DE102012105976A1 - Steering system for follower axis of vehicle, has working cylinder delivering hydraulic fluid through central bore, so that piston is movably floated in center position in which follower axis of impellers is blocked in straight position - Google Patents

Abstract

The system (L) has a steering angle sensor (Salpha) detecting a steering angle of impellers (Rv) of a front axle (Av) of a vehicle (F). A vehicle speed sensor (Sv) detects a driving speed (v) of the vehicle. A controller (C) determines a caster angle (beta) of the impellers of a follower axis (An) of the vehicle from the steering angle and the speed. A working cylinder (Z) delivers hydraulic fluid through a central bore (B), so that a piston (K) is movably floated in a center position (G) in which the follower axis of the impellers is blocked in a straight position and the bore is closed. An independent claim is also included for a method for utilizing steering wheels of a follower axis of a vehicle.

Description

FIELD OF THE INVENTION

The present invention relates to the technical field of the steering systems and more particularly to a steering system for a trailing axle of a vehicle according to claim 1 and a corresponding method for steering a vehicle according to claim 9.

BACKGROUND OF THE INVENTION

Heavy vehicles - especially commercial vehicles - often have more than two axes, so-called trailing axles (NLA). If the NLA are rigid, the vehicles have a large turning circle. Therefore, in addition to a front-axle steering system, a steerable NLA is often installed. The NLA may be force-deflected or adhesion-steered, i. be directed by the return movement of the wheels themselves. This additional NLA steering allows for smaller curve radii, resulting in greater maneuverability. In addition, the slip angle on the tire is reduced, thereby reducing the tire wear of the vehicle.

However, active steering of the NLA is desired only at low speeds. At higher vehicle speeds, no steering of the NLA is desired, as this negatively affects stable driving. The NLA must be fixed at a certain vehicle-dependent speed, so as not to cause an unstable driving condition.

The state of the art is that the NLA is articulated via a hydraulic cylinder. The oil is pumped into one or the other cylinder chamber via a pump that is driven by the internal combustion engine, depending on how the valves are switched. Recently, there are also vehicles in which the steering pump is not driven by the internal combustion engine, but via an electric motor. Since the electric motor can drive equally in both directions, one or the other cylinder chamber can be acted upon by a reversible pump depending on the direction of rotation.

In existing systems, there is the problem that in case of failure or at higher speeds, the axis must be kept in a straight-ahead position with a great deal of effort.

Thus, the German patent application DE 103 51 4S2 A1 shows a steering system in which a hydraulic hinged vehicle rear axle is held with an additional locking device in the current position or hinged back to a center position and then locked in adhesion. However, this requires more components and is therefore expensive; In addition, a lot of space is needed. In many hydraulic systems, the pump is also flanged to the internal combustion engine, so that it is always operated. Therefore, especially in the straight-ahead driving, in which the vehicle is a long time, the hydraulic pump would be constantly driven, although this is not required. In this operating condition, the hydraulics generate losses that are not countered by added value. This is contrary to the demand for a lower fuel consumption of the vehicle.

The German patent application DE 10 2006 008 436 A1 shows a mechanically coupled multi-axle steering system, in which only a steering force is applied to the additional steering axle, if this is also active - so when steering lock - is needed. However, this system can only be implemented with great effort for a rear-axle steering, which is to be locked in straight ahead driving from a certain speed range.

In the German patent DE 4414161 C1 a multi-axle steering system is described in which a master cylinder is controlled. Depending on the position of the master cylinder on the front axle, the slave cylinder reacts on the rear axle. However, a disadvantage of this system is the direct dependence on the respective position of the master cylinder. Thus, there is no possibility of a speed-dependent influence on the rear axle with this system.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a steering system for a trailing axle of a vehicle, which takes into account as fully as possible its current driving state, which operates energy-efficiently and reliably, and which is simple and inexpensive to implement.

This object is achieved with the features of claim 1. Additional embodiments of the invention are the subject of the dependent claims, which can be combined with each other in a technologically meaningful manner and show other advantages of the invention. The description, in particular in connection with the figures, additionally characterizes and specifies the invention.

