DE3112925A1 - HYDRAULIC BRAKE SYSTEM - Google Patents

Description

Hydraulic braking system

The present invention relates to improvements in load sensing hydraulic brake pressure control devices for use in the hydraulic circuit between the Master cylinder and the brake cylinders of the rear wheels · The device can change the distance between the Feel the vehicle chassis and the suspended axle shaft

It is known that changes in vehicle load lead to changes in braking performance. For example, if a vehicle is fully loaded, the rear wheels have almost the same braking power as the front wheels. However, if the vehicle is only slightly loaded, the rear wheels can have a lower braking capacity than the front wheels. Therefore, if the lightly loaded vehicle is stopped, there is a risk of premature locking of the rear wheels far greater than when stopping a fully loaded vehicle. To this imbalance between the braking power To balance the front and rear wheels, it has been common in the past to provide a metering valve, that the fluid connection to the brake cylinders the rear wheels are limited after reaching a predetermined pressure level. However, such metering valves provide a compromise between the desirable system properties for the full load condition and those for the condition

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low load. The selected metering valve is therefore in the end neither for the full load condition nor for the Suitable for low load conditions. There are already a variety of valve mechanisms for sensing the vehicle load or the vehicle height has been suggested in the past. However, these mechanisms are unnecessarily complex or otherwise Not suitable for modern vehicles. In this regard, reference is made to U.S. Patents 3,362,758, 3,503,657,

3,649,084, 3,684,329, 3,734,574, 3,768,876, 3,848,932,

4,150,855 and 4,159,855.

The present invention is concerned with improvements in load sensing pressure control devices for hydraulic systems Brakes in the hydraulic circuit upstream from the Rear wheels are arranged and distance changes between the vehicle chassis and the axis of the same feel as well the hydraulic pressure that is supplied from the master cylinder to the brake cylinders of the rear wheels, in response to such Control changes

According to the invention, a first and a second metering valve unit are provided, which are hydraulically connected in series. the The first metering valve unit is arranged downstream of the main cylinder, while the second metering valve unit is between the first metering valve unit and the rear wheels of the vehicle is arranged · The first metering valve is generated an output pressure suitable for a vehicle under full load. The second metering valve that controls the outlet pressure

of the first metering valve receives as input pressure, modifies or metered the pressure received from the first valve, whereby an output pressure is generated which is suitable for a lightly loaded vehicle.

The second metering valve unit is rigidly attached to the vehicle frame and includes a rotatable digital cam which is driven by a mechanical linkage is driven which is attached to the vehicle axle. When the vehicle is loaded, it is through the compression of the suspension system reduces the distance between the vehicle frame and the axle. The mechanical one Depending on this change in distance, the rod rotates the digital neck into a position in which the second Dosing valve mechanism is rendered ineffective. The output pressure of the first metering valve is thus undisturbed the second metering valve is fed to the brakes of the rear wheels.

The digital cam is rotatably seated on an axial drive shaft so that there is relative rotation between the two can. A torsion spring attached to the digital cam has one leg anchored to it, while the other is Leg is engaged with a flat diametrical cam surface provided in the drive shaft. The digital cam is thus caused to rotate together with the drive shaft. The torsion spring is a drive mechanism is made available that allows relative movement between the vehicle frame and the axle

picks up during vehicle operation and allows relative rotation between the cam and the drive shaft, whenever the cam is prevented from rotating by the operation of the metering valve mechanism.

Although the load sensing metering valve assembly is described herein as having a first metering valve assembly is connected in series, the load sensing valve can also be used alone in systems in which the Master cylinder outlet pressure without the interposition of a metering valve for direct transfer to the Vehicle brakes when the vehicle is heavily loaded is suitable.

