DE20319656U1 - Steering system for two-track vehicle, has pump controller to adjust storage pressure depending on speed of vehicle - Google Patents

Abstract

The steering system (10) comprises a power steering device (24) for discharging a servo power to a steering linkage (20) of the vehicle. A pump (26) delivers hydraulic fluid to a pressure storage device (38). The pump is controlled (64) so that the storage pressure is adjusted according to the speed of the vehicle.

Description

The invention relates to a steering system for one in particular two-lane motor vehicle with a power steering device for initiation a servo force on a steering linkage of the motor vehicle, the is provided with a pump, with the optional hydraulic fluid in promoted a pressure accumulator can be.

In today's motor vehicles in addition to simple steering systems, in which a driver-specified one Steering system without any power or Moments support transferred to steerable vehicle wheels steering systems with power or torque support is quite common.

The strength or moment support will usually done with so-called power steering devices, where with the help of a servo unit on a steering linkage or Steering gear of the steering system an additional servo torque or one additional Servo force is initiated. Serves as a servo unit, for example a power steering pump, with the optional hydraulic fluid in a hydraulic Synchronous cylinder is promoted.

A distinction is made between such Systems with hydraulically open center ("open center steering system") and systems with hydraulically closed center ("closed center steering system").

In systems with hydraulically open In the middle there is a load-free open power steering valve through which the hydraulic fluid continuously and especially without of a steering turn becomes. Such systems have due to the permanent circulation of the Hydraulic fluids have a comparatively poor efficiency.

To improve efficiency There are numerous approaches to power steering devices. So For example, a servo pump is not directly driven by a drive unit of the motor vehicle, but via an electric motor. The flow the servo pump is then electronically controlled. When steering of vehicle wheels the speed of the electric motor increased so that during the The required nominal volume flow is available. However, when driving without turning in, the servo pump must be on permanently be operated at a standby speed, so in the event of sudden steering operations the needed one Volume flow is available very quickly.

Another approach to improvement systems contribute to the efficiency of power steering systems represents a constantly stored supply pressure. The steering system is carried out with a closed center (closed center steering), i.e. while of driving without turning no volume flow. The hydraulic fluid delivered by a servo pump is temporarily stored in a pressure accumulator so that hydraulic Energy for a sudden Steering operation available stands. The pressure accumulator is controlled by switching on the servo pump is loaded. After a desired system pressure is reached the servo pump can be switched off again. With a Such a power steering device can in principle be saved energy Saving is however with regard to that in today's motor vehicles desired environmental unsatisfactory.

The invention is based on the object to improve a steering system of the type mentioned at the outset, that for the additional power applied to the power steering device is further reduced becomes.

The task is according to the invention with a steering system solved, as described above and in which a control device is provided to control the servo pump, by means of which the the servo pump storage pressure provided at a pressure accumulator depending the driving speed of the motor vehicle can be adjusted.

The invention is based on the knowledge that in known power steering devices, i.e. with steering systems with a constant or always the same supply pressure generation on a pressure accumulator that actually for the support the driver needed during the steering process Differential pressure on a synchronous cylinder of the steering system is often very high is much smaller than that available in the pressure accumulator constant supply pressure. The constant supply pressure to be generated the pressure accumulator is namely based on the maximum steering forces designed with the vehicle stationary. For example, with one required steering differential pressure of 10 bar and a storage pressure of 100 bar 90% of the energy introduced during the steering process in losses implemented.

According to the invention to avoid this circumstance Targeted energy savings achieved by using the pressure accumulator provided storage pressure adapted to the respective driving situation becomes. Lower steering forces occur at high driving speeds, than at low driving speeds. Therefore, at high driving speeds required differential pressure at the synchronous cylinder, which provides the steering assistance, less than the required differential pressure at low driving speeds. In principle, therefore, only a memory pressure that is little above that is required required differential pressure is.

Such a storage pressure can be provided by setting the system pressure fed in by the pump at the pressure storage device as a function of the speed. In particular, the long drive at high speed (for example, a long freeway trip) Storage pressure can be kept at a low level.

