Technical field

The present invention relates to a system for control of a gearbox installed in a motor vehicle. In particular, the invention relates to a system according to the preamble of claim 1. The invention further relates to a method, a motor vehicle, a computer programme and a computer programme product thereof.

Background to the invention

Figure 1 depicts schematically parts of a power train for a motor vehicle 1, such as a passenger car or a heavy vehicle, e.g. a truck or bus. The power train comprises an engine 10 mechanically connected by a shaft to a first end of a gearbox 20 via a clutch device 40. The gearbox 20 is also mechanically connected, at its other end, by a propeller shaft 50 to a differential gear 30 associated with a rear axle. The rear axle comprises respective left and right drive shafts 60 which drive the vehicle's powered wheels (not depicted in the diagram).

With this well-known arrangement, the mechanical work of the engine 10 is transmitted via various transmission devices (e.g. clutch device 40, gearbox 20, propeller shaft 50, differential gear 30 and drive shafts 60) to powered wheels in order to move the vehicle 1. An important device in the power train is the gearbox 20, which has a number of forward gears for moving the vehicle 1 forwards, and usually also one or more reverse gears. The number of forward gears varies but modern kinds of trucks are, for example, usually provided with twelve forward gears. The gearbox 20 may be of manual or automatic type (automatic gearbox), but also of the automatic manual gearbox type (automatic manual transmission, AMT). Automatic gearboxes and automatic manual gearboxes are automated gearbox systems usually controlled by a control unit 110 (sometimes also called electronic control unit, ECU) which is adapted to controlling the gearbox 20, e.g. during gear changing, as when choosing gears at a certain vehicle speed with a certain running resistance. The ECU may measure engine speed and the state of the gearbox 20 and control the gearbox by means of solenoid valves connected to compressed air devices. Information about the engine 10, e.g. its speed and torque, is also sent from the engine 10 to the ECU, e.g. via a CAN (controller area network) bus. In conventional gear change systems, the control unit 110 uses tabulated engine speed limits, also called shift points, which represent the engine speed at which a downshift or upshift should be effected in the gearbox 20, i.e. the vehicle 1 changes gear when the speed of its engine 10 passes a speed represented by a shift point. The shift points may therefore be construed as providing information not only about when a downshift or upshift should take place but also about the number of gear steps to be effected at each downshift or upshift. It is usual for each shift point to comprise one to three gear steps, although more steps are possible.

Figure 2 depicts schematically an example of various tabulated shift points represented by lines SP1-SP6 in a graph where the x axis represents engine torque and the y axis the speed of the engine 10 in revolutions per minute (rpm). So long as the engine speed is between shift lines SP1 and SP4 no gear change takes place, but if it rises above an upshift line, SP1-SP3, an upshift is initiated, and conversely a downshift is initiated if the engine speed drops below a downshift line, SP4-SP6. Table 1 below shows a number of upward or downward gear steps for each of the lines SP1-SP6. For example, an upshift by one step takes place if the engine speed rises above line SP1 and a downshift by two steps if the engine speed drops below line SP5.

Table 1: Downshift and upshift lines SP1-SP6

Shift point choices affect inter alia running characteristics, acceleration, comfort and fuel consumption for the vehicle 1 , so shift points have to be accurately calibrated by vehicle manufacturers. This calibration involves various gearshift strategies being tested in the field in different driving situations, e.g. with different amounts of acceleration applied, different road gradients and different vehicle-combination weights. The test results have then to be thoroughly analysed to determine appropriate shift points. This procedure for calibration of shift points is both time-consuming and expensive.

Moreover, the results of the calibration are not always satisfactory in that the calibrated shift points may be appropriate for certain driving situations but less so for others.

Specification EP 1070879 refers to a method and a system for control of an automated mechanical transmission system during upshifts. According to that specification, the way upshifts are effected takes an accelerator pedal position into account.

Brief description of the invention

An object of the present invention is to propose an alternative system for control of a gearbox. Another object of the invention is to propose for control of a gearbox a system which totally or partly solves the problems of the state of the art. A further object of the invention is to propose for control of a gearbox a system which fully utilises the engine's power output.

