DE102020127296B4 - Method for detecting leaks in a hydraulic steering system, control device, vehicle, computer program and computer-readable medium - Google Patents

Abstract

Method for detecting leaks in a hydraulic steering system (10) of a vehicle (1), the hydraulic steering system (10) comprising: a hydraulic cylinder (20) with a piston (22) movably arranged within the hydraulic cylinder (20), which forms a first chamber (24) and a second chamber (26) within the hydraulic cylinder (20), and a position sensor (30) arranged to detect the position of the piston (22) within the hydraulic cylinder (20), the piston (22) being connected to wheels (6) of a wheel axle (8) such that a movement of the piston (22) will steer the wheels (6), the method comprising: steering (s101) the wheels (6) from a central position (PC) to a first predetermined position (P1) by controlling the piston (22) in a first direction (D1), and detecting (s102) a leak in the hydraulic steering system (10) based on a detected Movement of the piston (22) in a second direction (D2) opposite to the first direction (D1), wherein any movement of the piston (22) is detected by means of the position sensor (30).

Description

The invention relates to a method for detecting leaks in a hydraulic steering system of a vehicle. The invention also relates to a control device for detecting leaks in a hydraulic steering system, a vehicle comprising such a control device, a computer program and a computer-readable medium.

Vehicles today may include hydraulic steering systems for steering the wheels of the vehicle. Such a system typically includes a hydraulic cylinder with a reciprocating piston that applies a force to steer the wheels. The piston is connected to the wheels such that moving the piston turns the wheels. Valves may be controlled to regulate the flow of working fluid/hydraulic fluid to the hydraulic cylinder based on the torque applied to the vehicle's steering wheel. A hydraulic steering system may further include a position sensor for sensing the position of the piston in the hydraulic cylinder and thus monitoring the steering angle. For example, vehicle axles may be locked in a position where the wheels point straight ahead when the vehicle is operating at high speed. This means that the piston should be held in a center position. If the piston moves out of its center position during such operation, it can be assumed that there is either a leak in the system or that the system has been subjected to large impulse forces induced by the road. Therefore, unexpected movement of the piston can indicate a leak or potentially reckless driving behavior. In today's systems, the driver can be informed of the unexpected movement and/or the operator can be prompted to visit a workshop to investigate the suspected leak.

There can be different reasons for leakage in a hydraulic steering system and the fact that the piston is moving does not explain where the leak is coming from. The reason for the leakage must therefore be sought in the workshop and this can be a time-consuming process. The vehicle can therefore spend a long time in the workshop, which is a disadvantage.

From the DE 19 47 205 A a hydraulic steering system of a vehicle is known which has a hydraulic cylinder with a piston which is movably arranged within the hydraulic cylinder and which forms a first chamber and a second chamber within the hydraulic cylinder, and a position sensor which is arranged to detect the position of the piston within the hydraulic cylinder, wherein the piston is connected to wheels of a wheel axle in such a way that a movement of the piston will steer the wheels. According to the cited publication, leaks in the hydraulic steering system are minimized in such a way that a comparison takes place between the piston position detected by the position sensor and the steering angle detected by a steering column sensor.

From the DE 199 18 354 A1 Leak and pressure sensors are known for determining leaks in a hydraulic cylinder.

From the JP S61-282 165 A A testing device for leak testing of a hydraulic cylinder is known.

Regardless of known solutions in this field, it would be desirable to develop a method for leak detection in a hydraulic steering system of a vehicle, which avoids or at least reduces disadvantages of the state of the art.

The aim of the present invention is therefore to achieve a new and advantageous method which enables detection and verification of small internal leaks in a hydraulic steering system of a vehicle. A further aim is to obtain a new and advantageous method for leak detection in a hydraulic steering system of a vehicle which leads to an accurate assessment of the faulty component causing the leak and thereby enables a quick and more accurate repair of the hydraulic steering system.

The objects mentioned here are achieved by a method for detecting leaks in a hydraulic steering system, a control device for detecting leaks in a hydraulic steering system, a vehicle, a computer program and a computer-readable medium according to the independent patent claims.

Consequently, according to one aspect of the present invention, a method for leak detection in a hydraulic steering system of a vehicle is provided, the hydraulic steering system comprising: a hydraulic cylinder with a piston movably arranged within the hydraulic cylinder, which piston forms a first chamber and a second chamber within the hydraulic cylinder, and a position sensor arranged to detect the position of the piston within the hydraulic cylinder, the piston being connected to wheels of a vehicle axle such that a movement of the piston will steer the wheels. The method comprises: steering the wheels from a central position to a first predetermined position by controlling the piston in a first direction, and detecting a leak in the hydraulic steering system based on a detected movement of the piston in a second direction opposite to the first direction, wherein any movement of the piston is detected by means of the position sensor.

According to a further aspect of the invention, a control device for detecting leaks in a hydraulic steering system of a vehicle is provided, the hydraulic steering system comprising: a hydraulic cylinder with a piston movably arranged within the hydraulic cylinder, which piston forms a first chamber and a second chamber within the hydraulic cylinder, and a position sensor arranged to detect the position of the piston within the hydraulic cylinder, the piston being connected to wheels of a wheel axle such that a movement of the piston will steer the wheels, the control device being arranged in communication with the position sensor and being adapted to detect a leak in the hydraulic steering system based on a detected movement of the piston in a second direction opposite to the first direction after the wheels have been steered from a central position to a first predetermined position by controlling the piston in a first direction, any movement of the piston being detected by means of the position sensor.

According to yet another aspect of the invention, there is provided a vehicle with a hydraulic steering system, the hydraulic steering system comprising: a hydraulic cylinder having a piston movably arranged within the hydraulic cylinder, the piston forming a first chamber and a second chamber within the hydraulic cylinder, and a position sensor arranged to detect the position of the piston within the hydraulic cylinder, the piston being connected to wheels of a wheel axle of the vehicle such that movement of the piston will steer the wheels, the vehicle further comprising a control device as disclosed herein.

