Abstract:
An automatic transmission having an operator control which has at least one manually actuable switching rocker which is arranged on a steering wheel. A sensor senses the actuation of the switching rocker and is connected via a signal path to a transmission control device of the automatic transmission. The switching rocker and the transmission control device are additionally connected to one another via a second signal path which is independent of the signal path.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is based on and hereby claims priority to International Application No. PCT/EP2012/005244 filed on Dec. 19, 2012 and German Application No. 10 2012 005 236.7 filed on Mar. 13, 2012, the contents of which are hereby incorporated by reference. 
     BACKGROUND 
     The invention relates to an automatic transmission having an operator control which has at least one manually actuable switching rocker which is arranged on a steering wheel and which comprises a sensor for sensing the actuation and is connected via a signal path to a transmission control device of the automatic transmission. 
     Nowadays, in vehicles with an automatic transmission the drive position (P, R, N, D, M, S) which is selected by a driver is sensed electronically by a switching signal and is transmitted to the transmission control device via a data bus. This technology is referred to as shift-by-wire. In this context, vehicles with an automatic transmission generally have a steering wheel with at least one switching rocker in order to be able to switch gear stages manually. The switching rockers usually have a microswitch and the transmission of the signal to the transmission control device is not secured. 
     EP 2 101 086 A1 describes an operator control for an automatic transmission in which the selection of drive positions and gearspeeds is carried out by switching rockers on the steering wheel. 
     DE 102 41 014 A1 discloses an automatic transmission having an operator control, in which in the case of manual actuation of an operator control, information is transmitted to an electronic transmission controller via a bus system. 
     DE 100 18 661 A1 proposes an operator control for changing a drive position or gear stage of an automatic transmission, switching information being transmitted via a vehicle-specific bus system here. 
     Conventional automatic transmissions have the disadvantage that for safety reasons actuation of the switching rockers does not permit drive positions to be selected. For example, it would be desirable to change from the drive position or gear stage P, R, N directly to M by actuating a switching rocker, in order to switch on a manual forward movement program. Since such switching processes are categorized as safety-relevant functions, the selection of the drive position cannot be carried out by simple actuation of a switching rocker which is characterized by“+” or “−”. 
     SUMMARY 
     One possible object therefore relates to specifying an automatic transmission having an operator control in which safety-relevant switching processes can be carried out by switching rockers. 
     The inventors propose an automatic transmission having an operator control which has at least one manually actuable switching rocker which is arranged on a steering wheel and which comprises a sensor for sensing the actuation, the sensor being connected via a signal path to a transmission control device of the automatic transmission. The inventors propose that the switching rocker and the transmission control device are additionally connected to one another via a second signal path which is independent of the signal path. 
     The proposal is based on the idea that conventional sensing and transmission of switching rocker signals can be extended with a second detection and transmission process which is independent thereof, with the result that safety-relevant functions can be carried out with the switching rockers. With the proposed automatic transmission it is possible to use the operator control to implement new functions which are prohibited with conventional automatic transmissions for reasons of safety. This includes the selection of drive positions or gear stages by actuating switching rockers on the steering wheel. For example, the gear stage N could be switched on by actuating both switching rockers on the steering wheel. 
     One variant proposes that the switching rocker has two sensors and each sensor is assigned a signal path. In this context, the second signal path can be a discrete signal path and the first, conventional signal path can be a component of a bus system. 
     With the automatic transmission it is preferred that the sensor, or a sensor, is embodied as a microswitch, a digital or analogue Hall sensor, a capacitive sensor, an inductive sensor or as a photoelectric barrier. Insofar as the switching rocker has two sensors, these may also be different sensors, for example a switching rocker can have a microswitch and additionally a capacitive sensor. 
     However, with the automatic transmission a variant is alternatively also possible, in which the switching rocker has a single sensor whose sensor signal is evaluated by two separate evaluation units. 
     The scope also includes the sensor being connected to an input of an evaluation unit via a resistance network. 
