GB2515181A - Evaluating an optimal route of a vehicle - Google Patents

Abstract

The invention relates to a method for evaluating an optimal route of a vehicle from a start to a destination. The method comprises the steps of choosing at least two different routes, estimating braking requirements for the different routes and evaluating stress factors of a braking system of the car for the different routes based on the estimated braking requirements. It also includes choosing a route as the optimal route that results in the stress factors of the braking system lying within a predetermined tolerable range of the braking system in order to reduce the costs for a vehicle travelling from a start to a destination. The stress factor may include a pressure within the braking system or the temperature of a brake pad, disk or fluid. The method may further include calculating an environment degradation factor that characterises the brake dust produced, in particular the particle size ration of the dust.

Description

Evaluating an Optimal Route of a Vehicle The present invention relates to a method for evaluating an optimal route of a vehicle according to the preamble of claim 1.

Currently, there are several approaches existing to determine an optimal route for a vehicle. Mostly they take into account travel time and fuel consumption, but an optimization with regard to the wear out of brakes is known as well.

The DE 10 2010 048 322 Al describes a method to provide a driver of a car with several alternative routes from a starting point to a destination. Here, the different routes each feature a different wear out of tires and different fuel costs as well as a different cost of time.

It is an objective of the present invention to reduce the costs for a vehicle travelling from a start to a destination.

According to the invention, there is provided a method for evaluating an optimal route of a vehicle according to independent claim 1. Further advantages and embodiments are set out according to the dependent claims, the detailed description and the figures.

The inventive method for evaluating an optimal route of a vehicle from a start to a destination comprises the steps of choosing at least two different routes and estimating braking requirements for the different routes. In order to reduce the costs caused by the vehicle due to the travel from the starting point, or start, to the destination, the invention provides an evaluating of stress factors of a breaking system of the car for the different routes based on the estimated braking requirements and a choosing of a route as optimal route that results in the stress factors of the braking system lying within a predetermined tolerable range of the braking system. Here, in particular, the tolerable range can be limited by specific values that characterize the braking system at hand. Especially, it can be limited by a maximal admissible operating temperature of the braking system or of specific components of the braking system. The estimating of the braking requirements can be based on road information, such as global-positioning-system-(GPS)-based information or recorded information, in particular an information on the steepness or gradient of a road and/or road sign information. In particular, the road sign information may contain information from one or more of the following road signs: Stop, Slow, Reduce Speed, Curve Ahead, Cattle Crossing, Rail Crossing, School Zone, Pedestrian Walkway, U-Turn, or others. Also a life information feed, in particular from a radio, a traffic messenger information service, or a weather report, especially with information on temperature and humidity, may provide relevant information. Furthermore, the estimation of the braking requirements may be based on a history of recorded data for the different routes. Using more information than described into estimating the braking requirements will yield a bettor, i.e. more precise estimating of the braking requirements. When evaluating the stress factors of the braking system that are to be expected for the different routes, additional vehicle data like the mass of the vehicle or thermal coefficients of components of the braking system may be considered. The method may also be executed when the vehicle is already in motion. In this case, the starting point may be the actual position or a future position of the vehicle. This method gives the advantage that a driver of the vehicle knows which route to take in order to achieve low stress factors for the braking system. On the one hand, this lowers the maximal load of the braking system and results in a maximally efficient braking while travelling from the start to the destination. Such an efficient braking leads to an increase in the braking performance and lowers the costs for the braking system as it allows to refrain from the use of high cost construction materials for the braking system that might be required otherwise. On the other hand, by considering the quality of a brake dust that is expected to be set free on the travel from the start to the destination this method makes it possible to control the influence or the environment, i.e. the environmental degradation. Again, it lowers the costs for the braking system as it allows to retrain from the use of high cost construction materials for the braking system that might be required otherwise in order to fulfil e.g. legal requirements regarding the quality of the brake dust.

