Adaptive cruise control device and method for operating a host vehicle in a low-speed scenario, vehicle and computer program

Abstract

The invention is directed to a method (100) for operating a host vehicle (150) wherein a speed value (VH) of the host vehicle is controlled in a low-speed scenario The method comprises ascertaining (102) a moveoff speed value (VM) of the host vehicle being indicative of a minimum vehicle speed at which the host vehicle (150) can be driven with a clutch in a fully engaged state, ascertaining (104) a target vehicle speed value (VT) of a target vehicle (152) driving ahead of the host vehicle (150); and upon determining that the target vehicle speed value (VT) of the target vehicle (152) driving ahead is lower than the moveoff speed value (VM) of the host vehicle (150), operating (106) the host vehicle (150) in a coasting operation mode (CM), thereby increasing fuel consumption efficiency and reducing the wear of vehicle components such as clutch and brakes.

Description

[0001] Adaptive cruise control device and method for operating a host vehicle in a low-speed scenario, vehicle and computer program

[0002] The present invention relates to a method for operating a host vehicle in a low-speed scenario. The invention is also related to an adaptive cruise control device for controlling a speed value of a host vehicle, to a vehicle, in particular a commercial vehicle, and to a computer program.

[0003] Conventional assistance systems like adaptive cruise control (ACC) systems currently play a very important role in assisting the driver of a vehicle hosting said system, hereinafter referred to as host vehicle. In low traffic scenarios where the host vehicle can be driven at relatively high speeds, the adaptation of the speed value of the host vehicle is efficiently implemented. However, light and moderate traffic scenarios, wherein the speed value of the host vehicle lies in the vicinity of a so called moveoff speed currently poses a challenge to the known driver assistance systems. The moveoff speed is defined as the minimum speed at which a given vehicle can be driving with the clutch in a fully engaged state, and typically depends on the vehicle state (e.g. load, tire pressure, etc.) and on the current gear ratio. Thus, when a vehicle travels at a speed lower than the moveoff speed with a fully engaged clutch, the vehicle will tend to stall. Following a target vehicle, e.g., the closest vehicle driving ahead of the host vehicle in the same road lane, at a safe distance in light and moderate traffic scenario without excessive stressing and / or loading of the vehicle components (e.g., clutch, brake) is challenging.

[0004] Low speed scenario refers, in the frame of this disclosure, to a driving scenario where the vehicles are driving at a low average speed, in particular at a speed where the use of the clutch is necessary to avoid stalling of the vehicle’s engine. Current ACC systems handle the low-speed scenario (e.g. moderate traffic jam scenario) in two different approaches. In a first approach, the host vehicle follows the target vehicle even at low speeds under a so-called partial clutch operation. In this case, the clutch is operated at a partial closure condition for a prolonged time, which causes an excessive load on the clutch and increases wear and tear thereof. Also, fuel is spent continuously to maintain the host vehicle at the desired speed. Alternatively, in a second approach, when the target vehicle ahead moves at slow speeds, the ACC system handles this slow speed by frequently accelerating and braking. Typically, the ACC system accelerates the host vehicle above a minimum speed it can drive without overloading the clutch (moveoff speed value). Since this moveoff speed value is higher than the speed of the target vehicle in front, the host vehicle moves closer and closer to the target vehicle in front. The ACC system then decelerates the host vehicle by applying brakes, typically bringing the host vehicle to stop. Once a sufficient gap is opened up between the host and the target vehicle, the ACC system accelerates the host vehicle again until a speed value equal to or higher than the moveoff speed is reached, and this operation repeats. In this approach, when the ACC system accelerates and decelerates, the clutch has to close and open frequently. Also, during deceleration, the ACC system operates the brakes which causes wear and tear. Frequent acceleration and deceleration also cause increased fuel consumption and emissions. Thus, fuel efficiency is reduced and wear and tear of components like clutches and brakes is increased.

[0005] This is where the invention comes in, wherein it is an objective of the present invention to provide a method and an adaptive cruise control device for operating a host vehicle in a low-speed scenario with improved fuel efficiency and reduced wear of components.

