Arrangement and method for a cruise control brake in a vehicle

Abstract

A cruise control arrangement is provided with a cruise control speed function and where the cruise control arrangement is provided with a set cruise speed value and a set brake cruise speed value, and where the cruise control brake function is active when the vehicle travels downhill, where the cruise control arrangement is adapted to activate at least one auxiliary brake when the vehicle speed reaches the set brake cruise speed, to apply a service brake of the vehicle in order to reduce the speed of the vehicle to a predefined first speed if the vehicle speed exceeds the set brake cruise speed when the least one auxiliary brake is delivering full brake power, where the predefined first speed is lower than the set brake cruise speed. Undesired acceleration during downhill travel can be avoided when the brake power of the auxiliary brake is not sufficient. Further, a required downshift can be delayed, which will improve the fuel consumption of the vehicle.

Claims

1. A cruise control arrangement for a vehicle, where the cruise control arrangement is provided with a cruise control brake function and where the cruise control arrangement is provided with a set cruise speed value and a set brake cruise speed value, and where the cruise control brake function is active when the vehicle travels downhill, wherein the cruise control arrangement is configured to first, activate at least true auxiliary brake when the vehicle speed reaches the set brake cruise speed, second, apply a service brake of the vehicle in order to reduce the speed of the vehicle to a predefined first speed if the vehicle speed exceeds the set brake cruise speed when the at least one, auxiliary brake is delivering full brake power, where the predefined first speed is lower than the set brake cruise speed, third, deactivate the service brake when the speed of the vehicle is equal to the predefined first speed, fourth, allow the vehicle speed to increase and to exceed the set brake cruise speed again, and fifth apply the service brake again in order to reduce the vehicle speed to the predefined first speed, wherein the cruise control arrangement is configured to provide the deactivation of the service brake while controlling the auxiliary brake to continue delivering full brake power.

2. The arrangement according to claim 1, wherein the cruise control arrangement is further adapted to repeat deactivating the service brake when the speed of the vehicle is equal to the predefined first speed while controlling the auxiliary brake to continue delivering full brake power, allowing the vehicle speed to increase and to exceed the set brake cruise speed again, and then applying the service brake again in order to reduce the vehicle speed to the predefined first speed, to thereby repeatedly apply the service brake of the vehicle to reduce the speed of the vehicle to the predefined first speed if the vehicle speed exceeds the set brake cruise speed value when the at least one auxiliary brake is delivering full brake power.

3. The arrangement according to claim 2, wherein the cruise control arrangement is adapted to repeat the application of the service brake until a predetermined condition is reached.

4. The arrangement according to claim 1, wherein the predefined first speed is equal to the set cruise speed.

5. The arrangement according to claim 1, wherein the predefined first speed is higher than the set cruise speed.

6. The arrangement according to claim 1, wherein the cruise control arrangement is further adapted to apply the service brake of the vehicle before the vehicle reaches the set brake cruise speed if the vehicle is travelling down a slope having an inclination exceeding a predefined value.

7. The arrangement according to claim 3, wherein the cruise control arrangement is adapted to perform a down shift of a gear-box when the predetermined condition is reached.

8. The arrangement according to claim 7, wherein the cruise control arrangement is adapted to control the vehicle speed to a speed that allows the downshift of the gear-box.

9. The arrangement according to claim 8, wherein the cruise control arrangement is adapted to use the speed that allows the downshift of the gear-box as a new, intermediate brake cruise speed.

10. The arrangement according to claim 3, wherein the predetermined condition is a predetermined number of repetitions.

11. The arrangement according to claim 3, wherein the predetermined condition is the time interval between two applications of the service brake.

12. The arrangement according to, claim 3, wherein the predetermined condition is dependent on the amount that the service brakes has been used.

13. The arrangement according to claim 1, wherein the at least one auxiliary brake is a compression brake, a hydraulic or electric retarder brake or an electric machine.

14. Vehicle comprising an arrangement according to claim 1.

15. A method for controlling braking of a vehicle having a brake cruise control function when the vehicle is travelling downhill and when the brake cruise control function is active, where the cruise control brake function is provided with a set cruise speed and a set brake cruise speed, the method comprising: first, activating at least one auxiliary brake when the vehicle speed reaches the set brake cruise speed, second, determining if the at least one auxiliary brake is delivering full brake power, third, determining if the vehicle speed exceeds the set brake cruise speed when the at least one auxiliary brake is delivering hill brake power, fourth, applying a service brake of the vehicle to reduce the speed of the vehicle to a predefined first speed if the vehicle speed exceeds the set brake cruise speed when the at least one auxiliary brake is delivering full brake power, where the predefined first speed is lower than the set brake cruise speed, fifth, deactivating the service brake when the speed of the vehicle is equal to the predefined first speed, sixth, allowing the vehicle speed to increase and to exceed the set brake cruise speed again, and seventh, applying the service brake again in order to reduce the vehicle speed to the predefined first speed, wherein the deactivation of the service brake is performed while controlling the auxiliary brake to continue delivering full brake power.

