Abstract:
A method for influencing a shift process connected with a change in transmission ratio when driving a motor vehicle that has a set of driven wheels subject to longitudinal and transverse forces, the method including detecting whether or not the vehicle is traveling around a curve and, if doing so when the shift process is in progress, influencing the shift process so as to decrease the longitudinal forces that act on the driven wheels as a result of the shift process. Also disclosed is an apparatus for performing the disclosed method including a detector for detecting whether or not the vehicle is traveling around a curve and a transmission ratio shifter responsive to the detector that, if the vehicle is traveling around a curve when the shift process is in progress, performs the shift process so as to decrease the longitudinal forces that act on the driven wheels as a result of the shift process.

Description:
BACKGROUND 
     1. Field of the Invention 
     The invention relates to a method for influencing a shift process connected with a change in transmission ratio when driving a motor vehicle. 
     2. Description of Related Art 
     It is known to control automatic transmissions so that up-shifting into a higher gear is prevented when traveling around a curve. The purpose is that a driver who, for example, lets upon on the accelerator immediately before a curve or in a curve and depresses the accelerator again after leaving the curve will have the same amount of torque available after the curve as when entering the curve. It is thus intended that a driver who for example lets up on the accelerator immediately before a curve or in a curve, after travelling past the curve when pushing down on the accelerator again has the same power and performance as when driving into the curve. During normal shift programs, letting up on the accelerator would lead to the transmission shifting into a higher gear and on leaving the curve there would be insufficient acceleration power or the transmissions would only shift back to a lower bear before renewed acceleration. 
     It is known from DE 196 18 804 to develop a method where shifts are suppressed in curves to the extent that in addition the type of driver is determined and the type of shift suppression is influenced. 
     In many cases, for example when travelling around very long curves or in the case of vehicles with manual shift transmissions it is neither desirable nor possible to fully suppress gear changes when travelling around curves. In these cases it is however desirable in order to let the shifting process take place in a manner that is adapted to the momentary conditions of a curved course of travel. 
     Accordingly the invention is concerned with the problem of providing a method for influencing a shift process connected to a change in transmission ratio when driving a motor vehicle which also leads when driving round curves to comfortable shifting which does not impair driving safety. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a method for influencing a shift process connected to a change in transmission ratio when driving a motor vehicle that results in comfortable shifting when driving around curves and does not impair driving performance or safety. 
     It is a further object of the present invention to provide an apparatus capable of performing the above described process. 
     The present invention influences the shift process that occurs during a change in transmission ratio when a motor vehicle follows a curved path, such as a curve in the road. This allows the driving character of the vehicle during the shift process to be altered as desired, such as the performance of the vehicle or maintaining adequate safety and control over the vehicle. 
     Preliminarily, the state of the vehicle in a curved path must be detected. This may be accomplished by detecting one or more characteristics of the vehicle that indicate the vehicle is driving in a curved path. Various characteristics, by way of example, may include the transverse force exerted on the drive wheels of the vehicle, the transverse acceleration of the vehicle, the steering angle, difference in speed between wheels on an axle, operating condition of vehicle systems, and the navigational position of the car. In addition, the measured characteristics may be compared against predetermined values or using algorithms to determine amount of actual or desired curvature of the vehicle path. 
     Once it is detected that the vehicle is traveling on a curved path, which may include the degree, the shift process during a transmission ratio change may be influenced in a predetermined way. The result of this influence may be, for example, to decrease the longitudinal forces that act on the driven wheels, increasing comfort, safety or performance. Ways to influence the shift process may include, by way of example, altering the rate of ratio change or clutch engagement, or modifying the activation of various running modes. 
     According to the present invention, an apparatus is provided for accomplishing the processes of the invention. The apparatus can include a detector for detecting whether the vehicle is traveling around a curve, and a transmission ratio shifter that is responsive to the detector and influences the shift process. The detector may be capable of detecting one or more characteristics of the vehicle that indicate that the vehicle is driving in a curved path. Examples of such detectors may include sensors to detect forces exerted on the driven wheels, vehicle acceleration, wheel speeds, steering angle, vehicle system operating parameters and navigational position of the car. The apparatus may also evaluate the vehicle characteristics, to which the transmission ratio shifter may respond in predetermined ways. The transmission ratio shifter, for example, may alter the rate of ratio change or clutch engagement, or modify the activation of various running modes. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other than objects and features of the present invention will be described hereinafter in detail by way of certain preferred embodiments with reference to the accompanying drawings in which: 
     FIG. 1 is a schematic plan view of a motor vehicle in which a method according to an embodiment of the present invention may be utilized; 
     FIG. 2 s a schematic flow chart of a method according to an embodiment of the present invention; 
     FIG. 3 is a schematic chart of a method according to an embodiment of the present invention; 
     FIG. 4 is a diagrammatic illustration of an apparatus according to an embodiment of the present invention; and 
     FIG. 5 is a diagrammatic illustration of an apparatus according to an embodiment of the present invention. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     According to FIG. 1 a motor vehicle has an engine  2  connected to a gearbox  6 . A drive shaft  8  leads from the gearbox  6  through a differential  10  to the rear wheels  12 . 
