Lubrication and pressure maintenance in a hydraulic drive system

Abstract

System (10) for lubrication and pressure maintenance in a drive system with hydraulic clutch control of a vehicle, in particular a commercial vehicle or working machine, comprising a main hydraulic circuit (1) for providing system pressure with a main hydraulic pump (2) and with an electric motor (3) for driving the main hydraulic pump, a hydraulic lubrication circuit (4) for lubricating mechanical components (5) by means of a lubrication pump (6), wherein the lubrication circuit (4) is connected to the main hydraulic circuit (1) via a unidirectional connecting line (7) in which fluid from the lubrication circuit (4) enters the main circuit (1) and a backflow from the main circuit (1) to the lubrication circuit (4) is blocked, such that that during operation of the main hydraulic pump (2) a hydraulic system pressure in the main circuit (1) is provided by means of the main hydraulic pump (2) and after switching off the main hydraulic pump (2) a hydraulic pre-pressure in the main circuit (1) is provided by means of the lubrication pump (6), wherein the pre-pressure is lower than the system pressure, wherein the electric motor (3) is designed as a drive for the main hydraulic pump (2) and a power take-off (19).

Description

AREA OF INVENTION

[0001] The present invention relates to a system for lubrication and pressure maintenance in a drive system with hydraulic clutch control of a vehicle, in particular a commercial vehicle and a work machine.

[0002] DE 10 2019 202 138 A1 discloses a hydraulic system for a motor vehicle transmission, wherein the hydraulic system comprises a first pump for supplying pressure to a first pressure circuit and a second pump for supplying pressure to a second pressure circuit. The first pressure circuit is intended for supplying pressure to at least one shift actuator of the transmission, and the second pressure circuit is intended for cooling and / or lubricating at least one component of the transmission. An outlet of the second pump is connected to the first pressure circuit via a check valve. A connecting line between the outlet of the second pump and the second pressure circuit can be shut off as needed by a spring-loaded switching valve, and the switching position of the switching valve depends on the pressure in the first pressure circuit.

[0003] DE 10 2005 013 137 A1 relates to a method and a device for controlling an oil supply for an automatic transmission and a starting element, which, by means of an oil pump mechanically driven by a traction motor and a second electrically driven oil pump, can ensure a sufficient oil supply to a hydraulic control unit of the automatic transmission and / or the starting element both when the traction motor is running and when it is stationary. Furthermore, the cooling oil supply of this starting element is ensured by the fact that, at least during starting operation, the electrically driven oil pump provides a low-pressure oil flow for cooling the starting element.

[0004] From US Patent 2021 / 0207708A1, a hydraulic pressure supply system for an automatic transmission is known. The hydraulic pressure supply system comprises a first hydraulic pump that generates a first hydraulic pressure from hydraulic fluid stored in an oil pan, and a second hydraulic pump that increases the received hydraulic pressure to a higher pressure. The hydraulic pressure supply system further comprises a control valve located on the upstream side of a low-pressure section, which regulates the hydraulic pressures supplied by the first and second hydraulic pumps to supply the low-pressure section with the regulated pressure, as well as a plurality of hydraulic lines that deliver the hydraulic pressure from the first hydraulic pump to the control valve and a high-pressure section, and that deliver the hydraulic pressure from the second hydraulic pump to the high-pressure section and the control valve.

[0005] US Patent 2019 / 0128399A1 discloses an oil pressure supply system that distributes lubricant for a dual-clutch transmission and includes a mechanical oil pump that pumps oil stored in an oil pan when the engine is driven, and a line control valve that delivers a lubricant flow rate directly to an input shaft and a countershaft by controlling the oil pressure supplied by the mechanical oil pump, while simultaneously delivering the lubricant flow rate to a transmission cable and clutch via a separate path. The oil pressure supply system further includes a line pressure control valve that variably releases the lubricating oil pressure when the lubricating oil pressure supplied to the input shaft and countershaft reaches or exceeds a predetermined value, and an electric oil pump that pumps the oil depending on a control signal from a transmission control unit.A first lubricant switching valve of the oil pressure supply system selectively blocks the oil pressure supplied by the electric oil pump to the transmission cable and clutch, and a second lubricant switching valve switches a flow path so that the oil pressure supplied by the line control valve and the first lubricant switching valve is selectively delivered to the transmission cable and clutch. SUMMARY OF THE INVENTION

