# Patent

## Title
Method and device for operating a clutch

## Abstract

A method and device for operating a clutch between an internal combustion engine and at least one driven wheel of a vehicle, a torque being transmitted between the internal combustion engine and the driven wheel by pressing the clutch together via an application force or an application pressure, and the application force or the application pressure being controlled or regulated as a function of the temperature of the clutch.

## Background
BACKGROUND INFORMATION
The present invention relates to a method and a device for operating a clutch between an internal combustion engine and at least one driven wheel of a vehicle, a torque being transmitted between the internal combustion engine and the driven wheel by pressing the clutch together via an application force or an application pressure.
If a clutch is operated with slip, it is possible to draw inferences concerning the clutch torque transmitted if the coefficient of friction is known. This torque information is intended to be used to determine the transmission input torque. Precise knowledge of the transmission input torque is of particular significance for continuously variable transmissions (CVT) so that the safety pressure when controlling the belt tension of belt transmissions can be reduced and the transmission efficiency can be increased.
The object of the present invention is to improve the operation of a clutch.
The object is achieved by a method and a device for operating a clutch between an internal combustion engine and at least one driven wheel of a vehicle according to Claim 1 and Claim 8 respectively, a torque being transmitted between the internal combustion engine and the driven wheel to operate a clutch between an internal combustion engine and at least one driven wheel of a vehicle by pressing the clutch together via an application force or an application pressure and the application force or the application pressure being controlled or regulated as a function of the temperature of the clutch.
In an advantageous embodiment of the invention, the application force or the application pressure is controlled or regulated as a function of the temperature of a friction surface of the clutch.
In a further advantageous embodiment of the invention, the application force or the application pressure is controlled or regulated as a function of the temperature of oil used to lubricate or cool the clutch.
In a further advantageous embodiment of the invention, the torque to be transmitted between the internal combustion engine and the driven wheel is increased by a specified value when the temperature of the clutch, the temperature of a friction surface of the clutch or the temperature of oil used to lubricate or cool the clutch exceeds a threshold value.
In a further advantageous embodiment of the invention, the application force or the application pressure is regulated as a function of a clutch slip in the clutch, when the torque is transmitted between the internal combustion engine and the driven wheel, and a setpoint clutch slip, in particular when the temperature of the clutch, the temperature of a friction surface of the clutch or the temperature of oil used to lubricate or cool the clutch is less than or equal to the threshold value.
In a further advantageous embodiment of the invention, the application force or the application pressure is regulated as a function of the difference between the clutch slip and the setpoint clutch slip, in particular when the temperature of the clutch, the temperature of a friction surface of the clutch or the temperature of oil used to lubricate or cool the clutch is less than or equal to the threshold value.
In a further advantageous embodiment of the invention, the application force or the application pressure is regulated by an inverse clutch model which calculates the application force or the application pressure as a function of the torque transmitted via the clutch.
The device according to the present invention for operating a clutch between an internal combustion engine and at least one driven wheel of a vehicle, a torque being transmitted between the internal combustion engine and the driven wheel by pressing the clutch together via an application force or an application pressure, is provided with a pressure regulator to control or regulate the application force or the application pressure as a function of the temperature of the clutch, the temperature of a friction surface of the clutch or the temperature of oil used to lubricate or cool the clutch.
In a further advantageous embodiment of the invention, means are provided to determine the temperature of the clutch, the temperature of a friction surface of the clutch or the temperature of oil used to lubricate or cool the clutch.
In a further advantageous embodiment of the invention, the pressure regulator has a regulator to regulate the application force or the application pressure as a function of a clutch slip in the clutch, when the torque is transmitted between the internal combustion engine and the driven wheel, and a setpoint clutch slip.
In a further advantageous embodiment of the invention, the pressure regulator has an inverse clutch model to calculate the application force or the application pressure as a function of the torque transmitted via the clutch.
In a further advantageous embodiment of the invention, the coefficient of friction of the clutch is a parameter of the inverse clutch model.
In a further advantageous embodiment of the invention, an adapter is provided to adapt the coefficient of friction of the clutch.



