Whether an accident with a related damage occurs frequently depends on shortening the stopping distance by only very short distances. Apart from a number of other factors, it is therefore very important that the function of the brake system (e.g. service brake of a vehicle) is optimal. This applies also to brake operations which usually perform only a mere parking function such as the parking brake system of a vehicle or the blocking brake of a cabin of an elevator.
DE 19947903 A1 discloses that the effect of a brake can be improved for any possible future brake operation in such a fashion that the linings of the brake are dried by friction as a precaution. The same holds true with the precautionary removal of a layer of dirt on the lining or on the friction partner (e.g. the brake disc).
It has shown that not only external foreign materials on the brake linings can reduce the effect of the brake but that even the coefficient of friction of a brake lining itself can vary. This applies, for example, if a brake lining has not yet been worn in, if the lining exhibits tapered wear, or if it changes its surface due to chemical influences. Influences of this type can alter the coefficient of friction of a brake lining by 20% and higher and cause, under certain circumstances, negative consequences in a possible brake operation.
In view of the above, disclosed is a method for improving the coefficient of friction of brake linings of a friction brake of a vehicle or a cabin of an elevator. An object of the invention involves improving the coefficient of friction of a brake lining under defined conditions, leading to the nominal range of the coefficient of friction or leading back thereto. As this occurs, it is insignificant whether the brake system is a service brake system, a combined service and parking brake system, or a pure parking brake system.
This object is achieved by a method that automatically actuates a brake according to a predetermined program depending on a predetermined parameter and that terminates the program based on a second predetermined parameter. Thus, the invention principally resides in finding out whether a defined first condition (first parameter) has occurred, in taking certain predetermined measures (program) after determination of this first parameter and in terminating the program after determination of the second parameter.
An important factor which does not yet allow a brake lining to reach its optimal coefficient of friction is that the brake lining has not yet been worn in. Brake linings reach their operational coefficient of friction only after a wear-in process. Thus, the necessary clamping force/pressure for a defined deceleration increases until the operational coefficient of friction is reached. In this arrangement, the first parameter represents the commencement of the driving operation of a vehicle or an elevator cabin. However, the first parameter may also consist in equipping the vehicle or the cabin with new brake linings, i.e. in exchanging the brake linings.
This means that the program is switched on when the vehicle or the cabin has been equipped with new brake linings, irrespective of whether the brake linings of the original equipment are still new, or whether the brake linings have just been exchanged. An additional condition for the commencement of the first parameter can be that the vehicle or the cabin is moved so that the program is switched on as soon as the vehicle or the cabin moves for the first time or after new installation or exchange of the brake linings, what may be identified e.g. by way of the speedometer.
The second parameter can be defined as follows: the program runs
only for a defined time period, e.g. a maximum of two months after initiation of the vehicle or the cabin, and/or
within a defined distance/kilometer reading, e.g. >0 km start, 500 km end.
A combination of time/distance for deactivating the program is likewise possible for the determination of the second parameter. Activation or deactivation according to the above criteria can also be triggered after brake lining replacement. The identification of lining exchange and the type of the lining fitted in the exchange is possible by way of a coding on the brake lining or by an input at an appropriate control unit (ECU). The determination of the second parameter, the form of the program itself, and its termination can be input into the vehicle or into the elevator system by means of an online update according to manufacturer's regulations. This also allows inputting modifications for the program run and parameters based on up-to-date findings of the manufacturer (software update).
The second parameter and, hence, the deactivation of the system may even be triggered if a predefined relation between clamping force or pressure versus deceleration is reached (optional when deceleration sensors are provided). For deceleration purposes, it is also possible to use accelerometers or weighing cells (in an escalator), as they are employed in connection to controlled brake systems. Deactivation may possibly occur when a predefined relation between clamping force or pressure versus slope gradient or weight of elevator car/elevator cabin is detected in an electric parking brake (EPB). What is meant is that e.g. in parking brakes a defined clamping force or hydraulic pressure is adjusted depending on an angle of slope/weight in such a manner that the vehicle or the elevator cabin just refrains from starting to move. If there is a force in excess of the nominal value in this case, the coefficient of friction is not yet optimal. This method is particularly favorable when the vehicle is anyway equipped with a gradient sensor.
The third parameter restricts the start of the program in the presence of the first parameter to the following additional marginal conditions or influences the run of the program:
Another important factor which does not yet allow a brake lining to reach its optimal coefficient of friction is that the brake lining suffers from tapered wear. Due to tapered wear, the clamping travel or piston travel for a defined clamping force will increase, that means the characteristic curve of rigidity of the system becomes flatter.
It is possible to measure the first parameter that serves to initiate the program as follows: based on a characteristic curve of rigidity (clamping force/pressure in relation to piston travel) stored in the piston it is detected when the tapered wear recovery must be activated. As soon as the measured values correspond to the stored characteristic curve again, the second parameter is considered to prevail, and the program for the regeneration is completed. A new activation is possible any time in case the parameters do not correspond to the characteristic curve of rigidity.
The characteristic curve of rigidity can be detected due to possibly different lining compressibilities after brake lining exchange. Detection is executed by way of the coding on the brake lining or by manual input into a control unit. The online update described hereinabove is possible again.
The recovery of tapered wear takes place under the following marginal conditions:
An additional important factor which does not allow a brake lining to reach its optimal coefficient of friction is that due to an insufficient use of the brake system, the brake lining no longer reaches its operational coefficient of friction (the linings ‘becoming glass-like’, ‘becoming numb’). This occurs due to chemical processes on the surface of the lining. As this occurs, the necessary clamping force or pressure for a defined deceleration increases.
The first parameter initiating the program and the second parameter closing the program can be determined as follows. A characteristic curve ‘clamping force in relation to deceleration or weight’ which is stored in the system allows detecting when the brake linings need to be regenerated because a lining became ‘numb’. When the measured values clamping force/pressure in relation to deceleration correspond again to the stored characteristic curve, the second parameter is considered to prevail, and the regeneration is completed. Activation of the program is also possible when the stored characteristic curve (clamping force or pressure in relation to slope gradient) is not complied with upon actuation of an electric parking brake (EPB). This has been explained already hereinabove. A deactivation of the program occurs when the measured values correspond again to the characteristic curve in the EPB actuation. A new activation of the program is possible again at any time when the measured actual values are not in conformity with the characteristic curve. After a brake lining exchange due to possibly different lining coefficients of friction, the characteristic curve is updated (identification by way of coding on the brake lining, online update or separate input into the control unit as described hereinabove).
The regeneration of brake linings takes place under the following marginal conditions (third parameter or program):
In the elevator operation it is possible to install fewer or more brakes than the four brakes shown herein.
Number | Date | Country | Kind |
---|---|---|---|
103 22 451.3 | May 2003 | DE | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
---|---|---|---|---|
PCT/EP04/50843 | 3/18/2004 | WO | 11/21/2005 |