Cooling circuit and method for cooling a drive motor of a vehicle

Abstract

The invention relates to a cooling circuit (1) and to a method for cooling a drive motor (2) of a vehicle, comprising a coolant pump and a mechanical system pressure control unit (3) which is configured to restore an operating pressure of a coolant circulating in the cooling circuit (1) by introducing pressure from an exhaust gas turbocharger, in particular downstream of a charge air cooler (5), or from a compressed air circuit or a pressure accumulator, in which pressure is generated by an air compressor, after the cooling circuit (1) has been opened, wherein the system pressure control unit (3) comprises the following: a pressure controller (7) which is configured to limit a refilling pressure to a defined target pressure; a throttle (8) which is arranged in an inflow line (10); a check valve (9) for preventing the return flow of pressure from the cooling circuit (1); a thermostatic valve (11), wherein the thermostatic valve (11) is configured to enable the pressure control starting from a predefined coolant temperature, wherein a feed of the compressed air into the cooling circuit (1) is provided into a region that is not or barely influenced by a delivery head of the coolant pump, in particular on a suction side of the coolant pump, into a venting line or into a filling line of the compensation container (4).

Description

[0001] Daimler Truck AG Orlich

[0002] August 26, 2025

[0003] Cooling circuit and method for cooling a vehicle drive motor

[0004] The invention relates to a cooling circuit for cooling a drive motor of a vehicle according to the preamble of claim 1 and a method for cooling a drive motor of a vehicle according to the preamble of claim 2.

[0005] Cooling circuits in vehicle applications are closed systems with positive pressure, which raises the boiling point of the coolant to a higher temperature. This allows for greater cooling capacity (cooling capacity essentially consists of the temperature difference to the ambient temperature; the greater this difference, the greater the achievable cooling capacity). The pressure in the cooling system typically builds up passively through the heating and subsequent expansion of the coolant and the air in the expansion tank. If the circuit is opened while already warm (e.g., for a necessary coolant top-up), or if an unintended leak occurs, the pressure escapes from the system and can only be rebuilt once the entire system has cooled down.As long as this cooling has not taken place, the system will be operated at too low a pressure and will be exposed to the risk of local boiling causing component damage, or of local cavitation events causing significant component damage.

[0006] External pressure control is a known technology. This is an electrically controlled system that depends on a pressure sensor and an electronic control unit. While the system can regulate the pressure more precisely and also actively release pressure, it requires significantly greater overall vehicle integration.

[0007] US 2020 / 0072119 A1 describes an internal combustion engine of a motor vehicle. The internal combustion engine comprises a coolant, a liquid / gas heat exchanger, a coolant temperature-dependent control element, an expansion tank, fluidic connections between the components, and a coolant pump. At least one direct or at least one control-dependent fluidic connection, or at least one force-transmitting connection, is established between a medium in the expansion tank and a medium in at least one other fluid path or circuit of the motor vehicle.

[0008] The invention is based on the objective of providing a novel cooling circuit and a novel method for cooling a drive motor of a vehicle.

[0009] The problem is solved according to the invention by a cooling circuit for cooling a drive motor of a vehicle with the features of claim 1 and a method for cooling a drive motor of a vehicle with the features of claim 2.

[0010] Advantageous embodiments of the invention are the subject of the dependent claims.

[0011] A cooling circuit for cooling a vehicle's drive engine is proposed, comprising a coolant pump and a mechanical system pressure control unit configured to restore an operating pressure of a coolant circulating in the cooling circuit by introducing pressure from an exhaust gas turbocharger, particularly downstream of an intercooler, or from a compressed air circuit or pressure accumulator in which pressure is generated by an air compressor, after the cooling circuit has been opened, wherein the system pressure control unit comprises the following:

[0012] - a pressure regulator configured to limit refill pressure to a defined target pressure,

[0013] - a throttle located in an inlet line,

[0014] - a check valve to prevent backflow of pressure from the cooling circuit,

[0015] - a thermostatic valve.

[0016] Limiting the refill pressure does not limit the pressure in the cooling system. If, for example, the pressure is insufficient at a coolant temperature of 85°C, this pressure control unit will raise or correct the pressure to, for example, 500 mbar. If the cooling circuit heats up further (due to increased engine load), the coolant pressure will also rise further due to the thermal expansion of the coolant (to, for example, 1.6 bar). This further increase (due to passive volume expansion as a result of the coolant's thermal expansion) is desirable and should not be prevented. The only purpose is to ensure that the pressure cannot drop below 500 mbar (the lower operating limit for safe and damage-free engine operation).

[0017] Therefore, a defined minimum pressure or minimum setpoint pressure (for example, 500 mbar) is set, preferably no higher. A (significantly) higher pressure increase at, for example, 80°C could lead to excessively high pressure at, for example, 105°C. A pressure of 500 mbar at 105°C is still sufficient, however, 500 mbar at 20°C would be too high (hence the use of a thermostatic valve), as this would result in excessively high pressure at 105°C. Similarly, a pressure of 1.0 bar at 80°C would be too high and would have the same effect (excessive pressure at 105°C).