[0006] Accordingly, the following is planned: - a system for lubrication and pressure maintenance in a drive system with hydraulic clutch control of a vehicle, in particular a commercial vehicle or work machine, comprising a main hydraulic circuit for providing system pressure with a main hydraulic pump and with an electric motor for driving the main hydraulic pump, a hydraulic lubrication circuit for lubricating mechanical components by means of a lubrication pump, wherein the lubrication circuit is connected to the main hydraulic circuit via a unidirectional connecting line in which fluid from the lubrication circuit enters the main circuit and backflow from the main circuit to the lubrication circuit is prevented, such that during operation of the main hydraulic pump a hydraulic system pressure is provided in the main circuit by means of the main hydraulic pump,and after the main hydraulic pump is switched off, a hydraulic pre-pressure is provided in the main circuit by means of the lubrication pump, whereby the pre-pressure is lower than the system pressure.

[0007] When a commercial vehicle is to start moving again after a standstill, the electric motor for providing system pressure, often a motor that drives the power take-off (e.g., for the working hydraulics), must first start. The pump connected to it draws the fluid (oil) from a reservoir, such as a sump. Afterwards, lines and valves must be filled with the fluid before a gear can be engaged. This process usually takes a considerable amount of time. The invention aims to shorten this time and also to save energy and reduce noise emissions.

[0008] PTO (Power Take-Off) refers to a power take-off or independent drive, often to which a hydraulic pump for the working hydraulics is adapted. This drives hydraulic components such as steering, brakes, lift cylinders, and hydraulic pumps that are not responsible for propelling the vehicle's drive system. This hydraulic circuit is frequently independent of the drive system's hydraulic circuit.

[0009] The working hydraulics in a commercial vehicle refer to the hydraulic circuit used to control specific working functions of the vehicle that are unrelated to the vehicle's drive system. It is used to operate attachments or machine components by moving hydraulic cylinders, hydraulic motors, hydraulic pumps, or other hydraulic actuators to generate forces or movements. An example is the control of the loading bucket system on wheel loaders or excavators, where the bucket is raised and lowered by hydraulic cylinders. Similarly, in trucks, the working hydraulics are used to control cranes or lifting devices, or in dump trucks to hydraulically raise the loading platform.

[0010] The drive hydraulics in a commercial vehicle refers to the hydraulic circuit used to control the movement or propulsion of the vehicle itself or its essential drive components. Drive hydraulics also encompasses the hydraulic actuation of valves, such as gearshift valves. Unlike the working hydraulics, which are responsible for controlling and driving implements, the drive hydraulics serve to propel the vehicle or perform drive functions.

[0011] Lubrication refers to the introduction of oil or another lubricant into the mechanical components of a system, such as bearings, gears, or moving parts, to reduce friction. Lubrication ensures that the mechanical parts of the system operate smoothly despite high loads and temperatures.

[0012] Pressure maintenance means that a certain pressure is maintained in the hydraulic system even when the main pump is not active. This prevents lines from draining and ensures that the system is ready for operation more quickly after a shutdown. By maintaining a reduced pressure, valves and other hydraulic components can respond quickly and reliably once the system is restarted. In a system with hydraulic components, such as valves and couplings, responsible for driving the power take-off (PTO), for example, for work hydraulics or the drive system, this function is performed by an electrically driven lubrication pump that maintains a lower pressure during shutdown to allow for a smooth restart.

[0013] The term "main circuit" refers to a central hydraulic circuit within a system, responsible for providing essential drive energy or for the hydraulic control of valves and their actuators within the drive system. This is a circuit that performs a primary function, such as driving the drive system or controlling switching elements like valves. A fluid circulates in such a circuit, moved by a pump, often a hydraulic pump, and provides the energy to operate a specific system or machine.

[0014] A main circuit differs from a secondary circuit, such as a lubrication circuit. The main circuit serves to provide motion-related functions, e.g., actuating switching elements, while a secondary circuit serves additional tasks such as lubrication or cooling.

