Vehicles frequently approach town signs or speed-restricted zones on rural roads at high speeds. The kinetic energy of these vehicles is then dissipated by braking to avoid exceeding the prescribed speed limit. This would not occur with an economical, fuel-saving driving style in which the vehicle is allowed to coast until reaching the speed-restricted zone.
However, it is difficult for the driver to choose the exact moment to start coasting so that the vehicle reaches the required speed precisely at the sign (or a user-defined speed, e.g., permissible speed + 10 km/h).
Modern GPS-based navigation systems for cars and trucks possess detailed information about the route, including the permissible maximum speed on the current section, the vehicle's actual speed via changes in GPS position, and the locations of speed-limiting signs.
This data can be used to determine the exact time (or rather, the location) to disengage the engine and let the vehicle coast until the beginning of a zone with a lower speed limit. This could be signaled via a simple acoustic alert or a voice prompt, such as: "Coast now, 50 km/h ahead."
Technical Implementation:
Two variants are possible for the technological implementation:
Advantages:
The following version was filed for patent in December 2008:
The invention relates to a method for informing drivers of road-based vehicles about speed-limiting traffic facilities (3, 4) located on the route. The vehicle's position (1), its current distance from the traffic facility (3, 4), and its current speed are recorded and compared in a computer with a geographical database.
According to the invention, data determining the coasting behavior of the vehicle (1) as well as data regarding the elevation profile of the route are also entered into the computer. The computer notifies the driver of the distance or point in time at which the vehicle (1) covers the remaining distance to the respective traffic facility (3, 4) solely by coasting, ensuring that the permissible maximum speed at that traffic facility (3, 4) is not exceeded upon arrival.
This enables the driver to adopt a self-determined, economical driving style based on conscious, forward-looking driving with regard to speed limits on the route.
The invention is based on a method for informing drivers of road-based vehicles, such as cars and trucks, about speed-limiting traffic facilities located on the travel route, according to the preamble of the main claim, as well as an information system according to the preamble of claim 10.
The term "traffic facility" refers not only to traffic signs -for example, those explicitly indicating a maximum speed or those prescribed by traffic regulations, such as town signs and traffic lights -but also includes conditions necessitated by the technical layout of the route that inevitably require a reduction in speed, such as curves, intersections, or junctions. Finally, the term "traffic facility" also encompasses conditions that arise only temporarily, for example, due to unpredictable events in road traffic, such as traffic jams, which require a timely reduction in speed.
To achieve economical operation of a commercial vehicle, particularly to reduce fuel consumption and wear, various methods and devices for driver assistance are known. In these methods, in addition to adjusting the driving components of the vehicle -such as vehicle speed, acceleration, braking, gear control, and shifting -the upcoming topography of the route is evaluated with computer assistance. For this purpose, topography data from geographic positions is assigned to elevation data for one or more routes and stored in a memory. The driver assistance device features an evaluation unit that analyzes the topography ahead. The geographic position can be determined during operation, for example, with a GPS receiver.
The disadvantage of this existing technology is that the determined data is only usable for the optimization of automated driver assistance systems. Consequently, the invention is only applicable to vehicles that already possess such a system. In this context, it should also be noted that assistance systems used in commercial vehicles are hardly transferable to passenger cars, as they significantly restrict the individual desire of each driver for a self-determined driving style, despite any interest in an economical driving mode.
Also known is an information device for drivers that predictively informs them of imminent traffic states or values -for example, changes in or exceedances of speed limits, or advisory speed zones -so that the driver can adjust their behavior to ensure the vehicle already possesses the correct speed upon reaching the indicated traffic state. This device consists of a map database, a localization unit, and an indicator that transmits the calculated signal to the driver.
The disadvantage of this invention is that the device offers no possibilities for an economical driving style. The driver is merely given a hint about an upcoming traffic state at a pre-defined, fixed distance or a fixed point in time. These distances or times are chosen so that the driver, after receiving the hint, can still avoid exceeding the speed limit by targeted braking or can bring the vehicle to a halt in time.
The method according to the invention with the characterizing features of claim 1, as well as the information system according to claim 10, have the advantage that the driver is enabled to adopt a self-determined, economical driving style based on conscious, anticipatory driving.
It informs the driver of upcoming traffic facilities or conditions on the route -which are generally not yet visually perceivable at the time of information and are associated with a speed limit -early enough so that the vehicle reaches the speed limit by immediately throttling or interrupting the fuel supply by the driver or by disengaging the clutch. This is achieved using the kinetic energy inherent in the vehicle at that time and considering the topography of the path (i.e., with the potential energy inherent in the vehicle due to its elevation relative to the traffic facility), ensuring that the prescribed maximum speed is not exceeded at that point or, if the situation requires, the vehicle can be stopped immediately.
