Slip-controlled hydraulic vehicle braking system

Abstract

Slip-controlled hydraulic vehicle braking system with a master brake cylinder (2) to which a brake circuit I, II is connected via a separating valve (4), with a wheel brake (5) which is connected via a pressure build-up valve (6) to the separating valve (4) and via a pressure reduction valve (7) to a hydraulic accumulator (8), a hydraulic pump (9) whose suction side is connected on a side facing away from the wheel brake (5) to the pressure reduction valve (7) and to the hydraulic accumulator (8) and whose pressure side is connected between the separating valve (4) and the pressure build-up valve (6), and with a further hydraulic pump (10) whose suction side is connected to the master brake cylinder (2) and whose pressure side is connected between the separating valve (4) and the pressure build-up valve (6), wherein the hydraulic pumps (9, 10) have a common drive motor (11), characterized in that the further hydraulic pump (10), whose suction side is connected to the master brake cylinder (2),a larger delivery volume than a single hydraulic pump (9).

Description

[0001] The invention relates to a slip-controlled hydraulic vehicle braking system with the features of the preamble of claim 1. State of the art

[0002] German patent application DE 195 01 760 A1 discloses a slip-controlled hydraulic vehicle braking system with two brake circuits connected to a tandem or dual-circuit master cylinder. Each brake circuit is connected to the master cylinder via a shut-off valve, which allows the brake circuit to be hydraulically disconnected from the master cylinder during slip control. Each wheel brake is connected to the shut-off valve of its respective brake circuit via a pressure build-up valve. A pressure release valve is assigned to each wheel brake, connecting it to a hydraulic accumulator and the suction side of a hydraulic pump. A pressure side of the hydraulic pump is connected between the shut-off valve and the pressure build-up valves. The hydraulic accumulator serves to temporarily store brake fluid when the wheel brake pressures are reduced during slip control by opening the pressure release valves.The pressure build-up valve and the pressure drop valve of each wheel brake form a pressure modulation valve assembly, which allows wheel brake pressures to be individually regulated for slip control. Wheel brake pressure modulation is known per se and will not be explained in detail here. The hydraulic pump can pump brake fluid that has flowed out of the wheel brakes by opening the pressure drop valves back towards the master cylinder or back into the wheel brakes for re-pressure build-up via the pressure build-up valves. Furthermore, the known vehicle brake system has a suction valve in each brake circuit that connects the suction side of the hydraulic pump to the master cylinder. By opening the suction valve, the hydraulic pump can draw brake fluid from the master cylinder.

[0003] The hydraulic pumps, also sometimes referred to as return pumps, of such slip-controlled hydraulic vehicle braking systems are subject to diametrically opposed requirements: When the hydraulic pump is driven by the vehicle's braking system, i.e., when brake pressure is built up by the master cylinder, to activate the anti-lock braking system, it must pump against the pressure generated by the master cylinder, with the pressure on the suction side of the hydraulic pump being low. If one or more vehicle wheels lock up under optimal road and tire conditions, the brake pressure generated by the master cylinder, which causes one or more of the vehicle wheels to lock, is very high. The hydraulic pump must pump against this pressure and must not stall.

[0004] The diametrically opposite scenario is the build-up of pressure to actuate one or more wheel brakes when the master cylinder is not actuated and the vehicle's braking system is depressurized. This is typical for traction control, i.e., the automatic braking of a driven wheel that spins when a vehicle starts moving. Anti-skid control, i.e., the braking of one or more wheels to counteract a tendency to skid, can also occur when the master cylinder is not actuated and the braking system is consequently depressurized. Here, a very rapid, though not necessarily high, build-up of brake pressure to brake one or more wheels is crucial, because the faster the targeted braking intervention occurs at one or more wheels, the more effectively a tendency to skid can be countered.The braking intervention must occur within a maximum of approximately one to two tenths of a second; if it takes longer, especially longer than approximately three to five tenths of a second, a skid can usually no longer be prevented. These times are examples and depend on the circumstances, including the specific vehicle, tires, and road conditions.

