METHOD FOR CONTROLLING AN ACTUAL SPEED OF A MOTOR VEHICLE

Abstract

A method is provided for controlling an actual speed of a motor vehicle. The method comprising the steps of: based on a vehicle configuration of the present vehicle, setting a threshold speed for the vehicle; obtaining a set speed of the vehicle; comparing the set speed to the threshold speed; if the set speed is below the threshold speed; determining a desired reference speed of the vehicle between the set speed and the threshold speed; and adjusting the actual speed of the vehicle toward the reference speed.

Claims

1. A method for controlling an actual speed of a motor vehicle, said method comprising the steps of: based on a vehicle configuration and a vehicle mass of the present vehicle, setting a threshold speed for the vehicle; obtaining a set speed of the vehicle; comparing the set speed to the threshold speed; if the set speed is below the threshold speed, determining a desired reference speed of the vehicle between the set speed and the threshold speed; and adjusting the actual speed of the vehicle toward the reference speed.

2. The method according to claim 1, wherein an allowed speed range having a lower limit and an upper limit is defined, and wherein the reference speed is determined so that it is a speed defined between the lower and upper limits of the allowed speed range.

3. The method according to claim 1, wherein the reference speed is determined as a function of the set speed.

4. The method according to claim 1, wherein the reference speed is determined in dependence on external conditions.

5. The method according to claim 1, wherein the step of setting the threshold speed comprises determining an energy consumption per travelled selected distance amount of the vehicle as a function of vehicle speed, and based thereon setting the threshold speed.

6. The method according to claim 5, wherein said threshold speed is set so that, at the threshold speed, the determined energy consumption per travelled selected distance amount of the vehicle is within a desired energy consumption range.

7. The method according to claim 5, wherein determining the energy consumption per travelled selected distance amount of the vehicle as a function of vehicle speed comprises determining power losses relating to at least an air resistance of the vehicle.

8. The method according to claim 7, wherein determining the energy consumption per travelled selected distance amount of the vehicle as a function of vehicle speed further comprises determining power losses relating to at least one of roll resistance, friction in a power train of the vehicle, auxiliary systems of the vehicle, and/or an electric motor of the vehicle.

9. The method according to claim 1, wherein the step of setting the threshold speed is carried out at least following a detection of a change in vehicle mass.

10. The method according to claim 1, wherein the step of determining a desired reference speed comprises: given the actual vehicle speed, determining a lowest possible vehicle speed increase for which a shift to a higher transmission mode of the vehicle is possible; and based on said determination, setting the reference speed.

11. The method according to claim 10, wherein the reference speed is set to the determined lowest possible speed for which a shift to a higher transmission mode of the vehicle is possible.

12. The method according to claim 1, wherein the step of adjusting the actual speed to the reference speed is conducted automatically using a cruise control of the vehicle.

13. (canceled)

14. A computer program product comprising a non-transitory data storage medium which can be read by a computer and on which program code of a computer program is stored, said program code used for controlling an actual speed of a motor vehicle, said program code comprising computer instructions to cause one or more computer processors to perform the following operations: based on a vehicle configuration and a vehicle mass of the present vehicle, setting a threshold speed for the vehicle; obtaining a set speed of the vehicle; comparing the set speed to the threshold speed; if the set speed is below the threshold speed, determining a desired reference speed of the vehicle between the set speed and the threshold speed; and adjusting the actual speed of the vehicle toward the reference speed.

15. An electronic control unit of a motor vehicle comprising: an execution means; a memory connected to the execution means; and a data storage medium which is connected to the execution means and on which program code of a computer program is stored, said program code used for controlling an actual speed of a motor vehicle, said program code comprising computer instructions to cause one or more computer processors to perform the following operations: based on a vehicle configuration and a vehicle mass of the present vehicle, setting a threshold speed for the vehicle; obtaining a set speed of the vehicle; comparing the set speed to the threshold speed; if the set speed is below the threshold speed, determining a desired reference speed of the vehicle between the set speed and the threshold speed; and adjusting the actual speed of the vehicle toward the reference speed.

16. A motor vehicle comprising an electronic control unit, said electronic control unit comprising: an execution means; a memory connected to the execution means; and a data storage medium which is connected to the execution means and on which program code of a computer program is stored, said program code used for controlling an actual speed of a motor vehicle, said program code comprising computer instructions to cause one or more computer processors to perform the following operations: based on a vehicle configuration and a vehicle mass of the present vehicle, setting a threshold speed for the vehicle; obtaining a set speed of the vehicle; comparing the set speed to the threshold speed; if the set speed is below the threshold speed, determining a desired reference speed of the vehicle between the set speed and the threshold speed; and adjusting the actual speed of the vehicle toward the reference speed.

