SE541378C2 - Method for controlling a parking brake system, a parking brake system, a vehicle comprising such a parking brake system, a computer program and a computer program product - Google Patents

Method for controlling a parking brake system, a parking brake system, a vehicle comprising such a parking brake system, a computer program and a computer program product

Info

Publication number
SE541378C2
SE541378C2 SE1651135A SE1651135A SE541378C2 SE 541378 C2 SE541378 C2 SE 541378C2 SE 1651135 A SE1651135 A SE 1651135A SE 1651135 A SE1651135 A SE 1651135A SE 541378 C2 SE541378 C2 SE 541378C2
Authority
SE
Sweden
Prior art keywords
parking brake
pneumatic pressure
brake means
brake
valve unit
Prior art date
Application number
SE1651135A
Other versions
SE1651135A1 (en
Inventor
Johan Thorsell
Original Assignee
Scania Cv Ab
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Scania Cv Ab filed Critical Scania Cv Ab
Priority to SE1651135A priority Critical patent/SE541378C2/en
Priority to DE102017006423.7A priority patent/DE102017006423A1/en
Publication of SE1651135A1 publication Critical patent/SE1651135A1/en
Publication of SE541378C2 publication Critical patent/SE541378C2/en

Links

Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60T—VEHICLE BRAKE CONTROL SYSTEMS OR PARTS THEREOF; BRAKE CONTROL SYSTEMS OR PARTS THEREOF, IN GENERAL; ARRANGEMENT OF BRAKING ELEMENTS ON VEHICLES IN GENERAL; PORTABLE DEVICES FOR PREVENTING UNWANTED MOVEMENT OF VEHICLES; VEHICLE MODIFICATIONS TO FACILITATE COOLING OF BRAKES
    • B60T8/00—Arrangements for adjusting wheel-braking force to meet varying vehicular or ground-surface conditions, e.g. limiting or varying distribution of braking force
    • B60T8/17—Using electrical or electronic regulation means to control braking
    • B60T8/176—Brake regulation specially adapted to prevent excessive wheel slip during vehicle deceleration, e.g. ABS
    • B60T8/1766—Proportioning of brake forces according to vehicle axle loads, e.g. front to rear of vehicle
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60T—VEHICLE BRAKE CONTROL SYSTEMS OR PARTS THEREOF; BRAKE CONTROL SYSTEMS OR PARTS THEREOF, IN GENERAL; ARRANGEMENT OF BRAKING ELEMENTS ON VEHICLES IN GENERAL; PORTABLE DEVICES FOR PREVENTING UNWANTED MOVEMENT OF VEHICLES; VEHICLE MODIFICATIONS TO FACILITATE COOLING OF BRAKES
    • B60T13/00—Transmitting braking action from initiating means to ultimate brake actuator with power assistance or drive; Brake systems incorporating such transmitting means, e.g. air-pressure brake systems
    • B60T13/10—Transmitting braking action from initiating means to ultimate brake actuator with power assistance or drive; Brake systems incorporating such transmitting means, e.g. air-pressure brake systems with fluid assistance, drive, or release
    • B60T13/24—Transmitting braking action from initiating means to ultimate brake actuator with power assistance or drive; Brake systems incorporating such transmitting means, e.g. air-pressure brake systems with fluid assistance, drive, or release the fluid being gaseous
    • B60T13/26—Compressed-air systems
    • B60T13/38—Brakes applied by springs or weights and released by compressed air
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60T—VEHICLE BRAKE CONTROL SYSTEMS OR PARTS THEREOF; BRAKE CONTROL SYSTEMS OR PARTS THEREOF, IN GENERAL; ARRANGEMENT OF BRAKING ELEMENTS ON VEHICLES IN GENERAL; PORTABLE DEVICES FOR PREVENTING UNWANTED MOVEMENT OF VEHICLES; VEHICLE MODIFICATIONS TO FACILITATE COOLING OF BRAKES
    • B60T13/00—Transmitting braking action from initiating means to ultimate brake actuator with power assistance or drive; Brake systems incorporating such transmitting means, e.g. air-pressure brake systems
    • B60T13/10—Transmitting braking action from initiating means to ultimate brake actuator with power assistance or drive; Brake systems incorporating such transmitting means, e.g. air-pressure brake systems with fluid assistance, drive, or release
    • B60T13/24—Transmitting braking action from initiating means to ultimate brake actuator with power assistance or drive; Brake systems incorporating such transmitting means, e.g. air-pressure brake systems with fluid assistance, drive, or release the fluid being gaseous
    • B60T13/26—Compressed-air systems
    • B60T13/38—Brakes applied by springs or weights and released by compressed air
    • B60T13/385—Control arrangements therefor
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60T—VEHICLE BRAKE CONTROL SYSTEMS OR PARTS THEREOF; BRAKE CONTROL SYSTEMS OR PARTS THEREOF, IN GENERAL; ARRANGEMENT OF BRAKING ELEMENTS ON VEHICLES IN GENERAL; PORTABLE DEVICES FOR PREVENTING UNWANTED MOVEMENT OF VEHICLES; VEHICLE MODIFICATIONS TO FACILITATE COOLING OF BRAKES
    • B60T13/00—Transmitting braking action from initiating means to ultimate brake actuator with power assistance or drive; Brake systems incorporating such transmitting means, e.g. air-pressure brake systems
    • B60T13/10—Transmitting braking action from initiating means to ultimate brake actuator with power assistance or drive; Brake systems incorporating such transmitting means, e.g. air-pressure brake systems with fluid assistance, drive, or release
    • B60T13/66—Electrical control in fluid-pressure brake systems
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60T—VEHICLE BRAKE CONTROL SYSTEMS OR PARTS THEREOF; BRAKE CONTROL SYSTEMS OR PARTS THEREOF, IN GENERAL; ARRANGEMENT OF BRAKING ELEMENTS ON VEHICLES IN GENERAL; PORTABLE DEVICES FOR PREVENTING UNWANTED MOVEMENT OF VEHICLES; VEHICLE MODIFICATIONS TO FACILITATE COOLING OF BRAKES
    • B60T13/00—Transmitting braking action from initiating means to ultimate brake actuator with power assistance or drive; Brake systems incorporating such transmitting means, e.g. air-pressure brake systems
    • B60T13/10—Transmitting braking action from initiating means to ultimate brake actuator with power assistance or drive; Brake systems incorporating such transmitting means, e.g. air-pressure brake systems with fluid assistance, drive, or release
    • B60T13/66—Electrical control in fluid-pressure brake systems
    • B60T13/662—Electrical control in fluid-pressure brake systems characterised by specified functions of the control system components
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60T—VEHICLE BRAKE CONTROL SYSTEMS OR PARTS THEREOF; BRAKE CONTROL SYSTEMS OR PARTS THEREOF, IN GENERAL; ARRANGEMENT OF BRAKING ELEMENTS ON VEHICLES IN GENERAL; PORTABLE DEVICES FOR PREVENTING UNWANTED MOVEMENT OF VEHICLES; VEHICLE MODIFICATIONS TO FACILITATE COOLING OF BRAKES
    • B60T13/00—Transmitting braking action from initiating means to ultimate brake actuator with power assistance or drive; Brake systems incorporating such transmitting means, e.g. air-pressure brake systems
    • B60T13/10—Transmitting braking action from initiating means to ultimate brake actuator with power assistance or drive; Brake systems incorporating such transmitting means, e.g. air-pressure brake systems with fluid assistance, drive, or release
    • B60T13/66—Electrical control in fluid-pressure brake systems
    • B60T13/68—Electrical control in fluid-pressure brake systems by electrically-controlled valves
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60T—VEHICLE BRAKE CONTROL SYSTEMS OR PARTS THEREOF; BRAKE CONTROL SYSTEMS OR PARTS THEREOF, IN GENERAL; ARRANGEMENT OF BRAKING ELEMENTS ON VEHICLES IN GENERAL; PORTABLE DEVICES FOR PREVENTING UNWANTED MOVEMENT OF VEHICLES; VEHICLE MODIFICATIONS TO FACILITATE COOLING OF BRAKES
    • B60T13/00—Transmitting braking action from initiating means to ultimate brake actuator with power assistance or drive; Brake systems incorporating such transmitting means, e.g. air-pressure brake systems
    • B60T13/10—Transmitting braking action from initiating means to ultimate brake actuator with power assistance or drive; Brake systems incorporating such transmitting means, e.g. air-pressure brake systems with fluid assistance, drive, or release
    • B60T13/66—Electrical control in fluid-pressure brake systems
    • B60T13/68—Electrical control in fluid-pressure brake systems by electrically-controlled valves
    • B60T13/683—Electrical control in fluid-pressure brake systems by electrically-controlled valves in pneumatic systems or parts thereof
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60T—VEHICLE BRAKE CONTROL SYSTEMS OR PARTS THEREOF; BRAKE CONTROL SYSTEMS OR PARTS THEREOF, IN GENERAL; ARRANGEMENT OF BRAKING ELEMENTS ON VEHICLES IN GENERAL; PORTABLE DEVICES FOR PREVENTING UNWANTED MOVEMENT OF VEHICLES; VEHICLE MODIFICATIONS TO FACILITATE COOLING OF BRAKES
    • B60T7/00—Brake-action initiating means
    • B60T7/02—Brake-action initiating means for personal initiation
    • B60T7/04—Brake-action initiating means for personal initiation foot actuated
    • B60T7/045—Brake-action initiating means for personal initiation foot actuated with locking and release means, e.g. providing parking brake application
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60T—VEHICLE BRAKE CONTROL SYSTEMS OR PARTS THEREOF; BRAKE CONTROL SYSTEMS OR PARTS THEREOF, IN GENERAL; ARRANGEMENT OF BRAKING ELEMENTS ON VEHICLES IN GENERAL; PORTABLE DEVICES FOR PREVENTING UNWANTED MOVEMENT OF VEHICLES; VEHICLE MODIFICATIONS TO FACILITATE COOLING OF BRAKES
    • B60T8/00—Arrangements for adjusting wheel-braking force to meet varying vehicular or ground-surface conditions, e.g. limiting or varying distribution of braking force
    • B60T8/17—Using electrical or electronic regulation means to control braking
    • B60T8/1755—Brake regulation specially adapted to control the stability of the vehicle, e.g. taking into account yaw rate or transverse acceleration in a curve
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60T—VEHICLE BRAKE CONTROL SYSTEMS OR PARTS THEREOF; BRAKE CONTROL SYSTEMS OR PARTS THEREOF, IN GENERAL; ARRANGEMENT OF BRAKING ELEMENTS ON VEHICLES IN GENERAL; PORTABLE DEVICES FOR PREVENTING UNWANTED MOVEMENT OF VEHICLES; VEHICLE MODIFICATIONS TO FACILITATE COOLING OF BRAKES
    • B60T8/00—Arrangements for adjusting wheel-braking force to meet varying vehicular or ground-surface conditions, e.g. limiting or varying distribution of braking force
    • B60T8/17—Using electrical or electronic regulation means to control braking
    • B60T8/176—Brake regulation specially adapted to prevent excessive wheel slip during vehicle deceleration, e.g. ABS
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60W—CONJOINT CONTROL OF VEHICLE SUB-UNITS OF DIFFERENT TYPE OR DIFFERENT FUNCTION; CONTROL SYSTEMS SPECIALLY ADAPTED FOR HYBRID VEHICLES; ROAD VEHICLE DRIVE CONTROL SYSTEMS FOR PURPOSES NOT RELATED TO THE CONTROL OF A PARTICULAR SUB-UNIT
    • B60W30/00—Purposes of road vehicle drive control systems not related to the control of a particular sub-unit, e.g. of systems using conjoint control of vehicle sub-units, or advanced driver assistance systems for ensuring comfort, stability and safety or drive control systems for propelling or retarding the vehicle
    • B60W30/02—Control of vehicle driving stability

