DE102013216314A1 - Brake system for motor vehicles and associated operating method - Google Patents

Abstract

A brake system (50) for motor vehicles which can be actuated in a "brake-by-wire" mode both by the driver and independently of the vehicle driver and has a hydraulic fallback mode in which it can only be operated by the driver, with two brake circuits ( 94, 96), wherein each brake circuit (94, 96) are each associated with two wheel brakes (98, 100, 102, 104), with a brake pedal (56) for actuating a pedal decoupling unit (62), with a travel detection device (220) detects the actuation travel of the brake pedal (56) or a piston connected to the brake pedal, with a simulator (68) with a simulator release valve (222), which gives the driver a brake pedal feel in the "brake-by-wire" mode, and which in the Is hydraulically separated fall-back, with an electro-hydraulic pressure supply device (86) which can be controlled by a control unit (80) to build up brake pressure, with a pressure modulation device (92) which has an inlet valve (110, 112, 114, 116) and an outlet valve (120, 122, 124, 126) for setting wheel-specific brake pressures for each wheel brake (98, 100, 102, 104), and wherein two normally closed Aktuatorkreis-separating valves (120, 212) are provided, through which the pressure supply means (86) is hydraulically connectable to the two brake circuits (94, 96), to enable precise pressure modulation, especially during a recuperative braking process. For this purpose, an outlet valve (124) of a rear wheel brake (102) is designed as a normally closed analog outlet valve and an actuator circuit isolation valve (212) is designed as a normally closed analog actuator circuit isolation valve.

Description

The invention relates to a brake system for motor vehicles, which is actuated in a "brake-by-wire" mode both by the driver and independently controllable by the driver and has a hydraulic fallback level in which it is actuated only by the driver, with two brake circuits, wherein each brake circuit are each associated with two wheel brakes, with a brake pedal for actuating a pedal decoupling unit, with a position detecting device which detects the actuation of the brake pedal or a piston connected to the brake pedal, with a simulator with a Simulatorsfreigebeventil, in the mode "Brake-by -wire "gives the driver a brake pedal feel and is hydraulically separated in the fallback level, with an electro-hydraulic pressure supply device, which can be controlled by a control unit to build up brake pressure, with a pressure modulation device, the setting for radi individual brake pressures for each wheel brake each having an inlet valve and an outlet valve, wherein isolation valves are provided, through which the pressure chambers of the pedal decoupling unit can be hydraulically separated from the wheel brakes, and wherein two normally closed Aktuatorkreis separating valves are provided, through which the pressure supply means hydraulically with the two brake circuits is connectable. It further relates to an operating method for such a brake system.

The "brake-by-wire" mode of brake system, in particular electro-hydraulic brake systems, leads to a mechanical-hydraulic decoupling of the operation of the brake pedal by the driver. The driver operates a simulator or a brake pedal feel simulation device, which gives him a pleasant and familiar pedal feel. By this operation, but not directly, as in conventional hydraulic brake systems, brake fluid displaced into the brake circuits. Rather, due to the operation of the simulator of the driver's braking request is determined, which then enters into the determination of a desired braking torque or target brake pressure. The actual braking is then carried out by active pressure build-up in the brake circuits by means of a pressure supply device, which is controlled by a control and regulating unit. Due to the hydraulic decoupling of the brake pedal actuation from the pressure build-up, many functionalities such as ABS, ESC, TCS, hill-start assist etc. can be realized in such brake systems in a comfortable way.

In such brake systems, a hydraulic fallback stage is usually provided, by means of which the driver can decelerate or bring the vehicle to a standstill by muscular force when the brake pedal is actuated, if the "by-wire" mode of operation fails or is disturbed. While in normal operation by a pedal decoupling unit, the above-described hydraulic decoupling between brake pedal operation and brake pressure build-up, this decoupling is canceled in the fallback so that the driver can move brake means directly into the brake circuits.

From the DE 10 2010 040 097 A1 a brake system is known, which is operated in normal operation in the operating mode "brake-by-wire".

