SE1451079A1 - Method and system related to determination and utilization of a highest permitted freewheeling speed - Google Patents

Description

lO l5 20 25 30 In descents, for example, or in situations in which the vehicle must reduce its actual speed, fuel savings have historically been made by a reduced request for positive engine torque, alternatively with the aid of motor/engine braking. The reduced request for positive engine torque means that the driving force in the direction of travel, which the internal combustion engine delivers via the drive wheels, is reduced, for example by reduced fuel injection in the engine, thereby reducing the fuel consumption.

Motor/engine braking means driving the vehicle with closed drive train, that is to say with the combustion engine connected to the drive wheels of the vehicle, at the same time as the fuel supply to the internal combustion engine is shut off. One advantage with this type of measure is that, since fuel supply to the internal combustion engine is shut off, the consumption of the internal combustion engine is also equal to zero. The measure also means, however, that the internal combustion engine will be driven by the drive wheels of the vehicle via the drive train due to the kinetic energy of the vehicle. Hereby, motor/engine braking is achieved, wherein the internal losses of the internal combustion engine give rise to a braking action, that is to say that the vehicle is engine braked. In other words is the internal combustion engine here in a drag operation mode, in which a drag torque of the internal combustion engine acts as a braking force on the drive wheels.

Although a reduction in requested engine torque and/or engine braking lowers the fuel consumption, this lowering is not always optimized, firstly since the reduced engine torque, despite everything, generally consumes more fuel than is necessary, and secondly since the engine braking of the vehicle is often not economical regarding fuel consumption. lO l5 20 25 30 Freewheeling, which also is called coasting, has been proposed for providing further fuel savings in some driving situations.

Freewheeling is achieved by having the engine of the vehicle disengaged from the drive wheels of the vehicle, i.e. by having the drive train opened. This disengagement of the drive wheels from the engine, also referred to as opening of the drive train, can be achieved, for example, by setting the gearbox in a neutral position or by opening the clutch. In other words, essentially no force is transmitted from the engine to the drive wheels during the freewheeling. Disengagement of the engine from the drive wheels of the vehicle when the vehicle is in motion is thus referred to in this document as freewheeling/coasting.

Freewheeling causes a considerable reduction in the forces acting against the motion of the vehicle, since the force resulting from the engine friction then diminishes to a value essentially equal to zero (0). To this end, freewheeling can considerably lower the fuel consumption by virtue of this reduced resistance against the vehicle movement. In certain cases of freewheeling, idling fuel have to be supplied to the engine to prevent it from stalling, while in other cases the engine can be allowed to stall. The result is that, from a fuel aspect, it is often more advantageous to drive the vehicle with open drive train, i.e. in a freewheeling mode, than with engine braking, i.e. when the drive train is closed at the same time as the fuel supply to the engine is shut off.

The reason for this is that the limited quantity of fuel which is required to keep the internal combustion engine running when the internal combustion engine is disengaged is counterbalanced by the fact that the vehicle can continue with disengaged internal combustion engine for a longer distance, for example after a 10 l5 20 25 30 downhill slope has been passed. This is due to the fact that the vehicle will reach a higher speed on, for example, the downhill slope when driven with disengaged internal combustion engine compared with when the vehicle is driven with closed drive train without fuel supply.

In freewheeling, moreover, the force which counteracts the movement of the vehicle will be lower when the internal combustion engine of the vehicle is disengaged from the drive shaft, since there is no engine brake force counteracting the progress of the vehicle. This makes the vehicle decelerate more slowly, for example, when the vehicle reaches the end of the downhill slope, which in turn means that freewheeling can often be utilized for a relatively long distance after, for example, an end of a descent. A considerable reduction in fuel consumption is hereby obtained.

Motor vehicles, and especially heavy motor vehicles such as trucks and buses, are influenced by gravity on downhill gradients in such a way that their speed increases, which can be utilized for freewheeling functions in the vehicle.

However, because of other vehicles on the road, and/or because of speed limits, the vehicle may not be permitted to freely increase its speed on downhill gradients for example. For this reason a function of downhill speed control has been developed. Thus, many heavy vehicles are equipped with a downhill speed control system, which is arranged to restrict the speed of the vehicle so that it does not exceed a predetermined downhill speed value vdmc.

A set speed vætßhm for the downhill speed control system is set by the driver of the vehicle for example. Then, the downhill speed control system ensures that this set speed vætßhm is not exceeded by control of one or more brake devices lO l5 20 25 30 in the vehicle being carried out against a reference speed vm?ßhæ for the downhill speed control system. The reference speed vmg?hæ depends on the set speed væt?hæ. In fact, the reference speed vm?ßhæ often corresponds to the set speed všüyüsß Braking devices are designed to create a brake torque, which acts to reduce the speed of the vehicle, for example by reducing the speed of rotation of the wheels. The braking devices can comprise one or more auxiliary brakes, such as an engine brake, exhaust brake, electromagnetic retarder and/or hydraulic retarder.

The speed of the vehicle may need to be restricted also in other situations, which do not have to be related to downhill slopes or downhill speed control. Due to e.g. conditions of the road, to traffic conditions, to vehicle settings and/or conditions, or for other reasons, there can be a highest/maximum permitted vehicle speed vmm defined which the vehicle should not exceed. These other situations will be described more in detail below. Thus, there can be defined a highest permitted vehicle speed vmm, which could relate to downhill speed control situations as well as to these other mentioned situations. Thus, the speed of the vehicle could generally be controlled by one or more systems not to exceed this highest permitted vehicle speed vm?.