Consequently, it is possible to refrain from using special materials in order to achieve a required braking quality, i.e. high braking efficiency and low environmental degradation.

For example, one can refrain from using expensive ceramic brake pads that usually are preferred over semi-metallic material because of their better performance in a high-heat operation range. Also, costly alternate braking methods like electro-mechanical braking or regenerative braking can be spared.

In this setting, the stress factors can be weighted and pooled into one or more pooled factors. In particular, temperature-related stress factors, i.e. stress factors that are related to a temperature in the braking system, can be pooled into an efficiency factor and pressure related stress factors, i.e. stress factors that are related to a pressure in the braking system, can be pooled into an environment degradation factor. In particular, the efficiency factor of the brake or, in particular, the brake pads, is proportional to the inverse of the temperature of the brake pads. The brake pad temperature can for instance be estimated using the heat energy gained during the braking. The heat energy of the brake pad or the brake system gained during the braking can in particular be calculated by subtracting the heat energy lost by cooling from the kinetic energy of the vehicle absorbed while braking.

So, the stress factors can either be stress factors that are measured directly or stress factors that are calculated based on stress factors that are measured directly. In the latter case, additional information like vehicle mass and speed or environmental information like humidity might be used to calculate the stress factors.

The method can be adapted so that the pressure within the braking system and/or a temperature of a brake pad and/or a temperature of a brake disc and/or a temperature of a brake fluid is selected as a stress factor. As pressure and/or temperature characterize the efficiency of a braking system especially well, these parameters are ideally suited to be monitored in order to optimize the brake efficiency and consequently reduce costs. A critical limit of the tolerable range for the temperature-related stress factors of the system is determined by the vaporization temperature of the braking fluid. This vaporization temperature may depend on the moisture of an ambience which can be taken into account when evaluating the stress factors. Operating the braking system within an operational range with a high brake efficiency allows to spare expensive materials that are made to resist high stress particularly well.

The method can further be refined so that based on an evaluated pressure within the braking system and an evaluated speed of the vehicle, an environment degradation factor that characterizes the brake dust of the braking system is calculated for the different routes and taken as an additional stress factor. Here, the characterization of the brake dust refers to a characterization of its quality, not its quantity. This gives the advantage, that the impact of the brake dust on the environment can be monitored. In particular, it can be monitored how harmful the brake dust is for biological organisms like humans and animals.

Here, the environment degradation factor can represent a ratio or a distribution of different diameters of particles of the brake dusts. In particular, it may represent the ratio of respirable particles with a diameter smaller than 2.5 pm within the total of all particles of the brake dust. In particular, the environment degradation factor may be proportional to the inverse of a characteristic diameter of the brake dust given a specific brake application. The characteristic diameter of the brake dust can be proportional to the product of a velocity of the vehicle during brake application, i.e. while braking, and a pressure of the brake system, in particular a pressure of the brake pads while braking.

The pressure of the brake pads while braking may be a function of the velocity of the vehicle here. As the diameter of the brake dust particles is very relevant to determine whether a specific particle is harmful to biological systems or not, this gives the advantage that for every route the actual impact can be monitored very closely with the use of a single parameter as characterizing mean. The particles with the diameter of less than 2.5 pm are respirable, thus enter and harm biological systems. The present method makes it possible to minimize the ratio of these specific brake dust particles by choosing the route with the lowest environment degradation factor as optimal route. As a consequence, official requirements or regulations concerning the brake dust can be met with standard braking systems, sparing the use of more expensive components.

By considering the following detailed description of an exemplary embodiment in conjunction with the accompanying drawing, the teachings of the present invention can be readily understood, and at least some additional specific details will appear. Herein, the Fig. shows the results of estimating the braking requirements and evaluating some stress factors for one exemplary route according to an exemplary embodiment of the inventive method.

