EP2513517A1

EP2513517A1 - Cruise control for a motor vehicle and control method

Info

Publication number: EP2513517A1
Application number: EP10837990A
Authority: EP
Inventors: Mikael WÅGBERG
Original assignee: Scania CV AB
Current assignee: Scania CV AB
Priority date: 2009-12-17
Filing date: 2010-12-16
Publication date: 2012-10-24
Also published as: SE534647C2; SE1050546A1; WO2011075063A1; EP2513517A4

Abstract

The present invention relates to a cruise control for a motor vehicle (1) provided with a power train which is adapted to assuming various transmission ratios for propulsion of the vehicle (1) and which comprises at least one engine (10) and at least one gearbox (20), such that the cruise control (40) is adapted to being controlled on the basis of a first parameter Rp which is defined as a difference between a first motive force F Max and a second motive force For, the first motive force F Max being a maximum motive force available for the vehicle (1) at a current power train transmission ratio and the second motive force For a current running resistance for the vehicle (1). The invention relates also to a computer programme and a computer programme product, and to a motor vehicle provided with such a cruise control.

Description

CRUISE CONTROL FOR A MOTOR VEHICLE AND CONTROL METHOD

Technical field

The present invention relates to a cruise control for a motor vehicle and a method for control of such a cruise control. In particular, the invention relates to a cruise control and a method according to the preambles of the independent claims. The invention relates also to a computer programme and a computer programme product, and to a motor vehicle provided with such a cruise control.

Background to the invention

A cruise control 40 is a device for regulating the speed of a motor vehicle 1 which may be a passenger car or a heavy vehicle, e.g. a truck or bus. Simple cruise controls 40 maintain a set desired speed for the vehicle 1 by increasing or decreasing the amount of power applied. The cruise control 40 is usually activated/deactivated and operated by means of an operating device most commonly situated close to the steering wheel of the vehicle 1 . It is also usual that the cruise control 40 in an activated state is deactivated by the driver depressing the brake pedal or the clutch pedal.

It has recently become increasingly usual for motor vehicles 1 to be provided with a so-called adaptive cruise control (ACC). Such an adaptive cruise control 40 keeps the vehicle 1 at a given distance or a given time gap from a nearest vehicle 30 ahead. This is usually achieved by the vehicle 1 being fitted with a radar device or laser device by means of which the current spacing between the vehicle 1 and the vehicle 30 is calculated. The vehicle 1 is accelerated or braked on the basis of the current spacing in such a way that the distance from the vehicle 30 ahead is kept constant at an indicated value.

Specification US6208106 refers to an adaptive cruise control which takes into account inter alia the friction of the road surface. Specification US20040140143 further refers to an adaptive cruise control adapted to operating in a short-distance mode or a long-distance mode. Brief description of the invention

An object of the present invention is to propose an improved cruise control for a motor vehicle as compared with prior art cruise controls. Another object of the invention is to propose a cruise control which helps to reduce the vehicle's fuel consumption as compared with prior art cruise controls. A further object of the present invention is to propose an alternative cruise control for motor vehicles.

According to an aspect of the invention, the aforesaid objects are achieved with a cruise control for a motor vehicle provided with a power train which is adapted to assuming various transmission ratios for the propulsion of the vehicle and which comprises at least one engine and at least one gearbox, such that

- the cruise control is adapted to being controlled on the basis of a first parameter R_F which is defined as a difference between a first motive force FM_OX and a second motive force F _r, and

- the first motive force F_Max is a maximum motive force available for the vehicle at a current power train transmission ratio and the second motive force Fo_r is a current running resistance for the vehicle.

According to an embodiment of the invention, the cruise control is further adapted to

operating with automatic regulation of spacing relative to a vehicle ahead, which automatic regulation causes the vehicle to be accelerated, be retarded or maintain a constant speed in order to maintain a given distance 77 D from the vehicle ahead, so that

- a current spacing T_P; D_P between the vehicle and the vehicle ahead is allowed to

deviate from the given distance 77 D on the basis of the first parameter RF and/or a second parameter RA_CC which is defined as the ratio between the first parameter R_F and a standardising factor.

According to another embodiment of the invention, the cruise control is further adapted to:

- operating in a first mode in which automatic regulation of spacing relative to a vehicle ahead takes place in such a way that the vehicle is accelerated, is retarded or maintains a constant speed in order to maintain a given distance T; D from the vehicle ahead, and - operating in a second mode in which a current spacing T_P; D_P between the vehicle and the vehicle ahead is allowed to deviate from the given distance 7V D on the basis of the first parameter R_F and/or the second parameter R_Acc, Further embodiments of the aforesaid cruise control are expressed in the dependent claims pertaining to the cruise control.

The invention relates also to a motor vehicle, e.g. a passenger car, truck or bus, which is provided with at least one cruise control as above.

According to another aspect of the invention, the aforesaid objects are achieved with a method for control of a cruise control for a motor vehicle provided with a power train which is adapted to assuming various transmission ratios for propulsion of the vehicle and which comprises at least one engine and at least one gearbox, which method comprises the steps of - determining a first parameter RF which is defined as a difference between a first motive force and a second motive force _/>, the first motive force FM_OX being a maximum motive force available for the vehicle 1 at a current transmission ratio and the second motive force F_DR a current running resistance for the vehicle; and controlling the cruise control on the basis of the first parameter R_F and/or a second parameter R_Acc which is defined as the ratio between the first parameter Rf and a standardising factor.