SUMARY OF INVENTION For downhill speed control systems, it has been noted that it could be fuel efficient to temporarily increase the downhill reference speed vmfjhæ used in the downhill speed control system in the final part of a downhill gradient to an increased value vmißmgjdwww, which results in an increased actual vehicle speed væï at the end of the downhill gradient.

This increase in actual vehicle speed vax means that the lO l5 20 25 30 vehicle leaves the downhill gradient with a kinetic energy being increased in relation to the increased downhill speed control value v¿?¿&ßQjdWm@ and/or the increased actual vehicle speed vax. This increased kinetic energy can be utilized in the propulsion of the vehicle following the downhill gradient, for example on an uphill gradient that starts after the downhill gradient, or can be utilized such that the vehicle can be driven for a longer distance before fuel needs to be injected in order for the vehicle to maintain a set speed vætym for a cruise control system in the vehicle.

In known systems, this increased value downhill speed control value v¿H¿&ßQ§dWm@ has been calculated and determined essentially at the time instant when the actual vehicle speed vax exceeds the set-value for the downhill control speed vætßhæ. However, the known systems providing an increased downhill speed control value v¿¶¿üßQ§dWw@ have not properly considered combination of, and cooperation with, such a system with a freewheeling system. The known calculation and determination of the increased value downhill speed control value v¿?¿üßQ§dWw@ has therefore lead to that freewheeling/coasting of the vehicle has not been possible to utilize, or has only been possible to utilize in small parts of a downhill slope. Thus, the known systems providing an increased value downhill speed control value v¿H¿&ßQ§dWw@ have not been optimized regarding freewheeling, and therefore provide poor, or at least non-optimal, fuel consumption reductions.

It is therefore an object to at least partly solve at least some of the above mentioned problems.

This object is achieved by the above mentioned method for for determination and utilization of a highest permitted 10 15 20 25 freewheeling speed v@æL?É%mæl according to the characterizing portion of claim l.

The object is also achieved by the above mentioned system arranged for determination and utilization of a highest permitted freewheeling speed v?M_Üemm&¿ according to the characterizing portion of claim Zl.

The object is also achieved by the above mentioned computer program and computer program product.

The method and system according to the present invention are characterized in that they determine and utilize a highest permitted freewheeling speed vmxínæmæ? which is to be used for freewheeling of a vehicle on a road section ahead of the vehicle.

The system includes a determination unit, which is arranged for determination, at or before a time instant tmm when simulations simfæemæelrelated to the freewheeling on the road section are performed, of a value for the highest permitted freewheeling speed vm?_?eÜm&¿. The determination unit is further arranged for determining the value for the highest permitted freewheeling speed vmxínæmæ? at or before a time instant tüm as a generally used highest value v?w; vm@¿ræwmel== vmm; or as a temporarily increased highest value vm?l?fæt being higher than the generally used highest value v?m; v@m_?e%mæl = Vmax+offset and Vmaxafoffset > Vmax- The system also includes a utilization unit, which is arranged for utilizing determined highest permitted freewheeling speed vmm_ñemm&¿ when the simulations simfmemæ@,being related to the freewheeling on the road section ahead of the vehicle are evaluated. lO l5 20 25 Thus, when the present invention is used, the highest permitted freewheeling speed vm?_üemm&¿ is determined and ready to be used already at the time instant tg? when freewheeling simulations simfæemææ are made. Thus, the determined highest permitted freewheeling speed v?M_?e@m&¿ may be utilized in the freewheeling simulations sim?emmüg, and/or in their evaluations, when the present invention is used. This makes the freewheeling simulations and evaluations more accurate.

Also, a temporarily increased highest value vm?l?f might be available for use at the time instant t$m when freewheeling simulations sim?eümæl and/or evaluations are made, which makes it possible to identify more freewheeling sequences and/or longer freewheeling sequences as possible/admissible at the time for the simulations and/or evaluations. Hereby, the vehicle can utilize freewheeling during more and/or longer freewheeling sequences, which lowers the total fuel consumption for the vehicle.

Detailed exemplary embodiments and advantages of the method and system according to the present invention will now be described with reference to the appended drawings illustrating some preferred embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS Embodiments of the invention are described in more detail with reference to attached drawings illustrating examples of embod- iments of the invention, in which: Figure 1 is a schematic example vehicle, Figure 2a is a flow sheet diagram, Figure 2b is a is a flow sheet diagram, Figure 3 is a schematic illustration of a driving situation, 10 15 20 25 30 Figure 4 is a schematic illustration of a control unit.

DETAILED DESCRIPTION OF INVENTION Fig. 1 shows in schematic representation a drive train in a vehicle 100. The drive train comprises an engine 101, e.g. a combustion engine, which is connected in a conventional manner, via an output shaft 102 from the engine 101, usually via a flywheel, to an input shaft 109 of a gearbox 103 by means of a clutch 106. The clutch 106 can be constituted, for example, by an automatically controlled clutch, and can be controlled by the control system of the vehicle via a control unit 400 (also shown in figure 4). The control unit 400 can possibly also control the gearbox 103. The gearbox 103 is here illustrated schematically as a unit. The gearbox 103 can also, however, physically consist of a plurality of interacting gearboxes, for example of a range gearbox, a main gearbox and a split gearbox, which are arranged along the drive train of the vehicle. The gearbox can comprise a suitable number of gear positions. In contemporary gearboxes for heavy duty vehicles are usually found twelve forward gears, two reverse gears and a neutral gear position.