Because internal leakage at the synchronous cylinder and in the rest of the power steering system disproportionately with the adjacent one System pressure will rise at the comparatively low system pressure according to the invention the leakage rate is greatly reduced. With the provided according to the invention The servo pump must therefore compensate for a lower proportion of leakage become. Overall, there is considerable energy savings. About that In addition, the invention has the advantage that compared to known Steering systems on the shaft of the pump and with the appropriate design also on the crankshaft of the internal combustion engine driving the pump no high moment loads occur.

Technically, the speed-dependent set according to the invention System pressure can be provided in individual pressure levels especially for predetermined speed ranges can be realized. At a Reaching a lower limit of a pressure level switches the one provided according to the invention Pump on, and when the pressure limit is reached accordingly. By using a continuous flow adjustable pump (e.g. suction-controlled pump, variable pump or electrically operated constant speed pump with variable speed) the system pressure in the power steering device also continuously above the Driving speed can be set. This may be in favor of higher Regulatory effort required, but worth comparing to the energy saving achieved.

The in the power steering device according to the invention provided pressure accumulator needs to store hydraulic energy to be able a preload pressure, for example by a compressed Gas volume generated behind a flexible wall of the pressure accumulator becomes. If the preload pressure is above the system pressure, the pressure accumulator is inactive and there is none Hydraulic fluid added. If the system pressure reaches the preload pressure, so the flexible wall of the pressure accumulator is deflected and that Gas volume above compresses the preload pressure. The associated reduction of the gas volume leads to enlarge the Hydraulic fluid volume in the pressure accumulator, which is under system pressure stands and thus stored hydraulic energy in the form of a Represents storage pressure. This stored energy is used to operate the steering system in the intended manner can.

If the storage pressure, as proposed according to the invention, depending on speed must be set to ensure that a sufficient fluid volume or storage volume for the steering process available stands. This can be ensured in particular by using the steering system according to the invention Two pressure accumulators are provided in which the pump holds the hydraulic fluid promote can and that with preloading means with different specific preload forces are provided. A pressure accumulator for very high system pressures, e.g. be used when the vehicle is at a standstill ("travel speed zero"), while the other accumulator for low system pressures and is designed for high driving speeds.

The steering system according to the invention can also continue can be improved by a synchronous cylinder of the power steering device driving valve device designed in the form of a slide valve is. In known steering systems with constant supply pressure in contrast to this development according to the invention, seat valves for Controlling the hydraulic pressure used in the associated synchronous cylinder. Seat valves prevent permanent internal leakage current when driving without steering by reducing the leakage to zero, however, they have the disadvantage that they are already used for small opening paths large opening cross-sections release. Therefore arise when opening of a seat valve for a short time very large volume flows that the pressure increases quickly on a connected synchronous cylinder and can lead to cavitation or outgassing of dissolved air. These effects can be tactile (on the steering wheel) or as a sound to make noticable. You can also problems with the regulation of the differential pressure on the synchronous cylinder to lead. The slide valves provided according to the invention have against it a significantly better opening behavior, by making the flow correspondingly slow with increasing valve slide travel increases. The volume flow and thus the pressure increase at the synchronous cylinder can therefore be regulated much better.

Due to the principle, slide valves unfortunately have the disadvantage that an internal, albeit small, leakage current always flows through the slide valve. However, this disadvantage can advantageously be compensated for by a further shut-off valve in the form of a seat valve being arranged upstream and / or downstream of the slide valve. When driving without turning in, this seat valve remains closed so that no leakage current flows. If a driver initiates a steering process or a steering torque on the steering handle, the seat valve is opened from a certain size of the steering torque. If the poppet valve is arranged upstream of the slide valve, a pressure surge can occur during opening on the slide valve, but this does not continue to the synchronous cylinder, since even an open slide valve in the middle position has a considerable throttling effect. If the poppet valve is arranged downstream of the slide valve, the supply pressure is when driving without turning, ie with the poppet valve closed or system pressure in both chambers of the synchronous cylinder. When a steering process begins, the seat valve opens and the pressure in the associated chamber of the synchronous cylinder drops. If the slide valve is still in the middle position or close to the middle position, this pressure drop is sufficiently slow due to the throttling action of the slide valve. A sudden drop in pressure that would be felt or heard on the steering handle is thus avoided.