A hydraulic steering system for a vehicle comprises a large number of components which can fail and/or cause a leak for various reasons. An external leak may be easily detected visually, but an internal leak of the hydraulic steering system can be very difficult to detect and it can be very difficult to find out which component is causing the leak. An internal leak can be caused, for example, by faulty pressure valves, which are typically located on each side of the piston, or by a defective piston seal. Today it is known to detect an unexpected movement of the piston in a hydraulic steering system and thereby detect a possible leak. In order to find out where the leak is located, tests must be carried out in a workshop or the entire assembly with the cylinder, piston and valves may have to be replaced to ensure that the leak is eliminated. This is very expensive. Steering the wheels from a central position to a first predetermined position means, according to the present invention, that the piston is controlled to be displaced in a first direction. The first chamber of the hydraulic cylinder is formed on one side of the piston and the second chamber of the hydraulic cylinder is formed on the other side of the piston. Thus, by controlling the piston in one direction, one of the first chamber and the second chamber will become smaller and the other chamber will become larger. More specifically, the chamber on the side of the piston in which direction the piston is controlled to move will become smaller. The first chamber may be on a first side of the piston and the second chamber is on the second side of the piston. Thus, controlling the piston in a first direction may decrease the volume of the first chamber and increase the volume of the second chamber and vice versa. After the wheels have been steered to the first predetermined position, a force directed to rotate the wheels back to the center position will be generated due to the elastic hysteresis of the tires of the wheels and a force in the second direction will thereby be exerted on the piston. The pressure within the second chamber, which had previously been actively increased by controlling the piston in the first direction, will thereby increase. If no leakage exists, the piston will remain in the same position despite the force exerted. If there is a leak associated with the second chamber or in the piston seal, the force on the piston caused by the tire hysteresis will cause the hydraulic fluid to move out of the second chamber, to the outside in the case of an external leak, or into the first chamber in the case of an internal leak, to reduce the pressure in the second chamber. The piston will thereby move in the second direction. Any detected movement of the piston in the second direction thus represents a reaction movement caused by the tire hysteresis. By controlling the wheels and the piston in a first direction and then detecting movement of the piston in the second direction opposite to the first direction, it can thus be concluded that a leak associated with the second chamber or in the piston seal. In this way, not only is a leak detected, but also the defective component is identified or the cause of the leak is at least narrowed down, for example to the exact side of the piston. The workshop can therefore spend less time identifying the defective component and can carry out a quick and accurate repair. The vehicle will spend less time in the workshop, which reduces costs for the vehicle owner, and instead of the entire cylinder assembly, only the defective component can be replaced. Furthermore, by using the natural phenomenon of hysteresis in the wheel tires, the method does not require active control or external loads/forces applied to the piston to detect a leak in the hydraulic steering system. The method according to the present invention is therefore less complex, cheaper and more efficient.

Additional objects and advantages of the present invention will become apparent to one skilled in the art from the following details and from practice of the invention. While examples of the invention are described below, it is to be understood that the invention is not limited to the precise details described. Those skilled in the art having access to the teachings contained herein will recognize further applications, modifications and incorporations into other fields that are within the scope of the invention.

Short description of the characters

• 1 schematisch eine Seitenansicht eines Fahrzeugs gemäß einem Beispiel darstellt,
• 2 schematisch Details eines hydraulischen Lenksystems für ein Fahrzeug gemäß einem Beispiel darstellt,
• 3 schematisch ein Blockdiagramm eines Verfahrens zur Leckageerkennung in einem hydraulischen Lenksystem gemäß einem Beispiel darstellt,
• 4 a - b schematisch Details eines Fahrzeugs während eines Verfahrens zur Leckageerkennung in einem hydraulischen Lenksystem gemäß einem Beispiel wiedergeben,
• 5 Kurven darstellen, die ein Verfahren zur Leckageerkennung in einem hydraulischen Lenksystem gemäß einem Beispiel betreffen, und
• 6 schematisch eine Steuereinrichtung oder einen Computer gemäß einem Beispiel darstellen.

For a better understanding of the present invention and further objects and advantages thereof, the following detailed description should be read in conjunction with the accompanying figures, in which like reference numerals designate like items in the several drawings, and in which:

• 1 schematically illustrates a side view of a vehicle according to an example,
• 2 schematically illustrates details of a hydraulic steering system for a vehicle according to an example,
• 3 schematically illustrates a block diagram of a method for leak detection in a hydraulic steering system according to an example,
• 4 a - b schematically illustrate details of a vehicle during a method for detecting leaks in a hydraulic steering system according to an example,
• 5 illustrate curves relating to a method for detecting leaks in a hydraulic steering system according to an example, and
• 6 schematically illustrate a controller or computer according to an example.

Detailed description

In order to improve the handling of leaks in a hydraulic steering system, a method, a control device and a vehicle according to the invention have been developed.

Thus, according to one aspect of the present invention, there is provided a method for detecting leaks in a hydraulic steering system, the hydraulic steering system comprising: a hydraulic cylinder with a piston movably arranged within the hydraulic cylinder, which piston forms a first chamber and a second chamber within the hydraulic cylinder, and a position sensor arranged to detect the position of the piston within the hydraulic cylinder, the piston being connected to wheels of a wheel axle such that movement of the piston will steer the wheels. The method comprises steering the wheels from a central position to a first predetermined position by controlling the piston in a first direction, and detecting a leak in the hydraulic steering system based on a detected movement of the piston in a second direction opposite to the first direction, any movement of the piston being detected by means of the position sensor. As previously described, any detected movement of the piston in the second direction is caused by tire hysteresis. The detected movement of the piston in the second direction is thus a reaction movement or non-controlled movement.

It is understood that the precise structure of the hydraulic steering system and how the piston is connected to the wheel axle does not per se form part of the invention. The hydraulic steering system can thus be designed as a conventional hydraulic steering system.