[0005] The diametrically opposed requirements result in an inherently oversized hydraulic pump, which must both operate against very high back pressure and deliver a large flow rate with little or no back pressure. Furthermore, the hydraulic pump must be self-priming to build up pressure in the unpressurized vehicle brake system. These requirements necessitate a powerful, and therefore large and heavy, electric motor to drive the hydraulic pump, which in turn requires a correspondingly powerful power supply.

[0006] A slip-controlled hydraulic vehicle braking system according to the features of the preamble of claim 1, which comes closest to the invention, is known from EP 1 733 942 A1.

[0007] In addition to the features described above, this vehicle braking system is equipped with an additional hydraulic pump per brake circuit. The suction side of this pump is connected to the master brake cylinder, and the pressure side is connected to the brake circuit between the isolating valve and the pressure build-up valve. The hydraulic pumps also share a common drive motor. Disclosure of the invention

[0008] The slip-controlled hydraulic vehicle braking system with the features of claim 1 can be a single-circuit or a multi-circuit, in particular a dual-circuit, vehicle braking system. It comprises a single-circuit, multi-circuit, or dual-circuit master brake cylinder to which the brake circuit(s) are hydraulically connected separately from one another. Each brake circuit is connected to the master brake cylinder via its own isolation valve. Each brake circuit has one or more wheel brakes, each of which is assigned a pressure build-up valve through which it is connected to the isolation valve. Furthermore, each wheel brake is assigned a pressure release valve through which the wheel brakes are jointly connected to a hydraulic accumulator and to a suction side of a hydraulic pump, the pressure side of which is connected between the isolation valve and the pressure build-up valves.Furthermore, the vehicle's braking system features an additional hydraulic pump in each brake circuit. The pressure side of this pump, like the pressure side of the first hydraulic pump, is connected between the isolating valve and the pressure build-up valves. The suction side of this additional hydraulic pump is connected to the master cylinder. An intake valve connecting the suction side of either hydraulic pump to the master cylinder is not provided, but its existence is not excluded.

[0009] The return of brake fluid, which is released from the wheel brakes to reduce pressure by opening the pressure-reducing valves during an anti-lock braking system (ABS), is accomplished by a single hydraulic pump whose suction side is connected to the hydraulic accumulator and the pressure-reducing valves. Since the master cylinder is actuated during ABS activation, and the vehicle's braking system is therefore pressurized, the single hydraulic pump must, in the described case, pump against the pressure prevailing in the vehicle's braking system. It is therefore preferably designed for a high pressure build-up (claim 2), but can have a comparatively low delivery volume. The second hydraulic pump runs simultaneously, at least when driven together with the first. Its suction side is subject to the brake pressure generated by the master cylinder; therefore, it pumps with little or no hydraulic load.If the separating valve is open, the pump circulates through the separating valve. In the described case, the additional hydraulic pump, which runs without load or almost without load, does not significantly increase the required drive power of the two hydraulic pumps and therefore does not necessitate a more powerful drive motor.

[0010] To achieve rapid pressure build-up when the master brake cylinder is not actuated and the vehicle brake system is depressurized, the isolating valve is closed, and the additional hydraulic pump, whose suction side is connected to the master brake cylinder, is driven. Since rapid pressure build-up is important for the anti-lock braking system as explained above, the additional hydraulic pump, according to the invention, has a larger delivery volume than the single hydraulic pump used for returning brake fluid in an anti-lock braking system. Because the pressure build-up valves in one or more wheel brakes are open and all pressure release valves are closed for pressure build-up, the single hydraulic pump runs without load in this case without significantly increasing the drive torque required to drive both hydraulic pumps. The necessary mechanical drive power is not significantly increased in this case by the single hydraulic pump running without load.

