EP2555942A1

EP2555942A1 - Method and module pertaining to cruise control

Info

Publication number: EP2555942A1
Application number: EP11766238A
Authority: EP
Inventors: Oskar Johansson; Jörgen HANSSON; Maria SÖDERGREN; Henrik Pettersson
Original assignee: Scania CV AB
Current assignee: Scania CV AB
Priority date: 2010-04-08
Filing date: 2011-03-30
Publication date: 2013-02-13
Also published as: EP2555942A4; SE534752C2; SE1050335A1; WO2011126431A1

Abstract

The invention relates to a method for determining speed set-point values v_ref for a control system in a vehicle, which method comprises: A) determining a horizon by means of location data and map data for an itinerary made up of route segments and at least one characteristic for each segment; B) calculating speed set-point values v_ref for the vehicle's control system along the horizon on the basis of rules pertaining to characteristics of segments, and when a lowering of the vehicle's entry speed V_in, i to a segment is calculated to be necessary if the end speed v_slut, i in the segment is to be ≤ v_max and unnecessary braking thereafter is consequently to be avoided, the method comprises: C) calculating within the horizon a trigger location from which the fuel injection to the vehicle has to be throttled in order to achieve a lowering to V_in, i, provided that vm;n ≤ v_ref≤ v_max, where v_min and v_max set the limits for permissible speeds for v_ref, which trigger location is subject to continued calculations of speed set-point values v_ref, and D) regulating the vehicle according to the speed set-point values v_ref. The invention relates also to a module arranged to calculate speed set-point values v_ref for a control system in a vehicle.

Description

Method and module pertaining to cruise control Field of the invention

The present invention relates to a method and a module for calculating speed set-point values v_ref for a control system in a vehicle, and for calculating in particular when a lowering of the vehicle's speed has to be effected.

Background to the invention

Many vehicles today are equipped with a cruise control to make them easier to drive. A desired speed can then be set by the driver, e.g. via a control device in the steering wheel console, and a cruise control system in the vehicle thereafter causes a control system to accelerate and brake the vehicle in order to maintain the desired speed. If the vehicle is equipped with an automatic gear change system, it changes gear in such a way that the vehicle can maintain the desired speed.

When a cruise control is used in hilly terrain, the cruise control system will try to maintain a set speed uphill. This results inter alia in the vehicle accelerating over the crest of a hill and possibly into a subsequent downgrade, making it necessary for it to be braked to avoid exceeding the set speed. This is a fuel-expensive mode of driving.

By varying the vehicle's speed in hilly terrain it is possible to save fuel as compared with a conventional cruise control. This may be done in various ways, e.g. by calculations of the vehicle's current state (as with Scania Ecocruise ®). If an upgrade is calculated, the system then accelerates the vehicle uphill. Towards the end of the climb, the system is programmed to avoid acceleration until the gradient has levelled out at the top, provided that the vehicle's speed does not drop below a certain level. Lowering the speed at the end of a climb makes it possible to regain it on a subsequent downgrade without having to use the engine to accelerate. When the vehicle approaches the bottom of a dip, the system endeavours to use the kinetic energy in order to begin the next climb at a higher speed than an ordinary cruise control. The system provides slight acceleration at the end of the downgrade to maintain the vehicle's momentum. In undulating terrain, this means that the vehicle begins the next climb at a higher than normal speed. Fuel can be saved by avoiding unnecessary acceleration and utilising the vehicle's kinetic energy.

We next describe examples of cruise controls which try to reduce the amount of fuel used when there is a change in the nature of the road. The cruise control described in US patent 6,206,123 Bl endeavours to ensure that the vehicle maintains a desired reference speed. A control unit controls how much fuel is to be injected into the engine, depending on the vehicle's speed at the time. If it is higher than a desired target speed, the control unit determines that the vehicle is travelling downhill, and the fuel injection is throttled.

US 2008/0306669 Al describes a cruise control which interacts with throttling of fuel injection in the engine when the vehicle is on a steep downgrade. The cruise control endeavours constantly to maintain the reference speed, which means that signals to an accelerator pedal to increase speed or signals to throttle fuel injection may be sent several times on the same downgrade, which may result in jerky running. To achieve gentle transitions between the various states, the signal to the fuel injection may be ramped. The gradient of the road is determined by continuously evaluating the vehicle's speed.

The object of the present invention is to propose an improved method for reducing fuel consumption and/or shortening driving time when a vehicle is driven with the assistance of cruise control.

Summary of the invention

The object described above is achieved by a method for calculating speed set-point values v_ref for a control system in a vehicle, comprising A) determining a horizon by means of location data and map data for an itinerary made up of route segments and at least one characteristic for each segment; B) calculating speed set-point values v_ref for the vehicle's control system along the horizon on the basis of rules pertaining to characteristics of segments, and when a lowering of the vehicle's entry speed i to a segment is calculated to be necessary if the end speed v_si_ut, i in the segment is to be < v_max and unnecessary braking thereafter is consequently to be avoided, the method comprises: C) calculating within the horizon a trigger location from which the fuel injection to the vehicle has to be throttled in order to achieve a lowering to ν;_Πι provided that v_mj_n < v_ref < v_max, where v_min and Vmax set the limits for permissible speeds for v_ref, which trigger location is subject to continued calculations of speed set-point values v_ref, and D) regulating the vehicle according to the speed set-point values v_ref.

According to another aspect, the object is achieved by a module for determining speed set- point values v_ref for a vehicle's control system, which module comprises a horizon unit arranged to determine a horizon by means of location data and map data for an itinerary which is made up of route segments and at least one characteristic for each segment; the module also comprises a processor unit arranged to: calculate speed set-point values v_ref for the vehicle's control system along the horizon on the basis of rules pertaining to characteristics of segments, and when a lowering of the vehicle's entry speed v;_n, i to a segment is calculated to be necessary if the end speed v_smt, , in the segment is to be < v_max and unnecessary braking thereafter is consequently to be avoided, the processor unit is arranged to calculate within the horizon a trigger location from which the fuel injection to the vehicle has to be throttled in order to achieve a lowering to Vj_n, provided that v_mj„ < ref≤ max, where Vmin and Vmax set the limits for permissible speeds for v_ref, which trigger location is subject to continued calculations of speed set-point values v_ref, the vehicle being thereafter regulated according to the speed set-point values v_ref.