The hydraulic cylinder may be a double-acting cylinder. The hydraulic cylinder houses a hydraulic fluid. The first chamber of the hydraulic cylinder may be formed on a first side of the piston and the second chamber may be formed on a second side of the piston. Detected movement of the piston in the second direction may indicate a leak in connection with the second chamber. This may also be referred to as a leak on the second side of the piston. The hydraulic steering system may include a piston seal arranged to be between the piston and the hydraulic cylinder and thereby ensure that hydraulic fluid cannot flow past the piston between the chambers. Displacing the piston in the first direction may reduce the volume of the first chamber and increase the volume of the second chamber, and vice versa. The first chamber and the second chamber may be in fluid communication with a container for the hydraulic fluid. To steer the wheels, the hydraulic steering system is controlled so that hydraulic fluid flows from one chamber to the other, thereby increasing the pressure in the chamber receiving the hydraulic fluid. The piston will thereby be displaced so that the volume of the receiving chamber increases and the pressure decreases. Since the piston is connected to the wheels, the wheels will be turned when the piston is displaced. Thus, steering the wheels by controlling the piston in a first direction includes controlling the flow of hydraulic fluid in the hydraulic steering system such that the piston is displaced in the first direction. As an example, to steer the wheels in a first steering direction, the hydraulic steering system may be controlled such that hydraulic fluid in the first chamber will flow into the second chamber. The amount of hydraulic fluid in the second chamber is thereby increased and the piston is thereby controlled to be displaced in the first direction. Similarly, to steer the wheels in a second steering direction, the hydraulic steering system may be controlled such that hydraulic fluid in the second chamber will flow into the first chamber so that the amount of hydraulic fluid in the first chamber is increased and the piston is thereby controlled to be displaced in the second direction. The hydraulic fluid may flow between the chambers via the reservoir.

The hydraulic steering system may further comprise a hydraulic pump. The hydraulic fluid may be circulated in the hydraulic steering system by means of the hydraulic pump. A predetermined and controlled displacement of the piston is thus achieved by a hydraulic pump, whereas the detected movement caused by hysteresis of the wheels is a movement that is achieved without the influence of the hydraulic pump. Steering the wheels from a central position to a first predetermined position by controlling the piston in a first direction may thus comprise controlling the hydraulic pump such that the piston is displaced in the first direction. The flow of hydraulic fluid into the associated chamber may further be regulated by controlling a valve arrangement. The hydraulic steering system may therefore comprise a valve arrangement.

The piston may have a center position corresponding to the center position of the wheels. The center position of the wheels means that the wheels are directed straight ahead. The center position of the piston may be a position in which the first chamber and the second chamber have substantially the same volume. The piston may be directly or indirectly connected to the wheels, as long as displacement of the piston in the first or second direction can turn the wheels.

The position sensor may be arranged in connection with the piston in the hydraulic cylinder. The position sensor may therefore be referred to as a cylinder piston sensor. The position sensor may be a sensor with a relatively high accuracy to enable detection of small movements of the piston. As an example, the position sensor may be designed to detect piston movements of 0.1 mm or more. The precision and accuracy of the position sensor may be adapted to the degree of leakage that is to be detected. The smaller movements the position sensor can detect, the smaller leaks can be detected. The position sensor may be a linear sensor. For example, the position sensor may be a linear transducer. It is understood that the position sensor may be any sensor that is arranged anywhere in the hydraulic steering system to directly or indirectly detect piston movements.

In accordance with an example, the method further comprises steering the wheels to a second predetermined position by controlling the piston in the second direction and detecting a leak in the hydraulic steering system based on a detected movement of the piston in the first direction. Detecting a movement of the piston in the first direction may indicate a leak in connection with the first chamber. This may also be referred to as a leak on the first side of the piston. As previously explained, by controlling the piston in a first direction and then detecting a movement of the piston in the second direction opposite the first direction, it may be inferred that a leak may be present in connection with the second chamber or in the piston seal. The detected movement of the piston in the first direction after controlling the piston in the second direction is a reactive or non-controlled movement caused by tire hysteresis. In order to be able to determine whether a leak is also present in the other chamber, it may be necessary to perform the method in both directions. Steering the wheels into the second predetermined position thus includes steering the wheels in a direction opposite to that in which the wheels were steered into the first predetermined position. Thus the wheels can be steered from the center position to the first predetermined position and the tire hysteresis will then generate a force directed to rotate the wheels back to the center position. This will apply a force to the piston in the second direction opposite to the first direction. If a leak exists, hydraulic fluid will flow from the second chamber into the first chamber and the piston will move in the second direction. The piston movement will be detected by the piston sensor and a leak in the second chamber or in the piston seal can be concluded. The wheels are then steered to a second predetermined position by controlling the piston in the second direction. The tire hysteresis will then generate a force directed to rotate the wheels back to the first predetermined position. This will apply a force to the piston in the first direction and if a leak exists, hydraulic fluid will flow from the first chamber into the second chamber and the piston will move in the first direction. The piston movement will be detected by the piston sensor and a leak in the first chamber or in the piston seal can be concluded. In this way, a leak on both sides of the piston can be detected in a time-saving and easy manner.

The first predetermined position of the wheels may be a position halfway to the maximum turning position of the wheels. The first predetermined position may have been empirically determined to be a position in which the force generated by tire hysteresis is as large as possible. The second predetermined position of the wheels may be the center position of the wheels. The wheels may thus first be turned halfway to detect a leak in one of the chambers and then steered back to the center position to detect a leak in the other chamber. Alternatively, the second predetermined position is a position halfway to the maximum turning position of the wheels in the opposite direction to the first predetermined position. The first predetermined position may thus be a right-turned position and the second predetermined position may be a left-turned position, or vice versa. In this case, the step of steering the wheels to the second predetermined position may comprise steering the wheels from the center position to the second predetermined position. The wheels may thus have been steered to the center position after a leak has been detected in one of the chambers before being turned to detect a leak in the other chamber.