Accordingly, a steering system is provided for at least one trailing axle of a vehicle, comprising: a steering angle sensor for detecting a steering angle of wheels of a front axle of the vehicle; a vehicle speed sensor for detecting a vehicle speed of the vehicle; an electric motor for driving a hydraulic pump, which is in turn connected to at least one working cylinder for articulating the wheels of the trailing axle; a control unit, which on the one hand communicates with or communicates with the steering angle sensor and the vehicle speed sensor, and on the other hand with the electric motor, and is adapted to determine from the steering angle and the vehicle speed a caster angle of wheels on the trailing axle of the vehicle, and to switch the engine based on this caster angle, wherein the working cylinder has a center bore, via which hydraulic fluid can be discharged from the working cylinder, so that the piston is adhesion driven to a center position in which it closes the central bore, and the wheels of the Trailing axle are blocked in a straight-ahead position.

Thus, initially there is an electro-hydraulic steering system for a trailing axle, in which the steering wheel is not mechanically connected to the axle to be steered, i. whose articulation of the trailing axle can take place independently of the front axle. In addition, this system is decoupled from the internal combustion engine, so that on the one hand a needs-based control and on the other hand - by the few and also freely placeable components - a high spatial flexibility is ensured during its installation. At low speeds and when stationary, this system enables active steering depending on the steering angle of the front axle and on the driving speed. In particular, the wheels of the trailing axle are automatic at any time even in the event of a failure of the electronics and / or hydraulics, i. Adhesion-driven from each deflection angle in their straight-ahead position can be brought and there reliably blocked, without the need for additional electronics and / or hydraulics would be necessary. In the adhesion-driven movement of the piston in the direction of the center bore, the hydraulic fluid whose cylinder chamber is discharged from the working cylinder, while in the other cylinder chamber - without pump insert - liquid is sucked. As soon as the center bore is closed by the piston, its further movement is blocked by the hydraulic fluid caged on both sides, so to speak, so that the wheels of the trailing axle are securely held in their straight-ahead position. In case of failure of the hydraulic and / or electrical system at low speeds, there is thus the possibility that the trailing axle is driven attenuated adhesion-controlled in the center position and held there. A trailing axle should be understood to mean any axle which follows the deflection of a steered axle and which can be arranged behind or ahead of a rigid rear or front axle, ie also as a leading axle.

According to an advantageous embodiment, the steering system according to the invention comprises a valve which is connected in a fluid connection between the central bore and the pump, and which releases a fluid flow between the center bore of the working cylinder and the pump in a basic position, and in a working position a fluid flow between the center hole of the working cylinder and the pump prevents, and in which the control unit is designed to detect malfunctions and in case of failure to switch the valve to its normal position, so that the piston is adhesion driven to its center position movable, in which the piston Center hole closes, and the wheels of the trailing axle are blocked in a straight-ahead position. In case of failure e.g. the pump can be the system by appropriate switching of the valve in a safe state to be transferred. While the valve is e.g. is in its working position in the trouble-free operation of the steering system, in which the piston is movable only via the pump, it can then, if it comes to a fault, by opening the center bore allow its movement to the center position. In this basic position, the valve is de-energized and can thus keep energy-free and thus very reliable, with the deactivated pump no additional energy needed. The center position of the piston can be reliably held because it closes the center bore of the cylinder and a further discharge of hydraulic fluid is no longer possible.

The control unit can be designed to switch the motor off when a predeterminable vehicle speed is exceeded. The trailing axle is thus - automatically from a certain presettable speed - i. driven by adhesion in their center position and held there, so that their wheels are in straight-ahead driving position. Since this center position can be maintained without further energy consumption, the power consumption of the system is minimal.

The at least one working cylinder can be designed as a double-acting cylinder or as a double-acting combination of two individual cylinders, which results in a further spatial flexibility in its installation. The volume compensation of different cylinder chambers of the at least one cylinder is preferably carried out via a combination of a 2-pressure valve and a fluid tank. From this fluid tank, a hydraulic fluid can be sucked in and conveyed, in order to effect a corresponding fluid compensation. In particular, when the piston moves back to the center position, hydraulic fluid can be sucked in, for example via suction valves or hydraulic fluid back into the tank be encouraged. In principle, however, instead of eg a differential cylinder, two cylinders with identical volumes of the cylinder chambers can be used, which does not necessarily require a fluid tank.