[0006] This objective is achieved in a first aspect by the invention by a method according to claim 1. Claim 1 is directed to a method for operating a host vehicle wherein a speed value of a host vehicle is controlled in a low-speed scenario. A low-speed scenario involves following a target vehicle travelling at a reduced speed, in particular lower than a moveoff speed. The method of the first aspect of the invention comprises ascertaining a moveoff speed value of the host vehicle, wherein the moveoff speed value is indicative of a minimum vehicle speed at which the host vehicle can be driven with a clutch in a fully engaged state. In particular, the moveoff speed value is dependent on a current gear ratio and / or on a load state of the host vehicle. The method also comprises ascertaining a target vehicle speed value of a target vehicle driving ahead of the host vehicle, in particular on the same road lane. Upon determining that the target vehicle speed value of the target vehicle driving ahead is lower than the ascertained moveoff speed value of the host vehicle, the method of the first aspect of the invention includes operating the host vehicle in a coasting operation mode. The method of the first aspect of the invention addresses the low-speed scenario by enabling the coasting operation mode when determining that the target vehicle is driving at a target vehicle speed that is below the moveoff speed. In the coasting operation mode, the wheels are disengaged from the engine and the vehicle moves using the vehicle’s momentum. Thus, when the coasting operation mode is active, the host vehicle starts to roll freely, and the kinetic energy of the host vehicle is used to move the host vehicle in this scenario. The external resistances are responsible for slowing down the target vehicle and include, air resistance and rolling resistance or friction with the roads. This minimizes wear of the clutch and brakes and reduces fuel consumption.

[0007] Further advantageous developments of the method of the first aspect of the invention are found in the dependent claims and indicate in detail advantageous possibilities to realize the concept described above within the scope of the object as well as with regard to further advantages.

[0008] In a development, the host vehicle is operated in the coasting operation mode before the host vehicle is operated in a brake operation mode, in which a brake unit is actuated. Thus, during operation in the coasting operation mode, the brakes are not used. In a development, the brake operation mode can be initiated when a distance between the target vehicle and the host vehicles is less than a predetermined minimum distance. In another development, the brake operation mode can be initiated when it is determined that at a given current host vehicle speed value (during the free rolling phase), the rate of change of distance is above a predetermined threshold value, i.e. , at a given speed value, the distance between both vehicles decreases faster than a predetermined safety threshold.

[0009] In another development, operating the host vehicle in the coasting operation mode involves activating a first free-rolling driving phase by providing a transmission control signal to a transmission system for operating the clutch in a disengaged state or, alternatively, operating the host vehicle in a neutral gear, and operating the vehicle in the coasting operation mode before a brake operation mode by remaining in the first free- rolling driving phase until the current host vehicle speed reaches a predetermined lower speed threshold value that is lower than the target vehicle speed. Thus, the end of the first free-rolling phase, in which the host vehicle is in the coasting operation mode is determined when the host vehicle reaches the predetermined lower speed threshold value that is lower than the target vehicle speed. This lower speed threshold value can be predetermined as a function of the target vehicle speed value and / or as a function of the moveoff speed value. The lower speed threshold value can be a fixed value, e.g., 20 km / h, 10km / h, 5 km / h, 2 km / h. Alternatively, the lower speed threshold value can be determined as a percentage of the current moveoff speed value, such as, for example, 60% of the current moveoff speed value, 50% of the current moveoff speed value, 40% of the current moveoff speed value, 30% of the current moveoff speed value or 20% of the current moveoff speed value.

[0010] In yet another development, the method further comprises, upon determining that the current host vehicle speed reaches a lower speed threshold value that is lower than the target vehicle speed at which the target vehicle is moving, activating an acceleration driving phase. Thus, when the host vehicle reaches the lower speed threshold value, the host vehicle begins an acceleration driving phase in which the vehicle is accelerated.

[0011] It is preferred that the lower speed threshold value is higher than 0, in particular that the acceleration driving phase begins when the host vehicle is still rolling, i.e. , has a nonvanishing speed value, or, in other words, has not stopped. In this development, as the host vehicles does not come to full stop before accelerating in the acceleration driving phase, the energy spent to accelerate is less compared to an acceleration from standstill and hence the fuel efficiency is improved.

[0012] In yet another development, the acceleration driving phase begins upon determining that a current distance amount to the target vehicle has increased beyond a predetermined acceleration distance threshold amount.

[0013] In a particular development, the acceleration phase involves operating the clutch in an engaged state and accelerating the host vehicle until the host vehicle speed value reaches a predetermined upper speed threshold value that is equal to or higher than the moveoff speed value. Thus, the host vehicle is accelerated until it reaches a speed value that is at least equal to the moveoff speed, and at which the clutch does not need to be actuated for maintaining the reached speed value. In particular, in another development, the method further comprises, upon determining that the host vehicle speed value has reached the predetermined upper speed threshold value, activating a subsequent free-rolling driving phase, in particular by providing the transmission control signal to the transmission system for operating the clutch in the disengaged state when the upper speed threshold value is reached. Thus, in the low- speed scenario, the host vehicles alternates between free-rolling driving phases and acceleration driving phases, that are initiated and end in dependence on the lower speed threshold value, or the predetermined acceleration distance threshold amount, and the upper speed threshold value. With this novel approach, fuel (or power from a battery in the case of battery-powered host vehicles) is only spent during short acceleration driving phases and the kinetic energy of the host vehicle is used to follow the target vehicle, thereby improving fuel consumption. Additionally, the use of the braking units is also reduced, even avoided. The clutch actuation (engaging / disengaging) is also performed during short phases, and therefore the load on the clutch is limited. Preferably, the acceleration driving phase is initiated when the vehicle is still rolling and, therefore, less fuel or energy is spent when compared to acceleration from standstill.

