Method for operating an electric motor, control device, piston pump

Abstract

The invention relates in particular to a method for operating an electric motor (1) of a piston pump (9). The electric motor (1) has a rotor shaft (3) and is controlled with a target rotation speed (nSoll) and a target direction of rotation for the rotor shaft (3) depending on the power demand, and the actual rotation speed (nIst) of the rotor shaft (3) is monitored. The method according to the invention is characterized in that the target direction of rotation is changed for a set duration (t) with the actual rotation speed (nIst) equal to zero and the target rotation speed (nSoll) not equal to zero, and then the electric motor (1) is again controlled with the target rotation speed (nSoll) and the target direction of rotation.

Description

Technical Field

[0001] The present invention relates in particular to a method for operating an electric motor of a piston pump, the electric motor having a rotor shaft and being controlled with a target rotational speed and a target rotational direction for the rotor shaft depending on an output requirement, and the actual rotational speed of the rotor shaft being monitored.

[0002] Furthermore, the present invention relates to a control device for an electric motor and to a piston pump.

Background Art

[0003] A brake control system as part of a motor vehicle's braking equipment, in particular an anti-lock system (ABS) or vehicle dynamic control (electronic stability program ESP), usually has at least one piston pump that can be driven by an electric motor. The piston pump is operable to generate hydraulic pressure in the brake circuit of the braking equipment. For this purpose, the rotor shaft of the electric motor is non-rotatably coupled to a cam or an eccentric disk. The cam may in particular be arranged directly on the rotor shaft or may be non-rotatably coupled to the rotor shaft via a transmission. The rotor shaft rotates about the axis of rotation. By means of the cam, the rotational movement of the rotor shaft is converted into a translational or longitudinal movement of the piston of the piston pump. The cam abuts against the piston such that the piston is biased by the pressing force of the cam and the piston, which is slidably supported by this pressing force, is displaced in the longitudinal direction. This displacement is carried out against the spring member and / or the pressure in the brake circuit. The electric motor has to apply a driving torque in order to overcome the load torque that is caused when the piston is displaced against the spring force depending on the displacement distance and / or the pressure in the brake circuit. At this time, the maximum driving torque that can be provided by the electric motor is usually greater than the maximum load torque. The load torque reaches its maximum only once during one rotation of the cam, which is when the maximum displacement of the piston is reached. This is because both the spring force depending on the displacement distance and the pressure in the brake circuit reach their maximum at that time. When the rotor shaft rotates further, the piston is displaced so as to return to its original direction again. This is because the piston is pressed against the cam based on the initial stress of the spring member. The control of the electric motor is usually carried out with a target rotational speed and a target rotational direction for the rotor shaft in order to reach a specific pressure depending on the output requirement or to reach the pumping volume of the piston pump in the brake circuit. However, if the driving torque of the electric motor is not sufficient to overcome the load torque, the electric motor may be locked.Such cases can occur, in particular, based on the low automotive electrical system voltage of the vehicle, which limits the consumption output of the electric motor and thus the maximum drive torque associated therewith, or based on the high temperature of the motor windings of the electric motor, which leads to an even higher electrical resistance, or based on an increase in friction at the pistons. Depending on the locked electric motor, it may not be possible to meet the output requirements or to operate the pistons of the piston pump. To overcome such locks, it is known to configure the electric motor to have a maximum drive torque that is higher than would be required to overcome the maximum load torque that is assumed, such that cases in which the electric motor is locked do not occur. SUMMARY OF THE INVENTION

