METHOD AND APPARATUS FOR CONTROLLING AN AUTOMATIC GEARBOX

Abstract: A process and an arrangement for control of an automated gearbox is distinguished: in that possible gear combinations for the driving are determined; that the operating points for the gear combination are determined; that the specific fuel consumption at said operating points is determined; that the gear combination with the lowest specific fuel consumption is selected; and that a command signal for changing to the gear selected is emitted.

Description: Method and apparatus for controlling an automatic gearbox Technical field The present invention relates to a process and an arrangement for control of an automated gearbox. The invention is particularly applicable to mechanical servo-assisted gearboxes for heavy vehicles. State of the art Today's gearboxes of this kind are controlled by a control unit which controls gear selection so as to achieve engine operation which is appropriate in the light of experience. This has hitherto involved determining engine reference speeds at which changing up/down is in principle initiated. However, the control unit may also be designed to incorporate in the calculations the vehicle's acceleration and the accelerator pedal position in order to modify the control so that gear changing takes place at an engine speed which may be somewhat lower or somewhat higher than said reference speed. It is also possible for gear changing to be initiated in, for example, two stages instead of one. However, the known system is to be regarded as approximate and no optimisation of operation is possible on vehicles where that system is applied. Object and most important characteristics of the invention An object of the present invention is to indicate a process and an arrangement for control of an automated gearbox, whereby control is further refined so that the operation of the vehicle can be optimised. This object is achieved according to the invention by means of the features in the characterising part of patent claims 1 and 5 respectively. The result is the possibility of selecting in each situation a gear combination which optimises or in practice minimises the vehicle's specific fuel consumption. By means of the invention, various possible and permissible gear alternatives can thus be compared with respect to specific fuel consumption at the operating point concerned so that the latter can be caused to lead to as economic driving as possible. The process according to the invention involves: - the necessary drive power F being determined on the basis of the calculated running resistance at the prevailing running speed and in the prevailing operating conditions, - possible gear combinations for driving being determined, - possible gear combinations being monitored with respect to torque delivered and permissible engine speed, - the operating points for the possible and permissible gear combinations being determined, - the specific fuel consumption at said operating points being determined, - the gear combination with the lowest specific fuel consumption being selected, and - a command signal for changing to the selective gear being emitted. The initiation of gear changes which involve one or more gears being skipped is thus not excluded. A preferred aspect of the invention involves the process being initiated as an economy position after the control unit has, for example, detected that the running speed has for a certain period of time been approximately constant or that the accelerator pedal position has for a certain period of time been below a certain threshold value. This means that the control unit can independently initiate the process sequence, including the economy position, and achieve optimum specific fuel consumption. Suppressing changes to a new gear combination so that the latter may only be initiated after a certain period of time eliminates excessive gear changing and the driver irritation involved in frequent gear changes. The invention also relates to a control system suitable for implementing the process. This results in corresponding advantages. Further advantages are achieved by means of the other claims, as indicated by the following detailed description. Description of the drawings The invention will now be described in more detail on the basis of an embodiment and with reference to the attached drawings, in which: Fig. 1 shows a flow diagram of a process according to the invention, and Fig. 2 illustrates an arrangement according to the invention in connection with the driveline for a heavy vehicle. Description of an embodiment In Fig. 1, ref. 1 represents the beginning of the sequence and ref. 2 the monitoring of running data with respect to whether the economy position can be initiated. This entails monitoring, for example, whether the running speed has for a certain period of time been approximately constant, whether the degree to which the accelerator pedal is depressed corresponds to the set-point for the prevailing operating conditions, etc. Ref. 3 represents determination of the necessary drive power on the basis of the calculated running resistance at the prevailing running speed and in the prevailing operating conditions. The running resistance value is preferably updated continuously by evaluation of incoming data concerning the engine, driveline, vehicle, roadway etc. Ref. 4 represents the determination of possible and permissible gear combinations for the prevailing driving situation and ref. 5 represents determination of the operating points for driving with these various gear combinations. Ref. 6 represents determination of the specific fuel consumption at these various operating points, which involves using information which may be derived from a so-called "mussel" diagram which shows the relationship between engine torque and engine speed with respect to the specific fuel consumption of the engine concerned. Ref. 7 represents comparison of the various operating points with respect to specific fuel consumption, resulting in selection of the gear combination corresponding to the lowest consumption. If the selected gear combination is not the gear combination engaged at the time, the length of the time which has passed since the previous gear change is monitored and if it exceeds a prescribed period of time, signals are transmitted to the relevant components to engage the selected gear combination. Ref. 8 represents the completion of the sequence. Fig. 2 illustrates schematically an arrangement for control according to the invention, in which ref. 9 represents a control unit which advantageously incorporates devices for control according to the invention which are integrated into or connected to the normal engine control system. Ref. 16 represents a memory for registering running parameters, vehicle weight, running resistance etc. which have to be taken into account in connection with the present invention. In the driveline, the engine is denoted by 10, the clutch by 11 and the here triple gearbox by 12, 13 and 14, which may represent a division into split, main and range gearboxes. An output speed sensor is denoted by 15 and the final gear by 17. The control unit 9 is designed to: - determine the necessary drive power F on the basis of the calculated running resistance at the prevailing running speed and in the prevailing operating conditions, - determine possible gear combinations for driving, - monitor possible gear combinations with respect to torque delivered and permissible engine speed, - determine the operating points for the possible and permissible gear combinations, - determine the specific fuel consumption for said operating points, - select the gear combination with the lowest specific fuel consumption, and - emit a command signal for changing to the gear selected. The invention may be varied within the scope of the patent claims set out below. Thus the input data for the calculations may to some extent be varied but should preferably cover running speed, accelerator pedal position, vehicle weight, road gradient, fuel consumption information, gearchange conditions in the gearbox and, where applicable, in the various constituent gearboxes forming part of the gearbox, engine speed and torque curve. Gearchange times may also be incorporated in the calculations, in which case short changing times to certain gear combinations may result in their being preferred. The process according to the invention, including an economy position, is thus relevant when the vehicle speed is relatively constant, the accelerator pedal is preferably not more than 50% depressed and the engine torque set-value is below a certain specified threshold level. Studies of the driving of heavy vehicles have shown that the economy mode is applicable during as much as 70-80% of running time, which indicates that there is substantial potential for saving which can be utilised by means of the invention, even if the reduction in consumption achieved by means of the invention is not more than a few percent. EXAMPLE: In one example studied, a vehicle with a total weight of 60 tonnes was driven at a speed of 50 km/h. The gearbox used was a triple gearbox incorporating range, main and split gearboxes, designated SCANIA GRS900. The engine was a SCANIA DSCl 1413 and the vehicle was driven on a smooth horizontal stretch of road, with the results shown in the following table: In the driving situation described above, gear 11 is selected for optimum fuel economy. If the vehicle had for example been driven in gear 10, the specific fuel consumption would have been about 9% higher. With previously known control systems, the vehicle might very well have been driven in that gear, resulting, in this specific case, in substantially higher fuel consumption for the run.