[0014] In another development of the method of the first aspect of the invention, the method further comprises ascertaining, or otherwise determining or monitoring, a distance value indicative of a current distance amount between the host vehicle and the target vehicle, and activating the coasting operation mode, in particular activating the first free-rolling driving phase, or the subsequent free-rolling driving phases, further upon determining that the determined distance value is lower than an activation-distance threshold. In this development, the activation the coasting operation mode, in particular of the free-rolling driving phases, in particular the first free-rolling driving phase, is further based on a current distance amount being lower than an activation-distance threshold. In particular, the host vehicle can be operated at the moveoff speed value (or at a slightly higher speed) until the distance between the host vehicle and the target vehicle, which is moving at a lower speed value, reaches the activation-distance threshold. At this point, the coasting operation mode is activated.

[0015] In another embodiment, the method further comprises ascertaining (e.g. receiving, determining, or otherwise monitoring) a distance value indicative of a current distance amount between the host vehicle and the target vehicle, and upon determining that the distance value is equal to a minimum distance threshold value, activating a braking operation mode, in particular by providing a brake control signal to a braking system for actuating a brake unit for braking the host vehicle. This developments provides an emergency braking feature in case the target vehicle brakes or otherwise reduces its velocity such that a distance between both host and target vehicle is reduced, in particular, such that, if no measure is taken, the distance would be reduced beyond a minimum safety distance, which can be a fixed value or a value that depends on the current state of the host vehicle (speed, gear, load, etc.). Thus, when the monitored distance reaches a minimum distance threshold value, which is equal to or higher than the minimum safety distance, the brakes as applied to reduce the host vehicle’s speed, or to fully stop the host vehicle.

[0016] To achieve the object, the invention also in a second aspect leads to an adaptive cruise control (ACC) device, as defined by claim 10.

[0017] The adaptive cruise control device of the second aspect is suitable for controlling a speed value of a host vehicle, in particular in a low-speed scenario as described above. The adaptive cruise control unit comprises a moveoff speed ascertaining unit configured to ascertain (e.g., to receive or to determine) a moveoff speed value of the host vehicle. As discussed above, the moveoff speed value is indicative of a minimum vehicle speed at which the host vehicle can be driven with clutch in a fully engaged state. The ACC device also comprises a target vehicle speed ascertaining unit, in particular comprising, or connected to, a velocity sensor, and configured to ascertain a target vehicle speed value of a target vehicle driving ahead, in particular the closest vehicle driving ahead in the same direction, and in particular on the same road lane. The ACC device further includes a control unit that is configured, upon determining that the target vehicle speed of the target vehicle driving ahead is lower than the moveoff speed of the host vehicle, to operate the host vehicle in a coasting operation mode, in particular to activate a first free-rolling driving phase, in particular by providing a transmission control signal to a transmission system for operating the clutch in a disengaged state until the current host vehicle speed reaches a predetermined lower speed threshold value that is lower than the target vehicle speed.

[0018] The ACC device of the second aspect thus shares the advantages of the method of the first aspect of the invention. In the following, developments of the ACC device of the second aspect of the invention will be described.

[0019] In a development, the adaptive cruise control device further comprises a distance ascertaining unit, in particular comprising, or connected to, a distance sensor, and configured to ascertain a distance value indicative of distance amount between the host vehicle and the target vehicle. In this development, the control unit is further configured to operate the host vehicle in the coasting operation mode, in particular to activate the first free-rolling driving phase, further upon determining that the determined distance value is lower than an activation-distance threshold.

[0020] In another development, the control unit is additionally or alternatively configured, upon determining that the distance value is equal to a minimum distance threshold value, to activate a braking phase by providing a brake control signal to a braking system for operating a brake unit for braking the host vehicle.

[0021] In yet another development, the control unit of the inventive ACC device is further configured, upon determining that the current host vehicle speed reaches a lower speed threshold value that is lower than the target vehicle speed at which the target vehicle is moving, to activate an acceleration driving phase, in particular to operate the clutch in an engaged state and accelerate the host vehicle until the host vehicle speed value reaches a predetermined upper speed threshold value that is equal to or higher than the moveoff speed value, and, optionally, upon determining that the host vehicle speed value has reached the predetermined upper speed threshold value, to activate a subsequent free-rolling driving phase, in particular by providing the transmission control signal to the transmission system for operating the clutch in the disengaged state when the upper speed threshold value is reached.