Abstract

The invention relates to a vehicle parking brake system (100), comprising a front parking brake circuit (20); a rear parking brake circuit (30) and an air supply system (110) arranged to supply pressurized air to the respective parking brake circuit (20; 30), wherein the front parking brake circuit (20) comprises pneumatic front braking means (22) for the wheels (8) of at least one front axle (6) and the rear parking brake circuit (30) comprises pneumatic rear braking means (32) for the wheels (12) of at least on rear axle (10). The front parking brake circuit (20) comprises a valve unit (24) adapted to control the pneumatic pressure (P) supplied to the front brake means (22) to be lower than the pneumatic pressure (P) supplied to the rear brake means (32).The invention relates also relates to a method for controlling such a parking brake system (100), a vehicle comprising such a parking brake system (100), a computer programme (Pg) and a computer program product.

Description

Method for controlling a parking brake system, a parking brake system, a vehicle comprising such a parking brake system, a computer program and a computer program product TECHNICAL FIELD The present invention relates to a parking brake system. The invention also relates to a vehicle comprising such a parking brake system, a method for controlling a parking brake system, a computer program and a computer program product comprising program code for implementing a method according to the invention.
BACKGROUND Motor vehicles of today are equipped with a parking brake system mainly for use when the vehicle is standing still, such as when being parked. A brake force is hereby applied to the wheels of the vehicle when the operator of the vehicle manually operates a manoeuvre means, such as a parking brake lever, a push button or similar. The parking brake system is separated from the conventional brake system comprising one or more service brake circuits which are used during propulsion of said vehicle. The conventional brake system typically comprises two service brake circuits, one for the wheels on the front axle(s) and one for the wheels on the rear axle(s) of the powertrain.
Legal requirements for vehicles state that a vehicle must be able to brake with a certain deceleration in the case of a problem with the conventional brake system, for example if loss of pressure in one brake circuit occurs. This required deceleration should be able to be achieved by both service brake circuits individually or alternatively by means of a parking brake. It is thus known to use said parking brake system for emergency braking as well as for any other situation requiring a relatively large amount of braking force for reducing speed of said vehicle. This way, an operator of the vehicle may use said parking brake system for applying additional braking force to said one or more service brake circuits for more effectively braking said vehicle.
However, use of said parking brake system during propulsion of the vehicle is associated with a number of drawbacks. A parking brake system suitable for emergency braking typically comprises front spring brakes arranged in connection to the front wheels and rear spring brakes arranged in connection to the rear wheels. Spring brakes are configured such that pneumatic pressure is acting on a pre-stressed spring in a spring brake chamber. When the spring is compressed no brake force is applied on the wheels and when the pressure decreases and the spring is decompressed, brake force is applied on the wheels. The brake force of the parking brake thus increases when the pressure in the respective spring brake chamber decreases. A parking brake system may comprise a plurality of separate circuits, such as a front circuit associated with a front axle and a rear circuit associated with a rear axle. Normally, the same pneumatic pressure is supplied to the front circuit and the rear circuit. Depending on the how the spring brakes are configured, the brake force provided by the front circuit and the rear circuit may differ and there is a risk for instable behaviour of the vehicle due to the rear axle locking before the front axle. Also, for unladen vehicles the load on the rear axle may be smaller than the load on the front axle, whereby the traction of the rear wheels will be less than the traction of the front wheels. The rear axle will thereby lock before the front axle and the vehicle may obtain an unstable behaviour.
There is thus a need for providing a reliable parking brake system which provides safe application of brake force during propulsion of the vehicle so that instability is avoided or reduced. In order to reduce the risk of unstable behaviour additional valves and/or spring brakes may be added to the vehicle.
EP 2615003 relates to parking brake module for a pressure operated brake system of a vehicle being suitable for coupling a trailer.
SUMMARY OF THE INVENTION An object of the present invention is to propose a novel and advantageous parking brake system, which enables improved vehicle stability during emergency braking of said vehicle.
Another object of the invention is to propose a novel and advantageous method for controlling a parking brake system of a vehicle, which improves the vehicle stability during emergency braking of said vehicle.
Yet another object of the invention is to propose a method, a parking brake system and a computer program pertaining to safe emergency braking of a vehicle where a state of instability is avoided.
Some of these objects are achieved with a parking brake system, a method for controlling such a parking brake system, a vehicle comprising such a parking brake system, a computer program and a computer program product according to the appended claims.
According to an aspect of the invention a vehicle parking brake system is provided. The vehicle parking brake system comprising a front parking brake circuit; a rear parking brake circuit and an air supply system arranged to supply pressurized air to the respective parking brake circuit, wherein the front parking brake circuit comprises pneumatic front brake means for the wheels of at least one front axle and the rear parking brake circuit comprises pneumatic rear brake means for the wheels of at least one rear axle. The front parking brake circuit comprises a valve unit adapted to control the pneumatic pressure supplied to the front brake means to be lower than the pneumatic pressure supplied to the rear brake means. This way, the brake force provided by the parking brake system is more evenly distributed between the front parking brake circuit and the rear parking brake circuit.
The front brake means and the rear brake means of said parking brake system suitably comprises spring brakes, one arranged at each braked wheel. Each spring brake suitably comprises a spring brake chamber with a pre-stressed spring device. The spring device may be a coil spring. The pneumatic pressure supplied to the spring brake chamber acts on the spring device such that it is compressed or decompressed and thereby releases or applies the brake. When the spring device is compressed no brake force is applied on the associated wheel and the parking brake is thus not applied. Normally, the pneumatic pressure in the spring brake chamber is thus such that the spring device is compressed. The pneumatic pressure in the spring brake chamber is normally around 8-8,5 bar and is provided by the air supply system. The air supply system suitably comprises a compressor unit, at least one reservoir and a valve arrangement arranged upstream of the brake means. The pressurized air provided by the compressor unit is suitably stored in the at least one reservoir. The valve arrangement is suitably arranged in association with the at least one reservoir to distribute the air from the reservoir to the front parking brake circuit and the rear parking brake circuit and thereby controlling the pressure in the front parking brake circuit and the rear parking brake circuit. The valve arrangement may be an air processing unit, an air processing system or a circuit protection valve. When the parking brake system is activated the pneumatic pressure provided by the air supply system is decreased, such that the pneumatic pressure in each spring brake chamber is decreased, whereby the springs are decompressed and the parking brake means are applied. The brake force of the parking brake system thus increases when the pneumatic pressure in the respective brake means (spring brake) decreases.
Legal requirements for vehicles state that a vehicle must be able to brake with a certain deceleration if the conventional brake system fails. It is known to use parking brake systems in case of emergency but the use of parking brake systems during propulsion of the vehicle may be associated with a number of drawbacks. A common problem is how to distribute the brake force between the front parking brake circuit and the rear parking brake circuit. If a larger brake force is provided to the wheels of the rear axle, the rear axle will be locked before the front axle and the risk for instable behaviour of the vehicle is high. By arranging a valve unit in the front parking brake circuit to control the pneumatic pressure supplied to the front brake means, such that it is lower than the pneumatic pressure supplied to the rear brake means, a larger brake force may be applied on the front wheels in relation to the brake force applied on the rear wheels. This way, the risk that the rear axle will lock before the front axle is reduced and a parking brake system is achieved, which enables a safe emergency braking with improved vehicle stability.
The air supply system is suitably adapted to provide the same pneumatic pressure in the front parking brake circuit and the rear parking brake circuit. The air supply system is thus arranged in fluid communication with the front parking brake circuit and the rear parking brake circuit. The front parking brake circuit and the rear parking brake circuit are separate circuits, not connected to each other. The valve unit is suitably arranged in the front parking brake circuit, downstream of the air supply system and upstream of the front brake means for the wheels of the at least one front axle. The pneumatic pressure entering the valve unit, the input pressure, is the pneumatic pressure provided by the air supply system. The input pressure to the valve unit is thus the same as the pneumatic pressure supplied to the rear parking brake circuit. The pneumatic pressure leaving the valve unit, the output pressure, is lower than the input pressure. The valve unit is thus adapted to ensure that the output pressure is lower than the input pressure. The output pressure is thereby lower than the pneumatic pressure supplied to the rear parking brake circuit and the rear brake means. This means that without the valve unit, the pneumatic pressure supplied to the front brake means would be the same as the pneumatic pressure supplied to the rear brake means. The valve unit is thus adapted to ensure that the pneumatic pressure supplied to the front brake means is lower than the pneumatic pressure supplied to the rear brake means. The valve unit is thereby adapted to ensure that the pneumatic pressure supplied to the front brake means is lower than the pneumatic pressure provided by the air supply system.