According to an embodiment of the above method, the cruise control is further adapted to operating with automatic regulation of spacing relative to a vehicle ahead, such that the vehicle is accelerated, is retarded or maintains a constant speed in order to maintain a given distance T; D from the vehicle ahead, and the method further comprises the step of

- allowing a current spacing T_P; D_P between the vehicle and the vehicle ahead to deviate from the given distance TV D on the basis of the first parameter RF and/or the second parameter RA_CC-

The invention relates also to a computer programme and a computer programme product related to the above method. The present invention proposes a cruise control and a method which utilise information about the vehicle's maximum available motive force and running resistance. This makes it possible for a cruise control according to the invention to set the vehicle's speed so that its fuel consumption can be reduced as compared with using a prior art cruise control.

The invention also proposes an adaptive cruise control which uses information about the vehicle's maximum available motive force and running resistance to determine a current distance from a vehicle ahead, which may be varied in relation to a given desired spacing between the vehicles, depending on the motive force and the running resistance. Here again, the fuel consumption of the vehicle 1 can be reduced.

Further advantages and applications with a cruise control and a method according to the invention will be indicated by the detailed description set out below. Brief description of the drawings

The detailed description of the present invention set out below describes embodiments of the invention 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 maximum torque as a function of the speed of an engine;

- Figure 3 is a graph of a mapping function which converts values representing a motor vehicle's acceleration capacity to virtual accelerator pedal values;

Figure 4 is a graph of a mapping function which converts values representing a motor vehicle's acceleration capacity to virtual accelerator pedal values with reference to a cruise control setting;

- Figure 5 depicts a situation where a current spacing between a vehicle and a vehicle ahead is substantially equal to a given distance;

Figure 6 depicts a situation where a current spacing is greater than a given distance;

- Figure 7 depicts a situation where a current spacing is smaller than a given distance;

Figure 8 is a flowchart for calculation of acceleration capacity for use in a cruise control application;

- Figure 9 is a flowchart for control of an adaptive cruise control according to the

invention;

- Figure 10 is a state diagram for an adaptive cruise control according to the invention; Figure 1 1 depicts a control unit intended to form part of a motor vehicle according to the invention;

- Figure 12 shows how a first motive force and a second motive force act upon a motor vehicle on an upgrade; and

- Figure 13 shows how a first motive force and a second motive force act upon a motor vehicle on a level running surface.

Detailed description of the invention

A cruise control 40 for a motor vehicle 1 according to the present invention is adapted to being controlled on the basis of a first parameter Rf which is defined as a difference between a first motive force FM_UX and a second motive force F_Dr, the first motive force FM_OX being a maximum motive force available for the vehicle 1 at a current transmission ratio and the second motive force F_/> a current running resistance for the vehicle 1 . More specifically, the first parameter RF may be construed as a difference between a first motive force F^ax which represents the maximum sum of the available motive forces which "help" to propel the vehicle 1 in its direction of movement at a current power train transmission ratio, i.e. the available motive force of the vehicle 1 , minus a second motive force For which is the sum of the motive forces which act upon the vehicle 1 in its direction of movement or the opposite direction thereto, and is its current running resistance.

For the sake of better understanding of the invention, there follows a brief description of a power train of a vehicle 1 and the torque curve for an engine 10 of a vehicle 1 with reference to Figures 1 and 2 respectively.

Figure 1 depicts schematically parts of a power train for a motor vehicle 1. The power train comprises an engine 10 which in this case is mechanically connected by a shaft to a first end of a gearbox 20 via a clutch device 40. The gearbox 20 has its second end mechanically connected by a propeller shaft 50 to a differential gear 30 associated with a rear axle. The rear axle comprises left and right drive shafts 60 which drive the undepicted powered wheels of the vehicle 1.

By this well-known arrangement the mechanical work of the engine 10 is transferred, via a number of transmission devices such as clutch device 40, gearbox 20, propeller shaft 50, differential gear 30 and drive shafts 60, to powered wheels for propulsion of the vehicle 1. The gearbox 20 is a transmission device which has a number of forward gears for propelling the vehicle 1 forwards and usually also one or more reverse gears. The number of forward gears varies but twelve forward gears are for example usual in trucks of modern kinds.

The transmission ratio of a power train may vary, enabling it to assume various ratios (i.e. various transmission ratio configurations). The various ratios depend inter alia on the gear currently engaged in the gearbox 20 and on the ratio of the differential gear 30. It may further be noted that there are power trains which can assume a number of different discrete transmission ratios and also power trains which have a continuous range of ratios, e.g.

automatic gearboxes 20 with so-called converters or other types of gearboxes 20 with continuously variable transmissions.

