DE2133884A1 - Hydraulic power steering for vehicles - Google Patents

Description

PATENT LAWYERS

DR. L MAAS

D R. W. P F E I F F E R DR. F. VOITHENLEITNER

8 MUNICH 23 UNGERERSTR. 25 - TEL. 39 02 36

10135/4239

CAM GEARS LIMITED, Hitchln _r England Hydraulic power steering for vehicles

The invention relates generally to fluid actuated Control devices and in particular improvements for hydraulic power steering for vehicles » where there is no mechanical connection between the manually operated steering wheel and the steering links of the steering gear, a device for which the designation "hydrostatic steering" has become known.

Although the invention is described below as applied to land vehicles, under the designation "Vehicle" means all forms of transport and handling equipment into which a hydrostatic steering can be installed, for example in boats or hydrofoils.

109886/1206

There were hydraulic power steering for wheel drive Proposed witnesses that are provided with a control valve with "open, open center", which the Advantage of a steering with a follow-up or self-centering effect result, whereby the driver constantly a certain "feeling" of the steering is conveyed. In such systems, constant correction of the The direction of travel of a vehicle is required, which effect is particularly pronounced on uneven terrain is what leads to driver fatigue.

Although such "open center" systems are generally satisfactory for normal on-road or off-road conditions It is believed that it is in the case of tractors and similar vehicles traveling over uneven terrain Terrain operated, it is advantageous to provide a "closed center" steering in which the Steering members are hydraulically locked in a selected position until a steering command is given by the driver is, whereby the possibility is obtained of a set direction of travel without constant correction and with practically no impact on the steering wheel ("kick-back"). Vehicles that operated over uneven terrain are improved accordingly, and there is less benefit to the driver Fatigue.

It is further believed that it is advantageous to provide a facility by which a "closed center" system is progressive and controllable can be switched to an "open center" system, a feature that makes it possible for the to choose the most suitable arrangement for each terrain.

109 8 8671206

The object of the invention is to create an improved hydraulic power steering, in which the steering wheel bumps ("kick-back") as a result of sudden forces on the Steering members are turned off or reduced to an insignificant degree and at which the permanent Correction of the direction of travel of the vehicle due to external influences acting on this is reduced to a negligible level.

A further aim of the invention is to create a device by means of which the operating properties an improved hydraulic power steering option from a "closed center" operation in an "open center" mode can be switched to provide the most beneficial steering effect for the terrain over which the vehicle is moving.

A hydraulic power steering system according to the invention for a vehicle has a steering element, which with a hand drive pump interacts, a sensing element that determines the size and direction of the steering forces measures, which are effective on the steering element, and which is connected to a control valve, a pressure oil tank, a pressure oil source, a device for bypassing the pressure oil source, a servo motor, the is connected to a steering device through which the vehicle is steered, the manual drive pump, the pressurized oil source and the servomotor are in flow connection with the control valve that is used for this serves to conduct pressure oil from the pressure oil source to the servomotor proportionally via the hand drive pump to the steering forces and the pressure oil source, the hand drive pump and to keep the servomotor isolated when no steering forces are in effect.

109886/1206

If the system is to operate without oil pressure from the pressure oil source 'and is given a steering command _r sucks the hand drive pump pressure oil from the container directly or through the bypass to the pressure oil source and promotes the pressure oil to the servo motor via the control valve in proportion to the size and speed of the steering forces and in which right sense.

Furthermore, an independent valve arrangement is provided according to the invention, which makes it possible to use the hand. to set the drive pump and the servomotor selectively and increasingly in flow connection with one another, if no steering forces are effective, and another valve arrangement that is connected to the sensing element stands, which measures the steering forces acting on the steering element become effective, and the further valve arrangement causes the flow connections of the hand drive pump and the servomotor to throttle increasingly among each other when the mentioned steering forces increase, so that a servo pressure can build up. The mentioned further valve arrangement can expediently be an extension of the control valve.

According to the invention, a bypass valve can also be provided which is assigned in a similar manner to the filling element and which is expediently an extension of the control valve can form. If no steering forces are effective, the bypass valve causes the power-driven ones to bypass Pump, and when steering forces occur, the bypass valve closes, so that a servo pressure builds up can.

According to the invention, an additional independent Valve assembly can be provided to isolate the bypass of the power pump and ineffective to be made when oil pressure is required independently for an additional hydraulic circuit.