Further details and advantages can found in the following description of exemplary embodiments in which:
FIG. 1 shows a drive unit for a motor vehicle.
FIG. 2 shows a clutch.
FIG. 3 shows a clutch controller.
FIG. 4 shows a pressure regulator.
FIG. 5 shows a flow chart.
FIG. 6 shows a characteristic curve.
FIG. 7 shows a flow chart.
FIG. 8 shows a coefficient of friction-slip characteristic curve.
FIG. 9 shows a flow chart.
FIG. 10 shows an illustration of the flow chart of FIG. 4.
FIG. 11 shows an illustration of the flow chart of FIG. 6.



FIG. 1 shows a drive unit for a motor vehicle. Reference symbol 1 identifies an internal combustion engine which is connected to an automatic transmission 2 via a shaft 4. Automatic transmission 2 is formed in a particularly advantageous manner as a belt transmission. Automatic transmission 2 is connected via a clutch input shaft 5, a clutch 3, a clutch output shaft 6, a differential 7 to driven wheels 8, 9 for the purpose of propelling the motor vehicle. By pressing clutch 3 together with an application pressure p, it is possible to adjust the torque which is transmitted via clutch 3. In order to adjust the torque transmitted via clutch 3, a clutch controller 12 is provided, which by specifying a desired application pressure p*, adjusts the application pressure in clutch 3. The application pressure is synonymous with an application force with which clutch 3 is pressed together.
Input variables in clutch controller 12 include rotational speed nE of clutch input shaft 5 which is measured by a rotational speed sensor 10, rotational speed nA of clutch output shaft 6 which is measured by a rotational speed sensor 11, transmission ratio i of automatic transmission 2, an oil temperature θOIL of clutch 3 and a desired value Δn* for the clutch slip of clutch 3 (setpoint clutch slip) as well as optionally torque TM of internal combustion engine 1 as well as information ΔTM relating to the inaccuracy of the information relating to torque TM of internal combustion engine 1. Clutch slip Δn is defined as

Δn=nE−nA 

Torque TM of internal combustion engine 1 and information ΔTM relating to the inaccuracy of the information relating to torque TM of internal combustion engine 1 are provided, for example, by an engine management which is not illustrated.
FIG. 2 shows a clutch 3 in an exemplary embodiment. Reference symbol 83 identifies a lubricating oil supply for hydraulic oil, reference symbol 84 an outer carrier, reference symbol 85 an inner carrier, reference symbol 86 an outer blade, reference symbol 87 an inner blade, reference symbol 88 a restoring spring, reference symbol 93 a cylinder, reference symbol 94 a piston, reference symbol 95 a pressure plate and reference symbol 96 a pressure medium supply. Outer carrier 84, which is connected to clutch input shaft 5, is provided with outer blades 86, and in an advantageous embodiment, with steel blades without a friction lining. Inner carrier 85 which is connected to clutch output shaft 6 accommodates inner blades 87 which are coated with a friction lining. Upon the introduction of hydraulic oil at a defined pressure level via pressure medium supply 96 into cylinder 93, piston 94 moves against the force of restoring spring 88 in the direction of pressure plate 95 and presses together the blade package which include inner and outer blades 87 and 86. In order to cool the blade package, hydraulic oil is directed to inner and outer blades 87 and 86 via lubricating oil supply 83. The temperature of the lubricating oil is supplied to clutch controller 12 as oil temperature θOIL.
FIG. 3 shows clutch controller 12. It has a subtractor 20 and a pressure regulator 21 as well as optionally an adapter 22 and/or a protection device 81. Pressure regulator 21 is explained in greater detail with reference to FIG. 4 and the adapter with reference to FIG. 7. Subtractor 20 determines clutch slip Δn, which is the input variable in pressure regulator 21. Additional input variables of pressure regulator 21 include setpoint clutch slip Δn*, engine torque TM, transmission ratio i of automatic transmission 2 and coefficient of friction μ. Coefficient of friction μ is formed by adapter 22. Input variables in optional adapter 22 include setpoint clutch slip Δn*, transmission ratio i of automatic transmission 2, torque TM of internal combustion engine 1, information ΔTM relating to the inaccuracy of the information relating to torque TM of internal combustion engine 1 as well as a differential torque TR which is formed by pressure regulator 21. In addition to coefficient of friction μ, a corrected engine torque TMK is an additional output variable of adapter 22. Pressure regulator 21 also forms desired application pressure p*.
Clutch controller 12 optionally has a protection device 81 to protect the drive unit, automatic transmission 2 in particular, against torque shocks. A shock torque TS is an output variable of protection device 81. In an advantageous embodiment, shock torque TS is calculated according to the following equation




