Transmission control module

Abstract: The transmission control module (14) of an automatic transmission (12) includes a shift control module (16) adapted to command a gear or gear range increment or decrement in dependence upon the switching of an enable switch (18) and one of an upshift switch (20) and a downshift switch (22), the switches being provided on the vehicle steering wheel (24). The performance of the engine (10) can thereby be controlled by the driver. The transmission control module (14) can also be operated in an automatic mode, a semi-automatic mode and a manual mode in dependence upon the mode selected by selecting means.

Description: The present invention relates to a transmission control module for a vehicle. Existing automatic transmissions are controlled by a transmission control module, often of electronic type, which selects the appropriate gear from a plurality of gears in dependence upon vehicle operating parameters, which normally include vehicle speed and throttle position. The transmission generally includes a gear lever movable by the driver between a plurality of gear ranges, which for a four gear transmission conventionally includes Reverse, Drive, Third, Second and First. In Drive, the transmission determines which of the four forward gears is appropriate for the engine operating conditions and selects that gear. In Third, the fourth forward gear is disabled so that the highest gear available to the transmission is third, i.e. the available range of gear ratios is first gear to third gear ratio. In Second, the forth and third gears are disabled; thus, the available range of gear ratios is first and second gear ratio; while in First, only the first gear is available for use by the transmission. Disabling the higher gears is useful in situations such as in mountains and the like to prevent one of the higher gears from being selected. However, this arrangement is not convenient in situations where high acceleration is constantly required, for example during cornering and the like. Furthermore, when changing gear range, it is necessary for the driver first to find the position of the gear lever, and then to move the gear lever, which is time consuming and requires the driver to look down to the gear lever, thereby temporarily losing sight of the road. EP-A-365,715 discloses a system in which the gear lever can be moved in one of two shifting lanes, the first providing the conventional functions, and the second allowing the gear lever to be moved forwardly or backwardly to cause the transmission to carry out a gear increment or decrement from the then engaged gear. Although this allows for the possibility of faster acceleration than with the conventional automatic transmission, it is necessary for the gear lever to be disconnected from its original function, that is from its position in the main shifting lane, moved to the second lane, and then moved forwardly or backwardly as necessary. As will be appreciated, there is the possibility that by the time this is done, it may no longer be necessary to change gear. Similarly, if the gear lever is in the second shifting lane, it can take a significant time to move it to the desired position in the first shifting lane. This could, of course, add danger in some situations. DE-A-3337930, which forms the closest prior art according to the preamble of claim 1, discloses a gear selector for a motor vehicle which includes two levers or a set of switches which set the upper and lower limits of the range of gears available for automatic selection by the transmission. The selector includes means by which movement of the levers or depression of the switches is blocked when speed or driving conditions would be made unacceptable. The present invention seeks to provide an improved automatic transmission. According to the present invention there is provided a transmission control module as specified in claim 1. With these arrangements, it is not necessary to disable the gear lever physically, where it is provided, before carrying out the desired gear or gear range increment or decrement, which can therefore be rapid. Furthermore, by having the actuating means fitted to the vehicle steering wheel or steering column, it is not necessary for the driver to remove his grip from the steering wheel to increment or decrement gear ranges. The separation of the gear range increment and decrement facility from the remainder of the transmission control module makes it possible to place the actuating means on the steering wheel or steering column, which is not possible with other arrangements due to their complexity. This arrangement can be used with the gear lever of a conventional automatic transmission, making its incorporation into existing vehicles possible. Preferably, the manually operable actuating means comprises at least one shifting switch operable in predetermined manner in dependence upon the action to be taken by the shift control means. Appropriate control could be provided by coded actuation of a single switch, for example a certain number of depressions of the switch representing a particular command. Advantageously, the manually operable actuating means comprises at least two shifting switches operable in predetermined manner in dependence upon the action to be taken by the shift control means. One of the shifting switches may be operable to effect a gear range increment, and the other shifting switch operable to effect a gear range decrement. This would make the system more driver friendly by avoiding the necessity to