17. A motor vehicle according to claim 16, wherein the motor vehicle is a truck or a bus.

18. The method according to claim 1, wherein the selected distance amount is a kilometer, and wherein the step of setting the threshold speed comprises determining an energy consumption per travelled kilometer-of the vehicle as a function of vehicle speed, and based thereon setting the threshold speed.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Embodiments of the invention will in the following be described with reference to the appended drawings, in which:

[0040] FIG. 1 shows total energy consumption E of a vehicle as a function of vehicle speed,

[0041] FIG. 2 is a flow chart showing a method according to the invention,

[0042] FIG. 3 shows an exemplary speed curve of a vehicle,

[0043] FIG. 4 schematically shows a control unit according to the invention, and

[0044] FIG. 5 schematically shows a vehicle according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0045] The energy consumption E per travelled kilometer as a function of actual vehicle speed v_actual for an exemplary motor vehicle travelling on a flat road is shown in FIG. 1. Here, the solid line shows the energy consumption E for a gearbox with discrete steps, while the dashed line shows the energy consumption E for an ideal transmission. As can be seen, the total energy consumption E, after an initial increase as the vehicle is set into motion, decreases with vehicle speed. Each gear shift to a higher transmission mode results in a sudden reduction in energy, or fuel, consumption. In this specification, the term shifting to a higher transmission mode covers an upshift to a higher gear position for a gearbox, i.e. an upshift to a gear with lower gear ratio (engine speed/drive wheel speed). This assumes a gearbox with discrete steps in gear ratio (a classic manual, an automated manual, a double clutch, or an automatic gearbox).

[0046] As the vehicle speed continues to increase, the vehicle reaches a minimum energy consumption per travelled kilometer. Above a certain optimum vehicle speed, the energy consumption starts to increase, mainly due to the increased air resistance as the speed increases. The numeric value of the optimum vehicle speed depends on the configuration and mass of the vehicle. In order to save time and fuel, it is generally advantageous to reduce the speed at relatively high speeds, such as above the optimum vehicle speed, and to increase the speed when driving at relatively low speeds. The threshold speed v_threshold of the vehicle can be set close to the optimum vehicle speed as determined e.g. from an estimation of the total energy consumption of the vehicle.

[0047] By a motor vehicle is here intended a vehicle which is powered by an internal combustion engine and/or by an electric motor. In particular, but not exclusively, the method is intended for use in a heavy motor vehicle such as a truck or a bus.

[0048] A method according to the invention is schematically shown in FIG. 2. In a first step S1, a threshold speed v_threshold is set. The threshold speed v_threshold is set based on the present vehicle configuration and several parameters may be taken into account, such as vehicle mass and an estimated air resistance of the vehicle, as well as other estimated power losses resulting from auxiliary systems, roll resistance, engine friction, transmission friction, and electrical losses. The threshold speed v_threshold may preferably be determined on the basis of a determined energy consumption E per travelled kilometer of the vehicle as a function of vehicle speed, taking the above mentioned power losses into account. Driver or haulage company preferences, foreseen driving conditions, gear changing schemes or vehicle type, may also be taken into account. For example, it may be desirable to set a low threshold speed v_threshold, since the potential savings in energy consumption E are largest for small speeds. Setting the threshold speed v_threshold to a higher value results in a more offensive driving pattern, since it will result in speed increases also from relatively high set speeds v_set. The threshold speed v_threshold of the vehicle is preferably set independently of any external factors such as legal speed limits.

[0049] In a second step S2, the set speed v_set is obtained. This set speed v_set may be the speed requested by a driver of the vehicle, e.g. via a cruise control or via an accelerator pedal. It may also be a speed set by external conditions, based on e.g. a legal speed limit or a central communication and control system controlling the vehicle.

[0050] In a third step S3, the set speed v_set is compared to the threshold speed v_threshold. If the set speed v_set is higher than the threshold speed v_threshold, the reference speed v_ref is determined independently of the method according to the present invention. Once the set speed v_set is changed, a new comparison is performed. If on the other hand the set speed v_set is below the threshold speed v_threshold, a desired reference speed v_ref between the set speed v_set and the threshold speed v_threshold is determined in a step S4. An allowed speed range with an upper limit v_max and a lower limit v_min may additionally be defined. In this case, the reference speed v_ref is determined so that it falls within the allowed speed range. The lower limit v_min of this allowed speed range may, but must not necessarily, equal the set speed v_set. The upper limit v_max may e.g. be set to vary with the set speed v_set, or to deviate from the set speed v_set by a fixed value.

