Technical field

The present invention relates to a method for determination of one or more downshift and upshift points for a gearbox in a motor vehicle. In particular, the invention relates to a method according to the preamble of claim 1. The invention further relates to a system, 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 a reverse gear. The number of forward gears varies but modern kinds of trucks are 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. Specification US5479345 refers to a method and device for choice of shift points. The factors of road gradient, the vehicle's speed and its gross weight relative to the power, in hp, needed to maintain its current speed, and the engine speed and available power expected upon completion of a gear change are taken into account in determining whether a gear change is or is not allowed.

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, but 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 similarly 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.

Brief description of the invention

An object of the present invention is to propose an alternative method for determining one or more downshift and upshift points. Another object of the invention is to propose a method which totally or partly solves the problems of the state of the art. A further object of the invention is to propose a method which allows flexible and simple determination of one or more downshift and upshift points.

According to an aspect of the invention, the above objects are achieved with a method for determination of one or more downshift and upshift points for a gearbox in a motor vehicle which comprises an engine connected to, in order to drive, said gearbox, where a downshift point represents a first engine speed at which said gearbox is adapted to effecting a downshift, and an upshift point represents a second engine speed at which said gearbox is adapted to effecting an upshift. Said method comprises said one or more downshift and upshift points being determined relative to an engine target speed co _r which is a desired speed for said engine.

Embodiments of the above method are referred to in the dependent claims 2-11.

The invention further relates to a computer programme comprising programme code which, when said programme code is executed in a computer, causes said computer to effect the method according to any one of claims 1-11. The invention further relates to a computer programme product belonging to said computer programme. According to another aspect of the invention, the above objects are achieved with a system for determination of one or more downshift and upshift points, comprising at least one control unit adapted to controlling a gearbox in a motor vehicle which comprises an engine connected to, in order to drive, said gearbox, where a downshift point represents a first engine speed at which said gearbox is adapted to effecting a downshift, and an upshift point represents a second engine speed at which said gearbox is adapted to effecting an upshift. Said system is further adapted to determining said one or more downshift and upshift points relative to an engine target speed co _r which is a desired speed for said engine.

The system according to the invention may also be modified according to the various embodiments of the above method. The invention further relates to a motor vehicle which comprises at least one system as above. A method and a system according to the invention provide a flexible and simplified solution for determination of one or more downshift and upshift points. The fact that the shift points are related to a desired engine target speed makes it substantially easier to alter them. This makes it very easy to adjust gear change configurations to changing needs by raising or lowering the engine target speed. Another advantage is that shift point changes do not entail having to recalibrate every shift point. Calibration work is generally reduced substantially by a method and a system according to the invention.

A further advantage of the invention is that the shift points can be altered without the gear change logic, e.g. in a control unit, having to risk becoming logically unstable, since the shift points are controlled indirectly via the engine target speed, so the relationship between the shift points can be controlled in such a way as to avoid instability.

Further advantages and applications of a method and a system 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 with rear wheel drive;

Figure 2 is a graph of downshift and upshift lines;

Figure 3 is a graph of downshift and upshift lines related to an engine target speed line; and

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

Detailed description of the invention

The present invention relates to determination of one or more downshift and upshift points for a gearbox 20 preferably situated in a motor vehicle 1. A downshift or upshift point represents an engine speed at which the gearbox 20 is respectively adapted to effecting a downshift or upshift. The engine speed for upshift points is higher than the engine speed for downshift points.

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 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 such a 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. According to the invention, the downshift and upshift points are determined relative to an engine target speed co _r which is a desired speed for the engine 10 of the vehicle 1. This means that the downshift and upshift points are always determined on the basis of the engine target speed C0 _r . In Figure 3 an engine target speed line Φ in the form of a dotted line appears between upshift lines SP1-SP3 and downshift lines SP4-SP6. The diagram contains arrows showing how upshift lines SP1-SP3 and downshift lines SP4-SP6 are related to the engine target speed line Φ . They indicate that if the engine target speed line Φ is altered (by being moved upwards or downwards in parallel according to the dotted arrows) the engine speed for the shift lines SP1-SP6 will also move in parallel. The shift lines SP1-SP6 may for example accompany the target speed line Φ proportionally to a scale factor which may be different for upshift and downshift lines respectively but may also be the same, in which case an established mutual relationship between the upshift and downshift points is achieved. It is also possible to have an individual scale factor for each shift line SP1-SP6, i.e. certain shift lines SP1-SP6 may change more or less than other shift lines SP1-SP6 on the basis of the same change in the target speed line Φ .

The invention thus proposes a method which makes it easier to determine the downshift and upshift points in that they are always related to an engine target speed C0 _r , which means that a change in the value of the target speed co _r also affects the engine speed values of the shift points, so the procedure of calibration according to the state of the art described above can be avoided. The invention thus makes it possible to save time and reduce costs. The engine target speed C0 _r may be determined on the basis of assumptions and knowledge about the mode of operation and performance of the engine 10. An engine 10 usually runs more efficiently and better at certain speeds than at others. More efficient and better may mean less fuel consumption, lower vibration levels and quieter running. According to an embodiment, the target speed C0 _r will be within the range 500-2500 rpm for all downshift and upshift points for the engine 10, and according to another embodiment preferably within the range 1000-1400 rpm.

