ARRANGEMENT FOR ENSURING THE FUNCTION OF A VEHICLE BRAKE

Abstract: The invention relates to an arrangement (11) for ensuring the functionning of a brake configuration for a vehicle with a multiplicity of wheels which are arranged with reference to a front axle and at least one rear axle and which support the vehicle, the brake configuration incorporating at least two brake devices (5a-f), each of them designed to act upon one of said wheels, and a brake control (12) with which the brake devices (5a-f) can be activated with a total brake action. The arrangement (11) incorporates a memory unit (14) designed to store at least one value of a parameter for said brake devices, said parameter relating to at least one previous braking operation performed by the respective brake device (5a-f), and a control unit (13) designed to distribute said brake action to said brake devices (5a-f), taking into account the value of said parameter of the respective brake devices (5a-f) when the brake control (12) is actuated. Said brake devices (5a-f) preferably consist of disc brakes and the value of said parameter indicates to what extent a film has accumulated on the brake lining surfaces which come into contact with the respective discs, which film reduces the friction between discs and brake linings at least incipiently. If the value indicates that such a film has formed, the whole or a major portion of the brake action called for by the driver, i.e. the total brake action, is distributed to the disc brakes (5a-f) whose value of said parameter indicates the presence of such a film.

Description: Arrangement for ensuring the function of a vehicle brake BACKGROUND TO THE INVENTION, AND STATE OF THE ART The present invention relates to an arrangement for ensuring the functioning of a brake configuration for a vehicle according to the preamble to patent claim 1. That the brakes of a vehicle, e.g. a heavy vehicle, function as intended is of the greatest importance, particularly today, when the total weights of heavy vehicle combinations (e.g. truck and trailer) are increasing and hence also the axle pressures of the respective vehicle combinations. In addition, average speeds are higher and timetables tighter. Traffic density is increasing. All this results in heavy demands upon the brake systems of heavy vehicles, particularly that they should function as intended. Conventional trucks use pneumatic configurations for controlling the braking process. More recent trucks use electronics for controlling the braking process. Compressed air is only used for applying the wheel brakes, which may include disc brakes or drum brakes, one wheel brake for each wheel. The driver of a heavy vehicle can communicate with the electronically controlled brake system via some brake control, preferably the brake pedal. Such electronically controlled brake systems may also incorporate load sensors designed to measure, for example, the vehicle's respective axle weights or total weight. The electronically controlled brake system is designed to communicate with the pneumatic configuration which is designed to control the brake cylinders of the respective wheel brakes. The brake cylinders are connected to the friction linings of the respective wheel brakes which are intended to act upon, for example, a brake disc or a brake drum. In such electrically controlled brake systems, all the wheel brakes are usually applied simultaneously. However, the brake system may be designed in such a way that the brake pressure delivered to one wheel brake of the vehicle differs from the brake pressure delivered to another wheel brake of the same vehicle, with a view to maintaining vehicle stability. This method is used in order, inter alia, to prevent skidding and overturning of the vehicle, e.g. if the brake action called for by the driver on a sharp bend would result in too much brake action on an individual axle, the brake system may be designed in such a way that the brake action called for is limited. Electronically controlled brake systems of the aforesaid type may also incorporate ABS control, i.e. the brake action called for by the driver being limited by the available friction between ground and tyres with a view to preventing wheel locking. In addition, an electronic brake system of the aforesaid type may incorporate functions to prevent wheel spin. Many electronically controlled brake systems incorporate at least one additional brake, e.g. a retarder which generates an outward braking moment by means of, for example, viscous friction. Such a retarder may be arranged to brake the universal shaft of the vehicle concerned. Further examples of supplementary brakes which may be included in an electrically controlled brake system are exhaust brakes and compression brakes which increase the engine's natural braking effect. Light braking and recurring light braking by means of the wheel brakes, particularly where the wheel brakes incorporate disc brakes, may reduce the friction between discs and linings. This may lead to the driver finding the vehicle difficult to brake and hence possibly to the driver pressing the brake pedal harder, which may lead to unnecessarily great brake action, so-called overbraking. Said reduction in friction between discs and brake linings depends on the brake lining material. The reduction in friction may be due, inter alia, to changes in the brake lining material which may arise because of low thermal and mechanical loading, particularly during light braking. This may result in the formation of a film which accumulates on the brake lining surfaces. The film accumulating on the brake lining surfaces which make contact with the disc causes reduction in friction between discs and brake linings. It is also possible for brake lining material to react with the road surface, e.g. with salts, in which case a film may form and accumulate on the brake lining surfaces and hence reduce the friction between discs and brake linings. Said film may thus, at least at an initial stage of brake application, reduce friction between brake linings and brake devices. SUMMARY OF THE INVENTION The object of the present invention is to provide an arrangement by which the problems associated with reduced friction between discs and linings of a disc brake are eliminated. This object is achieved with the arrangement indicated in the introduction which has the features defined in the characterising part of patent claim 1. Such an arrangement, which may incorporate a computer and is designed to store at least one value of a parameter for each brake device, said parameter being related to at least one previous braking operation performed by the respective brake device, makes it possible by means of