The vehicle's speed is predicted along a horizon which is typically 1 to 2 km long. When the speed predicted is above or below respective predetermined thresholds v_mi_n and v_max about the set speed selected by the driver, the algorithm tries to adjust the reference speed v_ref, i e. the speed applied to the vehicle's cruise control, on preceding segments (nearer to the vehicle) of the horizon within the range defined by v_mj_n and v_max-

To effect throttling of the fuel supply to its engine, the vehicle's reference speed may be lowered quickly in a single step. Throttling the fuel supply means that no fuel is injected into the engine. The amount of speed lowering needs to be sufficient to result in drag torque. Throttling the fuel supply to the engine to avoid unnecessary braking due to too high speed on, for example, a downgrade or a bend makes it possible to reduce driving time as compared with ramping the vehicle's speed down. Ramping the vehicle's speed may be effected by applying Torricelli's formula (1), which means the vehicle's reference speed increasing or decreasing in a substantially linear manner. By throttling the fuel supply the same lowering of speed can be effected in a shorter time, resulting in less loss of driving time. The reduced driving time may instead be converted to fuel saving by lowering the vehicle's speed on level roads. The driver will usually notice the lowering of speed, which makes it safer in that he/she is aware of what is going to happen.

If lowering the vehicle's speed by throttling the fuel supply is to meet comfort

requirements, the vehicle needs to have a significant weight, otherwise the driver may find its behaviour unexpected and uncomfortable, and other road users may have difficulty in anticipating such a driving style.

Preferred embodiments are described in the dependent claims and the detailed description. Brief description of the attached drawings

The invention is described below with reference to the attached drawings, in which:

Figure 1 depicts a module according to the invention, arranged to determine speed set- point values v_ref.

Figure 2 illustrates the length of a control system's horizon in relation to the length of the itinerary for the vehicle.

Figure 3 is a flowchart for the method according to an embodiment of the invention.

Figure 4 illustrates a comparison of the vehicle's speed when various different cruise control methods are used.

Figure 5 illustrates how the fuel injection varies between the various methods in Figure 4. Figure 6 depicts an example of how the trigger location for fuel supply throttling to begin is calculated according to an embodiment of the invention.

Detailed description of preferred embodiments of the invention

Information about a vehicle's itinerary can be used to determine its reference speed v_ref for the engine control system in the vehicle when using cruise control in order to save fuel, increase safety and enhance comfort. Other set-point values for other control systems may also be regulated. Topography greatly affects the control of, in particular, the power train of heavy vehicles, since much more torque is required uphill than downhill and to make it possible to climb some hills without having to downshift.

The vehicle is provided with a positioning system and map information, and location data from the positioning system and topology data from the map information are used to construct a horizon which represents the nature of the itinerary. In the description of the present invention, GPS (Global Positioning System) is indicated for determining location data for the vehicle, but other kinds of global or regional positioning systems are also conceivable to provide vehicle location data, e.g. systems which use radio receivers to determine the vehicle's location. The vehicle may also use sensors to scan the

surroundings and thereby determine its location.

Figure 1 illustrates how a unit incorporates map and GPS information about the itinerary. The itinerary is exemplified below as a single route for the vehicle but it should be appreciated that various conceivable itineraries are incorporated as information via maps and GPS or other positioning systems. The driver may also register the starting point and destination point for the intended journey, in which case the unit uses map data etc. to calculate a suitable route. The itinerary or, if there are two or more possible alternatives, the itineraries are sent bit by bit via CAN (controller area network) to a module for calculation of set-point values. The module may be separate from or be part of the systems which are to use the regulating set-point values. Alternatively, the unit with maps and positioning system may also be part of a system which uses the regulating set-point values. In the module, the bits are put together in a horizon unit to construct a horizon and are processed by the processor unit to create an internal horizon on which the control system can regulate. If there are two or more alternative itineraries, a similar number of internal horizons are created for the various alternatives. The control system may be any of the various control systems in the vehicle, e.g. engine control system, gearbox control system or some other control system. A horizon is usually constructed for each control system, since control systems regulate on different parameters. The horizon is then continually provided with new bits from the unit with GPS and map data, to maintain a desired length of horizon. The internal horizon is thus updated continuously when the vehicle is in motion, as illustrated in Figure 2. β

CAN is a serial bus system specially developed for use in vehicles. The CAN data bus makes digital data exchange possible between sensors, regulating components, actuators, control devices, etc. and provides assurance that two or more control devices can have access to the signals from a given sensor in order to use them to control components connected to them.

Various notations with the following meanings are used in the description:

v_set: cruise control set speed preselected by, for example, the driver

Vref-: reference speed displayed within v_mi_n < v_ref < v_max in order if possible to keep vehicle speed within the range v_mj_n to v_max

Vi_ni j: entry speed to segment (i)

siut, end speed in segment (i) with entry speed Vj„, i, under normal cruise control pred, i-i ^' predicted end speed in segment (i-1) with some other low or negative engine torque, e.g. drag torque

Avin, tot: desired lowering of speed before segment (i)

Avpred, i-i : possible lowering during segment (i-1), predicted with, for example, drag torque Δνίη, rest: remaining lowering needed, Av,_n, tot - Δν_ρΓβ(ι, M - Av_pred, \-i which decreases continuously after segments ahead have been taken into account.

Other notations are explained in the course of the text.