[0022] A third aspect of the invention is formed by a vehicle, in particular commercial vehicle, comprising an adaptive cruise control device in accordance with the second aspect of the invention, further including a transmission system for operating a clutch, and a braking system for actuating a brake unit.

[0023] A fourth aspect of the invention is formed by a computer program comprising instructions, which, when executed by a processor of an adaptive cruise control device, e.g. a control unit, in accordance with the second aspect of the invention, cause the adaptive cruise control device to carry out the method of the first aspect of the invention.

[0024] These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.

[0025] The embodiments of the invention are described in the following on the basis of the drawing in comparison with the state of the art, which is also partly illustrated. The latter is not necessarily intended to represent the embodiments to scale. The drawing is, where useful for explanation, shown in schematized and / or slightly distorted form. With regard to additions to the teaching immediately recognizable from the drawing, reference is made to the relevant prior art. It should be kept in mind that numerous modifications and changes can be made to the form and detail of an embodiment without deviating from the general concept of the invention. The features of the invention disclosed in the description, in the drawing and in the claims may be essential for a further development of the invention, either individually or in any combination. In addition, all combinations of at least two of the features disclosed in the description, drawing and / or claims fall within the scope of the invention.

[0026] The general concept of the invention is not limited to the exact form or detail of the preferred embodiments shown and described below or to a subject matter, which would be limited in comparison to the subject matter as claimed in the claims.

[0027] For specified design ranges, values within specified limits of the ranges are also disclosed as limit values and thus are arbitrarily applicable and claimable.

[0028] The following drawing shows in:

[0029] FIG. 1 shows a host vehicle and a target vehicle in a low-speed scenario wherein the speed value of the target vehicle is lower than the moveoff speed value of the host vehicle;

[0030] FIG. 2 shows time diagrams of a plurality of driving parameters of a host vehicle implementing a first known approach for controlling the speed in a low speed scenario; FIG. 3 shows time diagrams of a plurality of driving parameters of a host vehicle implementing a second known approach for controlling the speed in a low speed scenario;

[0031] FIG. 4 shows time diagrams of a plurality of driving parameters of a host vehicle implementing an exemplary method for controlling the speed in a low-speed scenario in accordance with a first embodiment of the invention;

[0032] FIG. 5 shows a flow diagram of an exemplary method for controlling the speed of a host vehicle in a low-speed scenario in accordance with a second embodiment of the invention; and

[0033] FIG. 6 shows an exemplary block diagram of a vehicle comprising an adaptive cruise control device in accordance with the invention.

[0034] FIG. 1 represents a host vehicle 150 and a target vehicle 152 that is the closest vehicle driving ahead of the host vehicle 150 in the same direction, in particular on the same road lane. The situation depicts a so-called low speed scenario, wherein the speed value VT of the target vehicle 152 is lower than a moveoff speed value VM of the host vehicle 150. The host vehicle 150 has a moveoff speed value VM that is indicative of of a minimum vehicle speed at which the host vehicle can be driven with the clutch in a fully engaged state. In particular, the moveoff speed value VM is dependent on a current vehicle state, including a current gear ratio, a current load, etc. At a given point in time, the distance between the host vehicle and the target vehicle is D. Since the current speed value of the host vehicle VH is higher than the current speed value of the target vehicle VT, the distance will decrease with time. Lowering the speed of the host vehicle to match that of the target vehicle would reduce the speed of the host vehicle to a value lower than the moveoff speed value, which would result in a stalling of the engine if no proper measure is performed.

[0035] FIG. 2 shows time diagrams of a plurality of driving parameters including speed V (such as current speed values of a host and a target vehicle, VH, VT, and moveoff speed value VM of the host vehicle), current distance D between the target and the host vehicle, fuel consumption F, brake usage B, and clutch usage C, of a host vehicle implementing a first known approach for controlling the speed in a low speed scenario. In this first known approach, an adaptive cruise control (ACC) system controls the host vehicle 150 such that the host vehicle 150 follows the target vehicle 152 even at low speeds, e.g., speeds below the moveoff speed value VM, under a so-called partial clutch operation. In this case, the clutch C is operated at a partial closure condition for a prolonged time, which causes an excessive load on the clutch and increases wear and tear thereof. Also, fuel F is spent continuously to maintain the host vehicle at the desired speed.