[0004] The method according to the invention having the features of claim 1 is characterized in that it is changed during a set duration with a target rotation direction set under an actual rotation speed equal to zero and a target rotation speed not equal to zero, and subsequently the electric motor is controlled again with the target rotation speed and the target rotation direction. The control of the electric motor is first carried out, as known from the prior art, with a target rotation speed and a target rotation direction for the rotor shaft of the electric motor depending on the output requirement. At this time, the actual rotation speed of the rotor shaft is also monitored. The locked electric motor is recognized based on the fact that the actual rotation speed is equal to zero and the target rotation speed is not equal to zero. According to the invention, in order to release the lock of the electric motor, when the locked electric motor is recognized, the target rotation direction is changed during the set duration, whereby the rotor shaft rotates temporarily in the opposite direction. After this set duration, the electric motor is controlled again with the target rotation speed and the target rotation direction, whereby the rotor shaft rotates again in the initially set direction. At this time, the change in the rotation direction is carried out on the assumption that when rotating in the opposite direction, the electric motor only has to overcome a lower load torque than when rotating in the initially set direction, and accordingly, the requirement related to the drive torque of the electric motor decreases or at least becomes lower. This assumption is based on the arrangement of the piston on the cam described at the beginning. Under this arrangement, the load torque only reaches its maximum once during one rotation of the cam, when the maximum displacement of the piston is reached. At that time, both the spring force depending on the displacement distance and the pressure of the brake circuit reach their maximum values. The change in the rotation direction leads to the piston being displaced so as to return, and the load torque, and accordingly the requirement related to the drive torque of the electric motor, decreases. When the electric motor is controlled again in the target rotation direction after the set duration, the additional kinetic energy resulting from the acceleration can be utilized to overcome the load torque generated in the target rotation direction from the rotation in the direction of the maximum load torque. This kinetic energy can overcome the load torque, and therefore it is not necessary to increase the target torque.Thus, the method of the present invention has the advantage that a locked electric motor is recognized and the operation of the piston can be made possible again by appropriate control of the electric motor, which is achieved by rotating the rotor shaft of the electric motor temporarily in the opposite direction and then again in the target rotation direction. This is achieved without increasing the target torque of the electric motor. In particular, it is not necessary to use an electric motor having an even higher maximum torque.

[0005] In a preferred embodiment of the present invention, the motor windings are energized depending on the angular position of the rotor shaft to control the electric motor, the actual angular position of the rotor shaft is detected, an offset is applied for a set duration, and the angular position is intended to be determined therefrom, the offset being selected such that the direction of rotation of the rotor shaft is changed. When the electric motor is an electronically commutated or brushless motor, it is preferred that the motor windings be energized depending on the angular position of the rotor shaft to control the electric motor. For that purpose, first the actual angular position of the rotor shaft is detected. In particular, for that purpose a permanent magnet is attached to the rotor shaft, and a sensor aligned therewith, in particular a sensor based on the Hall effect, detects the alignment of the magnetic field of the permanent magnet, and the actual angular position is determined therefrom. The angular position used to control the electric motor is determined by applying an offset to the actual angular position for a set duration after the locked electric motor has been recognized. That is, the angular position corresponds to the sum of the actual angular position and the offset. This offset is selected such that the direction of rotation of the rotor shaft is changed due to the windings being energized in a manner different from what would have been done without the offset. That is, due to the offset, the motor windings are energized such that, based on the actual angular position, this leads to the rotor shaft rotating temporarily in the opposite direction. In that way, when the rotor shaft rotates to a new actual angular position and the electric motor then changes its direction of rotation again, it has to overcome a lower load torque than when rotating in the direction initially set. After the set duration, the angular position is no longer given an offset, such that this angular position then corresponds to the actual angular position. That is, applying an offset to the angular position has the advantage that it does not have to be left to a control device configured in particular for controlling the electric motor to change the target direction of rotation as a parameter, and instead a change is directly effected from the angular position being operated.

[0006] In another preferred embodiment, the set duration is intended to be between 2 and 5 milliseconds. By defining the set duration within an interval of 2 to 5 milliseconds, there is an advantage that the electric motor is guaranteed to be controlled over a sufficiently long duration, thereby enabling the actual rotation of the rotor shaft in a direction opposite to the initial target rotation direction. This duration also has the advantage of being sufficiently short depending on the rotational speed of the rotor shaft, whereby the rotor shaft rotates in the changed target rotation direction only for a specific number of rotations or only for a specific part of one rotation. This is particularly preferred when the load torque to be overcome by the electric motor has at least one maximum value within one rotation of the rotor shaft, especially when a cam is directly arranged on the rotor shaft.