As mentioned above, is in the steering system according to the invention advantageously a valve device which drives the synchronous cylinder provided, which is closed in the center position (closed center steering system). alternative a valve device can be used in the middle position the work connections of the synchronous cylinder are connected to a storage container and at which then in particular closed the pressure connection leading out of the pump is (Opera center steering system especially with blocked pressure connection). The valve device stops in In this case, none attacking the steering linkage of the motor vehicle Loads more, which seems reasonable for energy reasons. at the same time will it be possible that bumps which from the roadway over Tires of the motor vehicle are directed to the steering linkage via a mechanical transmission of the steering column of the steering system directly be forwarded to the driver.

This will make road bumps better perceived on a steering handle, especially a steering wheel.

The invention is also special advantageously solved with a steering system of the type mentioned, at a device for heating and / or cooling the / the pressure accumulator / s and a control device for controlling the temperature of the pressure accumulator (s) especially dependent the driving speed of the motor vehicle are provided.

This solution according to the invention is based on the knowledge that the steering system according to the invention is only a small one preloaded pressure accumulator with a certain change the pressure provides only a small hydraulic fluid working volume, i.e. the gradient of the volume change to change the pressure is very small. In the steering system according to the invention is at lower Driving speed or a high system pressure when the vehicle is stationary needed. In such a driving situation, the volume requirement of the Steering system high and it would be beneficial if a big one Working volume available would. To for such driving situations and the associated steering processes are sufficient Working volume available in one of the developments explained above Invention proposed that two pressure accumulators are provided one of which has a high preload pressure. This pressure accumulator then has a sufficient working volume with high system pressure. The system pressure e.g. lowered due to a high driving speed, so goes the wall or membrane of this pressure accumulator against a stop and there is only the pressure accumulator with a low preload pressure to disposal.

Alternatively or in addition to Such a development of a steering system is further inventively suggested that the temperature of a pressure accumulator, in particular the temperature of its gas volume, depending on the driving speed of the motor vehicle is regulated. By changing the temperature of the Gas volume or storage gas can the bias pressure of the pressure accumulator changed become. It is therefore possible to the usable work volume within a certain pressure range to optimize and thus to the driving speed of the steering system adapt.

By the proposed change the accumulator pressure of a pressure accumulator on a power steering device can be done by heating or cooling of the storage gas compared to known solutions through the storage capacity of the pressure accumulator a continuous temperature control can be changed continuously.

The change in temperature and so that the bias pressure of the pressure accumulator according to the invention occurs by supplying heat and / or heat dissipation.

The heat supply can vary Devices are made, for example with an electric filament, an electrically heatable storage wall, an electrically heatable membrane, by means of exhaust gases from an internal combustion engine, by means of the waste heat of a Internal combustion engine or other heat sources. The heat source is advantageous directly in the pressure accumulator, in particular arranged with direct contact to the storage gas.

The dissipation of heat can be advantageous over free or forced convection using a fan. Depending on the temperature range can about it also the coolant an internal combustion engine for the heat dissipation be used.

The two processes of heating and cooling one pressure accumulator according to the invention can advantageously combined in a single facility by this is designed with a Peltier element. With such a Pettier element becomes the surface of the element by applying defined electrical voltages targeted cooling or warmed.

Another advantage of the heating and / or cooling of a pressure accumulator according to the invention on a steering system with a power steering device is the compensation achieved in this way of particularly low or high ambient temperatures. In a cold automobile drops at a temperature of for example - 40 ° C the preload pressure of a pressure accumulator from a normal operating temperature. At a very low temperature, there is only a very small working volume available. If the storage tank is to remain at a maximum permissible operating temperature of + 130 ° C with its preload pressure just below the minimum system pressure of, for example, 50 bar, the preload pressure drops to 29 bar at a temperature of - 40 ° C. In order to be able to increase the working volume of the pressure accumulator from the start of the journey even at low outside temperatures, the prestressing pressure of a pressure accumulator can be increased to approximately 40 bar by increasing the temperature of the gas to, for example, + 50 ° C. The stored hydraulic fluid volume can thereby be increased considerably.

An additional positive effect of one Preheating a pressure accumulator on a power steering device Steering system results from the fact that the wall or membrane of the pressure accumulator heated becomes. If this wall is made of an elastomer, elevated their elasticity and in particular by increasing the temperature to above -30 ° C. the risk of breakage becomes considerable reduced.

