Electro-hydraulic dual-system auxiliary power brake system

Abstract

In order to hydraulically separate the two brake circuits (I, II) of an electrohydraulic dual-system auxiliary power brake (1), the present invention proposes a piston-cylinder unit (2) having two pistons (4, 5), of which a first piston (4) is slidable by a first electric motor (6) via a screw transmission (7) and a second piston (5) is slidable by the pressure load of the first piston (4).

Description

[Technical Field]

[0001] The invention relates to an electrohydraulic dual-system auxiliary power braking system having the features of the preamble of claim 1 . [Background technology]

[0002] Electrohydraulic auxiliary power brake systems generate hydraulic brake pressure using auxiliary power to operate hydraulic wheel brakes. For this purpose, for example, a piston is moved in a cylinder by an electric motor via a screw transmission. A muscle-operable master brake cylinder can be provided to operate the auxiliary power brake system instead, for emergency braking, for example in the event of failure of the electric motor or its power supply.

[0003] Auxiliary power brake devices of this type are disclosed in Patent Documents 1 and 2, and are characterized in that the cylinder for the auxiliary power brake device is configured as a dual-system cylinder that hydraulically separates the connection of two brake circuits, like the master brake cylinder of a hydraulic dual-system vehicle brake device. Like the dual-system master brake cylinder, the cylinder for the auxiliary power brake device in the two patent documents also has two pistons arranged coaxially in tandem and spaced apart from each other within the cylinder, with the first of these two pistons, also called the primary piston or rod-type piston, sliding within the cylinder by an electric motor via a ball screw transmission, and the second piston, also called the secondary piston or floating piston, being loaded by the hydraulic brake pressure generated by the first piston, thereby generating the same brake pressure. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] European Patent Publication No. 1970271 [Patent Document 2] European Patent Publication No. 2641788 Summary of the Invention

[0005] The electrohydraulic dual-system auxiliary power brake system according to the present invention, having the features of the preamble of claim 1, comprises a piston-cylinder unit in whose cylinder two pistons are arranged, similar to those in a dual-system master brake cylinder operated by muscle power. To generate hydraulic brake pressure using auxiliary power, a first of the two pistons can slide in the cylinder of the piston-cylinder unit by a first electric motor via a rotational-translation transmission, for example, a screw transmission. The back surface of the second of the two pistons facing the first piston is subjected to the brake pressure generated by the first piston, and the second piston either slides in the cylinder of the piston-cylinder unit in the same way, or generates hydraulic brake pressure on its front surface opposite the first piston. The back surface of the second piston is the end surface facing the first piston or the piston face of the second piston, and the front surface is the end surface or piston face of the second piston opposite the first piston. When the first piston slides in the cylinder of the piston-cylinder unit, if no pressure is generated due to, for example, a leak, the first piston will collide with the second piston as it slides, causing the second piston to mechanically slide in the cylinder.

[0006] The two brake circuits are hydraulically separated from one another by a second piston and connected to the cylinder of the piston-cylinder unit, for example in a dual-path master brake cylinder.

[0007] To increase the operability of the auxiliary power brake system according to the present invention, the auxiliary power brake system has an auxiliary power brake pressure generator, which generates hydraulic brake pressure independently of and instead of the brake pressure generated by the piston-cylinder unit. This makes the auxiliary power brake system according to the present invention suitable for autonomous driving. The auxiliary power brake pressure generator can be, for example, a hydraulic pump of the slip control system of the auxiliary power brake system. In a preferred embodiment, the auxiliary power brake system has one hydraulic pump in each brake circuit.

[0008] According to the present invention, for example, the auxiliary power brake pressure generators are connected to the brake fluid tank by check valves, which allow the auxiliary power brake pressure generators to draw brake fluid from the brake fluid tank, bypassing the piston-cylinder units, to generate hydraulic brake pressure. The auxiliary power brake pressure generators may be connected to the brake fluid tank by one common check valve. Preferably, one check valve is provided for each auxiliary power brake pressure generator or for each brake circuit to hydraulically separate the brake circuits. Configurations of the present invention in which only one auxiliary power brake pressure generator is connected to the brake fluid tank by a check valve are also possible. The check valves allow the auxiliary power brake pressure generators to generate hydraulic brake pressure even if, due to a malfunction, one or both pistons of the piston-cylinder units become stuck in their cylinders in the forward-sliding position that hydraulically separates the brake circuits from the hydraulic tank.