The vehicle parking brake system is suitably adapted to be activated manually by the operator of the vehicle. The parking brake system may be adapted to be activated by manual operation of a parking brake control means such as a lever, a push button or similar. The parking brake system suitably comprises a control unit arranged in communication with the air supply system, the valve unit and the parking brake control means. The control unit is suitably adapted to control the air supply system and thus to control the compressor unit and the valve arrangement. The control unit may be adapted to control the valve unit. The control unit may be adapted to receive a signal indicating a request for activation/deactivation of the parking brake system from the parking brake control means.
The valve unit may be configured such that substantially no brake force is provided to the at least one front axle when said valve unit is open and so that maximal brake force is provided to the at least one front axle when the valve unit is closed.
The valve unit is suitably adapted to control the pneumatic pressure supplied to the front brake means, such that it differs from the pneumatic pressure supplied to the rear brake means. According to an aspect of the invention the valve unit is adapted to control the pneumatic pressure supplied to the front brake means based on the configuration of the brake means at the respective axle. How much lower the pneumatic pressure supplied to the front brake means is compared to the pneumatic pressure supplied to the rear brake means thus depends on the configuration of the pneumatic brake means at the respective axles. The front brake means in the front parking brake circuit may be differently configured than the rear brake means in the rear parking brake circuit. Thus, the spring brakes in the front parking brake circuit may be differently configured than the spring brakes in the rear parking brake circuit. Typically, the spring devices of the spring brakes in the front parking brake circuit are weaker than the spring devices of the spring brakes in the rear parking brake circuit. This can be due to lack of space at the front axle. When the pneumatic pressure supplied to the brake means in the respective parking brake circuit is the same, the spring brakes with the strongest spring devices will apply before the spring brakes with a weaker spring device. That is, the spring devices of the spring brakes in the rear parking brake circuit will decompress before the spring devices of the spring brakes in the front parking brake circuit when the pneumatic pressure is decreased from the normal pressure. The spring brakes of the rear parking brake circuit will thus be applied before the spring brakes of the front parking brake circuit. This way, the rear axle will lock before the front axle and there is a great risk for instability of the vehicle. Emergency braking with such a parking brake system may not be safe. By configuring the parking brake system with a valve unit which is adapted to control the pneumatic pressure supplied to the front brake means based on the configuration of the front brake means and the rear brake means, the risk that the rear axle locks before the front axle is reduced. To improve the distribution of brake force between the front parking brake circuit and the rear parking brake circuit, the pneumatic pressure supplied to the front brake means suitably depends on the characteristics of the spring devices in the front brake means and the rear brake means. Thus, the stronger the spring device is in the rear brake means compared to the spring device in the front brake means, the lower is the pneumatic pressure supplied to the front brake means. The larger the difference is between the spring force in the front brake means respective the rear brake means, the larger is the difference in pneumatic pressure supplied to the front brake means and the rear brake means. This way, it is ensured that enough brake force can be provided by the parking brake system in a safe way.
According to an aspect of the invention the valve unit is adapted to control the pneumatic pressure supplied to the front brake means based on the load on the respective axle. A vehicle which is unladen typically has a smaller load on the rear axle than on the front axle. The traction of the rear wheels will thereby be less than the traction of the front wheels. The rear axle will therefore lock before the front axle and the vehicle may obtain an unstable behaviour. By configuring the parking brake system with a valve unit which is adapted to control the pneumatic pressure supplied to the front brake means based on the load distribution on the vehicle, the risk that the rear axle locks before the front axle is reduced. The greater the difference is between the load on the front axle and the load on the rear axle, the larger is the difference in pneumatic pressure supplied to the front brake means and the rear brake means. Thus, the smaller the load is on the rear axle compared to the load on the front axle, the lower is the pneumatic pressure supplied to the front brake means.
According to an aspect of the invention the valve unit is adapted to control the pneumatic pressure supplied to the front brake means, such that it is lower than the pneumatic pressure supplied to the rear brake means with a constant offset value. As the pneumatic pressure provided by the air supply system decreases, the difference between the pneumatic pressure supplied to the front brake means and the pneumatic pressure supplied to the rear brake means remains the same. The constant offset value is suitably determined based on the configuration of the brake means of the front and rear axle respectively. The offset value may alternatively or additionally be determined based on the load distribution of the vehicle. The offset value may be within the range of 0,5 -2 bar.
According to an aspect of the invention the valve unit is adapted to control the pneumatic pressure supplied to the front brake means, such that it is lower than the pneumatic pressure supplied to the rear brake means with a constant ratio. The pneumatic pressure supplied to the front brake means will thus always be a certain percentage of the pneumatic pressure supplied to the rear brake means. The constant ratio is suitably determined based on the configuration of the brake means of the front and rear axle respectively. The constant ratio may alternatively or additionally be determined based on the load distribution of the vehicle.
According to an aspect of the invention the valve unit is a pneumatic valve unit. The valve unit is thus suitably configured such that the output pressure leaving the valve unit is lower than the input pressure entering the valve unit. The input pressure is the same as the pneumatic pressure supplied to the rear brake means. The valve unit may thereby be configured such that the output pressure is lower than the input pressure with a constant offset value or such that there is a constant ratio between the input pressure and the output pressure. The valve unit may comprise a membrane ensuring that only air with a certain pressure is provided at the output, in accordance with conventional pneumatic valve units. The pneumatic valve unit is a passive valve unit. By arranging a pneumatic valve unit in the parking brake system a cheap and easy way of controlling the pneumatic pressure and thus the brake force in the parking brake system is achieved.
According to an aspect of the invention the valve unit is an electrically controlled valve unit. The valve unit is thus suitably controlled by the control unit of the parking brake system. The valve unit may thereby be adapted to control the pneumatic pressure supplied to the front brake means independently of the pneumatic pressure supplied to the rear brake means. This way, finer adjustments of the pneumatic pressure supplied to the front brake means are possible. An electrically controlled valve unit also makes it possible to increase or decrease the difference between front and rear axle brake force depending on the driving situation, load etc. A further advantage is that in normal operation the parking brake system operates as it would without the valve.
According to an aspect of the invention the valve unit comprises a quick release function. Quick release functions are commonly known for speeding up the release of air from a service brake chamber such that the service brake releases quicker. The quick release function in the parking brake system according to the invention speeds up the release of air from the front parking brake circuit such that the front brake means are applied quicker. In the case where the valve unit is a pneumatic valve, the valve unit is suitably configured with an internal quick release function. The quick release function may thus be a separate port in the valve unit. In the case were the valve unit is an electrically controlled valve, the valve unit may be controlled to activate the quick release function and thereby release the air from the front parking brake circuit. The control unit is suitably adapted to control the valve unit to activate the quick release function.
According to an aspect of the invention a method for controlling a vehicle parking brake system is provided. Said parking brake system comprising a front parking brake circuit; a rear parking brake circuit and an air supply system arranged to supply pressurized air to the respective parking brake circuit, wherein the front parking brake circuit comprises pneumatic front braking means for the wheels of at least one front axle and the rear parking brake circuit comprises pneumatic rear braking means for the wheels of at least on rear axle, the method comprising the steps of: - identifying a request for activation of the parking brake system; - gradually decreasing the pneumatic pressure supplied to the respective parking brake circuit; and - controlling the pneumatic pressure supplied to the front brake means by means of a valve unit arranged in the front parking brake circuit, to be lower than the pneumatic pressure supplied to the rear brake means.
The step of identifying a request for activation of the parking brake system suitably comprises to receive a signal indicating a request for activation of the parking brake system from a parking brake control means. The signal from the parking brake control means is suitably received by the control unit, such that the control unit is able to identify a request for activation of the parking brake system.