In vehicles with electric motor - pure electric vehicles or hybrid vehicles with additional combustion engine - is advantageously the battery that supplies the electric motor with power during driving, charged by recuperative braking. In this case, the electric motor acts as a generator and generates on the corresponding axis a recuperative braking torque. Especially with such recuperative braking operations, it is important to distribute the desired braking torque precisely to a recuperative component and a hydraulic component. That is, the admixture of the hydraulic portion is just the difference between the desired braking torque and the recuperative share correspond.

The invention is therefore based on the object of specifying a brake system in which precise pressure modulations, in particular during a recuperative braking process, are possible. Furthermore, a method for operating such a brake system is to be specified.

With regard to the brake system, this object is achieved in that an exhaust valve of a rear brake as normally closed analog outlet valve and Aktuatorkreis separation valve is designed as a normally closed analog Aktuatorkreis separation valve.

Advantageous embodiments of the invention are the subject of the dependent claims

The invention is based on the consideration that a very precise pressure modulation is required for the necessary during recuperative braking admixtures of hydraulic braking torque. The pressure reduction is preferably carried out via the control of the exhaust valves.

As has now been recognized, particularly accurate pressure modulations or pressure settings can be achieved by a combination of two analogously designed valves, namely an outlet valve and an actuator circuit isolation valve is used. All other valves can be digital. Due to the analogous functionality, pressure profiles that correspond to an admixture of a hydraulically generated braking torque can essentially be imaged or realized with a smooth course and continuously. This eliminates the pressure stages associated with the frequent and rapid opening and closing of digital valves.

Advantageously, exactly one analogue outlet valve and exactly one analogue actuator circuit isolation valve are provided. In other words, with four wheel brakes, each with an outlet valve through which brake fluid can be discharged from the respective wheel brake, three of the four exhaust valves are designed digital, and only one of them as an analog valve. This is based on the consideration that in vehicles with recuperative energy recovery recuperative braking usually takes place on an axle, especially the rear axle, so that an analog exhaust valve for the pressure reduction can be used for both rear brakes.

Accordingly, in a preferred embodiment, a first brake circuit comprises the two front wheel brakes and a second brake circuit the two rear wheel brakes, wherein the analog outlet valve is associated with a rear wheel brake and wherein the analog Aktuatorkreis-separating valve is associated with the second brake circuit. If a braking torque is built up recuperatively on the rear axle, a hydraulic braking torque can be mixed very precisely and without undesired jumps by the targeted control of the analog exhaust valve on one of the wheel brakes on the rear axle and the analog Aktuatorkreis separating valve, so that the target braking torque is achieved.

The pedal decoupling unit preferably comprises two pressure chambers, in each of which a piston is movably arranged, separating valves being provided, by means of which the pressure chambers of the pedal decoupling unit can be hydraulically separated from the wheel brakes. As a result, hydraulic decoupling from the pedal decoupling unit and the wheel brakes is achieved in the "by-wire" mode. In the fallback mode, the isolation valves are opened, so that the driver can hydraulically actuate the wheel brakes by muscle power.

The simulator advantageously has a pressure chamber into which brake fluid is displaced in the "brake-by-wire" mode from at least one of the pressure chambers of the pedal decoupling unit. The driver thus shifts braking means in the simulator and is decoupled from the immediate operation of the brakes. This is important, for example, in the case of recuperative braking processes, in which the currently maximally available recuperative braking torque is to be used, and the additional hydraulic braking torque is dimensioned just large enough for the nominal braking torque to be present overall.

In a preferred embodiment, a piston is pressed against an elastic spring element in the simulator to produce a pedal feel. The piston is preferably actuated by the pressure medium flowing in the pressure medium.

The simulator release valve is preferably a check valve connected in parallel, which ensures an unthrottled inflow of pressure medium in the pressure chamber.

With respect to the method for operating such a brake system, the above object is achieved according to the invention by the analog exhaust valve is controlled during the pressure reduction in the rear brakes and the intake valves of the rear wheel brakes are opened. This results in a hydraulic pressure equalization between the two rear brakes and the analog exhaust valve can be used for analog controlled and even pressure equalization of both rear brakes.

Advantageously, the actuator circuit isolation valve is actuated, in particular completely closed, to prevent an influx of brake fluid from the pressure supply device or a return flow into it.

In a fallback mode, the actuator circuit isolation valves are preferably closed and the simulator release valve closed, so that brake fluid can be displaced from the pressure chambers of the pedal decoupling unit into the brake circuits.