[0015] In a commercial vehicle, mechanical components are lubricated to reduce friction. Important components include the engine, where pistons, crankshaft, camshaft, and connecting rods are lubricated by engine oil to prevent overheating. The transmission is also lubricated to prevent wear on gears, bearings, and synchronizers. Similarly, axles and the differential are lubricated to protect gears and bearings and ensure power transmission.

[0016] A typical example can be found in vehicles with hydrostatic drive, where the drive hydraulics ensure that hydraulic motors drive the wheels or tracks.

[0017] A check valve is a valve that allows fluid to flow in only one direction and mechanically blocks backflow. It operates automatically and closes as soon as the fluid begins to flow in the opposite direction. The check valve may be spring-loaded to build up lubrication pressure. The spring can be designed so that the check valve opens when the target lubrication pressure is reached. Excess fluid not used for lubrication flows through the check valve into the main hydraulic circuit, replenishing it.

[0018] A fluid reservoir is a container that stores fluids such as hydraulic oil, lubricating oil, or coolant in a system. It serves as a storage tank from which fluid is drawn and replenished as needed. Two typical examples of a fluid reservoir are the tank and the sump.

[0019] A tank is a closed container, usually located above the system, that serves as a reservoir for the fluid. The fluid is pumped from the tank into the system and circulates there before flowing back into the tank. Tanks often have a large capacity to ensure that sufficient fluid is available for the system to operate.

[0020] A sump is an open or closed reservoir, often located at the lowest point of a system, particularly in lubrication or cooling systems. A sump not only collects the fluid that returns after circulating through the system, but can also serve as a collection point for fluid that escapes due to small leaks or leaks in the system. In the case of minor leaks, the escaping fluid collects in the sump instead of escaping uncontrollably.

[0021] A central electronic control unit (eDCU = electronic Drive Control Unit) manages and controls the electric motor for the drive system and the electric motor for the working hydraulics. This is achieved by sending commands to the inverters, which are responsible for driving the electric motors. The eDCU is powered by the low-voltage battery (LV battery).

[0022] A high-voltage battery (HV battery = High Voltage Battery) supplies the inverters with direct current and provides the energy for operating the drive system and the working hydraulics.

[0023] The power source for transmission electronics is typically the vehicle's electrical system, which usually supplies a voltage of 12 or 24 volts. This electrical energy is used to power the transmission's electronic control units and sensors. The transmission electronics thus control gear shifting, monitor the transmission's condition, and ensure optimal adjustment of shift points to the driving situation. In electric vehicles, the energy can also come from a hybrid or fully electric drive system. The transmission electronics can be powered by a high-voltage system derived from the vehicle battery or an electric generator.

[0024] As part of the electrification process, drive systems are being developed to be as efficient and comfortable as possible. Unnecessary components, such as electric motors, are switched off or at least not operated when the vehicle is stationary or in the parking position. This saves energy and reduces noise. When the vehicle is to be put back into operation, it is desirable to quickly restore the drive system to operational readiness.

[0025] Inverters are electrical devices that convert a direct current (DC) source into alternating current (AC), which is necessary for operating electric motors. The inverters are controlled by a drive electronics unit (eDCU).

[0026] Pressure specifications refer to a temperature of 20°C.

[0027] Ideally, a system would have one electric motor powering the working hydraulics, while a second electric motor is responsible for propelling the vehicle. The second electric motor would thus be responsible for driving, while the first electric motor ensures the power take-off, i.e., the working hydraulics, is driven.

[0028] The basic idea of ​​the invention is that one of the two electric motors, in particular the second electric motor, provides system pressure via a hydraulic pump connected to it, so that couplings can be actuated via valves. Another, smaller, less powerful electric pump, called a lubrication pump, supplies the system with fluid, in particular oil, at a lower pressure level to serve all lubrication points.

[0029] When the first electric motor is out of service, the lubrication pump primarily ensures lubrication. If the lubrication pump delivers a higher flow rate than intended for lubrication, the pressure in the fill line increases and a connecting line opens, allowing a flow of fluid into the main hydraulic circuit lines to prevent them from emptying due to internal leaks.