  
    T
    s
  
  =
  
    
      T
      c
    
    -
    
      
        ∑
        /
      
      ⁢
      
        
          J
          /
        
        ·
        
          
            2
            ⁢
            
              
            
            ⁢
            
              π
              ·
              Δ
            
            ⁢
            
              
            
            ⁢
            
              n
              max
            
          
          
            Δ
            ⁢
            
              
            
            ⁢
            t
          
        
      
    
  




where

    J1 is the moment of inertia of a 1st component of the drive unit on the side of clutch 3, on which internal combustion engine 1 is arranged.
    Δnmax is the maximum permissible clutch slip
    Tc is a constant torque
    Δt is the period of time, in which a torque shock leads to an increase in slip.


If the duration of slip Δt is of secondary importance, then shock torque TS may be made equal to constant torque TC.
In an advantageous embodiment, it is possible to transmit shock torque TS to a transmission controller so that, for example, the application pressure can be increased accordingly in a belt transmission. The application pressure required in the belt transmission is to be increased as a function of shock torque TS.
FIG. 4 shows the internal structure of pressure regulator 21. Pressure regulator 21 has a filter 31 for the purpose of filtering clutch slip Δn. An adder 36 serves to produce the difference between setpoint clutch slip Δn* and clutch slip Δn which is filtered by filter 31. This difference is negated by a negater 32 and is an input variable in a regulator 33, which in an advantageous embodiment, is designed as a PID controller. A differential torque TR is the output variable of regulator 33. Differential torque TR is an input variable in a minimum value calculator 82. Minimum value calculator 82 compares differential torque TR and shock torque TS and outputs the greater torque as an output value. The minimum of differential torque TR and shock torque TS is an input value in a selector 79.
A filter 34 serves to filter engine torque TM which is multiplied by a multiplier 90 by transmission ratio i of automatic transmission 2. Engine torque TM which is filtered in this manner and multiplied by transmission ratio i of automatic transmission 2 is sent to a selector 79.
Moreover, a temperature model 78 is provided to calculate temperature θSL Of the steel blades of clutch 3. In an exemplary embodiment, the relation




  
    
      θ
      SL
    
    ⁢
    
      (
      
        t
        n
      
      )
    
  
  =
  
    
      
        θ
        OIL
      
      ⁢
      
        (
        
          t
          n
        
        )
      
    
    -
    
      ∫
      
        (
        
          
            π
            
              15
              ·
              
                z
                R
              
              ·
              
                m
                SL
              
              ·
              
                c
                SL
              
            
          
          ·
          
             
            
              |
              
                
                  
                    T
                    k
                  
                  ⁢
                  
                    (
                    t
                    )
                  
                
                ·
                
                  (
                  
                    
                      
                        n
                        E
                      
                      ⁢
                      
                        (
                        
                          t
                          n
                        
                        )
                      
                    
                    -
                    
                      
                        n
                        A
                      
                      ⁢
                      
                        (
                        
                          t
                          n
                        
                        )
                      
                    
                  
                  )
                
              
              |
              
                 
                
                   
                  
                    
                      
                        -
                        
                           
                          
                             
                            
                              α
                              ⁢
                              
                                
                                  2
                                  ⁢
                                  
                                    A
                                    R
                                  
                                
                                
                                  
                                    m
                                    SL
                                  
                                  ·
                                  
                                    c
                                    SL
                                  
                                
                              
                              ⁢
                              
                                (
                                
                                  
                                    
                                      θ
                                      SL
                                    
                                    ⁢
                                    
                                      (
                                      
                                        t
                                        
                                          n
                                          -
                                          1
                                        
                                      
                                      )
                                    