[0036] FIG. 3 also shows time diagrams of the plurality of driving parameters of a host vehicle, as explained with reference to Fig. 2 for implementing a second known approach for controlling the speed in a low-speed scenario. In this second approach, when the target vehicle 152 ahead moves at slow speeds VT, e.g., slower than the moveoff speed value VM of the host vehicle 150, the ACC system handles this slow speed scenario by frequently accelerating and braking. Typically, the ACC system controls the speed of the host vehicle at, or slightly above, a minimum speed it can drive without overloading the clutch (moveoff speed value). Since this moveoff speed value VM is higher than the speed VT of the target vehicle 152 in front, the host vehicle 150 moves closer and closer to the target vehicle 152 in front and the distance value between them is reduced. Once the distance value D reaches minimum distance threshold value DMin, indicative of a probable collision, at time ta, the ACC system decelerates the host vehicle by applying brakes B, typically bringing the host vehicle 150 to stop, i.e. VH=0, at tb. Once a sufficient gap is opened up between the host and the target vehicle, at tc, the ACC system accelerates the host vehicle again until a speed value equal to or higher than the moveoff speed is reached at td, and this operation repeats. In this approach, when the ACC system accelerates and decelerates, the clutch C has to close and open frequently. Also, during deceleration, the ACC system operates the brakes B which causes wear and tear. Frequent acceleration and deceleration also cause increased fuel consumption and emissions. Thus fuel efficiency is reduced and wear and tear of components like clutch C and brakes B is increased.

[0037] FIG. 4 shows time diagrams of a plurality of driving parameters of a host vehicle 150 implementing an exemplary method for controlling the speed in a low-speed scenario in accordance with a first embodiment of the invention. Here again, the host vehicle 150 is initially driving following a target vehicle 152 that is moving at a speed value VT that is lower than the moveoff speed value VM of the host vehicle, which is indicated as a constant value and thus as a horizontal line in the velocity V diagram. Upon determining that the target vehicle speed value VT of the target vehicle 152 driving ahead is lower than the moveoff speed value VM of the host vehicle 150, the host vehicle is operated in a coasting operation mode CM. In the example shown in Fig. 4, the coasting operation mode starts at a time tawhere, after having been driven at the moveoff speed value for a certain timespan, the distance D to the target vehicle is lower than an activation-distance threshold DAT. The activation of the coasting operation mode at ta shown in Fig. 4 includes activating a first free-rolling driving phase FRi, for example by providing a transmission control signal TC to a transmission system for operating the clutch C in a disengaged state CD and also operating the host vehicle 150 in the coasting operation mode CM by remaining in the first free-rolling driving phase FRi until the current host vehicle speed value VH reaches at tb a predetermined lower speed threshold value VLT that is lower than the target vehicle speed VT. At this point in time, i.e. , upon determining that the current host vehicle speed value VH has reached the lower speed threshold value VLT that is lower than the target vehicle speed VT at which the target vehicle 152 is moving, an acceleration driving phase AD is activated. The acceleration driving phase AD, which takes place in the timespan between tb and tc, involves operating the clutch C in an engaged state CE and accelerating the host vehicle 150 until the host vehicle speed value VH reaches a predetermined upper speed threshold value VHT that is equal to or higher than the moveoff speed value VM (equal to the moveoff speed value in the example shown in Fig. 4).

[0038] In addition, upon determining that the host vehicle speed value VH has reached the predetermined upper speed threshold value VHT, a subsequent free-rolling driving phase FR2, is activated at tc, in particular by providing again the transmission control signal TC to the transmission system for operating the clutch C in the disengaged state CD when the upper speed threshold value VHT is reached. The subsequent free-rolling driving phase FR2ends when the host vehicle speed value VH reaches again the lower speed threshold value VLT at td, when the acceleration driving phase AD is again activated during the timespan between td and te. At time te, a third free-rolling driving phase FR3 begins and again the transmission control signal TC to the transmission system for operating the clutch C in the disengaged state CD is provided. However, in this example, during the third free-rolling driving phase FR3, the target vehicle 152 further reduces its speed value VT, to an extent where a distance D between the host vehicle 150 (which is slowly decelerating due to friction and air resistance) reaches a minimum distance threshold value DMin. According to the example of Fig. 4, upon determining that the current distance value D between the host vehicle and the target vehicle is equal to said minimum distance threshold value DMin, a braking operation mode BM is activated. In particular a brake control signal BC is provided to a braking system 158 for actuating a brake unit B for braking the host vehicle 150.