Another advantage of the method according to the invention is that adaptation of gearboxes to different engines 10, and vice versa, is substantially facilitated. Once an engine target speed C0 _r has been established for a specific engine model or a specific automatic gear system, the control unit 110 can then determine the shift points related to the target speed C0 _r . This makes it possible to reduce the lead times for putting new engines 10 and/or automated gear change systems on the market. According to another embodiment of the invention, other parameters may also be taken into account when determining the engine target speed ω _Γ , e.g. accelerator pedal position, driving mode, cruise control setting, running resistance (i.e. the force acting against the vehicle 1 in its direction of movement), road gradient, engine power and map data.

The parameters of accelerator pedal position, driving mode (in terms of various predetermined running states selectable in an automatic gear change system, e.g. economy state or power state) and cruise control setting involve the driver being able to affect directly the engine target speed C0 _r and hence indirectly the downshift and upshift points, since they are related to the target speed C0 _r . For example, this embodiment may be so implemented that the target speed C0 _r is determined by driving mode and acceleration pedal position. The position of the accelerator pedal may affect the target speed C0 _r by application of a table which converts the pedal position to the change in engine target speed so that more acceleration results in a higher target speed co _r .

The other parameters, viz. running resistance, road gradient, engine power and map data, may also be used for determining the engine target speed C0 _r and may be provided by means of sensors and intelligent signal and control systems which are present in today's motor vehicles 1. It should be noted that not all of the aforesaid parameters need be taken into account, since one or more in combination may produce good results, or they may alternatively be used by a control unit 110, e.g. an ECU.

The engine target speed C0 _r may also be a preset parameter which can be adjusted by a service technician at an engine workshop. With such a version of the invention, the target speed C0 _r is a parameter which is kept static between adjustments. Adjustment of the target speed C0 _r may entail its trimming for better performance and/or for individual setting of running characteristics to suit the customer's preferences.

According to another embodiment of the invention, the engine target speed C0 _r is a dynamic parameter. For example, a dynamic parameter may be altered by the driver by means of a control unit (manual control), e.g. a cruise control, accelerator pedal etc. A dynamic parameter may also be altered by a system of sensors and signalling and control systems (automatic control) described above. It is also possible to combine manual and automatic control, with or without map data to provide, for example, topographical information about roads, which can be used in conjunction with GPS technology. It is also possible to control the engine target speed C0 _r dynamically by means of wireless communication (e.g. satellite communication systems or mobile communication systems such as GSM, GPRS, EDGE or LTE) by a communications centre sending control signals via a wireless communication system to the vehicle 1 to control the target speed C0 _r . With an embodiment as above, in which the target speed C0 _r is a dynamic parameter, the running characteristics may be controlled continuously according to prevailing circumstances. According to a further embodiment of the invention, downshift and upshift points are calculated in real time, and in addition to being related to an engine target speed C0 _r they may also depend on one or more of the parameters belonging to the category which comprises the following: change in engine speed during gear changing, defined as a difference in engine speed between a point in time when a gear change is initiated and a time when it is completed; change in running speed of the vehicle 1 during gear changing; and the torque curve for said engine 10. It is for example possible to use the change in engine speed during gear changing to calculate what engine speed before the gear change results in a specific engine target speed after the gear change, and vice versa. The torque of the engine 10 may be used to calculate the acceleration of the vehicle 1 during and after the gear change, which itself affects how much the engine speed needs to be changed. The advantage of this embodiment is for example that the target speed C0 _r can immediately be adjusted to prevailing running conditions for the vehicle 1.

Specialists will appreciate that a method for determination of one or more downshift and upshift points 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. The invention also relates to a system for determination of one or more downshift and upshift points. The system comprises at least one control unit (e.g. an ECU for a gearbox 20) adapted to controlling a gearbox 20 in a motor vehicle 1. The gearbox 20 is connected to an engine 10 which drives the gearbox 20 and other parts of the power train. The system is adapted, according to the concept of the invention, to determining one or more downshift and upshift points relative to an engine target speed co _r which is a desired engine speed for the engine 10.

Figure 4 depicts schematically a control unit 110. 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 for it 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 112.

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 which are 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, eg 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 or sending output signals may take the form of one or more from among the following: cable, data bus, e.g. CAN (controller area network) bus, 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.

Specialists will also appreciate that the above system may be modified according to the various embodiments of the method for determination of one or more downshift and upshift points according to the invention. The invention relates also to a motor vehicle 1, e.g. a truck or bus, comprising at least one system for determination of one or more downshift and upshift points according to the invention. 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.