The present invention relates to a method illustrated in the flowchart in Figure 3 according to an embodiment of the invention. The example described below refers to only one horizon but it should be appreciated that two or more horizons for various alternative itineraries might be constructed in parallel. The method comprises a first step A) of determining a horizon based on location data and map data for an itinerary made up of route segments and at least one characteristic for each segment. A characteristic may for example be the segment's length, gradient, radius of curvature, road signs, sundry hindrances etc. When the vehicle is in motion, the horizon module puts the bits together progressively to construct a horizon of the itinerary, the length of the horizon being typically of the order of 1 to 2 km. The horizon unit keeps track of where the vehicle is and continually adds to the horizon so that its length is kept constant, as illustrated in Figure 2. According to an embodiment, when the destination point of the journey is within the length of the horizon, the horizon is no longer added to, since travelling beyond the destination point is not relevant.

The horizon is made up of route segments which have various inter-related characteristics. The horizon is here exemplified in matrix form in which each column contains a characteristic for a segment. A matrix covering 80 m ahead on an itinerary might take the following form:

dx, %

20, 0.2

20, 0.1

20, - 0.1

20, - 0.3

where the first column is the length of each segment in metres (dx) and the second column the gradient in % of each segment. The matrix is to be taken to mean that for 20 metres ahead from the vehicle's current location the gradient is 0.2%, followed by 20 metres with a gradient of 0.1 %, and so on. The values for segments and gradients need not be expressed in relative values but might instead be expressed in absolute values. The matrix is with advantage vector- formed but might instead be of pointer structure, in the form of data packages or the like.

Thereafter, at step B), speed set-point values v_ref are calculated for the vehicle's control system along the horizon on the basis of rules pertaining to characteristics of segments. Each segment is preferably placed in a category according to its characteristic or characteristics, and the category in which each segment is placed then determines which rules are applicable to the segment when speed set-point values v_ref are to be calculated. How this works is explained in more detail below.

According to an embodiment, the method comprises calculating threshold values for at least one characteristic for segments, depending on one or more vehicle-specific values, and these threshold values serve as boundaries for division of segments into different categories. In the example where the characteristics of segments are gradients, threshold values are calculated for their gradients. The threshold values for the relevant

characteristic are calculated, according to an embodiment of the invention, by one or more vehicle-specific values, e.g. current transmission ratio, current vehicle weight, the engine's maximum torque curve, mechanical friction and/or the vehicle's estimated running resistance at current speed. A vehicle model internal to the control system is used to estimate running resistances at current speed. Transmission ratio and maximum torque are known magnitudes in the vehicle's control system, and vehicle weight is estimated online.

The following are examples of five different categories in which segments may be placed when their gradients are used for taking decisions about the control of the vehicle:

Level road: Segment with zero gradient ± a tolerance.

Steep upgrade: Segment too steep for vehicle to maintain speed in current gear.

Gentle upgrade: Segment with gradient between tolerance and threshold value for sharp upgrade.

Steep downgrade: Segment so steep downhill that vehicle is accelerated by gradient alone.

Gentle downgrade: Segment with downward gradient between negative tolerance and threshold value for sharp downgrade.

According to an embodiment of the invention, the characteristics of segments are their length and gradient, and placing them in the categories described above involves calculating threshold values in the form of two gradient threshold values l_mi„ and l_ma , where l_mi_n is the minimum gradient for the vehicle to be accelerated downhill by the gradient alone, and l_max the maximum gradient on which the vehicle can maintain speed uphill without changing gear. Thus the vehicle may be regulated according to the gradient and length of the road ahead so that it can be driven in a fuel-economising way by means of cruise control in undulating terrain. In another embodiment, the characteristics of segments are their length and lateral acceleration, and threshold values are calculated in the form of lateral acceleration threshold values which classify segments by how much lateral acceleration they cause. The vehicle's speed may then be regulated so that it can be driven in a way suited to fuel economy and traffic safety with regard to road curvature, i.e. any lowering of speed before a bend is as far as possible effected without use of service brakes. For example, the tolerance for the "level road^'' category is preferably between -0.05% and 0.05% when the vehicle travels at 80 km/h. On the basis of the same speed (80 km/h), l_mj_n is usually calculated to be of the order of -2 to -7%, and l_max usually 1 to 6%. However, these values depend greatly on current transmission ratio (gears + fixed rear axle ratio), engine performance and total weight.

The characteristic or characteristics of each segment are then compared with the calculated threshold values, and each segment within the horizon is placed in a category on the basis of the comparisons.

There might instead or in addition be for example similar classification by radius of curvature of the road, in which case bends might be classified by how much lateral acceleration they cause.

After each segment within the horizon has been placed in a category, an internal horizon for the control system can then be calculated on the basis of rules pertaining to the categories in which segments within the horizon have been placed. The internal horizon comprises speed set-point values v_ref which incorporate entry speeds Vj_n, i to each segment and which the control system has to aim at. All the segments within the horizon are stepped through continuously, and as new segments are added to the horizon the entry speeds Vj_n, i to them are progressively adjusted as necessary, within the range for the vehicle's set speed v_set. v_set is the set speed selected by the driver and desired to be maintained by the vehicle's control system when travelling within a range. The range is bounded by two speeds v_mi_n and v_max which may be set manually by the driver or be set automatically by calculations of suitable ranges, preferably calculated in the module. According to an embodiment, a speed increase is ramped to arrive at an entry speed Vi_n, , and to provide the control system with set-point values v_ref which cause a gradual increase in the vehicle's speed. Ramping a speed increase results in calculation of gradual speed changes which have to be made in order to achieve the speed change. In other words, ramping achieves a linear speed increase.

The various rules for the segment categories thus regulate how the entry speed v, to each segment is to be adjusted. If a segment (i) has been placed in the "level road' category, no change will take place in the entry speed v;_ni j to the segment. When the reference speed has to be increased, Torricelli's equation (1) as below is used to calculate the constant acceleration a by which the vehicle has to accelerate make it possible to drive it in such a way as to meet comfort requirements:

where v;_n, is the entry speed to segment (i), v_si_ut, i the vehicle's speed at the end of segment (i), a the constant acceleration and s the length of the segment. The following explanation applies in cases where the vehicle is predicted to reduce speed.

