Fluid-pressure and analogous brake systems – Speed-controlled – Having a valve system responsive to a wheel lock signal
Reexamination Certificate
1999-12-09
2001-09-18
Oberleitner, R (Department: 3613)
Fluid-pressure and analogous brake systems
Speed-controlled
Having a valve system responsive to a wheel lock signal
C417S418000
Reexamination Certificate
active
06290308
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a pump assembly for use in a brake system of a vehicle. The pump assembly is intended in particular for use in a hydraulic brake system of a vehicle, where the pump assembly serves the purpose of brake pressure modulation in wheel brake cylinders during slip control or for brake pressure buildup in an electrohydraulic power brake system.
Such pump assemblies today typically have two piston pumps, each with one piston that is received axially displaceably in a cylinder. The two piston pumps are disposed coaxially (boxer arrangement) with the pistons facing one another. Located between the pistons is an eccentric element, which is mounted in a manner fixed against relative rotation on a shaft of an electric motor that is disposed perpendicular to the piston pumps. When the electric motor is turned on, the eccentric element drives the two pistons to execute a reciprocating stroke motion in the cylinders, and this motion brings about the feeding of brake fluid in a manner known per se.
The known pump assemblies have the disadvantage that they are complicated in structure and complex to install and are expensive. Because of the electric motor, the known pump assemblies are large. The electric motor is the dominant member of known hydraulic control circuits, housed in a hydraulic block, of anti-lock brake systems. In addition, the rotary motion of the electric motor has to be converted into a linear reciprocating motion of the pistons of the piston pumps, which involves major shear forces and friction losses, which impair efficiency and cause wear. Yet another factor is a high startup current of the electric motor and a pumping output of piston pumps that does not begin until the engine rpm is increasing. Still another disadvantage of the known pump assemblies is the noise they produce, and with the electric motor a pressure limitation is not possible, so that in the event of a malfunction, very high pressures can occur in the piston pumps, with the attendant risk that the pump assembly will explode.
OBJECT AND SUMMARY OF THE INVENTION
The pump assembly according to the invention has no conventional electric motor; instead, it has an electromagnet with a permanent magnet and a coil. Either the permanent magnet or the coil is stationary, while the respective other part is movable. Supplying current to the coil moves the moving part of the electromagnet in one direction, while supplying current of reverse polarity moves the moving part in the opposite direction relative to the stationary part. By applying an alternating voltage to the coil, the moving part of the electromagnet is driven to execute a reciprocating stroke motion. A voltage course of the current for supplying current to the coil can be in sine-wave or square-wave form, for example.
The piston of the piston pump of the pump assembly of the invention is connected to the moving part of the electromagnet and accordingly goes along with the reciprocating motion of the moving part of the electromagnet; as a result, in a manner known per se, the piston pump pumps brake fluid, or some other medium to be pumped. The electromagnet of the pump assembly of the invention accordingly forms a linear motor, with a permanent magnet whose moving part is driven into a reciprocating stroke motion by supplying alternating current to the coil; this motion is used directly, and without further conversion or deflection, for driving the piston. Instead of the piston, the cylinder of the piston pump may be movable while the piston itself is stationary. In that case, the cylinder of the piston pump is connected to the movable part the electromagnet and executes the reciprocating stroke motion.
The invention has the advantage that the pump assembly is simple in construction, has only a few parts, and can be put together at little effort or expense. The pump assembly has intrinsically only one moving part, namely the moving part of the electromagnet, and the piston that moves along with this part; the piston and the moving part of the electromagnet are preferably solidly joined to one another. The piston may for instance be embodied integrally, as a peg protruding from the moving part of the electromagnet. Because the reciprocating motion of the electromagnet is utilized directly to drive the piston pump without conversion or deflection, the pump assembly has good efficiency. Other advantages are low friction, low wear, and little noise. The pump assembly of the invention has a low current consumption of approximately one fourth the rated current consumption of the conventional pump assembly of the same capacity that is driven by an electric motor. Furthermore, the startup current of the pump assembly of the invention is not elevated, and the pump assembly of the invention has its full pumping capacity immediately after being turned on.
The permanent magnet of the electromagnet makes it possible to drive the moving part of the electromagnet by reversing the polarity of the current supplied to the coil in both directions; as a result, a restoration of the moving part go of the electromagnet, for instance by means of a restoring spring, becomes unnecessary. As a result, not only is the restoring spring dispensed with, but the electromagnet also need not work counter to the force of such a restoring spring; this reduces the structural size of the electromagnet and lessens its current consumption.
Advantageous features and refinements of the invention defined herein are the subject matter set forth hereinafter.
The pump assembly of the invention may have only a single piston pump. Preferably, the pump assembly has two piston pumps that are driven contrary to one another; that is, one piston pump executes an intake stroke while the other piston pump is executing a pumping stroke. The contrary disposition of the two piston pumps means that the force of the electromagnet is utilized uniformly in both directions. The use of two piston pumps has the advantage that the pump assembly of the invention is especially readily applicable to a dual-circuit brake system that has two independent brake circuits.
In a feature of the invention defined herein, the coil is embodied as a plunger coil. This means that over a portion of its length, the coil protrudes (plunges) into a complimentary recess of the permanent magnet, or of a pole piece that is magnetized by the permanent magnet. A plunging depth, that is, the length by which the coil protrudes into the permanent magnet, varies along with the reciprocating motion of the coil rpm; in a terminal position of the coil or permanent magnet, it can be zero, or the coil can have risen fully out of the permanent magnet. Embodying the coil as a plunger coil has the advantage that a magnetic force exerted on the moving part of the electromagnet is increased, for a particular current consumption of the coil. In addition, the magnetic force exerted on the moving part of the electromagnet is somewhat constant over the entire stroke course, unless the coil has moved completely out of the permanent magnet or the pole piece magnetized by the permanent magnet, while conversely in a conventional embodiment of the coil, the magnetic force drops off sharply with the distance from the permanent magnet. In the context of the invention, for the sake of uniform terminology, the term “plunger coil” should also be understood to mean a stationary coil that protrudes into a movable permanent magnet or a movable pole piece, even if in that case the term plunging armature would actually be more apt.
The pump assembly of the invention is intended in particular as a pump in a brake system of a vehicle and is used to control the pressure in wheel brake cylinders. Depending on the type of brake system, the abbreviations ABS (for anti-lock brake system), TCS (traction control system), ESP (electronic stability program) and EHB (electrohydraulic brake system) are used for such brake systems. In the brake system, the pump serves for instance to return brake fluid from a wheel brake cylinder or a plu
Greigg Edwin E.
Greigg Ronald E.
Oberleitner R
Robert & Bosch GmbH
Torres Melanie
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