[0030] This allows energy to be saved and noise emissions to be reduced.

[0031] Advantageous designs and further developments result from the further sub-claims as well as from the description with reference to the figures in the drawing.

[0032] According to a preferred embodiment of the invention, the unidirectional connecting line has a spring-loaded check valve. This prevents the backflow of fluid into the lubrication circuit and ensures that the pressure in the main circuit remains stable. Furthermore, the spring preload ensures that lubrication pressure can be built up. Thus, lubrication pressure can be built up even when the main hydraulic pump is stationary or when there is increased internal leakage in the main hydraulic circuit.

[0033] The function can therefore be ensured by means of a control valve that regulates the fluid flow manually or electronically. Alternatively, the function can be ensured by means of a bladder accumulator, in which fluid is temporarily stored in a reservoir to maintain pressure in the system when needed and to prevent backflow through a controlled release.

[0034] According to a preferred embodiment of the invention, the lubrication circuit and the main circuit are connected to a common fluid reservoir, in particular a tank and / or a sump, from which fluid flows into the lubrication circuit and into the main circuit.

[0035] This allows for efficient distribution of fluid between the circuits and reduces the need for separate reservoirs.

[0036] According to a preferred embodiment of the invention, the lubrication pump is operated by means of an energy source that also supplies energy to the transmission electronics. This reduces the complexity and energy consumption of the system.

[0037] It is conceivable to operate the lubrication pump instead of continuing to operate the electric motor to provide lubrication and maintain hydraulic pressure.

[0038] According to a preferred embodiment of the invention, the pre-pressure is provided during a limited, in particular predetermined, period of time after the main hydraulic pump is switched off, such that the discharge of a main energy storage device is reduced.

[0039] Accordingly, intermittent operation of the lubrication pump is also conceivable, in which the pump is not activated continuously, but at regular intervals to maintain the pre-pressure in the main hydraulic circuit. After the main hydraulic pump is switched off, the lubrication pump would operate at specific intervals to keep the pressure stable and then switch off again as soon as the desired pre-pressure is reached.

[0040] Furthermore, the lubrication pump can be switched on and off based on specific conditions and / or signals. For example, a seat switch or the activation of vehicle controls, such as a turn signal lever, accelerator pedal position, or parking brake position, could serve as the switching criterion for the lubrication pump. Alternatively, the lubrication pump can be switched on and off based on a time delay. For instance, the lubrication pump could be operated for a certain period after the ignition is switched on and then switched off again after the last use of the vehicle.

[0041] According to a preferred embodiment of the invention, the lubrication pump is configured to provide a lubrication pressure in the lubrication circuit and a pre-pressure or lubrication pressure of 1-5 bar in the main circuit for filling the lines in the main hydraulic circuit, in particular 2 bar, while the main hydraulic pump is out of operation.

[0042] The pre-charge pressure in the system ensures that the hydraulic components remain operational even when the main hydraulic pump is switched off, enabling a quick restart. This pressure range is sufficient to maintain the system's basic operational readiness even when the main hydraulic pump is shut down. The lubrication pressure of 1 to 5 bar ensures continued lubrication of the mechanical components, and the flow rate through the check valve refills the system, allowing for a rapid restart. Choosing 2 bar as the preferred value represents a good compromise between sufficient pressure retention and energy efficiency.

[0043] According to a preferred embodiment of the invention, the main hydraulic pump is configured to provide a system pressure of 15-25 bar, in particular 20 bar, in the main circuit while the main hydraulic pump is in operation. This pressure range is intended for normal system operation, in which the main hydraulic pump supplies all hydraulic components of the vehicle's drive system with pressurized oil. A pressure of 15 to 25 bar ensures that the drive hydraulics and related functions can operate efficiently under full load. A value of 20 bar as the preferred operating pressure provides a reliable and powerful pressure supply, which is necessary in most commercial vehicles to guarantee stable and consistent performance of the hydraulic components.

[0044] Accordingly, these pressure ranges in the respective operating states of the system (with and without main hydraulic pump) allow optimal adaptation to the requirements of the operation, whether for standby mode or regular working operation.

