The present invention relates to a method for determination of a braking location for regenerative braking of a vehicle to a known stop location, said regenerative braking being effected with a braking force which comprises a regenerative force component F _e created by a regenerative brake system of the vehicle.

The present invention relates also to a device for determination of the braking location, a brake system for regenerative braking and a vehicle which is provided with either the device or the brake system.

PRIOR ART Vehicles with means for regenerative braking are adapted to recovering energy during regenerative braking with F _e . This entails the vehicle's kinetic energy being used to charge an energy store of the veh icle instead of going to waste in the form of heat in a brake device of the veh icle. The stored kinetic energy is intended to be reused by discharge from the energy store during subsequent acceleration of the vehicle. The energy consumption of vehicles which use regenerative braking is thus reduced as compared with those in which the kinetic energy arising during braking goes to waste. The means for regenerative braking converts for example the kinetic energy to electrical energy, hydrau lic energy, pneumatic energy etc. , and the energy store is adapted to storing corresponding converted energy.

Regenerative braking is for example used in vehicles such as cars, trains, trucks etc. wh ich have an electric motor adapted to using electrical energy during acceleration and to regeneratively reusing the vehicle's kinetic energy which arises during its braking . The electric motor thus has the function both of an electric motor and an electrical generator. Hybrid vehicles with two or more prime movers powered by different energy sources also usually have means for regenerative braking , e.g . one or more electric motors.

As the means for regenerative braking is only able to deliver braking effect up to a maximum, the vehicle is also provided with non-regenerative means for braking it, e.g . wheel brakes etc. A brake system of the vehicle which comprises the means for regenerative braking and the means for non-regenerative braking is adapted to providing a combined braking force.

A problem with vehicles according to the state of the art is that a driver of the vehicle without assistance has difficulty in braking it in an optimum way with regard to recovering kinetic energy and driving on time. If the braking distance for braking the vehicle to the stop location is shorter than the means for regenerative braking is able to provide, energy will go to waste in the means for non-regenerative braking . The wear on the means for non-regenerative braking will also increase as compared with if the braking is on ly effected by the means for regenerative braking . Conversely, if the braking distance for braking the vehicle to the stop location is longer than the means for regenerative braking needs for regenerative braking , its braking will take more time than necessary. It is also desirable to brake the vehicle with a braking force which is below a specific level , for the sake of comfort for the driver and any passengers. This means the vehicle's braking taking place in a non-optimum way with regard to time, with consequent adverse effects on traffic flow and/or time schedules.

GB2460528 A refers to a system for regenerative braking of an electric vehicle. The regenerative braking begins when the vehicle passes over an electrical coil. A problem with this system is that the braking takes place between predetermined braking and stop locations. US201 0/0042304 A1 refers to a method for controlling the power flow in a vehicle on the basis of the probability of braking when the vehicle is in motion .

SUMMARY OF THE I NVENTION

The object of the present invention is to propose a method for solving the problems of the state of the art. A first object of the invention is a method for helping the driver in braking the vehicle by regenerative braking . A second object of the invention is to help the driver so that the braking of a vehicle takes place in an optimum way with regard to recovering kinetic energy, to driving on time and to comfort. The invention relates also to a device according to claim 1 3 for applying the method , a brake system accord ing to claim 14 and a vehicle according to claim 1 5.

These objects are achieved with the method indicated in the introduction which is characterised by the steps of:

- receiving information about a momentary location , a momentary speed and said known stop location for the vehicle,

- determin ing a distance between the veh icle's momentary location and the stop location on the basis of the momentary location and the stop location,

- determining a braking distance for said regenerative braking of the vehicle to said stop location on the basis of the momentary speed and F _e ,

- determining whether the distance between the vehicle's momentary location and the stop location is within said braking distance, and

- generating a signal that said braking location has been reached if the braking distance between the vehicle's momentary location and the stop location is within said braking distance, otherwise the above method steps are repeated .

The determination of the braking distance between the vehicle's momentary location and the stop location is for example based on their respective coordinates and a specific length scale between the coordinates. The information about the vehicle's momentary location is conveyed by a position ing system. The vehicle's stop location arises from stop locations along the vehicle's route which are each predetermined or conveyed during the veh icle's journey. The vehicle's momentary speed is provided by a speedometer of the vehicle. The veh icle's braking distance depends on the momentary speed and F _e . Indicating to the driver when the braking distance between the vehicle's momentary location and the stop location is within braking d istance for regenerative braking helps the driver to drive the vehicle in an optimum way with regard to recovering kinetic energy and driving on time. He/she thus receives information about the braking location where the vehicle's regenerative braking has to be initiated for optimum regenerative braking .