have coded switching or the like. The two shifting switches could be located at opposite sides of the steering wheel for use by a respective hand of the driver. In an embodiment, the manually operable actuating means comprises an enabling switch adapted to be actuated to allow operation of the shifting switches. Use of an enabling switch would avoid the possibility of actuating a gear shift by inadvertent actuation of one of the switches. Alternatively, the system could be arranged such that it responds only to a particular actuation of the shifting switches, for example only to a double depression of one of the switches. Each switch of the manually operable actuating means is preferably connected to the transmission control module through a resistance network adapted to cause each switch to produce an individual identifying voltage to the transmission control module on actuation thereof. Advantageously, the switch or switches of the manually operable actuating means are connected to the transmission control module through a common electrical wire. With this arrangement, it is not necessary to have many wires between the steering wheel and the transmission control module. In cases where a horn actuator is fitted to the vehicle steering wheel or steering column, the manually operated actuating means is preferably connected to the transmission control module through the electrical wire of the horn. This saves the need to have any separate wires for the actuating means, and makes it a simple task to incorporate the gear or gear range changing facility in an existing vehicle. For the avoidance of doubt, the term steering wheel is intended to include any other suitable form of vehicle steering device, such as a steering stick. An embodiment of the present invention is described below, by way of illustration only, with reference to the accompanying drawings, in which:- Figure 1 shows an embodiment of transmission control module connected to an engine transmission; Figure 2 shows an embodiment of shift control means forming part of the transmission control module of Figure 1; Figure 3 is a flow chart of an embodiment of routine for use in the transmission control mode of Figure 1; and Figure 4 is a flow chart of an embodiment of increment/decrement routine for use in the transmission control module of Figure 1. Referring to Figure 1, the output shaft of a vehicle engine 10 is shown connected to an automatic transmission unit 12. A transmission control module 14, of computerised type, is connected to the transmission unit 12 and is responsible for controlling the selection of the gears in dependence upon detected engine operating conditions, which may include vehicle speed and throttle position/engine load. This aspect of the transmission control module 14 is well known in the art so will not be described further here. The transmission control module 14 also includes algorithms to ensure that the engine 10 is never run in such a manner that it can be damaged, for example if the engine speed is made to exceed a maximum safe level, as will become apparent below in connection with Figures 3 and 4. It may also include facilities to enable the engine to be run in an "economy" mode to reduce consumption, or in a "sport" mode to increase performance, as is known in the art. Forming part of the transmission control module 14 is a shift control module 16 which in this embodiment comprises three push-button switches 18,20,22 fitted to the vehicle steering wheel 24. Outputs of the switches 18,20,22 are connected to the transmission control module 14 through an output line 26 passing through the steering column 28. A first switch 18, located at the centre of the steering wheel 24, is an enabling switch which enables operation of the other two switches. The other two switches 20,22 are located diametrically opposite one another on the steering wheel 24 and are shifting switches, one being a gear increment, or upshift switch 20 and the other being a gear decrement, or downshift switch 22. Of course, the position of the upshift and downshift switches could be reversed, or other suitable arrangement used. Not shown in Figure 1, is a conventional automatic transmission gear lever which is movable in a shifting lane between Park, Reverse, Neutral, and the gear ranges Drive, Third, Second and First, as is well known in the art. Figure 2 shows an example of circuitry for the gear shifting module 16 for use in controlling the transmission control module 14. Each of the switches 18,20,22 is connected at one terminal to a respective resistance R1,R2,R3, and at the other terminal to an input of the microprocessor 30 of the transmission control module 14 via a pull-up resistor R4. The other terminal of each of the resistors R1,R2,R3 is connected to ground; while the other terminal of the pull-up resistor R4 is connected to a voltage source V s , which may be a reference voltage source already supplied by the transmission control module 14 for other purposes (such as for sensors and the like). Each of the resistors R1,R2,R3 has an individual value which is chosen such that, when the respective switch is closed, one of three distinct voltages appears at node 32 between the relevant resistor R1,R2,R3 and the resistor R4. Node 32 is connected to an input of the microprocessor 30 through an analogue-to-digital converter (not shown), or alternatively through a series of voltage comparators, to provide the microprocessor 30 with an indication of the voltage at node 32, and thereby an indication of which switch 18,20,22 is