The advantages of the invention are, in particular, that precisely analogous pressure modulations are possible by using two analog valves at the points described above, without all valves having to be configured in an analogous manner. Thus, by using only one analog exhaust valve for a rear wheel brake (the other rear wheel brake has a digital exhaust valve associated with it) a precise pressure reduction is possible in both brakes. The use of an analog exhaust valve to build up pressure in the rear brakes, closing the two intake valves, prevents the formation of yawing moments due to pressure variations in the two brakes, thus increasing driving stability.

By using an analog actuator circuit isolation valve, a pressure differential between both brake circuits can be adjusted in proportion to a current demand according to a pressure reducing valve function. This is also infinitely possible, so that a continuously decreasing braking torque from the electric recuperation can be fully compensated by correspondingly increasing hydraulic braking torque on the rear axle. In conjunction with the analogue exhaust valve on a rear-wheel circuit, so ascending and descending brake force curves can be infinitely realized in any desired form.

If only two analogue valves are used at the above-described positions, costs can be saved compared to configurations with other analogue valves. Compared to a configuration with two fully-balanced wheel pressure regulators (one analogue intake valve and one analogue exhaust valve per rear wheel), two current-controlled analogue intake valve final stages can be replaced by digital if the intake valve is using digital ABS control and does not apply brake torque distribution. Also, the intake valve itself can be deferred due to the omission of the fully-analogous function.

An embodiment of the invention will be explained in more detail with reference to a drawing. In it show in a highly schematic representation:

1 the exemplary time course of braking torques during a recuperative braking process,

2 which to 1 associated course of brake pressures,

3 the course of flows in the analogue exhaust valve and the analogue actuator circuit inlet valve, and

4 a brake system in a preferred embodiment.

Identical parts are provided with the same reference numerals in all figures.

On an x-axis 2 in the 1 is the time and on a y-axis 8th the braking torque applied. The total braking torque 14 During a braking operation of a motor vehicle (in particular a car) with an electric motor, which is used for recuperative braking, is composed of a recuperative braking torque 20 on the rear axle, a hydraulic braking torque 26 at the front axle and a hydraulic braking torque 32 at the rear axle. The braking moments 20 . 26 . 32 Adds the total braking torque 14 (the drawing is not to scale). Between times t ₁ and t ₂ , the total braking torque increases 14 in a linear manner, in order to then be substantially constant between the time t ₂ and a time t ₃ . Between the time t ₆ and a time t ₇ it then decreases linearly again. The hydraulic braking torque 26 At the front axle runs between t ₂ and t ₆ also constant.

The recuperative braking torque 20 however, initially runs between t ₂ and t ₃ constant, then rises linearly between t ₃ and t ₄ on, in order to then extend between t ₄ and t ₅ is constant and between t ₅ and t to drop linearly. ₆ Such a time course of the recuperative braking torque corresponds to a braking example of high speed to a standstill, resulting in the characteristic of the electric machine as a result of the recuperatively usable torque increases first with decreasing speed, but then drops sharply to a standstill. The course of the hydraulic braking torque 32 results from the difference between the total braking torque 14 and recuperative braking torque 20 and hydraulic braking torque on the front axle, it is effectively mixed in such a way that the total braking torque is realized.

In 2 is on the x-axis 2 again the time shown while on the y-axis 8th now the brake pressure is applied. A brake pressure 40 on the front axis runs linearly after a linear increase between the times t ₁ and t ₂ , in order then again to become linearly smaller between t ₆ and t ₇ . A brake pressure 46 however, at the front axle runs between the times t ₂ and t _{6 is} not constant, since at the rear axle of the brake pressure in each case from the current recuperative braking torque 20 depends.

The in the 3 illustrated current curves of an exhaust valve on the rear axle and an actuator circuit-separating valve, which are provided in a brake system according to the invention, are described below in connection with a in 4 illustrated embodiment of a brake system 50 discussed.