The step of steering the wheels can be performed manually or automatically. The step of steering the wheels can thus be performed by manually moving a steering wheel of the vehicle, thereby controlling the piston to be displaced and thereby turning the wheels. Alternatively, the wheels are steered automatically by automatically controlling the steering column and thereby controlling the piston.

According to one example, a movement of the piston in the first direction indicates a leak in a first valve arranged in communication with the first chamber of the hydraulic cylinder. That is, a non-controlled movement of the piston in the first direction may indicate a leak in a first valve arranged in communication with the first chamber of the hydraulic cylinder. If the first valve leaks, the increased pressure in the first chamber caused by the force acting on the piston in the first direction causes hydraulic fluid to leak out of the first chamber via the defective first valve. The hydraulic fluid leaking out of the first chamber may flow back into a container for the hydraulic fluid. In the same way, a non-controlled movement of the piston in the second direction may indicate a leak in a second valve arranged in communication with the second chamber of the hydraulic cylinder. The valve arrangement of the hydraulic steering system may thus have a first valve arranged in communication with the first chamber and a second valve arranged in communication with the second chamber. The first valve and the second valve may be controllable to regulate the flow of hydraulic fluid into the first chamber and the second chamber, respectively. The first valve and the second valve may be pressure relief valves that allow hydraulic fluid flow in one direction to reduce the pressure in the chambers. Alternatively, the first valve and the second valve are pressure relief valves that are designed to allow flow in only one direction.

According to one example, a leak may be detected if the sensed piston movement exceeds a predetermined threshold distance. Thus, a slight movement of the piston caused by tire hysteresis may be acceptable and may not indicate a leak. The predetermined threshold distance may be within the range of 0.2 - 0.5 mm. This means that if the position sensor senses a movement of the piston that exceeds 0.2 mm, for example, it is concluded that a leak is present. If the piston does not move or moves less than the predetermined threshold distance, it is concluded that there is no leak in the hydraulic steering system. As an example, an unexpected movement of the piston may have been detected during operation of the vehicle and the method according to the present invention is subsequently carried out in a workshop to verify the leakage and/or identify the defective component. If the result of the method is that no leakage is detected, the previously detected movement of the piston may have been caused by high impulse forces induced by the road on the wheels, causing the first and/or second valve to open and thereby allowing movement of the piston.

The method may include issuing an alarm when a leak is detected. The alarm may be an audible, visual or tactile alarm. Additionally or alternatively, the method may include providing instructions to take the vehicle to a repair shop. Such instructions may be issued on a display in the vehicle or a display in a control center if the vehicle is an autonomously operated vehicle.

In accordance with an example, the method according to the invention is carried out in a workshop. Vehicles today may already have a function for detecting a possible leak in the hydraulic steering system. However, there may still be a need to determine the cause of the leak and in this way where the leak is located. The operator of the vehicle may thus receive an alarm or be prompted to take the vehicle to a workshop where the method according to this invention can be carried out. The method can thus be carried out as a troubleshooting method to identify the cause of the leak when the vehicle has already concluded that a leak may be present. The method can be started manually. For example, the maintenance technician can connect to a control unit of the vehicle and initiate the method. If the method is carried out in a workshop, the method may further comprise displaying information about where in the hydraulic steering system the leak is located. As an example, the method may comprise displaying an image of the hydraulic steering system to visually show where the leak is located. This allows the maintenance technician to easily determine where to start looking for the leak and quickly resolve the problem.

According to a further example, the method according to the invention is carried out automatically. The method may, for example, be carried out during starting of the vehicle. In this case, the method may comprise issuing an alarm if a leak is detected. Alternatively, the method may comprise providing instructions to take the vehicle to a workshop as soon as possible. Such alarm and/or instructions may be designed such that they cannot be cancelled by the vehicle operator, but require a maintenance engineer to cancel them. The vehicle will thus have to be taken to a workshop to investigate the problem and to cancel the instructions. The information given to the vehicle operator may depend on the size of the detected leak. Typically, if the detected leak is relatively small, an alarm may be issued, and if the detected leak is relatively large, the operator may be instructed to visit a workshop immediately. If the control device has detected a leak, the control device may be arranged to store this in a memory of the control device. When a maintenance technician connects to the control device, the maintenance technician is able to obtain information about the detected leak and where the leak is located.

Detecting a leak in the hydraulic steering system based on the sensed movement of the piston may also include determining the size of the leak based on the speed of the piston movement. The larger the leak, the faster the piston moves. The speed of the piston movement may be determined/calculated by sensing the movement of the piston over time. For example, the piston movement may be measured for a predetermined period of time and the piston speed may be calculated based on the movement during that predetermined period of time. The predetermined period of time may be referred to as a detection time. The piston movement may be defined as the distance the piston has moved from a piston position corresponding to the first predetermined position of the wheels or the second predetermined position of the wheels. The predetermined period of time may vary depending on the design of the hydraulic steering system and the current application. The predetermined period of time may also depend on the accuracy of the position sensor and how small leaks of interest are to be detected. Typically, the piston will move from the exact moment the wheel is steered to the predetermined position until the hydraulic fluid has leaked out to the point where the pressure caused by the hysteresis force is negligible. Small leaks will therefore require more detection time than large leaks. In general, the piston will move quickly at the beginning. ler move when the wheels have been turned and the hysteresis force begins to act on the piston. This is because the pressure in the chamber associated with the leak is initially greater, i.e. before the hydraulic fluid has leaked out. Therefore, to determine the size of the leak, it may be appropriate to choose a detection time of between 15 to 30 seconds. As an example, a piston speed below a speed threshold may be considered as a small leak and a piston speed above the speed threshold may be considered as a large leak. Alternatively, the controller may include a lookup table or list of predetermined piston speeds and associated leak sizes stored in a database, wherein determining the size of the leak comprises comparing the detected piston speed with the list. The leak size may thus be determined by data mapping.

