Safety system for an automatic transmission

• US 6,397,138 B1
• Filed: 06/09/1999
• Issued: 05/28/2002
• Est. Priority Date: 12/17/1996
• Status: Expired due to Fees

• Current Assignee: ZF Friedrichshafen AG (Zeppelin - Stiftung der Stadt Friedrichshafen)
• Original Assignee: ZF Friedrichshafen AG (Zeppelin - Stiftung der Stadt Friedrichshafen)
• Inventors: Sigg, Peter
• Primary Examiner(s): Louis-Jacques, Jacques H.
• Assistant Examiner(s): Broadhead, Brian J
• Application Number:
  US09/319,613
• Time in Patent Office: 1,084 Days
• Field of Search: 701/61,62,66 477/109,115,116,125,110,117
• US Class Current: 701/61
• CPC Class Codes: F16H 35/10 Arrangements or devices for absorbing overload or preventing damage by overload for screw mechanisms F16H25/2021
• CPC Class Codes: F16H 59/70 dependent on the ratio established
• CPC Class Codes: F16H 61/0213 characterised by the method for generating shift signals
• CPC Class Codes: F16H 61/10 Controlling shift hysteresis
• CPC Class Codes: F16H 61/16 Inhibiting or initiating shift during unfavourable conditions, e.g. preventing forward reverse shift at high vehicle speed, preventing engine over speed unintentional control input F16H61/18

Abstract

For an automatic transmission (2), a safety system is proposed in which a virtual reduction ratio is calculated when a driver moves the selector lever from a drive position to neutral and then from neutral back to a drive position. The virtual reduction ratio is then compared with the reduction ratio resulting from a shift characteristic field. In case of divergence, the virtual reduction ratio is assigned to a characteristic field having a linearly constant reduction ratio surrounded by a reduction ratio range. The electronic control unit (5) selects as a set reduction ratio, the one containing in its range the virtual reduction ratio.

Claims

1. A safety system for an electrohydraulically controlled automatic transmission (2) driven by an internal combustion engine (1), said safety system comprising:

an electronic control unit (5) for determining a reduction ratio (i(K), K=1 . . .

     5) via a shift characteristic field (i(K)=f (DKI, nAB)), with said reduction ratio depending on a throttle valve position (DKI) and a transmission output speed (nAB), and each of said characteristic fields having a line of constant reduction ratio included within a reduction ratio range (B(K), K=1 . . .

     5);

a selector lever (21) coupled to the automatic transmission (2) for facilitating control of said automatic transmission (2) during use by a driver;

said electronic control unit (5) including a mechanism for determining, while driving (nAB>

limit value), whether a first change of said selector lever (21) occurs, from a forward driving position to a neutral position, and whether the first change is followed by a second change of the selector lever (21) from the neutral position to the forward driving position;

said electronic control unit (5) includes means for deriving, upon detection of the first change and said selector lever (21) being moved to the neutral position, a virtual reduction ratio (iV) from a transmission input speed (nT) and the transmission output speed (nAB), and said electronic control unit, upon detection of the second change, including means for determining a set reduction ratio (iSOLL) with the set reduction ratio (iSOLL) containing the virtual reduction ratio (iV);

when the virtual reduction ratio (iV) is between first and second reduction ratio ranges, said electronic control unit (5) including means for determining a first difference (DIFF) of the virtual reduction ratio (iV) and the first reduction ratio range and a second difference (DIFF) of the virtual reduction ratio (iV) and the second reduction ratio range; and

said electronic control unit (5) including means for selecting the set reduction ratio (iSOLL) based upon a lesser of the first difference (DIFF) and the second difference (DIFF).

2. The safety system according to claim 1, wherein the electronic control unit includes means for selecting the set reduction ratio (iSOLL) only once the virtual reduction ratio (iV) is outside a hysteresis band overlapping the first and the second reduction ratio ranges (B(K)).