[0018] According to the invention, the thermostatic valve is configured to release the pressure control from a predetermined coolant temperature, wherein the compressed air is fed into the cooling circuit into an area that is not or hardly influenced by a delivery head of the coolant pump, in particular on a suction side of the coolant pump, into a vent line or into a filling line of the expansion tank.

[0019] The present invention ensures, in the case described above, that a required minimum pressure is restored quickly, thus guaranteeing safe vehicle operation. Any system pressure loss, for example due to opening and / or topping up coolant, is corrected immediately after the engine is started. This prevents potential engine damage. The system can be implemented by combining three valves: a test valve, a pressure reducing valve, and a thermostatic valve. A throttling device can be installed downstream of the pressure reducing valve for precise pressure control.

[0020] The solution according to the invention prevents damage to components of the cooling circuit due to insufficient system pressure. Coolant refills should normally only be carried out when the cooling circuits have cooled down, as otherwise the correct system pressure cannot be guaranteed. This is particularly important for vehicles operating in multiple shifts or for vehicles without engine shutdown or equipped with a parking heater (in the USA, some people live in their vehicles; these vehicles are never switched off in winter or summer for the purpose of interior climate control, and the cooling circuit remains warm). The solution according to the invention can also be used in such vehicles. In contrast to known systems, no mechatronic integration into the engine or vehicle electrical / electronic system is necessary. The system according to the invention can be implemented entirely within the engine. This is advantageous in third-party business (e.g.,Off-highway applications) can be advantageous because the vehicle circuit design can be simplified.

[0021] Exemplary embodiments of the invention are explained in more detail below with reference to the drawings. These show:

[0022] Fig. 1: a schematic view of a vehicle cooling circuit with a mechanical system pressure control unit, and

[0023] Fig. 2: a schematic view of the system pressure control unit.

[0024] Corresponding parts are marked with the same reference symbols in all figures.

[0025] Figure 1 is a schematic view of a cooling circuit 1 of a vehicle, for example, a commercial vehicle, a bus, or a passenger car. The cooling circuit 1 serves, for example, to cool a drive motor 2, in particular an internal combustion engine or an electric motor, and / or an exhaust gas recirculation cooler 6. The cooling circuit 1 has a mechanical system pressure control unit 3, which is configured to restore the operating pressure of a coolant circulating in the cooling circuit 1 after the cooling circuit 1, for example, an expansion tank 4, has been opened at operating temperature. In a conventional cooling circuit 1, the coolant pressure could only be restored after cooling and subsequent reheating.

[0026] According to the present invention, pressure can be introduced into the cooling circuit 1 by taking boost pressure from an exhaust gas turbocharger, in particular after an intercooler 5, or from a compressed air circuit in which pressure is generated by an air compressor.

[0027] The guidance of the pressurized fluid (e.g., air) in the system pressure control unit 3 can be achieved by different arrangements of valves.

[0028] Figure 2 is a schematic view of a possible embodiment of the system pressure control unit 3.

[0029] The system pressure control unit 3 can, for example, include a pressure regulator 7 configured to limit the refill pressure to a defined setpoint pressure of, for example, approximately 500 mbar. Furthermore, a throttle 8 can be arranged in an inlet line 10. A check valve 9 can also be arranged to prevent backflow of pressure from the cooling circuit 1 and / or, for example, to equalize pressure between the exhaust gas turbocharger, the pressure circuit, or a pressure accumulator. Finally, a thermostatic valve 11 can be provided, configured to enable pressure control from a predetermined coolant temperature, for example, 80°C.

[0030] In one embodiment, it may be provided that the compressed air is introduced into an air reservoir 12 of the expansion tank 4.

[0031] Furthermore, it may be possible to introduce the compressed air into an area that is hardly affected by the delivery head of a coolant pump (not shown) of the cooling circuit 1, for example on a suction side of the coolant pump, into a vent line or into a filling line of the expansion tank 4.

[0032] A lack of pressure in cooling circuit 1 is thus compensated for by drawing boost pressure downstream of the turbocharger (preferably downstream of the intercooler 5). The amount of boost drawn is very small and only occurs once, so that it has no effect on the charge air system (supply of charge air to the combustion chamber). Alternatively, the boost pressure can also be drawn from the vehicle's compressed air system (generated by the air compressor).

[0033] The variable boost pressure of the turbocharger or the compressed air circuit or a

[0034] The pressure in the accumulator is reduced to a constant setpoint pressure (e.g., 500 mbar) by a preset pressure reducer or pressure regulator 7. If the pressure in the cooling circuit 1 is lower, the pressure is increased to this preset value (by pressure equalization). The connection shown in the upper left of Figure 2 connects the exhaust gas turbocharger or the charge air cooler 5 to the thermostatic valve 11. The connection shown in the upper right leads from the pressure reducer 7 to the expansion tank 4 or to a suction side of a water pump (filling line). The connection at the bottom left (the inlet line 10) is the coolant inlet (e.g., from a vent line of the exhaust gas recirculation cooler 6) and serves to transmit the coolant temperature to the thermostatic valve 11. The coolant flows from the vent line of the exhaust gas recirculation cooler 6 to the expansion tank 4 for separation via the connection at the bottom right (after the throttle 8).