An in 4 illustrated brake system according to the invention 50 in a preferred embodiment, one comprises a brake pedal 56 actuatable hydraulic cylinder-piston arrangement 62 , one with the cylinder-piston assembly 62 hydraulically interacting simulator 68 , one of the cylinder-piston assembly associated with it and hydraulically connectable pressure fluid reservoir 74 , one of an electronic control unit 80 electrically controllable pressure supply device 86 and a hydraulic pressure modulation device 92 , This includes one each wheel brake 98 . 100 . 102 . 104 associated intake valves 110 . 112 . 114 . 116 and exhaust valves 120 . 122 . 124 . 126 , The brake 98 . 100 are designed as front brakes and to a first brake circuit 94 connected, the brakes 102 . 104 are designed as rear-wheel brakes and a second brake circuit 96 connected. The brake circuit distribution is thus "black and white".

To brake pressure builds up the wheel brakes 98 . 100 . 102 . 104 Braking agent via supply lines 132 . 134 . 136 . 138 fed into the intake valves 110 . 112 . 114 . 116 are switched. The pressure reduction in the wheel brakes 98 . 100 . 102 . 104 takes place through discharge lines 140 . 142 . 144 . 146 into which the exhaust valves 120 . 122 . 124 . 126 are switched.

The hydraulic cylinder-piston arrangement 62 , as it were as a pedal decoupling unit for the brake system 50 acts, has two successively arranged pressure piston 150 . 152 on, the hydraulic chambers or pressure chambers 154 . 156 limit, which together with the pressure piston 150 . 152 a dual-circuit tandem master cylinder 160 form. The two pressure chambers 154 . 156 stand over in the pressure piston 150 . 152 trained radial bores 162 . 164 with the pressure medium reservoir 74 in connection. The holes 162 . 164 are by relative movements of the respective pressure piston 150 . 152 shut off. Via hydraulic lines 168 . 170 can from the pressure chambers 156 . 156 Brake fluid in the supply lines 130 . 132 . 134 . 136 be encouraged. Into the supply lines 130 . 136 are normally closed isolating valves 172 . 174 connected.

The simulator 68 is hydraulically designed with a simulator chamber 176 or a pressure chamber, a piston 178 in a simulator spring chamber 180 is movable, and one in the simulator chamber 180 arranged spring element 182 , The simulator chamber 172 is via a hydraulic line 186 with the pressure room 154 of the tandem master cylinder 160 hydraulically connected. In the normal operating mode of the brake system, the "brake-by-wire" mode, when the brake pedal is actuated 56 by the driver from the pressure room 154 Braking agent via the line 186 in simulator chamber 176 pushed, causing the piston 178 against the spring element 182 into the simulator spring chamber 180 is pressed. This gives the driver the most familiar and comfortable brake pedal feel possible.

The pressure delivery device 86 is designed as a single-cylinder hydraulic cylinder-piston assembly with a hydraulic pressure chamber 190 , in the need for active pressure build-up in the "brake-by-wire" mode when driving an electric motor 192 through the control unit 80 a piston 196 is shifted, whereby pressure medium through a line 200 in the brakes 98 . 100 . 102 . 104 can be directed. About a line 204 is the pressure chamber 190 with the pressure medium reservoir 74 with the interposition of a check valve 206 which opens when the pressure in the brake fluid reservoir 74 higher than in the pressure room 190 , ie negative pressure in the pressure chamber 190 prevails.

Two normally closed actuator circuit isolating valves 210 . 212 are in two of a common point of account 214 in the pipe 200 outgoing lines 216 . 218 connected.

In the normal operating mode "brake-by-wire", the two actuator circuit isolation valves 210 . 212 energized or opened and the two separating valves 172 . 174 closed. A simulator release valve 222 which is a check valve 230 is connected in parallel, opens.

Upon actuation of the brake pedal 56 is provided by a redundant displacement sensor 220 the path of the brake pedal measured (alternatively or in combination, for example, an angle sensor may be provided). The displacement sensor 220 is input side with the control unit 80 connected. From the signal of the travel sensor 220 the braking request of the driver is determined and thus a target braking torque. In order to realize this desired braking torque, the brake pressure build-up of the control unit 80 the pressure delivery device 86 driven.

By one - each redundant - pressure sensor 226 . 228 is the pressure in the pipe 170 or the line 200 measured and by means of the pressure supply device 86 regulated.