[0039] FIG. 5 shows a flow diagram of an exemplary method 100 for controlling the speed of a host vehicle in a low-speed scenario in accordance with a second embodiment of the invention. The method 100 comprises, in a step 102, ascertaining the moveoff speed value VM of the host vehicle 150, which is indicative of a minimum vehicle speed at which the host vehicle 150 can be driven with a clutch C in a fully engaged state CE, and is in particular dependent on a current gear ratio GR. The method also comprises, in a step 104, ascertaining a target vehicle speed value VT of a target vehicle 152 driving ahead of the host vehicle 150, upon determining that the target vehicle speed value VT of the target vehicle 152 driving ahead is lower than the moveoff speed value VM of the host vehicle 150, the method includes, in a step 106, operating the host vehicle in a coasting operation mode CM. This operation in the coasting operation mode CM (step 106) may include activating a first free-rolling driving phase FRi by providing a transmission control signal TC to a transmission system 156 for operating the clutch C in a disengaged state CD and operating the host vehicle 150 in the coasting operation mode before a brake operation mode BM by remaining in the first free-rolling driving phase FRi until the current host vehicle speed value VH reaches a predetermined lower speed threshold value VLT that is lower than the target vehicle speed value VT.

[0040] Additionally, the method 100 may further comprise, upon determining, in a step 108, that the current host vehicle speed value VH reaches a lower speed threshold value VLT that is lower than the target vehicle speed VT at which the target vehicle 152 is moving, activating, in a step 110, an acceleration driving phase AD.

[0041] Additionally, the method 100 may further comprises, upon determining, in a step 112, that the host vehicle speed value VH has reached the predetermined upper speed threshold value VHT, activating, in a step 114, a subsequent free-rolling driving phase FR2, FR3, in particular by providing the transmission control signal TC to the transmission system for operating the clutch C in the disengaged state CD when the upper speed threshold value VHT is reached. Also, optionally as indicated by the dashes lines in Fig. 5, the method may comprise, in a step 116, ascertaining a distance value D indicative of distance amount between the host vehicle 150 and the target vehicle 152, and then activating, as explained with reference to step 106, the coasting operation mode CM, in particular activating the first free- rolling driving phase FRi, further upon determining, in a step 118, that the determined distance value D is lower than an activation-distance threshold DAT.

[0042] FIG. 6 shows an exemplary block diagram of a vehicle 1000 comprising an adaptive cruise control device 500 in accordance with the invention. The adaptive cruise control (ACC) device 500 comprises a moveoff speed ascertaining unit 502 that is configured to ascertain, that is, to determine or to receive, a moveoff speed value VM of the host vehicle 150 that is indicative of a minimum vehicle speed at which the host vehicle 150 can be driven with clutch C in a fully engaged state CE. This value can be determined by the moveoff speed ascertaining unit 502 based for instance on the current gear ratio GR and / or on current driving conditions, including a current load, or can be determined by an external unit and provided to the moveoff speed ascertaining unit 502 as suitable data, for instance via a CAN bus.

[0043] The ACC device also comprises a target vehicle speed ascertaining unit 504, in particular comprising, or connected to, a velocity sensor 505. The velocity sensor is configured to determine a target vehicle speed value VT of a target vehicle 152 driving ahead and to provide data indicative of said target vehicle speed value VT to the target vehicle speed ascertaining unit 504 as suitable data, for instance via a CAN bus.

[0044] The ACC system may additionally comprise a distance ascertaining unit 516, in particular comprising, or connected to, a distance sensor 517 that is configured to determine a distance value D indicative of distance amount between the host vehicle 150 and the target vehicle 152 and to provide data indicative of said distance value D to the distance ascertaining unit 516 as suitable data, for instance via a CAN bus.

[0045] The above referenced sensors 505, 517 can be dedicated sensors of the adaptive cruise control device 500 or sensors of the commercial vehicle, whose data is for instance received at an electronic control unit of the vehicle, which in turn provides the relevant data to the relevant ascertaining units 502, 504 and 516 via a wired (e.g., CAN bus) or wireless connection. The ACC device further comprises a control unit 506 that is configured, upon determining that the target vehicle speed VT of the target vehicle 152 driving ahead is lower than the moveoff speed VM of the host vehicle 150, to operate the host vehicle 150 in a coasting operation mode CM. In particular, the control unit 506 is configured to activate a first free- rolling driving phase FRi by providing a transmission control signal TC to a transmission system 156 for operating the clutch C in a disengaged state CD until the current host vehicle speed VH reaches a predetermined lower speed threshold value VLT that is lower than the target vehicle speed VT.

[0046] The control unit 506 of the ACC device 500 can optionally be configured, upon determining that the current host vehicle speed VH reaches a lower speed threshold value VLT that is lower than the target vehicle speed value VT at which the target vehicle 152 is moving, to activate an acceleration driving phase AD, in particular to operate the clutch C in an engaged state CE and accelerate the host vehicle 150 until the host vehicle speed value VH reaches a predetermined upper speed threshold value VHT that is equal to or higher than the moveoff speed value VM, and, optionally, upon determining that the host vehicle speed value VH has reached the predetermined upper speed threshold value VHT, to activate a subsequent free-rolling driving phase FR2, in particular by providing the transmission control signal TC to the transmission system 156 for operating the clutch C in the disengaged state CD when the upper speed threshold value VHT is reached.