In addition, most motor vehicles 1 have a control system comprising one or more electronic control units 1 10 (ECUs). The purpose of said control system is to control/regulate one or more functions in the vehicle 1 , e.g. by means of one or more actuators which may be related to various functions in the vehicle 1 , such as engine control, gear changing, cruise control, suspension configuration, etc., and said control system uses a number of different parameters, e.g. current engine speed, current accelerator pedal position, current engine torque, and data from various sensors, to control the various functions of the vehicle 1.

Figure 2 is a graph of a maximum torque curve for an engine 10 as a function of its speed. The points P1 -P3 in the graph represent various break points for the maximum torque curve. The graph also pertains to an example of a situation where an engine 10 runs at a speed Rl with an engine torque M l , thus operating below its maximum torque curve by a difference equal to M2-M1 which is illustrated by an arrow. Maximum motive force means the motive force which, via the power train, propels the vehicle 1 in its direction of movement if the engine 10 operates on its maximum torque curve at a current engine speed. On basic understanding of the torque curve of the engine 10 and the power train as described above, the first motive force FM_OX according to an embodiment of the invention is defined as

(1 ) where Eng_lol denotes an available twisting moment at maximum engine torque for the engine 10 at current engine speed, and ;_/n, a current transmission ratio for the power train up to and including the powered wheels of the vehicle 1 , taking the wheel radius into account.

According to another embodiment, the second motive force For is a motive force which can assume a positive value (e.g. on upgrades) or a negative value (e.g. on downgrades) and acts in the opposite direction to the direction of movement of the vehicle 1. Figures 12 and 13 show how the first motive force and the second motive force F _r act upon a vehicle 1 on an upgrade and on a level running surface. The second motive force For depends on one or more parameters from among air resistance, rolling resistance, friction in said power train, moment of inertia, weight of said vehicle 1 and road gradient, i.e. the factors which influence the current running resistance. However, topographical map data and the like may also be used in determining the second motive force For, since for example the road gradient can be derived from relevant map data.

More specifically, the second motive force Fo_r according to an embodiment of the invention is defined as where F _f denotes a current actual motive force for the engine 10, m the weight and a the acceleration of the vehicle 1. In the example in Figure 2, the actual motive force of the engine 10 is equal to Ml .

In the great majority of cases, the second motive force F_Dr will be the motive force which varies the more, since for example the road gradient is a parameter which affects it. However, the first motive force FM_OX will also vary, since the power train transmission ratio varies, depending on such factors such as current transmission ratio in the gearbox 20, wheel radius of the vehicle 1 , variations of the maximum torque curve of the engine 10, etc.

According to a further embodiment of the invention, the first parameter is determined as Dr (3) i.e. the first parameter R_F is defined as a difference according to equation (3) and will assume a negative value, a positive value or a zero value. A negative difference means that the vehicle 1 cannot accelerate at the current power train transmission ratio, i.e. the vehicle 1 is in power deficit and will lose speed (i.e. be retarded); a zero difference means that the vehicle 1 is in a state of power equilibrium in which it can maintain the current speed but not accelerate to a higher speed; and a positive difference means that the vehicle 1 has the potential to accelerate, at least if the engine 10 operates on its maximum torque curve for a given engine speed, as depicted in Figure 2, i.e. the vehicle 1 has a power surplus.

The first parameter R provides an absolute measure of the current motive force

capacity/acceleration capacity of the vehicle 1 , since it is related to the vehicle's current characteristics and running situation, which means inter alia that for the first parameter RF to be usable it needs to be related to said characteristics and running situation. Examples of characteristics are vehicle weight, engine power, and power train configuration; and examples of running situation are road gradient and road surface. Since the first parameter Rp is an absolute measure, a value of, for example, /?,, = 10000 N represents a large acceleration capacity for a vehicle 1 weighing 1000 kg and a very small acceleration capacity for a vehicle 1 weighing 100000 kg.

In contrast, a standardisation of the difference according to equation (3) with reference to the current available motive force capacity of the vehicle 1 provides a relative measure of the vehicle's current acceleration capacity (specialists will appreciate that acceleration may of course also be derived from the first parameter RF on the basis of the relation between acceleration and power according to the laws of physics), which is to be construed as its ability to accelerate. The result is a dimensionless unit comprising information about the engine power of the vehicle 1 , the road gradient, rolling resistance, wind resistance etc. The advantage of a relative measure as above is that it provides a value which indicates how much of the available engine power will be required to be able to accelerate the vehicle 1. This means that said value can with advantage be used directly or indirectly in various applications related to different functions, e.g. control strategies as regards, for example, choice of transmission ratio, running of generator, running of air compressor etc. If the calculation R_ACC produces the result that the engine power will not be sufficient to accelerate the vehicle 1 , the control system can try to "go easy" on the resources which absorb energy (e.g. air compressor, generator etc.), while at the same time trying to run the engine 10 at a speed which delivers maximum motive force. This means the control system trying to use as much as possible of the torque of the engine 10 to propel the vehicle 1 instead of, for example, filling the air tanks with air, which the system will endeavour to do at times when it has scope for using energy "free of charge", e.g. during engine braking of the vehicle 1 on downgrades. It will therefore be appreciated that said parameter is usable in many different functions in a vehicle 1 , and in the description below it is referred to as a second parameter

R

A further embodiment of the invention relates to a cruise control 40 adapted to being controlled on the basis of a second parameter R_ACC which is itself based on the first parameter RF- The second parameter R _CC represents an acceleration capacity of a motor vehicle 1 , which is determined as a ratio between the first parameter RF and a standardising factor. In a preferred embodiment, the second parameter is determined as

¹ Max ' Max where the term in the denominator is a standardising factor, so the vehicle 1 is in acceleration surplus if R_{A I}. > 0 , in acceleration deficit if R_AN. < 0 and in acceleration equilibrium if R_ALC = 0 . Moreover, if R_AIL > 1 , the whole of the engine power can be used to accelerate the vehicle 1 , in which case it gains speed without any power having to be supplied from the engine 10 (as on steep downgrades).