In the steering system according to the invention is finally the power steering device provided therein advantageously with a superimposed steering device combined, by means of a on the steering linkage of the steering system Amount and / or variable overlay angle in the direction of rotation are introduced can. With the superimposed steering device, if necessary independently from the steering direction specified by a driver to the steerable wheels of the motor vehicle for the respective driving dynamic situation of the motor vehicle required Wheel angle can be set.

Exemplary embodiments of a steering system according to the invention based on the attached schematic drawings closer explained. It shows:

1 2 shows a highly schematic illustration of a first exemplary embodiment of a steering system according to the invention,

2 a highly schematic representation of a second embodiment of a steering system according to the invention, and

3 a highly schematic representation of a third embodiment of a steering system according to the invention.

In 1 is a first embodiment of a steering system 10 shown for a motor vehicle, not further illustrated, in which a driver of the motor vehicle on a steering handle 12 in the form of a steering wheel a steering torque or a steering target to a steering column 14 can transmit. On the steering column 14 is a torque measuring device 16 arranged, by means of which the steering torque introduced is converted into an electrical signal. The steering torque is also via a steering gear 18 on a steering linkage 20 transmitted to the steerable vehicle wheels 22 are articulated.

On the steering system 10 is also a power steering device 24 provided on the with the help of a servo pump 26 via a synchronous cylinder 28 optionally a servo force for the steering torque initiated by the driver of the motor vehicle or its steering force on the steering linkage 20 can be transferred.

The servo pump 26 is controlled on demand with the help of an electric motor 30 driven and then delivers hydraulic fluid with a constant flow rate against a check valve 32 into a pressure line 34 , The pressure line 34 can through a check valve 36 be closed, which is designed as a seat valve. On the pressure line 34 is upstream of the check valve 36 a pressure accumulator 38 connected, which is designed as a gas pressure accumulator with a storage membrane, not shown, and a gas volume delimited by this. At the pressure accumulator 38 is also a pressure measuring device 40 provided, by means of which the storage pressure existing in a storage volume of the pressure storage device can be measured.

In the direction of flow behind the check valve 36 leads a pressure connection 42 to a slide valve 44 , which is designed as a valve with a closed center (closed center principle). On the slide valve 44 are also a first line 46 and a second line 48 connected individually to a first chamber 50 and a second chamber 52 of the synchronous cylinder 28 to lead. Between the chambers 50 and 52 is a connecting line 54 provided in which a pressure measuring device 56 is arranged. With the help of the pressure measuring device 56 can be the pressure difference between the two chambers 50 and 52 be determined.

On the slide valve 44 is also a return connection 58 provided that to an unpressurized reservoir 60 leads. From this storage container 60 can the servo pump 26 the hydraulic fluid through a suction line 62 suck in again.

The steering system 10 is a control device 64 assigned, in particular with the torque measuring device 16, the electric motor 30 , the pressure measuring device 40 and the pressure measuring device 56 is operationally connected. At the control device 64 a device 66 for measuring the driving speed of the associated motor vehicle is also connected. Such a facility 66 can be, for example, a single or multiple wheel speed sensors.

The control device 64 is designed so that it from the servo pump 26 on the pressure accumulator 38 memory pressure provided depending on that of the facility 66 can control measured vehicle speed. The control device 64 can so especially with a gerin Set a comparatively high storage pressure against the speed, while the storage pressure can be kept at a relatively low level at high vehicle speed. A low accumulator pressure leads in particular to reduced leakages in the system, and so does the servo pump 26 must be operated less overall. Compared to known steering systems with a hydraulically closed center, the steering syste 10 and its power steering device 24 improved efficiency.

In 2 is an embodiment of a steering system 10 shown, which is essentially like that in 1 illustrated steering system 10 is constructed. On the steering system 10 according to 2 but is next to the first pressure accumulator 38 on the pressure line 34 another pressure accumulator 68 arranged. Of these two accumulators 38 respectively. 68 one is designed with a high prestressing pressure of the associated gas volume and the other pressure accumulator with a low prestressing pressure. The pressure accumulator with a low preload pressure is used in the area of low accumulator pressures, while the pressure accumulator with a high preload pressure is only preloaded at higher system pressures and is therefore used for areas with high accumulator pressures. This arrangement of two pressure accumulators 38 and 68 can, as already explained above, a high work volume from the two pressure accumulators even at low vehicle speed and low accumulator pressure 38 and 68 to be provided.