According to an aspect of the invention, the above objects are achieved with a system for control of a gearbox, which system comprises at least one control unit adapted to controlling said gearbox, where said gearbox is installed in a motor vehicle which comprises an engine connected to, in order to drive, said gearbox, said system being adapted to:

- effecting a first upshift from a first gear to a second gear if the acceleration a for said vehicle is greater than nil for said second gear and the current engine speed is within a first engine speed range, and

- effecting a second upshift from said first gear to a third gear if the current engine speed is within a second engine speed range, said first speed range being a lower speed range than said second speed range of said engine.

Embodiments of the above system are referred to in the dependent claims 2-11. The invention relates also to a motor vehicle comprising at least one system as above.

According to another aspect of the invention, the abovementioned objects are achieved with a method for changing gear in a gearbox installed in a motor vehicle which comprises an engine connected to, in order to drive, said gearbox, which method comprises the steps of: - effecting a first upshift from a first gear to a second gear if the acceleration a for said vehicle is greater than nil for said second gear and the current engine speed is within a first engine speed range, and

- effecting a second upshift from said first gear to a third gear if the current engine speed is within a second engine speed range, said first speed range being a lower speed range than said second speed range of said engine.

The invention relates also to a computer programme comprising programme code, which programme, when said programme code is executed in a computer, causes said computer to effect the above method. The invention relates also to a computer programme product belonging to said computer programme.

The method according to the invention may also be modified according to the various embodiments of the above system.

A system and a method according to the invention provide improved drivability sensation in that upshifts are imposed when the engine so allows. The engine's full power output is also utilised in a better way than in the state of the art, making it possible, for example, to achieve higher vehicle speeds.

Further advantages and applications of a system and a method according to the invention are indicated by the detailed description set out below.

Brief description of the drawings

In the detailed description of the present invention set out below, embodiments of the invention are described with reference to the attached drawings, in which:

- Figure 1 depicts schematically part of a power train for a motor vehicle;

- Figure 2 is a graph of downshift and upshift lines;

- Figure 3 is a graph of engine torque as a function of engine speed;

- Figure 4 depicts a control unit forming part of a system according to the invention; and.

- Figure 5 is a flowchart of an embodiment of the invention. Detailed description of the invention

As described above, conventional systems use tabulated shift points. Despite these shift points being carefully calibrated by vehicle manufacturers, driving situations may occur in which these calibrated shift points are not satisfactory from a drivability perspective. Nor is the full power output of the engine 10 utilised with such calibrated shift points.

For example, a situation which may arise when a motor vehicle 1 is travelling uphill is that a shift point for effecting an upshift, e.g. one step up, is at such a high engine speed that the vehicle 1 is unable to accelerate to that engine speed. This situation means that an upshift does not take place despite the fact that the vehicle 1 can accelerate in the next higher gear and should therefore be able to reach a higher running speed in that higher gear. To prevent such a situation occurring, calibration usually involves keeping upshift points at low engine speeds to make upshift possible. However, the result of such calibration is that the vehicle 1 seems to be "tired" in that the upshift takes place at a lower engine speed than is usually desired.

The present invention therefore relates to a system for control of a gearbox 20. The gearbox 20 is preferably of the kind which forms part of an automated gear change system controlled by a control unit 110, e.g. an ECU. In such a gear change system, gear changes are effected automatically by the control unit 110, but it is also usual for the driver to be able to execute manual gear changes in an automatic gear change system, what is known as manual gear change in automatic state (automatic mode). The gearbox 20 also has a plurality of gears, e.g. twelve forward gears and one or more reverse gears are usual in modern trucks. The system comprises at least one control unit 110 adapted to controlling said gearbox 20.