If the gearbox 103 physically consists of a plurality of interacting gearboxes according to the above, these twelve forward gears can be distributed as two gears in the range gearbox, three gears in the main gearbox and two gears in the split gearbox, which together constitute twelve gear positions (2x3x2=12).

The vehicle 100 further comprises drive shafts 104, 105, which are connected to the drive wheels 111, 112 of the vehicle and which are driven by an output shaft 107 from the gearbox 103 via an axle gearing 108, such as, for example, a conventional differential. 10 15 20 25 30 10 The vehicle 100 further comprises a variety of different braking systems 121, 122, 123, 124, such as a conventional service braking system, which can comprise, for example, brake disks with associated brake linings arranged next to each wheel. The engine 101 can be controlled on the basis of instructions from a cruise control device, in order to maintain a constant actual vehicle speed and/or vary the actual vehicle speed so that a fuel consumption which is optimized within reasonable speed limits is obtained. The engine 101 can also be controlled by a driver of the vehicle.

The control systems for the braking system 121, 122, 123, 124 and/or the cruise control system may be arranged logically and/or physically together with and/or apart from the above mentioned control unit 400.

The control unit 400 according to the present invention comprises at least a determination unit 410 and a utilization unit 420. These units are described more in detail below. In figure 1, these units are illustrated as being comprised within a single control unit 400. However, as is clear for a skilled person, the control unit 400 may also be physically and/or logically split into two or more control units.

The freewheeling functionality used in connection with the present invention includes simulations sinqmemæa related to freewheeling on a road section ahead of the vehicle that are performed at defined time instants t?m.

In order to be able to decide if freewheeling is possible to utilize, one or more simulated future speed profiles væ? corresponding to the actual vehicle speed vax for the road section ahead of the vehicle are simulated. Often, the simulated vehicle speed væm and the resulting actual vehicle speed vax have the same or nearly the same values, since the 10 l5 20 25 30 ll simulations can be performed with very high accuracy. Thus, the simulated vehicle speed vän and the actual vehicle speed væï are often more or less identical if the control systems in the vehicle decide to control the vehicle in accordance with the simulations. Thus, the simulations are conducted such that they are based on the current position and situation of the vehicle and looks forward over the road section, wherein the simulations are made on the basis of e.g. a road slope for the road section and a transmission mode for the vehicle.

For example, the simulation can be conducted in the vehicle at a predetermined frequency, such as for example at the frequency of l Hz, which means that a new simulation result is ready every second. The road section for which the simulation is conducted comprises a predetermined section ahead of the vehicle, which for example can be l km, 2 km or longer. The road section can also be seen as a horizon ahead of the vehicle, for which the simulation is to be conducted.

Apart from the above-stated parameters of road slope and transmission mode, the simulation can also be based on one or more of a driving method, a current actual vehicle speed, at least one engine characteristic, such as maximum and/or minimum engine torque, a vehicle weight, an air resistance, a rolling resistance, a gear ratio in the gearbox and/or the drive train, and a wheel radius.

The information of the road section, such as the road slope, on which the simulations are based can be obtained in a number of different ways. The information can be determined on the basis of map data, for example from digital maps comprising topographical information, in combination with positioning information, such as, for example GPS information (Global Positioning System). With the aid of the positioning information, the position of the vehicle in relation to the 10 15 20 25 30 12 map data can be established, so that the information can be extracted from the map data.

In many present-day cruise control systems, map data and positioning information are utilized in the cruise control.

Such systems can then provide map data and positioning information to the system for the present invention, the effect of which is that the added complexity for the determination of the information related to the road section is minimized.

The road slope, on which the simulations can be based, can also be obtained by estimating the road slope encountered by the vehicle in the simulation instance. There are many ways of estimating this road slope, for example on the basis of an engine torque in the vehicle, of an acceleration for the vehicle, on an accelerometer, on GPS information, on radar information, on camera information, on information from another vehicle, on positioning information and road slope information stored earlier in the vehicle, or on information obtained from a traffic system related to said road section.

In systems in which information exchange between vehicles is utilized, road slope estimated by one vehicle can also be made available to other vehicles, either directly, or via an intermediate unit such as a database or the like.

Also, the freewheeling simulations and/or the evaluations of the simulations are based on a highest permitted vehicle freewheeling speed vm?_?eÜm&¿ and a lowest/minimum permitted vehicle freewheeling speed vmnp?eämæl for the road section. For example, freewheeling can according to some embodiments only be allowed if the actual vehicle speed vax is kept within the vehicle speed interval being defined by the highest permitted lO l5 20 25 30 l3 freewheeling speed v@æL?É%mæl and a lowest permitted freewheeling speed vmnp?ewmü?.

In other words, if the simulated vehicle speed vgm, which is estimated at the simulations related to freewheeling sim?eümæl, indicates that the simulated vehicle speed væm, and thus also the actual vehicle speed væï corresponding to the simulated vehicle speed vàm, will exceed the highest permitted freewheeling speed vm?_?eÜmæl during the road section, freewheeling will according to the evaluations not be allowed/utilized for the road section. Correspondingly, if the simulated vehicle speed vgm indicates that the simulated vehicle speed vmm, and thus also the actual vehicle speed væt corresponding to the simulated vehicle speed vgm, will be lower than the lowest permitted freewheeling speed vmnjræwmel in the road section, freewheeling will according to the evaluations not be allowed/utilized for the road section.

According to an aspect of the present invention, a method for determination and utilization of a highest permitted freewheeling speed vmæiræwmelto be used by a vehicle 100 if it is going to freewheel on a road section ahead of the vehicle is provided.