[0009] The cylinder of the piston-cylinder unit is likewise connected to a brake fluid tank or, if necessary, to a separate brake fluid tank. The cylinder may be connected to the brake fluid tank directly, without an intervening check valve, by a check valve connecting the auxiliary power brake pressure generator to the brake fluid tank, or by a separate check valve. The invention does not exclude other possibilities for connecting the cylinder of the piston-cylinder unit to the brake fluid tank.

[0010] The dependent claims are subject to implementations and preferred embodiments of the invention set out in the independent claims.

[0011] According to the present invention, the auxiliary power brake device can be configured without a muscle-operable master brake cylinder (claim 8).

[0012] All features disclosed in the specification and drawings may be realized individually or in essentially any combination in the embodiments of the present invention. Configurations of the present invention having only one or several features, but not all of the embodiments or claims of the present invention, are fundamentally possible. For example, configurations of the auxiliary power brake device according to the present invention are also possible in which a check valve is not provided between the brake fluid tank and the auxiliary power brake pressure generator. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a hydraulic circuit diagram of an embodiment of an electrohydraulic auxiliary power braking device according to the present invention; [Figure 2] 1 is a hydraulic circuit diagram of an embodiment of an electrohydraulic auxiliary power braking device according to the present invention; DETAILED DESCRIPTION OF THE INVENTION

[0014] The invention will be explained in more detail below using embodiments shown in the drawings.

[0015] The electrohydraulic dual-system auxiliary power brake system 1 shown in FIG. 1 has a piston-cylinder unit 2 with a cylinder 3 in which two pistons 4, 5, similar to those in a conventional dual-system master brake cylinder operable by muscle power, are slidably arranged. A first piston 4 of the two pistons is slidably moved in the cylinder 3 by a first electric motor 6 via a screw transmission 7 to generate hydraulic brake pressure using auxiliary power. In this embodiment, the screw transmission 7 is a ball screw transmission. The screw transmission 7 may generally be understood as a rotational / translational motion conversion transmission device. A reduction gear, particularly a planetary gear (not shown), may be arranged between the first electric motor 6 and the screw transmission 7. According to the invention, the first electric motor 6, the screw transmission 7 and (if provided) the reduction gear are arranged coaxially to the piston-cylinder unit 2, i.e. coaxially to the cylinder 3 and coaxially to the two pistons 4, 5, although the invention does not fundamentally exclude other arrangements of the first electric motor 6, the screw transmission 7 and, if applicable, the reduction gear in relation to the piston-cylinder unit 2, the cylinder 3 and the pistons 4, 5.

[0016] The hydraulic braking pressure generated by the first piston 4 in the cylinder 3 acts on the end side or piston face of the second piston 5 facing the first piston 4, which is referred to herein as the back side 8 of the second piston 5, causing the second piston 5 to slide in the cylinder 3 and generate hydraulic braking pressure on the side or piston face opposite the first piston 4, which is referred to herein as the front side 9 of the second piston 5.

[0017] If the first piston 4 does not generate pressure in the cylinder 3 when sliding (for example due to a leak), it will collide with the second piston 5 when sliding, and the abutment of the first piston 4 will cause the second piston 5 to slide mechanically, so in this case the second piston 5 will also generate hydraulic braking pressure in the cylinder 3 with its front surface 9.

[0018] A pressureless brake fluid reservoir 10 is arranged in the cylinder 3 of the piston-cylinder unit 2, to which the cylinder 3 is connected between the two pistons 4, 5 and to the front face 9 of the second piston 5.

[0019] The auxiliary power brake device 1 according to the present invention is configured as a dual-system brake device having two brake circuits I and II and, in the illustrated embodiment, four hydraulic wheel brakes 11, with two of the four wheel brakes 11 connected to one of the brake circuits I and II. The first brake circuit I of the two brake circuits is connected to the cylinder 3 of the piston-cylinder unit 2 between the two pistons 4 and 5 so that the first brake circuit I is loaded with hydraulic brake pressure generated when the first piston 4 slides in the cylinder 3.

