WO2002051682A1

WO2002051682A1 - Method and system for brakes of utility vehicles

Info

Publication number: WO2002051682A1
Application number: PCT/SE2001/002894
Authority: WO
Inventors: Magnus Staaf; Peter Engelke; Nils-Gunnar VÅGSTEDT
Original assignee: Scania Cv Ab (Publ)
Priority date: 2000-12-27
Filing date: 2001-12-21
Publication date: 2002-07-04
Also published as: DE10197123B4; DE10197123T5; SE0004858L; SE0004858D0; SE518048C2

Abstract

On a utility vehicle which includes a towing vehicle, e.g. a truck or tractor unit arranged to haul, for example, a trailer or semitrailer, and which incorporates a brake system, an expected vehicle retardation (Rbf), an actual vehicle retardation (Rbv) and a vehicle wheel brake efficiency (nb) are determined for the towing vehicle's wheel brakes on the basis of the expected towing vehicle retardation (Rbf) and the actual towing vehicle retardation (Rbv). According to one embodiment, when the towing vehicle is travelling with a trailer, a trailer brake pressure (Ps) on the trailer brakes is set on the basis of a trailer wheel brake efficiency (ns) which is determined on the basis of an excepted combination retardation (Rkf) and an actual combination retardation (Rkv). According to another embodiment the vehicle incorporates an information means (8) which is arranged to be activated in order to warm the vehicle driver if the vehicle wheel brake efficiency (nb) is below a predetermined value.

Description

METHOD AND SYSTEM FOR BRAKES OF UTILITY VEHICLES

TECHNICAL FIELD

The present invention relates to a method and a system according to the preambles to patent claims 1 and 7 respectively.

BACKGROUND

In traditional brake systems for a utility vehicle such as a truck, truck with trailer or tractor unit with semitrailer, the wheel brakes are controlled by pressure regulation while the vehicle is in motion. This means that both in pneumatic and in hydraulic brake systems there is a certain brake pressure which corresponds to each position of the foot brake pedal operated by the driver. Wheel brakes have a limited service life during which their efficiency gradually decreases. This decrease in efficiency may be due to diminishing friction between their rotating part and their movement-inhibiting part, a phenomenon known as "glassing". The cause of glassing is often low-pressure braking over relatively long periods. Diminishing efficiency may also be due to brake mechanism jamming. Reduced efficiency can be counteracted by applying greater brake pressure in order to achieve the same retardation of the vehicle as when the efficiency of its wheel brakes was undiminished. This is usually done by the driver increasing the deflection of the foot brake pedal. This increase in deflection of the foot brake pedal also warns the driver that the efficiency of the wheel brakes has decreased.

In some electronic brake systems the wheel brakes are retardation-regulated. This means that for each position of the foot brake pedal there is a corresponding retardation of the vehicle. An electronic control unit receiving information from wheel speed sensors regulates the brake pressure so as to provide a retardation which corresponds to the retardation "ordered" by the pedal deflection. A disadvantage of this type of electronically controlled brake system is that the pedal deflection does not warn the driver of reduced efficiency of the wheel brakes, since a given pedal deflection always produces the same retardation.

In modern systems for setting wheel brake pressures on a semitrailer for a tractor unit or on a trailer for a truck, the brake pressure on the semitrailer or trailer is adapted so as to reduce the loads in the coupling between the tractor unit or truck and the semitrailer or trailer respectively when braking while the vehicle is in motion. However, this does not cater for any possible reduction in efficiency of the wheel brakes on the tractor unit or truck.

OBJECT OF THE INVENTION

One object of the present invention is to improve the monitoring of the state of retardation-regulated wheel brakes of utility vehicles.

DESCRIPTION OF THE INVENTION

The object stated above is achieved by a method and a system with the characterising features in patent claims 1 and 7 respectively.

Determining the efficiency of a towing vehicle's wheel brakes on the basis of comparing an expected towing vehicle retardation with an actual towing vehicle retardation makes it possible to obtain information about the state of the brakes, information which can be used for settings and activation of corrective or remedial measures.

When the towing vehicle is travelling with a trailer, an expected and an actual combination retardation for the combination of the vehicle and the trailer, and a trailer wheel brake efficiency are preferably determined and a brake pressure is set on the trailer. This reduces loads on a coupling between towing vehicle and trailer during braking. Information means are preferably activated to warn the driver of the towing vehicle that its wheel brake efficiency is below a predetermined value. Thus a driver who in the case of retardation-control brakes is not warned by the brake pedal reflection that the efficiency of the wheel brakes has decreased nevertheless receives information in this respect.

A wheel brake conditioning function of the utility vehicle is preferably activated if the towing vehicle wheel brake efficiency is below a predetermined value. A diagnosed reduction in brake efficiency thus results in immediate action to improve same.

