Method for operating a speed-controlled electric motor of a motor pump unit for an active suspension system

Abstract

Method for operating a speed-controlled electric motor (62, 66) of a motor pump unit (60) for an active chassis (10) of a motor vehicle, comprising the following steps: Determining at least one target torque (Msoll) of a speed control (110), a target speed (nsoll) of the speed control (110) and an actual speed (nist) of the speed control (110), wherein the speed control (110) comprises a feedforward control (114) and a controller (112), and wherein the target torque (Msoll) is a sum of a feedforward target torque and a controller target torque, Comparison of the target torque (Msoll) with a target torque threshold value, the target speed (nsoll) with a target speed threshold value, and the actual speed (nist) with an actual speed threshold value. Detection of an inactive phase when the target torque (Mtarget) is below the target torque threshold, the target speed (ntarget) is below the target speed threshold, and the actual speed (nist) is below the actual speed threshold. Switching off the speed control (110) of the electric motor (62, 66) when the inactive phase is detected.

Description

[0001] The invention relates to a method for operating a speed-controlled electric motor of a motor pump unit for an active suspension.

[0002] An active suspension system typically comprises one damper and one pressure-control assembly for each vehicle wheel. The damper, which can be designed, for example, as a monotube damper, has a working cylinder, which is essentially a damper tube, and a working piston arranged on a piston rod. The working piston is located inside the damper tube and seals against an inner wall of the damper tube in such a way that an upper damper chamber is separated from a lower damper chamber. The pressure-control assembly essentially comprises a motor-pump unit with a bidirectional pump, which can be driven by an electric motor, a storage volume, and several check valves and adjustable throttle devices.The bidirectional pump is fluidically connected to the upper damper chamber via a first hydraulic line connected to a first pump port, and to the lower damper chamber via a second hydraulic line connected to a second pump port. The check valves are arranged on a first hydraulic connection linking the two hydraulic lines. The check valves are designed to act in opposite directions. The adjustable throttle valve devices are arranged on a second hydraulic connection linking the two hydraulic lines. The two hydraulic connections are parallel to each other.The storage volume is fluidically connected to the first and second hydraulic connections via a third hydraulic line, with a junction point located between the check valves and the adjustable throttle assemblies. The motor-pump unit can also be assigned to an axle of the vehicle, in which case the motor-pump unit comprises two pumps, each with an electric motor. A first pump is assigned to a damper of the left wheel of the axle, and a second pump is assigned to a damper of the right wheel of the axle.

[0003] From DE 102021 117081 A1, DE 102020 105270 A1, US 2017 / O 320 368 A1, DE 10 2018 221 576 A1 and DE 100 55 108 A1, an active suspension system for a motor vehicle and a method for operating a pump for the active suspension system are each known. DE 102022206 540 B3 discloses a method for controlling variable-speed fluid pumps.

[0004] During vehicle operation, a simple, passive damping system can be implemented, in which the working piston is moved, for example, towards the second damper chamber, while an active damping system, for example for roll stabilization, does not move the working piston. Active damping is achieved using the pump. Passive damping occurs without pump operation.

[0005] To operate the motor-pump unit or the pump's electric motor, the electric motor must be operated according to demand. For this purpose, the electric motor is typically controlled by a control unit, such as an inverter, depending on a manipulated variable that specifies a particular speed of the electric motor. The manipulated variable is usually provided by a torque controller, which converts a predetermined target torque into the manipulated variable. The target torque consists of two components: a first component, generated by a controller, where a controller-generated target torque is determined from the difference between a target speed and an actual speed, preferably detected by a speed sensor; and a second component, generated by a feedforward control system.The feedforward control serves for compensation, in particular inertial compensation and friction compensation, and for presetting for upcoming driving situations or sections. For example, vertical and lateral accelerations of an upcoming driving section can be determined by appropriate sensors, and a feedforward target torque can be defined from this. The feedforward control then controls the pump in such a way that the electric motor provides a target torque regardless of the target or actual speed.

[0006] A disadvantage of operating the electric motor in this way is that the speed control remains active even when the vehicle is inactive, for example, when stationary (i.e., when the target speed is zero), thus controlling the electric motor. This control results in energy consumption. The speed control in the vehicle's inactive state is due to the presence of measurement noise during the actual speed measurement and external excitations of the damper, even when the vehicle is inactive, leading to a non-zero actual speed. This creates a difference between the actual speed and the target speed, which activates the control system and controls the electric motor. Furthermore, in the vehicle's inactive state, the electric motor is controlled based on the target torque specified by the feedforward control unit.