The invention is explained in detail below with the aid of exemplary embodiments in conjunction with the drawing described. Show it:

Figure 1 is a schematic view of a hydraulic brake system with an inventive trained load-sensing metering valve is provided;

FIG. 2 is a diagram which illustrates the operating behavior of a metering system according to the invention;

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FIG. 3 shows a typical vehicle assembly of a load-sensing metering valve designed according to the invention;

FIG. 4 shows a partial cross section through the metering valve used in the brake system of FIG. 1;

Figure 5 shows a cross section along line 5-5 in Figure 4} Figure 6 is a partial cross-section along line 6-6 in Figure 4; Figure 7 is a partial cross-section along line 7-7 in Figure 4;

Figure 8 is an exploded view showing the assembly of the digital cam portion of the load-dependentη Shows the elements comprising the dosing valve}

Figure 9 is an isolated view of the digital cam,

which has been rotated 180 ° with respect to the position in Figure 8;

Figure 10 is a schematic view of the load-dependent Dosing valve for a lightly loaded vehicle;

FIG. 11 shows a schematic representation of the load-dependent metering valve when the vehicle is heavily loaded;

the figures
12 and 13

schematic representations of load-dependent metering valves, which allow the Allow digital cam drive shaft; and

Figure 14

a partial cross-section through a load-dependent metering valve, in a manner similar to Figure 6, in which the digital cam mechanism is adapted to be driven by a clockwise direction subsequent rotation of the digital cam drive shaft is actuated.

In Figure 1, a hydraulic brake system is shown. A Master cylinder 11 provides hydraulic fluid pressure via a line F for actuating the front wheel brakes 13L and 13R are available for the vehicle, this pressure being first through one in the combination valve contained, not shown metering valve unit is performed. The line R also represents an independent source of hydraulic pressure for brake actuation for a first metering valve unit 14, which is shown schematically in the combination valve 12 is shown to apply the brakes 15L and 15R of the vehicle rear wheels to operate.

The metering valve 11 may be of a known type as described, for example, in US Pat. No. 3,423,936 is, with a single branch point between the

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hydraulic input pressure and the hydraulic output pressure is present. The metering valve 14 is in accordance with the invention Way designed so that it creates a relationship between the outlet pressure and the inlet pressure, like them is shown in Figure 2 and labeled "Loading". The branch point at which the valve 14 starts dispensing is marked as point L. The curve labeled "loading" in FIG is indicative of a master cylinder-rear wheel brake pressure relationship, which is acceptable for vehicles that exceed a given average load up to the gross vehicle weight are loaded. The outlet pressure of the dosing valve 14 is provided by lines R1 and R2 which extend through the load sensing metering valve device 20, transferred to the rear wheels of the vehicle.

The device 20 includes a second metering valve assembly 16 which will be described in detail hereinafter. This unit has a similar construction to the metering valve unit 14 contained in the combination valve 12 rear wheel brake pressure (output pre-metering valve is illustrated by the designated in Figure 2 with "empty" Kurvs 16} "Dis in Figure 2 of =" [JG ^ ^- OsIItS ^K i5 ^ r ^H "'Kurvs embodied sins Hs _L:? pt yl. ln, dor ^

Rear brake pressure relationship acceptable for a vehicle load condition that is among the selected middle ones Load state falls.

Inside the load sensing metering valve 20 is a Digital cam mechanism 25 is provided to selectively operate the metering valve unit 16 in the fully open state shut down if the vehicle is heavily loaded. Thus, when the vehicle load reaches the predetermined average load condition exceeds, the metering valve 16 is stopped by the action of the digital cam 25, whereby the undisturbed transmission of hydraulic pressure through the valve is possible, which leads to the "loaded" line in FIG. illustrated pressure characteristic leads. However, when the vehicle is only lightly loaded, the metering valves work 14 and 16 in series and create a master cylinder pressure / rear wheel brake pressure relationship as shown by the line "empty" is illustrated in FIG.

FIG. 3 shows a typical vehicle assembly of the load sensing metering valve. The valve 20 is rigidly attached to a non-suspended portion of the vehicle frame 35 "The drive shaft 50 is fixedly connected to dera Bestinge 30, so that upon rotation of the linkage 30, the Anth> iEbsoell! 2 SQ dmrn Digitalnocksn 25 übsr buckets AnferiebsraodhiGifiicEaus in Drefoungeini wegsetzt ₅ umr hereafter la © insslnien hBScfrv-L & faQfö öiL ^ äc The Bestäfägs 30 is fgsfc roifc UQa FahrzGugeshiCircsi'r- 21 qcugt * anyone

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suitable element of the suspended portion of the rear wheel unit tied together.