The step of gradually decreasing the pneumatic pressure supplied to the respective parking brake circuit suitably comprises to control the air supply system by means of the control unit. The air supply system is suitably controlled, such that the pneumatic pressure provided by the air supply system is gradually decreased until a maximum brake force is provided by the front brake means and the rear brake means. Alternatively, the air supply system is controlled, such that the pneumatic pressure provided by the air supply system is gradually decreased until a predetermined pressure limit value has been reached.
The pneumatic pressure supplied to the front brake means is suitably controlled to be lower than the pneumatic pressure supplied to the rear brake means with a constant offset value or a constant ratio. The pneumatic pressure supplied to the front brake means is thus suitably controlled such that the difference between the pneumatic pressure supplied to the front brake means and the pneumatic pressure supplied to the rear brake means is a constant offset value or a constant percentage.
The pneumatic pressure supplied to the front brake means is suitably controlled based on the configuration of the brake means at the respective axle and/or the load on the respective axle. The pneumatic pressure supplied to the front brake means is suitably controlled, such that it is lower than the pneumatic pressure supplied to the rear brake means, based on the configuration of the brake means at the respective axle and/or the load on the respective axle. The difference between the pneumatic pressure supplied to the front brake means and the pneumatic pressure supplied to the rear brake means thus suitably depends on the configuration of the pneumatic brake means at the respective axle and/or the load on the respective axle. The pneumatic pressure supplied to the front brake means may be controlled to be lower than the pneumatic pressure supplied to the rear brake means by controlling the valve unit, wherein the valve unit is controlled depending on the configuration of the brake means at the respective axle and/or the load on the respective axle. The pneumatic pressure supplied to the front brake means may alternatively be controlled by providing a valve unit configured such that the pneumatic pressure supplied to the front brake means is lower than the pneumatic pressure supplied to the rear brake means, depending on the configuration of the brake means at the respective axle and/or the load on the respective axle. The control of the valve unit and/or the configuration of the valve unit may thus depend on the configuration of the front brake means and the rear brake means and/or the load on the respective axle. The configuration of the brake means suitably involves a spring device and the spring force associated with such spring device is suitably considered when determining how much lower the pneumatic pressure should be at the front brake means. If the spring force of the rear brake means is stronger than the spring force of the front brake means, the rear brake means will apply before the front brake means and the rear axle will thereby lock before the front axle. This is disadvantageous. By controlling the pneumatic pressure supplied to the front brake means based on the spring force of the respective brake means, the pneumatic pressure supplied to the front brake means can be controlled, such that the brake force is distributed between the front parking brake circuit and the rear parking brake circuit whereby the risk of the locking the rear axle before the front axle is reduced. Also, by controlling the pneumatic pressure supplied to the front brake means based on the load distribution on the vehicle, the risk that the rear axle locks before the front axle is further reduced.
According to an aspect of the invention the valve unit is electrically controlled by a control unit. The valve unit may thus be controlled independently of the pneumatic pressure provided by the air supply system and thus the pneumatic pressure supplied to the rear parking brake circuit.
Further objects, advantages and novel features of the present invention will become apparent to one skilled in the art from the following details, and also by putting the invention into practice. Whereas the invention is described below, it should be noted that it is not confined to the specific details described. One skilled in the art having access to the teachings herein will recognise further applications, modifications and incorporations in other fields, which are within the scope of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS For fuller understanding of the present invention and its further objects and advantages, the detailed description set out below should be read in conjunction with the accompanying drawings, in which the same reference notations denote similar items in the various diagrams, and in which: Figure 1 schematically illustrates a vehicle according to an embodiment of the invention; Figure 2 schematically illustrates a parking brake system for the vehicle depicted in Figure 1, according to an embodiment of the invention; Figure 3 schematically illustrates a flowchart of a method according to an embodiment of the invention; Figure 4a schematically illustrates a diagram according to an embodiment of the invention; Figure 4b schematically illustrates a diagram according to an embodiment of the invention; Figure 4c schematically illustrates a diagram according to an embodiment of the invention; and Figure 5 schematically illustrates a computer according to an embodiment of the invention.
DETAILED DESCRIPTION OF THE DRAWINGS Figure 1 schematically shows a side view of a vehicle 1 according to an embodiment of the invention. The vehicle 1 comprises a propulsion unit 2 and a gearbox 4 connected to the propulsion unit 2. The vehicle 1 further comprises at least one front axle 6 with front wheels 8 and at least one rear axle 10 with rear wheels 12. In this figure the vehicle 1 comprises two rear axles 10 wherein the rear wheels 12 are the driving wheels of the vehicle 1. The rear axles 10 are thus connected to the gearbox 4 and the propulsion unit 2. The vehicle 1 also comprises a parking brake system 100. The vehicle 1 may be a heavy vehicle, e.g. a truck, a bus, a forest machine, a mining vehicle, a construction vehicle, a rescue vehicle or similar. The vehicle 1 may alternatively be a passenger car. The vehicle 1 may be a hybrid vehicle comprising two propulsion units 2, namely an electric machine and a combustion engine. The parking brake system 100 in the vehicle 1 will be further described in Figure 2.
The term "link" herein refers to a communication link which may be a physical connection such as an opto-electronic communication line, or a non-physical connection such as a wireless connection, e.g. a radio link or microwave link. Herein provided links are illustrated as being arranged for bi-directional communication. However, in some cases communication between units via such a link may be one-directional.
Figure 2 schematically illustrates a parking brake system 100 of a vehicle 1. The vehicle 1 may be configured as described in Figure 1. The parking brake system 100 comprises a front parking brake circuit 20 and a rear parking brake circuit 30. The front parking brake circuit 20 includes pneumatic front brake means 22 for braking the front wheels 8 of at least one front axle 6. One front brake means 22 is suitably arranged at each front wheel 8. The rear parking brake circuit 30 includes pneumatic rear brake means 32 for braking the rear wheels 12 of at least one rear axle 10. One rear brake means 32 is suitably arranged at each rear wheel 12. In this example, the vehicle 1 comprises two rear axles 10 and thus four rear brake means 32.
The parking brake system 100 further comprises an air supply system 110. The air supply system 110 is arranged to supply pressurized air with a pneumatic pressure P to the front parking brake circuit 20 and the rear parking brake circuit 30. The air supply system 110 is thus arranged to control the brake force F applied by the front brake means 22 at the front wheels 8, by means of controlling the pneumatic pressure P supplied to the front parking brake circuit 20. Said front parking brake circuit 20 may comprise at least one passage arranged to provide pressurized air to said front braking means 22. Said air supply system 110 is also arranged to provide a pneumatic pressure P in the rear parking brake circuit 30. According to this embodiment the air supply system 110 provides the same pneumatic pressure P to the front parking brake circuit 20 and the rear parking brake circuit 30. Said air supply system 110 is arranged to supply pressurized air to the rear braking means 32, which are arranged to brake the rear wheels 12. Said air supply system 110 is thus arranged to control a braking force F at said rear wheels 12 by means of controlling said pneumatic pressure P in said rear parking brake circuit 30. The rear parking brake circuit 30 suitably comprises at least one passage arranged to provide said pressurized air to said rear braking means 32.
The front brake means 22 and the rear brake means 32 are suitably spring brakes, each comprising a pre-stressed spring device in a brake chamber. Pressurized air in the brake chamber acts on the spring device and thereby determines the brake force F applied by the brake means 22, 32 on the associated wheel 8, 12. In a non-braking state, the pneumatic pressure P in the brake chamber is so high that the spring device is compressed. By decreasing the pneumatic pressure P in the brake chamber the spring force overcomes the pressure P and the spring device decompresses. When the spring device is decompressed the brake means 22, 32 applies a brake force F on the wheels 8, 12 and the parking brake is thereby applied. The brake force F applied by the brake means 22, 32 is increased by lowering the pneumatic pressure P in the brake chamber, and vice versa. This is illustrated in Figure 4a. Thus, when the parking brake system 100 is activated the air supply system 110 is controlled to decrease the pneumatic pressure P provided to the front and the rear parking brake circuit 20, 30 whereby the front and rear brake means 22, 32 brakes the wheels 8, 12 of the vehicle 1.
A control unit 120 is arranged for controlling the brake force F provided by the brake means 22, 32 by controlling the pneumatic pressure P of the brake chamber of said brake means 22, 32. The control unit 120 is thus adapted to control the air supply system 110 to supply pressurized air to the front parking brake circuit 20 and the rear parking brake circuit 30. The control unit 120 is arranged for communication with the air supply system 110 via a link L110. A computer 130 may be arranged for communication with the control unit 120 via a link L130. The computer 130 may be detachably connected to the control unit 120. The computer 130 may be arranged external to the vehicle 100. The computer 130 may be used to cross-load software to the control unit 120.