The method is illustrated in a flow sheet in figure 2. In a first step 210 of the method, which e.g. may be performed by the below described determination unit 410, a value for a highest permitted freewheeling speed v?M_Üe@m&¿ is determined at or before a time instant tan when the simulations sim?emmæl related to freewheeling on the road section ahead of the vehicle are performed, i.e. before the vehicle has entered the road section. At this determination, the highest permitted freewheeling speed vm?_?emmæl can be given a value equal to a generally used highest value v??; v@m_?eümæl = vmm. At this 10 15 20 25 30 14 determination, the highest permitted freewheeling speed mmxj?æmæ? can also be given a value equal to a temporarily increased highest value v@M+Mfæt, which is higher than the Vmaxwffset and generally used highest value vm?; vm?_ÜeÜmæl = Vmax+offset > Vmax- Here and in this document, the generally used highest value vmm is the non-increased highest permitted value. In other words is the generally used highest permitted value vmm the value that would be generally used if there was no functionality for temporarily increasing the highest permitted value. Thus, the generally used highest value vm? is related to a vehicle speed at which an additional acceleration of the vehicle is generally unwanted and/or at which a retardation of the vehicle is generally wanted. If, for example, the highest permitted value is related to downhill speed control, the generally used highest value v?w would correspond to the downhill control speed vdmc, while the temporarily increased highest value v?mi?fæt would correspond to the increased downhill speed control value våßgßdmwg. If, for example, the highest permitted value is related to a speed limit for the road section, the generally used highest value vm? could correspond to speed limit, e.g. 90 km/h, while the temporarily increased highest value vm?i?fæt could correspond to a temporarily increased internal speed limit, e.g. 95 km/h. The utilization of the generally used highest value vm? is described more in detail below.

In a second step 220 of the method, the determined value for the highest permitted freewheeling speed vmM_üe@m&¿ is utilized in evaluations of the freewheeling simulations sim?eümæl, e.g. by the below described utilization unit 420. The actual simulation and/or evaluation algorithms used for determining if freewheeling is possible and appropriate can here include 10 15 20 25 30 15 for a skilled person well known such simulation and/or evaluation algorithms, as long as they include usage of a highest permitted freewheeling speed vmwinæwmel.

If the evaluations of the freewheeling simulations simfæemæa determine that freewheeling should be allowed for the road section, the method proceeds to the third step 230, in which freewheeling is activated. By use of the present invention, more possible freewheeling situations can be identified if the highest permitted freewheeling speed vmxinæmæ? has been given the temporarily increased highest value vmM+?fæt.

If the evaluations of the freewheeling simulations simfæemæa determine that freewheeling should not be allowed for the road section, the method proceeds to the fourth step 240, in which freewheeling is not activated.

The method then may start again in the first step 210.

For example, if downhill speed control is also utilized during the freewheeling according to an embodiment of the present invention, the generally used highest value vmm can correspond to the downhill reference speed vm?ßhæ used in the downhill speed control system and the temporarily increased highest value v?ml?fæt can correspond to the increased value vnílwsgsdmmg for the downhill speed control. However, a major difference from the known downhill speed control algorithms is that according to the present invention, the highest permitted freewheeling speed vmm_?e@mæl is determined at or before the time instant tsm when the freewheeling simulations simfæemæ? for the road section ahead of the vehicle are performed. As stated above, for known systems the increased value vnfymsgßdmwg for the downhill speed control was determined much later than the freewheeling simulations sim?gmmä?, since it 10 15 20 25 30 16 was then determined first when the actual vehicle speed vam exceeded the downhill control speed vmwc.

Therefore, the determined highest permitted freewheeling speed vm?_?emm&¿ may be utilized in the freewheeling simulations sim?emmæl and/or evaluations when the present invention is used. This makes freewheeling, and thus also fuel consumption reductions, possible in a large number of situations where no freewheeling would have been allowed if known systems had been used.

According to an embodiment of the present invention, the evaluations are performed essentially at the time instant t?m when the simulations sim?æ@me@_related to freewheeling are performed. According to another embodiment of the present invention, the evaluations are performed essentially directly after the time instant tgm when the simulations sim?lümæl related to freewheeling are performed. According to another embodiment of the present invention, the evaluations are performed after the time instant tæm and before the time instant when the actual vehicle speed vax exceeds the highest permitted speed vmm.

According to an embodiment of the present invention, the simulations related to freewheeling sim?æmmü? being performed at the time instant tan are limited to the first over speed occurrence/situation ahead of the vehicle. Thus, the simulated vüm and/or actual vax vehicle speed are analyzed from the position of the vehicle corresponding to the simulations time instant tüm until the simulated vä? and/or actual vax vehicle speed has exceeded the generally used highest value vm? once and then has dropped below the generally used highest value vmm again. 10 15 20 25 30 17 According to an embodiment of the present invention, the determination of the value for said highest permitted freewheeling speed vm?_?e@mæl is based on a simulated vehicle speed v$m over said road section ahead of the vehicle corresponding to the actual vehicle speed vax for the road section. This simulated vehicle speed väm is based on knowledge of the road section, as is described above. Thus, the simulated vehicle speed v$m can e.g. be based on knowledge of the road section and on one or more of a driving method, a current actual vehicle speed, at least one engine characteristic, such as maximum and/or minimum engine torque, a vehicle weight, an air resistance, a rolling resistance, a gear ratio in the gearbox and/or the drive train, and a wheel radius.