the control unit to distribute the brake action called for by the driver to said brake device, taking into account the value of said parameter of the respective brake device. Said parameter which relates to at least one previous braking operation performed by the respective brake device may be created in various ways. In addition, the value of the parameter of the respective brake device indicates the extent to which any film has accumulated on the brake linings of the respective brake device. This will be discussed in more detail below. Particularly in the case of disc brakes there is a tendency for a film to be able to accumulate on the linings of disc brakes and reduce the friction between discs and brake linings, resulting in the disc brakes not being able to provide maximum brake action. When the value of the parameter of a respective brake device indicates that a film has accumulated on the brake lining surfaces, particularly the contact surfaces, the control unit of the arrangement may be designed to deliver a larger proportion of the brake action called for by the driver to that brake device. Delivering a larger proportion of the brake action to that brake device will result in the development of a higher temperature than if the brake action was uniformly distributed over all the brake devices. This higher temperature is capable of removing said film, and consequently the brake device concerned can thereafter provide maximum brake action. It should be noted that the arrangement according to the invention may be applied on vehicles whose wheel brakes consist of both drum brakes and disc brakes, but brake devices in said patent application refers preferably to disc brakes. As mentioned above, said parameter may be created in various ways and the arrangement according to the invention incorporates means designed to calculate the value of said parameter. According to one embodiment of the invention, said parameter is formed on the basis of the actual brake action from the respective brake device and the desired brake action from the respective brake device. A braking operation may entail different brake pressures being delivered to the various wheel brakes, inter alia in order, as previously mentioned, to maintain vehicle stability. In addition, the desired brake action from the respective wheel brake, i.e. the brake action expected from the respective wheel brake when a certain brake pressure is delivered to it, is calculated on the basis of the vehicle's weight and the brake pressure delivered to the respective wheel brake. The vehicle's actual brake action, i.e. the brake action resulting from the brake pressure delivered, may thus differ from the desired brake action. This difference may be due to a film having accumulated on the brake lining surfaces of the respective wheel brake which are intended to abut against, for example, a disc. The film reduces the friction between brake linings and discs and prevents the achievement of desired brake action. The actual brake action may be calculated, e.g. on the basis of the retardation of the wheel which the respective brake device is intended to act upon. According to a further embodiment of the invention, said parameter is formed on the basis of brake power supplied to the respective brake device and the time when said brake power is delivered to the respective brake device. Low brake pressure delivered to a certain brake device for a prolonged period is a particular case of risk that a film of the aforesaid kind may form on that brake device. According to a further embodiment of the invention, the control unit incorporates a comparison unit in which a predetermined value of said parameter is stored, and if the value of said parameter of one of the respective brake devices corresponds to or exceeds said predetermined value the control unit is designed to distribute the whole or a major portion of said brake action to that brake device when the brake control is actuated. Consequently and as mentioned previously, the control unit may be designed to distribute the whole or a major portion of the brake action called for by the driver to the brake device whose value of said parameter is the most critical. If the value of said parameter for all the brake devices corresponds to or exceeds said predetermined value, the control unit may be designed to distribute the whole or a major portion of said brake action to one of said brake devices at a time. The purpose of this is to enable the heat developed at the time of braking to eliminate the film accumulated on the brake lining surfaces of the respective brake device, after which that brake device can provide maximum brake action. According to a further embodiment of the invention, the control unit may be designed to distribute the whole or a major portion of said brake action to that brake device upon recurring actuation of the brake control. According to one embodiment of the invention, the brake configuration incorporates at least four brake devices, each of them designed to act upon one of said wheels. All the wheels of heavy trucks may be provided with a disc brake. According to one embodiment of the invention the control unit is designed to distribute the whole or a major portion of the brake action called for by the driver (also called the total brake action in said patent application) to the brake device which is arranged on the axle which includes the wheel which the brake device whose value of said parameter corresponds to or exceeds said predetermined value is designed to act upon. Distributing the brake action to the brake devices on one and the same axle maintains the vehicle's stability. The object of the arrangement is, as previously mentioned, to ensure the functioning of a brake configuration of a vehicle, i.e., as previously mentioned, to ensure that respective disc brakes can provide the desired brake action. To make this possible, the control unit is designed to distribute the brake action called for in proportion to the value of said parameter of respective brake devices. However, the distribution of brake action does not take place in such a way as to jeopardise the vehicle's stability, as the magnitude of the brake action distributed to the respective brake devices is limited in such a way as to maintain the vehicle's stability. The brake action distributed to the respective brake devices is also limited in such a way as to take into account the available friction between ground and tyres. BRIEF DESCRIPTION OF THE DRAWINGS The present invention will now be explained by describing a preferred embodiment with reference to the attached drawings. Fig. 1 depicts schematically a brake configuration for a heavy vehicle and Fig. 