[0047] The control unit 506 can be also configured to activate the first free-rolling driving phase FR1 further upon determining that the determined distance value D is lower than an activation-distance threshold DAT.

[0048] Also, optionally, the control unit 506 can be further configured, upon determining 120 that the distance value D is equal to a minimum distance threshold value DMin, to activate a braking phase BP by providing a brake control signal BC to a braking system 158 for operating a brake unit B for braking the host vehicle 150.

[0049] In summary, the invention is directed to a method for operating a host vehicle wherein a speed value of the host vehicle is controlled in a low-speed scenario. The method comprises ascertaining a moveoff speed value of the host vehicle being indicative of a mini- mum vehicle speed at which the host vehicle can be driven with a clutch in a fully engaged state, ascertaining a target vehicle speed value of a target vehicle driving ahead of the host vehicle, and upon determining that the target vehicle speed value of the target vehicle driving ahead is lower than the moveoff speed value of the host vehicle, operating the host vehicle in a coasting operation mode, thereby increasing fuel consumption efficiency and reducing the wear of vehicle components such as clutch and brakes.

[0050] Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims.

[0051] In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality.

[0052] A single unit or device may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

[0053] Any reference signs in the claims should not be construed as limiting the scope.

[0054] REFERENCE LIST (PART OF THE DESCRIPTION)

[0055] 100 Method

[0056] 102 Method step of method 100

[0057] 104 Method step of method 100

[0058] 106 Method step of method 100

[0059] 108 Method step of method 100

[0060] 110 Method step of method 100

[0061] 112 Method step of method 100

[0062] 114 Method step of method 100

[0063] 116 Method step of method 100

[0064] 118 Method step of method 100

[0065] 120 Method step of method 100

[0066] 150 Host vehicle

[0067] 152 Target vehicle

[0068] 156 Transmission system

[0069] 158 Braking system

[0070] 500 Adaptive cruise control (ACC) device

[0071] 502 Moveoff speed ascertaining unit

[0072] 504 Target vehicle speed ascertaining unit

[0073] 505 Velocity sensor

[0074] 506 Control unit

[0075] 516 Distance ascertaining unit

[0076] 517 Distance sensor

[0077] 1000 Vehicle

[0078] AD Acceleration driving phase

[0079] B Brake, braking unit

[0080] BC Brake control signal

[0081] BM Braking operation mode

[0082] BP Braking phase

[0083] C Clutch, clutch unit

[0084] CD Disengaged state of clutch

[0085] CE engaged state of clutch

[0086] CM coasting operation mode

[0087] D Distance DAT Activation-distance threshold

[0088] DMin Minimum distance threshold value

[0089] F Fuel consumption

[0090] GR Gear ratio

[0091] TC Transmission control signal

[0092] V Speed

[0093] VH Host vehicle speed value

[0094] VHT Upper speed threshold value

[0095] VLT Lower speed threshold value

[0096] VM moveoff speed value

[0097] VT Target vehicle speed value

Claims

CLAIMS1. Method (100) for operating a host vehicle (150) wherein a speed value (VH) of the host vehicle (150) is controlled in a low-speed scenario, the method (100) comprising:- ascertaining (102) a moveoff speed value (VM) of the host vehicle (150) being indicative of a minimum vehicle speed at which the host vehicle (150) can be driven with a clutch (C) in a fully engaged state (CE), in particular wherein the moveoff speed value (VM) is dependent on a current gear ratio (GR);- ascertaining (104) a target vehicle speed value (VT) of a target vehicle (152) driving ahead of the host vehicle (150); and- upon determining that the target vehicle speed value (VT) of the target vehicle (152) driving ahead is lower than the moveoff speed value (VM) of the host vehicle (150), operating (106) the host vehicle (150) in a coasting operation mode (CM).

2. The method of claim 1 wherein the host vehicle (150) is operated in the coasting operation mode (CM) before the host vehicle (150) is operated in a brake operation mode (BM), in which a brake unit (B) is actuated.

3. The method of claim 1 or 2 wherein the host vehicle (150) is operated in the coasting operation mode (CM) by- activating (106) a first free-rolling driving phase (FRi) by providing a transmission control signal (TC) to a transmission system (156) for operating the clutch (C) in a disengaged state (CD) and operating the host vehicle (150) in the coasting operation mode before a brake operation mode (BM) by remaining in the first free-rolling driving phase (FRi) until the current host vehicle speed value (VH) reaches a predetermined lower speed threshold value (VLT) that is lower than the target vehicle speed value (VT).