The knowledge of the road section can for example be obtained from map data, for example from digital maps comprising topographical information, in combination with positioning information, such as, for example GPS information (Global Positioning System). With the aid of the positioning information, the position of the vehicle in relation to the map data can be established, so that the knowledge can be extracted from the map data. The map data can include topography information, i.e. road slope information. The knowledge may also be obtained from sensors, such as cameras, radar equipment or the like, identifying characteristics of the road section. Also information retrieved from other vehicles may be utilized for providing such knowledge of the road section.

According to an embodiment of the present invention, the determination of the value for the highest permitted freewheeling speed vm?_ñeÜmæl, i.e. the above described first step 2l0 of the method, can include the steps being 10 15 20 25 30 18 illustrated in figure 2b. These steps may also be performed by the below described determination unit 410.

In a first step 211 in figure 2b, the simulated vehicle speed van is compared with the generally used highest value vm?. In a second step 212, the simulated vehicle speed vgm is also compared with the temporarily increased highest value vm?l?fæt.

If the simulated vehicle speed vgm is lower than the temporarily increased highest value vh?r?fæt; vgm < vmxwfüe? during the road section, and if the simulated vehicle speed vüm is higher than the generally used highest value vmm; væ? > mmx; for a time period Twæn?æšbeing shorter than a predetermined over speed time period Towrjpæd; Taæåmm < Tmæpßpæd; during the road section, the value for the highest permitted freewheeling speed v@M_?e@m&¿ is in a third step 213 set to the temporarily increased highest value vm?+?fæt; Vmax_freewheel I Vmax+offset~ If instead the simulated vehicle speed vän is higher than the temporarily increased highest value vm?l?fæt ; v¶m > vm?l?fæt; during the road section, or if the simulated vehicle speed v?m is higher than the generally used highest value vmu; væm > vmm; for a time period Tmæn?æšbeing longer than a predetermined over speed time period Tmæpßpæd; Tmæäm? > Tmæpßpæd; during the road section, the value for the highest permitted freewheeling speed vmM_üemm&¿ is in a fourth step 214 set to the generally used highest value vm?; v?w_Üe@m&¿ = vmß.

The predetermined over speed time period Tmæïßpæd can here have a value, i.e. have a length, being related to a performance mode used in the vehicle. Such possible performance modes may include at least an Economy mode, a normal mode and a power mode. The predetermined over speed time period Tmænßyæd can also be related to a driver input, such that the driver can 10 15 20 25 30 19 influence the choice of the value for the highest permitted freewheeling speed vm?_?eÜm&¿. The predetermined over speed time period Tmæpjpæd might have a constant value. As a non- limiting example, the predetermined over speed time period Tmæpßpæd can be 45 seconds.

Figure 3 schematically describes the principles of some prior art solutions and of the present invention for a driving situation including a downhill slope.

The actual vehicle speed, væï (solid line) for the present invention and væpy?ßram (dashed line) for prior art, respectively, increase from e.g. a set speed v?ï for a cruise control system when the vehicle has entered the downhill slope.

According to the present invention, the highest permitted freewheeling speed vm?_?eÜmü¿ is determined at or before a time instant tgm when the simulations sinqnæmæelrelated to freewheeling is performed. Thus, at or before the time instant täm, the highest permitted freewheeling speed v@M_?eÜmæl can be set to the generally used highest value vmm; vm?_Üemmü¿ = vm? or to the temporarily increased highest value vm?i?fæt; vmaxifreewheel = vmaxwffset and vmaxwffset > vmax- This determination Of the highest permitted freewheeling speed vmM_üeÜm&¿ is made as described above, i.e. based on the values for the simulated vehicle speed væm and for the time period Tmæåmw.

According to the present invention, already at the time for determination of the highest permitted freewheeling speed mwxjnæmæ?, i.e. at or after the time instant tgm, the freewheeling system knows that the highest permitted freewheeling speed vmw_?e@mæl will be given an increased highest value vm?i?fæt when the actual vehicle speed vad reaches the generally used highest value vmm. Thus, if the l0 l5 20 25 30 20 highest permitted freewheeling speed v?w_?eüm%¿ is regulated based on a reference speed vn?_HWHmnm (dot-dashed line), such as if the generally used highest value vmm is a downhill control speed vm? = vüwc and the temporarily increased highest value vmml?fæt is an increased downhill control speed v@w+?fæt = vüßmo?sü, the reference speed vn?_nWHmnm, which then could be a downhill control reference speed vm?ßhæ, is increased when the actual vehicle speed vad reaches the generally used highest value vmm.

An important feature of the present invention is that this is known already at the time instant tæm when the freewheeling simulations are made. Therefore, the vehicle could in this example start freewheeling already at the time instant t?m, since it is known at the simulations and/or evaluations being performed at or direct after that time instant tgm that the highest permitted freewheeling speed v?%_?e@m&¿ will have the temporarily increased highest value vm?r?fwt when the actual vehicle speed vax reaches the generally used highest value vmm, and thus that freewheeling then will be possible for the whole period TfmeWæ?_nWamiw of the downhill slope. This is due to that the simulated vehicle speed vän, which is estimated at the simulations related to freewheeling sim?eümæl, indicates that the simulated vehicle speed vmm, and thus also the actual vehicle speed väx corresponding to the simulated vehicle speed v@m, will not exceed the highest permitted freewheeling speed mwxjnæmæ? during/within the road section. Thus, freewheeling will be allowed/utilized for the road section. The simulation and/or evaluation algorithms used for determining if freewheeling is possible and appropriate can here include for a skilled person well known such simulation and/or evaluation algorithms, as long as they include usage of a highest permitted freewheeling speed vmM_Ü@Wmæ1. lO l5 20 25 30 Zl As stated above, the simulations related to freewheeling sim?æama? and being performed at the time instant twm are according to an embodiment of the present invention concentrated only to the first over speed occurrence ahead of the vehicle. Thus, the simulated væm and/or actual vax vehicle speeds are analyzed from the position of the vehicle corresponding to the simulations time instant tsnluntil the simulated vsm and/or actual vax vehicle speed has exceeded the generally used highest value v?? once and then has gone below the generally used highest value vmm again.