                                  
                                  -
                                  
                                    
                                      θ
                                      SL
                                    
                                    ⁢
                                    
                                      (
                                      
                                        t
                                        n
                                      
                                      )
                                    
                                  
                                
                                )
                              
                            
                          
                        
                      
                      )
                    
                    ⁢
                    
                      d
                      t
                    
                  
                
              
            
          
        
      
    
  




is implemented in temperature model 78 where

θSL is the temperature of the steel blades

θOIL is the temperature of the hydraulic oil

AR is the friction surface of the steel blades

ZR is the number of friction surfaces

mSL is the mass of the steel blades

CSL is the heat capacity of the steel blades

tn is the present time

α is the heat transmission coefficient

Temperature θSL of the steel blades of clutch 3 calculated in this manner is an input variable in selector 79. The output variable of selector 79 is clutch torque TK to be transmitted by clutch 3, which together with coefficient of friction μ, is an input value in an inverse clutch model 35.
FIG. 5 shows a flow chart which in an advantageous embodiment is implemented on selector 79. The start of the sequence 100 is followed by a step 101 in which temperature θSL of the steel blades of clutch 3 is input. Step 101 is followed by an interrogation 102 inquiring whether

θSL>θSllim 

where θSllim is a threshold value for temperature θSL of the steel blades of clutch 3. If the condition

θSL>θSLlim 

is met, interrogation 102 is followed by a step 103 in which clutch torque TK to be transmitted by clutch 3 is calculated according to

TK=min(TS,TR)+i·TM,

Toffset, for example, being determined according to a relation such as is shown, for example, in FIG. 6.

If, however, the condition

θSL>θSLlim 

is not met, interrogation 102 is followed by a step 104 in which clutch torque TK to be transmitted by clutch 3 is calculated according to

Tk=min(TS,TR)+i·Tm,

Steps 103 and 104 respectively are followed by an interrogation 105 inquiring whether the determination of clutch torque TK to be transmitted by clutch 3 as a function of the temperature of clutch 3 is to be terminated. If this is not the case, then step 101 follows interrogation 105. If, however, it is the case, the end of the sequence 106 follows interrogation 105.
In inverse clutch model 35, the following equation is implemented in an exemplary embodiment:




  
    T
    K
  
  =
  
    
      
        T
        offset
      
      +
      
        
          i
          ·
          
            T
            M
          
        
        ⁢
        
          
        
        ⁢
        
          p
          *
        
      
    
    =
    
      
        1
        
          A
          R
        
      
      ⁢
      
        (
        
          
            
              T
              K
            
            
              μ
              ·
              r
              ·
              
                Z
                R
              
            
          
          +
          
            F
            0
          
        
        )
      
    
  




A is the piston surface of clutch 3, r the effective friction radius of clutch 3, ZR the number of friction surfaces of clutch 3 and F0 is the minimum force required for transmitting torque via clutch 3.

FIG. 7 shows a flow chart as an implementation of adapter 22. Reference symbol 40 identifies the start of the sequence and reference symbol 49 the end of the sequence. In step 41, information TM relating to the engine torque, information ΔTM relating to the inaccuracy of the information relating to engine torque TM, differential torque TR, setpoint clutch slip Δn* and application pressure p are input.
In a subsequent step 42, a coefficient of friction μ is formed from setpoint clutch slip Δn* and application pressure p. In an advantageous embodiment, this is achieved by a coefficient of friction-slip characteristic curve which is a function of application pressure p. A characteristic curve of this type is illustrated for example in FIG. 8 and is identified by reference symbol 50.
Step 42 is followed by interrogation 43 inquiring whether

ΔTM≦T1 

where T1 is a (first) tolerance value. If

ΔTM≦T1 

then step 44 follows in which a new coefficient of friction μ of the clutch is formed according to





  μ
  =
  
    μ
    +
    
      
        
          T
          M
        
        ·
        i
      
      
        
          
            T
            M
          
          ·
          i
        
        +
        
          T
          R
        
      
    