A valve unit 24 is arranged in the front parking brake circuit 20. The valve unit 24 is arranged downstream of the air supply system 110 and upstream of the front brake means 22. The control unit 120 may be arranged for communication with said valve unit 24 via a link L24. Said valve unit 24 is adapted to ensure that the pneumatic pressure Pfsupplied to the front brake means 22 is lower than the pneumatic pressure Prsupplied to the rear brake means 32. The pneumatic pressure Pfsupplied to the front brake means 22 and the pneumatic pressure Prsupplied to the rear brake means 32 are illustrated in Figs 4b and 4c. The valve unit 24 is thus adapted to ensure that the pneumatic pressure on the output side of the valve unit 24 is lower than the pneumatic pressure on the input side of the valve unit 24.
Since the air supply system 110 provides the same pneumatic pressure P to the front parking brake circuit 20 and the rear parking brake circuit 30, the pneumatic pressure Pfleaving the valve unit 24 and thus being supplied to the front brake means 22 is lower than the pneumatic pressure Prsupplied to the rear brake means 32.
The valve unit 24 may be a pneumatic valve unit or an electrically controlled valve unit. The valve unit 24 may be arranged so that substantially no brake force is applied when said valve unit 24 is open. In the case where the valve unit 24 is electrically controlled, the control unit 120 is adapted to control the valve unit 24. The valve unit 24 is suitably configured and/or controlled, so that the pneumatic pressure Pfsupplied to the front brake means 22 is lower than the pneumatic pressure Prsupplied to the rear brake means 32 with a constant offset value O or with a constant ratio R. This is further illustrated in Figures 4b-4c.
The valve unit 24 is suitably adapted to control the pneumatic pressure Pfsupplied to the front brake means 22 based on the configuration of the brake means 22, 32 at the respective axles 6, 10 and/or the load on the respective axle 6, 10. The valve unit 24 may be adapted to control the pneumatic pressure Pfsupplied to the front brake means 22 based on at least one of vehicle configuration, vehicle mass, vehicle speed, lateral acceleration, yaw rate of said vehicle and steering angle of said vehicle. That is, the difference between the pneumatic pressure supplied Pfto the front brake means 22 and the pneumatic pressure Prsupplied to the rear brake means 32 depend on at least one of vehicle configuration, brake means configuration, load distribution, vehicle mass, vehicle speed, lateral acceleration, yaw rate of said vehicle and steering angle of said vehicle. Vehicle configuration may relate to the number of wheel axles being provided with parking brake means 22, 32. Vehicle configuration may also relate to a state of a gearbox of the vehicle 1, e.g. which gear is engaged and/or a prevailing state of a clutch arrangement of a transmission of said vehicle 1.
A parking brake control means 140 may be arranged for communication with the control unit 120 via a link L140. Hereby an operator of the vehicle 1 may manually operate said parking brake control means 140 for activating the parking brake system 100, for example during emergency braking of the vehicle 1. This is in particular advantageous in a case where other conventional service brake circuits are malfunctioning or in a case where additional applied braking force of the vehicle 1 is required. The parking brake control means 140 is thus suitably arranged in the vehicle cab and may be a parking brake lever, a push button or similar.
Figure 3 schematically illustrates a flow chart of a method for controlling a parking brake system 100 of a vehicle 1. The parking brake system 100 is suitably configured as described in Figure 2. Said parking brake system 100 comprises a front parking brake circuit 20; a rear parking brake circuit 30 and an air supply system 110 adapted to supply pressurized air to the respective circuit 20, 30, wherein the front parking brake circuit 20 comprises pneumatic front braking means 22 for the wheels 8 of at least one front axle 6 and the rear parking brake circuit 30 comprises pneumatic rear braking means 32 for the wheels 12 of at least one rear axle 10 of said vehicle 1. The method comprising the steps of: identifying slOl a request for activation of the parking brake system 100; gradually decreasing sl02 the pneumatic pressure P supplied to the respective parking brake circuit 20, 30; and controlling sl03 the pneumatic pressure Pfsupplied to the front brake means 22 by means of a valve unit 24 arranged in the front parking brake circuit 20, such that it is lower than the pneumatic pressure Prsupplied to the rear brake means 32.
The step of identifying slOl a request for activation of the parking brake system 100 suitably comprises to receive a signal from a parking brake control means 140. The parking brake control means 140 is suitably manoeuvred by an operator of the vehicle 1. A control unit 120 of the parking brake system 100 is suitably arranged in communication with the parking brake control means 140 and the control unit 120 thus identifies the request for activation of the parking brake system 100.
The step of gradually decreasing sl02 the pneumatic pressure P supplied to the respective parking brake circuit 20, 30 suitably comprises to control the air supply system 110 such that the pneumatic pressure P is decreased. The control unit 120 suitably controls the air supply system 110. By decreasing the pneumatic pressure P supplied to the front and rear parking circuit 20, 30 the brake force F provided by the front and rear brake means 22, 32 is increased.
The step of controlling s103 the pneumatic pressure Pfsupplied to the front brake means 22 such that it is lower than the pneumatic pressure Prsupplied to the rear brake means 32 may comprise to provide a pneumatic valve unit 24 in the front parking brake circuit 20, configured such that the pneumatic pressure Pfsupplied to the front brake means 22 is lower than the pneumatic pressure Prsupplied to the rear brake means 32. The step of controlling sl03 the pneumatic pressure Pfsupplied to the front brake means 22 such that it is lower than the pneumatic pressure Prsupplied to the rear brake means 32 may comprise to control an electrically controlled valve unit 24 in the front parking brake circuit 20, such that that the pneumatic pressure Pfsupplied to the front brake means 22 is lower than the pneumatic pressure Prsupplied to the rear brake means 32.
The step of controlling sl03 the pneumatic pressure Pfsupplied to the front brake means 22 such that it is lower than the pneumatic pressure Prsupplied to the rear brake means 32 may comprise to ensure that the pneumatic pressure Pfsupplied to the front brake means 22 is lower than the pneumatic pressure Prsupplied to the rear brake means 32 with a constant offset value O or a constant ratio. The pneumatic pressure Pfsupplied to the front brake means 22 is thus suitably controlled such that it differs from the pneumatic pressure Prsupplied to the rear brake means 32 with a constant offset value or a constant percentage.
The step of controlling sl03 the pneumatic pressure Pfsupplied to the front brake means 22 suitably comprises to control the pneumatic pressure Pfsupplied to the front brake means 22 based on the configuration of the pneumatic brake means 22, 32 at the respective axle 6, 10 and/or the load on the respective axle 6, 10. The step of controlling sl03 the pneumatic pressure Pfsupplied to the front brake means 22 suitably comprises to ensure that the difference between the pneumatic pressure Pfsupplied to the front brake means 22 and the pneumatic pressure Prsupplied to the rear brake means 32 depends on the configuration of the pneumatic brake means 22, 32 at the respective axle 6, 10 and/or the load on the respective axle 6, 10. The valve unit 24 may be controlled based on the configuration of the pneumatic brake means 22, 32 at the respective axle 6, 10 and/or the load on the respective axle 6, 10. The valve unit 24 may alternatively or additionally be configured based on the configuration of the pneumatic brake means 22, 32 at the respective axle 6, 10 and/or the load on the respective axle 6, 10. The control of the valve unit 24 and/or the configuration of the valve unit 24 may thus depend on the configuration of the pneumatic brake means 22, 32 at the respective axle 6, 10 and/or the load on the respective axle 6, 10. The configuration of the brake means 22, 32 suitably involves a pre-stressed spring device and the spring force is suitably considered when determining how much lower the air pressure should be at the front brake means 22. If the spring force of the rear brake means 32 is stronger than the spring force of the front brake means 22, the rear brake means 32 will apply before the front brake means 22 and the rear axle 10 will thereby lock before the front axle 6. This is disadvantageous. By considering the spring force of the respective brake means 22, 32, the pneumatic pressure Pfsupplied to the front brake means 22 can be controlled, such that the brake force is better distributed between the front parking brake circuit 20 and the rear parking brake circuit 30, whereby the risk of the locking the rear axle 10 before the front axle 6 is reduced.
The valve unit 24 may be electrically controlled by the control unit 120. The valve unit 24 may thus be controlled independently of the pneumatic pressure P provided by the air supply system 110 and thus the pneumatic pressure Prsupplied to the rear parking brake circuit 30.
Figure 4a shows a diagram over the relationship between the pneumatic pressure P in a brake means 22, 32 and the brake force F provided by the brake means 22, 32, according to an embodiment of the invention. As discussed in relation to Figure 2 the front brake means 22 and the rear brake means 32 are suitably spring brakes, each comprising a pre-stressed spring device in a brake chamber. The pneumatic pressure P in the brake chamber acts on the spring device and thereby determines the brake force F applied by the brake means 22, 32 on the associated wheel 8, 12. As shown in the diagram, the brake force F applied by the brake means 22, 32 is increased by lowering the pneumatic pressure P in the brake chamber, and vice versa.
Figure 4b shows a diagram over the relationship between the pneumatic pressure supplied to the front brake means Pfand the pneumatic pressure supplied to the rear brake means Prin a parking brake system 100 according to an embodiment of the invention. The diagram thus shows the relationship between the pneumatic pressure supplied to the front brake means Pfand the pneumatic pressure supplied to the rear brake means Prduring a method of controlling a parking brake system 100 according to an embodiment of the invention. The relationship illustrated in this diagram is only an example and the pneumatic pressure supplied to the front brake means Pfmay be controlled to achieve another outcome. The pneumatic pressure shown in this diagram has been obtained by means of the valve unit 24 as described in Figures 2 and 3. The valve unit 24 may be a pneumatic valve unit or an electrically controlled valve unit.