[0007] The control device for an electric motor according to the present invention is characterized in that, with the constituent elements of claim 4, the control device is specially set up to implement the method according to the present invention. From this, the advantages already described are brought about. Other preferred constituent elements and combinations of constituent elements will become apparent from the above description and the claims.

[0008] The piston pump of the present invention having the constituent elements of claim 5 has an electric motor, the electric motor has a rotor shaft, the rotor shaft has a cam or an eccentric disk, and the piston of the piston pump abuts against the cam or the eccentric disk such that the rotation of the rotor shaft causes a longitudinal slide of the piston in the axial direction. The piston pump is characterized by having a control device according to the present invention. From this too, the advantages already mentioned are brought about. Other preferred constituent elements and combinations of constituent elements will become apparent from the above description and the claims.

[0009] Next, the present invention will be described in detail with reference to the drawings. For that purpose, the following are shown.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

DETAILED DESCRIPTION OF THE INVENTION

[0011] FIG. 1 shows an electric motor 1 having motor windings 2 and a rotor shaft 3 with permanent magnets 4 arranged on the end face side. The electric motor 1 is an electronically commutated or brushless electric motor. The control of the electric motor 1 is usually carried out with a target rotational speed n Soll and a target rotational direction for the rotor shaft 3 depending on the output requirement. To control the electric motor 1, in this example, the alignment of the magnetic field 5 of the permanent magnets 4 is detected by a sensor 6 aligned therewith, and from this, the actual angular position φ Ist of the rotor shaft 3 is determined. A control device 7 controls an inverter 8 that energizes the motor windings 2 depending on the output requirement and the angular position φ. At this time, in the normal case, the angular position φ is the actual angular position φ Ist corresponding thereto.

[0012] Figure 2 shows a part of a piston pump 9 having a piston 10 and a spring member 11. The piston pump 9 is operable, in particular, to generate hydraulic pressure in a brake circuit of a braking facility. The piston 10 of the piston pump 9 abuts against a cam 12. The cam 12 is non-rotatably coupled to the rotor shaft 3 of the electric motor 1. In this example, the cam 12 is directly attached to the rotor shaft 3 of the electric motor 1. The cam 12 is configured as an eccentric disk, that is, it is circular and eccentrically attached to the rotor shaft 3. However, it is equally possible that the cam 12 is not directly attached to the rotor shaft 3 but is non-rotatably coupled to the rotor shaft 3 via a transmission. The rotor shaft 3 rotates about the axis of rotation. By means of the cam 12, the rotational movement of the rotor shaft 3 is converted into a translational or longitudinal movement of the piston 10 of the piston pump 9. The cam 12 abuts against the piston 10 such that the piston 10, which is biased by a pressing force by the cam 12 and is slidably supported by this pressing force, is displaced in the longitudinal direction. This displacement is carried out against the spring member 11 and / or the pressure in the brake circuit. After the piston 10 has been displaced maximally, when the rotor shaft 3 rotates further, the piston 10 is displaced back in the original direction. This is because, based on the initial stress by the spring member 11, the piston 10 is pressed against the cam 12.

[0013] Next, with reference to FIG. 3, a preferred method for operating the electric motor 1 of the piston pump 9 will be described. For this purpose, FIG. 3 shows this method using a flowchart. In particular, by this method, it is ensured that a locked electric motor 1 is recognized and the operation of the piston 10 can be made possible again by appropriate control of the electric motor 1.

[0014] In step S1, depending on the output requirement, in particular to achieve a specific pressure or delivery volume of the piston pump 9 in the brake circuit, the control device 7 determines the target rotational speed n Soll and the target rotational direction for the rotor shaft 3. At the same time, the sensor 6 determines the actual angular position φ of the rotor shaft 3 Istis determined. In step S2, the control device 7 determines the actual rotational speed n Ist and compares it with the target rotational speed n Soll . Steps S1 and S2 are continuously executed.