The Fig. shows four graphs that are each plotted over a distance d that corresponds to the distance from a start A to a destination B according to the exemplary route under consideration here. In an application of the invention, more than one route will be evaluated. The top graph shows an estimated braking requirement R, the second graph an evaluated stress factor, a brake temperature T, and the lower two graphs a pooled stress factor each, a brake efficiency E in the third graph and an environment degradation D in the fourth graph.

The top graph shows the exemplary braking requirement H against the distance d. The maximal braking requirement His 100%. A curve 1 represents the braking requirement H along the distance d from start A to destination B here. This brake requirement H forecast or estimate can be based on e.g. road information and/or OPS-based signals as well as on a life information feed for a history of recorded data for that specific driving route. It can also be based on a combination of information of different sources. In the current example, the estimated braking requirement is 0 % from the start A of the travel to the first way point d0. Then the braking requirement R rises until the maximal braking requirement H of 100 % at way point d1. It remains at 100 % until the way point d2. For example, this high braking requirement R may be due to a gradient of the road between way points d1 and d2 along the route under consideration. After way point d2, the braking requirement H descents back to zero at way point d3. Then, the braking requirement H remains at 0 % until, at way point d4, there is a sudden increase in the braking requirement H and it jumps to 100 % until way point d5 that is very close to way point d4.

Such a sharp increase in the braking requirement H may be due to e.g. a stop sign or alike. Afterwards, there are several parts of the route where the braking requirement R varies between 0% and 100%. It is important that an estimate for a braking requirement H is defined by the curve 1 along the travel from start A to destination B. This allows the subsequent evaluating of stress factors of a braking system of a car for the complete travel. In an alternative, equivalent presentation, the braking requirement R may be plotted against a time instead of against distanced. In this case, an estimate of the vehicle speed is needed in order to calculate the specific points in time that correspond to each way point d0 to d3.

In the second graph from top, a curve 2 illustrates the brake temperature T against the distance d of the travel from the start A to the destination B. Also, the brake fluid vaporization temperature Tvap is highlighted in the graph. The brake temperature T can be forecast by taking into account not only the braking requirement H as it is shown in the top graph, but also the vehicle's mass and speed, as well as thermal coefficients of the braking system, e.g.. Note that the different graphs are aligned, so the way points d0 to d6 in the graphs correspond to one another. In this example, initially, for instance because the vehicle has been parking for a while, the brake temperature T is equal to the temperature of the environment T0. Even when the braking requirement R is different from zero at way point d0, the brake temperature T remains unchanged at first. It is after a certain while though, that the brake temperature I begins to rise. When the braking requirement H reaches 100% at way point d1, the brake temperature T is already exceeding the temperature of the environment T. Whenever the braking requirement R is different from 0 % the brake temperature I is rising. This results in a rise of the brake temperature I between way point d0 until the braking requirement R drops back to zero for the first time at way point d3. In the present example, the brake temperature T almost reaches the brake fluid vaporization temperature Tvap at way point d3. Then, between the way points d3 and d4, where the braking requirement is 0 %, the stress factor under consideration here, i.e. the brake temperature 1, slightly decreases again. The sharp increase of the braking requirement H at way point d4, though, leads to an increase of the brake temperature I again. Here, at way point d5, the brake temperature I exceeds the brake fluid vaporization temperature Tvap for the first time. As the way points d4 and d5 are very close to each other, i.e. the braking requirements R are 100 % only for a short time here, the brake temperature I drops back beneath the brake fluid vaporization temperature Tvap shortly after way point d5. The brake temperature I remains close to the brake fluid vaporization temperature yap until way point d5 though. After way point d6. as the braking requirement H rises again, the brake temperature T surpasses the brake fluid vaporization temperature vap As there are no large sections of the travel from the start A to the destination B with a braking requirement H equal zero after way point d6, the brake temperature T remains above the brake fluid vaporization temperature yap until the end of the travel, that is until destination B. The third graph from the top shows a pooled stress factor, the brake efficiency E, against the distance d. In this example, the brake efficiency E is calculated taking into account the brake temperature T and other parameters such as, for instance, specific characteristics like a heat capacity of brake pad and brake discs. In this graph, the curve 3 that describes the braking efficiency E over the distance d remains very close to 100 % until a first dip at way point a3, where it shortly drops to about 90%. Slightly later, at way point d5, it drops again, this time to about 80%. Similarly at way point d5. Comparing the curve 3 that represents the brake efficiency E with curve 2 that represents the brake temperature T, it becomes obvious that the brake efficiency E drops whenever the brake temperature T reaches the brake fluid vaporization temperature Tvap in this example. Therefore, it is not surprising that at way point d8, where the brake temperature T exceeds the brake fluid vaporization temperature Tvap the brake efficiency E drops again. As the curve 2 remains above the brake fluid vaporization temperature between the way point d6 and destination B, the brake efficiency E drops and does not reach 100 % before the destination B is reached. Here, the drop goes down to as much as 50 % of the original brake efficiency at way point d7. So, in this example, the second half of the route under consideration after way point d7 gives an unadvantageous stress factor, i.e. a bad brake efficiency E. The fourth graph from the top shows another pooled stress factor, the environment degradation D, that ranges from 0 to 1. In this example, the environment degradation D describes the ratio of particles with a particle diameter smaller than 2.5 pm in the brake dust. In this example, it is calculated in by taking into account the pressure in the brake system and a velocity of the vehicle and further parameters of the braking system, for instance parameters depending on the materials used in the braking system. Obviously, the environment degradation D is zero when the braking requirement H is zero. This means the environment degradation D begins to be different from zero at way point d0.