The solid line represents the relationship between the pneumatic pressure supplied to the front brake means Pfand the pneumatic pressure supplied to the rear brake means Praccording to prior art. The same pneumatic pressure is here supplied to the front brake means 22 and the rear brake means 32. When the parking brake system 100 is activated at time ti the air supply system 110 decreases the pneumatic pressure P supplied to the front parking brake circuit 20 and the rear parking brake circuit 30. The pneumatic pressure supplied to the front brake means Pfand the pneumatic pressure supplied to the rear brake means Pris thereby also decreased but the pneumatic pressure supplied to the front brake means Pfis always the same as the pneumatic pressure supplied to the rear brake means Pr.
The dashed line illustrates the relationship between the pneumatic pressure supplied to the front brake means Pfand the pneumatic pressure supplied to the rear brake means Prwith the parking brake system 100 according to an embodiment of the invention. In this embodiment the pneumatic pressure supplied to the front brake means Pfis controlled such that it is lower than the pneumatic pressure supplied to the rear brake means Prwith a constant offset value O. Thus, at the activation of the parking brake system 100 at time ti the difference between the pneumatic pressure supplied to the front brake means Pfand the pneumatic pressure supplied to the rear brake means Pris the offset value O. The offset value O is suitably within the range of 0,5 -2 bar. The offset value O may for example be 2 bar, which means that if the pneumatic pressure supplied to the rear brake means Pris 5 bar the pneumatic pressure supplied to the front brake means Pfis 3 bar. As the pneumatic pressure P provided by the air supply system 110 decreases, the difference between the pneumatic pressure supplied to the front brake means Pfand the pneumatic pressure supplied to the rear brake means Prremains the same. The constant offset value O may be determined based on the configuration of the brake means 22, 32 of the front and rear axle respectively. The offset value O may alternatively or additionally be determined based on the load distribution of the vehicle 1.
The dotted line illustrates the relationship between the pneumatic pressure supplied to the front brake means Pfand the pneumatic pressure supplied to the rear brake means Prwith the parking brake system 100 according to an embodiment of the invention. In this embodiment the pneumatic pressure supplied to the front brake means Pfis controlled such that it is lower than the pneumatic pressure supplied to the rear brake means Prwith a constant ratio. As an example the ratio may be 40%. Thus, at the activation of the parking brake system 100 at time ti the difference between the pneumatic pressure supplied to the front brake means Pfand the pneumatic pressure supplied to the rear brake means Pris 40%. Taking the same example as in Figure 4b, if the pneumatic pressure supplied to the rear brake means Pris 5 bar the pneumatic pressure supplied to the front brake means Pfis 3 bar. As the pneumatic pressure P provided by the air supply system 110 decreases, the difference between the pneumatic pressure supplied to the front brake means Pfand the pneumatic pressure supplied to the rear brake means Pris proportional to the pneumatic pressure supplied to the rear brake means Pr. When the pneumatic pressure supplied to the rear brake means Pris 4 bar the pneumatic pressure supplied to the front brake means is thereby 2,4 bar.
Figure 4c shows a diagram over the relationship between the pneumatic pressure supplied to the front brake means Pfand the pneumatic pressure supplied to the rear brake means Prin a parking brake system 100 according to an embodiment of the invention. The diagram thus shows the relationship between the pneumatic pressure supplied to the front brake means Pfand the pneumatic pressure supplied to the rear brake means Prduring a method of controlling a parking brake system 100 according to an embodiment of the invention. The relationship illustrated in this diagram is only an example and the pneumatic pressure supplied to the front brake means Pfmay be controlled to achieve another outcome. The diagram shows the pneumatic pressure supplied to the front brake means Pfcontrolled by means of an electrically controlled valve unit 24. The valve unit 24 thereby controls the pneumatic pressure supplied to the front brake means Pfindependently of the pneumatic pressure supplied to the rear brake means Pr. This way, finer adjustments of the pneumatic pressure supplied to the front brake means are possible.
The solid line represents the relationship between the pneumatic pressure supplied to the front brake means Pfand the pneumatic pressure supplied to the rear brake means Praccording to prior art, where the same pneumatic pressure is supplied to the front brake means 22 and the rear brake means 32. The dashed line illustrates one example of the pneumatic pressure supplied to the front brake means Pfby actively controlling the valve unit 24. In this example, when the parking brake system 100 is activated at time ti, the pneumatic pressure supplied to the front brake means Pfand the pneumatic pressure supplied to the rear brake means Pris the same. When the pneumatic pressure P provided by the air supply system 110 has decreased to a first level, the valve unit 24 is controlled such that the pneumatic pressure supplied to the front brake means Pfis decreased rapidly compared to the pneumatic pressure supplied to the rear brake means Pr, down to a second level. After that the pneumatic pressure supplied to the front brake means Pfis decreased slowly compared to the pneumatic pressure supplied to the rear brake means Pr.
The dotted line illustrates another example of the pneumatic pressure supplied to the front brake means Pfby actively controlling the valve unit 24. In this example, when the parking brake system 100 is activated at time t1, the pneumatic pressure supplied to the front brake means Pfand the pneumatic pressure supplied to the rear brake means Pris the same but the valve unit 24 is immediately controlled, such that the pneumatic pressure supplied to the front brake means Pfis instantly decreased down to a first level while the pressure supplied to the rear brake means Prremains the same. After that the valve unit 24 is controlled such that the pneumatic pressure supplied to the front brake means Pfis kept at the first level while the pressure supplied to the rear brake means Pris decreased to the same first level. After that the pneumatic pressure supplied to the front brake means Pfand the pneumatic pressure supplied to the rear brake means Pris the same and decreases at the same rate.
Figure 5 schematically illustrates a device 500. The control unit 120 or the computer 130 described with reference to Figure 2 may in a version comprise the device 500. The term "link" refers herein to a communication link which may be a physical connection such as an optoelectronic communication line, or a non-physical connection such as a wireless connection, e.g. a radio link or microwave link. The device 500 comprises a non-volatile memory 520, a data processing unit 510 and a read/write memory 550. The non-volatile memory 520 has a first memory element 530 in which a computer program, e.g. an operating system, is stored for controlling the function of the device 500. The device 500 further comprises a bus controller, a serial communication port, I/O means, an A/D converter, a time and date input and transfer unit, an event counter and an interruption controller (not depicted). The non-volatile memory 520 has also a second memory element 540.
There is provided a computer program Pg which comprises routines for a method for controlling a vehicle parking brake system 100 according to the invention. The computer program Pg comprises routines for identifying a request for activation of the vehicle parking brake system 100. The computer program Pg comprises routines for gradually decreasing the air pressure supplied to the respective parking brake circuit. The computer program Pg comprises routines for controlling the pneumatic pressure supplied to the front brake means 22 by means of a valve unit 24 arranged the front parking brake circuit 20, such that it is lower than the pneumatic pressure supplied to the rear brake means 32 at the at least one rear axle 10. The computer program Pg comprises routines for controlling the valve unit 24 such that the pneumatic pressure supplied to the front brake means 22 is lower than the pneumatic pressure supplied to the rear brake means 32. The program Pg may be stored in an executable form or in a compressed form in a memory 560 and/or in a read/write memory 550.
Where the data processing unit 510 is described as performing a certain function, it means that the data processing unit 510 effects a certain part of the program stored in the memory 560 or a certain part of the program stored in the read/write memory 550.
The data processing device 510 can communicate with a data port 599 via a data bus 515. The non-volatile memory 520 is intended for communication with the data processing unit 510 via a data bus 512. The separate memory 560 is intended to communicate with the data processing unit 510 via a data bus 511. The read/write memory 550 is adapted to communicating with the data processing unit 510 via a data bus 514.
When data are received on the data port 599, they are stored temporarily in the second memory element 540. When input data received have been temporarily stored, the data processing unit 510 is prepared to effect code execution as described above.
Parts of the methods herein described may be effected by the device 500 by means of the data processing unit 510 which runs the program stored in the memory 560 or the read/write memory 550. When the device 500 runs the program, methods herein described are executed.
The foregoing description of the preferred embodiments of the present invention is provided for illustrative and descriptive purposes. It is not intended to be exhaustive or to restrict the invention to the variants described. Many modifications and variations will obviously be apparent to one skilled in the art. The embodiments have been chosen and described in order best to explain the principles of the invention and its practical applications and hence make it possible for specialists to understand the invention for various embodiments and with the various modifications appropriate to the intended use.