As mentioned above, the first parameter R or the second parameter R_ACC may also be used to determine a virtual accelerator pedal value. In this context, virtual accelerator pedal value means a theoretically calculated value which may be, and usually is, different from the actual accelerator pedal value, the latter being the actual value assumed by the accelerator pedal when a driver depresses it while the vehicle 1 is in motion. If the second parameter RA _C is used to calculate such a virtual accelerator pedal value, this may be done by means of a mapping function such as depicted in the graph in Figure 3, where the virtual accelerator pedal value (the y axis), Pv, is plotted against the second parameter R _CC (the x axis) which represents the acceleration capacity of the vehicle 1. Figure 3 shows how the virtual accelerator pedal value is converted by said mapping function to 100%, corresponding to full acceleration, when the second parameter RA_CC assumes a value smaller than 0, and to 0%, corresponding to no acceleration, when R_Acc assumes a value larger than 1. Such mapping of the second parameter R _CC means that the virtual accelerator pedal value is converted to 100% in situations of power equilibrium or power deficit, i.e. when R_ACC≤ 0 , and somewhere 0 and 100% when the vehicle is in power surplus (in Figure 3 the function is linear within this range).

When the whole of the engine power can be used to accelerate the vehicle 1 , i.e. when R_ACC -

1 , the accelerator pedal value is converted to 0%, a situation in which a possible application might be to try to mimic an accelerator pedal movement which an actual driver makes when he/she is driving economically and wishes to maintain constant speed, i.e. easing off the power at hillcrests and on downgrades and applying more power at the beginning of climbs and on upgrades. The behaviour of an actual driver is thus modelled by a virtual driver according to that application. It will therefore be appreciated that the virtual accelerator pedal value is usable in a range of applications which depend on an accelerator pedal value, e.g. modelling of virtual drivers in order to provide hints for drivers, control of ancillary units, indication of hints for drivers, etc. It should also be noted that the virtual accelerator pedal value may be used either as the sole input parameter in said applications or in combination with other input parameters, e.g. the actual accelerator pedal value.

Figure 4 depicts an example of a mapping function of a virtual accelerator pedal value when using the first parameter Rp or the second parameter R^_cc in a cruise control 40 according to the invention. The axis represents permissible values for a virtual accelerator pedal and the x axis a difference between a desired speed locked on the cruise control (i.e. the desired speed set on the cruise control) and the current actual speed of the vehicle 1. This difference between the two speeds will define permissible values which the virtual accelerator pedal may assume, and the virtual accelerator pedal value of the second parameter RACC is determined between these extreme values (e.g. by means of a mapping function depicted in Figure 3). For example, when running on cruise control, the control system knows the speed which the driver wishes the vehicle 1 to run at and it is therefore possible to take into account the deviation (offset) from Vsei, i.e. the desired speed corresponding to an offset value of 0 in Figure 4. If the speed drops below V_seh the freedom of movement of the pedal value decreases and the pedal value is forced towards the maximum value (Max in Figure 4).

Similarly, if the speed rises above ν_&,, the freedom of movement likewise decreases and the pedal value is forced consistently towards the minimum value (Min in Figure 4) with the object of keeping the vehicle 1 at the desired speed V_Sel. Such a version of the invention means that the second parameter R_Au. will be an input parameter in the accelerator pedal calculation relating to a cruise control application where the system tries to maintain a constant speed of the vehicle 1 , depending on various running conditions, e.g. road gradient, and the limitations of the accelerator pedal value indicate whether the system wishes to increase/decrease the vehicle's speed. In an application such as this, the system tries to use a virtual driver to model an actual driver trying to maintain a constant speed, which means that if the vehicle 1 is over/under the target speed this is compensated for by its speed being decreased or increased respectively. In contrast, if the vehicle 1 is at the desired speed, it is ambient factors such as road gradient, wind resistance, vehicle weight etc. which determine the accelerator pedal value ( R_Acc in the model).