Claims: Patent claims 1. Process for control of an automated gearbox, characterised - in that the necessary operating power F is determined on the basis of the calculated running resistance at the prevailing running speed and in the prevailing operating conditions, - that possible gear combinations for driving are determined, - that possible gear combinations are monitored with respect to torque delivered and permissible engine speed, - that the operating points for the possible and permissible gear combinations are determined, - that the specific fuel consumption at said operating points is determined, - that the gear combination with the lowest specific fuel consumption is selected, and - that a command signal for changing to the gear selected is emitted. 2. Process according to claim 1, characterised in that the gearchange times for the various gear combinations are calculated and incorporated in the calculation of the specific fuel consumption. 3. Process according to claim 1 or 2, characterised in that the running resistance and/or the vehicle weight is/are calculated during operation, on the basis of running data for the vehicle. 4. Process according to any one of the foregoing claims, characterised in that it is initiated as an economy mode after the variation in running parameters such as vehicle speed, accelerator position etc. has for a certain period of time been below a certain threshold value. 5. Process according to any one of the foregoing claims, characterised in that changing to a new gear combination may only be initiated after a certain period of time. 6. Arrangement for control of an automated gearbox which includes a control unit, characterised in that the control unit is designed: - to determine the necessary drive power F on the basis of the calculated running resistance at the prevailing running speed and in the prevailing operating conditions, - to determine possible gear combinations for driving, - to monitor possible gear combinations with respect to torque delivered and permissible engine speed, - to determine the operating points for the possible and permissible gear combinations, - to determine the specific fuel consumption for said operating points, - to select the gear combination with the lowest specific fuel consumption, and - to emit a control signal for changing to the gear selected. 7. Arrangement according to claim 6, characterised in that the control unit is designed to calculate the gearchange times for the various gear combinations and to incorporate them in the calculation of the specific fuel consumption. 8. Arrangement according to clam 6 or 7, characterised in that the control unit is arranged to calculate, on the basis of running data for the vehicle, the running resistance and/or the vehicle weight during operation.

Inventors: STAFNER SVEN, STAFNER, SVEN
Applicants: SCANIA CV ABP, STAFNER SVEN, SCANIA CV AKTIEBOLAG (PUBL), STAFNER, SVEN
Application year: 2000
Main classification: F16H61
IPC codes: F16H59, F16H61