16. The method according to claim 15, where the steps of deactivating the service brake when the speed of the vehicle is equal to the predefined first speed while controlling the auxiliary brake to continue delivering full brake power allowing the vehicle speed to increase and to exceed the set brake cruise speed again, and then applying the service brake again in order to reduce the vehicle speed to the predefined first speed are repeated until a predetermined condition is reached.

17. The method according to claim 16, where the predetermined condition is a predetermined number of repetitions.

18. The method according to claim 16, where the predetermined condition is the time interval between two applications of the service brake.

19. The method according to claim 16, where the predetermined condition is dependent on the amount that the service brake has been used.

20. The method according to claim 16, where a down shift of a gear-box is performed when the predetermined condition is reached.

21. The method according to claim 20, comprising controlling the vehicle speed to a speed that allows the downshift of the gear-box.

22. The method according to claim 21, comprising using the speed that allows the downshift of the gear-box as a new, intermediate brake cruise speed.

23. The method according to claim 15, where the predefined first speed is equal to the set cruise speed.

24. The method according to claim 15, where the predefined first speed is higher than the set cruise speed.

25. A computer comprising a computer program for performing all the steps of claim 15 when the program is run on the computer.

26. A non-transitory computer pr gram product comprising a computer program stored on a non-transitory computer readable medium for performing all the steps of claim 15 when program product is run on a computer.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) The invention will be described in greater detail in the following, with reference to the attached drawings, in which

(2) FIG. 1 shows a schematic view of a cruise control arrangement of a vehicle,

(3) FIG. 2 shows a typical speed graph of a vehicle travelling down a constant downhill slope, and

(4) FIG. 3 shows a schematic flow chart of an inventive method for supporting a cruise control system of a vehicle.

DETAILED DESCRIPTION

(5) The embodiments of the invention with further developments described in the following are to be regarded only as examples and are in no way to limit the scope of the protection provided by the patent claims. The arrangement is suitable for all kinds of vehicles, but is especially suitable for heavy vehicles such as trucks and busses, having brake cruise control functionality using auxiliary brakes.

(6) FIG. 1 shows a schematic cruise control arrangement of a vehicle. The arrangement 1 comprises a cruise control electronic control unit 4 which may be either a standalone control unit comprising the cruise control system or may be integrated e.g. as a software module in another electronic control unit in the vehicle. The cruise control arrangement further comprises a user interface 2. The user interface comprises buttons used by a driver to input cruise control parameters and to engage and disengage the cruise control system. The user interface may further comprise display means showing part of or all selected cruise control parameters.

(7) In this example, the vehicle 10 is powered by an engine 7 with a gearbox 6, preferably an automated manual transmission or an automatic transmission. The engine is provided with an auxiliary brake 9 which may be a compression release brake or exhaust brake or the like. This auxiliary brake is arranged upstream of the gear box and the delivered brake power will thus be dependent on the engine speed. The transmission is provided with an auxiliary brake in the form of a retarder 8, which may be a hydraulic or electric retarder. This retarder is arranged downstream of the gearbox such that the delivered brake power is dependent on the rotational speed of the propeller shaft. In the description, when an auxiliary brake is referred to, it is to be understood that one or more of the auxiliary brakes can be used. The vehicle is further provided with a service brake 5 which is controlled by a brake control unit 3.

(8) In the arrangement, a cruise speed can be set or selected, which is the reference speed that the vehicle will maintain when the cruise control is engaged. The cruise control system is provided with a preset speed interval around the set cruise speed, e.g. 1 km/h, in which the cruise speed will be held during cruise control regulation. When the vehicle travels on a substantially even road and the cruise speed is set to 70 km/h, the speed may vary between 69 km/h to 71 km/h.

(9) The driver can also set a brake cruise speed value, which is the speed value that the brake cruise control will maintain when the vehicle is travelling downhill. The brake speed value is normally set as a positive speed offset value that is added to the set cruise speed. If the brake speed offset is set to 4 km/h, the resulting brake cruise speed would in this case be 74 km/h. This speed will be maintained by the auxiliary brakes of the vehicle when the vehicle travels down a descent and where the vehicle will coast faster than the cruise speed. By allowing an excessive speed when travelling downhill, the travel efficiency can be improved. At the same time, the excessive speed should not be allowed to be too high, such that the vehicle will not be able to stop or such that it will exceed speed limits.

(10) The arrangement further comprises a brake control unit 3, which is used to control the service brake and additional service brake functions, such as an automated brake system (ABS) or an electronic stability program (ESP).