Preferably, the pump is designed as a reversibly operable pump or as a combination of a one-way operable pump with a valve block. A reversibly operable pump makes the least demands on the space requirements of the steering system, while a one-way operable pump requires a simpler electric drive. The valve can in principle be electromagnetically and / or hydraulically actuated in order to ensure high reliability. In particular, it can also be realized by a valve combination of three electrically controlled 2/2-way valves or via an electric 2/2-way valve in conjunction with a 4/2-way valves.

The above object is also achieved by a method for steering wheels of at least one trailing axle of a vehicle, in which a driving speed and a steering angle of wheels of a front axle of the vehicle are detected and from a caster angle of the wheels of the trailing axle is determined, the wheels of the trailing axle be articulated via a working cylinder which has a central bore, via which hydraulic fluid is discharged from the working cylinder when the piston is driven adhesion driven in a central position until it closes the central bore, and the wheels of the trailing axle are locked in a straight-ahead position.

This initially provides an electro-hydraulically decoupled steering method for a trailing axle, in which the trailing axle can be articulated independently of the front axle. As a result, each articulated to the current driving situation articulation of the trailing axle is possible, which also opens energy saving potential and guarantees high reliability. In particular, a simple and reliable mechanical return of the wheels of a trailing axle in their straight-ahead position is possible, i. even if there is a fault in the hydraulics and / or electrical system.

In a preferred embodiment of the method, the central bore is closable, and is opened in the event of a fault, so that the piston is driven adhesion driven to its center position, in which it closes the central bore, and the wheels of the trailing axle are locked in a straight ahead position. This allows the adhesion-bound return of the wheels of the trailing axle defined in their straight-ahead exhibition on or off.

The steering system according to the invention should preferably be used in a commercial vehicle, in particular in a truck or a coach.

BRIEF DESCRIPTION OF THE DRAWINGS

Further details and advantages of the invention will become apparent from the embodiments illustrated in the drawings. The same or equivalent parts are provided with the same reference numerals. Show it:

1 a functional diagram of a vehicle with a first steering system according to the invention;

2 the functional diagram of the steering system of the invention 1 , and

3 a functional diagram of a second steering system according to the invention.

DETAILED DESCRIPTION EXAMPLE

EMBODIMENTS

1 shows a functional diagram of a vehicle F with a first steering system according to the invention L. For detecting a steering angle α of wheels Rv a front axle Av here is a steering angle sensor Sα, and for detecting a vehicle speed v is provided a vehicle speed sensor Sv. Whose signals are transmitted via a signal line W1 a control unit C, which is designed for driving an electric motor M and thus directly operated reversible hydraulic pump P. On the other hand, the control unit C is connected via a signal line W2 to a linear sensor Sl of a double-acting cylinder Z, which can move the running wheels Rn of a trailing axle An of the vehicle F to a trailing angle β.

The system L is driven by the motor M only when active steering is required. With the reversibly operable pump P, it is possible to pump an oil flow in the direction of one or the other side of the cylinder Z. In order to be able to reduce the energy requirement even when driving straight ahead and to be able to keep the trailing axle An in straight ahead travel (α = 0, β = 0) in the event of system failure, a center bore B of the cylinder Z is connected to the pump P via a valve V1. In trouble-free operation of the steering system L is the valve V1 in his Working position A, in which the connection between the center bore B of the cylinder Z and the pump P is closed. A rash β of the wheels Rn the trailing axle An is then possible only on the activation of the pump P. On the other hand, if there is a fault, the valve V1 is de-energized and opened the connection between the center bore B of the cylinder Z and pump P. Via a spring, the valve V1 is then in its normal position N, so that a secure state is achieved. In this basic position N, an adhesion-driven return of the wheels Rn of the trailing axle An into its straight-ahead position is possible, in which the piston K is urged under its restoring force into a central position G until it closes the central bore B, so that no further hydraulic oil is displaced can.

Building on the 1 The following are the individual operating states of the steering system L based on 2 be explained in more detail. The 2 shows the function diagram of the steering system L of 1 on a larger scale.