3. The safety system according to claim 1, wherein the safety system, upon detection of said selector lever (21) being in the neutral position and the first change, includes means for forecasting a further curve of the virtual reduction ratio (iV).

4. The safety system according to claim 3, wherein the safety system includes means for:

ascertaining the transmission input speed (nT) from a first moment (t1) and a second moment (t2);

determining a gradient (GRAD) of the transmission input speed (GRAD=(nT(t1)−

nT(t2)/(t1−

t2));

calculating (nT(t3)=nT(t1)−

GRAD(t3−

t1)), from the gradient (GRAD) and the transmission input speed at the first moment (nT(t1)), a transmission input speed to be expected at a third moment (t3); and

forecasting the virtual reduction ratio (iV) at the third moment (iV=nT(t3/nAB).

5. The safety system according to claim 4, wherein the safety system includes means for identifying the third moment (t3) upon said electronic control unit (5) determining that the second change has occurred, and a signal transit time resulting from a temporary deceleration between an output command of said electronic control unit (5) and the reduction ratio (i(K)).

6. A method for electrohydraulically controlling an automatic transmission (2) driven by an internal combustion engine (1), the method comprising the steps of:

determining, via an electronic control unit (5), a reduction ratio (i(K), K=1 . . .

     5) via a shift characteristic field (i(K)=f (DKI, nAB)), with said reduction ratio depending on a throttle valve position (DKI) and a transmission output speed (nAB), and each of said characteristic fields having a line of constant reduction ratio included within a reduction ratio range (B(K), K=1 . . .

     5);

coupling a selector lever (21) to the automatic transmission (2) for facilitating control of said automatic transmission (2) during use by a driver;

determining, via said electronic control unit (5), while driving (nAB>

limit value), whether a first change of said selector lever (21) occurs, from a forward driving position to a neutral position, and whether the first change is followed by a second change of the selector lever (21) from the neutral position to the forward driving position;

deriving, via said electronic control unit (5), upon detection of the first change and said selector lever (21) being moved to the neutral position, a virtual reduction ratio (iV) from a transmission input speed (nT) and the transmission output speed (nAB), and said electronic control unit, upon detection of the second change, determining a set reduction ratio (iSOLL) with the set reduction ratio (iSOLL) containing the virtual reduction ratio (iV);

when the virtual reduction ratio (iV) is between first and second reduction ratio ranges, determining via said electronic control unit (5) a first difference (DIFF) of the virtual reduction ratio (iV) and the first reduction ratio range and a second difference (DIFF) of the virtual reduction ratio (iV) and the second reduction ratio range; and

selecting, via electronic control unit (5), the set reduction ratio (iSOLL) based upon a lesser of the first difference (DIFF) and the second difference (DIFF).

7. The method according to claim 6, further comprising the step of selecting the set reduction ratio (iSOLL) only once the virtual reduction ratio (iV) is outside a hysteresis band between the first and the second reduction ratio ranges (B(K)).

8. The method according to claim 6, further comprising the step of forecasting a further curve of the virtual reduction ratio (iV) upon detection of the first change and the selector lever (21) being in the neutral position.

9. The method according to claim 6, further comprising the steps of:

ascertaining the transmission input speed (nT) from a first moment (t1) and a second moment(t2);

determining a gradient (GRAD) of the transmission input speed (GRAD=(nT(t1)−

nT(t2)/(t1−

t2));

calculating a transmission input speed expected at a third moment (t3), from the gradient (GRAD) and the transmission input speed at the first moment, using the formula (nT(t1)), (nT(t3)=nT(t1)−

GRAD(t3−

t1)); and

forecasting the virtual reduction ratio (iV) at the third moment (iV=nT(t3/nAB).

10. The method according to claim 9, further comprising the step of determining the third moment (t3) from the moment at which the second change is detected by said electronic control unit (5), and a signal transit time resulting from a temporary deceleration between an output command of said electronic control unit (5) and the reduction ratio (i(K)).