As previously described, it has become increasingly usual for motor vehicles 1 to be provided with so-called adaptive cruise controls 40. The first parameter Rf or the second parameter R_Acc may also be used for controlling such a type of cruise control 40. For this reason, an embodiment of the invention relates to a cruise control 40 which is further adapted to operating with automatic regulation of spacing relative to a vehicle 30 ahead. The automatic regulation of spacing means that the vehicle 1 is accelerated, is retarded or maintains a constant speed in order to maintain a given distance T; D from the vehicle 30 either by accelerating the vehicle 1 by means of its engine 10 or by retarding it by engine braking or by use of brakes, e.g. wheel brakes and/or supplementary brakes, etc. The adaptive cruise control 40 is also adapted to allowing the current spacing T_p; D_p between the vehicle 1 and the vehicle 30 to deviate from the given distance T; D on the basis of the first parameter RF and/or the second parameter R_Acc The term "allow" in this context means that the cruise control 40, depending on the first parameter Rp or the second parameter R_Acc, allows the current spacing T_p; D_p between the vehicle 1 and the vehicle 30 to deviate at times from the given distance T; D before, for example, it retards or accelerates the vehicle 1 to cause the current spacing T_p; D_p to become equal to the given distance T; D, and this permitted deviation may be measured in terms of time or distance. For example, if the vehicle 30 ahead maintains a constant speed (e.g. with a conventional prior art cruise control 40), the vehicle 1 on an upgrade may initially allow the distance between the vehicles to increase (allow the current spacing T_p; D_p to become greater than the given distance T; D) and may on a subsequent downgrade "catch up on" the vehicle 30 (allow the current spacing T_p; D_p to become smaller than the given distance T; D) in order thereafter on a level road to "freewheel" (with the power train disconnected) or let the engine 10 "trail" (with engine braking) for a longer time before the cruise control 40 begins to accelerate the vehicle in order to cause the current spacing T_p; D_p to become equal to the given distance T; D. The vehicle 1 can thus save further fuel.

According to an embodiment of the invention, a current spacing T_p; D_p may assume a value greater than a minimum value and/or smaller than a maximum value. The maximum and minimum values may depend on a range of different factors and may be regarded as representing the outer limits for permissible variation of the current spacing T_p; D_p between the vehicle 1 and the vehicle 30. It is for example not desirable that the vehicle 1 should be so close to the vehicle 30 as to become a traffic hazard or be felt to be "intimidating" for the driver. If the vehicle 1 is running at high speed, the minimum spacing will usually be greater, since a certain distance at low speed represents a shorter "time gap" if the same distance is applied at a higher speed. Nor is it desirable for a current spacing T_p; D_p relative to a vehicle 30 ahead to be so great as to cause risk of the spacing detection (e.g. radar) losing contact with the vehicle 30.

The maximum and minimum values may also depend on a detected acceleration capacity of the vehicle 30 ahead, which might for example mean small permissible variations of the permissible spacing if the vehicle 30 has more acceleration capacity (and/or motive force capacity) than the vehicle 1 , and greater permissible spacing variations if the vehicle 1 has more acceleration capacity (and/or motive force capacity) than the vehicle 30. The spacing variation may also depend on the prevailing traffic situation in that if the vehicle 1 is in dense traffic the permissible spacing variation may be decreased to avoid causing irritation to other road users, since variations in the speed of the vehicle 1 will also force vehicles behind to vary/adjust their speed more or less according to the speed of the vehicle 1.

Another embodiment of a cruise control 40 according to the invention is further adapted to operating in a first mode C 1 in which there is automatic regulation of spacing relative to a vehicle 30 ahead. As previously mentioned, the automatic regulation means that the vehicle 1 is accelerated, is retarded or maintains a constant speed in order to maintain a given distance T; D from the vehicle 30. The adaptive cruise control 40 is also adapted to operating in a second mode C2 in which a current spacing T_P; D_P between the vehicle 1 and the vehicle 30 is permitted to deviate from the given distance T; D on the basis of the first parameter RF and/or the second parameter R_ACC.

A cruise control 40 capable of operating in a first mode C 1 or a second mode C2 may also be adapted, when operating in said first mode C 1 , to switching to said second mode C2 if the first parameter RF and/or the second parameter R_Acc assume/s a value greater than or smaller than zero. Similarly, if the cruise control 40 is operating in said second mode C2 it may switch to said first mode C I if the first parameter RF and/or the second parameter R_Acc assume/s a zero value.

In a practical application of a cruise control 40 according to the invention, a tolerance value T may be used, meaning that a range about zero, i.e. 0 +/- T, is defined and the first parameter RF or the second parameter R_ACC is treated as zero in a cruise control application if said parameters assume a value within that range. The tolerance value T may preferably be arrived at by calibration and will vary for different types of vehicle 1.

The choice of values for the tolerance value T affects how often the speed of the vehicle 1 will vary. If the tolerance value T is large, the spacing set by the driver as a desired distance from the vehicle 30 ahead will be maintained more often, with consequently less spacing variation relative to the vehicle 30. A smaller tolerance value T therefore means that the control system of the vehicle 1 allows deviations from the given distance T; D on more occasions. Choosing a large tolerance value T gives priority to the given distance T; D set by the driver, and a small tolerance value gives priority to reducing fuel consumption, since the control system will then vary the speed of the vehicle 1 more often, depending on the vehicle's running resistance. A tolerance value T is therefore usable as an input parameter for control inter alia of driving experience ("comfort parameters"), fuel consumption etc.