The hydraulic fallback level is automatically activated, for example, in the event of a power supply or on-board network failure, since then the current-lock closed actuator circuit isolating valves 210 . 212 Close, so no brake fluid back into the pressure chamber 190 can flow and the normally open isolation valves 172 . 174 open, allowing the driver by muscle power brake fluid from the pressure chambers 154 . 156 in the wheel brakes 98 . 100 . 102 . 104 can pump.

The brake system 50 is capable of allowing a precise pressure reduction on the rear axle, in particular yaw moments due to pressure variations between the rear brakes left and right are avoided.

These are the exhaust valve 124 and the actuator circuit isolation valve 212 as de-energized formed closed analog valves. For digital valves, the discrete switching states "on" or "open" and "off" or "closed" are provided. In the "closed" state, the valve completely blocks the hydraulic flow, while the valve in the "open" state predefines the hydraulic flow by a predetermined amount. In between there are no states of the valve. An analogous valve, on the other hand, allows the hydraulic flow to be controlled substantially continuously between full flow and no flow at all, this being preferably controlled by the magnitude of the current with which the analogue valve is operated.

In the time interval between t ₁ and t ₂ (see 3 ), in which hydraulic pressure is built up at the rear axle (brake pressure 46 ), is the exhaust valve 124 de-energized (current 242 is zero), so in the wheel brakes 102 and 104 Pressure can be built up. The actuator isolation valve 212 is energized (current 240 ), which causes it to open and out of the pressure chamber 190 Active brake fluid in the wheel brakes 102 . 104 can be promoted. At time t ₂ , the brake pressure 46 held constant until time t ₃ . The two valves 124 and 212 are de-energized, so that the flow of brake fluid is prevented by them and the pressure can be maintained.

In the time interval between t ₃ and t ₄ , the Aktuatorkreis-isolation valve remains 212 still de-energized, while for hydraulic pressure reduction on the rear axle, the exhaust valve 124 energized, the current strength 242 increases linearly between a first value at time t ₃ and a second value at time t ₄ in this time interval. By the desired differential pressure at the outlet valve 124 selected proportional linear increase in current 242 a pressure reducing function between the desired pressure in the discharge line 144 and the return to the pressure fluid reservoir 74 reached. Between times t ₄ and t ₅ is the hydraulic brake pressure 46 constant 0, so that both valves 124 . 212 are switched in de-energized state.

In the time interval between t ₅ and t ₆ is again hydraulic brake pressure 46 built to the declining recuperative braking torque 20 compensate. The outlet valve 124 therefore remains closed. The actuator circuit isolation valve 212 is contrasted with a linearly increasing current 240 energized, which increases linearly from a first value at t ₅ to a second value t ₆ .

In the time interval between t ₆ and t ₇ , the hydraulic brake pressure 46 diminished linearly until it reaches zero at time t ₇ ; the braking process is completed at this time. The outlet valve 124 is during this time interval with a linearly increasing current 242 which increases linearly between a first value t ₆ and a second value at t ₇ . The actuator circuit isolation valve 212 is switched off.

LIST OF REFERENCE NUMBERS

2

 X axis

8th

 y-axis

14

 Total braking torque

20

 recuperative braking torque

26

 hydraulic braking torque

32

 hydraulic braking torque

40

 brake pressure

56

 brake pressure

50

 braking system

56

 brake pedal

62

 Cylinder-piston arrangement

68

 simulator

74

 Pressure fluid reservoir

80

 Control unit

86

 Pressure supply device

92

 Pressure modulator

94

 first brake circuit

96

 second brake circuit

98

 wheel brake

100

 wheel brake

102

 wheel brake

104

 wheel brake

110

 intake valve

112

 intake valve

114

 intake valve

116

 intake valve

120

 outlet valve

122

 outlet valve

124

 outlet valve

126

 outlet valve

130

 supply line

132

 supply line

134

 supply line

136

 supply line

140

 discharge line

142

 discharge line

144

 discharge line

146

 discharge line

150

 pressure piston

152

 pressure piston

154

 pressure chamber

156

 pressure chamber

160

 Tandem master cylinder

162

 drilling

164

 drilling

168

 management

170

 management

172

 isolation valve

174

 isolation valve

176

 simulator chamber

178

 piston

180

 Simulator spring chamber

182

 spring element

186

 management

190

 pressure chamber

192

 electric motor

196

 piston

200

 management

204

 management

206

 check valve

210

 Actuator isolating valve

212

 Actuator isolating valve

216

 management

218

 management

220

 displacement sensor

222

 Simulator approver valve

226

 pressure sensor

228

 pressure sensor

230

 check valve

t ₁ , t ₂ , t ₃ , t ₄ , t ₅ , t ₆ , t ₇

 time

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102010040097 A1 [0004]

