FR2799801A1 - PIEZOELECTRIC ACTUATOR PUMP FOR A HYDRAULIC VEHICLE BRAKING SYSTEM AND METHOD FOR OPERATING SUCH A PUMP - Google Patents

Abstract

The invention relates to a piezoelectric actuator pump (36) for a hydraulic vehicle braking system (10), in particular for a braking installation provided with a slip control device. The invention proposes to arrange an elastic element (70) in a pump body (56), which encloses a cavity as a pumping chamber (76) and to urge said elastic element with the aid of a piezoelectric actuator ( 60) and, in this way, to modify the volume of the pumping chamber (76) and to displace brake fluid.

Description

Piezoelectric actuator pump for hydraulic installation of

  The invention relates to a piezoelectric actuator pump for a hydraulic vehicle braking installation, as well as a method of

operation of such a pump.

  A pump of this type is known from US-PS 4,738,493.

  The known pump comprises a piezoelectric actuator, the length of which increases when an electric voltage is applied to it. A piston which delimits a volume of a pumping chamber of the pump is applied against the piezoelectric actuator. Non-return valves are arranged as a suction valve and as a discharge valve in respectively a suction conduit communicating with the pumping chamber and in a discharge conduit communicating with the pumping chamber. When a pulsed voltage is applied to the piezoelectric actuator, it alternately lengthens and shortens. In doing so the actuator moves the piston in a reciprocating movement, that is to say that it drives the piston in an alternating reciprocating movement, during which the volume of the chamber alternately decreases and increases, the piezoelectric actuator pump delivering liquid from

  brake in a manner known to mechanically driven piston pumps.

  The piezoelectric actuator pump according to the invention comprises an elastic element, for example an elastomer body, which is housed in a pump body and closes a cavity of said pump body, forming a pumping chamber. The pumping chamber delimited by the elastic element communicates with a pump inlet and a pump outlet. The elastic element can be stressed using the piezoelectric actuator mounted on or in the pump body. When an electrical voltage is applied to the piezoelectric actuator, due to the ensuing variation in the length of the piezoelectric actuator, the elastic element is deformed, thus modifying

  a volume of the pumping chamber delimited by said elastic element.

  Then, when the voltage is cut, the length of the piezoelectric actuator returns to its initial value, the elastic element returns to its initial shape and the pumping chamber returns to its initial volume. A decrease in the pumping chamber results in the discharge of brake fluid from the chamber thereof, while an increase in the pumping chamber causes the suction of brake fluid through the pump inlet. By applying a pulsed voltage to the piezoelectric actuator, the pumping chamber of the piezoelectric actuator pump according to the invention decreases and

  alternately increases with the effect that brake fluid is displaced.

  A cross section of the pumping chamber is less than an internal cross section of the pump body where there is the elastic element delimiting the pumping chamber, this in order to produce, for a force

  actuator given, higher pressure.

  The elastic element firstly has the advantage that it seals the pumping chamber without the need for a separate seal and thus isolates the piezoelectric actuator from the brake fluid. This simplifies the construction of the piezoelectric actuator pump according to the invention. Another advantage of the invention resides in the fact that the elastic element fills to a large extent an interior chamber of the pump body, so that the dead volume, that is to say the residual volume of the pump which remains for maximum elongation of the piezoelectric actuator, obtained by applying a maximum voltage, is low. A small volume improves the efficiency of the pump. In addition, the elastic element makes it possible to obtain a pumping chamber of small volume, which taking into account the short stroke which characterizes a pump with piezoelectric actuator, is important in terms of the pump flow rate. Another advantage of the pump is that the elastic element largely fills the interior chamber of the pump body, thus avoiding an accumulation of air or gas in the interior chamber of said pump body, which would cause the flow rate of the piezoelectric actuator pump. Another advantage of the piezoelectric actuator pump according to the invention is still its compact, robust and light construction making

  call on a small number of elements.

  The piezoelectric actuator pump according to the invention is designed in particular as a pump for a braking installation and is used in the control of the pressure in the wheel brake cylinders. Depending on the type of installation, the abbreviations ABS, ASR, FDR or EHB are used to designate it. In the braking system, the pump is used, for example, to bring

  brake fluid from one or more wheel brake cylinders to a master

  cylinder (ABS) and / or to move brake fluid from a reservoir

  supply to one or more wheel cylinders (ASR, FDR or EHB).