According to an embod iment of the invention, the determination of the length of said braking d istance is mainly based on the magnitude of F _e and the veh icle's momentary speed . The braking distance is thereby optimised with regard to recovery of kinetic energy, with less significance attached to other parameters which affect the braking .

According to an embodiment of the invention, the method comprises setting said braking locations so that the braking distance for regenerative braking is minimised . The braking location is thus indicated so that as short a braking distance as possible is achieved , which is advantageous with regard to the vehicle's progress along its itinerary.

According to an embodiment of the invention, the determination of said braking location is done dynamically by setting the braking distance on the basis of the veh icle's momentary speed . This dynamic setting means that the braking location is determined continuously when the vehicle is in motion . The braking location is therefore not a fixed point along the vehicle's route.

According to an embodiment of the invention, the method comprises increasing the braking distance by a distance representing a reaction distance which the veh icle travels during a reaction time for effecting braking to the braking location.

Increasing the braking distance by the distance which the vehicle travels during a reaction time for effecting the braking provides assurance that the braking will not begin too late for it to be based on F _e .

According to an embodiment of the invention, the method comprises:

- receiving the signal that said braking location has been reached by a brake system which effects said regenerative braking with F _e .

The regenerative braking commences upon receipt of the signal that said braking location has been reached . This results in automatic braking of the veh icle as soon as the location for regenerative braking to the stop location is reached . According to an embodiment of the invention, the driver has the alternatives of rejecting or confirming the thus available automatic braking .

According to an embodiment of the invention, the braking is effected on the basis of a further force component F _r created by interaction between the surroundings and the vehicle whereby the determination of the braking distance is also based on F _r .

F _r depends on interaction between the surround ings and the vehicle, e.g . braking force from road gradient, rolling resistance, air resistance, power train losses etc. When braking uphill in the vehicle's direction of movement to the stop location the braking distance will be shorter than where there is no gradient. Conversely, when braking downhill in the vehicle's direction of movement to the stop location the braking distance will be longer than where there is no grad ient. Depend ing on local circumstances, the braking distance may thus be lengthened or shortened in consideration of F _r .

According to an embodiment of the invention, the method comprises determination of F _r with respect to time, F _r (t), so the determination of the braking distance is based on F _r (t).

According to an embodiment of the invention, the method comprises determination of F _e with respect to time, F _e (t), so the determination of the braking distance is based on F _e (t). F _e (t) depends on characteristics of the regenerative means. For example, the regenerative means results in F _e being different at different speeds of the vehicle, so the determination of F _e (t) depends on the vehicle's momentary speed .

According to an embodiment of the invention, the method comprises setting a number of stop locations which are predetermined along a route for the veh icle. Examples of stop locations are stopping places for the vehicle, e.g . bus stops, unloading places etc.

According to an embodiment of the invention, the stop locations comprise stopping places along a route for the veh icle, and the method comprises their activation when the veh icle is in motion . For example, the stop locations are activated by a passenger on board the vehicle or by a signal from a person at the stop location, or information is received about traffic lights, compulsory stops, etc.

According to an embodiment of the invention, the vehicle's momentary speed is determined by a GPS receiver. According to an embodiment of the invention, the vehicle's momentary speed is determined by information from location markers along its itinerary or dead reckoning from either a starting location or a location marker for its progress along the itinerary.

According to an embodiment of the invention, determination of the braking distance for said regenerative braking of the vehicle to said stop locations is based on a specific braking force. This makes it possible to brake the veh icle in such a way as to achieve desired comfort. According to an embod iment of the invention, the determination of the braking distance is based on a calcu lation process and/or tabulated values. According to an embod iment, the tabulated values are predetermined on the basis of a number of different momentary speeds of the veh icle and F _e , preferably also on the basis of F _r .

According to an embod iment of the invention, the determination of the braking distance is based on an iterative calculation process comprising the following steps:

- setting a counter n to zero and a time parameter t _n to zero upon receipt of the vehicle's momentary speed ,

a) setting a step length T for incrementing of t _n to a specific value,

b) determining a partial distance s(t _n ) over a period of time from t _n to the aggregate of t _n and T on the basis of the expression s(t _n ) = s(t _{n- 1} ) + v(t _{n- 1} ) ^* T + T ² /m (F _e (t _n ) + F _r (t _n )), in wh ich n and n- 1 are ind ices, t _n denotes the current period of time, t _n-1 any applicable preced ing period of time during which the information about s(t _n ) is saved , s(t _{n- 1} ) is a time-dependent distance component, v(t _{n- 1} ) a time-dependent speed component, m the vehicle's weight, F _e (t _n ) a time-dependent of F _e , and F _r (t _n ) a time- dependent of F _r ,

c) initiating a subsequent period of time by incrementing n by 1 and setting t _n to t + T, d) determining a partial speed v(t _n ) for the su bsequent period of time on the basis of the expression v(t _n ) = v(t _n-1 ) + T/m (F _e (t _n ) +

Fr(tn)) ,

e) determining whether v(t _n ) at step d) for the subsequent period of time exceeds a specific value,

f) repeating steps a) to f) for the subsequent period of time with v(t _n ) if v(t _n ) at step d) exceeds the specific value, otherwise summating s(t _n ) for the periods of time and setting the braking distance to the aggregate of s(t _n ).