According to prior art solutions, however, for example when the temporarily increased highest value vm?l?fæt corresponds to the increased value vnígwsgßdwwg for the downhill speed control, it is determined at the time instant tmigppnßram if the highest permitted freewheeling speed vmM_üe@m&¿ should be increased to its increased value vm??mqjdwww. Thus, the reference speed vnígmim af (double-dot-dashed line) could be increased at this time instant tn?gmgmim Mt. The time instant tnfgmgmim Mt occurs much later than the time instant t?m in which the freewheeling simulations are performed. Therefore, the freewheeling system does not know at the simulation and/or evaluation time instant tüm that the highest permitted freewheeling speed vm?_?emm&¿ will be increased in known systems. Thus, since the freewheeling simulations sim?æmmü? at tæm show that the simulated vehicle speed vsm and/or the actual vehicle speed vax will exceed the highest permitted freewheeling speed vm?_?emm&¿, freewheeling will not be deemed as allowed/usable.

For known systems, the increased value for the highest permitted freewheeling speed vmM_üemm@?, e.g. the increased value vm¿jhæ_¶mWmg for the downhill speed control, is determined when the actual vehicle speed vax exceeds the lO l5 20 25 30 22 generally used highest value v?w, e.g. the downhill control speed vüwc. Thus, the highest permitted freewheeling speed vmax_freewheel, is here set to the increased value vmaxloffset, e.g. vnfpwsgsdmmg for the downhill speed control, at the time instant tmí?gjnßram, which makes it possible for the vehicle to utilise freewheeling from that time instant tm?ggymßram. As can be seen in figure 3, the time instant trü¿¶¿m¿m af, from which freewheeling was possible for prior art solutions, occurs much later than the time instant when the freewheeling simulations sim?æämä? are performed, after which freewheeling can be used according to the present invention.

The freewheeling ends when the actual vehicle speed væï and vætyn?ram, respectively, have dropped to the set-speed væt again. The resulting freewheeling time period Tfæemæaynwa?im for the present invention is considerably longer than the freewheeling time period Tfmewæ&Lpn@ram for the prior art solutions, which is illustrated at the bottom of figure 3.

According to an embodiment of the present invention, the generally used highest value vm? corresponds to a downhill control speed vüwc; vmm=vüwc, at which a system for downhill speed control brakes the vehicle. The downhill speed control system, as well as the set speed and the reference speed being used when braking the vehicle, has been described more in detail above.

There is often set a predetermined/preprogrammed vehicle speed limit vWmp?a§Væ@¿m1for a vehicle. This predetermined/preprogrammed vehicle speed limit v@@ucm_¶æaLnm has e.g. for trucks in Europe a value of 89 km/h. According to an embodiment of the present invention, the generally used highest value vm? is related to such a predetermined vehicle speed limit vWhM¿ï§We¿¿m” e.g. as being an offset from, i.e. lO l5 20 25 30 23 having a higher value than, the predetermined vehicle speed Vvehicle_speed_lim - The generally used highest value vmm can also, according to an embodiment of the present invention, be related to behavior of the driver of the vehicle, i.e. based on the historical driving of the vehicle. The historical driving may for example be provided for by use of an adaptive algorithm which is updated during the vehicle's journeys.

The generally used highest value vmm can also, according to an embodiment of the present invention, be related to surrounding traffic on the road section. The surrounding traffic and/or distances to surrounding vehicles may be determined at least partly on the basis of radar and/or camera equipment, or based on information provided by information systems and/or by other vehicles. For example, the generally used highest value vm? may be given a relatively lower value if there are surrounding vehicles close to the vehicle.

The generally used highest value vmm can also, according to an embodiment of the present invention, be related to one or more characteristics of the road section, such as one or more of a speed limit, a curvature, presence of at least one speed camera, and a traffic situation, such as car queues, within the road section. For example, the generally used highest value vmm may be given a relatively lower value if there is a lower speed limit, a speed camera, one or more tight bends and/or car queues in the road section.

The generally used highest value v?? may, according to an embodiment of the present invention, change dynamically along road section, as is easily understood, since the presence of e.g. tight bends, speed cameras and/or car queues may change as the vehicle passes through the road section. 10 l5 20 25 30 24 The temporarily increased highest value vmM+?fæt is, according to an embodiment of the present invention, equal to the generally used highest value vmm plus a speed offset v?fæt; vmm??fæt = mmx + v?fæt. The speed offset v?fæt can here have a constant value, can have a value being related to a performance mode, e.g. l km/h for the normal performance mode and 2 km/h for the economy performance mode, or can have a value related to a driver input, such that the driver can influence the value for the temporarily increased highest value vm?l?fæt, and thereby also can influence the freewheeling possibilities for the vehicle.