Straight ahead at higher driving speed

When driving straight ahead (.alpha. = 0, .beta. = 0), the electric motor M can remain switched off and the axis An remains hydraulically held via the closure of the center bore B. The two hydraulic lines X1 and X2 of the cylinder Z are blocked via check valves V2 and V3 with respect to the pump P.

Active steering at low driving speed

With active steering of the electric motor M is controlled by the control unit C and the valve V1 is switched to its working position A, in which the center bore B of the working cylinder Z is closed. The steering angle α of the wheels Rv of the front axle Av or the steering angle of the steering wheel is detected by measurement and forwarded via the signal line W1 to the control unit C. With these and other values, e.g. of the vehicle speed v, the target displacement of the wheels Rn on the trailing axle An is calculated. The motor M, which in turn is connected to the pump P, which conveys the oil through the hydraulic lines X1, X2 in the corresponding cylinder chamber is controlled by the control unit C, whereby a piston movement is triggered. The control takes place via a corresponding control algorithm until the setpoint at the trailing axle An is reached.

Failure of the steering system

If there is a failure of the steering system L, e.g. by a fault of the electric motor M, the steering angle and / or vehicle speed sensor Sα, Sv or the control unit C, the motor M is turned off and the valve V1, e.g. Federgetrieben transferred to its normally open position N. In this basic position N, the center bore B of the working cylinder Z is opened, so that an adhesion-driven movement of the piston K is made possible to its center position G, in which the piston K is blocked. Thus, a secure state, namely a holding of the wheels Rn of the trailing axle An in straight ahead position or holding the trailing axle An in the middle as explained below.

Failure when driving straight ahead at higher driving speed

If the system L fails in straight-ahead driving, this has no effect. Since the piston K is hydraulically held in the cylinder Z, the wheels Rn of the trailing axle An and the trailing axle remain An in the straight-ahead position.

Failed assisted steering at low speed

If the system L fails during active steering, a valve control D such as e.g. a solenoid of the valve V1 is deenergized, whereby the valve V1, e.g. Federgetrieben its basic position N assumes and the center hole B is open. If the piston K of the cylinder Z is in the straight-ahead travel position, then it can not be moved any further - hence the trailing axle An remains held. If the axis is deflected against it, so there is no possibility in many cases of error to bring the wheels Rn and the axis An in a straight-ahead position. When cornering, the currentless switching of the valve V1 prevents the axis An from being deflected farther than it is at that moment. The Achsrückstellkräfte try to move the steering in the direction of straight travel, this movement is made possible by the center bore B in the cylinder Z, until the piston K reaches the center position. After reaching the center position, the axis An is held in this position, since the bore B is now closed by the piston K. The center hole B can be throttled, so that an attenuation of the axle movement is adjustable, which excludes a critical driving condition. For the return movement of the piston K in the direction of the center position G can be nachgesaugt from a fluid tank oil.

The 3 shows a functional diagram of a second steering system according to the invention L ', in which a valve V1' is not controlled electromagnetically, but via a valve control D 'such as hydraulically via a two-pressure valve.

Of course, other concrete technical embodiments of the steering system according to the invention are conceivable, which are in the knowledge and skill of the expert. It is important that the automatic mechanical return of the trailing axle is ensured in its center position in the event of a fault. All in all, this results in a steering system that comprehensively takes into account the current driving condition of a vehicle that is energy-efficient and reliable, and that can be implemented easily and cost-effectively. In principle, such a steering system is not only applicable to the guidance of trailing axles, but also to other steered rear axles, such as leading axles.

It should be noted that the term "comprising" does not exclude other elements or method steps, just as the term "a" and "an" does not exclude multiple elements and steps.

The reference numerals used are for convenience of reference only and are not to be considered as limiting, the scope of the invention being indicated by the claims.