     In the illustrated embodiment the gearbox  6  is a manual shift transmission which can be operated by a gear shift lever  14 . The clutch  4  is automated and is operated by a control device  16  to which in known way for example the throttle valve position or the position of an accelerator pedal  18  and through a gearbox sensor  20  the position of a shift member in the gearbox and a shift intent are supplied as input signals. 
     The construction and method of functioning of the units described up until now are known per se and are used in vehicles having automated clutches where the shift lever  14  is indeed still activated by hand but where the clutch pedal is omitted because the clutch  4  is operated automatically. 
     According to the basic laws of physics only a limited force can be transmitted between a road and a wheel without the traction friction changing into sliding friction which is dangerous for driving safety. Accordingly the force which can be transmitted in the longitudinal direction of the vehicle is greater the smaller the force which is to be transmitted in the transverse direction of the vehicle. When shifting gears in certain circumstances on engagement of the clutch, when the engine is suddenly braked when changing into a higher gear or is suddenly accelerated when changing into a lower gear, the result is forces which are too high acting in the longitudinal direction of the vehicle and which reach the limit of the forces which can be transmitted. When the vehicle is additionally travelling round a curve and lateral forces have to be transmitted by the driven wheels, during clutch engagement the entire force which can be safely transmitted can be exceeded so that the vehicle breaks away or skids which is extremely negative regarding driving safety. 
     According to the invention the vehicle described up until now maybe provided with a facility which makes it possible to detect when the vehicle is travelling around a curve and to control the operation of the clutch accordingly. To this end different sensors are provided individually or in combination and which can detect the state of travelling around a curve. By way of example wheel sensors  24  are provided on the non-driven front wheels  22  to determine the wheel speeds and these wheel sensors can supply at the same time signals for an anti-locking braking system. Furthermore a steering angle sensor  26  can be provided which detects the position of a track rod  28  connected to the front wheels  22 , and thus the steering angle. Furthermore or in addition a servo sensor  30  can be provided with which the operation of a servo system assisting steering is detected. In addition a transverse acceleration sensor  32  can be provided. 
     The sensors present in the vehicle are connected to the control device  16  in which algorithms are stored in the program memory to calculate from the determined input signals a value which describes the relevant state of travelling around a curve at that time. 
     There are various evaluating algorithms which can be used to determine a characteristic value for travelling around a curve. 
     By way of example the steering angle can be detected by means of the steering angle sensor  26  and exceeding a certain steering angle can be used alone as a characteristic of travelling around a curve. 
     Alternatively the steering angle can be detected and together with the vehicle speed and the fixed vehicle geometry a transverse acceleration can be calculated. 
     Alternatively the energy input of a servo pump or an electric servo motor can be detected by the servo sensor  30  and used as a characteristic for travelling around a curve. 
     If only the wheel sensors are present then the steering angle can be concluded from the differential speed of the wheels of one axle. The mean value of the wheel speeds is a measure of the vehicle speed so that the transverse acceleration can be calculated. 
     Again as an alternative or in addition the transverse acceleration can be used as a characteristic for the travel around a curve, the state of travelling around a curve being detected by the transverse acceleration sensor  32 . 
     FIG. 2 shows a flow chart for explaining one example of implementing the invention. 
     It is assumed that at stage  40  a new gear has been engaged by the gearshift lever  14 . Prior to stage  40  the clutch  4  was opened by controlling the control device  16  so that at stage  40  the driven wheels are free of forward drive or, if the vehicle brake is not activated, are free of deceleration forces. 
     As a new gear is engaged, which is detected by the gearbox sensor  20 , the signal of for example the steering angle sensor  26  is evaluated in the control device  16  in stage  42  so that in stage  44  it can be established whether the vehicle is or is not travelling around a curve. If no state of travelling around a curve is diagnosed then in stage  46  the clutch  4  is engaged according to the usual engagement process, this engagement process being optimized with regard to rapid shift, gear change comfort and energy consumption for shifting. 