Claims (15)

Claims
1. A vehicle parking brake system (100), comprising a front parking brake circuit (20); a rear parking brake circuit (30) and an air supply system (110) arranged to supply pressurized air to the respective parking brake circuit (20; 30), wherein the air supply system (110) is adapted to provide the same pneumatic pressure to the front parking brake circuit (20) and the rear parking brake circuit (30), wherein the front parking brake circuit (20) comprises pneumatic front braking means (22) for the wheels (8) of at least one front axle (6) and the rear parking brake circuit (30) comprises pneumatic rear braking means (32) for the wheels (12) of at least one rear axle (10), characterized in that the front parking brake circuit (20) comprises a valve unit (24) arranged downstream of the air supply system (110) and upstream of the pneumatic front braking means (22) for the wheels (8) of the at least one front axle (6), wherein the valve unit (24) is adapted to control the pneumatic pressure (Pf) supplied to the front brake means (22) to be lower than the pneumatic pressure (Pr) supplied to the rear brake means (32), whereby the pneumatic pressure (Pf) supplied to the front brake means (22) is lower than the pneumatic pressure provided by the air supply system (110).
2. The system (100) according to claim 1, wherein the valve unit (24) is adapted to control the pneumatic pressure (Pf) supplied to the front brake means (22) to be lower than the pneumatic pressure (Pr) supplied to the rear brake means (32) with a constant offset value (O).
3. The system (100) according to claim 1, wherein the valve unit (24) is adapted to control the pneumatic pressure (Pf) supplied to the front brake means (22)to be lower than the pneumatic pressure (Pr) supplied to the rear brake means (32) with a constant ratio.
4. The system (100) according to any of the preceding claims, wherein the valve unit (24) is adapted to control the pneumatic pressure (Pf) supplied to the front brake means (22) based on the characteristics of spring devices in the brake means (22; 32) at the respective axle (6,
5. The system (100) according to any of the preceding claims, wherein the valve unit (24) is adapted to control the pneumatic pressure (Pf) supplied to the front brake means (22) based on the load on the respective axle (6; 10).
6. The system (100) according to any of the preceding claims, wherein the valve unit (24) comprises a quick release function.
7. The system (100) according to any of the preceding claims, wherein the valve unit (24) is a pneumatic valve unit.
8. The system (100) according to any of claims 1-6, wherein the valve unit (24) is an electrically controlled valve unit.
9. A method for controlling a vehicle parking brake system (100), said parking brake system (100) comprising a front parking brake circuit (20); a rear parking brake circuit (30) and an air supply system (110) arranged to supply pressurized air to the respective parking brake circuit (20; 30), wherein the air supply system (110) is adapted to provide the same pneumatic pressure in the front parking brake circuit (20) and the rear parking brake circuit (30), wherein the front parking brake circuit (20) comprises pneumatic front braking means (22) for the wheels (8) of at least one front axle (6) and the rear parking brake circuit (30) comprises pneumatic rear braking means (32) for the wheels (12) of at least one rear axle (10), the method comprising the steps of: - identifying (slOl) a request for activation of the parking brake system (100); - gradually decreasing (sl02) the pneumatic pressure (P) supplied to the respective parking brake circuit (20; 30); and - controlling (sl03) the pneumatic pressure (Pf) supplied to the front brake means (22) by means of a valve unit (24) arranged downstream of the air supply system (110) and upstream of the pneumatic front braking means (22) for the wheels (8) of the at least one front axle (6)in the front parking brake circuit (20), to be lower than the pneumatic pressure (Pr) supplied to the rear brake means (32), whereby the pneumatic pressure (Pf) supplied to the front brake means (22) is lower than the pneumatic pressure provided by the air supply system (110).
10. The method according to claim 9, wherein the pneumatic pressure (Pf) supplied to the front brake means (22) is controlled to be lower than the pneumatic pressure (Pr) supplied to the rear brake means (32) with a constant offset value (0) or a constant ratio.
11. The method according to any of claims 9-10, wherein the pneumatic pressure (Pf) supplied to the front brake means (22) is controlled based on the characteristics of spring devices in the pneumatic brake means (22; 32) at the respective axle (6; 10) and/or the load on the respective axle (6; 10).
12. The method according to any of claims 9-11, wherein the valve unit (24) is electrically controlled by a control unit (120).
13. A vehicle (1) comprising a parking brake system (100) according to any of claims 1-8.
14. A computer program (Pg), wherein said computer program (Pg) comprises program code for causing an electronic control unit (120; 500) or a computer (130; 500) connected to the electronic control unit (120; 500) to perform the steps according to any of the claims 9-12.
15. A computer program product comprising a program code stored on a computer-readable medium for performing method steps according to any of claims 9-12, when said computer program is run on an electronic control unit (120; 500) or a computer (130; 500) connected to the electronic control unit (120; 500).
SE1651135A 2016-08-24 2016-08-24 Method for controlling a parking brake system, a parking brake system, a vehicle comprising such a parking brake system, a computer program and a computer program product SE541378C2 (en)