4. The method of any of the preceding claims, further comprising:- upon determining (108) that the current host vehicle speed value (VH) reaches a lower speed threshold value (VLT) that is lower than the target vehicle speed (VT) at which the target vehicle (152) is moving, activating (110) an acceleration driving phase (AD).

5. The method of claim 4, wherein the lower speed threshold value (VLT) is higher than 0.

6. The method of claim 4 or 5 in which the acceleration driving phase (AD) involves operating the clutch (C) in an engaged state (CE) and accelerating the host vehicle (150) until the host vehicle speed value (VH) reaches a predetermined upper speed threshold value (VHT) that is equal to or higher than the moveoff speed value (VM).

7. The method of claim 6, further comprising- upon determining (112) that the host vehicle speed value (VH) has reached the predetermined upper speed threshold value (VHT), activating (114) a subsequent free- rolling driving phase (FR2, FR3), in particular by providing the transmission control signal (TC) to the transmission system (156) for operating the clutch (C) in the disengaged state (CD) when the upper speed threshold value (VHT) is reached.

8. The method of any of the preceding claims, further comprising- ascertaining (116) a distance value (D) indicative of distance amount between the host vehicle (150) and the target vehicle (152); and- activating coasting operation mode (CM), in particular activating the first free- rolling driving phase (FR1), further upon determining (118) that the determined distance value (D) is lower than an activation-distance threshold (DAT).

9. The method of any of the preceding claims further comprising- ascertaining (116) a distance value (D) indicative of a distance amount between the host vehicle (150) and the target vehicle (152);- upon determining (120) that the distance value (D) is equal to a minimum distance threshold value (Di iin), activating (122) a braking operation mode (BM), in particular by providing a brake control signal (BC) to a braking system (158) for actuating a brake unit (B) for braking the host vehicle (150).

10. Adaptive cruise control device (500) for controlling a speed value (VH) of a host vehicle (150), in particular in a low-speed scenario, the adaptive cruise control device (500) comprising:- a moveoff speed ascertaining unit (502) configured to ascertain a moveoff speed value (VM) of the host vehicle (150) being indicative of a minimum vehicle speed at which the host vehicle (150) can be driven with clutch (C) in a fully engaged state (CE); and- a target vehicle speed ascertaining unit (504), in particular comprising, or connected to, a velocity sensor (505), configured to ascertain a target vehicle speed value (VT) of a target vehicle (152) driving ahead;- a control unit (506) configured, upon determining that the target vehicle speed (VT) of the target vehicle (152) driving ahead is lower than the moveoff speed (VM) of the host vehicle (150), to operate the host vehicle (150) in a coasting operation mode (CM), in particular to activate a first free-rolling driving phase (FRi) by providing a transmission control signal (TC) to a transmission system (156) for operating the clutch (C) in a disengaged state (CD) until the current host vehicle speed (VH) reaches a predetermined lower speed threshold value (VLT) that is lower than the target vehicle speed (VT).11 . The adaptive cruise control device (500) of claim 7, further comprising- a distance ascertaining unit (516), in particular comprising, or connected to, a distance sensor (517), configured to ascertain a distance value (D) indicative of distance amount between the host vehicle (150) and the target vehicle (152); and wherein the control unit (506) is further configured to operate the host vehicle (150) in the coasting operation mode (CM), in particular to activate the first free-rolling driving phase (FRi ) further upon determining (118) that the determined distance value (D) is lower than an activation-distance threshold (DAT).

12. The adaptive cruise control device (500) of claim 10 or 11 further comprising- a, or the distance ascertaining unit (516), in particular comprising, or connected to, a distance sensor (517), configured to ascertain a distance value (D) indicative of distance amount between the host vehicle (150) and the target vehicle (152); and wherein the control unit (506) is further configured, upon determining (120) that the distance value (D) is equal to a minimum distance threshold value (DMin), to activate (122) a braking phase (BP) by providing a brake control signal (BC) to a braking system (158) for operating a brake unit (B) for braking the host vehicle (150).

13. The adaptive cruise control device (500) of claims 10 to 12, wherein the control unit is further configured, upon determining (108) that the current host vehicle speed (VH) reaches a lower speed threshold value (VLT) that is lower than the target vehiclespeed (VT) at which the target vehicle (152) is moving, to activate (110) an acceleration driving phase (AD).

14. Vehicle (1000), in particular, commercial vehicle, comprising an adaptive cruise control device (500) of any of the preceding claims 10 to 13, a transmission system (156) for operating a clutch (C), and a braking system (158) for actuating a brake unit (B).

15. Computer program comprising instructions, which, when executed by a processor of an adaptive cruise control device in accordance to claims 10 to 13, cause the adaptive cruise control device to carry out the method of any of the claims 1 to 9.

Images