The distance or point in time transmitted by the information system is therefore a function of the vehicle's coasting behavior on the path remaining to the speed limit, whereby the elevation profile of this path is also taken into account in a known manner. This has the advantage that this path can be covered under certain circumstances without -but in any case with a significantly reduced -fuel consumption and, if necessary, without braking, which reduces overall fuel consumption per trip and increases the lifespan of the braking system. Thus, the information system is not limited only to the evaluation of the route's topography but also includes further criteria relevant to an economical driving style, namely traffic facilities on the route that require a speed reduction.
In an advantageous embodiment of the invention, the computer of the information system informs the driver of the upcoming traffic facilities or conditions on the route as well as the maximum speed prescribed in this section of the route. This is important for the general orientation of the driver, but in any case essential if the driver of a vehicle equipped with cruise control has decided to forward the information to the cruise control system, so that it automatically reduces or interrupts the fuel supply to the engine and disengages the clutch.
According to another advantageous embodiment of the invention, the driver themselves enters the speed-limiting traffic facility as well as the preferred speed at that location into the computer of the information system. Typically, map databases only reflect geographic conditions and road- or traffic-related traffic facilities of the route. Therefore, it is advantageous if the driver can manually enter a traffic facility at an intersection or junction on their route where they must turn and therefore need to reduce the vehicle's speed. However, this manual entry is not required if the vehicle is equipped with a navigation system and the route is fully entered.
At this point, it becomes clear that the invention is very well suited for use in connection with navigation systems. A combination of a navigation system with the additional data memories according to the invention and the calculation software would represent an optimal implementation of the invention.
According to an additional advantageous embodiment of the invention, the data regarding the coasting behavior of the vehicle is determined via a physico-mathematical model for each vehicle type. For this purpose, the vehicle mass, drag coefficients for rolling friction and air resistance, as well as the elevation profile of the traveled route and the road gradient angle resulting therefrom, are required. With knowledge of this data, the distance necessary to dissipate the vehicle's kinetic energy in the coasting state can be determined for each vehicle type at a given initial speed, so that at the end of this calculated distance, it possesses the speed that, for example, must not be exceeded according to the traffic sign located at the end of this distance.
According to another embodiment in this regard, the data regarding the coasting behavior of the vehicle is determined via a purely mathematical model without knowledge of vehicle data through a calibration process. This means that the driver informs the computer that they are letting the vehicle coast at a specified initial speed on a route with an elevation profile known to the software. With a sufficient number of calibration runs, the vehicle data for the mathematical model can be calculated. This is particularly advantageous for vehicles that regularly travel the same route. In this way, the coasting behavior of a vehicle can be determined more cost-effectively than with the aforementioned software, which first has to be determined for each vehicle type. Furthermore, the coasting behavior depends significantly on the vehicle's load, so that the method just described is particularly suitable for transport vehicles.
According to an additional advantageous embodiment of the invention, an advisory speed is indicated to the driver when driving on downhill gradients located on the route up to the respective traffic facility. If the driver maintains this advisory speed on the downhill gradient, it is ensured that the vehicle, upon reaching the respective traffic facility, does not exceed the maximum speed prescribed there or necessitated by traffic engineering. The driver can now decide for themselves whether to maintain this advisory speed on the downhill gradient by selecting a suitable gear or by active braking.
On downhill gradients, curves are naturally also considered traffic facilities, which may only be indicated by a corresponding danger sign and not necessarily by an explicit speed limit of a regulatory sign. Finally, the display of an advisory speed on longer downhill sections, for example on motorways, can also take place without reference to a specific traffic facility. This gives the driver the opportunity to coast with a nearly constant speed for a certain distance. The signal can, of course, also be applied to a cruise control system.
According to another advantageous embodiment of the invention, in the case of several speed-relevant traffic facilities following closely behind one another on the route, the one that possesses the greatest difference compared to the current speed of the vehicle is used to calculate the distance or the point in time for initiating the coasting process. This ensures that the start of the coasting process is signaled early enough so that no prescribed maximum speed is exceeded even if there is too short a distance between two traffic signs. Such a case is conceivable, for example, if a 70 km/h sign is placed before a town sign marking the entrance to a built-up area, but the distance between the two is so small that the speed cannot be reduced from 70 km/h to 50 km/h solely by letting the vehicle coast.
An additional advantageous embodiment of the invention consists in the driver entering a tolerance limit for the speed communicated to them. This allows the driver to better adapt the coasting process to their driving habits, such as driving slightly below or above the permissible speed.
Finally, an additional advantageous embodiment of the invention consists in electrically switching traffic facilities -such as traffic lights, traffic management systems, and the like -transmitting their switching status to the computer via radio. As a result, depending on the current switching status or the switching phase of the traffic facility, the computer can determine the distance or the point in time at which the driver should initiate the coasting process of the vehicle in order not to exceed the permissible maximum speed upon reaching this traffic facility. In the case of traffic signal systems, by specifying an advisory speed, it could also be achieved that the vehicle reaches or passes the traffic signal system at the time of the "green" switching phase or, in the case of several traffic signal systems arranged one after the other, passes them during the so-called "green wave."