The digital cam 25 speaks about the action of the linkage 30 attached to the vehicle axle 31 in response to compression or expansion of the vehicle suspension system (not shown). If the boom is extended, As indicated by the reference number 30, the vehicle is only slightly loaded, so that the metering valve 16 is in operation can be displaced · However, if the linkage is compressed, as indicated by reference numeral 30 · is, the vehicle is heavily loaded and the digital cam 25 is rotated to a position in which it can put the metering valve 16 out of operation.

The metering valve unit 16 shown in FIG. 5 is only one example of known metering valve mechanisms and represents does not form part of the invention. Since any known metering valve mechanism that can be converted in this way is anyway that it functions as described here, is suitable for the present invention, the description the functionality of the metering valve assembly 16 to the extent necessary to maintain the relationship with the digital cam and to understand how the valve works in relation to the entire hydraulic braking system.

The valve unit 16 comprises a valve caliper 40, which is disposed axially within a bore 45 and extends into a bore 45a of smaller diameter, the in turn opens into a cavity 70 of the digital cam. An O-ring seal 47 is provided around the bore 45 to be hydraulically sealed with respect to the bore 45a and thereby prevent the flow of hydraulic medium into the bore 45a. The piston 40 is provided with a pin-like extension 4Θ which protrudes into the bore 49. Of the Kalben can move axially within bore 45a so that pin 48 enters cavity 70 of the digital neck can protrude, as will be described in detail below.

The opposite end of the piston 40 includes a valve head 43 which is smaller in diameter than that Bore 45b and thus allows the unimpeded flow of the hydraulic medium. The piston 40 is also with equipped with an extension cap 41 in which a groove 42 is provided. The piston usually stands by a Spring 46 in the figure to the left under bias, so that the extension cap 41 against the end of the bore 45b is pressed and hits there. The hydraulic medium can thus penetrate into the inlet port R1, between the Piston 40 and the valve seat 44 made of elastomeric material flow freely through, flow past valve head 43, flow through groove 42 and exit through outlet opening R2. In the embodiment shown in Figure 5 is therefore

the fluid pressure at the outlet port R2 is the same like the fluid pressure at inlet port R1.

While the brake is being applied, the brake remains protruding
described fluid path through the metering valve 16 open until the fluid pressure supplied to the inlet port R1 reaches a predetermined level. To this
Point in time, the valve head 43 closes again against the valve seat 44. The pressure level at which this occurs,
depends on the force of the spring 46 compared to the effective area of the valve piston 40 being acted upon by inlet fluid pressure in a direction opposite to the spring force. This effective area corresponds to the diameter D of the piston 40 since the right hand end of the piston 40 which protrudes into the bore 45a is sealed by the O-ring seal 47 from inlet fluid pressure
is while the inlet fluid pressure is against all
remaining sections of the piston 40 acts.

After valve head 43 has closed against valve seat 44 and the fluid pressure at inlet port R1 has increased further, the increased pressure acts against piston 40 over an effective circular area with a diameter equal to the main seal diameter
of the valve head 43 minus the cross-sectional area of the piston 40 extending into the bore 45a. This creates a force which acts on the piston 40 in the same direction as an auxiliary spring 46,

to open the valve head 43 again and at least one To supply part of the increased fluid pressure to the outlet opening R2. The one supplied to the outlet opening R2 increased However, fluid pressure creates an opposing force on piston 40. The opposite Force tends to close the valve head 43 against the valve seat 44 again. By the opposing forces the valve head is held close to the valve seat 44, thereby reducing the flow of fluid from the inlet port R1 to the outlet port R2 is restricted and a pressure is generated at the outlet opening R2 which is at a lower speed increases as the pressure at the inlet port R1. The ratio of the pressures is given by the ratio between the effective areas previously referred to, hence the fluid pressure through the metering valve 16 can be modulated according to a predetermined relationship.

During that section of the actuation of the brake in which the pedal force applied after a brake actuation a sufficient magnitude is reduced so that the piston 40 is in the restricted flow position is moved, the forces moving the piston 40 to the left are reduced, and the piston 40 moves under the influence of the pressure at the outlet port R2 to the right · When the piston 40 moves to the right, the valve head 43 within the inner peripheral surface of the valve seat 44

slide} thereby the volume available for the fluid on the rear brake cylinders 15L and 15R increases and a pressure reduction is effected at the outlet port R2. The pressure at the outlet port R2 can never be greater than the pressure at the inlet port R1, since the valve seat 44 also acts as a check valve and fluid flow from port R2 into the Bore 45 allows.