If a segment is in the "steep upgrade" or "steep downgrade" category, the end speed v_si_utj i for segment (i) is predicted by solving equation (2) below:

(2)

^ slut , i (a - vl , + b) - (e ^ ^{I M )} - b)/a in which

a = - C_d - p - A/2

°— F t Ffoll

F_{r ll} = flatCorr^■ M^■ g/1000 · (C_rnso + C_h (6)

F_a = M^■ g - sin(arctan(or)) (V) flatCorr = (8) where Cd is the air resistance coefficient, p the density of the air, A the vehicle's largest cross-sectional area, F_track the force acting from the engine torque in the vehicle's direction of movement, F_ron the force from the rolling resistance acting upon the wheels, F_a the force acting upon the vehicle because of the gradient a of the segment, Teng the engine torque, i_f,_nai the vehicle's final gear, i_gear the current transmission ratio in the gearbox, i _e∞ the efficiency of the gear system, r_Wh_eei the vehicle's wheel radius, M the vehicle's weight, C_aF and C_b speed-dependent coefficients related to the rolling resistance of the wheels, CrrisoF a constant term related to the rolling resistance of the wheels and Vi_so an ISO speed, e.g. 80 km/h.

On segments in the "steep upgrade" category, the end speed v_si_ut< j is thereafter compared with v_min, and if v_si_ut, ,< v_mi_n, then Vj_n, i has to be increased by Δν^ _tot, where Δν,„ = min(v_max - v,„ , , v_mm - v_{slul l} ) (9) If Avjn, tot is zero or negative, there is no change in Vj_n>

On segments in the "steep downgrade" category, the end speed v_slut, , is compared with v_max, and if v_si_utj j> v_max, then Vi_n, i has to be decreased by Δν^ _tot, where

^Δν,„,,₍„ = ^min(^v„,,, - W^,,, - _max ) (10)

If Δν;_ηι tot is zero or negative, there is no change in Vj„, i.

When it is calculated that a lowering of the vehicle's entry speed Vi_n, ; to a segment is necessary if the end speed v_si_ut, , in the segment is to be < v_max and unnecessary braking thereafter is consequently to be avoided, the method comprises the step C) of calculating within the horizon a trigger location from which the fuel injection to the vehicle has to be throttled in order to achieve a lowering to Vj_n, j. This trigger location is subject to continued calculations of speed set-point values v_ref. As previously mentioned, a proviso for lowering of Vj_n, j is that v_mj_n v_ref < v_max. Thereafter, at a step D), the vehicle is regulated according to the speed set-point values v_ref.

Lowering the vehicle's speed by throttling the fuel injection and using the vehicle's kinetic energy to freewheel down to desired Vj_n, j allows the vehicle's speed to be lowered before a downgrade and the energy which the vehicle acquires on the downgrade to be utilised with no need for braking in order not to exceed any speed limit. The vehicle also gains a shorter driving time which may be converted to lower fuel consumption by lowering its average speed for the rest of the journey.

If its retardation by interruption of fuel supply is to meet comfort requirements, the vehicle needs to have significant weight. If it does not, the retardation is effected by applying Torricelli's equation (1) instead. According to an embodiment, the method therefore comprises determining the vehicle's weight, and if it exceeds a predetermined threshold value, then step C) is performed, otherwise the lowering of the vehicle's speed to Vj_n, j is calculated by applying Torricelli's equation (1). The vehicle's weight may for example be determined by the driver indicating what the cargo or the vehicle weighs or by the vehicle's weight being detected by sensors. Interruption of fuel supply is deemed preferable on vehicles with a train weight of more than about 30 tonnes. Interruption of fuel supply may be applicable on vehicles with a train weight greater than a predetermined weight within the range 10 to 30 tonnes. Otherwise the driver may find the vehicle's behaviour unexpected and uncomfortable. Other road users would also have difficulty in anticipating such a driving style.

To find out by how much the entry speed Vj_n? ; has to be reduced, the vehicle's highest speed v_slut, j after Vi_n> j is predicted by formula (2). A desired lowering of Vj_n, i is then calculated by calculating the speed difference Avj_{n, tot} according to formula (10).

The vehicle's speed v_ref thus needs to be reduced on the segment or segments before the beginning of said segment with the entry speed ν;_η, j. The method investigates whether it is possible to retard during the preceding segment, and if not, it then investigates the segment before that, and so on. To effect lowering of the speed, lowering of v_ref is simulated by formula (2) in the segment in which retardation is possible, Teng being set to, for example, drag torque of about -150 Nm, down to Vj_n, ;.

Calculation of trigger location

To see whether it is possible to effect a lowering of Vi„, ; by Δν^ _tot, which is the total desired lowering in segments ahead (nearer to the vehicle), a simulated possible speed lowering Av_pred, i-i = v_si_ut, M - v_pred, is calculated. v_si_ut, M is thus the same speed as j. Av_pred, i-i is therefore the lowering of v _n, i which is possible during the relevant segment (i-1) when the engine torque is low or negative, e.g. drag torque, and Avi_{n> tot} is the desired lowering of ν¾, If Δν¾, _tot < Av_pred; n, the trigger location for the fuel injection throttling to begin is calculated from the beginning of the segment as

Trigger location = -— ^pre/''^~' ^> w)_ · length of segment (1 1)

If the whole of the desired lowering is not possible during segment (i-1), a new desired lowering Δνί_η, _rest to Δνί_{η> to}t - Av_pred, i-i is calculated. Segments ahead are investigated to see whether further lowering is feasible. An interrupt condition for lowering the speed on segments ahead is that Vj_nj (where j < i-1) has reached v_mj_n or that the whole horizon has been stepped back to the vehicle. Thereafter the adjustments continue on segment i+1.

