deptorq) is determined based on engine torque (Cm), a coefficient based on n number of clutches with a surface area A and a radius r (nAr), and a friction coefficient (μ).

16. The system of claim 15 wherein said engine torque correction pressure (Deptorq) is determined based on:

17. The system of claim 14 wherein said commanded pressure correction (retat_action) is determined based on engine inertia (Im), a coefficient based on n number of clutches with a surface area A and a radius r (nAr), a friction coefficient (μ), a correction based on a state space feedback control matrix (ru), engine speed (ES), and a solution of pump torque (ES1).

18. The system of claim 17 wherein said commanded pressure correction (retat_action) is determined based on:

19. The system of claim 14 wherein said steady state correction pressure (intetat_action) is determined based on engine inertia (Im), a coefficient based on n number of clutches with a surface area A and a radius r (nAr), and a friction coefficient (μ), a correction based on a state space feedback control matrix (rcons), a difference between target slip and measured slip (error_u), engine speed (Es), and a first solution of pump torque (Es1).

20. The system of claim 19 wherein said steady state correction pressure (intetat_action) is determined based on:

21. The system of claim 13 wherein said hydraulic control module determines said pressure signal PTCC based on a position of a valve that supplies said pressure (x1), a capacity of the valve (C1), a nominal feedback force of the valve (F0), an area of the valve on an input side (Areg), an area of the valve on an output side (A1), a pressure that is output from the valve (Preg), and a coefficient factor that compensates a difference between a commanded pressure and an actual line pressure (coeffPlinecorrection).

22. The system of claim 21 wherein said hydraulic control module determines said pressure signal PTCC based on:

23. The system of claim 13 wherein said hydraulic module simulates hydraulic flow from a state space representation of a bond graph wherein x represents a system state vector, u represents an input vector and y represents an output vector, coefficients A and B, and {dot over (x)}=A.x+B.u y=C.x

24. The system of claim 13 wherein the mechanical module simulates the mechanical functions based on engine inertia (Im), a change in engine speed

25. The system of claim 13 wherein the mechanical module simulates the mechanical functions based on torque converter inertia (Iconv), a change in turbine speed