[0045] According to the invention, the electric motor is designed as a drive for the main hydraulic pump and a power take-off.

[0046] This provides a powerful solution that improves the functionality of the vehicle.

[0047] According to a preferred embodiment of the invention, the system further comprises an interface to a second electric motor for the vehicle's drive system, in particular for driving a wheelset or a running gear.

[0048] This interface allows the integration of a separate motor for the drive system.

[0049] According to a preferred embodiment of the invention, the vehicle is controlled by a system according to one of the preceding claims and in particular has a working hydraulic system. CONTENT OF THE DRAWINGS

[0050] The present invention will be explained in more detail below with reference to the exemplary embodiments shown in the schematic figures of the drawings. These show: Fig. 1 A schematic block diagram of an embodiment of the invention.

[0051] The accompanying drawings are intended to provide a further understanding of the embodiments of the invention. They illustrate embodiments and, in conjunction with the description, serve to explain the principles and concepts of the invention. Other embodiments and many of the advantages mentioned will become apparent with reference to the drawings. The elements of the drawings are not necessarily shown to scale.

[0052] In the figures of the drawings, identical, functionally equivalent and equally effective elements, features and components - unless otherwise stated - are each provided with the same reference symbols. DESCRIPTION OF EXAMPLES OF EXECUTION

[0053] Fig. Figure 1 shows a hydraulic system 10 for lubrication and pressure maintenance in a commercial vehicle. After a standstill, all non-essential components, including electric motors 3 and 12, are switched off to save energy and reduce noise. After a standstill or before a restart, the system must be made operational again, particularly in construction machinery. Electric motor 12 powers the drive system, and electric motor 3 drives a power take-off or, more commonly, a working hydraulic system. Electric motor 3 also drives a main hydraulic pump 2, which provides a system pressure of 20 to 25 bar to actuate couplings via valves.

[0054] System 10 uses a common tank 9 as a fluid reservoir for both a main circuit 1 and a lubrication circuit 4, with both circuits being supplied with identical fluid from tank 9. In the main circuit 1, the fluid is used by the main hydraulic pump 2 to generate the system pressure, while the lubrication pump 6 uses the same fluid to provide a lubrication pressure of approximately 2 to 5 bar, enabling the lubrication of mechanical components 5, such as bearings and gears. The lubrication pump 6 is driven by its own electric motor 103.

[0055] System pressure and lubrication pressure do not add up. The lubrication pressure results from the fluid volume delivered by the lubrication pump and the fluid volume flowing back into the lubrication system. When the main hydraulic pump 2 is out of operation, fluid flows into the main circuit 1 via the unidirectional filling line 7 and the spring-loaded check valve 8, provided the pressure in the filling line 7 is sufficient to open the spring-loaded check valve. During operation, the main hydraulic pump 2 alone provides the system pressure. When the main hydraulic pump 2 is switched off, the lubrication pump 6 maintains a reduced pre-pressure in the main circuit 1 via the unidirectional connecting line 7, or refills the lines of the main hydraulic circuit 1 due to internal leakage.This pressure is lower than the system pressure, but serves to prevent the lines from draining and to allow for a faster resumption of operation after the main hydraulic pump 1 is restarted. A check valve 8 is installed in the unidirectional connecting line 7 to prevent fluid from flowing back from the main circuit 1 into the lubrication circuit 4.

[0056] The main hydraulic pump 2, driven by electric motor 3, draws fluid from tank 9 via a suction line 101. This suction line 101 serves to operate the main hydraulic pump 2 and ensures that the electric motor 3 can draw fluid as needed to build up system pressure in the main circuit 1 as soon as the vehicle is started.

[0057] The lubricating oil pump 6 is connected to the main circuit 1 via a connecting line 7 to fill the oil lines to the clutch valves 102 with fluid even when the electric motor 3 is not running. This continuous filling of the lines prevents them from draining, which can occur particularly with warm oil and due to gravity as well as internal leaks. Pre-filling the lines allows for a rapid build-up of system pressure after the vehicle restarts, as the lines are already filled with fluid. This helps to engage a gear more quickly, thus restoring the vehicle's operational readiness rapidly.