In this description, unless indicated otherwise, spacing means an amount of time or a physical distance between a vehicle 1 and a vehicle 30 ahead. A current spacing T_P; D_P between the vehicle 1 and the vehicle 30 means the momentary distance between them, and a given distance T; D between the vehicle 1 and the vehicle 30 means the spacing which the cruise control 40 is set to try to maintain between the vehicle 1 and the vehicle 30.

An embodiment of an adaptive cruise control 40 according to the invention allows the current spacing T_P; D_P to be greater than the given distance T; D if the first parameter RF or the second parameter R_ACC assumes a value smaller than zero. Another embodiment of the invention allows the current spacing T_P; D_P to be smaller than the given distance 7^"; D if the first parameter RF or the second parameter R_ACC assumes a value greater than zero.

In a preferred embodiment of the invention the cruise control 40 is adapted to being a combination of the two above embodiments, allowing the current spacing T_P; D_P to be greater or smaller than the given distance T; D, depending on the value of the first parameter RF and/or the second parameter R_AC -

Figures 5-7 depict examples of how an adaptive cruise control 40 according to the invention may function. Figure 5 depicts how a vehicle 1 maintains a given distance T; D from the nearest vehicle 30 ahead, i.e. the current spacing T_P; D_P between the vehicle 1 and the nearest vehicle 30 ahead is equal to the given distance T; D owing to the value of the first parameter RF and/or the second parameter R_ACC being zero, e.g. because the running surface/road is level. In Figure 6, the current spacing T_P; D_P is allowed to be greater than the given distance T; D owing to the first parameter RF and/or the second parameter R_ACC assuming a value smaller than zero, e.g. on an upgrade, and the vehicle 30 maintains a constant speed as depicted in Figure 6. Conversely, the situation depicted in Figure 6 allows the current spacing T_P; D_P to be smaller than the given distance T; D in Figure 7, owing to the first parameter RF and/or the second parameter R_ACC assuming a value greater than zero, e.g. when the vehicle 1 is on a downgrade. In the light of the above it is sometimes or often advantageous from a fuel consumption point of view to increase the spacing between the vehicles rather than slavishly "follow" the vehicle 30 ahead, e.g. on an upgrade. It is also most commonly possible for on an increased current spacing T_P; D_P to be rectified after an upgrade by the cruise control 40 allowing the current spacing T_P; D_P to be smaller than the given distance T; D on a subsequent downgrade (Figure 7), e.g. by the brakes being used later than in the case of a prior art adaptive cruise control. The vehicle 1 can thus save further fuel. It should therefore be appreciated that it is advantageous that a current spacing T_P; D_P be allowed to vary relative to a given distance T; D, depending on the first parameter RF and/or the second parameter R_ACC in an adaptive cruise control 40, as the inventor has discovered.

In more detail, the control of a cruise control 40 according to the invention may for example take place according to the flowcharts in Figures 8 and 9. In Figure 8, the second parameter RA_CC, i.e. the acceleration capacity of the vehicle 1 , is calculated in this example as follows:

1. Reading of sensors and other information and/or data, e.g. gear currently engaged, given cruise control speed, etc.;

2. Reading in of vehicle data, e.g. maximum available engine torque for the vehicle 1 , total transmission ratio of the vehicle 1 , etc.;

3. Calculation of the running resistance of the vehicle 1 , which may be done on the basis of parameters such as current engine torque, road gradient, acceleration of the vehicle 1 , etc.;

4. Calculation of the maximum motive force of the vehicle 1 , which may be done by using parameters such as maximum available engine torque, total transmission ratio of the vehicle 1 , etc.; and

5. Calculation of the acceleration capacity R_Ac ox the vehicle 1 according to any of the embodiments described above.

Given the calculation in the flowchart in Figure 8, an adaptive cruise control 40 according to the invention may be controlled according to the flowchart in Figure 9 as follows: 6. Decide in which mode (C I or C2) the cruise control 40 should operate in the given calculation above, thus operating in the first mode CI if R_AC is zero and in the second mode C2 if R_ACC is not zero;

7. If operating in the first mode C I , the cruise control 40 endeavours to keep the current spacing T_P; D_P between the vehicles the same as the given distance T; D, i.e. the cruise control 40 allows no deviation from the given distance in this mode; and

8. If operating in the second mode C2, the cruise control allows the current spacing T_P; D_P to deviate from the given distance T; D, depending on the value of the acceleration capacity R_ACI , and hence

8a. the current spacing T_P; D_P is allowed to be greater than the given distance T; D if the acceleration capacity RA_CC is smaller than zero

and

8b. the current spacing T_P; D_P is allowed to be smaller than the given distance T; D if the acceleration capacity RA_CC «S greater than zero.

Figure 10 is a state diagram for an adaptive cruise control 40 according to the invention, illustrating conditions for switching between the two respective modes C I and C2 in which the adaptive cruise control 40 operates.