The braking distance is determined by the iterative method steps and is then compared with the distance between the vehicle's momentary location and the stop location. The number of iterations depends on T and the magnitude of the vehicle's momentary speed .

According to an embodiment of the invention, the method comprises memorisation of stop locations along a route, for use during a su bsequent journey along the route. The memorisation is for example done by stop locations being saved during journeys along a route, for use during subsequent journeys along it.

According to an embodiment of the invention, the stop locations comprise information about traffic lights, compulsory stops, etc. or information from an adaptive cru ise control . According to an embod iment of the invention, the determination of the braking distance depends also on rolling resistance, kinetic energy, weight, expected road gradients, etc. BRI EF DESCRI PTION OF THE DRAWI NGS

The invention will now be explained in more detail by describing various embodiments of it with reference to the attached drawings.

Figure 1 depicts a power train for a vehicle according to an embodiment of the invention.

Figure 2 is a flowchart of a method for activation of regenerative braking of a vehicle accord ing to the invention.

Figures 3a and 3b are each a flowchart of a method for determining the braking distance for regenerative braking of a vehicle according to an embodiment of the invention .

DETAI LED DESCRI PTION OF PREFERRED EMBODI MENTS OF THE I NVENTION

Figure 1 depicts a power train for a veh icle 1 which interacts with the method accord ing to the invention. The vehicle 1 comprises a first prime mover 3 and a second prime mover 5 which are preferably powered by d ifferent energy sources. According to an embodiment of the invention, the first prime mover 3 is a combustion engine powered by, for example, petrol or d iesel fuel, and the second prime mover is an electric motor 5.

The vehicle 1 is provided with a first energy store 7, a second energy store 9 and a generator 1 1 . The first energy store 7 is adapted to su pplying energy to the first prime mover 3 and is for example a fuel tan k. The first prime mover 3 is connected to the generator 1 1 , which generates electricity and uses it to charge the second energy store 9, which is for example an electrical battery. The case here described is that of a series hybrid but the invention may also be implemented with a parallel hybrid or complex hybrid .

The vehicle 1 is provided with a regenerative means 20 for braking of the vehicle. In the embod iment depicted the regenerative means is the same as the second prime mover 5. The regenerative means is adapted to braking the vehicle with a regenerative force component F _e , whi le energy is converted to a form appropriate to charging the second energy store 9. The regenerative means 20 is preferably an electric motor wh ich serves as a prime mover when the vehicle 1 is accelerated and as a generator when the veh icle is braked regeneratively.

The vehicle 1 comprises also one or more non-regenerative means 22 for braking the veh icle, comprising a brake means which exerts a braking action on the vehicle while at the same time evolving heat. According to an embodiment, the non- regenerative means 22 for braking the vehicle 1 comprise wheel brakes of the vehicle. The vehicle is adapted to being braked both by the regenerative means 20 and by the non-regenerative means 22. The vehicle is thus adapted to being provided with sufficient braking force for the braking irrespective of whether or not the regenerative means 20 is able to provide it.

The vehicle 1 has also a brake system 30 which comprises a device 40 for determining a braking location for regenerative braking of the vehicle. The device comprises calculation means 42, e.g . a logic unit, a computer processor etc. , adapted to receiving information for the determination of the braking location and to doing the determination of the braking location. The brake system comprises for example various types of known brake systems which may be provided with antispin , ABS etc. The device 40 comprises indicating means 44 adapted to provid ing a signal that the braking location for regenerative braking of the vehicle 1 has been reached . According to an embodiment of the invention , the device 40 is adapted to providing a signal to the regenerative means 20 to start regenerative braking of the vehicle with F _e .

Figure 2 is a flowchart of a method for activation of regenerative braking of a vehicle 1 accord ing to the invention. The method is adapted to being applied regu larly, e.g . ten times per second .

The method beg ins with a step 210 in which information is received about a momentary speed and location of the veh icle, and a stop location to which it is desired to be braked . Th is is followed at a step 220 by determination of the distance between the momentary location and the stop location.