[0011] The dependent claim relates to an advantageous further development of the invention specified in claim 1. Brief description of the drawing

[0012] The invention is explained in more detail below with reference to an embodiment illustrated in the drawing. The single figure shows a hydraulic circuit diagram of a slip-controlled hydraulic vehicle braking system according to the invention. embodiment of the invention

[0013] The slip-controlled hydraulic vehicle braking system 1 shown in the drawing according to the invention is a dual-circuit vehicle braking system with two brake circuits I, II, which are hydraulically separated from each other and connected to a dual-circuit master brake cylinder 2, which can also be referred to as a tandem master brake cylinder. The master brake cylinder 2, and thus the vehicle braking system 1, can be actuated by muscle power; in the exemplary embodiment, it has a vacuum brake booster 3 and is therefore auxiliary-operated, i.e., by muscle power and external force from the brake booster 3.

[0014] The two brake circuits, I and II, are identical in design and are explained below using brake circuit I, shown on the right, as an example. Brake circuit I is connected to the master brake cylinder 2 via a separating valve 4. Two wheel brakes 5 are assigned to brake circuit I and are connected to the separating valve 4 via pressure build-up valves 6. Each wheel brake 5 has its own pressure build-up valve 6. Like the separating valve 4, the pressure build-up valves 6 are designed as 2 / 2-way solenoid valves that are open in their de-energized state. Each wheel brake 5 has a pressure release valve 7, through which the wheel brakes 7 are connected to a hydraulic accumulator 8 and the suction side of a hydraulic pump 9. The pressure side of the hydraulic pump 9 is connected between the separating valve 4 and the pressure build-up valves 6.

[0015] The pressure-reducing valves 7 are designed as 2 / 2-way solenoid valves that are closed in their de-energized state. The wheel brakes 5 are connected via their pressure-reducing valves 7 to the hydraulic accumulator 8 and the suction side of the hydraulic pump 9. The pressure-building valve 6 and the pressure-reducing valve 7 of each wheel brake 5 can also be considered a brake pressure modulation valve arrangement, with which brake pressures in the wheel brakes 5 can be individually controlled. The wheel brake pressure control is known per se and will not be explained in detail here. It is possible to replace the pressure-building valve 6 and the pressure-reducing valve 7 of each wheel brake 5 with a common 3 / 3-way solenoid valve (not shown).

[0016] Brake circuit I has an additional hydraulic pump 10, whose suction side is connected to the master brake cylinder 2 and whose pressure side, like the pressure side of the first hydraulic pump 9, is connected between the isolating valve 4 and the pressure build-up valves 6. Both hydraulic pumps 9 and 10 of brake circuits I and II are driven by a common electric motor, the drive motor 11. The first hydraulic pump 9, whose suction side is connected to the pressure reduction valves 7, has a high pressure build-up capacity; that is, it is able to pump against a high pressure on its pressure side, even if its suction side is unpressurized or has only a low pressure. This is achieved, among other things, by a small displacement volume, for example, in a piston pump by a small pump piston and / or a small piston stroke.The drive motor 11 is designed to drive the hydraulic pumps 9 of both brake circuits I and II even at the highest pressures generated by the brake-assisted master cylinder 2, without stalling. The pressure build-up of one hydraulic pump 9 is greater than the pressure build-up of the other hydraulic pump 10. As already mentioned, brake circuit II is constructed identically to brake circuit I as described above.

[0017] The additional pump 10 has a large delivery volume, which, for example in a piston pump, is achieved through a large piston diameter and / or a long piston stroke. The delivery volume of the additional hydraulic pump 10 is greater than the delivery volume of the first hydraulic pump 9.