(11) The cruise control system is adapted to activate the auxiliary brake when the speed of the vehicle exceeds the set brake cruise speed. Due to the rolling resistance and the air drag of the vehicle, this situation will only occur when the vehicle is travelling downhill. When travelling along a horizontal road, the cruise control decreases the throttle before the brake cruise speed is reached. Preferably, all auxiliary brakes of the vehicle are engaged at the same time in order to increase the available brake power, but it is also possible to use only one auxiliary brake when the required brake power is relatively low.

(12) In the inventive cruise control arrangement, the arrangement is adapted to activate the auxiliary brake when the speed of the vehicle exceeds the set brake cruise speed. Due to the response time of the auxiliary brake, a small delay will occur before the auxiliary brake delivers full brake power which will lead to a small overshoot in vehicle speed. An auxiliary brake may have a response, time of several seconds depending on the type of auxiliary brake. A hydraulic retarder normally have a relatively short response time, in the range of a few seconds, and an exhaust brake normally have a response time of up to 5 seconds or more, depending on the required brake power. The response time is measured from the activation of the auxiliary brake until the auxiliary brake is fully applied and delivers the requested brake power.

(13) When the auxiliary brake delivers full brake power, it is determined if the vehicle speed exceeds the set brake cruise speed. If the vehicle speed exceeds the set brake cruise speed when the auxiliary brake delivers full brake power, it is determined that the brake power of the auxiliary brake is not sufficient to hold the vehicle speed at the set brake cruise speed. In this case, the service brake is applied in order to reduce the vehicle speed. The service brake is preferably applied relatively hard for a relatively short time interval, preferably less than 30 seconds, such that the vehicle speed is reduced without heating up the service brake too much. The vehicle speed is reduced to a predefined first speed, which is a speed that is lower than the set brake cruise speed. The predefined first speed may be a speed value that is equal to the set cruise speed or may be a speed value somewhere between the set cruise speed and the set brake cruise speed.

(14) When the vehicle speed is equal to the predefined first speed, the service brake is released. The auxiliary brake is still delivering full brake power. The vehicle speed will now increase until it reaches the set brake cruise speed. If the brake power delivered by the auxiliary brake is sufficient to hold the vehicle speed at the set brake cruise speed, the vehicle will continue to travel downhill with the set brake cruise speed. This may be the case if the inclination of the downhill slope has changed during the brake operation.

(15) However, if the inclination of the slope is the same, the brake power delivered by the auxiliary brake, which is delivering full brake power, will not be sufficient to hold the vehicle speed at the set brake cruise speed. The vehicle speed will increase and will again exceed the set brake cruise speed. The service brake is then applied again in order to reduce the vehicle speed to the predefined first speed. When the predefined first speed is reached, the service brake is released and the speed of the vehicle will increase again. If the mad conditions have changed, the brake power delivered by the auxiliary brake may be enough to hold the vehicle speed at the set brake cruise speed. If the vehicle speed exceeds the set brake cruise speed, the service brake is applied and the procedure is repeated.

(16) The brake procedure is preferably repeated until a predetermined condition is reached. One predetermined condition may be the number of repetitions. It is possible to limit the number of repetitions to e.g. 5 times, in order to limit wear of the service brake. The number of repetitions can of course be selected freely, and can e.g. correspond to a number required for a relatively short downhill. When travelling down such a downhill, the preselected number of repetitions will allow the vehicle to travel the downhill without having to perform a downshift.

(17) Another predetermined condition may be the remaining distance of the downhill. This requires that the vehicle control system is connected to a GPS navigation system having map access such that the topology of the road is known. In this case, it can be decided to let the vehicle travel downhill for e.g. 1 km before a downshift is performed.

(18) Another predetermined condition may be the amount that the service brake has been used. The amount can be calculated in different ways, such as the total delivered brake power, the time that the service brake has been applied or be based on the actual temperature of the brake discs of the service brake.

(19) Another predetermined condition may be the acceleration between the applications of the service brake, or the time interval between the applications of the service brake. The purpose of the invention is to be able to travel down a hill in a high speed interval without overusing the service brake. The service brake should thus have time to cool down between the applications of the service brake.

(20) When a predetermined condition is reached, a downshift of the gearbox is preferably performed. By performing a downshift, the efficiency of the auxiliary brake arranged upstream of the gearbox will increase due to the higher rotational speed of the engine that will be the result of the downshift. By delaying a downshift, it is possible to improve fuel consumption and to avoid an unnecessary gear change.

(21) If the predetermined condition is reached and it is decided to perform a downshift, the system controls the vehicle speed to a speed that allows a gear change. This speed is decided by the cruise control system and will be used as a new, intermediate brake cruise speed. It may be the predefined first speed, the set cruise speed or a lower speed. When the downshift has been performed, the auxiliary brake may be able to hold the vehicle speed at the intermediate brake cruise speed.