According to an embodiment, to effect throttling of the fuel supply, v_ref is set to v_mi_n - K, where K is a constant, e.g. 5 km/h. This has to cause sufficient lowering of speed to result in drag torque, since the lowering of the reference speed takes place in one step, which is comparable with throttling the fuel supply. Other ways of effecting throttling of fuel supply are also conceivable, e.g. it is possible for < 0% to be demanded in indicated engine torque, or in some other way to cause the fuel injection to be temporarily halted.

An example of the method is described next. Throttling the fuel supply has been predicted to take place a certain number of segments before a downgrade. v_set = 80 km/h, v_min = 73 km/h and v_max = 85 km/h. A low speed v_mi_n -5 km/h = 68 km/h is applied at this time as follows: Vpred = [80, 80, 80, 79, 78, 77, 76, 75, 74, 73, 72, 71 , 70, 70, 71, 72, 73, 74,

75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 85 ,84, 83, 82, 81, 80, 80, 80]

v_ref = [80, 80, ... , 80, 68, 68, 68, 68, 68, 68, 68, 68, 68, 68, 68, 68, 68, 68, 68, 68, 68, 68, 68, 68, 68, 68, 68, 68, 68, 68, 68, 68, 80, 80,80, 80, 80, 80]

Vp_red is the predicted speed along the horizon. Each element in the vectors corresponds to a segment with individual gradient, e.g. segments may be of fixed or variable L m. Here the method has thus been stepped back to where the prediction of v_ref = 80 km/h results in a maximum speed during the horizon which exceeds v_max, and here sets v_ref = 68 km/h to result in drag torque from the engine, and therefore no fuel injection. The fuel is throttled throughout the downgrade until the vehicle no longer gains speed by force of gravity and has to be accelerated in order to maintain v_set or avoid dropping below v_mi_n. Figures 4 and 5 illustrate what happens in terms of vehicle speed and amount of fuel supplied when fuel injection is throttled before and during a hill, as compared with traditional cruise control with constant speed brake and lowering by constant retardation by means of Torricelli's equation (1). Cruise control with constant speed brake means the vehicle's avoiding using the service brakes and using instead its supplementary brakes (e.g. retarder and exhaust brake, and possibly also electromagnetic brake (Thelma) and/or VEB (Volvo engine brake)) to brake away the vehicle's kinetic energy and maintain constant speed. In Figure 4, XI represents the speed for a vehicle using traditional cruise control set to v_set and constant speed brake set to keep the vehicle's maximum speed on steep downgrades down to Vkf¾. Yl represents a vehicle speed lowered by Torricelli's equation (1), and Zl a speed lowered by throttling the fuel supply. After the steep downgrade, v_ref = v_set. Figure 5 shows how much fuel is injected into the vehicle's engine during corresponding periods. Zl is initially v_ref = v_set, before being subsequently set to v_ref ⁼ Vmin - K at the trigger location for throttling the fuel supply, where K= 5 km/h. Figure 5 shows that the amount of fuel injected Z2 goes down in one step from current fuel injection D to 0 %. Current fuel injection D is a value between 0 and 100%. The vehicle's speed Zl then goes down to v_mj_n before being accelerated by the weight of the vehicle to v_max and thereafter being reduced to v_set, while the amount of fuel injected Z2 to the engine is still zero. Here it may be noted that the mode of driving for speeds Yl and Zl consumes approximately the same amount of fuel when v_set is the same, but that Zl is higher for a longer time. Modes of driving which result in speeds Yl and Zl do however consume less fuel than the mode which results in speed XI .

If it is desirable to reduce fuel consumption instead of shortening driving time, or to achieve a combination of both, the driving time tr for the vehicle along the segment is predicted. This driving time is then compared with the driving time t_ToR along the segment when the vehicle's speed is instead lowered by applying Torricelli's equation (1). A lowering of v_ref may then be calculated for the driving time tj to become txo_R, i e. the same length of time as when Torricelli's equation (1) is applied. According to an embodiment, the method comprises lowering the speed v_ref so that a desired trade-off between fuel reduction and shorter driving time is achieved. A desired trade-off may for example be half in terms of calculated time gain and the remainder in terms of reduced amount of fuel. The driver may also have the possibility of choosing whether to prefer shorter driving time, lower fuel consumption or a combination, e.g. by using a control device. The driving time for the journey is calculated as

driving time = (12) where v is the vehicle's speed and s₀ and s_T are respectively the beginning and end of the journey.

According to an embodiment, the fuel consumption is calculated by integrating the predicted fuel flow along the segment on which the speed decrease is to take place, as follows:

The fuel flow is nil during throttling of the fuel supply. During the part-segments where the engine's power is applied, the fuel flow is a function of its torque and speed: fuel flow = /(Μ, ω) (14)

This function describes the engine's efficiency. The torque in formula (14) is that required for achieving desired speed, i.e. the torque required to overcome running resistance and apply any acceleration/retardation.

According to an embodiment, the method comprises calculating speed set-point values v_ref so that the vehicle is calculated to reach desired set speed v_set after it has passed the segment for which the entry speed ν;_η, , has been lowered. The lowering of Vi„, i may then perhaps not be as great as when v_ref is allowed to go down to v_m;_n after the hill, but the vehicle may instead maintain a higher speed and hence achieve a shorter driving time.