Detected uncontrolled movement of the piston in the first direction and the second direction may indicate leakage of both the first valve and the second valve, or leakage of the piston seal between the first and second chambers. Typically, if the magnitude of the leakage is the same in both directions, i.e., if the magnitude of the leakage is the same on both sides of the piston, this may indicate that the leakage is in the piston seal.

According to a further aspect of the present invention, a control device for detecting leaks in a hydraulic steering system of a vehicle is provided. The hydraulic steering system comprises: a hydraulic cylinder with a piston movably arranged within the hydraulic cylinder, which piston forms a first chamber and a second chamber within the hydraulic cylinder, and a position sensor arranged to detect the position of the piston within the hydraulic cylinder, wherein the piston is connected to wheels of a wheel axle such that a movement of the piston will steer the wheels, wherein the control device is arranged in communication with the position sensor and is adapted to detect a leak in the hydraulic steering system based on a detected movement of the piston in a second direction opposite to the first direction after the wheels have been steered from a central position to a first predetermined position by controlling the piston in a first direction, wherein any movement of the piston is detected by means of the position sensor.

It is understood that all embodiments described for the control device aspect of the invention are also applicable to the method aspect of the invention and vice versa. The control device can be implemented as a separate unit or distributed over two or more physical units. The control device can comprise one or more control units and/or computers. The control device can thus be implemented or realized in that the control device has a processor and a memory, wherein the memory contains instructions which, when executed by the processor, cause the control device to carry out the method disclosed herein. The control device can be included in the hydraulic steering system or the control device can be a vehicle-external control device.

The controller may be configured to detect a leak in the hydraulic steering system based on a detected movement of the piston in the first direction after the wheels have been steered to a second predetermined position by controlling the piston in the second direction. The controller may be configured to detect a leak when the detected piston speed exceeds a predetermined threshold distance. The controller may be configured to detect a leak when the detected piston movement exceeds a predetermined threshold distance within the range of 0.2 to 0.5 mm.

The control device may be arranged to determine the size of the leakage based on the speed of the piston movement. The control device may be arranged to determine the speed of the piston movement, also referred to as piston speed. The control device may be arranged to steer the wheels from the center position to the first predetermined position by controlling the piston in the first direction. The control device may further be arranged to steer the wheels to the second predetermined position by controlling the piston in the second direction. The control device is typically arranged to steer the wheels when the method according to the invention is carried out automatically, for example during starting of the vehicle. Alternatively, the control device is arranged to display instructions to a vehicle operator or maintenance technician for manually steering the wheels.

According to yet another aspect of the present invention, a vehicle with a hydraulic steering system. The hydraulic steering system comprises: a hydraulic cylinder with a piston movably arranged within the hydraulic cylinder, which piston forms a first chamber and a second chamber within the hydraulic cylinder, and a position sensor arranged to detect the position of the piston within the hydraulic cylinder, wherein the piston is connected to wheels of a wheel axle of the vehicle such that a movement of the piston steers the wheels. The vehicle further comprises a control device as disclosed herein. The control device can thus be part of the vehicle and the method can be carried out automatically by means of the control device. Alternatively, the control device is located in a workshop and is connected to the vehicle in order to carry out the method.

The present invention will now be further illustrated with reference to the accompanying figures.

1 shows schematically a side view of a vehicle 1 according to an example. The exemplary vehicle 1 may be a heavy vehicle in the form of a truck, bus or the like. The vehicle 1 may have a drive unit 2, a transmission 4 and a hydraulic steering system 10 for steering the wheels 6 of a wheel axle 8. The hydraulic steering system 10 is further described with reference to 2, 3, 4a - 4 and 5 explained. The drive unit 2 can comprise an internal combustion engine or an electric machine. The wheels 6, which are steered by means of the hydraulic steering system 10, have tires 12.

2 shows schematically details of a hydraulic steering system 10 for a vehicle 1 according to an example. The vehicle 1 can be as in 1 be clearly designed. 2 shows a wheel axle 8 with the wheels 6 in a central position P _C and thus arranged parallel and pointing straight ahead. The hydraulic steering system 10 comprises a hydraulic cylinder 20 with a piston 22 which is movably arranged within the hydraulic cylinder 20 and forms a first chamber 24 and a second chamber 26 within the hydraulic cylinder 20, and a position sensor 30 which is arranged to determine the position of the piston 22 within the hydraulic cylinder 20. The piston 22 is connected to the wheels 6 of the wheel axle 8 such that a movement of the piston 22 will turn the wheels 6.

The hydraulic cylinder 20 may be a double-acting cylinder. The hydraulic cylinder 20 houses a hydraulic fluid 28. The first chamber 24 of the hydraulic cylinder may be formed on a first side of the piston 22 and the second chamber 26 may be formed on a second side of the piston 22. The hydraulic steering system may include a piston seal 23 arranged to seal between the piston 22 and the hydraulic cylinder 20 and thereby ensure that hydraulic fluid 28 cannot flow past the piston 22 between the chambers 24, 26. The hydraulic steering system 10 may further include a reservoir 40 for hydraulic fluid 28. The first chamber 24 and the second chamber 26 may be in fluid communication with this reservoir 40.

The hydraulic steering system 10 may further include a hydraulic pump 42. The hydraulic fluid 28 may be circulated in the hydraulic steering system 10 by means of the hydraulic pump 42. The hydraulic steering system 10 may further include a valve assembly 50 for regulating the flow of hydraulic fluid 28 into the chambers 24, 26. The valve assembly 50 may include a first valve 52 and a second valve 54. The first valve 52 may be arranged in communication with the first chamber 24 and the second valve 54 may be arranged in communication with the second chamber 26.