The person skilled in the art will appreciate that a method for determination and utilization of a highest permitted freewheeling speed vm@¿ræwmelaccording to the present invention can also be implemented in a computer program, which, when it is executed in a computer, instructs the computer to execute the method. The computer program is usually constituted by a computer program product 403 stored on a non-transitory/non-volatile digital storage medium, in which the computer program is incorporated in the computer- readable medium of the computer program product. The computer- readable medium comprises a suitable memory, such as, for example: ROM (Read-Only Memory), PROM (Programmable Read-Only Memory), EPROM (Erasable PROM), Flash memory, EEPROM (Electrically Erasable PROM), a hard disk unit, etc.

Figure 4 shows in schematic representation a control unit 400.

The control unit 400 comprises a computing unit 40l, which can be constituted by essentially any suitable type of processor or microcomputer, for example a circuit for digital signal processing (Digital Signal Processor, DSP), or a circuit having a predetermined specific function (Application Specific Integrated Circuit, ASIC). The computing unit 40l is connected 10 15 20 25 30 25 to a memory unit 402 arranged in the control unit 400, which memory unit provides the computing unit 401 with, for example, the stored program code and/or the stored data which the computing unit 401 requires to be able to perform computations. The computing unit 401 is also arranged to store partial or final results of computations in the memory unit 402.

In addition, the control unit 400 is provided with devices 411, 412, 413, 414 for receiving and transmitting input and output signals. These input and output signals can comprise waveforms, impulses, or other attributes which, by the devices 411, 413 for the reception of input signals, can be detected as information and can be converted into signals which can be processed by the computing unit 401. These signals are then made available to the computing unit 401. The devices 412, 414 for the transmission of output signals are arranged to convert signals received from the computing unit 401 in order to create output signals by, for example, modulating the signals, which can be transmitted to other parts of and/or systems in the vehicle.

Each of the connections to the devices for receiving and transmitting input and output signals can be constituted by one or more of a cable; a data bus, such as a CAN bus (Controller Area Network bus), a MOST bus (Media Orientated Systems Transport bus), or some other bus configuration; or by a wireless connection. A person skilled in the art will appreciate that the above-stated computer can be constituted by the computing unit 401 and that the above- stated memory can be constituted by the memory unit 402.

Control systems in modern vehicles commonly comprise communication bus systems consisting of one or more communication buses for linking a number of electronic control l0 l5 20 25 30 26 units (ECU's), or controllers, and various components located on the vehicle. Such a control system can comprise a large number of control units and the responsibility for a specific function can be divided amongst more than one control unit.

Vehicles of the shown type thus often comprise significantly more control units than are shown in figure 4, which is well known to the person skilled in the art within the technical field.

In the shown embodiment, the present invention is implemented in the control unit 400. The invention can also, however, be implemented wholly or partially in one or more other control units already present in the vehicle, or in some control unit dedicated to the present invention.

Here and in this document, units are often described as being arranged for performing steps of the method according to the invention. This also includes that the units are designed to and/or configured to perform these method steps.

The at least one control unit 400 is in figure l illustrated as including separately illustrated units 410, 420. These units 410, 420 can, however be logically separated by physically implemented in the same unit, or can be both logically and physically arranged together. These units 4l0, 420 can for example correspond to groups of instructions, which can be in the form of programming code, that are input into, and are utilized by a processor when the units are active and/or are utilized for performing its method step, respectively.

According to an aspect of the present invention, a system arranged for determination and utilization of a highest permitted freewheeling speed vm?_ñemma? is presented. The highest permitted freewheeling speed v@M_?e@m&¿ is to be used lO l5 20 25 30 27 for freewheeling by a vehicle on a road section ahead of the vehicle.

The system includes a determination unit 4l0, which is arranged for determination, at or before a time instant t?m when simulations sinqnæmæelrelated to the freewheeling on the road section are performed, of a value for the highest permitted freewheeling speed v@M_?e@m&¿. The determination unit 4l0 is here arranged for determining the value for the highest permitted freewheeling speed vmxinæmæ? at or before a time instant tüm as a generally used highest value vm?; vm?_?eÜmæl = vmm; or as a temporarily increased highest value vm?i?fæt being higher than the generally used highest value vñ?; v@?_?eümæl = vmax+offset and Vmax+offset > Vmax- The system also includes a utilization unit 420, which is arranged for utilizing the by the determination unit 4l0 determined highest permitted freewheeling speed v@?_ñeÜm%¿ when the simulations sim?ewmælbm?grelated to the freewheeling on the road section ahead of the vehicle are evaluated.

Thus, when the system according to the present invention is used, the highest permitted freewheeling speed vm?_?e@mæl is determined and ready to be used already at the time instant tan when freewheeling simulations simfæemææ and/or evaluations of these simulation are made. Hereby, fresh and accurate values for the highest permitted freewheeling speed vmmgïæwmel can be utilized for the simulations and/or evaluations, thereby resulting in more accurate freewheeling simulations.

Also, since it is possible that a temporarily increased highest value vm?i?f might be available for use at the time instant tüm when freewheeling simulations sim?æ@me@_are made, more freewheeling sequences and/or longer freewheeling sequences can be identified as possible/admissible at the lO l5 28 simulations, which lowers the total fuel consumption in the vehicle.

The system according to the present invention can be arranged for performing all of the above, in the claims, and in the herein described embodiment method steps. The system is hereby is provided with the above described advantages for each respective embodiment.

A skilled person also realizes that the above described system can be modified according to the different embodiments of the method of the present invention. The present invention is also related to a vehicle lO0, such as a truck, a bus or a car, including the herein described system for determination and utilization of a highest permitted freewheeling speed Vmax_freewheel - The present invention is not limited to the above described embodiments. Instead, the present relates to, and encompasses all different embodiments being included within the scope of the independent claims.