2 depicts schematically an embodiment of an arrangement according to the present invention. DETAILED DESCRIPTION OF AN EMBODIMENT OF THE INVENTION Fig. 1 depicts schematically a brake configuration of a heavy vehicle such as a truck with a multiplicity of wheels la-f which are arranged with reference to a front axle 2 and two rear axles 3, 4 and which support the vehicle. The brake configuration of the vehicle includes a main brake which incorporates brake devices 5a-f designed to act upon the vehicle's wheels la-f. The brake devices 5a-f may include pneumatic disc brakes, in which case the main brake includes the equipment required for applying the brake linings of the respective disc brakes to the discs which rotate with the respective wheels la-f. The brake configuration of the vehicle includes a supplementary brake in the form of a retarder 6 which generates outward braking moment by means of viscous friction. The retarder 6 is connected to the universal shaft 7 and the vehicle's gearbox 8 and only brakes the powered wheels lc-d. In addition, the vehicle incorporates a further supplementary brake in the form of an exhaust brake 9. The exhaust brake 9 is connected to the vehicle's engine 10. Fig. 2 depicts an arrangement 11 for controlling the brake configuration of a heavy vehicle such as a truck according to an embodiment of the invention. Only the wheel brakes, i.e. in this case the brake devices 5a-f which include disc brakes and the retarder 6 of the brake configuration appear in Fig. 2. It should be noted that the brake configuration might also include the exhaust brake 9. Reference 12 denotes a brake control which may incorporate the brake pedal by which the brake devices 5a-f and the retarder 6 can be activated and by means of which a driver can call for a brake action of the vehicle, a so-called total brake action of the vehicle. The arrangement 11 includes a control unit 13 which may incorporate a computer, a memory unit 14, a comparison unit 15, computing means 16 and a sensor 17. How the constituent parts of the arrangement 11 according to Fig. 2 cooperate will be described in more detail later on in the description. It should be noted that the arrangement 11 according to the invention is also applicable to other types of vehicle, e.g. passenger cars, other types of freight vehicles, buses and similar utility vehicles. The brake pedal 12 defines the brake action of the vehicle called for by the driver, i.e. the total brake action of the vehicle. The sensor 17 is designed to continuously detect the brake action called for by the driver and transmit to the control unit 13 a signal which corresponds to the total brake action. Upon light braking, the control unit 13 may be designed to distribute the whole of the brake action called for by the driver to the retarder 6. However, the control unit 13 may be designed also to distribute the brake action to the disc brakes 5a-f Light braking of a vehicle by means of disc brakes entails risk that a film may accumulate on brake lining contact surfaces as previously mentioned in the introductory description, resulting in the disc brakes not providing the desired brake action. To ensure that the disc brakes 5a-f function as intended, the computing means 16 are designed to calculate a value of a parameter for all the disc brakes 5a-f, which parameter relates to at least one previous braking operation performed by the respective disc brakes 5a-f The parameter may be formed in various ways. The parameter may be formed on the basis of the actual brake action from respective brake devices 5a-f and the desired brake action from respective brake devices 5a-f The desired brake action, i.e. the brake action expected from a respective wheel brake when a certain brake pressure is distributed to it, may be calculated on the basis of the brake pressure delivered to respective disc brakes 5a-f and the vehicle's actual weight with reference to respective disc brakes 5a-f. At the same time, load sensors 18, only one of which appears in Fig. 2, may be designed to detect the axle load of respective disc brakes 5a-f The control unit 13 and the computing means 16 are thus designed to communicate with said load sensors 18. The actual brake action from respective disc brakes 5a-f, i.e. the brake action resulting from the brake pressure delivered to respective disc brakes 5a-f, may thus differ from the desired brake action. This difference may be due to a film having accumulated on the brake lining surfaces of the respective disc brake which are intended to abut against the disc. The actual brake action may for example be calculated on the basis of the retardation of the wheel la-f which the respective disc brake 5a-f is intended to act upon. At the same time, detection means 19, only one of which for one of the respective wheels appears in Fig. 2, are designed to detect the retardation of the respective wheels la-f. Thus the control unit 13 and the calculating means 16 are designed to communicate with said detection means 19. A further way of forming said parameter may be on the basis of brake power supplied to respective disc brakes 5a-f and the time when said brake power is delivered to respective brake devices 5a-f. On the occasion of a braking operation the computing means 16 are designed to calculate a value of the parameter for respective disc brakes 5a-f. These values are stored in the memory unit 14. At the time of the next braking operation the comparison unit 15, in which a predetermined value of said parameter is stored, is designed to compare the value stored in the memory unit 14 of the parameter of respective disc brakes 5a-f with the predetermined value, and if a value of the parameter of one of the disc brakes 5a-f corresponds to or exceeds the predetermined value, the control unit 13 may be designed to distribute the whole or a major portion of the brake action called for by the driver, i.e. the total brake action, to that disc brake. Consequently the brake linings of that disc brake will be applied with greater force, resulting in the development of a higher temperature capable of removing the film accumulated on that disc brake's linings. The magnitude of the brake action distributed by the control unit 13 to a disc brake 5a-f is limited in such a way as, inter alia, not to jeopardise the vehicle's stability. The control unit 13 may possibly be designed to distribute the whole or a major portion of the brake action to the disc brakes which are arranged with reference to one and the same axle 2, 3, 4 in order to avoid jeopardising the vehicle's stability. The invention is not limited to the embodiment depicted but may be varied and modified within the scopes of the ensuing patent claims.