The position sensor 30 can be arranged in connection with the piston 22 in the hydraulic cylinder 20. The position sensor 30 can be a sensor with relatively high accuracy to enable small movements of the piston 22 to be detected. The position sensor 30 can be a linear sensor.

The hydraulic steering system 10 may further comprise a control device 100. The control device 100 may be configured to detect a leak in the hydraulic steering system 10. The control device 100 may be arranged in connection with the position sensor 30, the valves 52, 54 and the hydraulic pump 42. The control device 100 is configured to, after the wheels 6 have been moved by controlling the piston 22 in a first direction D1 from a central position P _C to a first predetermined position P1 (see 4a) have been steered, to detect a leak in the hydraulic steering system 10 based on a detected self-movement or non-controlled movement of the piston 22 in a second direction D2 opposite the first direction D1, wherein any movement of the piston 22 is detected by means of the position sensor 30. The control device 100 can further be configured to steer the wheels 6 by controlling the piston 22 in a first direction D1 from the center position P _C to the first predetermined position P1. The control device 100 can be configured to control the hydraulic pump 42 and/or the valves 52, 54 such that the piston 22 is displaced in the first direction D1 in order to steer the wheels 6 from the center position P _C to the first predetermined position P1.

The control device 100 can be designed to, after the wheels 6 have been steered into a second predetermined position P2 by controlling the piston 22 in the second direction D2 (see 4b) to detect a leak in the hydraulic steering system 10 based on a detected movement of the piston 22 in the first direction D1. The control device 100 can also be configured to steer the wheels 6 into the second predetermined position P2 by controlling the piston 22 in the second direction D2. The control device 100 can be configured to control the hydraulic pump 42 and/or the valves 52, 54 such that the piston 22 is displaced in the second direction D2 in order to steer the wheels 6 into the second predetermined position P2.

The control device 100 may be further configured to detect a leak when the detected piston movement exceeds a predetermined threshold distance. The control device 100 may be further configured to detect a leak when the detected piston movement exceeds a predetermined threshold distance in the range of 0.2 to 0.5 mm. Furthermore, the control device 100 may be configured to determine the size of the leak based on the speed of the piston movement. The control device may be configured to determine the speed of the piston movement, also referred to as piston speed, based on the change in the piston position over time. The control device 100 may be configured to display instructions to a vehicle operator or maintenance technician for manually steering the wheels 6 to the first predetermined position P1 or the second predetermined position P2. The control device 100 may be further configured to display an image of the hydraulic steering system indicating where the leak is located.

3 shows schematically a block diagram of a method for leak detection in a hydraulic steering system 10 of a vehicle 1. The method can be a vehicle 1 as in 1 and a hydraulic steering system 10 as in 2 The method can be carried out by a control device 100 as in 2 or 6 revealed. The 4a and 4b show schematic examples of a vehicle which carries out the method. The method is therefore described with reference to both 3 as well as the 4a and 4b described. In the 4a and 4b For clarity, only the components associated with the hydraulic cylinder 20 of the hydraulic steering system 10 are shown. The method comprises: steering s101 the wheels 6 from a central position P _C to a first predetermined position P1 by controlling the piston 22 in a first direction D1, and detecting a leak in the hydraulic steering system 10 based on a detected movement of the piston 22 in a second direction D2 opposite the first direction D1, wherein any movement of the piston 22 is detected by means of the position sensor 30.

4a shows the vehicle 1 when the wheels 6 have been steered into the first predetermined position P1 by controlling the piston 22 in the first direction D1. The steering force acting on them when steering the wheels 6 into the first predetermined position P1 is shown with a dashed arrow. By controlling the piston 22 in the first direction D1, the first chamber 24 becomes smaller and the second chamber 26 becomes larger. After the wheels 6 have been steered into the first predetermined position P1, a steering force TF2 directed to turn the wheels 6 back to the center position P _C will be generated due to the elastic hysteresis of the tires 12 of the wheels 6. This steering force TF2 is shown in the figure with an arrow. A force F2 in the second direction D2 will thereby be applied to the piston 22. The pressure within the second chamber 26 will thereby increase. If no leakage exists, the piston 22 will remain in the same position despite the applied force F2. If a leak exists in connection with the second chamber 26 or the piston seal 23, the force F2 on the piston 22 caused by the tire hysteresis will cause the hydraulic fluid 28 to move out of the second chamber 26 into the first chamber 24 to reduce the pressure in the second chamber 26. The piston 22 will therefore move in the second direction D2. Thus, movement of the piston 22 in the second direction D2 indicates a leak in connection with the second chamber 26 or the piston seal 23.

Steering s101 of the wheels 6 from the center position P _C to the first predetermined position P1 by controlling the piston 22 in the first direction D1 may include controlling the flow of hydraulic fluid 28 in the hydraulic steering system 10 such that the piston 22 is displaced in the first direction D1. Steering s101 of the wheels 6 from the center position P _C to the first predetermined position P1 by controlling the piston 22 in the first direction D1 may include controlling the hydraulic pump 42 such that the piston 22 is displaced in the first direction D1. The flow of hydraulic fluid 28 into the corresponding chamber 24, 26 may be further regulated by controlling the valve arrangement 50.

The method may further comprise controlling s103 the wheels 6 to a second predetermined position P2 by controlling the piston 22 in the second direction D2 and detecting s104 a leak in the hydraulic steering system 10 based on a detected movement of the piston 22 in the first direction D1. 4b shows a situation in which the wheels 6 have been steered to the second predetermined position P2. The steering force acting on the wheels 6 when they are steered to the second predetermined position P2 is shown with a dashed arrow. In this example, the second predetermined position P2 is the middle position P _C . After the wheels 6 have been steered to the second predetermined position P2, due to the elastic hysteresis of the tires 12, a steering force TF1 will be generated on the wheels 6, directed to turn the wheels 6 back to the first predetermined position P1. This steering force TF1 is shown with an arrow in the figure. As a result, a force F1 in the first direction D1 is applied to the piston 22. The pressure within the first chamber 24 will thereby increase. If no leakage exists, the piston 22 will remain in the same position despite the applied force F1. If there is a leak associated with the first chamber 24 or the piston seal 23, the force F1 on the piston 22 caused by the tire hysteresis will cause the hydraulic fluid 28 to move out of the first chamber 24 into the second chamber 26 to reduce the pressure in the first chamber 24. The piston 22 will therefore move in the first direction D1. Thus, movement of the piston 22 in the first direction D1 indicates a leak associated with the first chamber 24 or the piston seal 23. Through these additional process steps, a leak on both sides of the piston 22 can be detected in a time-saving and simple manner.