109886/12 06

The following are two embodiments, for example of the invention in connection with the accompanying schematic drawings, namely show:

Figure 1 the two embodiments common basic shape the hydraulic auxiliary power device;

Figure 2 shows the first embodiment of the invention, which of that shown in Figure 1 differs insofar as the circuit of the power-driven pump has the property of "open center" by using an additional | torque dependent valve is imparted;

Figure 3 the second embodiment, in which the servomotor and hand drive pump circuits are normally of the "closed center" type, but by actuation additional valves can be given the property of the "open center". The cycle of the power-driven Pump is of the "open center" type as a result of a modified control valve.

Each of the embodiments described below, the common basic arrangement of Figure 1, wherein ά

which a steering wheel SW is provided which is attached to one end of a steering shaft 1, which Has drive connection with a hydraulic hand drive pump through MP at its other end, so that through rotation of the steering wheel SW actuates the manual drive pump MP. A sensing element SM, which is preferably used for Spindle 1 is coaxial, measures the size and direction of a torque on the spindle 1 and converts this torque into a movement of a control valve element 13 of a control valve Vl, which is proportional to the torque in terms of size and direction. Although the control valve Vl with

109886/1206

an axial design is shown, it can either a valve with a rotating movement or with a axial movement or a combination of both movements. The sensing element SM can be in the control valve arrangement be installed, so that the control valve Vl are referred to as a torque-dependent control valve can.

Furthermore, a hydraulic servo motor M is provided, which can be a double-acting hydraulic cylinder, as shown. or any other form of double acting hydraulic actuator which is suitable linear movement or rotary movement of its output member is generated when a hydraulic pressure difference occurs. The output member 2 is connected to a steering device (not shown) through which the output member 2 steer the steerable wheels (not shown) of the vehicle can.

A power-driven pump PP, which is connected to a pressurized oil tank R, forms a sufficient source of pressurized oil, which can meet all pressure oil requirements of the servomotor M. A bypass check valve V2 is P connected in parallel to the power-driven pump PP and connected in such a way that the power-driven The pressure generated by pump PP closes the bypass valve V2. The pump PP sucks oil from the container R via a line 6 and conveys the oil under pressure through a line 7 to the control valve Vl for distribution according to the steering requirements. The one emerging from the control valve Oil and excess pressure oil from the pressure pump PP flows from the control valve Vl to the container R via a line 12 back. The manual drive pump MP has a flow connection with the control valve Vl via lines 8 and 9, each of which as an inlet or outlet to or from the manual drive pump MP depending on the direction of the steering commands can serve. The servomotor M has a flow connection

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with the control valve Vl via lines 10 and 11, the also depending on the direction of the steering commands can serve as inlet or outlet lines.

In the absence of a steering command, i. H. in the zero state, the system of Figure 1 is of the "closed center" type because of the auxiliary elements 4 of the control valve Vl, which Auxiliary element, the manual drive pump MP, the servo motor and the power-driven pump PP with regard to the flow connections isolated and independent of each other. The steerable wheels of the vehicle can therefore |

not be pivoted, and all "kick-back" forces are absorbed by the steering device (not shown) and the servo motor M, which components of are of sufficient and robust design. In this zero state, no forces from the servomotor M can the manual drive track MP and thus transferred to the steering wheel SW.

When a steering command is given by the steering wheel SW is rotated in one direction or the other, the control valve Vl is actuated by pulling it out of its central zeroing in the direction and by the amount ^ is shifted to the input f

torque is proportional. Through this actuation, the circulatory interconnections (as through the Auxiliary elements 3 and 5 indicated schematically) progressively changed so that high pressure oil from the power pump PP to one side of the manual drive pump MP and is conveyed from the other side of the manual drive pump to one side of the servomotor M. The other The servomotor side is connected to the oil tank R. The hand drive pump measures that of the servo motor the amount of oil supplied and the pressure difference across the hand drive pump is a function of that which is exerted by hand Torque.

109886/1206

If the power pump PP is not driven, which may be the case when the vehicle is being towed, the same valve actuations take place. The manual drive pump MP now sucks pressure oil directly over the Low pressure line 12 from the container R or via the bypass valve V2 depending on the direction of rotation. The hand drive pump conveys the oil to the servomotor M, and the pressure difference across the hand drive pump is one Function of hand torque and a measure of total steering effort.