closed. This arrangement allows for a single wire connecting the switches 18,20,22 to the transmission control module 14, thereby making it simple to fit to the vehicle steering wheel. Although shown as being a separate connection, the ground terminal GND to which the second terminals of the resistors R1,R2,R3 are connected, may be coupled directly to the ground of the transmission control module 14 to avoid any problems of having a floating ground. In cases where a horn switch (not shown) is provided on the steering wheel, the switches 18,20,22 may be connected to the transmission control module 14 through the wire of the horn switch, saving the need to have an additional wire passing through the steering column. Operation of the system could be the same as if a separate connection were provided, as long as the voltage produced on closing of the horn switch (for activation of the horn) is different to those produced by the switches 18,20,22, to distinguish between closure of the horn switch and depression of the switches 18,20,22. Use of the horn wire is particularly advantageous when fitting the system to an existing vehicle. As will be apparent to the skilled person, a possible way of monitoring the state of the shift control circuit of Figure 2 is to have the microprocessor 30 check the voltage at node 32 at regular intervals, such as once every cycle of its control program, for which a sample and hold circuit may be provided. The description of the operation of the system will be based on this implementation. A second possibility is to have the shift control module 16 access an interrupt input to the microprocessor 30 to cause an interrupt when a suitable voltage at node 32 is detected. For example, an interrupt could be produced only when the voltage at node 32 is representative of the enabling switch 18 having been depressed. An interrupt routine could then be carried out to check the voltage at node 32 so as to determine which shifting switch 20,22 is then depressed. Any other suitable arrangement could, of course, be used. The operation of the shift control module 16 of Figure 1 will be described with reference to the embodiment of circuit shown in Figure 2. The shift control module 16 only becomes operative when the gear lever (not shown) of the automatic transmission 12 is placed in the Drive position. This prevents the gear lever and the shift control unit from making conflicting requests to the transmission control module 14. For example, it prevents the shift control module 16 from requesting a gear shift when the gear lever is in the Park position. When the gear lever is in the Drive position, monitoring of the voltage at node 32 is enabled. As long as none of the switches 18,20,22 is depressed, the voltage at node 32 remains high, thereby allowing the transmission control module 14 to continue in the normal Drive mode. On depression of the enabling switch 18 by the driver, the voltage at node 32 changes to the value produced by the voltage divider R4,R1, which is digitised by the analogue-to-digital converter (not shown). The microprocessor interprets the new voltage value as a request to enable upshifting or downshifting upon the subsequent depression of one of the shifting switches 20,22. If the upshift switch 20 is then depressed, the voltage at node 32 changes to the value given by voltage divider R4,R2, thereby producing the individual analogue voltage at node 32 and digitised voltage value at the output of the analogue-to-digital converter. This causes suitable determining means (not shown) in the transmission control module 14 to determine which gear is engaged and to determine therefrom which new gear has been requested by activation of the upshift switch 20. If it is possible to carry out a gear increment, that is if the transmission is not already in the top gear (in this case the fourth gear) and, where such a test is provided, it is determined that the upshift would not cause the engine speed to drop below a predetermined level, the transmission control module 14 carries out an upshift routine to increment a gear in accordance with the request. For example, if second gear is engaged when a valid request is made, the transmission control module 14 causes third gear to be engaged. By depressing the upshift switch 20 additional times, the gears can be incremented further until the highest gear is reached or, where such a test is provided, the engine speed would drop to below an acceptable level. If an upshift request is not allowed by the transmission control module 14, an indication is given to the driver, in the form of a message on a display or an acoustic signal, or in any other suitable form. On depression of the downshift switch 22, the voltage at node 32 changes to the value given by potential divider R4,R3, thereby producing the individual digital value at the output of the analogue-to-digital converter for switch 22, indicating that a downshift from the engaged gear is desired and causing the determining means to determine which gear is engaged and which new gear has been requested. If it is possible to decrement a gear, that is the lowest gear is not already engaged and, where such a test is provided, it is determined that the engine speed for the new desired gear would not exceed a predetermined maximum level, a downshift is carried out. On a further depression of the downshift switch 22, the transmission control module 14 decrements a further gear if such a decrement is allowed. As with the upshift routine described above, if a downshift request is