The system is also adapted to imposing one or more upshift steps, depending on which engine speed range the engine 10 is in and on whether certain other conditions are fulfilled. If the engine 10 is in a first speed range II in a first gear Gl and the acceleration a of the vehicle 1 is greater than nil for a second gear G2, an upshift from the first gear Gl to the second gear G2 is effected (is imposed); and if the engine is in a second speed range 12 and this second speed range 12 is a higher speed range than the first speed range II, an upshift from the first gear Gl to a third gear G3 is effected (is imposed). The advantage of such a system for control of a gearbox 20 is that the vehicle 1 will not always effect an upshift when it is possible for it to do so, i.e. when more power is achievable in a higher gear. A higher vehicle speed may therefore be reached and fuel be saved by running in the next gear at a lower engine speed. Moreover, an upshift can take place without the vehicle 1 seeming tired, since the upshift cannot be imposed at the same time as the vehicle 1 is accelerating if the engine 10 will not deliver more power in the next gear.

Deciding whether the condition of the acceleration a of the vehicle 1 being greater than nil for the second gear G2 is fulfilled involves calculating what engine speed on the torque curve will in the second gear G2 provide sufficient power to overcome the running resistance, i.e. the force which acts against the vehicle 1 in the direction of movement. According to an embodiment of the invention, the gear change system may use a threshold value which the acceleration a for the second gear G2 is compared with. If the acceleration a is found to be greater than this threshold value, the above condition is deemed fulfilled and an upshift from the first gear Gl to the second gear G2 is imposed. The threshold value may for example be greater than or equal to 5 rpm/s. It will be appreciated by specialists that this value is adjustable, e.g. by calibration, so that upshifts take place as desired with respect to other system parameters. Figure 3 is a graph of engine torque as a function of engine speed. PI is the point on the torque curve at which lowest engine speed for acceleration a of the vehicle 1 is possible, and P2 represents the lowest possible engine speed for an upshift which leads to the engine speed after changing gear becoming equal to or greater than the engine speed at PI . Point P3 may be construed as the engine speed at which the power output from the engine 10 is the same before and after an upshift. Point P4 represents the maximum speed of the engine 10.

According to the invention, speeds P2 and P3 define the first engine speed range II, and speeds P3 and P4 correspondingly define the second engine speed range 12.

As depicted in Figure 3, the first and second speed ranges II and 12 are mutually adjacent and are demarcated by point (engine speed) P3. The first speed range II comprises the engine speeds at which acceleration is possible in the second gear G2, and the second speed range 12 comprises the engine speeds at which the power output from the engine 10 is greater in the third gear G3 than in the first gear Gl . According to an embodiment of the invention, the second gear G2 and the third gear G3 are the same gear, and the upshift is preferably by a single gear step, although two or more steps are possible, as specialists will appreciate.

According to another embodiment of the invention, the second gear G2 and the third gear G3 are different gears, which means that the number of gear steps for the first and second upshifts will differ, e.g. the first upshift may involve a single step and the second upshift two steps, although the opposite is also possible.

The first and second upshifts may be effected by upshift points being moved downwards to correspond to a lower engine speed after such movement. The advantage of this is that no shift points will be so high that the maximum power output of the engine 10 is not used. The engine 10 is thus utilised more effectively.

In practice, imposition of upshift may be achieved by only the shift point for a single-step upshift (i.e. upshift by a single gear step) being lowered to below the current speed of the engine 10. The shift points for multi-step upshifts are not affected. In other words, this method of imposing upshifts will not affect the gear change system in situations where a two- step gear change is effected.