DESCRIPTION OF THE DRAWINGS

The invention is described below in more detail with reference to the accompanying drawings, in which

Fig. 1 is a diagram schematically illustrating a brake system according to one embodiment of the invention,

Fig. 2 depicts a flowchart illustrating a method according to one embodiment of the invention, and - Fig. 3 depicts a flowchart illustrating a method according to another embodiment of the invention.

DESCRIPTION OF EMBODIMENTS

In the ensuing, the term "towing vehicle" covers both trucks and tractor units. Tractor units are not arranged to carry directly any payload but to haul a so-called semitrailer. Trucks are arranged to carry payload and may (but need not necessarily) be arranged to haul a trailer. In the ensuing, the term "trailer" covers both trailers arranged to be hauled by a truck and semitrailers arranged to be hauled by a tractor unit. Referring to Fig. 1, the driver of a towing vehicle (such as a truck) which is intended to haul a trailer can, while the towing vehicle is in motion, operate a brake control 1 in its driving cab. The towing vehicle's wheel brakes are retardation-regulated, which means that for a certain retardation of it there is a corresponding specific position for the brake control 1. In Fig. 1, the position of the brake control 1 is measured by the distance δ.

A brake control sensor 2 is arranged to detect the distance δ which corresponds to the position of the brake control 1 and send signals corresponding to the distance δ to an electronic control unit (ECU) for the brake system. The ECU is arranged to send control signals to each of at least one brake operating device 3. Fig. 1 depicts schematically a compressed air brake system in which each brake operating device is connected to a compressed air reservoir 3'. Each brake operating device 3 is connected to the brake 4 on at least one of the towing vehicle's wheels 5 by means of at least one brake line 6. Instead of being pneumatic, the brake system may be hydraulic, in which case each brake line is filled with brake fluid in the form of hydraulic fluid instead of air.

The ECU is also arranged to receive from pressure sensors signals corresponding to the pressure in the brake lines 6. The ECU can thus receive separate signals about the brake pressure on each wheel axle or each wheel. The ECU may also receive information about the wheel brake force as a function of the brake pressure on the assumption of undiminished efficiency of the wheel brakes. This information may refer to each axle or wheel. Information received about the wheel brake force may for example take the form of a wheel brake factor for each axle, the unit of measure of which may be I N bar. A typical value for the wheel brake factor per axle of a towing vehicle is 10 kN/bar. Information about the wheel brake force as a function of brake pressure when the efficiency of the wheel brakes is undiminished can be stored in a memory which is accessible to the ECU.

A wheel speed sensor 7 on at least one of the vehicle's wheels is arranged to send signals to the ECU corresponding to the speed of the respective wheel. At least one torque sensor TS is arranged to detect the engine torque on the basis of known technology. The vehicle's weight can be calculated on the basis of signals from the wheel/speed sensor during a vehicle acceleration period and information about the engine torque over the same period. Weight information may also be derived from a memory in which it is stored.

Fig. 2 depicts a flowchart implementing a method according to one embodiment of the invention. The first step is the driver operating the brake control 1, thereby changing its position. One object of the method described in Fig. 2 is to determine the efficiency of the towing vehicle's wheel brakes. To this end, the method in Fig. 2 has to be applied when the towing vehicle is travelling without a trailer. The brake control sensor 2 detects the distance δ, which corresponds to a position of the brake control 1, and sends to the ECU a position signal LS corresponding to the distance δ.

An expected retardation Rέ_/is calculated on the basis of information about the respective brake pressure per axle, the wheel brake factor per axle for brakes with undiminished efficiency, and the vehicle's weight. The ECU sends to each of the brake operating devices 3 a signal to exert a pressure P in the respective brake line 6 so that the respective brake 4 is activated.

An actual retardation R^_v can be calculated by means of signals received by the ECU from the wheel speed sensor 7 over at least one predetermined period of time. A towing vehicle wheel brake efficiency ri_b is calculated, corresponding to the ratio between the actual towing vehicle retardation R_bv and the expected towing vehicle retardation Rb_f. Information on the towing vehicle wheel brake efficiency (ri_b) is stored to enable it to be used, for example, for settings or remedial measures.

As illustrated in Fig. 1, the ECU is arranged to send a signal when necessary in order to light up a warning lamp 8 on an information display in the driving cab. If the wheel brake efficiency ri is below a predetermined value (e.g. 0.75), a signal to light up the warning lamp 8 is sent. Alternatively, or in addition, an acoustic signal corresponding to a signal from the ECU may be activated in the driving cab when necessary. The warning lamp 8 lighting up informs the driver of reduced efficiency of the brakes, and appropriate measures such as servicing or repairs can be adopted.