The momentary location of the vehicle 1 is preferably received from a position ing system, e.g . a GPS receiver. The vehicle's momentary speed is received from a speedometer fitted permanently to the vehicle.

According to an embodiment of the invention, the stop location for the veh icle 1 is determined by predetermined stopping points along the route, e.g . stopping places, unloading places, stop signs etc. Accord ing to another embod iment of the invention, the stop location for the vehicle is determined by being activated when the vehicle is in motion , e.g . by a passenger operating a stop signal or receipt of information about traffic lights, compulsory stops, etc. According to another embodiment of the invention, the information about stop locations for the vehicle is provided by a traffic flow system whereby stop locations are continuously determined along the itinerary.

As a step 240, the braking d istance for regenerative braking to the stop location is determined on the basis of the veh icle's momentary speed , F _e (t _n ), F _r (t _n ) and the vehicle's weight m. According to an embodiment of the invention, the braking distance is increased by a distance which represents how far the vehicle will travel during a characteristic reaction time before the driver commences the regenerative braking . The determination of the braking distance between the momentary location and the stop location, and the determination of the braking distance, are followed by a step 250 of investigating whether the vehicle is within the braking distance for its regenerative braking .

If the vehicle is not within the braking distance, method steps 210 to 240 described above are repeated . The method is repeated continuously during operation of the veh icle until it is within the braking distance for regenerative braking .

If on the contrary the vehicle is within the braking distance, a signal is generated at a step 260 for the driver to initiate its regenerative braking to the stop location. After generating the signal, the method starts again from the beginning .

According to an embodiment of the invention, the signal causes the brake system 30 to initiate the veh icle's regenerative braking . The vehicle's braking thus takes place automatically.

According to an embodiment of the invention, the braking distance is determined by iterative calcu lation according to either of Figures 3a and 3b. Accord ing to another embodiment of the invention, the determination is based on tabulated values which are determined on the basis of a number of different momentary speeds of the veh icle and F _e , preferably also on the basis of F _r . The tabulated values are for example stored in a database, making it possible to determine the braking d istance quickly. Using tabulated values reduces the processing load as compared with determination by iterative calcu lation .

Figures 3a and 3b each depict a flowchart of a method for determination of the braking distance for regenerative braking of a vehicle according to an embodiment of the invention.

As a step 310, a counter n is set to zero and a time parameter t _n is set to zero upon receipt of information about the momentary speed .

As a step 320, a step length T is set to a specific value. The step length is used to increment t _n during the determination of the braking distance.

Compared with using a large step length , a small step length results in accurate determination at the cost of many iteration steps. Conversely, a large step length involves a smaller number of iterations compared with using a small step length , but at the cost of less accuracy of determination of the braking distance. The step length has therefore to be set according to how quickly the calculation means 42 is able to perform iteration steps. As a step 325, a determination of the time dependent of F _e , viz. F _e (t _n ) , is performed . F _e (t _n ) depends mainly on the vehicle's momentary speed . As a step 330, a determination of a partial distance s(t _n ) is done for each period of time from t _n to t _n + T. The determination is based on the expression s(t _n ) = s(t _{n- 1} ) + v(t _n-1 ) ^* T + T ² /m (F _e (t _n ) + F _r (t„)).

As a step 340, the determination of s(t) is followed by initiating a subsequent period of time by incrementing n by 1 and setting t _n to t _n + T. As a step 350, before a subsequent period of time begins, a partial speed v(t _n ) for it is determined on the basis of the expression v(t _n ) = v(t _{n- 1} ) + T/m (F _e (t _n ) + F _r (t _n )).

As a step 360, there is investigation whether v(t _n ) for the subsequent period of time exceeds a specific value. If it does, the method is repeated from step 320 on the basis of v(t _n ) for that period .

If on the contrary v(t _n ) for the su bsequent period of time is equal to or below a specific value, s(t _n ) is summated for that period , and the braking distance is set to the aggregate of s(t _n ) as a step 370. Thereafter the iterative calculation method is repeated .

In Figure 3b there is also, as a step 322, determination of the time dependent of F _r , viz. F _r (t _n ). The determination of F _r (t _n ) is based on interaction between the surroundings and the vehicle. For example, F _r (t _n ) depends on conditions in the surround ings, e.g . road gradient, bend radius, rolling resistance, air resistance and the veh icle's momentary speed . The calculation method for the regenerative braking is based on the physical relationship

Resolving the above relationsh ip entails discretising the equations, e.g . by using the Euler method backwards, resu lting in the expression according to claim 12 steps b) and d) .

The invention is not restricted to the embodiments referred to but may be modified and varied within the scope of the claims set out below.