Figure 5 is a flowchart of an exemplified embodiment of the invention. In the first step (at Fl), calculating whether a shift point should be lowered or not involves calculating the engine speed for point PI, compare also with Figure 3. This is done by using the torque curve of the engine 10 to calculate the engine speed at which the engine 10 delivers sufficient torque for the vehicle 1 to be able to accelerate or maintain the same vehicle speed in the next gear. When PI has been calculated, a check is done, at F2 in the diagram, to see whether the engine 10 is or is not above point P2 on the torque curve. This is done by simulating a gear change and using the engine speed difference during the gear change (i.e. a simulated loss of engine speed from when a gear change is initiated to when it is completed) to decide whether the engine 10 will, after the gear change, be above PI or not. At CI, if the engine speed after the gear change is above point PI, it means that the current engine speed is above point P2. If the engine speed is not above P2, an upshift is not imposed (F3). The next step, at C2, is to decide whether the engine 10 is above or below point P3. Deciding this involves calculating the power output in the next gear. This can be done on the basis of knowing the engine speed and the torque after the gear change. The engine speed after the gear change has been calculated at F2 and the torque at that engine speed is taken from the torque curve of the engine 10. Comparison is then possible with the engine speed and the torque before the gear change, since the power output is arrived at by multiplying the torque by the engine speed. If the power output is greater after than before the gear change, a gear change is imposed (at F5). At C3, if such is not the case, a gear change is only imposed if the acceleration (F6) of the vehicle 1 is substantially nil or low. To decide whether the acceleration of the vehicle 1 is substantially nil or low, a threshold value for the engine speed acceleration may be introduced, e.g. 5 rpm/s, which means that the engine speed acceleration has to have been below this threshold value for a certain time, e.g. 2 seconds, to fulfil the condition of being substantially nil or low.

The invention relates also to a motor vehicle 1, e.g. a truck or bus, which comprises at least one system for determination of one or more downshift and upshift points according to the invention. The invention relates also to a method for changing gear in a gearbox 20 which is installed in a motor vehicle 1. The method corresponds to the above system and comprises the following steps: effecting a first upshift from a first gear Gl to a second gear G2 if the acceleration a for said vehicle 1 is greater than nil in said second gear G2 and the current engine speed is within a first speed range II; and further effecting a second upshift from said first gear Gl to a third gear G3 if the current engine speed is within a second speed range 12, said first speed range II being a lower speed range than said second speed range 12 of said engine 10.

It should also be noted that the above method may be modified according to the various embodiments of a system for control of a gearbox according to the invention.

Specialists will also appreciate that a method for changing gear in a gearbox 20 according to the present invention might also be implemented in a computer programme which, when executed in a computer, causes the computer to effect the method. The computer programme is contained in a computer programme product's computer-readable medium which takes the form of a suitable memory, e.g. ROM (read-only memory), PROM (programmable read-only memory), EPROM (erasable PROM), flash memory, EEPROM (electrically erasable PROM), hard disc unit, etc.

Figure 4 depicts schematically a control unit 110 forming part of a system according to the invention. The control unit 110 comprises a calculation unit 111 which may take the form of substantially any suitable type of processor or microcomputer, e.g. a circuit for digital signal processing (digital signal processor, DSP) or a circuit with a predetermined specific function (application specific integrated circuit, ASIC). The calculation unit 111 is connected to a memory unit 112 which is incorporated in the control unit 110 and which provides the calculation unit 111 with, for example, the stored programme code and/or the stored data which the calculation unit 111 needs in order to be able to perform calculations. The calculation unit 111 is also adapted to storing partial or final results of calculations in the memory unit 1 12.

The control unit 110 is further provided with devices 113, 114, 115, 116 for respectively receiving input signals and sending output signals. These input and output signals may comprise waveforms, pulses or other attributes which the signal receiving devices 113, 116 can detect as information and which can be converted to signals processable by the calculation unit 111. The calculation unit 111 is then provided with these signals. The signal sending devices 114, 115 are adapted to converting signals received from the calculation unit 111 in order to create, e.g. by modulating the signals, output signals which can be transmitted to other parts of the system for determination of downshift and upshift points. One skilled in the art will appreciate that the aforesaid computer may take the form of the calculation unit 111 and that the aforesaid memory may take the form of the memory unit 112.

Each of the connections to the devices for respectively receiving input signals and sending output signals may take the form of one or more from among the following: cable, data bus, e.g. a CAN (controller area network) bus, a MOST (media orientated systems transport) bus or some other bus configuration, or a wireless connection. The connections 70, 80, 90, 100 in Figure 1 may also take the form of one or more of these cables, buses or wireless connections. Finally, the present invention is not limited to its embodiments described above, but relates to and comprises all embodiments within the scope of protection of the attached independent claims.