Figure 6 depicts a number of different route segments (i-3) to (i+1). The speed which would result from a traditional cruise control is represented by a continuous line v_cc in the lower diagram. We describe next an example where the vehicle's speed is predicted to exceed v_max on segment (i) (same pattern as in Figure 4). v_si_ut; which is the predicted end speed on segment (i), is calculated to exceed v_max by 5 km/h according to formula (2). The desired reduction of the entry speed Vj_n, j to segment (i) is then Δν;_{η, to}t = 5 km/h, an acceptable lowering also on the basis that there is no risk of Vi„, i being below v_mi„. The method first investigates whether it is possible to retard during segment (i-1), and the vehicle's end speed v_pred, M is calculated by formula (2) when the engine torque is low or negative, e.g. drag torque, and the possible lowering of speed during segment (i-1) is calculated, i.e. Av_pred, M. The speed which would result in this case is represented by a chain-dotted line. In the example it is not possible to retard Avi_{n, tot} fully during segment (i-1), which is a gentle downgrade, so the method has to go back to segment (i-2), which is level road, to be able to retard further. The vehicle's end speed v_pred, i_-2 is then predicted by formula (2) when the engine torque is low or negative, e.g. drag torque, and the possible lowering of the speed during segment (i-2) is calculated, i.e. Av_pred, i-₂. The speed which would have resulted in this case is represented by a broken line. Av_pred, i_-2 is calculated by subtracting v_pred, i_-2 from the calculated end speed v_slut, i_-2 in segment (i-2). If the remaining desired lowering (Avi_n, i-i) is smaller than or equal to Δν_ρπκ1, i_-2, the trigger location for throttling of fuel supply during segment (i-2) is calculated by applying formula (1 1 ). The fuel supply will then be throttled from the trigger location, while the vehicle is initially retarded before being subsequently accelerated by its own weight and thereafter retarded back to the set speed v_set. If instead not all of the desired lowering of 5 km/h is possible during segments (i-1) and (i-2), the amount by which the speed has to be lowered during preceding segments (i-3) to (i-x) is calculated. In such cases the above procedure is repeated until it is calculated that the whole lowering by Δν^ _tot = 5 km/h is achieved, supposing that it is feasible, otherwise the speed is lowered as much as possible and a higher vehicle speed than v_max is allowed if it is not possible to lower the speed more on segments ahead.

According to an embodiment, the method comprises adapting the running resistance by a scale factor by comparing estimated running resistances with measured actual running resistances, e.g. to compensate for headwind or tailwind. The running resistance estimated (rolling resistance, air resistance and perpendicular force (hill) and other losses in, for example, the power train) is therefore multiplied by a scale factor to enable the vehicle to adjust estimated running resistances, e.g. to cater for headwind/tailwind. The adaptation involves comparing estimated running resistances calculated on the basis of map data and parameters with how well the running resistance matches with measured running resistances in real time. The adaptation is done progressively to avoid having a fluctuating scale factor. Such adaptation results in reaching with greater certainty the predicted v_mj„, which might otherwise cost more than ramping down the reference speed.

The invention relates also to a module for determining speed set-point values v_ref for a vehicle's control system. The module comprises a horizon unit arranged to determine a horizon by means of location data and map data for an itinerary which is made up of route segments and at least one characteristic for each segment. The module comprises also a processor unit arranged to calculate speed set-point values v_ref for the vehicle's control system along the horizon on the basis of rules pertaining to characteristics of segments, and to calculate, when a lowering of the vehicle's entry speed v_ln> ; to a segment is calculated to be necessary if the end speed v_si_ut, ; in the segment is to be < v_max and unnecessary braking thereafter is consequently to be avoided, within the horizon a trigger location from which the fuel injection to the vehicle has to be throttled in order to achieve a lowering to Vj_ni , , provided that v_mi_n < v_ref≤ v_max, where v_mj„ and v_max set the limits for permissible speeds for v_ref, this trigger location being subject to continued calculations of speed set-point values v_ref, and the vehicle is regulated according to the speed set-point values v_ref. This module makes it possible to calculate where throttling the fuel injection has to take place within a predicted horizon of the vehicle's speed, so that the vehicle's speed is regulated in an optimum way from a fuel perspective.

The processor unit comprises necessary hardware and programme code for performing operations herein mentioned such as calculations and handling of data, and may for example comprise one or more CPUs with associated memories.

The processor unit is preferably arranged to predict the vehicle's maximum speed v_si_ut, i after the entry speed Vi_n, i during a segment and to calculate a desired lowering of Vj_n, j by calculating the speed difference Avj_{n, to}t by formula (10). The processor unit may thus know by how much it is desirable to lower the speed Vj_n, i to a segment.

According to an embodiment, the processor unit is arranged to simulate speed lowering of v_ref, with the engine torque Teng set to low or negative torque, e.g. drag torque, down to Vjn, i by applying formula (2). Simulating the vehicle's speed during drag torque makes it possible to find out by how much the speed drops and whether it is possible to lower the speed Avj_{n! tot}, to Vj_ni j. The simulated Vj_n> j is calculated and is called v_pred, i-i -

According to an embodiment, the processor unit is arranged to calculate simulated possible speed lowering Av_pred, i-i ^— v_siut, i - Vpred, i-i <ind if desired lowering Avj_n tot—

Avpred, i-i , the trigger location for throttling the fuel injection is calculated by formula (1 1). siut, i-i is thus the same speed as Vj_n, _x. Av_pred, is therefore the lowering of v;_n, i which is possible during the relevant segment (i-1) when the engine torque is set to negative or low torque, e.g. drag torque, and Avj_{ni to}t is the lowering of Vi„, ; which is desired. A location from which the fuel injection can be throttled is thus calculated. The module is preferably adapted to throttling the fuel injection by setting v_ref to v_mi_n - K, where is a constant, e.g.

5 km/h. The processor unit is preferably arranged to calculate whether Avi_{n> to}t > Δν_ρι¾(ι, i-i, which means that not all of the desired lowering is possible during segment (i-1), in which case it is also arranged to calculate a new desired lowering Avj_n, _rest to Δν;_η, _tot - Av_pred, M, and to investigate whether further lowering is feasible on segments (i-2) to (i-x) ahead. In this way all of the desired lowering of v;_n> ; can be effected, provided that it is possible.