The first embodiment of the invention is shown in FIG shown in which the circuit of the power-driven pump, the container R, the lines 6 and 7 and the power pump PP comprises the "open center" feature of a torque dependent valve V3 is communicated, which in the zero state a bypassing of the power-driven pump PP via lines 14 and 18 and the middle element 16 of the torque-dependent valve V3. In this way of working there is no oil pressure available until a steering command is given, whereupon the pressure is proportional to the torque on the spindle 1 because of the torque-dependent ™ valve V3, which progressively the bypass flow throttles when the torque increases. The auxiliary valve elements 15 and 17 cause their movement to one Middle position "within the torque-dependent valve V3 the necessary throttling for the bypass flow.

The second embodiment shown in Figure 3 is provided with a manually operable valve V5, which can optionally also be switched by hand, but either Can be operated electrically or hydraulically, through which the manual drive pump MP and the servomotor M flow connection can get together, thereby reducing the system

109886/1206

the property of the "open center" is conferred. To build up hydraulic pressure in such a To enable arrangement, a torque-dependent valve V4 is provided, which is proportional and progressive the flow connection throttles when the torque on the spindle 1 increases. The control valve Vl acts as in the first-described and last-described system with the exception that the middle element 4 is so modified is that the power pump circuit is of the "open center" type and is in the same Behaves like in the second system shown in FIG.

When actuated, the valve V5 connects the line to the line 11 (and 22) and the line 9 (and 23) to the line IO via the element 20 of the torque-dependent valve V4 when this is in the "zero" position. The valve V5 can be a valve with two switching positions or its effect can be so variable that the properties of the system can be changed accordingly to adapt to changing terrain conditions. The valve V5 can furthermore be spring-loaded and actuated by the hydraulic pressure difference in the lines 10 and 11, whereby either the torque-dependent valve V4 is replaced or the switchover from the state with "open center" to the state with "closed center" is directly dependent on ^{! L} The valve V5, when used in this way, can be provided with a manually operable override so that the ability of the vehicle operator to choose the properties is retained.

109886/1206

Claims (11)

Pat e nt a η s pr udes Γ 1J hydraulic power steering for vehicles, ^ - characterized by a steering device, which with a hand drive pump (MP) interacts, a sensing element (SM), the size and the direction of the Measures steering forces which are communicated by the steering device and which is connected to a control valve (Vl) is, a pressurized oil tank (R), a pressurized oil source (PP), a bypass organ (V2) to bypass the pressure oil source, a servo motor (M), which is connected to a Steering device is connected, whereby the vehicle is steered, the manual drive pump (MP), the Pressurized oil source (PP) and the servomotor (M) in flow connection with the control valve (Vl), which is used to proportionally transfer pressure oil from the pressure oil source (PP) to the servo motor (M) via the hand drive pump (MP) to direct the steering forces, and to keep the pressure oil source, the manual drive pump and the servomotor each flow-isolated when no steering forces are effective. 2. Power steering system according to claim 1, characterized in that the bypass member is through a valve is formed, which is connected to a further steering force sensing element and which is open to the pressure oil source to bypass when no steering forces are in effect, and increasingly closes when the steering forces gain weight. 3. Power steering system according to claim 1, characterized by means by which the pressure of the pressurized oil source is changed in relation to the steering forces. 109886/1206 4. Power steering system according to the preceding claims, characterized in that the pressure oil source is a hydraulic pump. 5. Power steering system according to the preceding claims, characterized in that the servomotor is a hydraulic cylinder. 6. Power steering according to the previous ( Claims, characterized in that a torque-dependent valve said sensing element and the control valve includes in combination. 7. Power steering system according to the preceding claims, characterized in that a torque-dependent Valve has the valve mentioned and an associated steering force ^ sensing element in combination. 8. Power steering system according to claim 4, characterized in that that the valve mentioned is combined with the control valve and assigned to the sensing element. 9. Power steering system according to the preceding claims, characterized by an independently operable Valve through which the hand drive pump and the servo motor, which are normally isolated are, if no steering forces are effective, can optionally and increasingly obtain pressure oil connection. 109886/1206 10- power steering according to claim 9, characterized in that that the independently operable valve is formed by a manually operable valve. 11. Power steering according to claims 9 and 10> characterized by a further valve / which is connected to a steering force sensing element / whereby each intermediate connection can be increasingly throttled by the independently operable valve when the steering forces gain weight. 12, auxiliary power steering according to claims 1 to 11 * characterized by a further independent valve for isolating and deactivating the pressure oil source bypass, in order to thereby increase the hydraulic pressure for actuating a further hydraulic circuit obtain. 109BS6 / 1206