[0020] The second brake circuit II is 5 9 at the front of the piston-cylinder unit 2 1 and is connected to the cylinder 3 of the second piston 5 and is subjected to a brake pressure generated by the second piston 5 or which prevails in the cylinder 3 on a front face 9 of the second piston 5 .

[0021] The second piston 5 has its back surface 8 connected to the first brake circuit I and its front surface 9 connected to the second brake circuit II by the cylinder 3 of the piston-cylinder unit 2, and this second piston 5 hydraulically separates the two brake circuits I, II from each other.

[0022] The auxiliary power braking system 1 has a slip control system 12 with an intake valve 13 and an outlet valve 14 for each wheel brake 11. The intake valves 13 control the slip of the wheel brakes. 11are connected to the cylinder 3 of the piston-cylinder unit 2, and in each of the brake circuits I and II, a separate valve 15 is arranged between the cylinder 3 and the intake valve 13. The first brake circuit I is connected to the cylinder 3 between the two pistons 4 and 5 by its separate valve 15, and the second brake circuit II is connected to the cylinder 3 at the front face 9 of the second piston 5 by its separate valve 15.

[0023] The wheel brakes 11 are connected to the suction side of a hydraulic pump 16 in each brake circuit I, II by means of a discharge valve 14. The two hydraulic pumps 16 of the two brake circuits I, II can be driven by a common second electric motor 17. The hydraulic pumps 16 with their associated second electric motors 17 are components of the slip control system 12 and form an auxiliary power brake pressure generator 18. The discharge sides of the hydraulic pumps 16 are connected between the separator valve 15 and the suction valve 13. On their suction sides, hydraulic pumps 16 each have a hydraulic accumulator 19 for intermediate storage of brake fluid from the wheel brakes 11 during slip control. Furthermore, the suction sides of the hydraulic pumps 16 are connected to cylinder 3 of the piston-cylinder unit 2 by means of a suction valve 20. Thus, similar to the separate valve 15, brake circuit I is connected to cylinder 3 between the two pistons 4, 5 by its suction valve 20, and brake circuit II is connected to cylinder 3 at the front 9 of the second piston 5 by its suction valve 20.

[0024] The components of the slip control system 12 are the intake valve 13, the discharge valve 14, the separate valve 15, and the intake valve 20 In this embodiment, the connecting valve 29 is a 2-port 2-position directional control valve, in which the suction valve 13, the separate valve 15 and the connecting valve 29 are open in their non-current basic positions, and the discharge valve 14 and the suction valve 20are closed in their current-free basic position. Wheel-individual brake pressure control is possible in the wheel brakes 11 by means of a slip control system 12. In particular, slip controls such as anti-lock control, traction slip control and vehicle dynamic control, which are commonly referred to by the abbreviations ABS, ASR and FDR, are possible. Such slip controls are known and will not be described in detail here.

[0025] Redundancy is ensured by the hydraulic pump 16 of the slip control system 12, which forms an auxiliary power brake pressure generator 18, drivable by a second electric motor 17. This means that hydraulic brake pressure is supplied to the piston-cylinder unit 18 by the hydraulic pump 16 of the slip control system 12. 2 This can be generated selectively by sliding the pistons 4, 5 in the cylinder 3, so that the operability of the auxiliary power brake device 1 according to the present invention is guaranteed even in the event of failure of the first electric motor 6, and therefore the auxiliary power brake device 1 is also suitable for autonomous driving.

[0026] As in the master brake cylinder, the cylinder 3 of the piston-cylinder unit 2 is connected to a brake fluid reservoir 10 such that when the pistons 4, 5 are slid from their basic positions to generate brake pressure, the pistons 4, 5 hydraulically isolate the cylinder 3 from the brake fluid reservoir 10.