[0035] In Figure 2, the two right-hand connections lead to the expansion tank. In Figure 1, these two lines are already joined in the system pressure control unit 3 (valve block) and then run as a single line to the expansion tank 4 (in this case, the compressed air is already mixed with the coolant flow in the valve block). Technically, both solutions are essentially identical; however, the solution shown in Figure 2 allows the compressed air to be supplied, for example, upstream of the water pump, and the coolant from the exhaust gas recirculation cooler 6 can still be separated in the expansion tank 4. With the solution shown in Figure 1, the compressed air must be introduced into the expansion tank 4 via the vent line.

[0036] If the pressure in cooling circuit 1 is higher than the preset value of the pressure reducer or pressure regulator 7, backflow is prevented by the check valve 9. However, since the pressure in cooling circuit 1 must not become too high at low temperatures (in this example, 500 mbar, which should not be present at coolant temperatures below 60°C), as otherwise excessive pressure loads could occur at high temperatures and the expansion tank 4 would release pressure, a thermostatic valve 11 can be added to the system, which only releases the pressure regulation at a predefined coolant temperature value (for example, at a coolant temperature of 80°C).

[0037] The present invention describes the interconnection of three valve units: pressure regulator 7, check valve 9, and thermostatic valve 11. Compressed air can be injected directly into the air reservoir 12 of the expansion tank 4 or into a section of the cooling circuit 1 that is not or hardly affected by the delivery head of the coolant pump, for example, on the suction side of the coolant pump, into a vent line, or into a filler line of the expansion tank 4. The valves can be arranged in different sequences. The airflow should be controlled by a throttle 8.

[0038] Daimler Truck AG Orlich

[0039] August 26, 2025

[0040] Reference symbol list

[0041] 1 cooling circuit

[0042] 2 Drive motor

[0043] 3 System pressure control unit

[0044] 4 expansion tanks

[0045] 5 intercoolers

[0046] 6 exhaust gas recirculation coolers

[0047] 7 pressure regulators

[0048] 8 throttle

[0049] 9 Check valve

[0050] 10 Inlet line

[0051] 11 Thermostatic valve

[0052] 12 air template

Claims

Daimler Truck AG Orlich August 26, 2025 Patent claims 1. Cooling circuit (1) for cooling a drive motor (2) of a vehicle, comprising a coolant pump and a mechanical system pressure control unit (3) configured to restore an operating pressure of a coolant circulating in the cooling circuit (1) by introducing pressure from an exhaust gas turbocharger, in particular downstream of an intercooler (5), or from a compressed air circuit or a pressure accumulator in which pressure is generated by an air compressor, after the cooling circuit (1) has been opened, wherein the system pressure control unit (3) comprises the following: - a pressure regulator (7) configured to limit a refill pressure to a defined setpoint pressure, - a throttle (8) arranged in an inlet line (10), - a check valve (9) to prevent backflow of pressure from the cooling circuit (1), - a thermostatic valve (11), characterized in that the thermostatic valve (11) is configured to release the pressure control from a predetermined coolant temperature, wherein the compressed air is provided to be fed into the cooling circuit (1) in an area that is not or hardly influenced by a delivery head of the coolant pump, in particular on a suction side of the coolant pump, into a vent line or into a filling line of the expansion tank (4).

2. Method for cooling a drive motor (2) of a vehicle by means of a cooling circuit (1), with a coolant pump and a mechanical system pressure control unit (3) which restores an operating pressure of a coolant circulating in the cooling circuit (1) by introducing pressure from an exhaust gas turbocharger, in particular after an intercooler (5), or from a compressed air circuit or a pressure accumulator in which pressure is generated by an air compressor, after the cooling circuit (1) has been opened, wherein the system pressure control unit (3) comprises the following: - a pressure regulator (7) that limits the refill pressure to a defined target pressure, - a throttle (8) arranged in an inlet line (10), - a check valve (9) that prevents backflow of pressure from the cooling circuit (1), and - a thermostatic valve (11), characterized in that the pressure control by the thermostatic valve (11) is released from a predetermined coolant temperature, wherein compressed air is fed into the cooling circuit (1) into an area that is not or hardly influenced by a delivery head of the coolant pump, in particular on a suction side of the coolant pump, into a vent line or into a filling line of the expansion tank (4).

3. Method according to claim 2, characterized in that the specified coolant temperature is 70°C to 85°C, in particular 70°C, 80°C, 82°C or 85°C.

4. Method according to claim 2 or 3, characterized in that the constant target pressure is 500 mbar.

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