A cruise control 40 according to the invention is preferably fitted, or implemented, in a motor vehicle 1 which comprises one or more control units 1 10, which may for example be an electronic control unit (ECU) adapted to controlling one or more functions in the vehicle 1 , e.g. gear changing, engine speed, braking, acceleration. The control unit 1 10 is further adapted to controlling the cruise control 40 by calculation of the first parameter R_F and/or the second parameter RA_CC in real time. Figure 10 depicts schematically a control unit 1 10 described above. The control unit 1 10 comprises a calculation unit 1 1 1 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 1 1 1 , is connected to a memory unit 1 12 which is incorporated in the control unit 1 10 and which provides the calculation unit 1 1 1 with, for example, the stored programme code and/or the stored data which the calculation unit 1 1 1 needs for it to be able to perform calculations. The calculation unit 1 1 1 is also adapted to storing partial or final results of calculations in the memory unit 1 12.

The control unit 1 10 is further provided with devices 1 13, 1 14, 1 15, 1 16 for receiving input signals and sending output signals. These input and output signals may comprise waveforms, pulses or other attributes which the signal receiving devices 1 13, 1 16 can detect as information and which can be converted to signals processable by the calculation unit 1 1 1. The calculation unit 1 1 1 is then provided with these signals. The signal sending devices 1 14, 1 15 are adapted to converting signals received from the calculation unit 1 1 1 in order, e.g by modulating them, to create output signals which can be transmitted to other parts of the system. One skilled in the art will appreciate that the aforesaid computer may take the form of the calculation unit 1 1 1 and that the aforesaid memory may take the form of the memory unit 1 12.

Each of the connections to the devices for receiving input signals and sending 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, an 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.

The invention relates also to a method for control of a cruise control 40 for a motor vehicle 1 provided with a power train which is adapted to assuming various transmission ratios for propulsion of the vehicle 1 and which comprises at least one engine 10 and at least one gearbox 20, which method comprises the steps of: determining a first parameter Rp which is defined as a difference between a first motive force F»_ax and a second motive force For, the first motive force FM_OX being a maximum motive force available for the vehicle 1 at a current transmission ratio and the second motive force For a current running resistance for the vehicle; and controlling the cruise control 40 on the basis of the first parameter RF and/or a second parameter RA_CC which is being defined as the ratio between the first parameter R_F and a standardising factor. The invention relates also to a method as above whereby the cruise control 40 is further adapted to operating with automatic regulation of spacing relative to a vehicle 30 ahead, such that the vehicle 1 is accelerated, is retarded or maintains a constant speed in order to maintain a given distance T; D from the vehicle ahead, which method further comprises the step of allowing a current spacing T_P; D_P between the vehicle 1 and the vehicle 30 to deviate from the given distance T; D on the basis of the first parameter Rp and/or the second parameter RA_CC-

Specialists will also realise that the method according to the invention can be modified to conform to the various embodiments of a cruise control 40 as above.

Specialists will appreciate that a method for control of a cruise control according to the present invention may also be implemented in a computer programme which, when executed in a computer, causes the computer to apply the method. The computer programme is contained in a computer-readable medium of a computer programme product, which medium 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), a hard disc unit, etc.

Finally, the present invention is not limited to its embodiments described above, but relates to and comprises all embodiments of the invention within the scope of protection of the attached independent claims.

Claims

1. A cruise control for a motor vehicle ( 1 ) provided with a power train which is adapted to adopting various transmission ratios for propulsion of the vehicle ( 1 ) and which comprises at least one engine (10) and at least one gearbox (20), characterised in that

the cruise control (40) is adapted to being controlled on the basis of a first parameter Rfr which is defined as a difference between a first motive force F_Max and a second motive force , and

- the first motive force F_Max is a maximum motive force available for the vehicle (1 ) at a current power train transmission ratio and the second motive force F_Dr is a current running resistance for the vehicle (1 ).

2. A cruise control according to claim 1 , in which

the first motive force FM_OX is a motive force which, via the power train, propels the vehicle ( 1) in its direction of movement at current maximum engine torque available for the engine (10), and

the second motive force Fo_r is a motive force which may assume a positive or a negative value and acts upon the vehicle (1 ) in the tatter's direction of movement and which depends on one or more parameters from among air resistance, rolling resistance, friction in said power train, moment of inertia, topographical map data, road gradient and weight of the vehicle ( 1 ).

3. A cruise control according to claim 2, in which

- the first motive force FM_OX is defined as F_Max = Eng_Tol x i_Tol , where Eng_lol denotes a maximum engine torque available for the engine ( 10) at current engine speed, and i_Tol denotes a current transmission ratio for the power train up to and including the powered wheels, taking the wheel radius into account, and

- the second motive force For is defined as F_nr - F_Rf - m x a , where F_Rf denotes a current actual motive force for the engine (10), m a weight and a an acceleration for the vehicle (1 ).

4. A cruise control according to any one of the foregoing claims, in which the first parameter R_F is defined by the equation R = F_MAX - F_DR , the vehicle ( 1 ) being in motive force surplus if R_F > 0 , in motive force deficit if R_R < 0 and in motive force equilibrium if R_R = 0 .

5. A cruise control according to claim 1 , which cruise control (40) is controlled on the basis of a second parameter R_ACC which is defined as the ratio between the first parameter RF and a standardising factor.