  The pump, for example, is required in a brake system with wheel slip control (ASB and ASR) and / or in a system

  pilot assistance (FDR) and / or in an electro-braking installation

  hydraulic (EHB). The wheel slip control (ABS or ASR) makes it possible to avoid a locking of the vehicle wheels during a braking action with high pressure on the brake pedal (ABS) and / or a slipping of the driving wheels of the vehicle when the accelerator pedal is strongly depressed (ASR). In a brake assist system (FDR), a brake pressure is established in one or more wheel brake cylinders, independently of an actuation of the brake pedal or the accelerator pedal, in order to avoid, for example, a stall of the vehicle with respect to the path desired by the driver. The pump can also be used in an electro-hydraulic braking system (EHB), in which the pump delivers brake fluid into the wheel brake cylinder (s), as soon as an electric brake pedal sensor detects actuation. of said brake pedal or in which the pump ensures the

  filling a brake system accumulator.

  The operating method of such a pump is as follows: a wheel brake cylinder is connected through a system of valves for modulating the wheel brake pressure at the inlet and outlet of the piezoelectric actuator pump and, by acting on an electric voltage applied to the piezoelectric actuator, the volume of the pumping chamber is varied and consequently a wheel brake pressure prevailing in the wheel brake cylinder. The wheel brake pressure is produced beforehand, for example using a master cylinder, which is isolated from a wheel brake cylinder by closing a valve, or using the pump. with piezoelectric actuator. The method according to the invention can be applied advantageously to control the wheel brake pressure in order to avoid locking of the wheels during braking or the like. The advantage of the method according to the invention lies in particular in the fact that, in order to vary the wheel brake pressure in order to avoid locking of the wheels, one acts only on the voltage applied to the piezoelectric actuator of the pump with piezoelectric actuator and it is not necessary to continuously control

  valves of the wheel brake pressure modulation valve system.

  The invention is described in detail in the following with the aid of a preferred embodiment shown in the drawings. These show: Figure 1, a schematic diagram of a hydraulic braking installation for a vehicle comprising a piezoelectric actuator pump according to the invention and Figure 2, detailed views of alternative embodiments of the pump

  piezoelectric actuator of figure 1.

  The drawings are simplified schematic representations.

  The hydraulic braking installation 10 for a vehicle according to the invention, shown in FIG. 1, comprises a tandem brake master cylinder 12 to which two mutually independent braking circuits I, II are connected. Only a braking circuit I is shown in Figure I; the other braking circuit II has a construction identical to the first and operates in the same way as the latter. One or more wheel brake cylinders 14 can be connected to each brake circuit I, II. In the example shown, two wheel brake cylinders 14 are

  connected to each brake circuit I, II.

  From the brake master cylinder 12, a main brake line -16 leads to a branch 18, at which the main brake line 16 divides into two wheel brake lines 20,

  each leading to a wheel brake cylinder 14.

  In the main brake line 16, between the brake master cylinder 12 and the branch 18, a switching valve 22 is arranged. This switching valve 22 is a 2/2 solenoid valve open by default, in which a differential valve 24 which, when the switching valve 22 is closed, limits a maximum pressure on the wheel brake cylinder side of the switching valve 22. A non-return valve 25 biased by a spring, which passes in the direction of the cylinder wheel brake 14, is

  connected in parallel with the switching valve 22.

  A pressure establishment valve 26 is mounted upstream of each wheel brake cylinder 14, i.e. the pressure establishment valve 26 is mounted in the wheel brake line 20, between the branch point 18 and the wheel brake cylinder 14. The pressure setting valve 26 is configured as a 2/2 solenoid valve open by default. A valve

  non-return 28 biased by spring, which is passing in the direction of the master-

  cylinder 12, is mounted in parallel with the pressure setting valve 26. A pressure relief valve 30 is mounted downstream of each wheel brake cylinder 14. The pressure relief valve 30 is mounted in a line return 32 which leads from wheel brake cylinders 14 to a suction side or to a pump inlet 34 of a hydraulic pump 36. The pressure relief valve 30 is configured as a 2/2 solenoid valve open by default. A hydraulic accumulator 38 is connected to the return line 32 and a spring-loaded non-return valve 40, which passes through

  direction of the hydraulic pump 36, is mounted in the return line 32.