The step of steering s101, s103 of the wheels 6 can be carried out manually or automatically. Detecting s102 a leak in the hydraulic steering system 10 based on a detected movement of the piston 22 in a second direction D2 can indicate a leak in the second valve 54. Detecting s104 a leak in the hydraulic steering system 10 based on a detected movement of the piston 22 in the first direction D1 can indicate a leak in the first valve 52.

A leak can be detected s102, s104 if the detected piston movement exceeds a predetermined threshold distance. Thus, a slight movement of the piston 22 caused by the tire hysteresis must not indicate a leak. The predetermined threshold distance can be within the range of 0.2 to 0.5 mm.

The method may optionally comprise issuing an alarm when a leak is detected. The alarm may be an audible, visual or tactile alarm. Additionally or alternatively, the method comprises providing instructions to take the vehicle 1 to a workshop. Such instructions may be issued on a display in the vehicle 1 or a display in a control center if the vehicle 1 is an autonomously operated vehicle.

The method may be carried out in a workshop for troubleshooting. The method may be initiated manually, for example by moving a steering wheel of the vehicle 1 to steer s101, s103 the wheels 6. The method may further comprise displaying information about where in the hydraulic steering system 10 the leak is located. As an example, the method may comprise displaying an image of the hydraulic steering system 10 to visualize where the leak is located. In this way, the maintenance technician can easily determine where to start looking for the leak and can quickly solve the problem.

The method may be performed automatically. The method may, for example, be carried out during starting of the vehicle 1. In this case, the method may comprise issuing an alarm if a leak is detected. Alternatively, the method may comprise providing instructions to take the vehicle 1 to a workshop as soon as possible. If the detected leak is relatively small, an alarm may be issued, and if the detected leak is relatively large, the operator may be instructed to visit a workshop immediately.

The step of detecting s102, s104 a leak in the hydraulic steering system 10 based on a detected movement of the piston 22 caused by tire hysteresis may further comprise determining the size of the leak based on the speed of the piston movement. The piston movement is defined as a distance. The larger the leak, the faster the piston 22 moves. This is shown in the curves of the 5 which show the piston position P changing over time T when a leak is present. The speed of the piston movement can be determined/calculated by detecting the position P of the piston 22 over time. The piston position P can, for example, be measured for a predetermined period of time and the piston speed can be calculated. net based on the change in piston position P (piston movement) during this predetermined period of time.

In the 5 In the example shown, the piston movement has been measured from a first time t1 to a second time t2. During this detection time, the piston 22 will move from a first piston position PP1 to a second piston position PP2. The upper curve shows an example in which the leakage is relatively small. The piston movement S1 is the distance between the first piston position PP1 and the second piston position PP2. The lower curve shows an example in which the leakage is relatively large. Compared to the upper curve, the distance S2 between the first piston position PP1 and the second piston position PP2 is now larger during the same period of time. Thus, with a larger leakage, the piston will move a longer distance during the same period of time compared to a case in which the leakage is smaller. In other words, a greater speed of the piston movement will indicate a larger leakage.

Typically, the piston 22 will move from the moment the wheel 6 has been turned to the predetermined position P1, P2 until the hydraulic fluid 28 has leaked out to such an extent that the pressure caused by the hysteresis force is negligible. Small leaks will thus require more detection time than large leaks. Generally, the piston 22 will initially move faster when the wheels 6 have been turned and the hysteresis force begins to act on the piston 22. This is because the pressure in the chamber 24, 26 connected to the leak is initially greater before the hydraulic fluid 28 has leaked out. Therefore, in order to determine the size of the leak, it may be appropriate to have a detection time of between 15 to 30 seconds. As an example, a piston speed below a speed threshold may be considered a small leak and a piston speed above the speed threshold may be considered a large leak. Alternatively, the controller 100 may have a look-up table or list of predetermined piston speeds and associated leak sizes stored in a database, wherein determining the size of the leak comprises comparing the determined piston speed with the list. The leak size may thus be determined by data mapping. If the size of the leak is the same in both directions, i.e., if the size of the leak on both sides of the piston 22 is the same, this may indicate that the leak is in the piston seal 23.

6 is a schematic of a version of a device 500. The device described with reference to 2 The control device 100 described may comprise the device 500 in one version. The device 500 has a non-volatile memory 520, a data processing unit 510 and a read/write memory 550. The non-volatile memory 520 has a first memory element 530 in which a computer program, e.g. an operating system, is stored for controlling the function of the device 500. The device 500 further comprises a bus controller, a serial data port, input/output means, an A/D converter, a time and date input and transmission unit, an event counter and an interrupt controller (not shown). The non-volatile memory 520 also has a second memory element 514.

A computer program P is provided which has routines for detecting leaks in a hydraulic steering system of a vehicle. The computer program P further comprises routines for steering the wheels from a center position to a first predetermined position by controlling the piston in a first direction and detecting a leak in the hydraulic steering system based on a detected movement of the piston in a second direction opposite to the first direction, wherein any movement of the piston is detected by means of the position sensor. The computer program P can also comprise routines for steering the wheels to a second predetermined position by controlling the piston in the second direction and for detecting a leak in the hydraulic steering system based on a detected movement of the piston in the first direction. The computer program P can also comprise routines for detecting leaks when the detected piston movement exceeds a predetermined threshold distance. The computer program P can also comprise routines for determining the size of the leak based on the speed of the piston movement. The program P can be stored in an executable form or in a compressed form in a memory 560 and/or in a random access memory 550.