The module described above makes it possible to reduce the vehicle's driving time. The shorter driving time may instead be converted in whole or in part to reduced fuel consumption. To effect reduced fuel consumption, the processor unit according to this embodiment is arranged to predict the driving time t_T for the vehicle along the segment. This driving time is then compared with the driving time tjoR along the segment when the vehicle's speed is instead lowered by applying Torricelli's equation (1), after which a lowering of the simulated speed is calculated for the driving time to become t_TOR, in order to achieve fuel reduction instead of shorter driving time. The module is preferably arranged to lower the speed v_ref so that a desired trade-off between fuel reduction and shorter driving time is achieved. To calculate the fuel consumption, the processor unit is arranged to integrate the predicted fuel flow along the segment where the speed reduction is to take place, see formulae (13) and (14).

According to an embodiment, the processor unit is arranged to calculate speed set-point values v_ref so that the vehicle is calculated to reach desired set speed v_set after it has passed the segment to which the entry speed Vj_n> j has been lowered, in order to achieve desired lowering of v_re . The lowering of Vj_n, i by interruption of fuel injection may therefore be done be adjusting Vj_n, j so that desired v_set is reached.

According to an embodiment, the processor unit is arranged to determine the weight of the vehicle and, if it exceeds a predetermined threshold value, to calculate within the horizon a trigger location for throttling the fuel supply in order to achieve a lowering to v;_n or, if the vehicle's weight is below or equal to the threshold value, to calculate the lowering of its speed to achieve a lowering to v;_n> j by applying Torricelli's equation (1). The processor unit is arranged, according to an embodiment, to calculate threshold values for at least one characteristic of segments, depending on one or more vehicle-specific values, which threshold values serve as boundaries for division of segments into different categories; to compare the gradient of each segment with the threshold values and place each segment within the horizon in a category on the basis of the comparisons; and to calculate speed set-point values v_ref for the vehicle's control system along the horizon on the basis of rules pertaining to the categories in which segments within the horizon have been placed. The processor unit is preferably arranged to determine vehicle-specific values by current transmission ratio, current vehicle weight, the engine's maximum torque curve, mechanical friction and/or the vehicle's estimated running resistance at current speed.

By adapting the running resistance, the module can, for example, compensate for headwind and tailwind. According to an embodiment, the processor unit is then able to adapt the running resistance by a scale factor by comparing estimated running resistances with measured actual running resistances.

The invention relates also to a computer programme product comprising computer programme instructions for enabling a computer system in a vehicle to perform steps according to the method described above when the computer programme instructions are run on said computer system. The invention comprises also a computer programme product which has the computer programme instructions stored in it on a medium which can be read by a computer system. The present invention is not confined to the embodiments described above. Sundry alternatives, modifications and equivalents may be used. The above embodiments therefore do not limit the scope of the invention, which is defined by the attached claims.

Claims

1. A method for calculating speed set-point values v_ref for a control system in a vehicle, c h a r a c t e r i s e d in that the method comprises:

A) determining a horizon by means of location data and map data for an itinerary made up of route segments and at least one characteristic for each segment;

B) calculating speed set-point values v_ref for the vehicle's control system along the horizon on the basis of rules pertaining to characteristics of segments, and when a lowering of the vehicle's entry speed v_m, j to a segment is calculated to be necessary if the end speed v_si_utj j in the segment is to be < v_max and unnecessary braking thereafter is consequently to be avoided, the method comprises:

C) calculating within the horizon a trigger location from which the fuel injection to the vehicle has to be throttled in order to achieve a lowering to v_m> i, provided that Vmin < v_ref≤ max, where v_mj_n and Vmax set the limits for permissible speeds for v_ref, which trigger location is subject to continued calculations of speed set-point values v_ref, and

D) regulating the vehicle according to the speed set-point values v_ref.

2. A method according to claim 1 which comprises predicting the vehicle's highest speed v_si_ut, i after the entry speed Vj_n, i, and calculating a desired lowering of Vj_n, i by calculating the speed difference Δν,„,₍₎, = min(v,„, - v_min , v ._/u, . - v_max ).

3. A method according to claim 2 which comprises simulation of speed lowering of v_ref, with the engine torque T_eng set to low or negative torque, e.g. drag torque, down to Vj_n, i.

4. A method according to claim 3 which comprises calculating simulated possible speed lowering Av_pre(1, n = v_si_ut, ,.\ - v_pre(j, M, where v_pred_, -\ is the predicted end speed in segment (i-1) with low or negative engine torque, e.g. drag torque, and if Av_{in, to}t < Avpred_, i-i, then the trigger location for throttling the fuel injection is calculated as Trigger location = length oj segment

5. A method according to claim 4 which , if Avj_{n, tot} > Av_pred, i-i and consequently not all of the desired lowering is possible during segment (i-1), comprises calculation of a new desired lowering Δν;_{η res}t to Δν;_η, _tot - Δν_ρΓ(¾ι, i-i, followed by investigation of segments ahead to see whether further lowering is feasible.

6. A method according to claim 4 which comprises predicting the driving time tx for the vehicle during the segment and comparing it with the driving time txo when the vehicle's speed is instead lowered by applying Torricelli's equation (1), followed by calculating a lowering of the simulated speed for the driving time to become ΐχοτ, in order to achieve fuel reduction instead of shorter driving time.

7. A method according to claim 6 which comprises lowering the speed v_ref so that a desired trade-off between fuel reduction and shorter driving time is achieved.

8. A method according to claim 6 or 7 which comprises calculating the fuel consumption by integrating the predicted fuel flow along the segment where the speed decrease is to take place.

9. A method according to any one of the foregoing claims which comprises calculating speed set-point values v_ref so that the vehicle is calculated to reach desired set speed after it has passed the segment to which the entry speed Vi_n, i has been lowered, in order to achieve desired lowering of v_ref.

10. A method according to any one of the foregoing claims which comprises throttling the fuel injection by setting v_ref to v_mj_n - , where K is a constant.

11. A method according to any one of the foregoing claims which comprises determining the weight of the vehicle and, if it exceeds a predetermined threshold value, performing step C), otherwise the lowering of the vehicle's speed to achieve a lowering to Vi_n> j is calculated by using Torricelli's equation (1).