Priority Applications (2)

Application Number Priority Date Filing Date Title
SE1651135A SE541378C2 (en) 2016-08-24 2016-08-24 Method for controlling a parking brake system, a parking brake system, a vehicle comprising such a parking brake system, a computer program and a computer program product
DE102017006423.7A DE102017006423A1 (en) 2016-08-24 2017-07-07 A method of controlling a parking brake system, parking brake system, vehicle having such a parking brake system, computer program and computer program product

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
SE1651135A SE541378C2 (en) 2016-08-24 2016-08-24 Method for controlling a parking brake system, a parking brake system, a vehicle comprising such a parking brake system, a computer program and a computer program product

Publications (2)

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SE1651135A1 SE1651135A1 (en) 2018-02-25
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DE102018120350A1 (en) * 2018-08-21 2020-02-27 Wabco Gmbh Electropneumatic parking brake arrangement with shut-off valve

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US20030217899A1 (en) * 2002-05-27 2003-11-27 Komatsu Ltd. Emergency brake apparatus for vehicle
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EP2615003A1 (en) * 2012-01-13 2013-07-17 WABCO GmbH Parking brake module for a pressure-driven brake system of a vehicle suitable for coupling a trailer, brake system and vehicle equipped with the parking brake module and method for same
SE1451591A1 (en) * 2014-12-19 2016-06-20 Scania Cv Ab System and method for improved vehicle stability

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JPH0231938A (en) * 1988-07-21 1990-02-01 Toyota Motor Corp Front and rear wheel differential limitting device
US5154491A (en) * 1989-11-01 1992-10-13 Graham John M Emergency and parking brake system
US20030217899A1 (en) * 2002-05-27 2003-11-27 Komatsu Ltd. Emergency brake apparatus for vehicle
US20080189019A1 (en) * 2004-12-21 2008-08-07 Continental Teves Ag & Co. Ohg Method for Operating a Hydraulic Braking System for Motor Vehicles
US20070068746A1 (en) * 2005-09-29 2007-03-29 Stefan Chittka Combined service and parking brake apparatus and method for executing an emergency braking action
EP2615003A1 (en) * 2012-01-13 2013-07-17 WABCO GmbH Parking brake module for a pressure-driven brake system of a vehicle suitable for coupling a trailer, brake system and vehicle equipped with the parking brake module and method for same
SE1451591A1 (en) * 2014-12-19 2016-06-20 Scania Cv Ab System and method for improved vehicle stability

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