  




and a corrected engine torque TMK is formed according to

TMK=TM 

Step 44 is followed by step 45 in which the coefficient of friction-slip characteristic curve 50 as a function of the application pressure is modified in such a manner that the new value for coefficient of friction μ and setpoint clutch slip Δn* form a pair of variates on modified coefficient of friction-slip characteristic curve 51. Step 45 is illustrated in FIG. 8. Reference symbol μ1 identifies the value for coefficient of friction μ for the relevant application pressure prior to execution of step 45 and μ2 identifies the value of coefficient of friction μ for the relevant application pressure after execution of step 45. Coefficient of friction μ1 is formed by characteristic curve 50 as a function of setpoint clutch slip Δn* (see step 42). In step 45, coefficient of friction-characteristic curve 50 is modified in such a manner that a coefficient of friction-clutch slip characteristic curve 51 is produced, on which value μ2 and setpoint clutch slip Δn* are a pair of variates.
If

ΔTM≦T1 

is not fulfilled, then instead of step 44, step 48 follows in which a corrected engine torque TMK is equated to the sum of engine torque TM generated by internal combustion engine 1 and differential torque TR which is divided by transmission ratio i of automatic transmission 2:

TM=TM+TR/i 

Step 46 or 48, respectively, is followed by an interrogation 47 inquiring whether the preceding sequence is to be repeated. If this is the case, then step 41 follows. If this is not the case, the sequence is terminated.
FIG. 9 shows a modification of the flow chart of FIG. 7. Interrogation 43 is not followed by step 48 but rather by an interrogation 60. Interrogation 60 inquires whether

ΔTM>T2 

is fulfilled, T2 being a second tolerance value. If this condition is fulfilled, then step 48 follows. However if the condition is not met, step 46 is performed.

FIGS. 10 and 11 illustrate the differences between the flow charts as shown in FIG. 7 and FIG. 9. Information ΔTM relating to the inaccuracy of the information relating to engine torque TM of internal combustion engine 1 is shown on the X-axis. The Y-axis in FIG. 10 and FIG. 11 indicates which steps are executed. The value −1 symbolizes the execution of steps 44 and 45, the value 1 symbolizes the execution of step 48 and the value 0 represents neither the execution of steps 44 and 45 nor of step 48. Interrogation 43 in FIG. 7 corresponds to a binary switch. The combination of interrogations 43 and 60 in FIG. 9 corresponds to a three-point switch. Instead of these two straightforward switch types, it is naturally also feasible to perform complicated switching procedures, such as flowing transitions, which can be performed, e.g., by fuzzy techniques.
LIST OF REFERENCE SYMBOLS


    1 engine
    2 automatic transmission
    3 clutch
    4 shaft
    5 clutch input shaft
    6 clutch output shaft
    7 differential
    8, 9 drive wheels
    10, 11 rotational speed sensors
    12 clutch controller
    20 subtractor
    21 pressure regulator
    22 adapter
    31, 34 filter
    32 negater
    33 regulator
    35 inverse clutch model
    36 adder
    40, 100 start of the sequence
    41, 42, 44, step
    45, 46, 48
    101, 103,
    104
    43, 47, 60 interrogation
    102, 105
    49 end of the sequence
    50, 51 coefficient of friction-slip characteristic curve
    78 temperature model
    79 selector
    81 protection device
    82 minimum value calculator
    83 lubricating oil supply
    84 outer carrier
    85 inner carrier
    86 outer blade
    87 inner blade
    88 restoring spring
    90 multiplier
    93 cylinder
    94 piston
    95 pressure plate
    96 pressure medium supply
    nE rotational speed of the clutch input shaft
    nA rotational speed of the clutch output shaft
    TM information relating to the engine torque
    ΔTM inaccuracy of the information relating to the engine torque
    TR differential torque (regulator output)
    TK clutch torque
    T1 first tolerance value
    T2 second tolerance value
    Δn clutch slip
    Δn* setpoint clutch slip
    i transmission ratio of the transmission
    p application pressure
    p* desired application pressure
    μ, μ1, μ2 coefficient of friction
    J1 moment of inertia of the drive unit on the side of clutch 1, on which the internal combustion engine is arranged.
    Δnmax maximum permissible clutch slip
    Tc constant torque
    Δt time period in which a torque shock causes an increase in slip
    θSL temperature of the steel blades of the clutch
    θSLlim threshold value for the temperature of the steel blades of the clutch
    θOIL Temperature of the hydraulic oil
    AR friction surface of the steel blades of the clutch
    ZR number of friction surfaces of the clutch
    mSL mass of the steel blades of the clutch
    CSL heat capacity of the steel blades of the clutch
    tn present time
    α heat transmission coefficient
    F0 minimum force required for transmitting torque via the clutch
    Ts shock torque
    Toffset no identification