[0051] The reference speed v_ref can be seen as an output signal from a cruise control of the vehicle, which is used to control the engine, providing control of the vehicle's actual speed. Thus, in a step S5, the actual speed v_actual of the vehicle is adjusted toward the reference speed v_ref, i.e. so that it reaches the reference speed v_ref. This can be achieved either automatically using the cruise control, or manually by the driver. In the latter case, presentation means are used to present the reference speed v_ref to the driver. The reference speed can e.g. be shown on a display, or presented in the form of an audio message.

[0052] FIG. 3 shows the actual speed v_actual, the set speed v_set, the defined upper limit v_max of an allowed speed range, and the threshold speed v_threshold of an exemplary motor vehicle as a function of distance travelled by the vehicle. The exemplary vehicle here travels on a flat road. For this particular vehicle configuration, the threshold speed v_threshold has been set to 40 km/h. The first set speed v_set is 30 km/h, which the vehicle reaches after a certain distance. The set speed v_set is here determined by external means, such as by reading of road signs or by data transmission to the vehicle, and/or from map-data stored in the vehicle. An allowed speed range with a lower limit v_min (not shown in FIG. 3) and an upper limit v_max is defined. The lower limit v_min here equals the set speed v_set and the upper limit v_max is set to vary with the set speed v_set as v_max=1.1*v_set. Thereby, the allowed speed range has an upper limit v_max of 33 km/h for a set speed v_set of 30 km/h. The actual speed v_actual of the vehicle is adjusted to a reference speed v_ref slightly lower than the allowed upper limit v_max. In FIG. 3, v_ref=v_actual except during the acceleration and deceleration of the vehicle. After driving at the reference speed v_ref for a while, the vehicle is braked and comes to a stop. When taking off again, the set speed v_set has changed to 50 km/h, which is above the threshold speed v_threshold. The upper limit v_max is here 55 km/h, but since the vehicle is travelling at an actual speed v_actual above the threshold speed, the actual speed of the vehicle is not increased above the set speed v_set, since such a speed increase would negatively affect the total energy consumption E of the vehicle.

[0053] One skilled in the art will appreciate that a method for controlling the actual speed of a vehicle according to the present invention may be implemented in a computer program which, when executed in a computer, causes the computer to conduct the method. The computer program usually takes the form of a computer program product which comprises a suitable digital storage medium on which the computer program is stored. Said computer-readable digital storage medium comprises a suitable memory, e.g. ROM (read-only memory), PROM (programmable read-only memory), EPROM (erasable PROM), flash memory, EEPROM (electrically erasable PROM), a hard disc unit, etc.

[0054] FIG. 4 depicts schematically an electronic control unit 400 of a vehicle provided with an execution means 401 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 execution means 401 is connected to a memory unit 402 which is situated in the control unit 400. A data storage medium 403 is also connected to the execution means and provides the execution means with, for example, the stored program code and/or stored data which the execution means needs to enable it to do calculations. The execution means is also adapted to storing partial or final results of calculations in the memory unit 402.

[0055] The control unit 400 is further provided with respective devices 411, 412, 413, 414 for receiving and sending input and output signals. These input and output signals may comprise waveforms, pulses or other attributes which the input signal receiving devices 411, 413 can detect as information and which can be converted to signals which the execution means 401 can process. These signals are then supplied to the execution means. The output signal sending devices 412, 414 are arranged to convert signals received from the execution means 401, in order to create, e.g. by modulating them, output signals which can be conveyed to other parts of the vehicle and/or other systems on board.

[0056] Each of the connections to the respective devices for receiving and sending input and output signals may take the form of one or more from among a cable, a 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. One skilled in the art will appreciate that the aforesaid computer may take the form of the execution means 401 and that the aforesaid memory may take the form of the memory unit 402.

[0057] Control systems in modern vehicles generally comprise a communication bus system consisting of one or more communication buses for connecting together a number of electronic control units (ECUs), or controllers, and various components on board the vehicle. Such a control system may comprise a large number of control units and the responsibility for a specific function may be divided between two or more of them.

[0058] In the embodiment depicted, the present invention is implemented in the control unit 400 but might also be implemented wholly or partly in one or more other control units already on board the vehicle or a control unit dedicated to the present invention. Vehicles of the type here concerned are of course often provided with significantly more control units than shown here, as one skilled in the art will surely appreciate.

[0059] The present invention according to one aspect relates to a motor vehicle 500 which is schematically shown in FIG. 5. The motor vehicle 500 may e.g. be a passenger car, a truck or a bus, comprising an engine 501, which via a driveline 502 drives driving wheels 503, 504, an exhaust treatment system 505, and a control unit 510, which corresponds to the above-mentioned control unit 400 in FIG. 4, and which is arranged to control the function in the engine 501.

[0060] The invention is of course not in any way restricted to the embodiments described above. On the contrary, many possibilities to modifications thereof will be apparent to a person with ordinary skill in the art without departing from the basic idea of the invention such as defined in the appended claims.