     If in stage  44  it is established that the vehicle is travelling around a curve, then in the control device  16  a program is activated for a slow engagement which becomes active in stage  48  in order to close the clutch  4  after shifting into the new gear. This slower engagement, when changing into a lower gear, takes place by engaging the engine and through the enforced increases in revs or, when changing into a higher gear, by reductions in revs. Thus, no sudden high forces in the longitudinal direction of the vehicle appear at the driven rear wheels  12  which could lead to the lateral forces which can be transmitted being exceeded and the vehicle skidding. 
     It is evident that the method described can be modified and refined in many respects. By way of example the engagement program which is activated when the state of travelling around a curve is determined can be slowed down proportional to the transverse acceleration determined. 
     In a more expensive embodiment, the longitudinal forces transmitted by the driven rear wheels  12  to the road can be determined for example by means of an acceleration sensor active in the longitudinal direction of the vehicle and the engagement process can be controlled so that the sum of the longitudinal forces and transverse forces does not exceed a certain amount. 
     The invention can be used not only for automated clutches used in conjunction with manual shift transmissions. It can likewise be used when the shift transmission  6  is automated for example with gear changes proceeding according to predetermined programs. It is possible depending on the relevant program also to change gear within a curve and in this case the algorithms stored in the control device  16  ensure that the engagement of the clutch  4  takes place so smoothly after a gear change that there is no danger of the vehicle skidding sideways. 
     Both in the case of automated shift transmissions and manual shift transmissions the control device  16  can, in addition to adapting the operation of the clutch to travelling around a curve, also control the engine itself for a limited period of time so that inadmissible accelerations or brakings are suppressed. A throttle valve or other power adjustment member of the engine is then not activated directly by the accelerator pedal  18  but instead the accelerator pedal  18  operates through a servo motor through a control device for adjusting a power adjustment member of the engine. 
     The gearbox  6  can also be a CVT gearbox, the operation of which is controlled when travelling around a curve so that predetermined acceleration and deceleration forces at the wheel surfaces are not exceeded. When driving in a straight line, the CVT gearbox changes for example its transmission ratio very rapidly according to requirements (when pressing down the accelerator, for example for overtaking, it switches very rapidly to a shorter (lower) transmission ratio or when letting up the accelerator switches to a longer (higher) transmission ratio). In contrast this change in transmission ratio takes place correspondingly more slowly when travelling around a curve. 
     The clutch  4  can in a modified embodiment also be a torque converter with integrated lock-up clutch. The converter characteristic and/or actuation of the lock-up clutch can be handled by the control device  16  in dependence on the curve. 
     In an alternative embodiment of the invention, see FIG. 3, if an emergency operation program has to be activated, and this takes place when travelling around a curve, this emergency operation program is activated with delay so that again high circumferential forces or longitudinal forces acting at the drive wheels are avoided. When changing over a control strategy program from a normal operating mode of the vehicle to a replacement strategy or emergency operation program relatively large gradients of the circumferential forces from the tires or axles of a vehicle can appear. This can be disadvantageous when changing over into an emergency operation program. Therefore it can also be advantageous if when changing into an emergency running operation the steering angle or the relevant angle included between the wheel and the longitudinal axis of the vehicle is detected and the change-over is delayed or even prevented when the state of travelling around a curve is detected. 
     FIG. 3 shows in block  100  the call-up of the control strategy according to the invention which undertakes in block  102  an evaluation of the steering angle, for example by means of a steering angle sensor. If the steering angle is within a predeterminable area outside of a central position, then in block  104  it concludes the state of travelling around a curve. If this is the case, then in block  108  the activation of an emergency running operation is delayed or prevented for a predeterminable amount of time. This prevention exists until following the inquiry in block  104 , the state of travelling around a curve no longer exists and the emergency running operation is activated in block  106 . With a delay in activating the emergency running operation, at the end of the waiting time the program is switched into emergency mode even if the state of travelling around a curve still exists. At block  110  the routine is first terminated and recalled again in the next control cycle at  100 . p In order to make an evaluation of the steering angle signal it is preferable to use for example the direct evaluation of a sensor signal of the steering angle sensor which on exceeding a predeterminable threshold value is a clear indication of the state of travelling around a curve. The threshold value can vary for example with the vehicle speed and/or the throttle valve angle and/or the gear engaged in the gearbox. Likewise filtering of the steering angle signal can take place so that a temporary change in the steering angle signal does not lead to drastic effects. Furthermore it is possible by means of a computer program to calculate from the steering angle signal and where applicable other signals, such as for example wheel speeds, the angular speed of the vehicle about its vertical axis (yaw rate). From reaching a predeterminable variable threshold value of the yaw rate the state of travelling around a curve can be concluded. 