[0007] The object of the invention is to provide a method for operating a speed-controlled electric motor of a motor pump unit for an active chassis, which can reduce energy consumption.

[0008] The problem is solved by the features of claim 1.

[0009] First, at least the target torque, target speed, and actual speed of the speed control system are determined. The speed control system comprises a feedforward control unit and a controller, and the target torque is the sum of the feedforward target torque and the controller target torque. Subsequently, the target torque, target speed, and actual speed are compared to target torque thresholds. If the target torque, target speed, or actual speed falls below the target torque threshold, an inactive phase is detected, and the speed control of the electric motor is deactivated accordingly.

[0010] By comparing the actual speed with the actual speed threshold, it can be determined that fluctuations or changes in the actual speed result solely from measurement noise during the actual speed acquisition and minor external excitations of the damper, and that no control of the electric motor is necessary in this regard. Comparing the target speed with the target speed threshold reveals that the electric motor is not being controlled based on a predetermined target speed. Comparing the target torque with the target torque threshold reveals, in particular, that no control torque specified by the feedforward control is present.

[0011] This allows for the reliable detection of an inactive state of the vehicle or the engine pump unit and thus the possibility of switching off the speed control, thereby reliably preventing an unwanted and safety-critical shutdown of the speed control.

[0012] Preferably, the actual speed of the vehicle, detected by appropriate sensors, is compared with a predefined speed threshold. The inactive phase is detected when the actual speed falls below this threshold. By considering the actual speed when detecting the inactive phase, the risk of the speed control being deactivated when it is actually needed can be further reduced. In a preferred embodiment, the predefined speed threshold is set above 0 km / h and below 5 km / h, thus detecting when the vehicle is stationary.

[0013] Additionally, the actual electrical current flowing through the electric motor is compared to a predefined current threshold. The inactive phase is detected when the actual electrical current falls below this threshold. Alternatively or additionally, the actual pressure at a pressure side of the motor-pump unit is compared to a predefined pressure threshold. The inactive phase is detected when the actual pressure falls below this threshold. This further reduces the risk of the speed control system shutting down when speed control is required.

[0014] Preferably, a control unit for controlling the electric motor is switched to a freewheeling state or a short-circuit state when the inactive phase is detected. The electric motor control unit, in particular an inverter, typically has three inverter branches, each with two switches connected in series. The center taps between the respective switches of each inverter branch represent the inverter outputs and are connected to the terminals of the electric motor. An active short circuit, i.e., the short-circuit state and the freewheeling state, constitute a so-called safe state of an electric motor. In the active short-circuit state, some or all phase windings of the electric motor are intentionally short-circuited by means of the switches, in particular semiconductor switches, of the inverter. This mode can be created with different switch positions of the semiconductor switches.In the freewheeling state, all switches are opened. This ensures that the windings of the electric motor are not energized during the inactive phase.

[0015] In a preferred embodiment, the target torque is compared to a target torque threshold, the target speed to a target speed threshold, and the actual speed to an actual speed threshold over a predefined time period. By comparing over a time period rather than at a single point in time, toggling—that is, constantly switching between active and deactivated speed control—is reliably avoided. The time period can be a few seconds or a few minutes.

[0016] An embodiment of the invention is explained in more detail with reference to the drawing. Fig. Figure 1 schematically shows an active chassis of a motor vehicle, and Fig. Figure 2 schematically shows a speed control of an electric motor of a motor pump unit of the active suspension. Fig. 1.

[0017] Fig. Figure 1 shows an active suspension system 10 on an axle of a motor vehicle. The active suspension system 10 has two shock absorbers 20, 40, i.e., a left shock absorber 20 and a right shock absorber 40, a motor pump unit 60, and two hydraulic guide devices 70, 90.

[0018] The struts 20, 40 each have a spring 22, 42 and a damper 24, 44, which are connected on one side to a body 12 of the motor vehicle and on the other side to a wheel carrier or a control arm 15, 17. A vehicle wheel 14, 16 is attached to the wheel carrier or control arm 15, 17. The dampers 24, 44 each have a working cylinder 26, 46, which is essentially a damper tube, and a working piston 28, 48 arranged on a piston rod 30, 50, wherein the working pistons 28, 48 are arranged in the respective working cylinders 26, 46 and bear against an inner wall of the working cylinder 26, 46 in such a way that an upper damper chamber 321, 521 is fluid-tightly separated from a lower damper chamber 322, 522.