Claims: Patent claims 1. Arrangement (11) for ensuring the functioning of a brake configuration for a vehicle with a multiplicity of wheels (la-f) which are arranged with reference to a front axle (2) and at least one rear axle (3, 4) and which support the vehicle, the brake configuration incorporating two brake devices (5a-f), each of them designed to act upon one of said wheels (la-f), and a brake control (12) by which the brake devices (5a-f) may be activated with a total brake action, characterised in that the arrangement (11) includes a memory unit (14) designed to store at least one value of a parameter for said brake devices (5a- f), said parameter relating to at least one previous braking operation performed by the respective brake devices (5a-f), and a control unit (13) designed to distribute said brake action to said brake devices (5a-f), taking into account the value of said parameter of the respective brake devices (5a-f) at the time of actuating the brake control (12). 2. Arrangement (11) according to claim 1, characterised in that the arrangement (11) incorporates means (16) designed to calculate the value of said parameter. 3. Arrangement (11) according to claim 2, characterised in that said parameter is formed on the basis of the actual brake action from respective brake devices (5a-f) and the desired brake action from respective brake devices (5a-f). 4. Arrangement (11) according to any one of the foregoing claims, characterised in that said parameter is formed on the basis of brake power supplied to respective brake devices (5a-f) and the time when said brake power is delivered to respective brake devices (5a-f). 5. Arrangement (11) according to any one of the foregoing claims, characterised in that the control unit (13) incorporates a comparison unit (15) in which a predetermined value of said parameter is stored, and if the value of said parameter of one of the respective brake devices (5a-f) corresponds to or exceeds said predetermined value the control unit (13) is designed to distribute the whole or a major portion of said brake action to that brake device (5a-f) when the brake control (12) is actuated. 6. Arrangement (11) according to claim 5, characterised in that if the value of said parameter for all the brake devices (5a-f) corresponds to or exceeds said predetermined value the control unit (13) is designed to distribute the whole or a major portion of said brake action to one of said brake devices (5a-f) at a time. 7. Arrangement (11) according to either of claims 5 and 6, characterised in that the control unit (13) is designed to distribute the whole or a major portion of said brake action to that brake device (5a-f) upon recurring actuation of the brake control (12). 8. Arrangement (11) according to claim 5, whereby the brake configuration includes at least four brake devices (5a- f), characterised in that the control unit (13) is designed to distribute the whole or a major portion of said brake action to the brake devices (5a-f) which are arranged on the axle (2, 3, 4) which incorporates the wheel (la-f) which the brake device (5a- f) whose value of said parameter corresponds to or exceeds said predetermined value is designed to act upon. 9. Arrangement (11) according to any one of the foregoing claims, characterised in that the magnitude of said brake action is limited in such a way as to maintain the vehicle's stability. 10. Arrangement (11) according to any one of the foregoing claims, characterised in that said brake devices (5a-f) include disc brakes.

Inventors: ANDERSSON HAAKAN, VAAGSTEDT NILS-GUNNAR, ANDERSSON, HAAKAN, VAAGSTEDT, NILS-GUNNAR
Applicants: ANDERSSON HAKAN, SCANIA CV ABP, VAAGSTEDT NILS GUNNAR, ANDERSSON, HAAKAN, SCANIA CV AKTIEBOLAG (PUBL), VAAGSTEDT, NILS-GUNNAR
Application year: 2001
Main classification: B60T8
IPC codes: B60T8, B60T13