     In a method for influencing a shift process connected with a change in transmission ratio when driving a motor vehicle, the state of travelling around a curve is detected and the shift process occurring while travelling around a curve is influenced so that the longitudinal forces which are active at the driven wheels as a result of a down shift. 
     FIG. 4 shows a vehicle  201  with a drive unit  202 , such as an internal combustion engine or hybrid drive assembly with an internal combustion engine and with an electric motor, a torque transfer system, such as a clutch  203  and a gearbox  204  wherein on the output side of the gearbox is a drive shaft  205  which drives by means of a differential  206  two drive shafts  207   a  and  207   b  which in turn drive the driven wheels  208   a  and  208   b.  The torque transfer system  203  is shown as a friction clutch with a flywheel  209 , a pressure plate  210 , a clutch disc  211 , a release bearing  212  and a disengagement fork  213 . The disengagement fork is biased by means of an actuator  215  through a master cylinder  216 , a pressurised medium line, such as a hydraulic line  217 , and a slave cylinder  218 . The actuator is shown as an actuator operated by pressurised medium which has an electric motor  219  which operates a master cylinder piston  220  through a gearbox. The torque transfer system can be engaged and disengaged through the pressurised medium line  217  and the slave cylinder  218 . Furthermore the actuator  215  includes the electronics for its operation and control, that is both the power electronics and control electronics. The actuator is provided with a valve  221 , e.g., a closeable opening for fluid exchange of a hydraulic system which is connected to a reservoir  222  for the pressurised medium. 
     The vehicle  201  with the gearbox  204  has a gear shift lever  230  on which is mounted a gear detection sensor  231  and a shift intent sensor  232  which detects a shift intent of the driver from the movement of the gearshift lever or from the applied force. Furthermore the vehicle is fitted with a speed sensor  233  which detects the speed of the gear output shaft and the wheel speeds respectively. Furthermore a throttle valve position sensor  234  is mounted which detects the throttle valve position and a rotation sensor  235  which detects the engine speed. 
     The gear detection sensor detects the position of shift elements inside the gearbox or the gear engaged in the gearbox so that at least the engaged gear is registered by the control unit by means of a signal from the sensor. Furthermore with an analog sensor the movement of the shift elements inside the gearbox can be detected so that it is possible to make an early detection of the next gear to be engaged. 
     The actuator  215  is powered from a battery  240 . Furthermore the vehicle has an (preferable multi-stage) ignition switch  241  which is operated preferable by means of an ignition key whereby the starter of the combustion engine  202  is operated through the lead  242 . A signal is forwarded through the lead  243  to the electronics unit of the actuator  215  after which the actuator is activated for example on operating the ignition. 
     FIG. 5 shows a diagrammatic view of a drive train of a motor vehicle with a drive unit  601 , such as an internal combustion engine or motor, a torque transfer system  602 , such as for example a friction clutch, a dry friction clutch or a wet-running friction clutch, a gearbox  603  as well as a differential  604 , output shafts  605  and wheels  606  driven by the output shafts. Speed sensors (not shown) can be mounted on the wheels to detect the speeds of the wheels. The speed sensors can also belong functionally to other electronics units, such as for example an anti-lock braking system (ABS). The drive unit  601  can also be a hybrid drive with for example an electric motor, a flywheel with freewheel and an internal combustion engine. 
     The torque transfer system  602  is formed as a friction clutch but can also be designed for example as a magnetic powder clutch, multi-plate clutch or torque converter with converter lock-up clutch or another type of clutch. Furthermore a control unit  607  is shown as well as an actuator  608  (shown diagrammatically). The friction clutch can also be formed as a self-adjusting clutch adjusting to wear. 
     The torque transfer system  602  is mounted on a flywheel  602   a  or is connected to the flywheel which can be a divided flywheel with a primary mass and a secondary mass, and with a damping device between the primary mass and secondary mass on which a starting gear ring  602   b  is mounted. The torque transfer system has overall a clutch disc  602   c  with friction linings and a pressure plate  602   d  as well as a clutch cover  602   e  and a plate spring  602   f.  The clutch is preferably self-adjusting and has in addition means which allow displacement and wear adjustment. A sensor, such as a force or displacement sensor is provided which detects a situation in which an adjustment is necessary and in the event of detection the adjustment is carried out. 
     The torque transfer system is operated by means of a release member  609  such as for example a pressurised medium operated, such as hydraulic, central release member which can support a release bearing  610 . The clutch can be engaged and disengaged by application of a force. The release member can however also be formed as a mechanical release member which operates, biases or governs a release bearing or comparable element. 