LIST OF REFERENCE SIGNS

• A

  Working position of the valve

  At

  trailing axle

  Av

  Front

  B

  center bore

  C

  control unit

  D, D '

  valve control

  F

  vehicle

  G

  Center position of the piston

  K

  piston

  L, L '

  steering system

  M

  engine

  N

  Basic position of the valve

  P

  pump

  rn

  Wheels of the trailing axle

  Rv

  Wheels of the front axle

  sl

  linear sensor

  Sv

  Vehicle speed sensor

  Sα

  Steering angle sensor

  v

  Speed of the vehicle

  V1, V1 '

  Valve

  V2, V3

  check valves

  W1, W2

  signal line

  X1, X2

  hydraulic lines

  Z

  working cylinder

  α

  steering angle

  β

  caster angle

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102006008436 A1 [0007]
• DE 4414161 C1 [0008]

Claims (9)

 Steering system (L; L ') for at least one trailing axle (An) of a vehicle (F), comprising: A steering angle sensor (Sα) for detecting a steering angle (α) of wheels (Rv) of a front axle (Av) of the vehicle; A vehicle speed sensor (Sv) for detecting a vehicle speed (v) of the vehicle (F); - An electric motor (M) for driving a hydraulic pump (P) which in turn with at least one working cylinder (Z) for articulating the wheels (Rn) of the trailing axle (An) is connected; - A control unit (C) on the one hand with the steering angle sensor (Sα) and the vehicle speed sensor (Sv), and on the other hand with the electric motor (M) is in communication or can connect, and is adapted from the steering angle (α ) and the vehicle speed (v) to determine a caster angle (β) of wheels (Rn) on the trailing axle (An) of the vehicle (F), and to switch the motor (M) based on this caster angle (β) - The working cylinder (Z) has a central bore (B), via which hydraulic fluid from the working cylinder (Z) can be dispensed, so that the piston (K) is adhesive driven to a center position (G) is movable, in which he the center bore ( B) closes, and the wheels (Rn) of the trailing axle (An) are blocked in a straight-ahead position.  Steering system (L; L ') according to claim 1, having a valve (V1; V1') connected in fluid communication between the central bore (B) and the pump (P) and in a normal position (N) fluid flow between the center bore (B) of the working cylinder (Z) and the pump (P) releases, and in a working position (A) prevents fluid flow between the central bore (B) of the working cylinder (Z) and the pump (P), and at in that the control unit (C) is designed to detect malfunctions and, in the event of a malfunction, to switch the valve (V1, V1 ') to its basic position (N), so that the piston (K) can be moved to its center position (G) in an adhesion-driven manner is, in which the piston (K) closes the central bore (B), and the running wheels (Rn) of the trailing axle (An) are blocked in a straight-ahead position.  Steering system (L; L ') according to claim 1 or 2, wherein the at least one working cylinder (Z) is designed as a double-acting cylinder or as a double-acting combination of two individual cylinders.  Steering system (L; L ') according to one of the preceding claims, in which the volume compensation of different cylinder spaces of the at least one cylinder (Z) via a combination of a 2-pressure valve and a fluid tank.  Steering system (L; L ') according to one of the preceding claims, wherein the pump (P) is designed as a reversibly operable pump or as a combination of a one-way operable pump with a valve block.  Steering system (L; L ') according to one of the preceding claims, in which the valve (V1; V1') is actuated electromagnetically and / or hydraulically.  Method for steering wheels (Rn) of at least one trailing axle (An) of a vehicle (F), in which a driving speed (v) and a steering angle (α) of wheels (Rv) of a front axle (Av) of the vehicle (F) are detected and from a caster angle (β) of the wheels (Rn) of the trailing axle (An) is determined, the wheels (Rn) of the trailing axle (An) via a working cylinder (Z) are hinged, which has a central bore (B) over which hydraulic fluid is discharged from the power cylinder (Z) when the piston (K) is driven by adhesion to a center position (G) until it closes the center bore (B) and the runners (Rn) of the trailing axle (An) in a straight ahead position are blocked.  Method according to Claim 7, in which the central bore (B) can be closed and, in the event of a malfunction, is opened, so that the piston (K) is driven in an adhesive-driven manner to its center position (G), in which it closes the central bore (B) , and the running wheels (Rn) of the trailing axle (An) are blocked in a straight-ahead position.  Use of a steering system (L; L ') according to one of claims 1 to 6 in a commercial vehicle, in particular in a truck or a coach.

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