A more detailed description of the design and functioning of the metering valve and of special elements of the same is contained in U.S. Patent 3,423,936.

The construction and mode of operation of the digital cam 25 will now be described with reference to FIGS Housing 19 of the load-sensing metering valve is with a two-stage bore 60 is provided. The bottom 69 of the bore 60 contains a semicircular slot 67 and a bearing recess 68. The cam drive shaft 50 is supported and fixed as shown in FIG. That Bearing 51 of drive shaft 50 is rotatably arranged within bearing recess 68. The shaft 50 extends generally perpendicular to the bore bottom 69 and extends through the end cap 61 and is rotatably supported thereby. The end cap 61 is tightly fixed within the bore 60a and against the shoulder 62 by a snap ring 63. An O-ring 55 is provided to seal the digital cam chamber 70 against the ingress of contaminants. the

Drive shaft 50 of the cam stands in a sufficient manner from the end cap 61 outwards and enables a firm engagement with the linkage 30 (see FIG. 3). Consequently the drive shaft 50 is rotated by the same angle as the linkage 30.

The digital neck 25 is rotatably mounted on the cam bearing 52 of the drive shaft 50 in such a way that the cam 25 can rotate relative to the drive shaft 50. The cam 25 is over at least its working circumference portion with a Circumferential recess 26 and axially directed knurls 24 are provided. The working portion of the cam 25 is connected are explained in more detail with the description of the mode of operation of the cam. A pin 32 stands in the axial direction from the cam 25 into the slot 67 in the bore bottom 69 and is slidably engaged therewith, whereby the angular rotation of the cam 25 is limited to the angular amount circumscribed by the slot. The inside 22 of the cam 25 is milled so that a stepped surface 27 is formed. A circular recess 21 extends in the axial direction through the cam 25 from the outer surface 2Θ and slightly over the inwardly directed stepped surface 27 addition, so that in this way a through channel 23 between the outer surface 28 and the Inner surface 27 is formed. A mandrel 33 is arranged in the axial direction within the circular recess 21 and extends outward and slightly beyond the outer surface 28. A torsion spring 34 is around the mandrel

arranged around, the helical portion of which sits within the circular recess 21 in such a way that that the inner leg 34a through the channel 23 in abutment with the inwardly directed stepped surface 27 extends and extends with dBm spring fixing hole 29 in Intervention is located. The outer leg 34b of the spring is in abutment with the outer surface 28 of the cam 25, extends into slot 54 of drive shaft 50 and engages flat cam surface 53. In the assembled normal state described above and shown in FIG. 6, the legs 34a and 34b are the torsion spring is spring loaded so that it exerts an angled outward force on the fixation hole 29 and the flat neck surface 53 of the drive shaft 50 exercise. A slot 56 is on the outer end of the cam drive shaft 50 provided in order to enable an adjustment from the outside.

In operation, the cam 25 is driven by the torsion spring 34, which exerts a spring force on the neck surface 53 of the shaft 50 exercises, rotated with the neck drive shaft 50. However, if the cam 25 due to a mutual Influence of the pin 32 and the slot 67 or the cam 25 and the pin 48 on the valve piston 40 on a Rotation is prevented, the neck drive shaft 50 can by further compressing the torsion spring 34 a Rotate relative to cam 25. Thus, there is a between the cam drive shaft 50 and the digital cam 25

A spring drive mechanism is provided which causes the shaft 50 to override when the rotation of the cam 25 in other way is restricted.

In Figures 3, 5 to 7 and 10 the load sensing is Metering valve 20 shown under light vehicle load conditions. The vehicle frame 35 lies in Relative to the suspended axle 31 is relatively high. Consequently, the digital cam 25 is arranged by the linkage 30 so that that the circumferential recess 26 the pin 48 of the piston 40 an axial movement into the digital neck chamber 70 into it and again made possible from this. The metering valve 16 can function freely, whereby a master cylinder pressure / Rear wheel brake pressure relationship arises, as defined by the Curve "empty" is illustrated in Figure 2.