     The actuator  608  controls via a mechanical connection or a pressurised medium line  611  or a transfer section, such as a hydraulic pipe, the mechanical or hydraulic release member or central release member  609  for engaging or releasing the clutch. The actuator  608  furthermore operates with one or several output elements the gearbox for shifting gear. For example a central selector shaft of the gearbox is operated by the output element or the output elements. The actuator thus operates shift elements inside the gearbox to engage, release or change gear stages or transmission ratio stages, such as a central selector shaft or shift rods or other shift elements. 
     The actuator  608  can also be formed or provided as a shift control cylinder which is mounted inside the gearbox. By being rotated about its own axis, the shift control cylinder moves elements that are guided by guides, e.g., shifter elements, and thereby performs the shift between gear stages. Furthermore the actuator for shifting the gear stages can also contain the actuator for operating the torque transfer system. In this case an active connection with the clutch release member is required. 
     The control unit  607  is connected through the signal connection  612  to the actuator so that control signals and/or sensor signals or operating state signals can be exchanged, forwarded or retrieved. Furthermore signal connection  613  and  614  are provided through which the control unit is in signal connection at least at times with further sensors or electronics units. Other electronics units of this kind can be for example the engine electronics, anti-lock braking system electronics or anti-slip regulating electronics. Further sensors can be sensors which generally characterise or detect the operating state of the vehicle, such as for example rotation speed sensors of the engine or of the wheels, throttle valve position sensors, accelerator pedal position sensors or other sensors. The signal connection  615  produces a connection to a data bus such as for example a CAN bus through which system data of the vehicle or other electronics can be made available since the electronics units are as a rule cross-linked with each other through computer units. 
     An automated gearbox can be shifted or a gear change can be performed in a driver-initiated mode where the driver, for example, by means of a selector switch, introduces a signal to shift up or down. Furthermore a signal can also be provided by means of an electronic shift lever to indicate into which gear the gearbox is to be shifted. An automated gearbox can however also carry out a gear change independently by means of for example characteristic values, characteristic lines or characteristic fields and on the basis of sensor signals at certain predetermined points, without the driver having to initiate a gear change. 
     The vehicle is preferably fitted with an electronic accelerator pedal  623  (or load lever). The accelerator pedal  623  governs a sensor  624  by means of which the engine electronics  620  control or regulate for example the fuel supply, ignition timing, injection time or throttle valve position through the signal lead  621  of the engine  601 . The electronic accelerator pedal  623  with sensor  624  is in signal connection with the engine electronics  620  through the signal lead  625 . The engine electronics  620  is in signal connection with the control unit  607  through the signal lead  622 . Furthermore gear control electronics  630  can also be in signal connection with the units  607  and  620 . An electromotorized throttle valve control is practical for this with the position of the throttle valve being governed by the engine electronics. With systems of this kind a direct mechanical connection with the accelerator pedal is no longer necessary or practical. 
     The typical friction losses of gearbox components and/or input speeds and/or output speeds of the gearbox can be used in order to determine or calculate for example a gearbox temperature, such as for example gearbox fluid temperature or a temperature of a gearbox element. Furthermore the amounts of fluid and fluid flows can be taken into account. The gearbox temperature designation need not however be restricted to the overrun time, but can also be carried out in other operating situations. 
     The current supply of the control unit of an automated gearbox and/or an automated torque transfer system can be maintained for example in order to implement specific operating functions according to one operating mode of the vehicle, such as for example if when determining temperature or calculating temperature for example by means of temperature models a critical state is detected, such as for example of the clutch, gearbox or synchronizing device or if for example adaptations are active or data are detected or stored such as for example a store of data or adapted values in an EEPROM. Further adaptations of system values of an electric motor, gearbox or of a pressurised medium system, such as hydraulic system can be carried out. Likewise adjustments in the gearbox or on the clutch (for example when the vehicle stopping device is operated) can be demanded or be required to determine friction forces (sliding and adhesive friction forces or friction values) and characteristic values of the actuator (e.g. engine constant, e.g. armature resistance or time constants in the case of the electric motor). Furthermore hydraulic values or other values, such as characteristic lines of valves or other values can be adjusted. 
     While the present invention has been particularly shown and described with reference to certain embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention. 
     The invention is also not restricted to the embodiments of the description. Rather numerous amendments and modifications are possible within the scope of the invention, particularly those variations, elements and combinations and/or materials which are inventive for example through combination or modification of individual features or elements or process steps contained in the drawings and described in connection with the general description and embodiments and claims and which through combinable features lead, to a new subject or to new process steps or sequence of process steps insofar as these refer to manufacturing, test and work processes.