[0019] The two damper chambers 321, 322 of the first damper 24 are fluidically connected to a first hydraulic guide device 70. The first hydraulic guide device 70 is also fluidically connected to a first bidirectional pump 64 of the motor-pump unit 60, the first pump 64 being driven by a first electric motor 62. The first hydraulic guide device 70 comprises several hydraulic lines 72, 74, several hydraulic connections 76, 78 connecting the two hydraulic lines 72, 74 in parallel, and a storage volume 88. The bidirectional pump 64 is fluidically connected to the upper damper chamber 321 via the first hydraulic line 72, which connects to a first pump port, and to the lower damper chamber 322 via the second hydraulic line 74, which connects to a second pump port.Two opposing check valves 80 and 82 are arranged on the first hydraulic connection 76. Two adjustable throttle valve devices 84 and 86 are arranged on the second hydraulic connection 78. The two hydraulic connections 76 and 78 are arranged parallel to each other. The storage volume 88 is connected to the first hydraulic connection 76 and the second hydraulic connection 78, with a junction point located between the check valves 80 and 82 and the adjustable throttle valve devices 84 and 86, respectively.

[0020] The two damper chambers 521, 522 of the second damper 44 are fluidically connected to a second hydraulic guide device 90. The second hydraulic guide device 90 is also fluidically connected to a second bidirectional pump 68 of the motor-pump unit 60, the second pump 68 being driven by a second electric motor 66. The second hydraulic guide device 90 comprises several hydraulic lines 92, 94, several hydraulic connections 96, 98 connecting the two hydraulic lines 92, 94 in parallel, and a storage volume 99. The second bidirectional pump 68 is fluidically connected to the upper damper chamber 521 of the second damper 44 via the first hydraulic line 92, which connects to a first pump port, and to the lower damper chamber 522 of the second damper 44 via the second hydraulic line 94, which connects to a second pump port.Two opposing check valves 100 and 102 are arranged on the first hydraulic connection 96. Two adjustable throttle valve devices 104 and 106 are arranged on the second hydraulic connection 98. The two hydraulic connections 96 and 98 are arranged parallel to each other. The storage volume 99 is connected to the first hydraulic connection 96 and the second hydraulic connection 98 of the second hydraulic guide device 90, with a junction point provided between each of the check valves 100 and 102 and the adjustable throttle valve devices 104 and 106.

[0021] The motor pump unit 60 also has a single control unit 69, which is connected to both electric motors 62 and 66. The control unit 69 has a speed controller 110 for each electric motor 62 and 66 to operate them.

[0022] Such a speed control 110 is in Fig.2 shown. The speed control 110 has a controller 112, a feedforward control 114, a torque control 116 and a control unit 118 for controlling the electric motor 62, 66.

[0023] During operation, the electric motor 62, 66 is controlled via the control unit 118, in particular a frequency converter, depending on a manipulated variable Isoll. The manipulated variable Isoll is provided by the torque controller 116, which converts a predetermined target torque Msoll into the manipulated variable Isoll. The target torque Msoll is the sum of two components: a first component, generated by a controller 112 (i.e., a controller target torque), and a second component, i.e., a feedforward target torque generated by the feedforward controller 114. The first component is determined from the difference between a target speed and an actual speed. The second component serves for compensation, in particular inertia compensation and friction compensation, and for presetting for upcoming driving situations or driving sections.For example, a target pressure can be used as an input variable for determining the pre-control target torque.

[0024] According to the invention, the speed control 110 is switched off during a detected inactivity phase, particularly when the vehicle is stationary, in order to avoid unnecessary current flow to the electric motors 62, 66 and thus save energy. To ensure reliable shutdown of the speed control 110, the shutdown is triggered by the target speed ntarget, the actual speed ntarget, and the target torque Mtarget. The target torque Mtarget is compared to a target torque threshold value, the target speed ntarget to a target speed threshold value, and the actual speed ntarget to an actual speed threshold value. If the target torque Mtarget, the target speed ntarget, and the actual speed ntarget are below the target torque threshold value, an inactivity phase is detected, and the speed control of the electric motors 62, 66 is switched off accordingly.

[0025] The comparison, in particular of the target torque Msoll with a target torque threshold value, the target speed nsoll with a target speed threshold value and the actual speed nist with an actual speed threshold value, takes place over a predefined time period, thereby avoiding so-called toggling.

[0026] Additionally, the travel speed is compared with a travel speed threshold, the actual current with a current threshold, and the actual pressure in the hydraulic guides with a pressure threshold to detect the inactive phase in a particularly reliable manner and to increase the safety that the speed control is not switched off during an active phase, when speed control is absolutely necessary. This provides a method for operating a speed-controlled electric motor 62, 66 of a motor-pump unit 60 for an active chassis 10, which reduces energy consumption. Only existing parameters are used to detect the inactive phase. In this way, no additional components, such as additional sensors or similar, are required.

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