## Claims

1. A method for operating a clutch between an internal combustion engine and at least one driven wheel of a vehicle, comprising:
transmitting a torque between the internal combustion engine and the driven wheel by pressing the clutch together via one of an application force and an application pressure; and
controlling one of the application force and the application pressure as a function of a temperature of the clutch by using a temperature model that is stored in memory and corresponds to a mathematical relationship for calculating the temperature of the clutch, wherein one of the application force and the application pressure is controlled as a function of a difference between a clutch slip and a setpoint clutch slip, when one of the temperature of the clutch, a temperature of a friction surface of the clutch and a temperature of an oil used to one of lubricate and cool the clutch is one of less than and equal to a threshold value.

2. The method according to claim 1, wherein one of the application force and the application pressure is controlled as a function of a temperature of a friction surface of the clutch.

3. The method according to claim 1, wherein one of the application force and the application pressure is controlled as a function of a temperature of an oil used to one of lubricate and cool the clutch.

4. The method according to claim 1, wherein the torque to be transmitted between the internal combustion engine and the driven wheel is increased by a specified value when one of the temperature of the clutch, a temperature of a friction surface of the clutch and a temperature of an oil used to one of lubricate and cool the clutch exceeds a threshold value.

5. The method according to claim 1, wherein one of the application force and the application pressure is controlled as a function of a clutch slip in the clutch, when the torque is transmitted between the internal combustion engine and the driven wheel, and given a setpoint clutch slip, and when one of the temperature of the clutch, a temperature of a friction surface of the clutch and a temperature of an oil used to one of lubricate and cool the clutch is one of less than and equal to a threshold value.

6. A method for operating a clutch between an internal combustion engine and at least one driven wheel of a vehicle, comprising:
transmitting a torque between the internal combustion engine and the driven wheel by pressing the clutch together via one of an application force and an application pressure; and controlling one of the application force and the application pressure as a function of a temperature of the clutch by using a temperature model that is stored in memory and corresponds to a mathematical relationship for calculating the temperature of the clutch, wherein one of the application force and the application pressure is regulated by an inverse clutch model which calculates one of the application force and the application pressure as a function of the torque transmitted via the clutch.

7. A system for operating a clutch between an internal combustion
engine and at least

one driven wheel of a vehicle, comprising:
means for transmitting a torque between the internal combustion engine and the driven wheel by pressing the clutch together via one of an application force and an application pressure; and
a pressure regulator for controlling one of the application force and the application pressure on the basis of a temperature model for calculating a temperature of the clutch by taking into account at least one of a temperature of a friction surface of the clutch and a temperature of an oil used to one of lubricate and cool the clutch, wherein:
the pressure regulator includes a regulator to control one of the application force and the application pressure as a function of a clutch slip in the clutch, when the torque is transmitted between the internal combustion engine and the driven wheel, and a setpoint clutch slip, and
the pressure regulator includes an inverse clutch model to calculate one of the application force and the application pressure as a function of the torque transmitted via the clutch.

8. The device according to claim 7, further comprising:
an arrangement for determining at least one of the temperature of the clutch, the temperature of the friction surface of the clutch and the temperature of the oil used to one of lubricate and cool the clutch.

9. The device according to claim 7, wherein the pressure regulator includes a selector for deciding, as a function of at least one of the temperature of the clutch, a temperature of a friction surface of the clutch and a temperature of an oil used to lubricate the clutch, as to whether one of the application force and the application pressure is determined independently of the clutch slip in the clutch.

10. The device according to claim 7, wherein a coefficient of friction (μ) of the clutch is a parameter of the inverse clutch model.

11. The device according to claim 10, further comprising:
an adapter to adapt the coefficient of friction (μ) of the clutch.