not allowed, an indication is given to the driver. In the above manner, the driver can manually override the automatic transmission and, if desired, change up and down gears by appropriate depression of the switches 18,20,22. The requirement that the enabling switch 18 is depressed each time it is desired to depress one of the shifting switches 20,22 ensures that inadvertent depression of the shifting switches 20,22 does not produce a gear change. When additional security is required, the upshift and downshift routines are only enabled if the appropriate shifting switch 20,22 is depressed within a predetermined time of depression of the enabling switch 18, with timing commencing again each time a shifting switch 20,22 is validly depressed or whenever the enabling switch 18 is depressed. Of course, any other suitable arrangement may be used. Furthermore, if after being enabled by the enabling switch 18, the microprocessor 30 receives an erroneous voltage, for example due to the simultaneous depression of two of the switches 18,20,22, the microprocessor 30 may take some form of remedial action, such as setting the gear range to Fourth (Drive), or to leave the semi-automatic mode, or to take no action in the manual mode. As will be apparent from the above, with this embodiment of the invention, it is not necessary for the driver to know what gear is engaged at the time a request for a gear shift is made, so that any such request can be made in dependence upon the actual requirements the driver has of the engine. According to the invention, the shift control module 16 acts to replace the gear lever once the enabling switch 18 has been depressed. Thus, in this alternative embodiment, a downshift, if allowed, decrements the then active gear range by one. For example, if the gear range active at the time of a valid decrement request is the Drive mode, this is decremented to the Third mode, and so forth. The operation is similar to that of moving the gear lever to one of the other positions provided, although it will be appreciated this will not actually involve the movement of the gear lever itself. Similarly, by depression of the upshift switch 20, the active gear range can be incremented, for example, from First to Second, and then to Third and finally to Drive in dependence upon the number of depressions of the upshift switch 20, assuming, of course, that the requests are allowed. As with the first-described embodiment, the transmission control module 14 will include means for determining the range of gears available for use by the transmission control module 14 and to determine therefrom the new range of gears which has been requested by the actuation of one of the switches 20, 22. For example, when the range of available gears is First, Second and Third and the downshift switch 22 is depressed, the determining means will determine at the time the request is made that the range of available gears is the first three forward gears and that, on acceptance of the request, the range will be reduced to the First and Second gears only. In either of the above described embodiments, the shift control module 16 is immediately disabled if the gear lever is moved from the Drive position to any other position. Thus, if the gear lever is moved to the Neutral or Park position, for example, the shift control module 16 is disabled to prevent the transmission control module 14 from receiving conflicting commands. The features of the above two embodiments can be combined together to enable the transmission to be operated selectively in a manual or a semi-automatic mode or in a conventional automatic mode. In order to allow this facility, a switch (not shown) is provided at a suitable location in the vehicle, such as on the steering wheel 24, to switch the transmission control module 14 into either a manual mode or a semi-automatic mode. An example of routines which provide such a facility are shown in Figures 3 and 4. Referring first to Figure 3, the transmission control module 14 periodically repeats a main routine 100 which is responsible for carrying out automatic control of the transmission together with downshifts in the manual mode. The routine 100 starts at step 102 at which it is determined whether an automatic/manual switch is set in the manual position. If this is the case, the routine passes to step 104 to determine whether a downshift has been requested. If no such request has been made, the routine is left at step 150. However, if a downshift has been requested, then the routine passes to steps 106 to 110 to determine whether the request can be met. At step 106, the routine obtains from memory a LIMIT DOWN value for the requested gear, representative of the maximum allowable vehicle speed in the requested lower gear. At step 108 the actual vehicle speed is measured and compared to the LIMIT DOWN value, and if the vehicle speed is not less than this value the routine is left at step 150. On the other hand, if the measured vehicle speed is less than the LIMIT DOWN value, the routine passes to step 110 at which a gear downshift is carried out. If it is determined that a downshift should not be made, a note of the request is stored in memory for use in subsequent passes through the routine 100 so as to repeat steps 106 and 108 until the downshift is effected. Returning to step 102, if the transmission is not in the manual mode, the routine passes to step 112 at which the vehicle speed is measured and compared to a transmission shift pattern map (of conventional type) stored in memory to determine