The environment degradation D is calculated in a non-trivial way, so when the braking requirement H is different from zero, the environment degradation D is different from zero as well, but no further general characterization is feasible at this point.

In order to choose a route as optimal route, one needs now to estimate the braking requirements and evaluate the stress factors for the alternative routes as well. To be able to compare different routes, one needs to calculate an index that allows a comparison of the alternative routes. For example, an integration of each stress factor along the travel distance from start A to destination B can deliver such an index for every stress factor under consideration for the specific route. So, for example one could take the brake efficiency E, integrate it over the distance from start A to destination B as well as the environment degradation D and integrate this stress factor from start A to destination B. If this is done for different routes, the resulting two numbers, one for brake efficiency E and one for environment degradation D will then characterize all the different routes. A route will then be chosen as optimal route if its stress factors, in the present example one for brake efficiency E and one for environment degradation D, are in a permissible range.

This process can, for instance, also be automatized so that a driver gets a recommendation for a route that has been chosen according to a predefined weighting of the different stress factors under consideration. In both cases, the automated case and the case where a driver chooses amongst alternative routes, it may be helpful to weight individual stress factors and pool them into a single summed stress factor.

List of reference signs 1 curve 2 curve 3 curve 4 curve A start B destination R braking requirement T brake temperature E brake efficiency D environment degradation d distance d1,.. d8 way point yap brake fluid vaporization temperature temperature of the environment

Claims (4)

1. Claims A method for evaluating an optimal route of a vehicle from a start to a destination, the method comprising the steps of -choosing at least two different routes; -estimating braking requirements for the different routes; characterized by an -evaluating stress factors of a braking system of the car for the different routes based on the estimated braking requirements; and -choosing a route as optimal route that results in the stress factors of the braking system lying within a predetermined tolerable range of the braking system.
2. 2. A method according to claim 1, wherein a pressure within the braking system and/or a temperature of a brake pad and/or of a brake disk and/or of a brake fluid is selected as a stress factor.
3. 3. A method according to one of the prior claims, wherein based on an evaluated pressure within the braking system and an evaluated speed of the vehicle, an environment degradation factor that characterizes a brake dust of the braking system is calculated and taken as an additional stress factor.
4. 4. A method according to claim 3, wherein the environment degradation factor represents a ratio or a distribution of different diameters of particles of the brake dust, in particular the ratio of respirable particles with adiameter smaller than 2.5 km.