(22) It is also possible that the auxiliary brake will not be able to, hold this new intermediate brake cruise speed. In this case, the service brake is applied when the vehicle speed exceeds the intermediate brake cruise speed and the speed is reduced to a lower, predetermined second speed value. The service brake is released when this speed is reached and the speed of the vehicle increases again to the intermediate brake cruise speed, when the service brake is applied again. Since the speed interval is now reduced the time interval between applications of the service brake will be increased such that the service brake will not overheat.

(23) If the inclination of the slope that the vehicle travels down exceeds a predefined value, the cruise control arrangement may be adapted to apply the service brake of the vehicle before the vehicle reaches the set brake cruise speed. The inclination of the slope can either be measured when travelling down the slope or can be obtained from a map database. By applying the service brake before the vehicle reaches the set brake cruise speed, a smoother behaviour of the vehicle can be obtained in steep slopes and the wear of the service brake may decrease some. This can be seen as a temporary lowering of the set brake cruise speed, which is only used during this downhill travel.

(24) FIG. 2 shows an example of a vehicle speed profile of a vehicle travelling down a slope having a constant inclination. In the graph, s is speed, t is time, vbc is the set brake cruise speed, vcc is the set cruise speed and VfS is the predefined first speed.

(25) At to, the vehicle is travelling along a horizontal road at a constant set cruise speed. At ti, the downhill start. The vehicle will now accelerate such that the vehicle speed increases. At t2, the vehicle speed reaches the set brake cruise speed and the auxiliary brake is activated. Due to the response time of the auxiliary brake, the auxiliary brake is delivering full brake power at t3. The vehicle control system detects that the vehicle speed continues to increase, and applies the service brakes of the vehicle at t4. This reduces the vehicle speed until the vehicle speed is equal to the predefined first speed at t5, where the service brake is deactivated.

(26) The vehicle speed increases again, until the vehicle speed exceeds the set brake cruise speed at t6, where the service brake is applied again. At t7, the vehicle speed equals the predefined first speed and the service brake is deactivated. At t8, the vehicle speed exceeds the set brake cruise speed again and the service brake is activated. At the same time, it is registered that a predetermined condition is reached, and that a downshift of the gearbox is required in order to be able to increase the interval between the applications of the service brake, i.e. to lower the use of the service brake to an acceptable value. In this case, the service brake will decrease the vehicle speed to a new, intermediate brake cruise speed vbC2 which will be used as a temporary new brake cruise speed value. This value is determined by the cruise control system based on different vehicle parameters and on the amount of use of the service brake. This lower speed is required in order to allow a gear change to a gear that will not overspeed the engine. At tg, the lower, intermediate brake cruise speed is reached and the downshift is performed. The vehicle speed increases and the service brake is applied in order to reduce the vehicle speed to a new temporary predefined second speed value VfS2At this predefined second speed, the service brake is released. Since the speed interval of the vehicle is now lower, the acceleration of the vehicle will now be lower, which means that the time until the service brake must be applied is increased. In this way, the time interval between the applications of the service brake is increased and the wear of the service brake will be decreased.

(27) FIG. 3 shows a schematic flow chart of a method for supporting a cruise control function in a vehicle according to the invention. The method is adapted to activate a service brake at the sane time as an auxiliary brake when the vehicle reaches a brake cruise speed, such that the service brake can compensate for the response time of the auxiliary brake.

(28) In step 100, the cruise control function compares the actual vehicle speed with the set brake cruise speed. If the actual vehicle speed reaches the set brake cruise speed, an activation signal is sent to the control unit of the auxiliary brake and the control unit of the service brake in step 110. The auxiliary brake is activated, in step 120 and it is determined if the acceleration of the vehicle continuous. The auxiliary brake is activated by a preset amount which corresponds to a requested brake power, which in this case means that the auxiliary brake is fully applied. If the acceleration continuous, the service brake is activated in step 130. The service brake is activated such that the brake power of the service brake allows the speed of the vehicle to be reduced to a predetermined first speed.

(29) In step 140, it is determined if the vehicle speed equals the predefined first speed. If the vehicle speed equals the predefined first speed, the service brake is deactivated in step 150. The speed of the vehicle will increase and in step 160, it is determined if the vehicle speed exceeds the set brake cruise speed. When the vehicle speed exceeds the set brake cruise speed, the service brake is applied in step 130, and the method is repeated until either the downhill slope decreases or ends, or until a predetermined condition is reached. If a predetermined condition is reached, a downshift of the gearbox is preferably performed, and the method can be repeated at a lower temporary set brake cruise speed.

(30) The invention is not to be regarded as being limited to the embodiments described above, a number of additional variants and modifications being possible within the scope of the subsequent patent claims.