[0027] The two brake circuits I, II are connected to the brake fluid tank 10 by a check valve 21, which is arranged between the brake fluid tank 10 and the separating valve 15 on the one hand and between the brake fluid tank 10 and the intake valve 20 on the other hand, and allows a flow from the brake fluid tank 10 towards the brake circuits I, II, i.e. towards the separating valve 15 and the intake valve 20. The check valve 21 allows the hydraulic pump 16 of the slip control system 12 to operate in the direction of the intake valve 20. 20is open, brake fluid can be drawn from the brake fluid reservoir 10 by passing by the cylinder 3 of the piston-cylinder unit 2. This allows brake pressure to be generated by auxiliary power, in particular if, for example, the pistons 4, 5 in the cylinder 3 of the piston-cylinder unit 2 are stuck or otherwise locked in the cylinder 3 in a forward-pushed position that hydraulically separates the brake fluid reservoir 10 from the cylinder 3.

[0028] The check valve 21 also connects the cylinder 3 of the piston-cylinder unit 2 to the brake fluid tank 10, so that the pistons 4, 5 can suck brake fluid from the brake fluid tank 10 into the cylinder 3 on the return stroke. The invention does not exclude configurations of the auxiliary power braking device 1 without the check valve 21 or in which the check valve 21 is provided in only one of the two brake circuits I, II (not shown).

[0029] A connecting valve 29 is arranged hydraulically parallel to the check valve 21, by means of which, when the connecting valve 29 is open, the brake fluid is displaced by the first piston 4 from the piston-cylinder unit 2 and can be pumped from the brake circuit I by the hydraulic pump 18 from the pressure regulating module 23 into the brake fluid tank 10. The connecting valve 29 is not essential to the invention.

[0030] The auxiliary power brake device 1 may also be configured such that the check valve 21 is not provided in the brake circuit II that is loaded with brake pressure by the second piston 5. In this case, the brake circuit II is directly connected to the brake fluid tank 10 (not shown).

[0031] 2, a check valve 21 connects the brake fluid tank 10 to the cylinder 3 of the piston-cylinder unit 2 in such a way that the cylinder 3 is always in communication with the brake fluid tank 10 via the check valve 21. In other words, when the two pistons 4, 5 are slid or being slid from their basic position, the pistons 4, 5 separate the connection between the brake fluid tank 10 and the cylinder 3 by the check valve 21 when they slide within the cylinder 3, just as the direct connection between the brake fluid tank 10 and the cylinder 3 is closed when the two pistons 4, 5 slide within the cylinder 3. In this configuration of the invention, too, the hydraulic pump 16 of the slip control system 12 forming the auxiliary power brake pressure generator 18 can suck brake fluid from the brake fluid tank 10 by means of the cylinder 3 of the piston-cylinder unit 2 and the check valve 21 when the pistons 4, 5 are caused to slide in the cylinder 3, so that in this configuration of the invention, too, hydraulic brake pressure can be generated by the hydraulic pump 16 when the pistons 4, 5 that slide in the cylinder 3 are fixed so as not to slide in the cylinder 3. Apart from the described arrangement of the check valve 21, the auxiliary power brake device 1 according to the invention is the same in the two drawings, and reference is made to the description of Figure 1 for the description of Figure 2.

[0032] In an embodiment of the present invention, the auxiliary power braking device 1 is configured in a modular manner, with the piston-cylinder unit 2 housed in a module referred to herein as a pressure generation module 22, and the slip control system 12 housed in another module referred to herein as a pressure regulation module 23. For a non-modular configuration of the auxiliary power braking device 1, the piston-cylinder unit 2 and the slip control system 12 may be housed in one common module (not shown).

[0033] For redundancy reasons, the pressure generating module 22 and the pressure regulating module 23 each have their own electrical power supply 24 and their own electronic control unit 25, so that the pressure generating module 22 or the pressure regulating module23 In the event of a failure of the auxiliary power braking system 10 or a failure of the slip control system 12, the operability of the auxiliary power braking system 1 is guaranteed.

[0034] A piston reset spring 26 is arranged in the cylinder 3 of the piston-cylinder unit 2 on the front surface 9 of the second piston 5, and this piston reset spring 26 biases the second piston 5 to its basic position. Although no piston reset spring is provided for the first piston 4, the present invention does not exclude such a piston reset spring. In this embodiment, the first piston 4 is connected to a screw transmission 7, which may generally be interpreted as a rotational / translational motion conversion transmission, with such high tensile strength that the first piston 4 can be slid in the cylinder 3 via the screw transmission 7 by the first electric motor 6 not only to generate brake pressure but also in the reverse direction.