  A discharge line 44, in which are arranged a damping chamber 46 and a diaphragm 48 leads from a discharge side or from an outlet 42 of the hydraulic pump 36 to the main brake line 16. A suction line 50 which leads to the pump inlet 34 is connected to the main brake line 16, between the brake master cylinder 12 and the switching valve 22. The wheel brake pressure modulation valve system may include instead of two solenoid valves 2/2 26, 30, for example a solenoid valve 3/3 which connects the wheel brake cylinder 14 to the wheel brake line 20 in its basic position, connects the wheel brake cylinder 14 to the return line 32 in a switching position and isolates the wheel brake cylinder 14 from the brake line

  wheel 20 and return line 32 in the other switching position.

  For anti-lock braking control (ABS), the

  skating (ASR) and / or driving dynamics control (FDR), the vehicle's braking system 10 includes an electronic control device 54 which receives signals from wheel rotation sensors 55 and

  controls the solenoid valves 22, 26, 30,52 as well as the hydraulic pump 36.

  The operation of the braking system 10 of the vehicle including the regulation of a wheel brake pressure in the wheel brake cylinders 14 by modulation of the brake pressure by means of the brake pressure modulation valve system wheel 26, 30 and by means of the hydraulic pump 36, for the purposes of checking anti-lock, anti-skid and driving dynamics, is familiar to the person skilled in the art and will not be not

described here.

  The hydraulic pump 36 is in accordance with the invention in the form of a piezoelectric actuator pump 36. It comprises a hollow cylindrical pump body 56 in two parts, which is divided in a radial plane and the two parts of which are linked to each other by screws 58. A

  piezoelectric actuator 60 is mounted in the pump body 56.

  The piezoelectric actuator 60 consists in a manner known per se of individual stacked piezoelectric elements, in the form of discs, or is produced according to a multilayer technique. An electrical voltage can be applied to the stacked elements or to the piezoelectric layers of the multi-layer actuator 60; we will talk about applying a voltage to the piezoelectric actuator in the following. When applying an electrical voltage to

  the piezoelectric actuator 60, this one, as a result of the piezoelectric effect-

  electric, lengthens in the axial direction. When we cut the voltage,

  the piezoelectric actuator 60 retracts to return to its initial length.

  A first piston 62 is applied against a front face of the piezoelectric actuator 60. The piston 62 is pressed against the piezoelectric actuator 60 by a spring washer 64 which bears in a groove arranged in an interior wall of the pump body 56. The spring washer 64 applies an axial mechanical prestress to the piezoelectric actuator, which avoids a tensile stress of said actuator 60, the piezoelectric actuators tolerating weakly the tensile stresses. Furthermore, the mechanical preload increases the elongation capacity of the piezoelectric actuator 60 in the presence of an electric voltage; the stroke and the capacity of the piezoelectric actuator pump 36 are thus increased by the mechanical prestressing of the piezoelectric actuator 60. Against a front face of the first piston 62 remote from the piezoelectric actuator 60 is applied a second piston 66, which is provided with a continuous annular shoulder 68 on the side facing the first piston 62,

  which shoulder provides free space for the spring washer 64.

  On an end face of the second piston 66 remote from the piezoelectric actuator 60 is arranged an elastic element 70. The elastic element 70 has the shape of a circular plate and it is mounted in the pump body 56,

  between the second piston 66 and a front wall 72 of said pump body 56.

  The elastic element 70 has a curved peripheral edge 74, by which it is in leaktight contact with the internal wall of the pump body 56, and this even in the relaxed state, not axially compressed. The elastic element 70, when no electric voltage is applied to the piezoelectric actuator, is slightly compressed axially between the second piston 66 and the front wall 72 of the pump body 56. When the piezoelectric actuator elongates axially under the action of a tension applied to it, the elastic element undergoes compression in the axial direction. The elastic element in the illustrated embodiment of the invention is formed of an elastomer having a low Shore hardness and a low internal damping. It almost instantly resumes its shape when the voltage applied to the piezoelectric actuator 60 is cut and the latter returns to

its initial length.