Where the data processing unit 510 is described as executing a particular function, this means that the data processing unit 510 executes a particular part of the program stored in the memory 560 or a particular part of the program stored in the random access memory 550.

The data processing device 510 can communicate with a data connection 599 via a data bus 515. The non-volatile memory 520 is for communication with the data processing unit 510 via a data bus 512. The separate memory 560 is provided to communicate with the data processing unit 510 via a data bus 511. The read-write memory 550 is designed to communicate with the data processing device 510 via a data bus 514.

When data is received on the data port 599, it is temporarily stored in the second storage element 540. When received input data has been temporarily stored, the data processing unit 510 is ready to perform code execution as described above.

Parts of the method described herein may be performed by the device 500 by means of the data processing unit 510 on which the program stored in the memory 560 or the random access memory 550 is executed. When the device 500 executes the program, methods described herein are performed.

The foregoing description of preferred embodiments of the present invention is for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the variations described. Many modifications and changes will be apparent to those skilled in the art. The embodiments were chosen and described in order to best explain the principles of the invention and its practical applications, and to thereby enable those skilled in the art to understand the invention in terms of different embodiments and with the various modifications suited to the intended use.

Claims (15)

Method for detecting leaks in a hydraulic steering system (10) of a vehicle (1), the hydraulic steering system (10) comprising: a hydraulic cylinder (20) with a piston (22) movably arranged within the hydraulic cylinder (20), which forms a first chamber (24) and a second chamber (26) within the hydraulic cylinder (20), and a position sensor (30) arranged to detect the position of the piston (22) within the hydraulic cylinder (20), the piston (22) being connected to wheels (6) of a wheel axle (8) such that a movement of the piston (22) will steer the wheels (6), the method comprising: steering (s101) the wheels (6) from a central position (P _C ) to a first predetermined position (P1) by controlling the piston (22) in a first direction (D1), and detecting (s102) a leak in the hydraulic steering system (10) based on a detected movement of the Piston (22) in a second direction (D2) opposite to the first direction (D1), wherein any movement of the piston (22) is detected by means of the position sensor (30). Procedure according to Claim 1 , further comprising: steering (s103) the wheels (6) to a second predetermined position (P2) by controlling the piston (22) in the second direction (D2), and detecting (s104) a leakage in the hydraulic steering system (10) based on a detected movement of the piston (22) in the first direction (D1). Procedure according to Claim 2 , wherein a movement of the piston (22) in the first direction (D1) indicates a leakage in a first valve (52) arranged in communication with the first chamber (24) of the hydraulic cylinder (20). A method according to any preceding claim, wherein movement of the piston (22) in the second direction (D2) indicates a leak in a second valve (54) arranged in communication with the second chamber (26) of the hydraulic cylinder (20). A method according to any preceding claim, wherein a leak is detected when the sensed piston movement exceeds a predetermined threshold distance. Procedure according to Claim 5 where the predetermined threshold distance is within the range of 0.2 to 0.5 mm. A method according to any preceding claim, wherein detecting a leak in the hydraulic steering system (10) comprises determining the size of the leak based on the speed of piston movement. Procedure according to Claim 3 and 4 , wherein movement of the piston (22) in the first direction (D1) and the second direction (D2) indicates a leak in both the first valve (52) and the second valve (54) or a leak in a piston seal (23) between the first chamber (24) and the second chamber (26). Computer program (P) with instructions which, when the program is executed by a computer (100; 500), cause the computer (100; 500) to carry out the method according to one of the preceding claims. A computer-readable medium having instructions which, when executed by a computer (100; 500), cause the computer (100; 500) to perform the method of any of the Claims 1 until 8th to carry out. Control device (100) for detecting leaks in a hydraulic steering system (10) of a vehicle (1), wherein the hydraulic steering system (10) comprises: a hydraulic cylinder (20) with a piston (22) movably arranged within the hydraulic cylinder (20), which forms a first chamber (24) and a second chamber (26) within the hydraulic cylinder (20), and a position sensor (30) arranged to detect the position of the piston (22) within the hydraulic cylinder (20), wherein the piston (22) is connected to wheels (6) of a wheel axle (8) such that a movement of the piston (22) will steer the wheels (6), wherein the control device (100) is arranged in communication with the position sensor ( ₃ ) and is designed to detect a leak in the hydraulic steering system (10) based on a detected movement of the piston (22) in a second direction (D2) opposite to the first direction (D1), wherein any movement of the piston (22) is detected by means of the position sensor (30). Control device (100) according to Claim 11 , wherein the control device (100) is adapted to detect a leak in the hydraulic steering system (10) based on a detected movement of the piston (22) in the first direction (D1) after the wheels (6) have been steered into a second predetermined position (P2) by controlling the piston (22) in the second direction (D2). Control device (100) according to Claim 11 or 12 , wherein the control device (100) is arranged to determine the size of the leakage based on the speed of the piston movement. Control device (100) according to one of the Claims 11 until 13 , wherein the control device (100) is adapted to steer the wheels (6) from the central position (P _C ) into the first predetermined position (P1) by controlling the piston (22) in the first direction (D1). Vehicle (1) with a hydraulic steering system (10), the hydraulic steering system (10) comprising: a hydraulic cylinder (20) with a piston (22) movably arranged within the hydraulic cylinder (20), which forms a first chamber (24) and a second chamber (26) within the hydraulic cylinder (20), and a position sensor (30) arranged to detect the position of the piston (22) within the hydraulic cylinder (20), the piston (22) being connected to wheels (6) of a wheel axle (8) of the vehicle (1) such that a movement of the piston (22) will steer the wheels (6), the vehicle (1) further comprising a control device (100) according to one of the Claims 11 until 14 having.

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