[0035] As a target value transmitter for the brake pressure to be generated by the piston-cylinder unit 2, the auxiliary power brake system 1 has a stroke sensor 28 or, optionally, a spring-loaded foot brake pedal 27 equipped with a force sensor. For redundancy, multiple stroke or force sensors, or one stroke and one force sensor, may be provided (not shown). Basically, either a single, muscle-operable master brake cylinder is provided, which can selectively apply hydraulic brake pressure to one of the two brake circuits I and II to generate pressure in the piston-cylinder unit 2, or a dual master brake cylinder is provided, which can apply pressure to both brake circuits I and II (not shown). Such a master brake cylinder allows the auxiliary power brake system 1 to be operated by muscle force, especially in the event of a failure of the first piston-cylinder unit 2 or of the hydraulic pump 16 of the slip control system 12. In the illustrated embodiment, the auxiliary power brake system 1 does not have a master brake cylinder and is not muscle-operable. However, in order to enable selective generation of brake pressure by the piston-cylinder unit 2 or the hydraulic pump 16, the auxiliary power brake device 1 can also be used for autonomous driving, in which the auxiliary power brake device 1 must be able to operate autonomously without operation by the vehicle driver.

[0036] In order to reset the pistons 4, 5 in the cylinders 3 of the piston-cylinder units 2 in the event of a malfunction, according to the invention, brake fluid is pumped from the hydraulic accumulator 19 by the hydraulic pump 16 of the auxiliary power brake pressure generator 18 through the opened separate valve 15 into the cylinders 3 of the piston-cylinder units 2, where a brake pressure can be generated that applies pressure to the pistons 4, 5 in the direction toward the first electric motor 6. If there is not enough brake fluid in the hydraulic accumulator 19, the brake fluid is pumped from the brake fluid tank 10 by the hydraulic pump 16 beforehand when the separate valve 15 is closed, through the intake valve 20, which must be opened, into the wheel brakes 11, from where it flows into the hydraulic accumulator 19 after the intake valve 13 and the intake valve 20 are closed and after the discharge valve 14 is opened. This process, i.e., the hydraulic pump 16 sucks brake fluid from the brake fluid tank 10 and pumps brake fluid into the hydraulic accumulator 19 in order to pump enough brake fluid into the cylinders 3 and generate sufficient pressure there for resetting the pistons 4, 5. 19 The pressure can be alternately pumped from the first piston 4 to the cylinder 3 of the piston-cylinder unit 2 several times. This method can be carried out simultaneously in the two brake circuits I, II or separately in each brake circuit I, II. Preferably, when the first piston 4 is reset, the separating valve 15 of the other brake circuit II is closed, so that at the same time, the second piston 5 does not force brake fluid out of the cylinder 3 due to pressure load, and the side facing the first piston 4 does not or hardly yields to pressure. [Explanation of symbols]

[0037] 1. Dual-system auxiliary power brake device 2 Piston Cylinder Unit 3 cylinders 4 First Piston 5 Second Piston 6. First Motor 7 Rotation / translation motion conversion transmission device, screw transmission device 8 Back 9 Front 10 Brake fluid tank 11 Wheel brake 12 Slip control system 13 Intake valve 14 Discharge valve 15 Separate valve 16 Hydraulic pump 17 Second electric motor 18 Auxiliary power brake pressure generator 19 Hydraulic accumulator 20 Suction valve 21 Check valve 22 Pressure Generation Module 23 Pressure Regulation Module 24 Power supply section 25 Electronic control device 26 Piston reset spring 27 Foot brake pedal 28 Stroke sensor 29 Connection valve I, II Brake circuit