  The elastic element 70 defines, with the front wall 72 of the pump body 56, a pumping chamber 76. The pumping chamber 76 is formed by a cavity in the form of a cap flattened at the center of a front surface of the elastic element 70, applied against the front wall 72 of the pump body 56. A diameter of the pumping chamber 76 is smaller than an inside diameter of the pump body 56. In the embodiment shown, the diameter of the pumping chamber 76 represents approximately 1/3 of the internal diameter of the pump body 56. This makes it possible to obtain a higher discharge pressure of the pump with piezoelectric actuator

  36 for a given actuator force.

  The pumping chamber 76 communicates through a central hole 78 in the front wall 72 of the pump body 56 with a bore 34, 42 passing radially through the front wall 72, which constitutes the pump inlet 34 and the pump outlet 42. In the transverse borehole 34, 42, on either side of the central hole 78, are fitted spring-loaded check valves 80, 82, one of which passes in the direction of the central hole 78 and forms a valve inlet 80 and the other is passing from the central hole 78 towards the outside and forms an outlet valve 82 of the actuator pump

piezoelectric 36.

  Due to the presence of the elastic element 70 which largely fills an interior chamber of the pump body 36, between the second piston 66 and the front wall 72 of said pump body 36, the dead volume of the piezoelectric actuator pump 36, that is to say the residual volume which remains for a maximum applied voltage and consequently a maximum elongation of the piezoelectric actuator 60, is low, which makes it possible to obtain a better efficiency of the pump. In addition, the elastic element 70 effectively isolates the piezoelectric actuator 60 from the brake fluid.

  the hydraulic braking system 10.

  When a pulsed voltage is applied to the piezoelectric actuator, the axial length of the latter increases and decreases alternately, the piezoelectric actuator 60, in doing so, alternately compressing and releasing the elastic element, therefore decreasing and then returning to its value initial, alternatively, the volume of the pumping chamber 76. Brake fluid is thus alternately discharged from the pumping chamber 76 through the outlet valve 82 and re-aspirated into the pumping chamber 76 through the inlet valve 80; the piezoelectric actuator pump 36 displaces fluid by applying a voltage to its piezoelectric actuator 60 in a pulsed manner. For this purpose, a voltage source 84 is provided, for example a vehicle battery, the electric voltage of which is converted by means of a voltage converter 86 of for example 12 volts into a voltage suitable for the control of the piezoelectric actuator, for example of approximately 100 volts for a piezoelectric actuator 60 at low voltage or of approximately 1000 volts for a high voltage piezoelectric actuator 60. The application of the electrical voltage to the piezoelectric actuator 60 is controlled by the electronic control unit 54 through a stage

final power 88.

  The control or regulation of a wheel brake pressure in one of the wheel brake cylinders 14, for example for anti-lock braking control according to the invention takes place as follows: after the establishment of wheel brake pressure by actuation of the brake master cylinder 12 and / or using the piezoelectric actuator pump 36 and after the electronic control unit 54 has detected via the rotation sensor wheel 55 a tendency to block a vehicle wheel, the switching valve 22 closes while the suction valve 52 remains closed. The brake master cylinder 12 is thus isolated from the rest of the vehicle's braking system 10. The pressure setting valve 26 of the wheel brake cylinder 14 concerned remains open while the pressure relief valve 30 concerned opens, so that the wheel brake cylinder 14 concerned is connected to the inlet 34 and at the outlet 42 of the piezoelectric actuator pump 36. At the same time, the pressure establishment valve 26 of a vehicle wheel which does not have a tendency to lock is closed, while the pressure release valve 30 corresponding remains closed, so that the wheel brake cylinder 14 is isolated from the piezoelectric actuator pump 36. Preferably is applied to the piezoelectric actuator 60 an electrical voltage between zero and a maximum voltage, before the closure of the switching valve 22. By raising or lowering the voltage applied to the piezoelectric actuator 60, the volume of the pumping chamber 76 of the actuating pump is reduced or increased eur piezoelectric 36, with the effect that the pressure of the brake fluid in the pumping chamber 76 increases or decreases. When the pressure in the pumping chamber 76 increases, the pressure in the wheel brake cylinder 14 increases through the outlet valve 82 of the piezoelectric actuator pump 36 and the pressure establishment valve 26 open. , and when the pressure in the pumping chamber 76 drops, the pressure in the wheel brake cylinder 14 drops through the pressure relief valve 30 open and the inlet valve 80

  of the piezoelectric actuator pump 36.