12. A method according to any one of the foregoing claims, which comprises:

- calculating threshold values for at least one characteristic of segments, depending on one or more vehicle-specific values, which threshold values serve as boundaries for division of segments into different categories;

- comparing the gradient of each segment with the threshold values and placing each segment within the horizon in a category on a basis of the comparisons;

- calculating speed set-point values v_ref for the vehicle's control system along the horizon on the basis of rules pertaining to the categories in which segments within the horizon have been placed.

13. A method according to claim 12 in which vehicle-specific values are determined by current transmission ratio, current vehicle weight, the engine's maximum torque curve, mechanical friction and/or the vehicle's estimated running resistance at current speed.

14. A method according to claim 13 in which the running resistance is adapted by a scale factor by comparing estimating running resistance with measured actual running resistance, e.g. to compensate for headwind or tailwind.

15. A module for determining speed set-point values v_ref for a vehicle's control system, c h a r a c t e r i s e d in that the module comprises a horizon unit arranged to determine a horizon by means of location data and map data for an itinerary which is made up of route segments and at least one characteristic for each segment;

the module also comprises a processor unit arranged to:

- calculate speed set-point values v_ref for the vehicle's control system along the horizon on the basis of rules pertaining to characteristics of segments, and when a lowering of the vehicle's entry speed ν;_Π; , to a segment is calculated to be necessary if the end speed v_si_ut, i in the segment is to be < v_max and unnecessary braking thereafter is consequently to be avoided, the processor unit is arranged to: - calculate within the horizon a trigger location from which the fuel injection to the vehicle has to be throttled in order to achieve a lowering to Vj_n, provided that

Vmin≤ v_ref≤ v_max, where Vmin and v_max set the limits for permissible speeds for v_ref, this trigger location being subject to continued calculations of speed set-point values v_ref, and the vehicle is regulated according to the speed set-point values v_ref.

16. A module according to claim 15 , in which the processor unit is arranged to predict the vehicle's highest speed v_si_ut, i after the entry speed Vi_n, j, and to calculate a desired lowering of Vj_n, ; by calculating the speed difference

A^v,_nJo, = min .,- - v_min , v_{slu l} - v_max ).

17. A module according to claim 16, in which the processor unit is arranged to simulate speed lowering of v_ref, with the engine torque Ten_g set to low or negative torque, e.g. drag torque, down to Vj_n, i.

18. A module according to claim 17, in which the processor unit is arranged to calculate simulated possible speed lowering Av_prei,, M = v_si_ut, - v_pred, , where v_pred, i-i is the predicted end speed in segment (i-1) with low or negative engine torque, e.g. drag torque, and if Av^ tot≤ Av_pred, i-i, then the trigger location for throttling the fuel injection is calculated as

; .■ (^^V n_re</,/-l Δ _;„ _tol )

I rigger location = length oj segment

19. A module according to claim 18, in which the processor unit is arranged to calculate whether Avi_{n> to}t > Δν_ρΓαι, i-i, which would mean that not all of the desired lowering is possible during segment (i-1), in which case it is further arranged to calculate a new desired lowering Av^ _rest to Avi_{nj tot} - Av_pred, j.| and to investigate whether further lowering is feasible on segments ahead.

20. A module according to claim 18 or 19, in which the processor unit is arranged to predict the driving time tj for the vehicle during the segment and to compare it with the driving time tjo_Twhen the vehicle's speed is instead lowered by applying Tomcelli's equation (1), followed by calculation of a lowering of the simulated speed for the driving time to become ίχοτ, in order to achieve fuel reduction instead of shorter driving time.

21. A module according to claim 20, in which the processor unit is arranged to lower the speed v_ref so that a desired trade-off between fuel reduction and shorter driving time is achieved.

22. A module according to claim 20 or 21 , in which the processor unit is arranged to calculate the fuel consumption by integrating the predicted fuel flow along the segment where the speed decrease is to take place.

23. A module according to any one of claims 15 to 22, in which the processor unit is arranged to calculate speed set-point values v_ref so that the vehicle is calculated to reach desired set speed after it has passed the segment to which the entry speed Vj_n, , has been lowered, in order to achieve desired lowering of v_ref.

24. A module according to any one of claims 15-23, in which the processor unit is arranged to throttle the fuel injection by setting v_ref to v_mj_n - K, where K is a constant.

25. A module according to claim according to any one of claims 15 to 24, in which the processor unit is arranged to determine the weight of the vehicle and, if it exceeds a predetermined threshold value, to calculate within the horizon a trigger location for throttling the fuel supply in order to achieve a speed lowering to v;_n, or, if the vehicle's weight is below or equal to the threshold value, to calculate the lowering of its speed to Vin, i by applying Tomcelli's equation (1).

26. A module according to any one of claims 15 to 25, in which the processor unit is arranged to: - calculate threshold values for at least one characteristic of segments, depending on one or more vehicle-specific values, which threshold values serve as boundaries for division of segments into different categories;

- compare the gradient of each segment with the threshold values, and place each segment within the horizon in a category on a basis of the comparisons;

- calculate speed set-point values v_ref for the vehicle's control system along the horizon on the basis of rules pertaining to the categories in which segments within the horizon have been placed.

27. A module according to claim 26, in which the processor unit is arranged to determine vehicle-specific values by current transmission ratio, current vehicle weight, the engine's maximum torque curve, mechanical friction and/or the vehicle's estimated running resistance at current speed.

28. A module according to claim 27, in which the processor unit is arranged to adapt the running resistance by a scale factor by comparing estimating running resistances with measured actual running resistances, e.g. to compensate for headwind or tailwind.

29. A computer programme product comprising computer programme instructions for enabling a computer system in a vehicle to perform steps according to the method of any one of claims 1 to 13 when the computer programme instructions are run on said computer system.

30. A computer programme product according to claim 29, which has the computer programme instructions stored in it on a medium which can be read by a computer system.