[0015] When the actual rotational speed n Ist is equal to the target rotational speed n Soll , this method continues with step S5. However, when the actual rotational speed n Ist is equal to zero and the target rotational speed n Soll is not equal to zero, the electric motor 1 is locked. In that case, in step S3, the offset φ Offset is determined. This offset φ Offset is selected such that, unlike the case where the offset φ Offset should have been absent, the energization of the winding 2 causes the rotational direction of the rotor shaft 3 to be changed. That is, the offset φ Offset causes the motor winding 2 to be energized so that, under this actual angular position φ Ist , the rotor shaft 3 rotates temporarily in the opposite direction. In that way, the motor winding 2 is energized so that the torque in the changed rotational direction is generated by the permanent magnet 4 attached to the rotor shaft 3. Thus, under the actual angular position φ Ist , especially as determined from the alignment of the magnetic field 5, the offset φ Offset is determined such that the angular position φ as the sum of the actual angular position φ Ist and the offset φ Offset leads to a favorable energization of the motor winding 2.

[0016] In step S4, the control device 7 controls the inverter 8 depending on the angular position φ. At this time, the angular position φ is the actual angular position φ Ist and the offset φ Offsetcorresponds to the sum. The motor winding 2 is energized in accordance with the output requirement, whereby the rotor shaft 3 of the electric motor 1 rotates in a direction opposite to the target rotation direction. The duration t set at this time is between 2 and 5 milliseconds. By defining the set duration t within the interval of 2 to 5 milliseconds, the electric motor 1 is controlled for a sufficiently long duration, whereby the rotor shaft 3 actually rotates in a direction opposite to the initial target rotation direction. Since the set duration t is sufficiently short even depending on the rotational speed of the rotor shaft 3, the rotor shaft 3 rotates only for a specific part of one rotation in the changed target rotation direction. In step S5, the control device 7 controls the inverter 8 depending on the angular position φ. At this time, the angular position φ is the actual angular position φ Ist corresponds to. The motor winding 2 is energized in accordance with the output requirement, whereby the rotor shaft 3 of the electric motor 1 rotates in the target rotation direction at the target rotational speed n Soll rotation.

Explanation of Signs

[0017] 1 Electric motor 2 Motor winding 3 Rotor shaft 7 Control device 9 Piston pump 10 Piston 12 Cam n Ist Actual rotational speed n Soll Target rotational speed t Duration φ Angular position φ Ist Actual angular position φ Offset Offset

Claims

1. A method for operating an electric motor (1) of a piston pump (9), the electric motor (1) having a rotor shaft (3), being controlled with a target rotational speed (n_Soll) and a target rotational direction for the rotor shaft (3) depending on an output requirement, and the actual rotational speed (n_Ist) of the rotor shaft (3) being monitored, wherein it is changed during a duration (t) in which the target rotational direction is set under an actual rotational speed (n_Ist) equal to zero and a target rotational speed (n_Soll) not equal to zero, and subsequently the electric motor (1) is again controlled with the target rotational speed (n_Soll) and the target rotational direction, the actual angular position (φ_Ist) of the rotor shaft (3) is detected, an offset (φ_Offset) is imparted during the set duration (t), an angular position (φ) is determined as the sum of the actual angular position (φ_Ist) and the offset (φ_Offset), the offset (φ_Offset) is selected such that the rotational direction of the rotor shaft (3) is changed, and the motor winding (2) is energized depending on the angular position (φ) of the rotor shaft (3) to control the electric motor (1). A method characterized by this.

2. The method according to claim 1, characterized in that the set duration (t) is between 2 and 5 milliseconds.

3. A control device (7) for an electric motor, the control device (7) being set up to carry out the method according to claim 1 or 2.

4. A piston pump (9) having an electric motor (1), the electric motor (1) having a rotor shaft (3), the rotor shaft (3) having a cam (12) or an eccentric disk, and the piston (10) of the piston pump (9) being in contact with the cam (12) or the eccentric disk such that rotation of the rotor shaft (3) causes a longitudinal slide of the piston (10) in the axial direction. A piston pump characterized by having the control device (7) according to claim 3.

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