  With the method according to the invention, it is not necessary, in order to regulate the wheel brake pressure, to constantly activate the solenoid valves 26, 30 of the braking system 10, to control or regulate the brake pressure. wheel brake is obtained by increasing or decreasing the electric tension

  applied to the piezoelectric actuator 60.

  In the piezoelectric actuator pump 36 according to the invention shown in FIG. 2, the pumping chamber 76 is shaped as a cavity

  flattened cap shape in the front wall 72 of the pump body 56.

  The elastic element 70 in the form of a circular plate, in this mode of

  embodiment, has two flat surfaces without recesses.

  Figure 3 shows another arrangement of a piezoelectric actuator pump 36 according to the invention. In this case, the pumping chamber 76 is produced in the form of a cavity, a kind of bladder 90, which communicates through a central hole 92 with the central hole 78 in the front wall 72 of the

  piezoelectric actuator pump 36.

  With the exception of the differences described, the piezoelectric pumps shown in Figures 2 and 3 are identical in construction to the pump of Figure 1 described in the foregoing and operate in the same manner as the latter. The same references designate the elements which are identical. The piezoelectric actuator pump 36 according to the invention shown in the figures has an internal body diameter of approximately 40 to 50 mm and provides a flow rate of approximately 5 cm3 for a frequency of 30 Hz of the voltage.

  electric applied to its piezoelectric actuator 60.

Claims (8)

  1. Piezoelectric actuator pump for a hydraulic vehicle braking installation, comprising a pump body and a piezoelectric actuator, the length of which can be modified by applying an electric voltage thereto, characterized in that the piezoelectric actuator pump (36) has an elastic element (70) which is mounted in the pump body (56) and can be deformed by the variation in length of the piezoelectric actuator (60), in that the elastic element (70) contains a cavity which forms a pumping chamber (76), communicates with a pump inlet (34) and a pump outlet (42) and the volume of which is modified by the deformation of the elastic element (70) and in that the pump (76) has a diameter   which is less than an internal diameter of the pump body (56).   2. Piezoelectric actuator pump according to claim 1, characterized in that the elastic element (70) closes so   seals the pumping chamber (76) in the pump body (56).   3. Piezoelectric actuator pump according to claim 1, characterized in that the pumping chamber (76) is formed between the elastic element (70) and a wall (72) of the pump body (56). 4. Piezoelectric actuator pump according to claim 1, characterized in that the pumping chamber (76) is surrounded by the elastic element (70).   5. Piezoelectric actuator pump according to claim 1, characterized in that the elastic element (70) is made of an elastomer. 6. Piezoelectric actuator pump according to claim 1, characterized in that the elastic element (70) has a low hardness. 7. Piezoelectric actuator pump according to claim 1, characterized in that the piezoelectric actuator pump (36) comprises a preload element (64) which preloads   mechanically the piezoelectric actuator (60).   8. A method of operating a vehicle hydraulic braking installation comprising a piezoelectric actuator pump according to one of the preceding claim, the braking installation comprising at least one wheel brake cylinder as well as a system of modulation modulation valves. the wheel brake pressure, through which the wheel brake cylinder is hydraulically connected to the vehicle brake system, characterized in that a wheel brake pressure is established in the wheel brake cylinder (14 ), in that an electrical voltage is applied to the piezoelectric actuator (60) of the piezoelectric actuator pump (36), in that it is connected through the wheel brake pressure modulation valve system ( 26, 30) the wheel brake cylinder (14) at the inlet (34) and at the outlet (42) of the piezoelectric actuator pump (36) and in that the wheel brake pressure is varied by varying the under tension   electric applied to the piezoelectric actuator (60).