     In addition, the inventors propose a motor vehicle. The motor vehicle is defined by the fact that it has an automatic transmission having an operator control of the type described. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other objects and advantages of the present invention will become more apparent and more readily appreciated from the following description of the preferred embodiments, taken in conjunction with the accompanying drawing of which: 
       The drawing shows schematically one embodiment of a proposed automatic transmission having an operator control. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawing, wherein like reference numerals refer to like elements throughout. 
     An automatic transmission  1  is assigned a transmission control device  2 . A multifunction steering wheel  3  comprises a control device  4  which is connected to two switching rockers  5 ,  6 . Each switching rocker  5 ,  6  has two microswitches  7 ,  8  or  12 ,  13 . Switching rockers  5 ,  6  are printed with the symbols “+” and “−”, respectively, and accordingly when the section of the switching rocker  6  which is labeled with “+” is actuated, the switching contact of the microswitches  7  and  8  is closed, and when the section which is printed with “−” is actuated, the switching contact of the microswitches  12  and  13  is closed. The microswitches  7 ,  12  are connected via a resistance network to an analogue input of the control device  4  (evaluation unit) of the multifunction steering wheel  3 , with the result that short circuits to positive or negative, disconnections or shunts can be detected. The control device  4  of the multifunction steering wheel  3  evaluates a switching signal and outputs via a data bus  9  a signal who plausibility is checked. The data bus  9  can have a gateway  10  and is connected to the transmission control device  2 . 
     The pushbutton-key signal of the switching rockers  5 ,  6  is additionally detected by second microswitches  8 ,  13  whose switching point corresponds to that of the microswitches  7 ,  12 . The second microswitches  8 ,  13  are directly and discretely connected via a resistance network and the cable harness  11  of the motor vehicle to the transmission control device  2 . Short circuits to positive and negative, disconnections and shunts from the transmission control device  2  are detected by the resistance network, with the result that the plausibility of the raw signal transmitted via the cable harness  11  can be checked. The cable harness  11  of the motor vehicle therefore corresponds to a second signal path, with the result that switching signals are transmitted both via the data bus  9  and via the cable harness  11 . Accordingly, switching signals of the microswitches  7 ,  12  are transmitted via the first signal path (data bus  9 ), and switching signals of the microswitches  8 ,  13  are transmitted via the second signal path (cable harness  11 ). Making two separate and independent signal paths available provides a redundancy. If the first signal path, i.e. the data bus  9 , is used, the data transmission occurs via the multifunction steering wheel  3 , and if the second signal path is used, the data transmission occurs via discrete lines, specifically the cable harness  11 . 
     As a result of the two evaluation paths data bus  9  and cable harness  11 , two completely independent signals are made available to the transmission control device  2 , the plausibility of which signals can be in turn checked against one another. With this redundancy which is ensured over the entire signal chain it is possible to carry out safety-relevant functions: 
     If detection occurs via both signal paths “+” at the switching rocker  6 , the drive position M is engaged, and this is also possible from the drive positions or gear stages P, R and N. On the other hand, if simultaneous actuation of both switching rockers  5  and  6  is detected via both signal paths, the gear stage N is engaged, provided that one of the drive positions or gear stages P, R, D, S or M was previously engaged. 
     The signal evaluation for the change of a gear can be restricted to the second signal path (cable harness  11 ) since the signals are present significantly more quickly by virtue of the discrete connection to the transmission control device  2 , which connection has low transmission latency. 
     In other embodiments, instead of microswitches for sensing, it is also possible to use other sensors, for example digital or analogue Hall sensors, capacitive sensors, inductive sensors, photoelectric barriers or the like. Instead of two sensors per switching rocker it is possible to use a single sensor whose sensor signal is evaluated on two different paths of two different evaluation units. Instead of a resistance network it is also possible to use respectively a digital input provided in the multifunction steering wheel and/or transmission control device or an analogue input without resistance coding. 
     The invention has been described in detail with particular reference to preferred embodiments thereof and examples, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention covered by the claims which may include the phrase “at least one of A, B and C” as an alternative expression that means one or more of A, B and C may be used, contrary to the holding in Superguide v. DIRECTV, 69 USPQ2d 1865 (Fed. Cir. 2004).