As long as the vehicle is only lightly loaded, the metering valve 16 functions. The circumferential slot 26 allows operation of the valve 16 to. However, if as a result of braking of the vehicle, the valve spool pin 48 protrudes into the cam chamber 70 and when the vehicle is on an extreme road condition which, due to excessive compression of the vehicle suspension system, causes momentary overspeeding of the When the cam drive shaft 50 causes the cam 25 to temporarily engage the valve piston pin 48 and stop the counterclockwise rotation of the cam. However, the cam drive shaft 50 can be counterclockwise

Carry out clockwise rotation by compressing the torsion spring 34. Such a state is in Figure 13 shown.

When the vehicle is heavily loaded, the suspension system is compressed so that the vertical distance between the frame 35 and the axle 31 is reduced. The linkage 30 takes a form as shown in Figure 11, thereby rotating the digital cam 25 counterclockwise as shown. In this embodiment, the outermost circumference of the cam 25 rotated into a position in which the metering valve 16 is put out of operation by free movement of the piston 40 is prevented. Thus, when the vehicle is loaded, as shown in FIG. 11 shows the master cylinder pressure / rear wheel brake pressure relationship by the curve shown in FIG "loaded" clarified. As long as the vehicle is loaded, the outer circumference of the remains Cam 25 in the position of FIGS. 11 and 12 which puts the valve piston out of operation. In this position and with such a high braking load that the valve piston 40 tries to move to the right, the valve piston pin 48 strikes against the cam 25 and occurs with the axial knurls 24 on the outer periphery of the cam 25 in engagement. This prevents the cam 25 from rotating freely. Another Rotation of the cam drive shaft 50, which results from fluctuations of the axis 31 caused by the road, is

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added by the compression of the torsion spring 34, as in FIG Figure 12 shown

The angle A (Figure 6) between the centerline of the pin and the step 26a of the digital cam defines that load condition of the vehicle, in which the metering valve 16 is put out of operation. It is therefore necessary that this angle is precisely determined. The angle A is determined for an unladen vehicle and represents that The angle through which the drive shaft 50 rotates when the vehicle is under the mean load condition in which a change from the "empty" curve to the "loaded" curve of Figure 2 is desired. The level 26b

she
is arranged so that the functioning of the metering valve 16 does not interfere. The pin 32 and the slot can also be designed in such a way that they limit the clockwise rotation of the cam 25 and thereby prevent the step 26b from interfering with the functioning of the metering valve 16.

The load sensing device shown in FIGS Metering valve is on counterclockwise rotation of cam drive shaft 50 upon compression of the vehicle suspension system Voted. However, the valve can also be adapted to a clockwise direction in a simple manner Rotation can be adjusted as shown in FIG. By shifting the slot 67 as shown in FIG the mechanism for clockwise rotation be made suitable.

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Claims (1)