whether a gear increment is required. If the determination at step 112 is negative, the routine passes to step 114 to determine whether the shift pattern map indicates that there should be a gear decrement. If this is negative, the routine is left via step 104; however, if step 114 indicates that there should be a gear decrement, the routine passes through steps 106 and 108 to step 110 to carry out the required gear decrement. Of course, the values in the shift pattern map will be appropriate for the LIMIT DOWN value so that step 110 can be performed. If it is determined at step 112 that the shift pattern map indicates that a gear increment is appropriate, the routine passes to step 116 to determine whether the selected gear range would allow such an increment. For example, an upshift from third to fourth would not be available if the selected transmission range is Third. If it is possible to carry out a gear increment, then the routine passes to step 118 to effect the increment, otherwise, the routine is left. Referring now to Figure 4, when the increment/decrement facility is activated, such as by depression of the enable switch 18, the transmission control module 14 performs the routine 200. This routine is also carried out when the transmission has been set into the manual mode and a gear increment has been requested. The first step in the routine 200 is step 202 at which it is determined whether an upshift has been requested, such as by depression of the upshift switch 20. If such a request has been made, the routine passes to step 204 to determine if the transmission has been set to the manual mode, in which case the routine passes to step 206 to carry out the gear increment immediately. If the transmission has not been set into the manual mode, the routine passes to step 208 to increment the gear range, for example from the gear range Third to the gear range Drive. On the other hand, if step 202 determines that an upshift has not been requested, the routine passes to step 210 to determine whether a downshift has been requested, such as by depression of the downshift switch 22. In this embodiment, when a downshift request is accepted, both the engaged gear and the gear range are decremented. This ensures that a downshift in gears is effected to provide an increase in acceleration. If no downshift request has been made, the routine passes to step 212 at which the gear range limit is set to fourth gear, that is to Drive, or to any previously set gear range (set, for example, by a previous actuation of one of the upshift or downshift switches 20,22). On the other hand, if step 210 determines that a downshift has been requested, the routine passes to step 214 to determine which gear is engaged and to obtain on the basis of the engaged gear a LIMIT DOWN value representative of the highest allowable vehicle speed for the requested gear. For example, if the transmission is in third gear when the downshift request is made, step 212 finds the maximum vehicle speed allowable in second gear. The actual vehicle speed is measured at step 216 and compared to the LIMIT DOWN value, and if the speed is less than LIMIT DOWN, the routine passes to step 218 to carry out the requested gear downshift. However, if the vehicle speed is not less than the LIMIT DOWN value, the routine passes to step 220 at which a note is made that a downshift has been requested, such as by setting a flag in a suitable register. This note is then used in subsequent passes through the routine 200 so as to repeat steps 214 and 216 until the downshift is made. At step 222, the routine decrements the transmission upshift limit by a gear, in other words carries out a gear range decrement. If it was determined at step 216 that a gear downshift was not allowable and the transmission was then in the highest allowable gear in the active gear range, a gear range downshift is not performed until the vehicle speed satisfies the requirements in a subsequent pass through the routine. However, step 222 will nevertheless prevent any upshift from the engaged gear. As will be apparent from Figures 3 and 4, it is possible to provide a system having a conventional automatic transmission with a manual transmission facility and an increment/decrement facility. In an alternative implementation, a steering column stick is provided instead of the push-button switches 18,20,22 shown in Figure 1. This stick could be used in a similar way to the indicator stick on a vehicle, with the shifting switches positioned at the two ends of travel of the stick and the enable switch located in such a manner that a deliberate movement of the stick is required to cause it to be actuated. By simple modification of the circuit, which will be apparent to the skilled person, the transmission control module 14 could be made to respond to simultaneous actuation of the enable switch 18 and one of the shifting switches 20,22. Of course, it is not necessary to have an enable switch 18. This could be omitted completely, or be replaced by some form of coding for the other two switches 20,22, such as a requirement to depress one of the switches 20,22 twice before a command is interpreted as having been intended. Modification to the above embodiments for use with a continuously variable transmission, or other type of transmission, will be apparent to the skilled person. Furthermore, a display may be provided for indicating information such as which gear and/or gear range is engaged, which gear and/or gear range has been requested and whether such a request has been accepted.