Claims (1)

Patentkrav 1. Method for determination and utilization of a highest permitted freewheeling speed vbe used by a vehicle max freewheel t (100) on a road section ahead of said vehicle (100); characterized by 1. determination, at or before a time instant tsim when simulations slm --freewheel related to freewheeling on said road section are performed, of a value for said highest permitted freewheeling speed v.ax freewheel r wherein said value can be determined to a generally used highest value vv max , - max freewheel — vmax ; or to a temporarily increased highest value vmax+off set being higher than the generally used highest value vv max , - max freewheel — Vmax+offset and Vmax+offset > vmax; at said determination; and 2. utilization of said determined highest permitted freewheeling speed vmax freewheel when said simulations slm --freewheel related to said freewheeling are evaluated. 2. Method as claimed in claim 1, wherein said determination of said value for said highest permitted freewheeling speed vmax freewheel is based on a simulated vehicle speed vsma over said road section. 3. Method as claimed in claim 2, wherein a determination of said simulated vehicle speed vsim is based on knowledge related to said road section. 4. Method as claimed in claim 3, wherein said knowledge is based on at least one in the group of 1. positioning information, 2. map information, and 3. topography information. 5. Method as claimed in any one of claims 2-4, wherein said determination of said value for said highest permitted freewheeling speed vmax freewheel includes: 1. comparing said simulated vehicle speed vsim generally used highest value vmax; and 2. comparing said simulated vehicle speed vsim temporarily increased highest value vmax+offset with said with said 6. Method as claimed in claim 5, wherein said value for said highest permitted freewheeling speed vmax freewheel is set to said temporarily increased highest value vmax+offset; Vmax freewheel — Vmax+offset; at said determination if said simulated vehicle speed vsim is lower than said temporarily increased highest value Vmax+offset ; Vsim < Vritax+offset ; during said road section, and if said simulated vehicle speed vsim is higher than said generally used highest value v.; vs-m > vmax; for a time period Tamer maxbeing shorter than a predetermined over speed time period T over speed; Tover max < Toyer speed during said road section. 7. Method as claimed in any one of claims 5-6, wherein said value for said highest permitted freewheeling speed Vmax freewheel is set to said generally used highest value vmax; Vmax freewheel — vmax; at said determination if said simulated vehicle speed vsin-, is higher than said temporarily increased highest value vnax+offset ; vsim > Vmax+offset; during said road section, or if said simulated vehicle speed vsim is higher than said generally used highest value yeas; vsm, > yeas; for a time period Tover max being longer than a predetermined over speed time period Toyer speed ; Toyer max > Tamer speed during said road section. 8. Method as claimed in any one of claims 6-7, wherein said predetermined over speed time period Toyer speed has a value according to anyone in the group of: - a constant value; 31 1. a value related to a performance mode; and 2. a value related to a driver input. 9. Method as claimed in any one of claims 1-8, wherein said generally used highest value vmax is related to a vehicle speed at which an additional acceleration of said vehicle is unwanted and/or at which a retardation of said vehicle is wanted. 10. Method as claimed in any one of claims 1-9, wherein said generally used highest value vmax corresponds to a downhill control speed vansc; vmax=vdhsc, at which a system for downhill speed control brakes the vehicle. 11. Method as claimed in any one of claims 1-10, wherein said generally used highest value vmax is related to a predetermined vehicle speed limit vvehicle speed lim for said vehicle. 12. Method as claimed in any one of claims 1-11, wherein said generally used highest value vmax is related to a driver behavior. 13. Method as claimed in any one of claims 1-12, wherein said generally used highest value vmax is related to surrounding traffic on said road section. 14. Method as claimed in any one of claims 1-13, in which said generally used highest value vmax is related to one or more characteristics of said road section. 15. Method as claimed in claim 14, wherein said one or more characteristics comprise at least one in the group of: 1. a speed limit for said road section; 2. a curvature of said road section; 32 3. the presence of at least one speed camera on said road section; and 4. a traffic situation within said road section. 16. Method as claimed in anyone of claims 1-15, wherein said generally used highest value v,„ changes dynamically along said road section. 17. Method as claimed in any one of claims 1-16, wherein said temporarily increased highest value vmax+of f set isequal to said generally used highest value vmax plus a speed offset Vof f set ; Vmax+of f set = VmaxVof f set • 18. Method as claimed in claim 17, wherein said speed offset Voffset has a value according to anyone in the group of: 1. a constant value; - a value related to a performance mode; and - a value related to a driver input 19. Computer program, characterized in code means, which when run in a computer causes the computer to execute the method according to any one of the claims 1-18. 20. Computer program product including a computer readable medium and a computer program according to claim 19, wherein said computer program is included in the computer readable medium. 21. System arranged for determination and utilization of a highest permitted freewheeling speed vmax freewheel to be used by a vehicle (100) on a road section ahead of said vehicle (100); characterized by

1. a determination unit (410), arranged for determination, at or before a time instant tsim when simulations slm --freewheel related to freewheeling on said road section are performed, of a value for said highest permitted freewheeling speed vmax freewheel r 33 wherein said determination unit (410) is arranged for determining said value at or before said time instant tsim as a generally used highest value Vmax; Vmax freewheel = vmax; or as a temporarily increased highest value vmax+offset being higher than the generally used highest value vmax , - : v max freewheel = Vmax+offset and vmax+offset > Vmax; and - a utilization unit (420), arranged for utilizing said determined highest permitted freewheeling speed vmax freewn- eel when said simulations slm --freewheel related to said freewheeling are evaluated. 2 101 1 06