Reverting to the flowchart in Fig. 2, an iterative process is conducted for adjusting the brake pressure of the towing vehicle's wheel brakes until the actual retardation R _v corresponds to the expected retardation Rbf. If the actual retardation Rj_v is less than the expected retardation R_bf, the ECU sends a signal to each of the brake operating devices 3 to increase the pressure in the respective brake line 6 by a predetermined step value i, whereupon the braking action of the respective brake 4 increases. This is followed by calculation of a new value of the actual retardation Rbv by means of signals received by the ECU from the wheel speed sensor 7. If the new actual retardation R v value is also less than the expected retardation R_bf, the ECU again sends a signal to each of the brake operating devices 3 to increase the pressure further in the respective brake line 6 by a predetermined step value i. This iterative process is repeated until the actual retardation Rb_v corresponds to the expected retardation R_bf.

Fig. 3 depicts a method according to another embodiment of the invention. The object here is to set the brake pressure of the wheel brakes on a trailer which is coupled to a towing vehicle, in order to minimise the loads in the coupling between the towing vehicle and the trailer during braking when the vehicle is in motion.

The first step is to determine the efficiency of the towing vehicle's wheel brakes. This is done in the same way as in the method described above in order to warn the driver that their efficiency has decreased below a certain level, i.e. when the towing vehicle is in motion without a trailer.

Referring to Fig.l, the driver operates the brake control 1 when the towing vehicle is travelling without a trailer. The ECU provides information about the distance δ, which corresponds to the position of the brake control 1. The towing vehicle's expected retardation R_bf is calculated from its weight (which may be stored in a memory in the ECU), its wheel brake factor per axle for brakes with undiminished efficiency, and its brake pressure per axle. The ECU sends a signal to each of the brake operating devices 3, whereupon a pressure P is exerted in the respective brake line 6. The towing vehicle's actual retardation R^_v is calculated by means of the wheel speed sensor 7. A towing vehicle wheel brake efficiency ri_b is determined, corresponding to the ratio between the actual towing vehicle retardation R_bv and the expected towing vehicle retardation R f.

When the towing vehicle is provided with a trailer, the above steps are repeated, i.e. the driver operates the brake control 1, and the ECU provides information about the distance δ corresponding to a position of the brake control 1. An expected combination retardation R_kf for the combination of towing vehicle and trailer is determined on the basis of the brake pressure per axle, the wheel brake factor per axle for brakes with undiminished efficiency, and the weight ri_k for the combination of towing vehicle and trailer. The weight is determined from information about the speed of at least one wheel and the engine torque.

An actual combination retardation R_kv for the combination is determined using information about the speed of at least one of the wheels. A trailer wheel brake efficiency n_s is determined by using information about the expected combination retardation R^-and the actual combination retardation R^. The trailer wheel brake efficiency n_s can be determined on the basis of the formula n = _s /(rrik *Rif R _> - m f rib), in which m_s is the trailer' s weight, which is determined as the difference between the combination's weight m and the towing vehicle's weight rtib.

The brake pressure P_s of the trailer brakes is set on the basis of the trailer wheel brake efficiency n_s. The trailer brake pressure E_ can then be adjusted by a factor which corresponds to the inverted value of the trailer wheel brake efficiency n_s. The vehicle may be equipped with a wheel brake conditioning function whereby the wheel brakes are conditioned to counteract a reduced efficiency of them caused by, for example, "glassing". This function reduces the pressure of certain brakes or puts them out of action, while the pressure of other brakes is increased.

According to a further embodiment of the present invention it is possible, if the vehicle wheel brake efficiency rib is below a predetermined value, for information about this to be sent to an electronic monitoring system in the vehicle. This information may be used for activating said wheel brake conditioning function. The information may also be used for activating other functions in the vehicle. Another such function may be to increase at the time of braking the action of a retarder brake and/or an exhaust brake, in order to increase the total braking power.

Information that the towing vehicle's wheel brake efficiency rib is below a predetermined value may also be used for activating a speed limiting and/or engine speed limiting function so that the vehicle does not travel above a certain speed during reduced wheel brake efficiency.

Claims

PATENT CLAIMS

1. A method for a utility vehicle including a towing vehicle, e.g. a truck or tractor unit, which may be arranged to haul, for example, a trailer or semitrailer respectively, whereby the utility vehicle comprises a brake system which comprises a brake control (1) and at least one brake operating device (3) which is arranged to activate at least one wheel brake (4) by regulating the pressure of a brake fluid in at least one brake line (6), characterised by, when the towing vehicle is travelling without a trailer, the steps of: - determining an expected towing vehicle retardation (RbJ) of the towing vehicle, determining an actual towing vehicle retardation (R ) of the towing vehicle, determining a towing vehicle wheel brake efficiency (rib) for the towing vehicle's wheel brakes on the basis of the expected towing vehicle retardation (R_bJ) and the actual towing vehicle retardation (R_b ), and transmitting information about the towing vehicle wheel brake efficiency (rib) to a driver of the utility vehicle or using the information for activating other functions.