Claims (10)

Brake system ( 50 ) for motor vehicles, which in a "brake-by-wire" mode can be actuated both by the driver and independently of the vehicle driver and has a hydraulic fallback mode in which it can only be actuated by the driver, with two brake circuits ( 94 . 96 ), each brake circuit ( 94 . 96 ) two wheel brakes ( 98 . 100 . 102 . 104 ), with a brake pedal ( 56 ) for actuating a pedal decoupling unit ( 62 ), with a path detection device ( 220 ), the the actuation of the brake pedal ( 56 ) or a piston connected to the brake pedal, with a simulator ( 68 ) with a simulator release valve ( 222 ), which in the operating mode "brake-by-wire" gives the driver a brake pedal feel, and which is hydraulically disconnected in the fall-back level, with an electrohydraulic pressure supply device ( 86 ), which is controlled by a control unit ( 80 ) can be controlled to build up brake pressure, with a pressure modulation device ( 92 ) for setting wheel-specific brake pressures for each wheel brake ( 98 . 100 . 102 . 104 ) each have an inlet valve ( 110 . 112 . 114 . 116 ) and an outlet valve ( 120 . 122 . 124 . 126 ), and wherein two normally closed Aktuatorkreis separating valves ( 120 . 212 ) are provided, through which the pressure supply device ( 86 ) hydraulically with the two brake circuits ( 94 . 96 ), characterized in that an outlet valve ( 124 ) a rear wheel brake ( 102 ) as a normally closed analog outlet valve and an actuator circuit isolation valve ( 212 ) is designed as a normally closed analog Aktuatorkreis-separating valve. Brake system ( 50 ) according to claim 1, wherein exactly one analogous outlet valve ( 124 ) and exactly one analog Aktuatorkreis-isolation valve ( 212 ) are provided. Brake system ( 50 ) according to claim 2, wherein a first brake circuit, the two front brakes ( 98 . 100 ) and a second brake circuit the two rear brakes ( 102 . 104 ) and wherein the analogue outlet valve ( 124 ) a rear wheel brake ( 102 ) and wherein the analog Aktuatorkreis-isolation valve ( 212 ) is assigned to the second brake circuit. Brake system ( 50 ) according to one of claims 1 to 3, wherein the pedal decoupling unit ( 62 ) two pressure chambers ( 154 . 156 ), in each of which a piston ( 150 . 152 ) is arranged to be movable, and separating valves ( 172 . 174 ) are provided, by which the pressure chambers of the pedal decoupling unit hydraulically from the wheel brakes ( 98 . 100 . 102 . 104 ) can be separated. Brake system ( 50 ) according to one of claims 1 to 4, wherein the simulator ( 68 ) a pressure chamber ( 176 ) in the "brake-by-wire" mode of at least one of the pressure chambers ( 154 . 1569 the pedal decoupling unit brake fluid is moved. Brake system ( 50 ) according to claim 5, wherein in the simulator ( 68 ) to produce a pedal feel a piston ( 178 ) against an elastic spring element ( 182 ) is pressed. Brake system ( 50 ) according to claim 5 or 6, wherein the simulator release valve ( 222 ) a check valve ( 230 ) is connected in parallel. Method for operating a brake system ( 50 ) according to one of claims 3 to 7, characterized in that during the pressure reduction in the rear wheel brakes ( 102 . 104 ) the analogue exhaust valve ( 124 ) and the inlet valves ( 114 . 116 ) of the rear wheel brakes ( 102 . 104 ). A method according to claim 8, wherein for pressurizing the respective Aktuatorkreis-isolation valve ( 212 ) is driven. Method according to claim 8 or 9, wherein in a fallback stage the actuator circuit isolation valves ( 210 . 212 ) are closed and the simulator release valve is closed, so that brake fluid from the pressure chambers ( 154 . 156 ) of the pedal decoupling unit can be moved into the brake circuits.

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