Claims

1. An electrohydraulic dual-system auxiliary power brake device, comprising a brake fluid tank (10) and a piston-cylinder unit (2), a cylinder (3) of the piston-cylinder unit (2) connected to the brake fluid tank (10), the piston-cylinder unit (2) having a first piston (4) and a second piston (5) slidable in the cylinder (3) of the piston-cylinder unit (2) by a first electric motor (6) via a rotation / translation motion conversion transmission (7) to generate hydraulic brake pressure, the second piston (5) being driven by hydraulic pressure load from the first piston (4). or the two pistons (4, 5) are mechanically slidable in the cylinder (3) by abutting against each other, and the system has two brake circuits (I, II) hydraulically separated from each other by the second piston (5) and connected to the cylinder (3) of the piston-cylinder unit (2), and an auxiliary power brake pressure generator (18), wherein the auxiliary power brake pressure generator (18) is capable of generating hydraulic brake pressure in one of the brake circuits (I, II) of the auxiliary power brake device (1) instead of generating brake pressure by the piston-cylinder unit (2), The auxiliary power brake device (1) has a check valve (21), and the auxiliary power brake pressure generator (18) is connected to the brake fluid tank (10) by the check valve (21), An electrohydraulic dual-system auxiliary power brake device, characterized in that the first piston (4) does not have a piston reset spring.

2. 2. An electrohydraulic dual-system auxiliary power brake system according to claim 1, characterized in that the auxiliary power brake system (1) has one auxiliary power brake pressure generator (18) in each of the brake circuits (I, II), which is connected to the brake fluid tank (10) by a check valve (21).

3. 3. The electrohydraulic dual-system auxiliary power brake system according to claim 1, wherein the first piston (4) is connected to the rotational / translational motion conversion transmission (7) in a manner that is strong against tension and strong against compression so that the first piston (4) can slide in the cylinder (3) of the piston-cylinder unit (2) in two opposite directions via the rotational / translational motion conversion transmission (7) by the first electric motor (6).

4. 3. The electrohydraulic dual-system auxiliary power brake system according to claim 1, wherein the auxiliary power brake system (1) comprises a slip control system (12), and the slip control system (12) comprises one or more auxiliary power brake pressure generators (18).

5. 3. The electrohydraulic dual-system auxiliary power brake system according to claim 1, wherein the first electric motor (6) and the rotational / translational motion conversion transmission device (7) are arranged coaxially with respect to the cylinder (3) of the piston-cylinder unit (2).

6. 5. The electrohydraulic dual-system auxiliary power brake system according to claim 4, characterized in that the auxiliary power brake system (1) has redundant power supplies (24) and / or redundant electronic control devices (25) for the first electric motor (6) of the piston-cylinder unit (2) and for the auxiliary power brake pressure generator (18) or the slip control system (12).

7. 3. The electrohydraulic dual-system auxiliary power brake system according to claim 1, wherein the auxiliary power brake system (1) does not have a muscle-operated device.

8. A method for resetting pistons (4, 5) of an electrohydraulic dual-system auxiliary power brake device (1), comprising: The electrohydraulic dual-system auxiliary power brake device includes a brake fluid tank (10) and a piston-cylinder unit (2), a cylinder (3) of which is connected to the brake fluid tank (10), and the piston-cylinder unit (2) includes a first piston (4) and a second piston (5) which are slidable in the cylinder (3) of the piston-cylinder unit (2) by a first electric motor (6) via a rotation / translation motion conversion transmission (7) to generate hydraulic brake pressure, and the second piston (5) is mechanically slidable in the cylinder (3) by the hydraulic pressure load from the first piston (4) or by the two pistons (4, 5) abutting against each other, and the second piston (5) is hydraulically slidable in the cylinder (3) by the hydraulic pressure load from the first piston (4) or by the two pistons (4, 5) abutting against each other. the auxiliary power brake device (1) has two brake circuits (I, II) and an auxiliary power brake pressure generator (18) separated from each other and connected to the cylinder (3) of the piston-cylinder unit (2), and the auxiliary power brake pressure generator (18) is capable of generating hydraulic brake pressure in one of the brake circuits (I, II) of the auxiliary power brake device (1) instead of generating brake pressure by the piston-cylinder unit (2); the auxiliary power brake device (1) has a check valve (21) by which the auxiliary power brake pressure generator (18) is connected to the brake fluid tank (10); and the auxiliary power brake device (1) has one auxiliary power brake pressure generator (18) in each of the brake circuits (I, II) connected to the brake fluid tank (10) by the check valve (21), 1. A method for resetting pistons (4, 5) of an electrohydraulic dual-system auxiliary power brake system (1), characterized in that the auxiliary power brake pressure generator (18) is connected to the cylinder (3) by a valve (15) and loads at least one of the pistons (4, 5) with hydraulic pressure.

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