[0058] The mechanical components 5 and the coupling valves 102 are each connected to a sump 104 via a return line 21. The return line 21 is in Fig.For clarity, the return flow 21 is shown as a dashed line; however, it actually occurs in a random direction along gear components that are lubricated and cooled by the oil. The oil runs off or drips from these gear components and eventually collects again in the sump 104.

[0059] The connecting line 7 between the lubricating oil pump 6 and the lines of the main circuit 1 thus serves to support the pressure build-up and to accelerate the filling of the lines without the electric motor 3 having to be active.

[0060] The control of the electric motor 103 of the lubrication pump 6, the electric motor 3 of the auxiliary drive 19 and the electric motor 12 of the drive is controlled as required via a central electronics unit 13.

[0061] The high-performance electric motor 3 of the power take-off 19 is operated via an inverter 14 and the electric motor 12 of the drive system via the inverter 15. The inverters are supplied by a high-capacity high-voltage battery 16 via high-voltage lines 18 and are connected to the central electric drive control via communication lines 20.

[0062] The smaller-sized lubrication pump 6 and its electric motor 103 are supplied with energy via a low-voltage line 22 using a low-voltage battery 17, usually the vehicle battery. Reference sign 1. Main hydraulic circuit 2 Main hydraulic pump 3 Electric motor 4 hydraulic lubrication circuit 5 mechanical components 6 Lubrication pump 7 unidirectional connection line 8 Check valve 9 Tank 10 System 11 couplings 12 Electric motor 13 central electric drive control 14 Inverter 15 Inverter 16 high-voltage batteries 17 Vehicle battery 18 high-voltage lines 19 Power take-off 20 Communications Management 21 Return 22 Low-voltage line 101 Suction line 102 clutch valves 103 Electric motor 104 Swamp

Claims

[1] System (10) for lubrication and pressure maintenance in a drive system with hydraulic clutch control of a vehicle, comprising a main hydraulic circuit (1) for providing system pressure with a main hydraulic pump (2) and with an electric motor (3) for driving the main hydraulic pump, a hydraulic lubrication circuit (4) for lubricating mechanical components (5) by means of a lubrication pump (6), wherein the lubrication circuit (4) is connected to the main hydraulic circuit (1) via a unidirectional connecting line (7) in which fluid from the lubrication circuit (4) enters the main circuit (1) and a backflow from the main circuit (1) to the lubrication circuit (4) is blocked, such that that during operation of the main hydraulic pump (2) a hydraulic system pressure is provided in the main circuit (1) by means of the main hydraulic pump (2) and after switching off the main hydraulic pump (2) a hydraulic pre-pressure is provided in the main circuit (1) by means of the lubrication pump (6), wherein the pre-pressure is lower than the system pressure, characterized by , that the electric motor (3) is designed as a drive for the main hydraulic pump (2) and a power take-off (19). [2] System according to claim 1, wherein the unidirectional connecting line (7) has a check valve (8). [3] System according to one of the preceding claims, wherein the lubrication circuit (4) and the main circuit (1) are connected to a common fluid reservoir from which fluid flows into the lubrication circuit (4) and into the main circuit (1). [4] System according to one of the preceding claims, wherein the lubrication pump (6) is operated by means of an energy source which further supplies energy to a transmission electronics. [5] System according to one of the preceding claims, wherein the pre-pressure is provided for a limited period of time after the main hydraulic pump (2) is switched off, such that the discharge of a main energy storage device is reduced. [6] System according to one of the preceding claims, wherein the lubrication pump (6) is configured to provide a pre-pressure of 1-5 bar in the lubrication circuit (4) and in the main circuit (1) while the main hydraulic pump (2) is out of operation. [7] System according to one of the preceding claims, wherein the main hydraulic pump (2) is configured to provide a system pressure of 15-25 bar in the main circuit (1) while the main hydraulic pump (2) is in operation. [8] System according to claim 1, which further comprises an interface to a second electric motor for the propulsion of the vehicle. [9] Vehicle with a hydraulic, electronic or mechanical drive system controlled by a system (10) according to any of the preceding claims.

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