Claims: A transmission control module (14) for controlling the operation of a transmission (12) of a vehicle in dependence upon engine operating conditions, which transmission includes a plurality of gear ratios which are individually selectable in dependence upon engine operating conditions, the transmission control module (14) including shift control means (16) operative to set an available range of gear ratios from the plurality of gear ratios and to select a gear ratio automatically according to engine operating conditions from the available range of gear ratios; characterised in that the transmission control module (14) includes determining means for determining the available range of gear ratios, in that the shift control means (16) includes one or more manually operable increment and/or decrement switches (18,20,22) adapted to be fitted to the vehicle steering wheel (24) or steering column (28), and in that the shift control means (16) is operative to command an increment or decrement of the available range of gear ratios on actuation of the manually operable switch or switches (18,20,22) and to ignore a command to increment or decrement the available range of gear ratios as long as such command is likely to cause the engine (10) to operate at a speed above a predetermined maximum speed and/or below a predetermined minimum speed. A transmission control module (14) according to claim 1, wherein the shift control means (16) is operative to command a gear ratio downshift when the switch or switches (18,20,22) are actuated to decrement the available range of gear ratios. A transmission control module (14) according to claim 2, wherein prior to a gear ratio downshift the shift control means (14) is operative to determine the vehicle speed at the gear ratio to be engaged by the downshift and to inhibit the gear ratio downshift if said vehicle speed exceeds a predetermined limit. A transmission control module (14) according to claim 3, wherein the shift control means (16) is operative to determine said vehicle speed periodically and to command the gear ratio downshift when said vehicle speed does not exceed the predetermined limit. A transmission control module (14) according to any preceding claim, wherein the manually operable switch or switches (18,20,22) comprise a first shifting switch (20) operable to increment the available range of gear ratios, and a second shifting switch (22) operable to decrement the available range of gear ratios. A transmission control module (14) according to claim 5, comprising an enabling switch (18) for enabling the shifting switches (20,22). A transmission control module (14) according to claim 5 or 6, wherein each switch (18,20,22) is connected to the transmission control module (14) through a resistance network (R1-R4) adapted to cause each switch to produce an individual identifying voltage to the transmission control module (14) on actuation thereof. A transmission control module (14) according to any preceding claim, wherein the switch or switches (18,20,22) are in the form of one or more push-button switches (18,20,22) adapted to be fitted to the vehicle steering wheel (24). A transmission control module (14) according to any preceding claim, wherein the switch or switches (18,20,22) are connected to the transmission control module (14) through a common electrical wire. A transmission control module (14) according to any preceding claim, wherein, where a horn actuator is fitted to the vehicle steering wheel or steering column, the switch or switches are connected to the transmission control module through the electrical wire of the horn. A transmission control module (14) according to any preceding claim, wherein the transmission control module (14) is adapted to disable the shift control mean (16) when a gear lever of the vehicle is in other than the drive mode. A transmission control module (14) according to any preceding claim, wherein the manually operable switch or switches (18,20,22) are actuated by a steering column stick. A transmission control module (14) according to claim 1 or 2, comprising an automatic mode in which a gear ratio from a plurality of gear ratios is selected automatically in dependence upon engine operating conditions, a semi-automatic mode in which an available range of the plurality of gear ratios is set and in which the available range of gear ratios can be incremented or decremented on the basis of an operator input and a manual mode in which the selection of gear ratios is determined by operator input; the shift control means (16) comprising selecting means (18) for selecting between the automatic mode, the semi-automatic mode and the manual mode and being adapted to select a gear ratio from the plurality of gear ratios when the transmission control module (14) is in the automatic mode, to increment and decrement the available range of gear ratios on the basis of operator input when the transmission control module (14) is in the semi-automatic mode and to increment and decrement gear ratios on the basis of operator input when the transmission control module (14) is in the manual mode.

Inventors: GRANGE JEAN PAUL, GRANGE, JEAN PAUL
Applicants: ACG FRANCE
Application year: 1992
Main classification: B60K20
IPC codes: F16H61, F16H59, B60K20