2. A method according to claim 1 which, when the towing vehicle is travelling with a trailer which is provided with trailer wheel brakes, comprises the further steps of: determining an expected combination retardation (R^ for the combination of towing vehicle and trailer, determining an actual combination retardation (R^ ) for the combination, - determining a trailer wheel brake efficiency (n_s) on the basis of the expected combination retardation (R_/J) and the actual combination retardation (RX), setting a trailer brake pressure (P_s) for the trailer brakes on the basis of the trailer wheel brake efficiency (n_s).

3. A method according to claim 2, whereby the step in which a frailer wheel brake efficiency (n_s) is determined comprises the step of determining a trailer wheel brake efficiency (n_s) on the basis of the towing vehicle wheel brake efficiency (ri_b), the expected combination retardation (R_/J), the actual combination retardation (R^ ) and the trailer's weight (m_s), which is determined on the basis of the combination's weight (rri_k ) and the towing vehicle's weight (rrib).

4. A method according to any one of the foregoing claims, whereby the towing vehicle comprises an information means (8) which is arranged to be activated in order to warn the driver of the towing vehicle of decreased efficiency of the wheel brakes, comprising the step of activating the information means (8) if the vehicle wheel brake efficiency (ri_b) is below a predetermined value.

5. A method according to any one of the foregoing claims, whereby the vehicle comprises an electronic monitoring system comprising a step whereby, if the vehicle wheel brake efficiency (ri_b) is below a predetermined value, information about this is sent to the electronic monitoring system.

6. A method according to claim 5, comprising the step of, if the vehicle wheel brake efficiency (ri_b) is below a predetermined value, activating a wheel brake conditioning function on the utility vehicle.

7. A system for a utility vehicle including a towing vehicle, e.g. a truck or tractor unit, which may be arranged to haul, for example, a trailer or semitrailer respectively, which system comprises a brake control (1) and at least one brake operating device (3) which is arranged to activate at least one wheel brake (4) by regulating the pressure of a brake fluid in at least one brake line (6) characterised by means for determining an expected towing vehicle retardation (R_bf) of the towing vehicle when travelling without a trailer, means for determining an actual towing vehicle retardation (Rbv ) of the towing vehicle when travelling ^"without a frailer,

means for determining a towing vehicle wheel brake efficiency ( i ) for the towing vehicle's wheel brakes on the basis of the expected towing vehicle retardation (Rb/) and the actual towing vehicle retardation (Rb ), and

means for transmitting information about the towing vehicle wheel brake efficiency (ri_b ) to the driver of the utility vehicle, or for using said information to activate other functions.

8. A system according to claim 7, comprising - means for, when the towing vehicle is travelling with a frailer which is provided with frailer wheel brakes, determining an expected combination retardation (R/J) for the combination of towing vehicle and trailer, means for, when the towing vehicle is travelling with a frailer which is provided with trailer wheel brakes, determining an actual combination retardation (R ) for the combination, means for determining a frailer wheel brake efficiency (n_s) on the basis of the expected combination retardation (R_$) and the actual retardation (R^ ), means for adjusting a frailer brake pressure (P_s) on the trailer brakes on the basis of the trailer wheel brake efficiency (n_s).

9. A system according to claim 8, comprising means for determining the trailer' s weight (m_s) on the basis of the combination's weight (rri_k) and the towing vehicle's weight (rrib), in addition to which the means for determining a trailer wheel brake efficiency (n_s) is arranged to determine a frailer wheel brake efficiency (n_s) on the basis of the towing vehicle wheel brake efficiency (ri_b), the expected combination retardation (R_/J), the actual combination retardation (R^ ) and the trailer's weight (m_s).

10. A system according to any one of claims 7-9, whereby the towing vehicle comprises an information means (8) which is arranged to be activated in order to warn a driver of the towing vehicle of reduced efficiency of the wheel brakes, in addition to which the system comprises means for activating the information means (8) if the towing vehicle brake efficiency (rib) is below a predetermined value.

11. A system which is according to any one of claims 7-10, whereby the towing vehicle comprises an electronic monitoring system, and which comprises in addition means for sending, if the vehicle wheel brake efficiency (rib) is below a predetermined value, information about this to the elecfronic monitoring system.

12. A system according to claim 11, comprising means for activating, if the vehicle wheel brake efficiency (rib) is below a predetermined value, a wheel brake conditioning function on the utility vehicle.