Claims 1 / Hydraulic brake system for vehicles with a master cylinder, wheel brake devices and fluid transfer devices for transferring hydraulic pressure from the master cylinder to the wheel brake devices, characterized by a first and second metering valve device (14, 16) between the master cylinder (11) and the wheel brake devices (13R, 13L; 15R, 15L), wherein the metering valve (14, 16) are hydraulically arranged in series and the second metering valve (16) downstream is hydraulically from the first metering valve (14) ^De ~ and wherein the first metering valve (14) is capable of to modulate the input / output hydraulic pressure according to a first input / output relationship and the second metering valve means (16) is capable of modulating the input / output hydraulic pressure according to a second input / output relationship, and vehicle load sensing Facilities (20) capable of to put the second metering valve device (16) out of operation when the vehicle is loaded to a predetermined load condition. 2. Brake system according to claim 1, characterized in that the load-sensing devices (20) means for Include sensing the relative distance between the vehicle frame (35) and the vehicle axle (31). 3. Brake system according to one of the preceding claims, characterized by a first and second metering valve device (14, 16) between the master cylinder (11) and the wheel brake devices (13R, 13L; 15R, 15L), which are arranged hydraulically in series and of which the second metering valve in-r direction (16) hydraulically downstream of the first metering valve device (14) is arranged and the first metering valve device (14) is able to calculate the input / output hydraulic pressure according to a first input / output relationship to modulate and the second metering valve device (16) is able to control the hydraulic input / output pressure modulating according to a second input / output relationship, and vehicle load sensing means (20), which are able to put the second metering valve device (16) out of operation and in an open bypass state to be fixed when the vehicle is loaded to a predetermined load condition, the hydraulic output pressure of the second metering valve device (16) essentially corresponds to the hydraulic output pressure of the first metering valve device (14) corresponds. 4. Metering valve for a hydraulic brake system of a vehicle with a lockout mechanism that selectively deactivates the valve under given vehicle load conditions can be made, characterized by: Valve devices with a piston (40) which responds to hydraulic pressure and actuates the valve devices, and rotatable cam means (25) having a cam profile which is in communication with the piston (40), a rotatable one Shaft (50), connecting means between the cam (25) and the shaft (SO), through which a rotation of the shaft causes a rotation of the rotatable cam (25), the neck profile being formed so that the movement of the Calving (40) is restricted when the cam is rotated to a predetermined angular position, whereby the valve means are fixed in the inoperative position, and wherein means for rotating the rotatable shaft (50) in dependence provided by the vehicle load conditions. 5 · Dosing valve according to claim 4, characterized in that the rotatable cam (25) comprises stop means by which the angle of rotation of the cam is limited to a predetermined one Arch area is limited. 6. Valve according to claim 5, characterized in that the Connecting means comprise elastic means whereby the rotatable shaft (50) is rotated through an angle which is larger than that of the rotatable cam (25). 7. Dosing valve according to claim 4, characterized in that the rotatable cam (25) is arranged coaxially to the rotatable shaft (50) and is rotatable about this, that the shaft (50) a axially extending, D-shaped portion and that the connecting means is a torsion spring (35), one leg (34a) of which is attached to the rotatable cam (25) and the other leg (34b) is drivingly engaged with the flat surface of the D-shaped portion of the rotatable shaft (50), so that the rotatable shaft (50) rotates independently of and relative to the rotatable neck (25) when the torque of the rotatable shaft (50) is always large enough to cause the torsion spring (35) to yield. Θ. Dosing valve for a hydraulic brake system of a vehicle with a valve lockout mechanism by which the valve is in an open bypass state under selected Vehicle load conditions can be made ineffective, indicated by t a housing having a first P bore (45) and a second Bore (6B), the axes of which intersect at a right angle, with a metering in the first bore (45) valve device is arranged with a piston (40) which extends in the axial direction through the bore and into the second bore (68) extends, a rotatable shaft (50) coaxial with the second Bore (6B) is arranged and extends axially to, circular cam means (25) which are coaxial to are disposed on the axis of the second bore and extend radially outward from the rotatable shaft (50), and connecting means between the rotatable shaft and the circular cam means so that a Rotation of the shaft causes rotation of the circular neck device (25), this circular neck device has a cam profile which is in communication with the piston (40) of the metering valve device, and said cam profile being adapted to restrict movement of said piston (40) when said cam means is rotated to a predetermined angular position, thereby placing the valve in an ineffective open bypass state to fix, and having means for rotating the rotatable shaft in response to vehicle load conditions are provided. 9. Dosing valve according to claim 8, characterized in that the rotatable cam means (25) has stop means through which the angle of rotation of the cam is limited to a given arc range is limited. -G- 10. Dosing valve according to claim 9, characterized in that the connecting means comprise elastic means by which the rotatable shaft (50) is rotated about the angle that can be rotated is greater than the rotatable one Cam device (25). 11. Dosing valve according to claim 8, characterized in that the circular cam device (25) is rotatable about the rotatable shaft (50) so that the shaft has an axially extending, D-shaped section and that the connecting means a torsion spring (35), one leg (34a) of which on the rotatable cam device (25) is attached and the other leg (34b) with the flat surface of the D-shaped portion of the rotatable shaft (50) is in driving engagement, so that the rotatable shaft (50) independent of the rotatable Cam means (25) and rotates relative thereto whenever the torque of the rotatable shaft (50) is sufficient is large to cause the torsion spring (35) to yield.