6. A cruise control according to claim 5, in which the second parameter RA_CC is

F - F R

determined by the equation R_ACC = =— ^!— , the vehicle (1 ) being in acceleration

^Max ^Max

surplus if R_ACC > 0 , in acceleration deficit if R_ACC < 0 and in acceleration equilibrium if

7. A cruise control according to claims 1 -6 which is further adapted to

- operating with automatic regulation of spacing relative to a vehicle (30) ahead, which automatic regulation causes the vehicle (1 ) to be accelerated, be retarded or maintain constant speed in order to maintain a given distance {T; D) from the vehicle (30), so that

- a current spacing (T_P; D_P) between the vehicle (1 ) and the vehicle (30) is allowed to deviate from the given distance (T; D) on the basis of the first parameter RF and/or a second parameter RA_CC-

8. A cruise control according to claims 1 -6 which is further adapted to:

operating in a first mode (CI) in which automatic regulation of spacing relative to a vehicle (30) ahead takes place in such a way that the vehicle (1 ) is accelerated, is retarded or maintains constant speed in order to maintain a given distance (77 D) from the vehicle (30), and

operating in a second mode (C2) in which a current spacing (T_P; D_P) between the vehicle (1 ) and the vehicle (30) is allowed to deviate from the given distance (T; D) on the basis of the first parameter RF and/or the second parameter RA_CC-

9. A cruise control according to claim 8, which cruise control (40) is also adapted - if operating in said first mode (C 1 ), to switching to said second mode (C2) if the first parameter Rp and/or the second parameter RA_CC assume/s a value greater or smaller than zero, and

- if operating in said second mode (C2), to switching to said first mode (CI) if the first parameter Rf and/or the second parameter RA_CC assume/s a zero value.

10. A cruise control according to claim 9, which cruise control (40) is further adapted to using a tolerance value T by which a range 0 +/- T is defined about zero, which first parameter RF or second parameter R_Acc is regarded as zero in the cruise control (40) if the first parameter RF or the second parameter R_Acc assumes a value within the range 0 +/- T.

1 1. A cruise control according to claims 7- 10, in which the current spacing (T_p; D_p) is allowed to be greater than the given distance (77 D) but not greater than a maximum distance if the first parameter R_F and/or the second parameter RA_CC assume/s a value smaller than zero, which maximum distance depends on one or more of the following factors; the vehicle's current speed, traffic safety, motive force capacity and/or acceleration capacity for the vehicle (30) ahead, traffic situation and driving experience.

12. A cruise control according to claims 7- 1 1 , in which the current spacing (T_p; D_p) is allowed to be smaller than the given distance (T; D) but not smaller than a minimum distance if the first parameter R_F and/or the second parameter RA_CC assume/s a value larger than zero, which minimum distance depends on one or more of the following factors: the vehicle's current speed, traffic safety, motive force capacity and/or acceleration capacity for the vehicle (30) ahead, traffic situation and driving experience.

13. A cruise control according to claims 7-12, in which the given distance (T; D) and the current spacing (T_p; D_p) are each an amount of time or a physical distance.

14. A cruise control according to claims 7- 13, in which the vehicle (30) ahead is the nearest vehicle ahead.

15. A motor vehicle (1 ), e.g. passenger car, truck or bus, which is provided with at least one cruise control (40) according to any one of claims 1 -14.

16. A motor vehicle (1 ) according to claim 15, further comprising a control unit (1 10), e.g. an electronic control unit (ECU), which is adapted to controlling one or more functions in the vehicle (1 ), e.g. gear changing, engine speed, braking, acceleration, and is further adapted to controlling the cruise control (40) by calculation of the first parameter R_F or the second parameter R_ACC in real time.

17. A method for control of a cruise control for a motor vehicle ( 1 ) provided with a power train which is adapted to assuming various transmission ratios for propulsion of the vehicle ( 1 ) and which comprises at least one engine ( 10) and at least one gearbox (20), characterised by comprising the steps of

determining a first parameter R_F which is defined as a difference between a first motive force FM_OX and a second motive force Fp_r, the first motive force being a maximum motive force available for the vehicle ( 1 ) at a current transmission ratio and the second motive force F_Dr a current running resistance for the vehicle (1 ); and - controlling the cruise control (40) on the basis of the first parameter R_F and/or a

second parameter RA_CC which is defined as the ratio between the first parameter RF and a standardising factor.

18. A method for control of a cruise control according to claim 17, which cruise control is further adapted to operating with automatic regulation of spacing relative to a vehicle (30) ahead, such that the vehicle (1 ) is accelerated, is retarded or maintains constant speed in order to maintain a given distance (7, D) from the vehicle (30), which method further comprises the step of

allowing a current spacing (T_P; D_P) between the vehicle ( 1 ) and the vehicle (30) to deviate from the given distance (T; D) on the basis of the first parameter R_F and/or the second parameter RA_CC-

19. A computer programme which comprises programme code and which, when said programme code is executed in a computer, causes said computer to apply the method according to claims 17-18.

20. A computer programme product comprising a computer-readable medium and a computer programme according to claim 19, which programme is contained in said computer- readable medium which is from among ROM (read-only memory), PROM (programmable ROM), EPROM (erasable PROM), flash memory, EEPROM (electrically erasable PROM) and hard disc unit.