In 3 is a steering system after all 10 illustrates, in turn, two pressure accumulators 38 and 68 are provided, but in contrast to that in 1 illustrated steering system 10 the slide valve 44 with a hydraulically open center (open center system) and then a closed pressure connection 42 is trained. With this steering system 10 according to 3 is the synchronous cylinder 28 in the middle position of the slide valve 44 so released and on the vehicle wheels 22 attacking forces are released on the steering linkage 20 and on to the steering handle 12 transfer.

10

steering system

12

Steering handle

14

steering column

16

Moment measuring device

18

steering gear

20

steering linkage

22

vehicle wheels

24

Power steering device

26

Power steering pump

28

Synchronizing cylinder

30

electric motor

32

check valve

34

pressure line

36

check valve

38

accumulator

40

Pressure measuring device

42

pressure connection

44

spool valve

46

first management

48

second management

50

first chamber

52

second chamber

54

connecting line

56

Pressure measuring device

58

Return connection

60

reservoir

62

suction

64

control device

66

Facility for measuring vehicle speed

68

second accumulator

Claims (11)

Steering system ( 10 ) for a two-lane motor vehicle in particular with a power steering device ( 24 ) to apply a servo force to a steering linkage ( 20 ) of the motor vehicle using a pump ( 26 ) is provided with which hydraulic fluid can optionally be fed into a pressure accumulator ( 38 ) can be funded, characterized in that a control device ( 64 ) to control the pump ( 26 ) is provided, by means of which the pump ( 26 ) on the pressure accumulator ( 38 ) provided storage pressure can be set depending on the driving speed of the motor vehicle. Steering system according to claim 1, characterized in that the control device ( 64 ) can set the accumulator pressure as a function of the driving speed of the motor vehicle in individual pressure stages, in particular for predetermined speed ranges. Steering system according to claim 1 or 2, characterized in that two pressure accumulators ( 38 . 68 ) into which the pump ( 26 ) can promote the hydraulic fluid and with the biasing means different specific biasing forces are provided. Steering system according to one of claims 1 to 3, characterized in that a synchronous cylinder ( 28 ) of the power steering device ( 24 ) controlling valve device ( 44 ) is provided in the form of a slide valve. Steering system according to claim 4, characterized in that upstream of the slide valve ( 44 ) a shut-off valve ( 36 ) is arranged in the form of a seat valve. Steering system according to claim 4 or 5, characterized in that downstream of the slide valve ( 44 ) a shut-off valve ( 36 ) is arranged in the form of a seat valve. Steering system according to one of claims 1 to 6, characterized in that a synchronous cylinder ( 28 ) of the power steering device ( 24 ) controlling valve device ( 44 ) is provided, which is closed in the middle position. Steering system according to one of claims 1 to 7, characterized in that a synchronous cylinder ( 28 ) of the power steering device ( 24 ) controlling valve device ( 44 ) is provided, which in one position, in particular the central position chambers ( 50 . 52 ) of the synchronous cylinder ( 28 ) with a hydraulic fluid reservoir ( 60 ) connects. Steering system, in particular according to one of claims 1 to 8, for an in particular two-lane motor vehicle with a power steering device ( 24 ) to apply a servo force to a steering linkage ( 20 ) of the motor vehicle using a pump ( 26 ) is provided, with which hydraulic fluid is optionally available in at least one pressure accumulator ( 38 ) can be funded, characterized in that a device for heating and / or cooling the pressure accumulator (s) ( 38 . 68 ) and a control device ( 64 ) to control the temperature of the pressure accumulator (s) ( 38 . 68 ) are provided in particular depending on the driving speed of the motor vehicle. Steering system according to claim 9, characterized in that the device for heating and / or cooling the / the pressure accumulator (s) ( 38 . 68 ) is designed with a Peltier element. Steering system according to one of claims 1 to 10, characterized in that a superimposed steering device for introducing a variable superimposition angle and / or in the direction of rotation onto the steering linkage ( 20 ) is provided.