The information system for drivers of road-based vehicles consists of a cartographic memory, which includes the data of the route as well as the data of all those traffic facilities relevant for limiting the driving speed as mentioned at the beginning. To include current but temporary traffic-related facts that require a reduction in speed -such as construction sites, high traffic volume, or traffic jams -this memory can be updated with relevant data via radio. The information system further includes a navigation system for determining the position of the vehicle along the route as well as a computer that determines the current distance of the vehicle from the respective traffic facility.
According to the invention, the information system also features a memory for those data that represent the coasting behavior of the vehicle as a function of its current speed and the elevation profile of the route. This memory is connected to an evaluation unit of the computer, which determines a distance or a point in time from these data and transmits it to the driver, at which the vehicle covers the remaining distance to the respective traffic facility solely by coasting -i.e., without active fuel supply -and upon reaching the same, does not exceed the maximum speed prescribed at that traffic facility.
According to an advantageous embodiment of the invention, the information system features a device for detecting the coasting process. This serves, on the one hand, to inform the driver about the state of the coasting process itself. On the other hand, this signal can be used to determine the coasting behavior of the vehicle as a function of its properties, the characteristics of the route, and the elevation profile, as described in the method according to claim 5.
In a further advantageous embodiment in this regard, this device is activated by operating a pedal. For this purpose, in vehicles with a manually operated clutch, a switch can be arranged on the clutch pedal which transmits the signal wirelessly to the computer. In the case of automatic vehicles, the switch would have to be arranged on the brake and accelerator pedals. According to an additional advantageous embodiment of the invention, the information system is connected to a driver assistance system which, upon receiving a corresponding signal, reduces or interrupts the fuel supply to the engine, thereby automatically initiating the coasting process. Further advantages and advantageous embodiments of the invention can be found in the following description, the drawing, and the claims.
An exemplary embodiment of the invention is shown in the drawing and described in more detail below. The drawing schematically shows the route of a vehicle with a downhill gradient.
A motor vehicle 1 is located on a path x, which includes a downhill gradient 2. The motor vehicle 1 is equipped with an information system comprising a computer, a GPS antenna, a geographical map database, a waypoint database for speed-relevant traffic facilities and software that characterizes the coasting behavior of the motor vehicle 1. Shortly before the end of the downhill gradient 2, at position P2, there is a regulatory sign 3 indicating a maximum speed of 70 km/h. At a short distance after the regulatory sign 3, at position P3, there is another regulatory sign 4 that permits a maximum speed of 50 km/h.
For the physico-mathematical model, the following energy balance is defined for the path to be covered by the motor vehicle 1 from position P1, where it has the velocity v1, to position P3, where it arrives with the velocity v3:
The sum of the energy loss due to the resistance forces FR from rolling friction and air resistance is to be equated with the difference of the potential and kinetic energy of the vehicle 1 at point P1 and point P3. This is the energy required so that the vehicle 1 arrives without drive at point P3 with the kinetic energy E_kin_P3. This kinetic energy corresponds to a specific velocity v3 of the vehicle 1 at this point. For every point on the traveled route 2, this energy balance is used to calculate the location from which the vehicle 1 can coast without drive to a specific final velocity (here V3 at position P3).
For this purpose, the distance x, its elevation profile Delta h, and the waypoints P2 and P3 of the speed limits are read from a map database located in the vehicle 1, each compared with current data via GPS, and the resulting values are supplied to the computer for calculation.
If the calculated final velocity for point P2 corresponds to the speed of 70 km/h required by regulatory sign 3, the driver is prompted to let the vehicle 1 coast without drive until point P2. However, if a speed of 70 km/h when continuing to coast from point P2 to point P3 would result in the vehicle arriving at point P3 with a higher velocity than the 50 km/h prescribed by regulatory sign 4, the driver is prompted to coast immediately toward the target velocity of 50 km/h at point P3. This, of course, results in the speed of 70 km/h at point P2 being undershot.
To reduce the computational effort, an alternative would be not to perform a coasting analysis for every point on the route, but only for points that lie at a critical or relevant distance from a speed limit ahead. Thus, far in advance, for a defined speed range of the initial velocity v1 before coasting, the point P1 could be calculated at which the driver merely lets their motor vehicle 1 coast.
For example, if a speed of 100 km/h is permitted at point P1, the exact location of point P1 can be calculated far in advance for an initial speed range from v1=70 to v1=120 km/h.
To inform the following traffic about the vehicle's coasting state, the vehicle can be equipped with a coasting tail light in the rear area, similar to the additional center brake light. Such a tail light could, for example, feature an LED light strip whose individual LED elements are designed as a chasing light chain. All features presented in the description, the following claims, and the drawing can be essential to the invention both individually and in any combination with one another.
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