[0018] In an anti-lock braking system (ABS), the brake pressures in the wheel brakes 5 are individually regulated by the pressure build-up valves 6 and the pressure reduction valves 7. The isolating valve 4 can be closed. This is generally known and will not be explained in detail here. In the anti-lock braking system, the hydraulic pumps 9 and 10 are driven by the drive motor 11. One hydraulic pump 9, whose suction side is connected to the pressure reduction valves 7, pumps brake fluid. This fluid is released to reduce the pressure in the wheel brakes 5 by opening the pressure reduction valves 7 and, if necessary, temporarily stored in the hydraulic accumulator 8. The fluid is then returned to the wheel brakes 5 so that the wheel brake pressures can be increased again by opening the pressure build-up valves 6, or, if the isolating valve 4 is open, it flows through the master brake cylinder 2.The one hydraulic pump 9 must pump against the brake pressure prevailing in the vehicle brake system 1, which is generated or has been generated by the auxiliary master brake cylinder 2.

[0019] The suction side of the second hydraulic pump 10 is subject to the pressure generated by the master brake cylinder 2, so that the second hydraulic pump 10 runs almost without load alongside the first hydraulic pump 9. When the separating valve 4 is open, the second hydraulic pump 10 circulates fluid. The mechanical drive power required for the second hydraulic pump 10 is so low that it does not stop the drive motor 11.

[0020] To build up pressure in the vehicle brake system 1 when the master brake cylinder 2 is not actuated, and consequently the vehicle brake system 1 is depressurized, the isolating valve 4 is closed, and the hydraulic pumps 9 and 10 are driven by the drive motor 11. The second hydraulic pump 10, whose suction side is connected to the master brake cylinder 2, draws brake fluid from the master brake cylinder 2 and delivers it to the wheel brakes 5. Pressure build-up valves 6 of wheel brakes 5 that are not to be actuated are closed, while pressure build-up valves 6 of wheel brakes 5 that are to be actuated remain open. Due to the large delivery volume of the second pump 10 and the lack of back pressure on the pressure side of the second hydraulic pump 10, at least initially, the brake pressure rises rapidly.One hydraulic pump 9 does not pump brake fluid because the pressure relief valves 7 are closed and the hydraulic accumulator 8 is empty; it runs almost without load along with the other hydraulic pump 10. Furthermore, at least at the beginning of the pressure build-up, there is no back pressure on the pressure side of one hydraulic pump 9 that could slow it down.

[0021] When the master brake cylinder 2 is actuated by an anti-skid system, pressure exists on the pressure side of the secondary hydraulic pump 10. However, this pressure also exists on its suction side, so a rapid pressure increase can be achieved without any problems when required. The drive torque of the drive motor 11 is always sufficient to drive the hydraulic pumps 9 and 10 without stalling.

[0022] Because of the additional hydraulic pump 10 which is directly connected to the master brake cylinder 2, the vehicle brake system 1 does not require an intake valve that connects the suction side of a hydraulic pump 9, 10 to the master brake cylinder 2.

Claims

[1] Slip-controlled hydraulic vehicle brake system with a master brake cylinder (2), to which a brake circuit I, II is connected via a separating valve (4), with a wheel brake (5) which is connected via a pressure build-up valve (6) to the separating valve (4) and via a pressure reduction valve (7) to a hydraulic accumulator (8), with a hydraulic pump (9), the suction side of which is connected on a side facing away from the wheel brake (5) to the pressure reduction valve (7) and to the hydraulic accumulator (8) and the pressure side of which is connected between the separating valve (4) and the pressure build-up valve (6), and with a further hydraulic pump (10), the suction side of which is connected to the master brake cylinder (2) and the pressure side of which is connected between the separating valve (4) and the pressure build-up valve (6), wherein the hydraulic pumps (9, 10) have a common drive motor (11), characterized bythat the further hydraulic pump (10), the suction side of which is connected to the master brake cylinder (2), has a larger delivery volume than the one hydraulic pump (9). [2] Vehicle braking system according to claim 1, characterized by that one hydraulic pump (9), the suction side of which is connected to the pressure reduction valve (7) and to the hydraulic accumulator (8), has a greater pressure build-up than the other hydraulic pump (10).

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